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Seismic Vulnerability Assessment of Hill Stations Mussoorie and

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Seismic Vulnerability Assessment of Hill Stations Mussoorie and Powered By Docstoc
					                                         Housing and Disaster Mitigation Efforts in India: Case Studies
                                                                                         April 18, 2009.


           Seismic vulnerability assessment of Mussoorie &
                    Josimath, Uttarakhand (India)

      Joshi, Girish Chandra 1, Rautela, Piyoosh 2 and Bhaisora, Bhupendra
  Disaster Mitigation and Management Centre, Department of Disaster Management, Government of
                  Uttarakhand, Uttarakhand Secretariat, Dehradun – 248 001, India
                      Email: 1 algirish@gmail.com, 2 piyooshrautela@gmail.com



Abstract
    The paper analyses the seismic vulnerability of Mussorie and Joshimath, Uttarakhand. It
examines how masons have switched over to alien building practices without formal training
of the same which makes structure vulnerable to seismic forces. When building stock of
Mussorie and Joshimath was surveyed using GIS facilities, they were divided into five classes.
Majority of the buildings fall in Grade 3 to Grade 5 damage in case of earthquake shaking of
intensity VIII.

Keywords
Seismic Vulnerability, Alien building practices, GIS facilities.


Brief
    Himalaya has evolved due to the convergence, subduction and eventual collision of Indian
and Eurasian plates. Ongoing tectonism is responsible for high seismic vulnerability of the
region. The region has been jolted by four Great Earthquakes (magnitude > 8 on the Richter
scale); 1897 Shillong Earthquake, 1905 Kangara Earthquake, 1934 Bihar–Nepal Earthquake
and 1950 Assam Earthquake, apart from Kumaun earthquake of 1720 and Garhwal earthquake
of 18031. Regions between the rupture zones of the Great Earthquakes are recognized as
seismic gaps that are interpreted to have accumulated potential slip for generating high
magnitude earthquakes.
    Entire State of Uttarakhand is located in the seismic gap of the 1934 Bihar–Nepal
Earthquake and 1905 Kangara Earthquake, and is categorized under zones IV and V of the
Earthquake Risk Map of India2. This region has been identified as a potential site for a future
catastrophic earthquake3,4 and has witnessed seismic events of lesser magnitude (1991
Uttarkashi Earthquake, 1999 Chamoli Earthquake) in the recent past. These earthquakes have
demonstrated seismic vulnerability of the building stock in the region that was primarily
responsible for large number of human casualties in these events.
    Most structures (almost 97 percent) in the region are non-engineered and seismic
performance of these structures is a function of the knowledge and skill of the masons, as also
awareness of the masses. Discontinuation of traditional building practices and switching over
to alien building material without formal training in the use of the same has added to the
seismic vulnerability of the region. The masons responsible for constructing the structures are
not fully trained in the use of building material as also earthquake resisting construction
techniques. The masses are at the same time ignorant of the nature of the threat and the



                                                                                                      1
                                                                            (HDME -09), IIT Roorkee


available technologies to mitigate the same. Inadequate building bye laws and lenient
regulatory regime only adds to the problem.
    Unsafe construction practices are going on unabated and unless stern action is initiated
soon the seismic risk is bound to rise with passage of time. Before initiating any plan to
mitigate the risk it becomes imperative to have stock of the existing vulnerability scenario.
Detailed assessment of the seismic vulnerability of the built environment was therefore carried
out in Mussoorie and Joshimath towns of Dehradun and Chamoli districts that fall in Zone IV
and V of Seismic Risk Map of India2 respectively. Every individual building of these towns
was assessed for its seismic vulnerability. Data collection form of FEMA for Rapid Visual
Screening (RVS) 5.6 was modified to suit local conditions and was utilized for this purpose.
The building stock surveyed was subsequently categorized on the basis of their differential
seismic vulnerability based on the European Macroseismic Scale (EMS–98). The data was
mapped on high resolution satellite images of the area and GIS facilities were utilized for
analysis. Based on their damageability the entire built environment of the two towns was
classified into five classes. Damage probability matrix has at the same time been drawn for
vulnerability assessment.
    The data of Mussoorie shows that a total 623 buildings (19 percent of the surveyed) show
high probability of Grade 5 damage and very high probability of Grade 4 damage, while 587
buildings (17 percent of the surveyed) show high probability of Grade 4 damage and very high
probability of Grade 3 damage in case of earthquake shaking of Intensity VIII or more. As
there are only a few multistoried structures in Josimath only 16 buildings (1 percent of the
surveyed) fall in high probability of Grade 5 damage and very high probability of Grade 4
damage, 25 buildings (1.5 percent of the surveyed) fall in high probability of Grade 4 damage
and very high probability of Grade 3 damage and 998 buildings (59 percent of the surveyed)
fall in high Probability of Grade 3 damage and very high probability of Grade 2 damage in
case of earthquake shaking of Intensity VIII.

References
[1]    Thakur, V. C., Seismotectonics and earthquake geology aspects of northwestern Himalaya. Geol.
Surv. India Spec. Publ., 2006, 85, 61–71.
[2]    Vulnerability Atlas of India, Parts I to III, Earthquake, Windstorm and Flood Hazard Maps and
Damage Risk to Housing, Building Materials and Technology Promotion Council, New Delhi, 1997, p.
712.
[3]    Bilham, R., Gaur, V. K. and Molnar, P., Himalayan seismic hazard, Science, 2001, 293, 1442–
1444.
[4]     Feldl, N. and Bilham, R., Great Himalayan earthquakes and the Tibetan plateau, Nature, 2006,
444, 165–170.
[5]      Rapid Visual Screening of buildings for potential hazards: A handbook, Federal Emergency
Management Agency, 2002, FEMA 154, Applied Technology Council, California.
[6]    ASCE, 1998, Handbook for the Seismic Evaluation of Buildings — A Pre-standard, prepared by
the American Society of Civil Engineers for the Federal Emergency Management Agency, FEMA 310
Report, Washington D. C.




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