Wednesday, December 21, 2011

Crazy About Rugby

I've been taking some time off and helping spread sports and particularly rugby in the rural areas around Pune. This is a project started by two of the rugby organizations in Pune - RFS Pune and KFANDRA .

Here are some pictures from Nanegaon which is about 40 km westwards of Pune. A friend farms here and its through him that we have started this initiative:

That's me looking very fit, surrounded by rugby crazy kids.

All Hands in groups of three:

The Pop-Up pass routine:

 Keen eyes and hands- what a picturesque setting to a sports scene not very common in rural India:

 All this action takes place against the backdrop of the vast layered Deccan Basalts. The village is quite attractive and has some of the classic elements and atmosphere of rural India like this temple square:

The countryside around is lush and there are some pretty picnic spots for the tired and weary - a basalt stream bed:

The idea is to encourage children to learn discipline, team work and good work ethics through sports. So far the children love taking part in this activity and we plan to keep this program running for the foreseeable future.

Tuesday, December 20, 2011

Monday, December 19, 2011

My Popular Posts Over The Last Two Years

Its nearly year end and time to get a little reflective. I'm basing this on Google Stats for the last two years. Here are 5 of my most popular posts:

Indian Sedimentary Basins And Shale Gas

Plate Motions: Is The Driver Bottom Up or Top Down

Mapping India: Land Degradation and Desertification

India Basin-Wise Shale Gas Estimates

Geology Will Be Central To India's Climate Change Challenge

Two of them are about the hot energy source of the day and two about ecological challenges we face. My post on the recent Sikkim / Nepal earthquake came a close sixth.

My blogging is not restricted to topics about India but in a sense I am pleased that my writings about Indian geology continue to capture a fair amount of attention. There is not much information about Indian geological issues in the popular media and in the public domain, so I guess I am contributing somewhat to redressing that lacunae.

Thanks all for supporting this blog.

Thursday, December 8, 2011

Insights Into Plate Interior Earthquakes Of Peninsular India

A paper in Current Science (open access) by Roger Bilham and Vinod K Gaur gives interesting insights into the patterns of occurrences and causes of earthquakes in the plate interior regions of Peninsular India. In south Maharashtra for instance there have been moderate size earthquake of 6.3 - 6.4 magnitude in recent decades at Koyna and Latur. Earthquake risk assessment has shot to prominence recently due to a proposal to site a large nuclear power station in Jaitapur, which is close to Koyna.

The general understanding of earthquakes in Peninsular India is that the Precambrian terrain  is heterogeneous in strength, criss-crossed with rifts, shear zones and old orogenic belts and these ancient zones of weak crust get reactivated from time to time and rupture.

But what is building up strain along these old faults? The graphic below from the paper is a good way to conceptualize the tectonic and stress situation.

The collision of the Indian plate with Tibet has resulted in the bending of the Indian plate underneath Tibet and the flexural buckling into a long waveform of the rigid Indian plate. At the northern end i.e. at the crest of the flexure the plate experiences tensional forces at shallow depths and compressional forces at the base of the plate. Farther south in the trough of the flexure known as the outer moat, the situation is reversed. The shallow part of the plate experiences compressional forces and the base of the plate experiences tensional forces.

 Imagine now that this waveform is static in the sense that the stress fields described remain fixed in space. The rocks of the Indian plate are however moving northwards. They pass through the compressional stresses in the trough and many millions of years later pass through the tensional stresses of the crest. At the base of the plate its the other way around. Geodetic studies using GPS i.e. studies aimed at understanding slip along faults to estimate how quickly strain is building up, suggest a very low rate of strain buildup in Peninsular India. Calculations suggest that replenishment of strain is on the order of 300,000 years, meaning on average faults won't slip more than 3 times per million years. But given the millions of years these rocks have remained in either compressional or tensional stress fields and given the rarity of historical and recent earthquakes, the authors thesis is that there would be many many faults reaching a state of critical stress i.e. close to rupturing.

One practical implication of this is that the seismic hazard maps issued by various agencies don't always portray future risk accurately. These are based on a very short historical record and since the cycle of strain buildup is much longer, faults that may have slipped thousands of years ago and have been building up strain since, will remain unnoticed. That is what likely happened at Latur, an area considered to be at low seismic risk based on history, until the sudden large earthquake. 

Koyna and Latur fall in the trough region of the flexure. So does Jaitapur. The faults at Koyna and Latur have slipped recently and given the low rate of strain buildup are unlikely to rupture for some time to come. But there is no record of recent or historical seismicity near Jaitapur. There is a lot of discussion in the paper on earthquake catalogs for India and their usefulness. The reliable historical record doesn't extend beyond a couple of hundred years or so. And further, its not known whether there is a subsurface fault underneath Jaitapur, but the regional picture tells us that Jaitapur would be subject to the same stress regime as Koyna and Latur and there is a possibility - albeit low - of a moderate size earthquake occurring underneath the proposed power plant site.

One quibble I have regarding the graphic above is the placing of Bhuj in the flexural trough. It is in fact located north of the flexural trough, in the crest domain. Bhuj refers to the town in Gujarat state which suffered a large 7. 6 magnitude earthquake in 2001. Bhuj had suffered an earlier earthquake of 7.9 magnitude in 1819.  The area falls within the Kutch rift which was initiated during the late Triassic breakup of Gondwanaland. Rifting was aborted during the late Cretaceous pre collisional stage of the Indian plate. Since then under a compressional stress regime, the rift has developed strike slip faults with local transpressional zones i.e. the stress is oriented is such a way so as to cause local reverse faulting and strike slip faulting. Both the Bhuj earthquakes were located in this transpressional zone in the eastern part of the rift. So Bhuj is something of a special case. A relatively younger crustal structure with complex local stress fields and faults reactivated by the ongoing collision of India with Tibet.

 Coming back to Maharashtra, it is difficult to get a handle on future seismic risk. This is because as I mentioned the historical record goes back only a couple of centuries and is patchy. Therefore, reliable statistics on the rate of earthquakes can't be developed so as to be used as a guide to future risk. Also because the Deccan volcanics have covered the Precambrian over most of the region, and because many of these ancient faults don't reach the surface,  examining these faults so as to understand their slip history is not possible. So only broad zones of weaknesses are interpreted by extrapolating the structural grain of Precambrian terrains at the margins of the Deccan volcanics or by using geophysical methods like mapping gravity lows (which might point to the presence of a sedimentary rift basin underneath the Deccan volcanics).

Under these constraints, site specific earthquake risk assessment is not done. But the broad picture developed in this paper does point out that much of Peninsular India may be under a high incipient state of stress and there are possibly many faults within the flexural trough between latitudes 16 deg N and 19 deg N which are not exposed at the surface that represent seismic hazards.

Wednesday, December 7, 2011

Mea Culpa By Simon Winchester About His Newsweek Earthquake Article?

Earlier this year the science writer Simon Winchester started a controversy by claiming a little too assertively that large earthquakes like the Tohoku earthquake on the Pacific plate boundary of the coast of Japan has increased the chances of a large earthquake in California which is located on the other end of the Pacific plate. His claim was that - "[A] significant event on one side of a major tectonic plate is often - not invariably, but often enough to be noticeable- followed some weeks or months later by another on the plate’s far side".

He was roundly criticized for this claim by earthquake experts.

Now Real Climate reports from the AGU meeting in San Francisco:

The second general talk was by author Simon Winchester who excellently demonstrated how to communicate about geology by using human stories. He gave a number of vignettes from his latest book about the Atlantic ocean – including stories of the shipwreck of the Dunedin Star on the ‘Skeleton coast’ of Southern Africa, time on St Helena, and the fate of his book on the Pacific that apparently only sold 12 copies… He finished with a mea culpa and gracious apology to the assorted geophysicists for his rather hurried comments on the Tohoku earthquake disaster that caused some consternation earlier this year. In his defense, he only had 90 minutes to write what he was unaware would be the Newsweek cover story that week.

Any of you Geo-Bloggers attending AGU heard anything about this?

Friday, December 2, 2011

Geological Monuments Of Hyderabad Disappearing

The disappearance of wetlands and forests makes for news and media articles, but a pile of rocks? I came across this slideshow in The Hindu on the natural rock piles so typically seen in the city of Hyderabad. The rock is granite and it has weathered along sets of cracks to form these rounded boulders that are left balancing precariously. These piles of balanced rocks that form hillocks are called Tors.  The graphic below depicts the formation of Tors.


These formations are being quarried for construction material and Hyderabad is fast losing its unique landscapes.


I hope the city decides to protect at least a few of these as national monuments.