The Orfeus Electronic newsletter aims at disseminating rapidly relevant information to the Orfeus community within the European-Mediterranean area. You are encouraged to submit contributions in the form of an article, technical note or announcement according to the authors instructions to Orfeus.
1) The Instituto Andaluz de Geofisica Universidad de Granada Seismic Network in Southern Spain (J. Morales et al.) (One of the several Spanish University networks) 2) Performance of the Seismic Network of the Republic of Slovenia - First Results (M. Kobal et al.) (The modernized network in Slovenia and its performance) 3) Source mechanism of the February 12, 2007, San Vicente Cape Earthquake Mw=5.9 (E. Buforn et al.) 4) The 5.9 ML Magnitude Earthquake of 2007.02.12, SW San Vincent Cape (F. Carrilho et al.) 5) The 12/02/2007 SW Cape San Vicente Earthquake: SFS (San Fernando SP) and WM (Western Mediterranean) networks preliminary report (J. Martin Davila et al.) (Three groups represented by as many articles presenting different aspects of the recent San Vincente Cape M=5.9 earthquake, February 12, 2007)
6) Commercial digital audio recorders - a new life for portable Lennartz PCM 5800 seismic stations (M. Capello et al.) (A technical article proposing an alternative recording solution) 7) SEISAN: Multiplatform implementation of MINISEED/SEED (J. Havskov et al.) (Facilitating the use of SEED)
8) ORFEUS announcements
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Current ORFEUS ExeCom ORFEUS ExeCom and ORFEUS board meeting ORFEUS WG2 workshop NERIES Annual meeting XML developments for earthquake data exchange
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J. Morales , G. Alguacil, J.B. Martin, A. Martos Instituto Andaluz de Geofisica, Universidad de Granada, Campus Universitario de Cartuja s/n. 18071Granada, Spain Introduction Since 1902, when several mechanical seismometers (pendula Stiattessi and Vicentini) were installed in Cartuja Observatory (now Instituto Andaluz de Geofísica-Universidad de Granada, IAG-UGR), the seismic instrumentation has been the focus of a permanent development. In 1983, the IAG-UGR started to operate a high-gain local short period network. In fact this was the first local radiotelemetered permanent seismic network installed in the Iberian Peninsula (Alguacil, 1986). The principal goals were the monitoring and recording of the microseismicity activity in the Granada depression (Southern Spain) and surrounding areas, and to overcome the lack of microseismic information in southern Spain due to scarcity and low-gain of seismic instrumentation. Until 1989, when the network was changed over to digital recording, it consisted of seven vertical short-period stations with central visual recording on paper. The network was increasing until 1995, up to a configuration with 13 short period seismometers, deployed around Granada depression and Almería province –these latter with central recording at Almería, with analogue transmission and digital recording in a central data acquisition system based on a PC-on board card system (Alguacil et al., 1990). By the end of the 90’s, 4 broad band (BB) stations (STS-2) were installed in southern Spain by the IAGUGR: SELV, VELZ, ANER and ORGV (last one no longer operating) in order to improve the dynamic range and bandwidth of the data. At a first stage, the acquisition system was DOS based, with a digitiser of effective resolution 18 bits, which required a manual interrogation via modem with proprietary software. The exception was station SELV (the first BB station installed) which was equipped with a Quanterra 360 datalogger with a dial up interrogation mode under TCP/IP. After 2000 a new project of mixed seismic network including short-period high-gain and broad band seismometers was planned and progressively deployed in Southern Spain. The main goal of the project was to extend the coverage and resolution of the network in order to be able to record on-scale small and moderate earthquakes generated in the Iberian-Magreb plate contact, with homogeneous instrumentation. We want with this article give an overview of this instrumentation. IAG regional network. Current state, configuration and communication. The present spatial configuration of the regional IAG broad band and short period network is shown in figure 1. The broad band network consists of a total of twelve seismic stations based on triaxial seismometers STS-2. An additional seismic station (ACBG) with a triaxial (To=5 s) seismometer (Lennartz LE-3D/5s ) is included in this net because it is using the same soft and hardware configuration except in the type of seismometer. The high resolution digitizer Earth Data 24 bits (PS2400) is time-synchronised with a Garmin GPS receiver. The digitiser is connected through a serial port to the datalogger, a SeisComP industrial PC from Alpha 2000 with a 30 Gbytes hard disk, where the sampled signal at 50 s.p.s is stored in half-hour ringbuffers, under the control of Seislog, a software package (Utheim and Havskov, 2001) installed in the stations and running under QNX operating system. Seislog writes continuous data files and by means of a simple STA/LTA detection algorithm also produces event files.
Figure 1. - Broad band and short period stations in southern Spain managed by the Instituto Andaluz de Geofisica. Red triangles are broad band stations except ACBG (see text) installed and operating. Yellow are planned in near future. Blue triangles represent short period seismic stations installed and operating.
The data communication between the central recording site (Instituto Andaluz de Geofisica) and the seismic stations is implemented in several ways, depending of the infrastructure available in each place. Digital telephone line is used for communication and interrogation in SELV and ANER at practical speed of 56 kbaud. GSM mobile communication for data transmission is used in VELZ, ESTP, ACLR, ASCB, JAND and ACBG (speed 9.6 kbaud). DSL line (presently 256 kbaud) is installed at SESP, ARAC, GORA and HORN and for CEUT we use the high speed intranet of the Granada University since this station is located at the Granada University Campus at Ceuta. The policy of the Institute for the future is to have all seismic stations linked by ADSL lines terrestrial or GPRS and to transfer continuous data in near real-time. Some of the main characteristics of the broad band stations are summarized in the table 1.
Table 1. - Broad band seismic station characteristics managed by the Instituto Andaluz de Geofisica - Universidad de Granada
* ED24= Earth Data 24 bits ** SCP= SeisComP with 30 Gbye H.D. *** T= trigger segments. C= continuous data storage since January 2004; From installation date to January 2004 the data were storage by trigger.
Additionally, nine short period stations are still operating at present, after several stations of the original 1990’s network have been upgraded to broad-band (especially those in the Almería province). The remaining stations are situated at distances of up to 60 km from the central recording site at Cartuja Observatory in Granada. The sensors are vertical 1 s, except for station CRT, with triaxial, extended period up to 10 s. Data transfer uses real-time analogue radio telemetry. The signals are recorded continuously on drum paper and the declared events in digital form. The data is acquired by a PC based data logger that was home-designed. The upgrade plan includes field digitisers and digital telemetry, as well as continuous digital recording at the central recording site. Network data collection The Seisnet (Ottemöller and Havskov, 1999) package to combine seismic stations of various types with communication capabilities into a network is installed on a Sun work station under Solaris 8.0 platform. The main routines carried out by Seisnet are transfer of parametric data, network event detection, transfer of waveform data and automatic determination of epicentre location and magnitude. The data are stored in a central Seisan database. Currently this system collects data automatically from the BB and SP networks and the PDE (USGS preliminary determination of recent epicentres) sources
The Seisnet process is started up every thirty minutes. It will then collect data from short period and BB’s with TCP/IP protocol (intranet or DSL facilities). Data from BB with modem (phone or GSM) are only collected regularly at night time in order to save communication costs, except in the case of an important local or regional event, in which case the data are gathered by the operator as soon as possible. For short period and broad band stations under dial-up protocol, only data segments (event data) are transferred. Broad band stations under TCP/IP protocol provide a continuous time series of half hour data blocks. To obtain and store continuous data for those broad band stations without TCP/IP protocol, every 3 to 4 months the stations are visited, checked and all the continuous data are recovered. The Seisan package (Havskov and Ottemöller, 1999) is used for most of the routine data analysis at the IAG. This system organizes data from all kind of seismic stations into a simple database. Seisan comprises all the tools needed for routine processing, and also conversion to other standard seismic data formats to be used in external software. The Seisan database facilitates research tasks, currently focused on regional studies of earth structure and seismic sources. Portable BB network More recently, a broad band “portable” set with fifteen BB sensors, was designed to be operative in the IAG for large scale experiments involving temporal seismic networks. This portable network is based on the same specifications that the permanent network: STS-2 triaxial seismometers, 24-bits Earth Data PS2400 digitisers with GPS receiver and a PC based data logger, except the remote communication facilities. Conclusions At present, waveforms collected by the broad band, both permanent and portable networks, together the short period net are used in several projects studying seismic sources (IAG-regional moment tensor for the Ibero-Maghrebian region; Stich et al. 2003a,b Stich 2006) and the velocity structure below southern Spain. Acknowledgments We received financial support by the Spanish DGI project CGL2005-04541-C03-01-BTE, FEDER founds and within the Research Group RNM#104 of Junta de Andalucía. References Alguacil, G. (1986). Los instrumentos de una red sísmica local telemétrica para microterremotos. La red sísmica de la Universidad de Granada. Ph.D. Tesis. Universidad de Granada, Granada 232 pp Alguacil, G, J. M. Guirao, F. Gomez, F., Vidal, F. de Miguel (1990). Red sísmica de Andalucia (RSA): A digital PC based seismic network. Cahier du Centre Européen de Geodynamique et de Seismologie, 1, 19-27. Havskov, J. and L. Ottemöller (1999). Electronic Seismologist – SeisAn Earthquake Analysis Software. Seismological Research Letters, 70, 5. Ottemöller, L. and J. Havskov (1999). SeisNet: A General Purpose Virtual Seismic Network. Seismological Research Letters, 70, 5. Stich, D., C.J. Ammon, and J. Morales, 2003a. Moment tensor solutions for small and moderate earthquakes in the Ibero-Maghreb region. J. Geophys. Res., 108, 2002JB002057. Stich, D., Morales, J., Mancilla, F. and G. Alguacil (2003b) Moment tensor determination for the IberoMaghrebian region. Orfeus Electronic Newsletters vol 5 nº2: 9-9.
Stich, D., E. Serpelloni, F. Mancilla and J. Morales (2006) Kinematics of the Iberia-Maghreb plate contact from seismic moment tensors and GPS observations. Tectonophysics 426: 295-317. doi:10.1016/j.tecto.2006.08.004 Utheim, T. and J.Havskov (2001). Seislog data acquisition systems. Seismological Research Letters. 72:77-79
M. Kobal, J. Kolar, J. Pahor, M. Živ•i• Environmental Agency of the Republic of Slovenia, Seismology and Geology Office , Dunajska 47/VII, 1000 Lubljana, Slovenia SNRS (Seismic Network of the Republic of Slovenia) After the M=5.8 earthquake on 12 April 1998 in the Krn mountain region the Government of the Republic of Slovenia secured the funds and appointed the Seismology and Geology Office (USG) of the Environmental Agency of the Republic of Slovenia (EARS), at that time organized as Geophysical Survey of Slovenia, to build a new national seismic network. After comprehensive site selection studies and an international bid for the instrumentation the network has gradually been built with the first new stations put into permanent operation at the beginning of 2002. At present (December 2006) 23 new permanent seismological stations are operating (Fig. 1) while three more are already built but not yet connected. All are broadband stations sending data in real time to the SNRS (Seismic Network of the Republic of Slovenia) data centre at the USG in Ljubljana. The standard equipment is Quanterra Q730 datalogger and Guralp CMG-40T seismometer. To secure on-scale seismograms in case of a strong earthquake five stations have also Episensor accelerometer (Tab.1). Due to thick weathered surface layer four stations use shallow borehole seismometres. Sampling rates are 200sps, 20sps and 1sps. At each site Flash memory in Q730 accommodates approx. 90 min data as data buffer in case of downlink. At the end of the project of the modernization of the SNRS, the network will consist of 26 broadband stations (Fig.1). For the financial reasons, lower quality and narrower band Guralp CMG-40T seismometers were originally purchased. Afterwards, three Streckeisen STS-2 and one Guralp CMG-3ESP seismometers were bought and installed. The USG still operates old six station Nanometrics digital network, a few portable stations and a small network of 8 digital strong motion instruments. (Near) real-time data transfer All stations of the SNRS are protected by the firewall of the Governmental INTRANET. Real time data acquisition is done using the Antelope software package. The data from most stations is transferred by use of the leased phone lines and from seven locations by use of the HSCSD mobile phone connection. In the Data Centre in Ljubljana the data are integrated with the data of the old Nanometrics digital six station network (Fig. 2). After the colaboration agreement was signed we are also receiving the data in real time from the selected stations from Central Institute for Meteorology and Geodynamics (ZAMG), Austria, the Department of Earth Sciences of the Trieste University (DST) and from the National Institute of Oceanography and Experimental Geophysics (OGS) from Trieste (Fig.2). Using Antelope orb2orb connections (orb = object ring buffer) we receive the data from the DST broadband network, as well as from OGS broadband and short period networks. We also installed guralp2orb process that collects data from several stations in Croatia. This data exchange is the result of the activities within the EC MEREDIAN project and the waveforms are regularly forwarded to the ORFEUS data centre. Some of the SNRS stations are part of the European VEBSN. Latitude Longitude Elev. Code (N) (E) (m)
Station type
Sensor type
Data Transfer
Installation
On Date
LJU CEY DOBS CRES GOLS LEGS PDKS ROBS GROS PERS CADS GCIS VISS JAVS KNDS KOGS BOJS GORS VOJS MOZS ZAVS VNDS SKDS
46.0438 45.7381 46.1495 45.8260 46.0108 45.9488 46.0612 46.2445 46.4610 46.6365 46.2281 45.8672 45.8033 45.8934 45.5276 46.4481 45.5043 46.3174 46.0322 46.2941 46.4342 46.1016 45.5464
14.5278 14.4221 15.4695 15.4569 15.6245 15.3177 14.9977 13.5095 15.5018 15.1139 13.7368 15.6275 14.8393 14.0643 14.3806 16.2504 15.2518 13.3999 13.8877 14.4433 15.0246 14.7014 14.0143
396 579 465 431 559 390 679 245 930 795 743 403 403 1100 1035 245 252 1048 1072 660 741 531 552
6C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 3C BB 6C BB 6C BB 6C BB 3C BB 3C BB 3C BB 3C BB 6C BB
CMG-40T, STS-2, Episensor CMG-3ESP CMG-40T CMG-40T CMG-40T/BH CMG-40T/BH CMG-40T/BH CMG-40T CMG-40T CMG-40T CMG-40T CMG-40T CMG-40T CMG-40T CMG-40T CMG-40T, Episensor STS-2 Episensor CMG-40T, Episensor CMG-40T CMG-40T CMG-40T/BH CMG-40T STS-2 Episensor
RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT leased lines RT HSCSD RT HSCSD RT HSCSD RT HSCSD RT HSCSD RT leased lines RT leased lines RT leased lines RT HSCSD RT leased lines RT HSCSD RT leased lines RT leased lines not connected not connected
Cellar 2m Surface pier Vault 4m Vault 4m Borehole 17m Borehole 15m Borehole 16m Cave 2m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Vault 4m Borehole 17m Vault 4m Vault 4m
2001-03-30 2001-03-30 2001-04-07 2002-04-02 2002-04-02 2002-09-02 2002-11-11 2002-11-20 2002-12-12 2002-12-14 2003-07-10 2003-08-11 2003-08-14 2003-08-21 2003-10-14 2004-01-26 2004-02-20 2004-05-17 2004-07-30 2005-07-07 2005-08-11 2005-12-16 2006-04-12 expected
CRNS
46.0807
14.2613
689
3C BB
CMG-40T
Vault 4m in 2007 expected Vault 4m in 2007
GBAS
45.9348
14.4423
538
3C BB
CMG-40T
GBRS
45.5311
14.8101
610
3C BB
CMG-40T
not connected
expected Vault 4m in 2007
Table 1. Seismic stations and instrumentation of the SNRS.
Figure 1. Seismic Network of the Republic of Slovenia (SNRS).
The two basic conditions for fluent data processing and archiving are good data flow and flawless operation of all the computers involved. The data flow is influenced by network traffic and by occasional remote hardware malfunction. When this is the case, a swift reaction is important since it can significantly reduce data loss. Data flow is being monitored by periodic five minute reading of the latency of the data coming to the main ORB. The latencies are then checked against the conditions with increasing severity and a SMS message is sent to several recipients when some or all data latencies exceed a certain amount of time (typically some minutes). To ensure SMS delivery we use two service providers and two GSM modems attached to two workstations. In case of failure non-delivered SMS messages are thus automatically forwarded to another provider. The network software runs on three Sun workstations. That enables us some redundancy in most critical functions as well as simple replacement in case of major failure in the acquisition server. One of the workstations is configured in-between the firewalls and is dedicated to data exchange tasks. The status of the workstations is being periodically monitored with several tests. Main methods are: - each machine checking that all the others are on and that acquisition and alerting software is running,
- moving failed SMS to the send queue of the other of the two computers equipped with wireless modems and notifying if the number of failed SMSs exceeds a specified threshold. Besides real-time problems detection, regular check of log and message files is essential.
Figure 2. Schematic representation of data acquisition and exchange at the SNRS data centre.
Data loss of the SNRS network is shown in figure 3. In average, there is 6.6% of unretrieved data for HH channels with 200 Hz sample rate, mostly as occasional dataloss of a single station for a period of several days. The difference of data loss between HH channels and BH channels with 20 Hz sample rate is related primarly to communication problems. Typically, the Quanterra ORB can hold approximately one hour of HH channels data whereas BH channels data are retrievable also after more than 10 hours of communication breakdown. The larger data loss in the period between June and August 2005 for example is due to three stations (out of 21) not operating most of the time.
Figure 3. Percentage of data loss of Seismic Network of the Republic of Slovenia between January 2004 and December 2006. HH channels represent 200 Hz sample rate data and BH channels represent 20 Hz sample rate data.
Data analysis, storage, archiving and availability The main task of the SNRS is fast alerting automatic procedure. Automatic detection and location algorithms are part of the Antelope Real Time System (ARTS) package. Antelope algorithm for automatic location of earthquakes uses pre-computed travel times for a given velocity model and a number of grids. When an event occurs, the node of the grid which is in accordance with the largest number of detections and gives the lowest RMS is reported as a location of the event. In comparing automatic and manual locations one has to bear in mind that manual locations done with HYPOCENTER cover the space uniformly. With the grid of 2 by 3 km for automatic location of local events even in an ideal case, where automatic epicentre is always selected at the node which is closest to the manual epicentre, the average distance between these two epicentres would be about 1 km. Although the configuration and the detection and location capabilities of the network are continuously changing by adding new stations, some preliminary results of the location accuracy can be evaluated. For the period between 1 January 2004 and 30 June 2005 we made analysis for the restricted area lying inside the polygon formed by the stations that were operating during the whole interval (CEY, OBKA, PERS, GROS, GOLS, GCIS and CRES). We compared 351 events with both automatic and manual epicenter calculated. Median distance between manual and automatic location was 5.15 km while 56 events had a distance greater than 25 km (Fig 4).
Figure 4. Relative mislocations of the automatic location algorithm – automatic locations are plotted relative to the manual location which is considered as the co-ordinates origin (0,0).
Collected data are daily manually analysed with the Antelope software package. For detailed analysis of teleseismic events we use Seismic Handler. The waveform data is stored in the Antelope database and available through autodrm service (autodrm.lju@gov.si). The continuous data are daily automatically archived on DLT tapes and selected event segments are periodically archived on CDs. The parametric data are stored locally in the SEISAN database (from the year 1996). Our final monthly bulletins are also available in the ISC database. Seismology and Geology Office regularly contributes parameter and waveform data to the international seismological data centres. We send automatic detections to EMSC, our weekly bulletins to neighboring countries, EMSC and NEIC, and final monthly bulletins to ISC.
E. Buforn, A. Udías and J. Martín Dávila Dpt. Geofisica, Facultad CC. Fisicas, Universidad Complutense, Madrid (Spain) Introduction On February 12, 2007 an earthquake occurred at 10h 35m 25.36s, 180 km SW of San Vicente Cape. The earthquake was felt without appreciable damage over a large area, in south and central Spain and Portugal. In Madrid the shock was felt in parts of the city and some tall buildings were evacuated. The earthquake occurred in the western part of the Ibero-Maghrebian region, a complex region which includes the western part of the plate boundary between Eurasia and Africa. It extends from Iberia to the Maghreb (northern Africa) including the Gulf of Cádiz and the Alboran Sea to both sides of the Strait of Gibraltar (figure 1). On the Gulf of Cádiz, the epicenters are distributed on an E-W narrow band that marks the plate boundary (Buforn et al. 1988), with the occurrence of large shallow earthquakes as the February 28, 1969 (Ms=8.1) or the March 15, 1964 (Ms=6.4) (figure 1). The area where the 2007 event has occurred is one of the hypothetical locations suggested for the 1755 Lisbon earthquake (Machado, 1966; Buforn et al., 1988).
Figure 1.- Focal mechanisms for earthquakes with magnitude greater than 4.0 for the Gulf of Cádiz region. In red reverse solutions, blue strike-slip and green normal solutions, symbols are proportional to the magnitude. The star shows the location of the 12-02-07 earthquake. Solutions are given in Buforn et al. (2004). Dashed line represents the plate boundary.
The preliminary hypocentral location given by the Instituto Geográfico Nacional (IGN) is 35.956º N, 10.409º W, depth=64 km, maximum intensity IV (EMS-98) in Sevilla, Cádiz, Huelva (SW Spain). This hypocenter is very close to the 1969 event (36.10ºN, 10.60ºW). The focus of the 1969 earthquake was estimated at 29km by Grimisson and Chen (1988) from waveform modelling. The focus of the 1964 event, located to the East of the 1969 and 2007 shocks, the focus was estimated by waveform modelling by Grimisson and Chen (1988) as a complex rupture, with two sources at 14 and 20 km respectively and at 12 km by Buforn et al (1988) using a single rupture. However, both these studies were carried out using WWSSN analogue data, and in consequence, no details about the rupture process were obtained. The 2007 earthquake is the first earthquake to occur in this area with magnitude larger than 5.5 for the last 38 years. Focal mechanism A preliminary solution for the focal mechanism of the 2007 event has been estimated from body wave inversion at teleseismic distances using the Kikuchi and Kanamori (1991) method. The Green functions have been generated using a crustal 3-layer 1-D model derived from local studies in the region composed by three flat layers (Gonzalez et al., 2001). A total of 12 P waves and 6 SH waves recorded at stations located at epicentral distances from 30º to 90º have been used. Data were converted to ground motion by removing the instrument response and were then filtered using a pass band 0.01 to 1Hz. The time window used on the inversion is 35 s. and the rupture velocity 3.0 km/s. As a preliminary solution in the inversion process the fault plane obtained from first motion of 58 observations located at teleseismic and regional distances has been used. We tried depths
ranging from 10 to 90 km for the focus and the fault plane has been divided into a 2.5 x 2.5 km grid. Best results (minimum rms) have been obtained for 30 km depth, with good agreement between observed and synthetic waveforms. The obtained focal mechanism corresponds to reverse faulting with planes dipping about 45º and oriented on E-W direction. Scalar seismic moment is 8.5 x 1017 Nm, which corresponds to a Mw=5.9. The source time function is a single impulse of 4s. From this solution we have carried out the slip distribution (figure 2).
Figure 2.- Slip distribution for the San Vicente 2007 earthquake. On top scalar seismic moment (Nm), magnitude Mw, source time function, focal mechanism and slip over the fault plane. On bottom observed and synthetic seismograms for P and SH waves, numbers corresponds to azimuth and amplitude of each station.
The rupture starts at 30 km depth, propagating upward and showing a possible asperity at 32 km depth and 0.63 m of maximum dislocation. Faulting takes place on a plane (azimuth 264º) of 14 km length and 12.5 km width, dipping to the north with the African plate underthrusting the Eurasian plate. The obtained solution is very similar to the moment tensor solutions obtained by other agencies (figure 3): Harvard (CMT), INGV (Italy) and ETH (Suitzerland). Depths obtained by Harvard, INGV and ETH are deeper (44 and 43 km respectively). The IGN solution shows a vertical plane trending NE-SW, depth 65 km and Mw=6. The USGS solution is similar to the IGN but with shallow depth (14km). These two solutions do not agree with those found for earthquakes in this area, specially that of 1969 earthquake. We prefer our solution due to the large number of stations used (18) and the good azimuthal coverage. For example, the ETH solution has been obtained using 4 stations with azimuths 24º to 56º or the IGNV has been obtained using only MEDNET station with a poor azimuthal coverage. The IGN solution has been obtained using only 3 stations at regional distances with azimuthal coverage between 43º to 59º.
Figure 3.- Depth versus Mw magnitude for the focal mechanism of the 2007 earthquake estimated by different agencies.
The focal mechanism estimated for the 2007 earthquake is very similar to the solutions obtained for the 1964 and 1969 shocks, the largest in this area (figure 1). This solution is in agreement with the stress pattern in this area, corresponding to horizontal NNW-SSE compression, a consequence of the convergence between the Eurasian and African plates. Acknowledgements This work has been supported in part by the Ministerio de Ciencia y Tecnología (Spain), project CGL2006-10311-C03-01 and by the Universidad Complutense de Madrid, project AE10/07. Part of data was provided by IRIS and ORFEUS. References Buforn, E., Udías, A. and Colombás, M.A. (1988). Seismicity, source mechanisms and seismotectonics of the Azores-Gibraltar plate boundary. Tectonophysics, 152, 89-118. Buforn, E., Bezzeghoud, M., Udías, A. and Pro, C. (2004). Seismic sources on the Iberia-African plate boundary and their tectonic implications. Pure Appl. Geophys. 161, 623-646.
Gonzalez-Fernández, A., Córdoba, D., Matías, L. and Torné, M. (2001). Seismic structure in the Gula of Cádiz (SW Iberian Peninsula). Mar. Geophys. Res. 22, 207-223. Grimison, N. and Chen, W. (1988). The Azores-Gibraltar plate boundary: focal mechanisms, depths of earthquakes and their tectonic implications. J. Geophys. Res. 91, 2029-2047. Kikuchi, A. and Kanamori, H. (1991). Inversion of complex waves III. Bull. Seism. Soc. Am. 81, 2335-2350. Machado, F. (1966). Contribuçao para o studio do terremoto de 1 de Nov. de 1755. Rev. Fac. Cienc., Univ. Lisboa, Ser. C., 14; 19-41
F. Carrilho, P.M. Alves, D. Vales, J.A. Pena, I. Abreu, S. Cortês Instituto de Meteorologia, I.P., Rua C ao aeroporto, 1749-077 Lisboa, Portugal Introduction On the 2007.02.12 (10:35 UTC) an earthquake of magnitude 5.9ML occurred approximately 160 km SW of San Vincent Cape, Portugal mainland. The earthquake was felt almost throughout mainland Portugal, the Madeira archipelago, and parts of Spain and Morocco, with felt reports up to 1000 km away from the epicentre. The macroseismic field extended for 3x106 km2, with a maximum intensity of 5 (EMS98) assigned to the Algarve region (Southern part of Portugal mainland) and part of Lisbon. This earthquake and its aftershocks were recorded by the Portuguese seismic network, and it can be considered as the best ever instrumentally recorded at the Portuguese national seismic network (Figure 1). A preliminary fault plane solution was computed from P-wave polarity inversion, pointing to an oblique reverse mechanism, which is in good agreement with the regional tectonic setting.
Figure 1. - Some records of the 2007.02.12 10:35 (UTC) earthquake recorded by the Portuguese national seismic network
1. Tectonic setting
Portugal is located at the western part of Iberian Peninsula. West of Portugal, the N-S oriented continental margin, related to the Atlantic opening and considered passive, crosses a tectonic boundary oriented E-W, between the Africa and Eurasia plates. Focal mechanisms and plate kinematics studies show that the Gorringe Bank (GB) and the Cadis Gulf (GC) are consistently characterised by compression (McKenzie, 1972; Auzende et al., 1978; Grimison & Chen, 1986, Cabral, 1993). However, it is hard to follow the precise location of the plate boundary close to Iberia. This is usually interpreted as the result of the relatively low inter-plate motion given by most kinematic plate models (e.g., De Mets et al., 1994; Sella et al. 2002; Fernandes et al., 2003), reaching about 4 mm/year along the NW-SE to WNW-ESE oriented eastern segment of the Azores-Gibraltar tectonic boundary. The Portuguese Instituto de Meteorologia (IM) network located the 2007.02.12 earthquake on the Horseshoe plane NW of the major Horseshoe thrust (HSF) trace (see Figure 2). This is an area where the major earthquake of 1969.02.28 (8.0MS [USGS]) took place and where the 1755 “Lisbon” earthquake (Magnitude 8¾ [Abe, 1979]) might have been originated. The dominant active structures in this region are the Gorringe Bank (GB), the Marquês de Pombal Fault (MPF), the Horseshoe Fault (HSF) and the Guadalquibir Fault (GQ) [Figure 2], which have been studied by several authors (Baptista et al., 2003; Terrinha et al., 2004; Zittelini et al., 2004). The 2007.02.12 (10:35 UTC) event is an expression of this interplate domain.
Figure 2. - Comparison between the fault plane solution obtained in this work by polarity inversion of 133 polarities from regional and global data (IM), and the fault plane solutions obtained from moment tensor solutions from regional and global data which were rapidly disseminated (ETHZ - Swiss Seismological Service, Zurich; INGV MEDNET network, Instituto Nazionale di Geofysica e Vulcanologia, Italy, IGN - Instituto Geografico Nacional, Spain; USGS - United States Geological Survey; HARV - Department of Earth and Planetary Sciences, Harvard University). Tectonic structures adapted from Terrinha et al. (2003), Matias et al. (2004) and Rovere (2002) [HAP - Horseshoe Abissal Plain; HSF - Horseshoe Fault; GB - Gorringe Bank; MPF - Marquês de Pombal Fault; PSF - Pereira de Sousa Fault; GQ - Guadalquivir Fault]
2. Seismic monitoring IM has recently introduced significant improvements in the Portuguese seismic network through a modernization project of the National Seismic Network (MODSISNAC). Since July 2006, seven new broadband stations have been installed on the mainland (Figure 3), connected in real-time by VSAT to the IM headquarters, in Lisbon. The data coming from two of them (PESTR and PVAQ) is sent to ORFEUS and IRIS/DMC in real-time. All of the new stations are equipped with very broadband sensors (3 Guralp 3T , 3 Guralp 3ESPCompact and 1 STS-2) and 24 bit digitisers (6 Guralp DM24 and 1 Quanterra Q330). Also, a short-period (SP) network is still in operation, with 15 stations installed on mainland (12) and Madeira archipelago (3), transmitting data by VSAT, public telephone lines and radio (UHF).
Figure 3. - Portugal mainland seismic network operated by the Instituto de Meteorologia
IM has adopted the SEISCOMP system (GEOFON, Potsdam) as the standard for data acquisition. Some of the older SP stations have already been integrated into the new acquisition system, and efforts are being made in order to integrate the remaining ones. Up to now, data from 17 seismic stations are concentrated at a central computer at IM, including available regional stations operating in real-time (RT) (MTE, from GEOFON with support from IM; EVO, from Évora University; MORF from Lisbon University, with support from IM) and part of the SP network. Also, data from other regional stations is being obtained from the ORFEUS Data Centre, using AutoDRM protocol. The data is analysed using SEISAN (Havskov & Ottemöller, 2005). With the availability of near real-time data, automatic processing is now possible. Two minutes after the 2007.02.12 event, 10:35:25 UTC, an automatic location was released by the AUTOLOC procedure (SEISCOMP) running on a test-bed at IM head-quarters. The manual solution was released 14 minutes after the earthquake occurred. 3. Hypocentre and Fault plane solution The local magnitude computed for the 2007.02.12 earthquake was 5.9ML. The hypocentre location (35.933ºN; 10.496W; 37 km depth) [Figure 4] was computed using 102 arrivals from 83 regional stations. The confidence ellipse (90%) has a major semi-axis of 4.3 km, oriented according to azimuth 135º, and a minor semi-axis of 2.5 km. The estimated hypocentre depth of 37 km is poorly constrained (±12km, computed at 90% confidence level) mostly due to the lack of nearby stations. However, centroid moment tensor inversions disseminated by several agencies pointed to a depth of about 42 km (e.g. HARV).
Figure 4. - Seismic activity in the 2007.02.12 epicentre area, between January 1961 and February 2007 (IM seismic catalogue 1961-2000 [Carrilho et al., 2004] and seismic bulletins). Red circles represent the epicentres within 150 km of the 2007.02.12 epicentre, and grey circles represents epicentres outside of 150 km distance from the referred epicentre.
Several source mechanisms based on rapid moment tensor inversion were released within a few hours after the event (IGN, HARV, ETHZ, USGS, INGV), where oblique reverse mechanisms type are determined but with small differences between them (Figure 2). Most of the moment magnitude determinations points to 5.9MW (HARV, ETHZ, USGS and INGV), which is in good agreement with the 5.9ML evaluation from IM. The exception is IGN, which computed 6.2MW. A preliminary fault plane solution was obtained using a method based on the inversion of the Pwave polarities (EXAUST algorithm, modified by Matias [pers. comm.] from Borges [1991]). A total of 133 polarities from regional and global stations were used. The solution points to a reverse mechanism with a slight strike-slip component (Figure 2). The fault planes have the following parameters: NP1- Strike 100º/Dip 40º/Slip 130º; NP2- Strike 232º/Dip 60º/Slip 62º. The resulting pressure axis has an orientation~N-S (Azimuth 342º). The preliminary focal mechanism computed in this work, showing oblique reverse faulting, is similar to what was obtained for the 1969 (7.5MS; Fukao, 1973) and 2003 (5.3MW; Stich et al., 2005) events that occurred nearby, but distinct from the one computed for the 2004.12.13 (5.4ML; Carrilho, 2005; 4.8MW; Stich et al., 2005), which corresponds to an event occurred some km to north-east. When considering the best epicentre solutions computed by the regional networks (IM and IGN), the correlation with significant major structural features, such as the Horseshoe thrust (HSF) is not straightforward. In fact, one of the nodal planes has an orientation
compatible with HSF surface trace and dip orientation, but the epicentre is located NNW of that structure. 4. Seismic activity The seismic activity observed in the Horseshoe abyssal plain is the result of the interaction of the Eurasia and Africa plates. Although most of the earthquakes are low to moderate magnitude, the offshore area located south-west of Portugal mainland coast is occasionally struck by strong earthquakes (M>6.0). Some of those larger earthquakes generated tsunamis. Examples of this activity are the 382 DC and the great 1755 “Lisbon” earthquakes. In more recent years, important instrumental events occurred here, like the mentioned 1969.02.28, which was the largest before the present event. Figure 4 shows significant seismic activity in the surrounding area, with 3 clusters of epicentres well identified. Figure 5 shows the distribution of earthquakes over time, where the developments of the seismic network explain the changes in detected activity. As it can be seen, the present earthquake was the largest in the last 38 years.
Figure 5. - Seismicity distribution over time, inside a region of 150 km around the epicentre of the 2007.02.12 earthquake
In the 10 days following the earthquake, only 6 aftershocks were recorded, with magnitudes ranging from 2.0 to 3.7ML, significantly lower than the main shock. This pattern is consistent with what was observed for the last larger earthquakes, like the July 29th, 2003, but very different from what happened in 1969, where significant aftershock activity was observed (Figure 5), which could be related with the large differences in magnitude of the main shocks. 5. Macroseismic effects The earthquake caused no damage, but it was widely felt with its macroseismic effects reaching large distances such as Madeira archipelago (~700km away from the epicentre region), Morocco and Spain, with felt effects at Santiago de Compostela (~800km) and Zaragoza (~1000km). A Web inquiry (http://www.meteo.pt/pt/sismologia/inquerito/sism_inq.jsp) was used by IM to collect macroseismic information, which proved to be a success with approximately 600 reports received. The estimated macroseismic field extends over an area of 3x106 km2. The maximum intensity of 5 (EMS-98) was reported from the Algarve region, southern part of Portugal mainland. Intensity 5 was also consistently assigned for one part of Lisbon, Campo Grande (Figure 6 and Figure 7). At Madeira archipelago, the earthquake was felt in city of Funchal with intensity 3. The punctual intensities felt over mainland are shown in Figure 6. It is very interesting to note that the intensities are extremely spread. According to EMS guidelines, reports concerning more than 5th floor were not considered. Nevertheless it was common that people in the same building or nearby zones felt the earthquake with a difference of one or even two degrees of intensity. Direct causes of these differences can be related to the site geology, building construction, human activity (usually high for that hour of the day) and human perception. The geographical pattern of responses follows the demographic distribution and Internet accessibility. It is noticeable that the region of Lisbon is consistently more affected (Figure 7), partially due to its higher vulnerability. But other causes can be considered present and should be studied in detail because this pattern is very common over available macroseismic history.
Figure 6. - Intensity distribution (EMS98) on Portugal Mainland - Effects of the 2007.02.12 earthquake
Figure 7. - Lisbon macroseismic effects (EMS98), from a preliminary assessment
6. Conclusions The 2007.02.12 (10:35 UTC) earthquake, while causing no damage, generated a large macroseismic field and a maximum intensity of 5 (EMS98) in the Portuguese territory. Its epicentre area is close to the large - 7.5MS earthquake on 1969.02.28. Few aftershocks were recorded during the following days. The fault planes computed from an inversion of a set of regional and global polarities, shows a reverse type mechanism with a component of strike-slip, similar to the solutions provided by other agencies from moment tensor inversion. The event was recorded by the new broadband stations which have been recently installed by IM in Portugal mainland, and it can be considered as the best ever instrumentally recorded earthquake in Portugal. The availability of extensive reports allowed the reformulation of all macroseismic data acquisition and analysis. New software tools were developed to gather and display macroseismic data based on the smallest administrative divisions of the Portuguese territory. Current outputs are GMT (Wessel and Smith, 1998) maps or layers for GoogleEarth® program. We intend to continue this strategy, aiming to compile automatically incoming e-mails with questionnaires in order to show
them in a graphic mode in the operational seismic centre to be used as preliminary macroseismic data in the alerts emitted by IM in the first minutes after the event. Validation seems still an important point and we noticed that questionnaires arriving in the first minutes are the most reliable of all. Acknowledgements The authors wish to thank Dr. Jose Morales, from Instituto Andaluz de Geofísica, Universidad de Granada, Spain, for providing part of the data. The authors also appreciate valuable comments given by Dr. Miguel Miranda. This work was partially supported by the Portuguese Science and Technology Foundation (FCT), project MODSISNAC. References Abe, K., (1979), Size of Great Earthquakes of 1837-1974 Inferred from Tsunami Data, J.Geophys. Res. 84 (NB4): 1561-1568. Auzende, J.M., Olivet, J., Charvet, J., LeLann, A., Le Pichon, X., Monteiro, J., Nicolas, A., Ribeiro, A., (1978), Sampling and Observation of Oceanic Mantle and Crust on Gorringe Bank, Nature, 273, pp45-48. Baptista, M.A., Miranda, J.M., Chierici, F., Zitellini, N., (2003), New Study of the 1755 Earthquake Source Based on Multi-Channel Seismic Survey Data and Tsunami Modeling, Natur. Haz. and Earth System Science, 3, 330-340. Borges, J.F., (1991), Métodos Automáticos na Determinação de Mecanismos Focais, Relatório de Licenciatura, Fac. Ciências, Univ. Lisboa, pp 93. Buforn E., M. Bezzeghoud, A. Udías, and C. Pro (2004), Seismic sources on the Iberia-African plate boundary and their tectonic implications, Pure Appl. Geophys. 161, doi: 10.1007/s00024003-2466-1. Cabral, J., (1993), Neotectónica de Portugal Continental, tese de doutoramento, Fac. Ciências, Univ.Lisboa, Portugal. Carrilho, F., Nunes, J.C., Pena, J., Senos, M.L., (2004), Catálogo Sísmico de Portugal Continental e Região Adjacente para o período 1970-2000, Instituto de Meteorologia, ISBN 972-9083-12-6. Carrilho, F., (2005), Estudo da Sismicidade da Zona Sudoeste de Portugal Continental, M.S. Thesis, Fac. Ciências, Univ. Lisboa, pp 172. DeMets, C., Gordon, R.G., Argus, D.F., and Stein, S. (1994), Effect of Recent Revisions to the Geomagnetic Reversal Time Scale on Estimates of Current Plate Motions, Geophys. Res. Lett., 26, 1921-1924. Fukao, Y., (1973), Thrust Faulting at a Lithosphere Plate Boundary: The Portugal earthquake of 1969, Eart Plan. Sci. Lett. 18, 205-216. Fernandes, R. M. S., Ambrosius, B. A. C., Noomen, R., Bastos, L., Wortel, M., Spakman, W. & Govers, R., (2003), The relative motion between Africa and Eurasia as derived from ITRF2000 and GPS data, Geophys. Res. Lett., 30(16), 1828, doi:10.1029/2003GL017089.
Grimison, N.L. and Chen, W.P. (1986), The Azores Gibraltar Plate Boundary: Focal Mechanisms, Depth of Earthquakes and their Tectonic Implications, Journal of Geophyical Research, 91, 20292047. Havskov, J., Ottemöller, L., (2005), SEISAN: The Earthquake Analysis Software, Version 8.1, Univ. Bergen, Norway. Matias, L., Terrinha, P., Mendes-Victor, L.M., MATESPRO team, (2004), The MATESPRO Multibeam Cruise Reveals Unknown Recent Tectonics in SW Ibéria. McKenzie, D.P. (1972), Active Tectonics of the Mediterranean Region, Royal Astronomic Society Geophysics Journal 30, 109-185. Rovere, M., (2002), Strutturazione del margine atlântico ibérico ed inversione miocenica in prossimità del limite di placca Eurásia-Africa, Tesi di Dottorato, Università degli Studi di Bologna. Sella, G., Dixon, T. H., & Mao, A.,( 2002), REVEL: a model for recent plate velocities from space geodesy, J. Geophys. Res., 107(B4), 2081, doi:10.1029/2000JB000033. Stich, D., Macilla, F., and Morales, J. (2005), Crust-Mantle Coupling in the Gulf of Cadiz (SWIberia), Geophys. Res. Lett., 32, doi:10.1029/2005GL023098. Terrinha, P., Pinheiro, L.M., Henriet, J.P., Matias, L., Ivanov, M., Monteiro, J., Akhmetzhanov; A., Volkinskaya, A., Cunha, T., Shaskin, P., Rovere, M., (2003), Tsunamigenic-seismogenic structures, neotectonics, sedimentary processes and slope instability on the southwest Portuguese Margin, Marine Geology, 195, pp 55-73. Wessel, P., Smith, W., (1998), New, improved version of the Generic Mapping Tools Released, EOS Trans. AGU, 79, 579. Zitellini, N., Rovere, M., Terrinha, P., Chierici, F., Matias, L., and BIGSETS Team, (2004), Neogene Through Quaternary Tectonic Reactivation of SW Iberian Passive Margin, Pure and Apl. Geophis., 161, pp 567-587.
J. Martín-Davila (1), A. Pazos (1), E. Buforn (2), A. Udías (2), M. Bezzeghoud (3), B. Caldeira (3), A. Rimi (4), M. Harnafi (4), W. Hanka (5), A. Nadji (6) 1.
Real Instituto y Observatorio de la Armada, San Fernando, Spain (mdavila@roa.es and pazos@roa.es) Departamento de Geofísica y Meteorología, Universidad Complutense, Madrid, Spain (ebufornp@fis.ucm.es) CGE and Physics Department., Universidad de Evora, Evora, Portugal (mourad@uevora.pt) Institut Scientifique, Université Mohammed V Agdal Rabat, Moroco (harnafi@israbat.ac.ma) GeoforschungsZentrum, Potsdam, Germany (hanka@gfz-potsdam.de) Université d’Oran – Es Sénia, Oran, Algeria (amansour.l@yahoo.fr)
2.
3. 4. 5. 6.
Introduction The western part of the Eurasia-Africa plate boundary crosses the Gulf of Cadiz at about 36ºN latitude, without a well defined boundary line. The plate convergence, at a rate of a few mm/year in a NNW/SSE to NW/SE direction (Buforn et al 2004), induces a moderate magnitude and shallow depth seismicity, but a clear intermediate activity (figure 1) is also present at the area and large magnitude historical events have been documented since the roman times (MartinDavila and Pazos, 2003), among them the 1755 Lisbon earthquake, with an estimated magnitude of 9.0. This event, with an epicentre located SW of Cape San Vicente, caused around 20000 casualties. More recently, on February 28, 1969, an 8.1 magnitude event was located in the same area. Both shocks induced a tsunami, with a measured wave height at Cadiz Bay of about ten meters for the 1755 event and one meter for the 1969.
Figure 1. - Distribution of epicenters at the Ibero-Maghrebian region for magnitude greater than 3.0 (IGN and ROA catalogues). The 12/02/2007 SW San Vicente Cape earthquake location is shown (yellow star). The different epicentral locations provided by several agencies are also plotted (right box).
On February, 12, 2007, at 10h 35m 25s UTC, a large earthquake, felt with Intensity IV (IGN) in the SW of Iberian Peninsula and NW Morocco, occurred in the same area. The preliminary parameters, provided by several agencies, estimated a magnitude close to 6.0 and located the epicentre in the vicinities of the 1755 and February 1969 events (figure 1). In this work we will describe briefly the seismological networks installed in the area by ROA (Real Instituto y Observatorio de la Armada) in collaboration with several Institutions, especially UCM (Universidad Complutense de Madrid), show some broad band stations records and provide the determined hypocentral parameters. ROA short period seismic network In order to study the viability of a tunnel or bridge between Spain and Morocco through the Gibraltar Strait, from a seismological point of view, a short period network (SFS Network) has been installed in that area by ROA in 1986 (figure 2), in collaboration with IGN (Instituto Geografico Nacional) and SECEGSA (Sociedad Española de estudios para la Comunicación fija a traves del Estrecho de Gibraltar). At present the network is operated by ROA and consists of eight vertical component analogue stations linked to ROA headquarters via radio UHF/VHF. These stations are presently being upgraded (Pazos et al 2005).
Figure 2, Left: ROA Short Period seismic network (SFS network). Right: February 12, 2007, San Vicente Cape earthquake records (P and S waves arrivals are picked with a red line).
Due to the characteristics of these stations and the relative short distance to February 12, 2007 earthquake epicentral location, the records are saturated. Some of them are shown on figure 2, where a clear impulsive P arrival has been marked, but only for MOMI station the S wave could be picked. Western Mediterranean (WM) broad-band seismological network To avoid the problems associated to the short period instruments, like those mentioned above, ROA and UCM, with the support of GFZ (Geoforschung Zentrum, Potsdam), have installed a broad band seismological network in Southern Spain and Spanish sites in Northern Africa. Since 2005, and because of the extension of the network outside Spain, the network code is WM (Western Mediterranean, FDSN), replacing the ROA/UCM initial one (Buforn et al 2002). At present nine stations are in operation (figure 3): three on the Spanish mainland (SFS, EMAL and CART), one on the Balearic Islands (MAHO), three stations at Spanish sites at Northern Africa: MELI, PVLZ, and CEU, one in SW Portugal (EVO, Evora University), and, one in Morocco (AVE, Institut Scientifique of Rabat, ISRABAT), with headquarters and data center at ROA. All stations have Streckeisen STS-2 sensors, Quanterra or Earth Data digitizers, and a Seiscomp acquisition system. Most data are available in near-real time (phone line or Internet) except for PVLZ, CEU and AVE, which will be available in the near future. Two more stations are planned for the near future, at Ifrane Observatory, Morocco (ISRABAT), and Oran, Algeria (Université d’Oran), both of them in collaboration with ROA and UCM. A deployment of Ocean Bottom Seismometers (“ALBORAN” permanent OBS and “Red FOMAR” temporal network), funded by Spanish Education and Research Ministry (MEC), with the collaboration of Spanish Navy, is planned to be carried out within 2007.
Figure 3, Left: Western Mediterranean (WM) BB seismic network. Right: February 12, 2007, San Vicente Cape earthquake records (P and S waves arrivals are picked with a black line).
Some broad band records of the February, 12, 2007 San Vicente earthquake from WM stations are shown in figure 3. Data plotted correspond to BH (20 sps), SH (50 sps) or HH (100 sps) channels. Earthquake parameters To determine the earthquake parameters we have used the HYPOCENTER 71 programme (Peters and Crosson, 1972), using all phases picked from SFS and WM network stations. Two more P phases from TAF and RBA analog stations (ISRABAT, Morocco) were also used (Ramdami, F. personal communication). As shown in figure 1, different epicentral locations have been given and the calculated hypocentral depth also shows large differences, from 10 km (IRIS, USGS) to 65 km (IGN). We have calculated the location by fixing the depth between 10 and 80 km. The best solution obtained from our data gives very similar solution residuals for a hypocentre located between 45 and 60 km depth: Date: 12/02/2007 Ho: 10:35:26.80 UTC Lat: 35.9740 N Long: 10.0131 W Depth: 45.0 km. Mag.: 6.07 Acknowledgements This preliminary report has been partly funded by the Spanish Ministry of Education and Science (MEC) through the projects: REN2006-10311-C03-01/02 (RISTE), RIOA05-23-002 (OBS ALBORAN) and CGL2005-24194-E (RED FOMAR). Bibliography Buforn, E., Bezzeghoud, M., Udías, A. and Pro, C. (2004). Seismic sources on the Iberia-African plate boundary and their tectonic implications. Pure Appl. Geophys. 161, 623-646. Buforn, E., Udías, A., Martín Davila, J., Hanka, W., and Pazos, A. (2002). Broadband station
network ROA/UCM/GFZ in south Spain and northern Africa. Seismological Research Letters, 73, 2, 173-176 Martin Davila, J.and Pazos, A. (2003), Seismicity of the Gulf of Cádiz and surrounding areas. Física de la Tierra, 15, 189-210. Pazos, A.; Alguacil, G.; and Davila, J.M. (2005), A simple technique to extend the bandwidth of electromagnetic sensors. Bulletin of the Seismological Society of America, 95, 1940-1946. Peters, D. and Crosson, R (1972). Application of prediction analysis to hypocenter determination using a local array. Bulletin of the Seismological Society of America, 62; 3; 775-788.
Commercial digital audio recorders: a new life for portable Lennartz PCM 5800 seismic stations M. Capello, M. Castellano, P. Ricciolino Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano, Via Diocleziano 328, 80124 Napoli, Italy Introduction In the last two decades the use of mobile digital seismic stations has become more and more widespread both for active and passive seismological studies. Many industries have designed and realized seismic stations suitable for portable use and characterized by small dimension and low power consumptions. The modern portable seismic instruments are generally provided with 24 bit AD converter, GPS time code and acquisition on high capacity hard disk and/or continuous data stream for telemetry. These data loggers are generally equipped with high sensibility broad-band seismometers. The PCM 5800 Digital Seismological System has been produced by LENNARTZ ELECTRONIC GmbH (Tubingen, D) since the middle Eighties. It became the first digital seismic equipment for many european and worldwide seismological institutions and laboratories, in many of which it is still in operation. This instrumentation, however, suffers of a weak point which is the acquisition based on a UHER magnetic tape recorder (13cm wheels) with low capacity (about 8 MB; 90 minutes of continuous recording at 4.75 cm/sec speed). This UHER recorder has high maintenance costs and it often needs expensive repairs. We propose to replace the UHER recorders with an easy and cheap solution based on commercial digital recorders with removable media in order to continue to use the high number of instruments (Encoder and Decoder) still held by the seismological community, without any modification to the existing hardware and software. The PCM 5800 System The PCM 5800 System is based on a 12 bit Analog-to-Digital Converter reaching a dynamic range of 120 dB by means of a gain ranging amplifier. This seismological system has been produced in three configurations: Encoder (4-to-16 input), Mixer (up to 63 telemetered digital data streams from Encoders) and Decoder (for playback with analog output and/or IEEE-488 digital output). The most widespread acquisition system is the first one in four-channel configuration (for a threecomponent seismometer plus one free channel) recording on UHER 13cm magnetic tape recorder and equipped with a Decoder unit for the data playback (Figure 1). In this paper we refer to this configuration as the standard equipment for portable use.
Software programming is realized through an alphanumeric display terminal (Figure 1). The acquisition is based on the classic STA / LTA (Short Term Average / Long Term Average) triggering algorithm. The software is easy to use and very adaptable. Standard time code is DCF77 (77.5 kHz), however a GPS-DCF Time Code Receiver is also available. The PCM output of an Encoder acquired by an UHER recorder set at 4.75 cm/sec tape speed is 10kbits/sec. The playback of the data is performed by means of a Decoder PCM 5800 unit linked to a REVOX B-77 MK II tape recorder. An IEEE-488 interface allows the transfer of the recorded signals on a personal computer for analyses and storage.
Figure 1. - A standard 4 channel PCM 5800 Encoder in a 19” rack (from Lennartz Electronic, 1983).
As mentioned before, the UHER recorder has been a weak point of the system because of its high maintenance costs. After about eight to ten years of intensive use, the motor of the recorders crashes and it can not be repaired! To solve this problem LENNARTZ ELECTRONIC GmbH introduced the so called “Digital UHER”, that is based on a MarsLite/HD system recording on a 4.3 GB hard disk. Although this system allows the continuous data acquisition in a modern format, it forces to “leave” the existing and working instruments such as PCM 5800 Decoders, playback recorders and IEEE-488 interface cards. Moreover, the software for data playback and analysis must be changed. We think that the alternative solution to the UHER recorder should fulfill some basis requirements: • Quick implementation in the PCM 5800 System, with the use of simple electronic controls. • Preservation of the recording and decoding data format, in order to use the existing instruments (encoder and decoder) and software. • The use of commercial cheap digital recorders with removable media, for easy data recovery. We suggest to use MiniDisc digital audio recorders as a simple solution to substitute the UHER recorders. These recorders are designed by SONY CORPORATION and also produced by other commercial firms. The MiniDisc System The SONY CORPORATION produced the first generation of MiniDisc recorders on 1992. This system allows to record the same amount of audio signals of a CD (650-700 MB) on a 2.5” magneto-optical disc of about 160 MB of capacity with practically the same audio quality. This is possible using innovative ATRAC (Adaptive TRansform Acoustic Coding; “SP” at 292kbps) data compression system and its ATRAC3 development (MDLP MiniDisc Long Play “LP2” at 132kbps and “LP4” at 66kbps). The recording duration is 60, 74 or 80 minutes according to the media format and the frequency response is 20 – 20.000 hz. The ATRAC and ATRAC3 audio encoding technologies are based on psychoacoustic principles
(Tsutsui et al., 1992; Sony Product, 2000). The audio signal in the time domain is converted in a signal in the frequency domain and then it is compressed by means of a psychoacoustic model of the human hearing. In the ATRAC coding (Figure 2) the signal is splitted in three sub-bands by means of two QMF's (Quadrature Mirror Filter). A gain control is applied to each band, which are then converted in the frequency domain using MDCT (Modified Discrete Cosine Transform). During the reproduction an IMDCT (Inverse MDCT) is applied for each band and the audio signal is generated using a band synthesis filter.
Figure 2. - Block diagram of ATRAC encoder (after Yoshida, 1994)
The ATRAC3 coding achieves twice the frequency resolution of ATRAC, splitting the signal in four sub-bands and using longer MDCT conversion blocks. This allows us to increase the output frequency domain signals (Sony Products, 2000). The compression ratio obtained with ATRAC SP is about 5:1, whereas with ATRAC3 LP2 and ATRAC3 LP4 it becomes 10:1 and 20:1 respectively. The ATRAC “SP” encoding at 292 kbps is able to record the 10kbits/sec PCM data stream without loss of information. The frequency bands in which the input signal is splitted and compressed do not compromise the completeness of the seismic signals. Unfortunately, the time duration of the MD media (60, 74 or 80 minutes) is too short compared to the 13cm magnetic tape. This problem has been overcome with the new generation of the MiniDisc, named Hi-MD and produced by SONY during 2004. The present SONY Hi-MD recorders/players use the new high capacity (1 GB) magneto-optical removable media. Hi-MD equipment enables uncompressed linear PCM recordings (16 bits / 44.1 kHz) and the up to date ATRAC3plus audio compression technology (Hi-SP: 256 kbps, Hi-LP: 64 kbps) with the same frequency response of the previous MD recorders (20 – 20.000 hz). The recording duration with 1 GB media is 94 minutes in linear PCM encoding and 475 minutes (7h 55m; more than five times the 13cm magnetic tape duration!) in Hi-SP encoding (Table 1). Moreover, the Hi-MD recorder can reformat traditional 80 minutes MD media in Hi-MD media with 305MB of capacity. In this case the recording duration becomes 28 minutes in linear PCM and 140 minutes (2h 20m) in Hi-SP encoding (Table 1). For our purpose both linear PCM and Hi-SP mode can be used to record PCM data in trigger configuration. The Hi-LP mode is not appropriate for our purpose, due to the data flow which is too low for the PCM data stream.
Hi-MD and Electronic controls Not all the SONY Hi-MD models currently on the market are useful to record and reproduce PCM 5800 signals. In order to record, an instrument with LINE-IN input and remote control is enough, whereas to reproduce the data an apparatus provided with LINE-OUT output, characterized by an output level of 194 mV, is necessary. The only headphone output is not enough to decode PCM signals due to its too low output level (~ 1.4 mV).
Table 1. – Audio encoding and capacity on Hi-MD. (after Sony Corporation 2004, modified).
Among the SONY Hi-MD production, we have selected, according to price-performance ratio, the MZ-NH700 and MZ-RH910 models to record data and the MZ-NH900 model to reproduce them linked with a Decoder PCM 5800 unit. In order to use the Hi-MD recorders, instead of UHER tape recorders, we have designed and realized two electronic circuits: the first one for the Recording Control, the second one for the Link with the PCM 5800 Decoder unit. Circuit for the Recording Control The PCM signal is characterized by a 0 / +5V level. In order to record data on the Hi-MD recorder, the signal must be characterized by a 0 centred level. Therefore, the PCM signal is high-pass filtered (0.1 Hz) before the Hi-MD LINE-IN input. The circuit for the Recording Control, as the following one realized by the Maintenance and Development of the Seismic Network Laboratory at OV-INGV, makes use of a characteristic of the MiniDisc “PAUSE” control. During a recording, the PAUSE command stops the recording itself and it leaves the apparatus in this stage indefinitely. A new PAUSE command restarts the recording in a new file, which is stopped with a further PAUSE command, and so on (see Table 2).
Table 2. – Block diagram of the control sequence and Hi-MD functions. Red controls are related to manual commands, the green ones are related to electronic circuit instructions. If the power supply decreases under 10V, the STOP command is enabled by the electronic circuit.
Using the keys of the wired remote control, the electronic circuit enables the PAUSE command in correspondence with the TRIGGER ON and TRIGGER OFF impulses resulting from the trigger algorithm of the PCM 5800 station. The electronic circuit diagram for the recording control is shown in Figure 3A. Note that the recorded data will be saved on disk only after the STOP command. To avoid that a too low power supply could cause the unexpected recorder switching off with the loss of the data, a voltage comparator is introduced in the electronic control circuit. If the power supply decreases under 10V, the circuit enables the STOP command on the wired remote control and the data will be saved on disk. The diagram of the voltage comparator is shown in Figure 3B.
Figure 3. - A) Diagram of the electronic circuit for the recording control, B) Diagram of the voltage comparator circuit
In Figure 4 the BKS (Mt. Vesuvius) PCM 5800 station equipped with a SONY Hi-MD (MZ-NH700 model) is shown. The power supply for the Hi-MD is taken from the DC/DC converter module of the PCM 5800 station.
Figure 4. - The PCM5800 station BKS (installed in a concrete bunker on Mt.Vesuvius) in 19” rack, equipped with SONY Hi-MD MZ-NH700. The black box on the left contains the circuit for the recording control.
Circuit for the Decoder Link The output signal of a Hi-MD is an audio signal characterized by variation both in amplitude and frequency. A simple electronic interface that maximizes and normalizes the signal amplitude at a level of +5V is necessary to connect the Hi-MD output to the Decoder unit. In this way the original squared shape of the PCM signal is reconstructed and the Decoder unit is able to elaborate it. The electronic circuit diagram for the Decoder link is shown in Figure 5.
Figure 5. - Diagram of the electronic circuit for the Decoder Link.
Discussion and Conclusions The PCM 5800 is an “old” system compared with the present available seismic instruments. Nevertheless, many seismological research institutes have a lot of these stations still working. The SONY Hi-MD recorder is not a concurrent of the LENNARTZ “Digital UHER”, because it is not suitable for continuous recording, however it is a good solution to give a “new life” to the PCM 5800 digital stations in trigger configuration. The Hi-MD recorder is cheap, small, light and has low power consumption. The electronic controls are simple to realize. The capacity of the new 1 GB Hi-MD media is large compared with the old 13cm magnetic tape (more than five times). With recording windows of about 50-60sec (pre-event + coincidence + triggering + post-event) about 500 events can be recorded on a Hi-MD (ATRAC3plus, Hi-SP at 256 kbps). In this case, we prefer removable media to hard disk recorders, as data recovery involves only a simple change of the media. Moreover, the magneto-optical media are rewritable for more than one million times without data deterioration (Yoshida, 1994). We believe that PCM 5800 stations can be usefully deployed during temporary surveys and to improve local seismic network geometry with high-dynamic digital three component stations in local recording, without the typical problems of the radio links (direct visibility, interferences). With this objective, the STA/LTA triggering algorithm can be set up at high values (6 or 8). In such way, even if the low magnitude earthquakes may be lost, it is possible to reduce “false” triggers caused by human activity and noise. In Figure 6 an example of seismic recording with SONY Hi-MD, relative to a regional earthquake, is shown.
Figure 6. - M 3.3 regional earthquake (D=50km) of October 14th 2004 recorded at Lennartz PCM5800 station BKS (Mt.Vesuvius) equipped with Sony Hi-MD MZ-NH700 recorder and Lennartz Le-3D/1s seismometer. Trigger parameters: STA=1s, LTA=51s, STA/LTA=8.
Acknowledgments SONY Italia is greatly acknowledged for its cooperation. We are grateful to F. Bianco for her continuous incentive to experiment with new technological solutions. Many thanks to C. Buonocunto and A. Caputo for their collaboration. All marks belong to lawful owners. References Lennartz Electronic (1983); Manual for PCM5800 Encoder. Tübingen, Germany, 189p. Tsutsui K., Suzuki H., Shimoyoshi O., Sonohara M., Akagiri K. and Heddle R.M. (1992); ATRAC: Adaptive Transform Acoustic Coding for MiniDisc. 93rd Audio Engineering Society Convention, San Francisco, 1992 October 1-4, n° 3456. Sony Corporation (2002); ATRAC3 Sony Corporation (2004); Sony Hi-MD Sony Products (2000); ATRAC3 High-Quality Audio Encoding Technology. CX-NEWS, vol. 22. Yoshida T. (1994); The Rewritable MiniDisc System. Proc. 1994 IEEE, USA, vol. 82 no. 10; pp. 1492-1500.
SEISAN: Multiplatform implementation of MINISEED/SEED J. Havskov 1, L. Ottemöller 2 and R.L.P. Canabrava 1
1 2
Department of Science, University of Bergen, Bergen, Norway Britisch Geological Survey, Edingburgh, UK
Introduction SEED (Standard for the Exchange of Earthquake Data) has been around for nearly 15 years and is the FDSN (International Federation of Digital Seismograph Networks) standard for storing and exchanging seismic data. At its introduction, there were plans to quickly make toolboxes for several computer platforms and programming languages so it should be easy to read and write for everybody. Some software were written for C and Unix, however it has taken a long time for SEED to spread to other platforms and languages and SEED has mainly been used for data storage by the big data centers. Essentially, there is currently only one good SEED reading program, rdseed, which works on Unix and Linux. At the time of writing this article, a Java version of rdseed is being developed at IRIS, which will work on different platforms. It is called jrdseed and is available for testing. While some SEED utilities and libraries are available, developed by different agencies, little has been done to facilitate use of SEED under Windows. In this communication, we describe an implementation of MINISEED/SEED routines with the SEISAN processing software. Considering the huge amount of SEED data and the easy availability of it, it is surprising that there has not been a lot processing software developed to use SEED. Although SEED was constructed for long term archiving and data exchange, there is no good reason for not using it for processing. However lack of generally available processing software has made the current practice to download SEED, get it to some other format like SAC and start processing. This seems very backwards. Here we have a format with all required information, fast to read due to compression and easy to adapt to direct access. So why fool around with many other formats? The answer seems to be that general reading software is scarce, a general reluctance to start programming from scratch, particularly since SEED has got the reputation of being the most complex format for seismic data on earth (probably true, was also the authors opinion). The mammoth SEED manual is enough to scare any potential programmer before even starting, it certainly is not bedside reading. A reduced version of SEED without the header information is MINISEED. MINISEED is easier to deal with. However, it is not complete data since the instrument response is missing. Fortunately, MINISEED has gained wider acceptance on a lower level and much more software is available for MINISEED than for SEED. An example is the SeismicHandler processing software that reads MINISEED data. For Java programmers, there is MINISEED reading software made by Lomax as implemented with SeisGram2K. The most important factor contributing to the wider acceptance is that nearly all commercial recorders now record directly in MINISEED and a de facto standard has
been established, not a small thing in the individualistic seismologist world. This was actually attempted before with SUDS, but never caught on due to problems of agreeing on a unified UnixWindows standard. Fortunately SEED has no such problems. SEISAN (Havskov and Ottemöller, 2000) is probably the only major processing system that works identically on several computer platforms (including Microsoft Windows). It has long been a wish to read MINISEED, however for the reasons mentioned above, it never got under way. Fortunately for us, we got some free programming time (co-author C. R.) and gave him the challenge to make a MINISEED reading routine. The initial idea was to fish out the reading routines from rdseed and link it to Fortran, however rdseed is a very integrated program and far from being a toolbox, so this proved not practical. Since the routines were to be written from scratch, it was done in Fortran77 which makes integration easier with SEISAN (also written in Fortran). Nevertheless, rdseed was an invaluable help in writing the programs. It turned out that reading MINISEED was not such a terrible job, making us wonder why we did not do it a long time before. Since SEISAN is a processing system, it would be even more useful to also read SEED, which is almost like reading MINISEED if the main headers are skipped so that was also implemented. This of course gives throws away the instrument response, which is in the SEED main headers. On the other hand, if we run a network, the instrument response does not change every day so it is enough to have the corresponding response files. So the last thing implemented was that SEISAN can read the SEED response files EXACTLY as extracted with rdseed without change of name. Finally MINISEED writing has also been implemented in SEISAN, also with Fortran routines. All these routines are identical for Solaris, Linux and Windows and written without any reference to SEISAN, so it should be possible to use them for other programs. Implementation The SEED format has very many possibilities of writing seismic and other data and rdseed is probably the only software that can deal with it all. We have no such aspirations, the main goal was to be able to read nearly all data written in SEED. The following will describe what was done and the limitation of the software. The reading routines we developed have the following capabilities:
q q q q q q
q
read SEED and MiniSEED files; read multiplexed files; use direct access to read; read sections of large files; the data can be in 32-bit integers, Steim 1 or Steim 2 compressed format; can read files with different compression formats in different blocks (only if the blocks have blockette 1000, see SEED manual); can read block sizes of up to 32 Kbytes.
The functions in the library were designed in order to be used in two steps. First, the file is summarized (by reading all headers in file), that is, we identify the number of channels, and the following information for each of them: station name, channel (component) name, start time, sample rate, number of samples, flag of timing quality, start and end position in the file. This summary is built by checking the information of the fixed header in the Data Records. It means that the SEED headers are mostly ignored. Only the block size and the encoding format are used, when there are SEED headers. After summarizing the file, it is possible to read the waveforms for each channel. Since some files may cover periods of time that are too large for the buffer in the calling program, the library offers a way to read just an interval of the channel.
Testing Different SEED and Mini-SEED file writers generate files with different particularities. That often forced us to change the way to read the files, so our program could work with all the different files tested. This probably covers most file types used, however, there will probably be files we cannot read. In order to get possible problem files, a test version of some SEISAN programs with SEED reading capability was made available to SEISAN users and this brought our attention to some problems. All files were tested on all 3 platforms. Here we will report some of the testing. For details, see Canabrava (2004). Mini-SEED files generated by: Orfeus SEED files tested from Orfeus had more than one blockette 30. This means that different channels can have different encoding formats. All files tested from Orfeus were ok. IRIS The files created by IRIS may also have different encoding formats for each channel. The files tested presented another difference in implementation. The record length of the Data Records may differ from the length in the headers. The only such combination seen so far was 4096-byte blocks for headers and 512-byte blocks for Data Records. The way we implemented this would fail if different channels have different block sizes. However we found no such files and all files tested were ok. It's worth noting that IRIS files use the 8 th byte of data records as a continuation code, although the SEED manual says it should always have a space character (ASCII 20). Quanterra data logger Quanterra files are multiplexed and required a different set of routines. Also the multiplexing is not regular, often you can find sequences like: BHE BHN BHE BHZ. It means that, when reading the waveform, we cannot take full advantage of direct access, unless all the blocks are indexed in memory. Since we only store the start and end point of each channel, by the time we decompress the waveform we have to go again through all blocks in between, check the headers and discard the ones that don't belong to the channel. Other files We also tried files from Seedlink, Kinemetrics and Guralp SCREAM and found that they are all well behaved MINISEED files. Writing MINISEED Functions for writing Mini-SEED were developed in Fortran as well. The Fortran routines are in the same library as the functions for reading SEED files. They have the following characteristics:
q q q q
the data can be written in 32-bit integers or in Steim 1compression; the block size can be up to 4096 bytes. write one channel at a time, using as many blocks as necessary; write the blocks to a file.
The writing routines were also tested on all 3 platforms. Closing remarks SEISAN in the latest release, fully supports reading SEED, including the response files so it should be very easy to download data from a data center and start processing right away. The ability to read directly a segment of a large SEED volume, or browsing through a big volume should further make it easy to process the data. However, due to the format's complexity it will take some time to further test and debug the software. Hopefully the SEISAN implementation will promote more use of SEED, which it certainly deserves. Acknowledgment During programming, Reinoud Sleeman provided help in figuring out some of the obscure sides of the SEED format and provided valuable suggestions. He also made many valuable suggestions/ corrections to this communication. We also appreciated discussions with Chad Trabant and have used his MSI tool to check miniseed files (http://www.iris.edu/chad/). References Canabrava, R. N. B. (2004). A toolbox for reading SEED and MiniSEED and writing MiniSEED. Norwegian National Seismic Network, Technical Report No. 18, department of Earth Science, University of Bergen. Havskov, J. and L. Ottemöller (2000). SEISAN earthquake analysis software. Seismological Research letters, 70, 532-534. IRIS Consortium. Standard for the Exchange of Earthquake Data – Reference Manual, 2nd Edition, February 1993.
Current ORFEUS ExeCom The current ORFEUS Executive Committee consists of:
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Peter Labak (Geophysical Institute, Slovak Academy of Sciences, Bratislava) (president) Thomas Meijer (University of Bochum) Alberto Michelini (INGV, Rome) Johannes Schweitzer (NORSAR, Oslo) Nikolai Shapiro (IPGP, Paris) Jan Zednik (Geophysical Institute, Academy of Sciences of the Czech Republikc, Prague)
The extended Executive Committee also includes the working group chairmen:
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WG1 WG2 WG3 WG4
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Josep Vila (IEC, Barcelona) Marco Olivieri (INGV, Rome) Alex Brisbourne (SEIS-UK, Leicester) Joachim Saul (GFZ, Potsdam)
The ExeCom of ORFEUS is assigned by the board of directors and is responsible for running ORFEUS and providing directions to the ORFEUS staff. ORFEUS ExeCom and ORFEUS Board meeting; Zurich, June 12 & 13, 2007 The ORFEUS ExeCom meeting and the ORFEUS board meeting will take place in conjunction with the NERIES Annual meeting on Wednesday, June 12 and Thursday, June 13 (respectively) (and not June 14 as stated in the earlier newsletter). Also the EMSC General Assembly will take place on Thursday, June 13, in Zurich (at ETHZ). ORFEUS WG2 workshop, preliminary scheduled at ZAMG, Vienna, October 8-11, 2007 The Zentralanstalt für Meteorologie und Geodynamik (ZAMG) will host the next ORFEUS WG2 workshop on 'Installation and operation of broadband stations'. This time extra attention will be given to temporary deployments BB stations and archival of data from such projects. More details will become available on both the ORFEUS web site (http://www.orfeus-eu.org) and the NERIES web site (http://neries.knmi.nl). NERIES Annual meeting; Zurich, June 11-13, 2007 NERIES will have its first year Annual meeting in Zurich, June 11-13 (at ETHZ). This meeting is an open meeting and provides an overview of the current infrastructure developments within NERIES. We do request you to register in advance. This can be done on the NERIES project web pages (http://neries.knmi.nl). Here you can also find the preliminary programme. Many of
the current activities within ORFEUS are driven by what is going on in the NERIES project. XML developments for earthquake data exchange (continuation) The XML developments reported in the last newsletter can now be followed on the ETHZ web pages (http://proto-quakeml.ethz.ch).
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Goal and ambition: The ORFEUS Electronic Newsletter intends to provide information on seismological monitoring and research infrastructure developments, i.e. technology, software, observational and analysis practices, standardization efforts, networks, instrumental deployments, and fast reports on recent events in and around Europe . We aim at material that is usually not accepted in scientific journals, but still has significant informative value to earth scientists, network and station operators and students. Our main area of interest will be Europe and its immediate surroundings. The ORFEUS website (newsletter) will be an archived, fully referable electronic publication. Original contributions with relevant practical and informational material on seismological observations are invited. Audience and distribution: Seismologists interested in ORFEUS activities and data monitoring infrastructures within the European-Mediterranean area (including the Middle East ). ORFEUS participants may, upon request, receive (color) printed hard copies. Others can order (on cost basis) individual printed copies of the Newsletter. This service will only be provided in limited form. Editor(s): Torild van Eck and Lars Ottemöller, ORFEUS is soliciting for additional editor (s). Contributions: Anybody within the ORFEUS related community is encouraged to submit contributions to one of the editors. The articles will go through a short review process, after which the authors will be informed of the decision. Articles should preferably have a length of about 3-4 A4 (single-spaced) pages (less than 1500 words) and contain about 2-6 figures.
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