Crustal Flow, Eastern Sichuan Earthquake China

Its been 10 days or so since the big earthquake in the eastern part of Sichuan province China and I haven't come across anything like a good geological explanation in the Indian media. So here is a quick summary. The earthquake measuring 7.9 on the Richter scale occurred at a depth of about 19 km most likely along the NE trending Longmenshan fault which is a long thrust fault marking the boundary between the eastern Tibetan plateau with the Sichuan basin. The region is seismically active. The map below show seismicity since 1990. You can see a concentration of brown dots marking earthquakes arranged in a linear fashion trending NE just at the boundary between the pale yellow region which is the Sichuan basin and the light brown region which is the Tibetan plateau. This marks approximately the zones of disturbance along the Longmenshan fault. The unusually large brown dot is the location of the big earthquake.

Source: USGS Earthquakes

In geology 101 we learn that most earthquakes take place at plate boundaries where the crust is being stressed and actively deformed. Earthquakes away from plate boundaries are not uncommon though. In India in recent memory the two big earthquakes around Bhuj Gujarat and Killari Maharastra are example of earthquakes which took place a long distance away from plate boundaries. The reasons for these intra-plate earthquakes can be usually traced to stress transmitted across plates from zones of plate boundary interaction. The Indian crust in under a compressional stress regime resulting from the collision of India with Eurasia. These compressional stresses can reactive ancient zones of weakness within the Indian plate causing slippage along old faults resulting in earthquakes. The Bhuj earthquake is thought to have occurred along zones of crustal weakness which originated during Mesozoic rifting and basin formation in the Gujarat region of India. Geologic studies show compressional ridges following the same trend as ancient graben structures suggesting that pre-existing zones of weaknesses are now being reactivated like old injuries flaming up during periods of stress. The reason for the Killari earthquake is less clear but a fair guess is that the Deccan Traps at that location sits on very ancient zones of weakness in the Indian crust which originated during the formation of Proterozoic mobile belts of south India. Just like the Indian plate, the Tibetan plateau which is part of the Asian plate, is also under a compression stress regime imposed by the continent-continent collision of India with Eurasia. Although some distance away from the zone of collision, the earthquake at Sichuan needs to be understood in this larger plate tectonic context.

Imagine a square block of dough say 6 inches thick and a foot across representing the Tibetan plateau. Now if you place one hand against one side of the square and drive your fist slowly into the dough from the other side, the dough will respond by thickening and also flowing in a direction perpendicular to the direction of the force you are putting against the dough. The dough has accommodated the shortening by thickening and flowing laterally. That is more or less what is happening to the Tibetan plateau is response to the NNE -SSW compressional stresses imposed by the plate collision. As India penetrates into Asia, the thick crustal material on the Asian plate is flowing eastwards out of India's path. Dont be misled by the term flow. The crust is not flowing like a liquid. The upper crust does break in a brittle manner and easterly movement (flow) of Tibetan crust occurs along faults in this case strike slip and normal faults . At depth the lower crust deforms as a continuous medium more like the dough model I presented. The rates of flow are a few 10's of mm per year. In a recent study by a group of Chinese and American geologists, a array of Global Positioning System locations measuring crustal velocities all over the Himalayas and the Tibetan plateau shows this flow of Tibetan crust with remarkable clarity. See map below. Thin blue arrows denote crustal velocities and direction of flow. Northerly flow dominates in the south central part of the Himalayas and the Tibetan plateau. Further north and east the crust is flowing eastwards towards Sichuan and rotating clockwise and flowing southerwards along the eastern syntaxis of the Himalayas.

Source: Continuous Deformation of the Tibetan Plateau from global positioning system data

This easterly flow of the Tibetan crustal material comes up against stronger crust in the Sichuan basin area. The resistance between the Sichuan basin and the Tibetan plateau results in compressive stresses and thrust faulting along the boundary between the two crustal blocks. The Longmenshan fault is one such thrust fault along which the Tibetian plateau is riding over the Sichuan basin. Map below shows the various tectonic features and fault movements in the Tibetan plateau and along its margins. Blue arrows indicated compression and shortening along the margins of the plateau. Purple arrows indicate shortening in the interior of the plateau. Open black arrows indicate relative motion of crust with respect to stable Eurasia.

Source: Continuous Deformation of the Tibetan Plateau from global positioning system data

The recent Sichuan earthquake was a result of the building up of stress along the Longmenshan fault in response to the convergence of the Tibetan crust against stronger crust underlying the Sichuan basin. High population density, poor construction and environmental damage in the form of deforestation has led to extraordinary losses in terms of lives and property. Large areas of China , southeast Asia and India fall under high seismicity risk zones. Often the remote locations and steep terrains especially in the Himalayan and Tibetian regions exacerbate the damage by making rescue efforts difficult . A more rigorous and structured earthquake damage management and mitigation plan needs to be put in place. But I sometimes wonder if scientific risk assessement whether of earthquakes or hurricanes will make any difference to human habitation patterns. By choice people are moving in large numbers to live next to active faults like the San Andreas in California or in the path of hurricanes as in Florida and Louisiana. In the Himalayas and Tibet people have little or no choice on where to live. Regardless of the risks they live where they have always lived on their ancestral lands. I don't see that pattern changing in the near future. NPR has USGS seismologist Walter Mooney giving a good talk on predicting aftershocks or rather how there is no real way to predict them and how stress changes along the Longmenshan fault zone after the big earthquake can trigger later earthquakes.

Groundwater Under The Sahara and Thar Deserts

From NPR Science Friday (I've been getting a lot of material from NPR of late) a discussion of a study that tracked the desertification of the Sahara using palynological evidence from sediments of Lake Yoa. The study suggests that desertification was a gradual process taking thousands of years, apparently contradicting earlier work which relied on evidence from the Mediterranean sea and indicated that desertification was rapid, probably taking place in a few hundred years. What was of interest to me was the talk about massive amounts of groundwater in the Nubian sandstone buried under the Sahara sands. This sedimentary aquifer which is made up of sedimentary sequences ranging in age from lower Paleozoic to the Cretaceous was last recharged in the early Holocene period when the climate in the Sahara region was much wetter. The aquifer contains an estimated 150,000 cubic km of water and currently about 6.5 million cubic metres per day are being extracted over its entire extent covering parts of Sudan, Chad, Libya and Egypt.

I am thinking of the situation under the sands of the Thar desert and see some parallels. I wrote about the recognition of paleochannels associated with the Ghaggar river system in the Jaisalmer district of Rajasthan. These channels contain groundwater which also like the Sahara was last recharged in the early part of the Holocene when this part of Rajasthan was wetter. The ancient river system is thought to have dried out by around 2500 B.C. due to aridification of western Rajasthan. There are grand plans today to exploit these water resources by targeted drilling, i.e identifying ancient river channels and drilling into them. Besides paleochannels it is entirely likely that the bedrock below the Thar sands may also contain aquifers. Recognizing these aquifers is going to be more difficult than paleochannels which show up as distinct linear features in radar images. What is important here is that we realize that just like the Nubian aquifer system this water under the Thar desert, stored either in ancient river channels or bedrock , is currently a non-renewable resource and draw up plans of exploitation with that in mind. As part of the Indira Gandhi Nahar Project (IGNP), the government wants to extend the canals of the Punjab into Rajasthan and use excess water from the Sutlej, Yamuna and the Ghaggar to recharge these potential aquifers. The aquifers will act as giant underground storage tanks, potentially advantageous over new surface water storage areas since no land will be submerged and losses due to evaporation minimized. This is a geo-engineering plan on a massive scale and will likely face a long period of opposition from environmentalists and economists. It might take a couple of decades for the benefits of this project to be realized if geologists and hydrologists ascertain that it makes sense in the first place. Meanwhile it won't take much to start sinking tube wells in the paleochannels and pumping out water from aquifers which have at present no natural recharge potential. Undue haste in exploiting this resource might degrade the system beyond repair. I am not at all certain given the water scarcity in this part of Rajasthan that politicians will show the necessary patience until science determines a sustainable water management plan. Global warming is expected to reduce the supply of water to north Indian rivers from Himalayan glaciers in the future. A planning commission report on water resources which did not take into account the projected shortfall from glacial sources finds

“Currently, total water use (including ground water) is 634 BCM (billion cubic metres), of which 83% is for irrigation. The demand for water is projected to grow to 813 BCM by 2025 and 1447 BCM by 2050, against utilisable quantum of 1123 BCM – 690 BCM from surface water and 433 BCM from ground water. Clearly, the overall demand will outstrip availability in another 35 to 40 years, while ground water in particular will come under even greater pressure in the intervening years.”

Global warming will likely make the situation even worse than the official projections. The non-renewable water resources under the Thar desert will gain even more importance given the expected scarcity of water resources in the Gangetic plains. They will have to be managed carefully.

Cutting Down On That Red Meat Mr. Bush?

I am not at all sure that even if our media and politicians had read in its entirety Mr. Bush's statements on increasing prosperity in China and India and its link to growing food prices, the reaction would have been any different. The false outraged, self righteous, preachy tone of the Indian response was childish and annoying. An instinctive America-bashing mentality seems to have taken deep roots in our civic discussions of global problems. In all this furore a much more interesting and informative study of American food habits, diets and its impact on climate change went relatively unnoticed. NPR covered it last week and the talk and the paper is worth following.

The study by Christopher Weber and Scott Matthews of Carnegie Mellon University , Pennsylvania did a life-cycle assessement of greenhouse gases emitted during all stages of growing, processing and transporting food consumed in the U.S. They broke it down according to food types and concluded that consumption of red meat and dairy accounted for about 50% of greenhouse gas emissions by an average U.S household. Their main conclusions:

Source: Food Miles and Relative Climate Impacts of Food Choices in the U.S.

..transportation creates only 11% of the 8.1 metric tons (t) of greenhouse gases (in CO2 equivalents) that an average U.S. household generates annually as a result of food consumption. The agricultural and industrial practices that go into growing and harvesting food are responsible for most (83%) of its greenhouse gas emissions.

For perspective, food accounts for 13% of every U.S. household's 60 t share of total U.S. emissions; this includes industrial and other emissions outside the home. By comparison, driving a car that gets 25 miles per gallon of gasoline for 12,000 miles per year (the U.S. average) produces about 4.4 t of CO2. Switching to a totally local diet is equivalent to driving about 1000 miles less per year, Weber says.

A relatively small dietary shift can accomplish about the same greenhouse gas reduction as eating locally, Weber adds. Replacing red meat and dairy with chicken, fish, or eggs for one day per week reduces emissions equal to 760 miles per year of driving. And switching to vegetables one day per week cuts the equivalent of driving 1160 miles per year.

What should the Indian response be to these findings? Indian agriculture food production chains are no doubt less energy intensive than the U.S. but industrial scale poultry and dairy production in India may be reaching comparable levels. The avoidance of beef by a majority of Indian seems to be helping in keeping industrial scale red meat production in check although we have lots and lots of cows that produce lots of milk and also plenty of methane. If you look at the breakdown of emissions during the dairy life -cycle production of gases in the above figure CO2, CH4 and N2O make up the dominant portion. Those ruminant stomachs are a real headache whether in U.S or in India! Our cattle are producing substantial amounts of greenhouse gases whether they are involved in industrial food processing cycles or not. The current debate on national responsibility for emissions have mostly involved people shouting at or worse past each other. I do feel that our response to statement's like the ones Mr. Bush made should involve more substance and less gas.

Selfish Genes and Altruism

Sometimes I just like to nitpick. David Brooks wrote a column in the New York Times exploring the ways science keeps explaining the way our brain works and the resulting conflict between those who are confident that all our experiences have a material basis and those who keep faith in the "something else", a soul, a ghost in the machine, a larger invisible unmeasurable presence that transcends material explanations.

Brooks writes:

Researchers now spend a lot of time trying to understand universal moral intuitions. Genes are not merely selfish, it appears. Instead, people seem to have deep instincts for fairness, empathy and attachment.

Brooks seems to imply that despite genes being selfish, people have altruistic tendencies. This is pet peeve of mine. The persistent misunderstanding that selfish genes lead to selfish behavior. I responded in a previous post about an article Nicolas Wade wrote about altruism and see no reason to change much:

The term “selfishness” in his article really reflects the metaphorical motives of genes and not the real motives of individuals. These are not necessarily the same motives. Both selfish and co-operative behaviors are contingent strategies which have evolved in certain circumstances such as living in highly social groups. Which one is employed depends upon an unconscious cost-benefit analysis of the greatest chance of reproductive success. The ultimate causation of both these behaviors is the gene's metaphorical selfish motive in getting the most copies of itself into the next generation. Thus ‘selfish genes’ (ultimate level) don't automatically produce selfish behavior (proximate level).

This clarification of the meaning of “Selfishness” is crucial since one of the biggest misapprehensions about evolution is that if genes have selfish motives then individuals will always behave selfishly with the obvious distasteful implications for human behavior. This need not be so since "selfishness" is the genes metaphorical motive which can lead to a wide range of behaviors ranging from selfishness to altruism in individuals.

More than 30 years since the publication of Richard Dawkins classic book The Selfish Gene, such misconceptions remain. If you were to glance through that book, you will find large sections devoted to explaining the evolution of altruism!

That's Dr. Brian May To You!!

One of my favorite rockers Brian May of Queen (love his little guitar riffs!!)

is now Astrophysicist Dr. Brian May, Ph.D in interplanetary dust from Imperial College, London


Listen to Dr. May belt it out on NPR's Day to Day. He's also co-authored a new book titled Bang: A Complete History of the Universe. Might not sell as much as A Brief History of Time but it's a fair bet that many unread copies will sit atop bookshelves. I got all nostalgic and listened to A Night At The Opera. Lazing On A Sunday Afternoon, Death On Two Legs, I'm In Love With My Car...

Dr. May is now chancellor of John Moores University in Liverpool. What is it with Liverpool and great rockers?