A Geological Study of Earthquakes in Kutch, Gujarat, India
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Two first order basement ridges orthogonal to the rift axis are the unique features of this rift basin: the Median High occurs across the middle of the basin along its hinge zone and Radhanpur-Barmer arch occurs along the eastern rift margin separating it from the N-S Cambay rift. The Radhanpur-Barmer arch along the western rift shoulder of Cambay rift, acts as a ramp for the present northeast-directed compressive stress. Due to this the strain build up in the eastern part of Kutch rift is relatively more than in the western part, west of the Median High. The mounting stress in the eastern part is responsible for repeated thrusting along SWF. Presumably, the SWF would tend to flatten towards a detachment surface close to the base of the seismogenic layer where thrusting is expected. Thus, SWF becomes the active segment (eastern trace of KMF) of the principal fault causing repeated thrust at depth in mid-crustal region. The fading KMF is likely to converge with SWF at dcpth. Aftershock data corroborate this interpretation. The transfer zone where the epicenters of both 1956 Anjar and the recent 2001 Bhuj earthquakes are located close to each other is the critical area for the occurrence of earthquakes. The focal depths (15-20 km) seem to be occurring in the zone of flattening of SWF, which appears to be the critical site for rupture nucleation. Accordingly this segment is interpreted as the vulnerable sire for repeated ruptures causing earthquakes.
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