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More Earth to shatter

Updated Apr 24, 2013 04:18pm

The massive 7.8 magnitude earthquake in Iran, which sent tremors across the border and flattened mud houses in Balochistan, killing more than two dozen people in Pakistan, was a reminder that big earthquakes are a regular feature of this part of the world. It has only been eight years since the last “big” quake hit Pakistan’s Azad Kashmir region in 2005; its epicenter was in the Himalayan Mountains, one of the youngest mountains on earth.

The Himalayan Mountains were formed around 50 million years ago when the northward moving Indian plate first collided with Asia. During the continued collision process, the Indian plate’s front edge was broken, folded and uplifted to form this youngest and highest mountain range on our planet. Even at present the Indian plate is constantly burrowing under the Tibetan plateau. This convergence builds up a very large storage of energy in the Himalayan region, which is eventually released in the form of massive earthquakes.

Since the mountain building process is still ongoing, the Himalayan Mountains and the surrounding region is seismically one of the most active parts on earth. The earthquakes occurring in the Himalayas are often devastating, as was the 2005 Kashmir earthquake. Unfortunately, there are more to come. According to the eminent seismologist, Roger Bilham of the University of Colorado, “What’s more important today is that the Himalayas are ruptured along less than half of their extent.” This means tremendous strain is building up every day and another “big” one could be due any time soon. Roger Bilham in fact visited Pakistan after the 2005 earthquake that registered 7.6 on the Richter scale.

He conducted a study that revealed the 2005 earthquake occurred in a region where a great plate-boundary earthquake had long been considered overdue. According to the study, “Although the 2005 earthquake resulted in widespread devastation, theoretical considerations suggest it may not have released more than one 10th of the cumulative elastic energy that has developed since the previous great earthquake in the region in 1555”. Bilham conducted the study using data collected through Global Positioning System (GPS) sensors placed in different locations of Azad Kashmir and Indian held Kashmir in past few years.

The findings of the study were made public in 2011 – and they created a storm because Bilham found that the relative movement of the Tibetan plateau was slowest (this indicates where compression is building up, and a rupture is eventually likely to occur) in the Zanskar Range to the north of the Kashmir Valley. This means that the zone likely to rupture when a quake eventually happens could be 200 km wide, and would encompass the entire Kashmir Valley. If slippage occurs over a length of 300 km, as is possible, a mega-quake of magnitude 9 is the likely result. What Bilham couldn’t predict from his GPS results was when such a disaster might happen. His warning was that: “I think you have to plan for the worst case.”

However, both the Indian government and the Pakistani Meteorological Department (PMD) downplayed the fears spread by his study. The PMD issued a statement that “seismologists cannot predict earthquakes” in December 2011, while the Indian government went a step further and refused to issue Bilham a visa on a subsequent visit to India in December 2012.

In Bilham’s defense, the well-known landslide expert Dave Petley at Durham University (who has also visited Pakistan several times) wrote in his blog that the study was “a quite measured piece about the potential for a large earthquake, and the likely consequences of such an event. This earthquake risk is very real, and urgently needs addressing through preparedness and measures such as improved building codes. This is not an issue that can be ducked”.

Bilham is not alone about predicting a “big” one in the Himalayas. Last year, research by Stanford scientists that focused on geologic features and activity in the Himalayas, predicted the same thing. A geophysics doctoral student at Stanford, Warren Caldwell, analysed seismic data from 20 seismometers deployed for two years across the Himalayas by colleagues at the National Geophysical Research Institute of India.

According to his research, “The data imaged a thrust dipping a gentle two to four degrees northward, as has been previously inferred, but also revealed a segment of the thrust that dips more steeply (15 degrees downward) for 20 kilometers. Such a ramp has been postulated to be a nucleation point for massive earthquakes in the Himalayas”.

Although Caldwell emphasized that his research focused on imaging the fault, not on predicting earthquakes, he noted that the Main Himalayan Thrust has historically been responsible for a magnitude 8 to 9 earthquake every several hundred years.

“What we’re observing doesn’t bear on where we are in the earthquake cycle, but it has implications in predicting earthquake magnitude,” Caldwell said. “From our imaging, the ramp location is a bit farther north than has been previously observed, which would create a larger rupture width and a larger magnitude earthquake.”

Caldwell’s adviser, geophysics Professor Simon Klemperer, added that recent detections of magma and water around the Main Himalayan Thrust indicate which segments of the thrust will rupture during an earthquake.

“We think that the big thrust vault will probably rupture southward to the Earth’s surface, but we don’t expect significant rupture north of there,” Klemperer said. The findings are important for creating risk assessments and disaster plans for the heavily populated cities in the region. But the question remains, are the governments of both India and Pakistan willing to take the findings of these studies seriously?

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The writer is an award-winning environmental journalist based in Islamabad, who also covers climate change and health issues. She can be reached at rinasaeed@gmail.com

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