A new insight into crustal heterogeneity beneath the 2001 Bhuj earthquake region of Northwest India and its implications for rupture initiations

作者：Singh A P; Mishra O P; Yadav R B S^*; Kumar Dinesh

来源：Journal of Asian Earth Sciences, 2012, 48: 31-42.

DOI：10.1016/j.jseaes.2011.12.020

• Earthquake hazard
• Seismic tomography
• The 2001 Bhuj earthquake
• Frequency-magnitude distribution
• Heterogeneity

The seismic characteristics of the 2001 Bhuj earthquake (Mw 7.6) has been examined from the proxy indicators, relative size distribution (3D b-value mapping) and seismic tomography using a new data set to understand the role of crustal heterogeneities in rupture initiations of the 2001 Bhuj earthquake of the Gujarat (India), one of the disastrous Indian earthquakes of the new millennium. The aftershocks sequence recorded by 22 seismograph stations of Gujarat Seismic Network (GSNet) during the period from 2006 to 2009, encompassing approximately 80 km x 70 km rupture area had revealed clustering of aftershocks at depth of 5-35 km, which is seismogenic layer responsible for the occurrence of continued aftershocks activity in the study region. The 3D b-value mapping estimated from a total of 3850 precisely located aftershocks with magnitude of completeness M-c >= 2.7 shows that a high b-value region is sandwiched within the main shock hypocenter at the depth of 20-25 km and low b-value region above and below of the 2001 Bhuj main shock hypocenter. Estimates of 3-D seismic velocity (Vp; Vs) and Poisson's ratio (o) over tilde structure beneath the region demonstrated a very close correspondence with the b-value mapping that supports the similar physicochemical processes of retaining fluids within the fractured rock matrix beneath the 2001 Bhuj mainshock hypocenter. The overall b-value is estimated close to 1.0 which reveals that seismogenesis is related to crustal heterogeneity, which, in turn also supported by low-Vs and high-(o) over tilde structures. The high b-value and high-(o) over tilde anomaly at the depth of 20-25 km indicate the presence of highly fractured heterogeneous rock matrix with fluid intrusions into it at deeper depth beneath the main shock hypocenter region. Low b-value and high-Vp in the region is observed towards the north-east and north-west of the main shock that might be an indication of the existence of relatively competent rock masses with negligible volume of cracks that may have contained over-pressurized fluids without molten rocks.

• 出版日期2012-4-2