Observations of Earth’s Free Oscillations by Gujarat Superconducting
Gravimeter and MPGO Network of Kachchh
Arun Gupta, Rashmi Pradhan and B.K.Rastogi
E-mail:akg_mgs@yahoo.com
Institute of Seismological Research, Raisan, Gandhinagar-382 009,Gujarat,India
Gujarat dual sphere superconducting gravimeter (SG-055) was installed
on March 01, 2009 at Badargadh (BG) in Kachchh (Lat 23.47ºN, Long 70.57 ºE).
Tonga region earthquake (M 7.6) of March 19, 2009 and Samoa earthquake (M
8.2) of September 29, 2009 excited the earth’s free oscillations. Besides some
large and moderate earthquakes these two earthquakes are very well recorded
on SG records. The frequency and amplitude of free oscillations have been
estimated and compared with earlier global observations of seismometer and
SG. Estimated free oscillations validate the quality of recorded data. SG was
installed as a part of Multi-parametric Geophysical Observatory (MPGO)
instruments and SG data will be supplemented by several other parameters.
Institute of Seismological Research (ISR) has established a network of
four MPGOs at Bhachau, Vamka, Desalpar and Badargadh in Kachchh which is
operational from March 2009 and fall in the aftershock zone of 2001 Bhuj
earthquake (Mw 7.7) for earthquake precursory research. Several seismological /
geophysical / geochemical parameters are under continuous monitoring through
other MPGO instruments like Very Broad Band Seismometer (VBBS), Strong
Motion Accelerometer (SMA), Global Positioning System (GPS) and radon
recorders at all the four sites. Borehole strainmeters have been procured and are
to be installed at three sites. Fluxgate magnetometer is installed at Desalpar and
Vamka. Further, water level recorder is installed at Desalpar. Four water level
recorders will be installed shortly in these areas. ULF/VLF induction coil
magnetometer, Declination/inclination magnetometer, overhauser magnetometer
and helium recorders are to be purchased.