Abstract
Primary and secondary surface deformation related to the 2001 Bhuj-Kachchh earthquake suggests that thrusting movement took place along an E-W fault near the western extension of the South Wagad Fault, a synthetic fault of the Kachchh Mainland Fault (KMF). Despite early reconnaissance reports that concluded there was no primary surface faulting, we describe an 830 m long, 15-35 cm high, east-west-trending thrust fault scarp near where the seismogenic fault plane would project to the surface, near Bharodiya village (between 23°34.912vN, 70°23.942vE and 23°34.304vN, 70°24.884vE). Along most of the scarp Jurassic bedrock is thrust over Quaternary deposits, but the fault scarp also displaces Holocene alluvium and an earth dam, with dips of 13° to 36° south. Secondary co-seismic features, mainly liquefaction and lateral spreading, dominate the area south of the thrust. Transverse right-lateral movement along the «Manfara Fault» and a parallel fault near Bharodiya suggests segmentation of the E-W master faults. Primary (thrust) surface rupture had a length of 0.8 km, maximum displacement of about 35 cm, and average displacement of about 15 cm. Secondary (strike-slip) faulting was more extensive, with a total end-to-end length of 15 km, maximum displacement of 35 cm, and average displacement of about 20 cm.
Highlights
The 2001 Bhuj-Kachchh earthquake was one of the largest events in the Stable Continental Regions (SCR) of the world
The 830 m long thrust scarp described previously clearly resulted from tectonic faulting, because it involves bedrock, crosses natural and man-made topography indiscriminately, and is not associated with any gravitational failures such as lateral spreads
Scarp morphology is similar to that of primary surface ruptures during other thrust earthquakes (Philip et al, 1992; McCalpin, 1996). At this time we cannot prove that this thrust scarp is the surface expression of the 26 January mainshock plane, or even that the thrust was produced during the mainshock, rather than during an aftershock between 26 January and 11 May 2001, when we began our reconnaissance
Summary
The 2001 Bhuj-Kachchh earthquake was one of the largest events in the Stable Continental Regions (SCR) of the world. The 2001 Bhuj-Kachchh earthquake (Mw 7.7) is an important event for the comparative study of two big earthquakes in the same tectonic province. Kachchh has a long history of earthquakes and has experienced two major events and tens of smaller events within the past 200 years. The vast wastelands and salty playas are probably the result of a few major earthquakes in the past 3000-4000 years. In the present paper we attempt to relate the nature of the 2001 Bhuj earthquake with the regional structures, especially with the. Quaternary morphotectonic features along the major E-W and transverse fault systems. In addition we excavated one exposure of the thrust fault in a streambank and logged another trench excavated by a previous French reconnaissance team
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