IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Oral Presentation 2370
High mantle heat flow and thermally induced stresses below Latur and
Koyna seismogenic regions of Deccan volcanic Province, India: a case
study
Dr. O.P. Pandey
Theoritical Geophysics National Geophysical Research Institute (NGRI) IASPEI
65 Ma old Deccan volcanic province, covered by a thick suite of tholeiitic basalt flows spread over
almost 1/6th of Indian landmass near western margin, has been experiencing large number of
moderate earthquakes since historical times. Many of these earthquakes like Koyna (1967), Latur (1993)
and Bhuj (2003) etc. were of devastating in nature claiming heavy loss of human life and property. In
spite of large number of studies in the past, possible seismogenic cause of such events are still not
understood clearly. In this view, an attempt is made here to study in detail the prevailing thermal
regime of the lithosphere beneath Latur and Koyna seismogenic regions, where a fairly accurate crustal
and compositional structure has now become available through recent initiatives. This study indicates
presence of high input of heat from the mantle (29-35 mW/m2) below these regions with temperatures
at Moho reaching between 490oC and 600oC. Similarly, these regions are also characterized by a thin
lithosphere, varying approximately between 90 km and 110 km , which is les than half to that usually
found in comparable late Archean shield terrains elsewhere. In some segments, close to western margin
of the Deccan volcanic province, where earthquakes are quite frequent, lithosphere has thinned down to
as much as 40 to 50 km with Moho temperatures exceeding 800oC. It is felt that the lithosphere
beneath Deccan volcanic terrain is quite warm which besides weakening the lithosphere, creating
additional intraplate thermal stresses which is getting accumulated in apparently exhumed denser crust,
where average crustal S velocities sometimes reach as high as 4.0 km/s. These thermal stresses act
over and above to that generated by northward movement of Indian plate, thereby accelerating the
process of earthquake nucleation beneath these regions.
Keywords: lithosphere, thermal state, seismogenesis