HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Mandal, P. Articles by Kousalya, M. Search for Related Content GeoRef GeoRef Citation

Results from Local Earthquake Velocity Tomography: Implications toward the Source Process Involved in Generating the 2001 Bhuj Earthquake in the Lower Crust beneath Kachchh (India)

National Geophysical Research Institute
Uppal Road
Hyderabad 500007
India
prantik_2k{at}hotmail.com.

Manuscript received 17 March 2003.

To comprehend the source processes of the 26 January 2001 Bhuj earthquake sequence of M_W 7.7 and its influence on the seismic hazard of the Kachchh, we estimate various seismological parameters using reliable and accurate aftershock data. The estimated parameters led to several important findings including the delineation of an east-west-trending, south-dipping (45°) fault (North Wagad fault [NWF]), which touches the surface about 25 km north of Kachchh Mainland fault (KMF). The aftershock zone is confined to a 60-km-long and 40-km-wide region lying between the KMF to the south and NWF to the north, extending from 10 to 45 km depth. Focal mechanism solutions of the mainshock and 25 significant aftershocks of M_W 3.0 obtained from waveform inversion of broadband data and local earthquake moment tensor inversion suggest that the region between the KMF and NWF is mainly characterized by reverse faults with east-west trend and southerly dip, matching with the geological faults in the region. The tomographic inversion technique is used to invert 5516 P-wave travel times and 4061 S-P travel-time differences from 600 aftershocks recorded at 8-18 stations. Tomographic results suggest a regional high-velocity body (characterized by high V_p [7.0-8.5 km/sec], high V_s [4.0-4.8 km/sec], and low [0.24-0.26]) with a head extending 60 km in north-south and 40 km in east-west at 10-40 km depths. This high-velocity anomaly is inferred to be a mafic pluton/rift pillow, which might have intruded during the rifting time (135 Ma). This crustal mafic pluton must be contributing significantly in accumulating large crustal stresses resulting in the generation of large earthquakes in this intraplate area. Another important result of our study is the detection of a low-velocity zone (low V_p [6.5-7.0 km/sec], low V_s [3.6-4.0 km/sec], large [0.26-0.265]) within the mafic body at the hypocentral depth of the mainshock (18-25 km), which is inferred to be a fluid-filled (trapped aqueous fluid resulting from metamorphism) fractured rock mass. The analysis of depth distribution of b-values suggests a high b-value zone between 15 and 25 km depths, which further supports this contention. Hence, the presence of fluids at the hypocenter might have facilitated the occurrence of the 2001 Bhuj earthquake within the inferred mafic body in the lower crust.

This article has been cited by other articles:

				B. Sharma, A. K. Gupta, D. K. Devi, D. Kumar, S. S. Teotia, and B. K. Rastogi Attenuation of High-Frequency Seismic Waves in Kachchh Region, Gujarat, India Bulletin of the Seismological Society of America, October 1, 2008; 98(5): 2325 - 2340. [Abstract] [Full Text] [PDF]

				D. Sarkar, K. Sain, P.R. Reddy, R.D. Catchings, and W.D. Mooney Seismic-reflection images of the crust beneath the 2001 M = 7.7 Kutch (Bhuj) epicentral region, western India Geological Society of America Special Papers, January 1, 2007; 425(0): 319 - 327. [Abstract] [Full Text] [PDF]