Spatiotemporal Perturbations of Pore fluid Pressure in Kumaon Himalayas
Abstract
Convergence of Indian and Eurasian Plate induces significant seismic activity in the regions around the plate boundaries and pose a serious seismic risk to population living around Himalayas. As important as this area is; the studies relating to seismic risk evaluation has been limited and severely inadequate. Advent of newer techniques and the seismic deployment done by National Geophysical Research Institute during 2004 and 2008 for collection of high quality data enables us to study the stress and pore fluid pressure state and rate changes in space and time to assess the seismic risk. Many studies have predicated the occurrence of earthquake sequences on overpressurized fluids which lead to the failure of the faults. Knowledge about pore fluid pressure at hypocentral depths can provide critical insights in to risk evaluation as pore fluid pressure and triggering of events are closely related. The methodology of Focal Mechanism Tomography developed by Terakawa Toshiko (2010) enables us to map a three dimensional distribution of pore fluid pressure. The scheme has been shown to exhibit good reliability in previous studies and has been applied to many seismically active regions. We make use of this methodology to study the spatiotemporal changes in pore fluid pressure at hypocentral depths in Kumaon Himalaya region. We analyzed well constrained 785 shallow events (Depth<35kms) in this region to estimate the pore fluid pressure field of the region. The events were first relocated using Hypo-DD reducing the error in estimates of location less than 1 Km. These relocated events were then distributed in overlapping temporal and spatial bins. For each bin we calculate the focal mechanism solutions by waveform inversion. This preliminary analysis was utilized to invert for tectonic stress patterns by the algorithm given by Hardebeck and Michael (2006). The stress patterns determined for all spatial bins in each temporal bin were collectively used to compute pore fluid pressure at hypocenters and eventually the three dimensional distribution of pore fluid pressure. The three dimensional map of pore fluid pressure for each temporal bin was used to depict its evolution in time from 2004 to 2008, which was the period of passive seismometer deployment. Distribution of events(black stars) which were analyzed to give focal mechanism for further analysis. The blue triangles represent the stations which were deployed during the period 2004-2008 for collection of this data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S43F2524M
- Keywords:
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- 7215 SEISMOLOGY / Earthquake source observations;
- 7223 SEISMOLOGY / Earthquake interaction;
- forecasting;
- and prediction;
- 7230 SEISMOLOGY / Seismicity and tectonics;
- 7290 SEISMOLOGY / Computational seismology