Ž.
Journal of Applied Geophysics 39 1998 109–120
Velocity modelling of Bengal Basin refraction data—refinement
using multiples
P.R. Reddy
)
, A.S.S.S.R.S. Prasad, Dipankar Sarkar
()
Controlled Source Seismology CSS Group, National Geophysical Research Institute, Hyderabad-500007, India
Received 2 September 1997; accepted 29 January 1998
Abstract
Free-surface multiples that are generated due to high-velocity gradients in the sedimentary layer sequence above the
basement of the West Bengal Basin were modeled to constrain a 2-D velocity–depth section of the southern part of the
basin. Modelling of the velocity structure utilizing free-surface multiples with the asymptotic ray method produced synthetic
record sections that could replicate the observed seismic phases better than those generated by matching only the primary
refractions. q1998 Elsevier Science B.V. All rights reserved.
Keywords: Bengal basin; seismic survey; refraction; raytracing; modelling and velocity structure
1. Introduction
The Bengal Basin, comprising part of eastern
India and almost the entire area of Bangladesh,
is extensively covered by Recent Alluvium. It is
bounded on the west by the Indian peninsular
shield and on the east by the Lushai–Naga fold
belt, which is part of the Himalayan–Burmese
mobile belt. To the south and to the north lie the
Bay of Bengal and the Shillong Plateau, respec-
tively. The formations from the Carboniferous
to the Tertiary periods crop out on the basin-
ward side of the peninsular shield and Shillong
Plateau. Nearly all the formations are exposed
as surface outcrops, particularly at the western
)
Corresponding author.
margin. Tertiary formations have mostly out-
cropped on the northern and eastern margins.
The Indian peninsular shield disappears below a
thick cover of alluvium in the Bengal Basin.
The lower Gondwana formations overlie the
Archaean basement and are supposed to be
deposited in grabens in the continental environ-
Ž.
ment Tiwari, 1983 . The regional dip of the
basement is eastward. The lower Gondwana
formations are overlain by a basalt flow known
Ž
as the Rajmahal Traps upper Jurassic to lower
.
Cretaceous . A thick column of Paleocene,
Eocene, Oligocene, Miocene, Pliocene and
Holocene sediments are deposited above the
Ž.
Cretaceous formations. Sengupta 1966 re-
ported on intensive geophysical exploration and
oil-drilling activities in the Bengal Basin. Ac-
cording to him, the Bengal Basin is structurally
0926-9851r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
Ž.
PII S0926-9851 98 00006-8