Thursday, January 3, 2013

Note To Indian Govt: It Is Pointless Banning Seismologist Roger Bilham

I wrote in my last post on the travel ban issued by the Indian Government to American seismologist Dr. Roger Bilham. The reason given was that he was engaging in activities inconsistent with his visitor visa status. These activities include attending scientific meetings and contributing towards understanding seismic risk at a proposed nuclear power plant at Jaitapur in southern Maharashtra. I do suspect that this is the real reason for the ban, which is that Dr. Bilham has irritated people in the Indian Government in charge of nuclear power plant safety by suggesting that the government's assessment of Jaitapur underestimates the risk of a large (6-7 mag.) earthquake.

Now he has answered his travel ban in the best way possible; by producing more science about the geology of the area around Jaitapur with implications for regional and site seismicity. He and his colleague Vinod Gaur have published this work in Current Science. It is open access and there is nothing the Indian Government can do to prevent his work from being widely discussed and disseminated (as I am doing now) and critically evaluated.

That by the way is what these scientists want as they outline several tests for their hypothesis and the hypothesis proposed by other geologists critical of Gaur and Bilham's earlier paper on this subject.

Of great interest here is a seaward tilted terrace (a flat surface created by marine erosion of the continental shelf in the Oligocene and which today is capped by laterite) which has been offset such that the eastern side has dropped about 25 meters relative to the west. This NNW trending escarpment can be traced for 50 km south of Jaitapur. According to Gaur and Bilham this feature which they term the Vijaydurg fault -since it passes close to the Vijaydurg fort- is a fairly recent fault which has slipped intermittantly over the last 50 thousand years and which could rupture again in the future. Offshore faults have been mapped about 5 km west of the Jaitapur site and could represent the NNW extension of this Vijaydurg lineament.  They suggest that the proposed nuclear power plant site is on the down thrown block or the hanging wall of this hypothetical normal fault and so a future earthquake may result in a vertical movement of the Jaitapur site. They estimate the maximum magnitude earthquakes possible along the Vijaydurg fault and observe that 50 km long faults are associated with earthquakes of 6.5 to 7.2 magnitude which may involve a slip of (vertical movement) half a meter to up to a meter.

The image below shows the NNW trending Vijaydurg "fault" (SRTM digital elevation data on left) along with the location of the Jaitapur proposed nuclear power plant. On right is a Google Earth image of the Vijaydurg "fault" manifested as a vegetated scarp running from lower left to the upper right of the image.

Source: Gaur and Bilham 2012

Other geologists don't think that this geomorphic feature is an active fault. B.K. Rastogi of the Institute of  Seismological Research Gandhinagar in a reply (also open access in Current Science) to Bilham and Gaur's earlier paper suggests that this linear feature is of Miocene age and there has been no faulting activity along it for the past several million years. In their view it is an inactive fault that poses no danger to the Jaitapur site. However, what struck me in Rastogi's response is that for all his arguments and mentions of detailed field work in the site area, there is not a single reference given to where this work is published so that other scientists can critically evaluate it. Gaur and Bilham do mention this problem of an inability to authenticate Rastogi's claims.  Apparently, the site specific geological study which Rastogi refers to and has participated in is yet to be made public.

So, establishing the age of faulting activity along this escarpment is of great importance in the seismic risk assessement of the Jaitapur site.

Here is a list of the studies that Gaur and Bilham think need to be done to strengthen either their view, or the view put forward by B. K. Rastogi.

1. Seismic profiling of the continental shelf ‘gap’ between onshore and midshelf regions with high-resolution seismic lines to identify subsurface structures associated with potentially active near-shore faults.

2. Improved high-resolution shallow seismic and core analysis studies to resolve uncertainties in the interpretation  of the already identified offshore faults and inferred igneous dikes near Jaitapur.

3. High-resolution imaging of the continental slope in a search for incipient scarps, and slump features associated with historical turbidites and tsunami.

4. Coring and dating of depositional turbidites in offshore basins to quantify, or refute, the existence of synchronous triggering of turbidites along the Konkan shelf by significant earthquakes.

5. Palaeoseismic trenching across the Vijaydurg scarp to establish the absence, or timing and amount of slip of the Vijaydurg Fault.

6. Trench studies of onshore palaeoliquefaction, clastic dikes and buried sand vents in terrestrial low-energy sedimentary environments within 50 km of Jaitapur.

7. A systematic search for palaeotsunami deposits along the western coast of India within 100 km of the Jaitapur site using shoreline and lagoonal deposits, cores and trenching.

8. An onshore search for precariously balanced rocks symptomatic of an absence of strong shaking in the past several thousands of years.

If the government appointed team has addressed these issues fully or partially then the results should be made public for an open evaluation. And further, the travel ban on Dr. Roger Bilham must be lifted without delay. It is extremely immature of the Indian government to think that keeping Dr. Bilham away from India will somehow stop discussion on the topic of seismicity around Jaitapur.

Update January 6 2012: Here is a link to an article from Dr. Bilham's website detailing the sequence of events leading to the blacklisting of Dr. Bilham from traveling to India.  He is too kind to the Indian government suggesting that they are not to blame and the blacklisting was done on the recommendation of influential scientists. The article names Dr. Harsh Gupta - former director of NGRI - as a possible key figure in these events.  Still, why did the Home Ministry feel the need to act on such an absurd recommendation? According to the article Dr. Gupta has denied any involvement.

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