SEISMIC REFLECTION IMAGES OF THE CRUST BENEATH THE 2001 M = 7.7 KUTCH (BHUJ) EPICENTRAL REGION, WESTERN INDIA

Three short (~35 km) seismic reflection profiles are presented from the region of the 2001 Mw = 7.7 Bhuj (western India) earthquake. These profiles imaged a 35-45 km thick crust that is highly reflective with strong, near-horizontal reflections at all depths. The crust thickens by 10 km over a distance of about 50 km from the northern margin of the Gulf of Kutch to the epicentral zone of the earthquake. Aftershocks of the Bhuj earthquake extend to a depth of 37 km. Our results show that all of these aftershocks are contained within the crust. Furthermore, there is no evidence for offsets in the crust-mantle boundary associated with deep (mantle) faulting. The existence of a thick (~45 km) and highly-reflective crust at the epicentral zone may be the result of crustal thickening due to the compressive regime of the past 55 Ma. Alternatively, this thickening could be attributed to magmatic intrusions which date back to Mesozoic rifting associated with the break-up of Gondwanaland.