29 Nov The Mullaperiyar Dam Controversey
“The plate tectonics revolution of the 20th century elegantly explained why most earthquakes occur where they do – at Earth’s plate boundaries. It didn’t explain, however, the occurrence of intraplate quakes and the deformation processes that give rise to them. As a result, geologists studying areas like the central U.S., western Europe, and Australia, don’t know what causes these quakes, how often they will happen in the future, and how dangerous they are.”(2007 GSA Press release)
The NGRI (under the leadership of Dr. Malaimani) has set up GPS stations in the Antartic India station, in the MS Univ., Tirunelveli (2010), in the NGRI and at a host of sites in the Himalayan front to monitor the Indian plate’s NEly motion. She says the rate is like 3.2 cm/yr. It is a sizable amount. This NEly motion can cause or trigger tremors in Mullaperiyar-Idukki and latest in the Indian ocean 400 km south of T’puram. I may consider these tremors worthwhile as it prevents huge stress build up and hence prevents a disastrous one.
Very large intraplate EQ can cause heavy damage, particularly because such areas are not accustomed to earthquakes and buildings are usually not seismically retrofitted, e.g. Bhuj EQ of 2001, the 1811-12 EQs of New Madrid, Missouri and1886 EQ of Charleston, S.Carolina.
Intraplate EQs occur away from plate boundaries and in the interior of plates and especially along the faults in the stable interior. There is a opinion that such quakes are along ancient failed rifts. Such breaks can easily accommodate the regional tectonic strain by causing tremors and adjustments. It is difficult quantify the damages of such intraplate events while with interplate quakes quantification and modeling are easier.
Ancient faults (now discernible as lineaments/deep crustal fractures in sat imageries) are the loci of EQ events. In Kerala the Edamalayar lineament (trend NNW-SSE) measurable in a few hundred kilometers is a geologically older major fault. The lineaments of Kerala fall into three or four major sets. The Mullaperiyar-Idukki tract in the SWG is one where we notice numerous lineaments – practically a sample or microcosm of all the lineament orientations- in Kerala crust. Lineaments occur to the north and south of this tract but micro-seismic activity is practically unreported from all such areas.
I am proposing a “shallow” magma chamber placed below the crust in the Mullaperiyar-Idukki area and the tremors are triggered by the partially of partly molten basement. Only this model could explain the local yet rather frequent tremors. At present my mind tells me that
1. Even prior to the dams in the area there had been frequent intraplate earth quakes in this tract.
2. It may take a deep crustal study to map the size extent or in fact the presence of this feature.
3. Even all mighty god will not help Keralites to get a >4.0 mag EQ to strike the terrain there.
4. We may convince politically the Keralites but not the Indians on the EQ thing.
5. Finally absolutely no one anywhere in the world even remotely thinks of the Dam surviving a >6 mag EQ anywhere in t he world.
6. I am stunned to notice the Geoscience Professionals/community outside of CESS keeping their fingers crossed and mouths shut in respect of the “impending” failure of the dam at Mullaperiyar.
7. If the “cracked base” of the dam as featured in TV graphics were true, I am sure that the structure would have failed right after the first tremor (out of the 26 after July this year), the reservoir would have become part of history.