indo–us workshop on “intraplate seismicity” - The CERI Blog

would require lesser stress/strain to rupture and hence can produce relatively more number of
earthquakes than the surrounding regions. The crustal zones of weakness are associated with rifts
where weak-­‐zone in lower crust can amplify the stresses in the upper crust, thereby, causing
earthquakes. The high heat flow due to thin lithosphere/crust in the failed rift like New Madrid, USA
and Kachchh, India, where the warm mantle can play a key role in weakening the crust, thereby,
causing earthquakes along pre-­‐existing zones of weakness. In Australia attempts have been made to
correlate high heat flow zones with seismicity (Holford et al. 2011 EPSL).
In general Generation of SCR earthquakes in the upper crust have been attributed to the
sudden movement along the pre-­‐existing weak zones due to local stress perturbation of the regional
plate tectonic stress due to surface as well as subsurface loading, reservoir loading, presence of
fluids and intersection of crustal weak zones (Richardson et al. 1979, Gupta and Rastogi 1976,
Talwani, 1988; Mareschal and Kuang, 1985; Andrews, 1989; Talwani and Acree, 1984; Ma et al.
1997).
Among the SCR regions worldwide, only the New Madrid and Kachchh regions have the
distinction of having earthquakes of magnitude approaching 8. The New Madrid seismic zone
(NMSZ) in the central United States was struck by three Mw≥7 earthquakes in 1811–1812, where
smaller earthquakes are occurring even today. While the Kachchh region, Gujarat, India is located
1000 km away from the Himalayan plate boundary in the north and 400 km away from the Herat-­‐
Chaman plate boundary in the west, has already experienced two large earthquakes within a time
span of 182 years viz., the 1819 Mw7.8 Allah Bund earthquake and the 2001 Mw7.7 Bhuj
earthquake. And, the aftershock activity of the 2001 main-­‐shock is continuing until today. In addition
to the plate tectonics stress, various local stress sources have been explored to explain the seismicity
associated with the NMSZ or KSZ. For instance, NMSZ seismicity has been attributed to stress
changes induced by melting of the Laurentide ice sheet or stresses generated by sinking of an
ancient high-­‐density mafic body or from a sudden weakening of the lower crust (Mooney et al. 1983;
Calais et al. 2010; Pollitz et al. 2001). Similarly, the seismicity in KSZ has been attributed to the
stresses caused by mafic crustal intrusive bodies and in-­‐plane plate compression, which has further
been facilitated by the presence of aqueous fluids or volatile CO2 released from the metamorphism
of olivine-­‐rich lower crustal rocks (Mishra and Zhao 2003; Mandal and Pujol 2006; Mandal and
Chadha 2008) as revealed by seismic tomographic studies. Seismic, gravity and magnetotelluric
surveys have revealed sedimentary thickness, basement configuration, crustal structure and
disposition of faults. Further, marked upwarping of Moho and astheonsthere underlying KSZ has
been modeled through receiver functions, which also revealed the presence of patches of partial
melts in the asthenosphere that can lead to emanation of volatile CO2 into the lower crust, thereby,
causing continued occurrence of aftershocks (Mandal, 2011). Further, GPS studies during 2001-­‐2006