Seismogenesis of earthquakes occurring in the ancient rift basin of Kachchh, Western India - Intraplate Earthquakes - page 143

Figure 6.11 Epicenters of earthquakes inGujarat during 2001-12. The epicenters of shocks ofM < 2.0
are mostly in areas of intense local monitoring.

10-15 km. The six shocks of M w 5.0 and about 25 strongly felt (M w 3 to 4.9) earthquakes

that occurred in the decade after 2000 are very well located.

6.3.1 Seismicity with time in Kachchh and the nature of seismic sources

Starting in 2001, up to 75 broadband seismographs have been operating in Gujarat
(500 km

600 km), of which some 40 are in Kachchh. During 2001 to 2003, the after-
shocks of the 2001 Bhuj earthquake were confined to the main rupture zone of 40 km

×

×
40 km area north of the KMF and along an inferred hidden North Wagad fault ( Figure
6.10 ) . During 2001 to 2012 some 10,000 M w 0.5 shocks were located in Gujarat

( Figure 6.11 ) .
Aftershocks of the 2001 Bhuj earthquake to M w

5 level have continued for over

a decade, including 16 M w 3 events, and some

5000 other well-located shocks of M w 1.0 to 2.9 (Mandal and Rastogi, 2005 ; Mandal et al .,
2007 ; Rastogi et al. , 2013a, b). Up to 2003 there were 15 aftershocks of M w

5, 250 M w 4, about 4000 M w

5 and one

in 2006. The latest significant aftershock was of M w 4.9 on March 9, 2008.

6.3.2 Orientation of faults and depth of the seismogenic zone in Kachchh

The parameters of the 2001 mainshock are: 23.419 E, focal depth 16 km

(USGS). Some other depth estimates are 22 km or 23 km (ISC; Antolik and Dreger, 2003 ) .

° N, 70.232 °