Balaji, S.
fall along major NE-SW trending dextral and NW-SE trending sinistral faults/lineaments. Valdiya (1994)
has observed that seismicity very mild and sparse of Peninsular shield is restricted to NW-SE and E-W
trending faults and fractures of strike-slip nature. Ramasamy and Balaji (1995) have also observed that the
neotectonism/Pleistocene tectonism played a role in earth tremors in Tamil Nadu.
All these facts suggest that the South Indian Peninsular shield is not stable and the neotectonics played a
role in seismicity in South India. These neotectonism or Pleistocene tectonism at many places in Tamil
Nadu caused migration of rivers, vertical upliftment of beds and drainage reversals etc. (Ramasamy and
Balaj 1995).
6.PLEISTOCENE TECTONISM AND SEISMICITY IN TAMIL NADU
The seismic data recorded by Gauribidanur seismic station and the data collected from available literature
(Sharma and Verghese 1979) were integrated with lineament/fracture network of Tamil Nadu. There is
good relationship exists between earth tremors and regional faults/lineaments. The analysis has shown that
most of the earth tremors falls on Precambrian lineaments/faults reactivated in Quaternary times and
Pleistocene younger fractures/lineaments (Ramasamy and Balaji 1995). These fractures/lineaments are
trending in NE-SW, NW-SE and N-S directions, which cause earth tremors at many places in Tamil Nadu
as shown in Fig.2. Along N-S trending Mettur —Tevaram lineament earth tremors occurred 4 times at
Mettur (A, Fig.2) and one time at Kodaikanal (L, Fig.2). Earth tremors occurred along N-S trending
Dharmapuri-Cape Comorin lineament at Krishnagiri (19 times), Dharmapuri (4 times) and Salem (1 time)
(E, D and C in Fig.2). Along NE-SW trending Madras-Cape Comorin lineament earth tremors occurred at
Madras (7 times), Tambaram (1 time) and Mamandoor (1 time) (L J and K, Fig.2). Another NE-SW
trending Pondicherry-Kambam lineament caused earth tremors at Pondicherry (12 times), Dindigul (2
times) and Kodaikanal (1 time) (G,B and L, Fig.2). Along NW-SE trending lineaments earth tremors
occurred in Sattanur and Tiruvannamalai (O and N, Fig.2). So all the N-Sof Vaigai river in Cochin-
Rameshwaram cymatogenic arch (Ramasamy and Balaji 1995). This fault/lineament also cause vertical
upliftment of beds in Mannargudi-Pattukottai area attributing Pleistocene tectonic activity. In addition,
because of regurgent tectonism in Quaternary times, the N-S segmented faults gave rise to linear and
isolated hillocks in Karnataka state (Valdiya 1998). He further observed that reactivation of faults caused
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
