________________
Shri Ashtapad Maha Tirth - II
.
EPICENTRES OF EARTHQUAKES 36
OF M<5
SRINAR
. DEN
DEPTN
Bosamen
NOO
..
SAMOO
MANDI
SAMOO.
:
FORCHULA
:
SADY
28°
.:
VGORAKYATI
...
HOMIMA
::
MPHAL
20°
M
980
E. KUMAUN
E NE PÁL
ARUNACHAL
20
.
*
•
60
DEPTH IN KM
Fig.8.26: (a) Distribution of earthquakes of magnitude 5 or above (upto 1975).
(Based on Chaudhury et al., 1974 and Valdiya, 1976), The lines represent faults, and the lined parts denote prongs
of the Indian Shield prodding the Himalaya. (b) Radial cross-sections across the Himalayan arc (ISS data, 1964-69). There is clear vertical linearity in the hypocenral
distribution in all the three sectors, (After Kaila and Narain, 1976)
In the Hindukush the hypocentres are distributed in a V-shaped pattern indicating, in the opinion of the author, differential vertical movement along faults or shear zones. It could also be taken to imply convergence of two steeply dipping lithospheric blocks down to a depth of 200 km. However, the fault mechanism indicates a dominant thrust movement in the western sector. Likewise, in the Indo-Burman mountain arc in the east the fault-plane solution of earthquake data (1881-1979) suggests dominant eastward under thrusting of the Indian plate, together with a subordinate component of strike-slip and normal fault movements (Rastogi et al., 1973; Chouhan and Srivastava, 1975; Verma et al., 1976; Chaudhury and Srivastava, 1976). The epicentres generally follow the trend of the mountain; and in the outer belt of the Himalayan arc though the frequency is less, their magnitude is higher and the movement mainly dip-slip
Tectonic design and evolution of the Himalaya
(202
