Balaji, S.
2.METHODOLOGY
The regional lineament/fracture pattern of Tamil Nadu was prepared using Landsat and IRS 1 series on
black and white and FCC satellite imagery on 1:250,000 scale on various indivudual bands and scenes and
subsequently they were transformed into a 1:100,000 planimetrically controlled map.
The seismic earth tremors recorded by Gauribidanur seismic station and the data from available literature
(Sharma and Verghese 1979) were collected and they were analysed with the lineament/fracture network
for the possible relationship and Pleistocene tectonism. Various geomorphic anomalies have also been
analysed for establishing the Pleistocene tectonism, which caused many earth tremors in South India.
3.REGIONAL GEOLOGY
The Sothern Indian Peninsula exposes olden Archaean crust and. supracrustals which comprise of
Khondalites, Charnockites, Migmatites, Sargurs, Peninsular gneiss and schists. In Tamil Nadu, the major
hills are Kolli, Pachai, Shevroy, Chitteri, Kalrayan of Eastern Ghats hill ranges which are all composed of .
Charnockitic rocks..
Apart from Charnockite rock, most of the region is covered by Gneissic rocks. The Eastern part of Tamil
Nadu is represented by Cretaceous, Tertiary rocks and Alluviam (Anon, 1969 and Balaji 1995). The
Northern part of Tamil Nadu is criss crossed by E-W trending doleritic dykes (Ramasamy and Balaji 1995).
4. REGIONAL LINEAMENT/FRACTURE NETWORK OF TAMIL NADU
Using Landsat and IRS 1A and 1B satellite imagery, the major fractures/lineaments were interpreted on
individual scenes and bands and they were subsequently mosaiced to get a regional picture (Fig.1). The
lineaments were interpreted on the basis of tonal linearities, straightness of drainages, vegetational
alignments, soil tonal contrast etc. The fractures /lineaments are regional in extent which cover 600 km in
lengthwise at some places traversing various geological terrains which controls minerals, ground water and
ultrabasics and thus, they are of tectonic importance. The fractures thus interpreted were trending in four
azimuthal frequencies viz NE-SW, NW-SE, N-S and E-W directions. The NE-SW lineament shows
signatures of dextral movements, NW-SE lineament shows sinistral movements and the E-W lineament
shows release geometry (Ramasamy and Balaji 1993). The fractures/lineaments, which show signs of
Pleistocene tectonic movements in the form of geomorphic anomalies and earth tremors, were grouped into
reactivated lineaments/faults of Pleistocene age (Fig.2). The reactivated lineaments/faults
of Pleistocene age were trending in three azimuthal frequencies viz NE-SW, NW-SE, and N-S directions.
. These lineaments/faults are of importance in the seismic analyses of South India.
S.SEISMICITY IN TAMIL NADU, SOUTH INDIA
Seismic tremors occur in South India at frequent intervals. The earth tremors are mostly of tectonic in
nature and at some places the impounding water in reservoir also causes earth tremors. In Tamil Nadu, in.
1900, an earthquake of magnitude 6.5 of Feb.8 occurred at a depth of 70 km in the fault striking NNW-SSE
(Rajendran and Rajendran 1996). According to him, the Coimbatore event is due to active faults of shear
Zones. A tectonic map of Eurasia published in 1968 show a submerged volcano in the Bay of Bengal, North
of Madras. This volcano is located along NE-SW trending faults, which caused many earth tremors in and
around Madras and Pondicherry (Grady 1971). Grady (1971) has observed that out of 38 earth quakes in
Southern part of Peninsular shield between 1823 and 1968, 19 occurred within 20 miles of carbonatite
bearing N45E faults/lineaments. Six occurred on or near Archaean-Cretaceous boundary fault. Singh
andVenketesh Raghavan (1989) observed that the earthquake centered 30 km to the North of Trivandrum
on 2 September 1988 falls in proximity of NNW-SSE to NE-SW trending faults. Ramasamy and Balaji
(1993) observed that the earth tremors in Tamil Nadu
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
