Seismogenesis of earthquakes occurring in the ancient rift basin of Kachchh, Western India - Intraplate Earthquakes - page 136

Moho Discontinuity

-5.00
-10.00
-15.00
-20.00
-25.00
-30.00
-35.00
-40.00
-45.00
-50.00
-55.00
-60.00
70.10

1.40
1.35
1.31
1.26
1.21
1.17
1.12
1.07
1.09
0.98
0.94
0.89
0.84
0.80
0.75

70.50
Longitude

70.90

Moho breakage

-5.00
-10.00
-15.00
-20.00
-25.00
-30.00
-35.00
-40.00
-45.00
-50.00
-55.00
-60.00
70.10

1.40
1.35
1.31
1.26
1.21
1.17
1.12
1.07
1.09
0.98
0.94
0.89
0.84
0.80
0.75

70.50
Longitude

70.90

Figure 6.6 (Upper part) Intact Moho in the Kachchh region 70 km north of the epicenter of the 2001
Bhuj earthquake. (Lower part) Disturbed Moho at the 23.3° N latitude of the 2001 Bhuj earthquake.
The profile length is 90 km. For color version, see Plates section.

as estimated according to the formula, ρ (g/cm 3 ) = 0.32 Vp (km/s) + 0.77 (Mandal and

Pandey, 2010 ) .
Due to magmatic intrusion, the Moho is likely to be broken, disturbed, and/or scattered.
This is revealed by 3DQ-structure in the epicentral zone of the 2001 earthquake in Kachchh
at a depth of around 40 km ( Figure 6.6 ; Sharma et al ., 2008 ) but intact Moho north of the
epicentral zone.
Such magmatic intrusives have been inferred for the Narmada Rift (Rajendran and
Rajendran, 1998) and most of the worldwide rifts that act as stress concentrators and cause
deepening of the brittle-ductile transition depth (Mukherjee, 1942 ; Mooney et al ., 1983 ;
Mechie et al ., 1994 ; Prodehl et al ., 1994 ; Johnston, 1994 , 1996 ; Mooney and Christensen,
1994 ; Nyblade and Langston, 1995 ; Liu and Zoback, 1997 ; Singh et al ., 1999 ; Kumar et al .,
2000 ; Deverchere et al ., 2001 ; Kruger et al ., 2002 ; Manglik and Singh, 2002 ; Wilson et al .,
2003; Gao et al ., 2004 ) .
The KR has a large-scale presence of alkaline rocks and mantle xenoliths at subsurface
depths in the form of plugs, cones, and sheet-like bodies containing olivine, opx, cpx,
and spinel (Karmalkar et al ., 2000 , 2008; Desai et al ., 2004 ; Sen et al., 2009 ) . Melts for
such alkaline rocks are reportedly generated by the partial melting of carbon dioxide-rich