Saturday, April 9, 2016

Hindu Kush quakes may have long-lasting effects

Islamabad, April 9 (IANS): The recent wave of tremors that have shaken the Hindu Kush regions of Pakistan and Afghanistan may have lasting impacts on the topography of areas as far afield as Islamabad, experts said.

On Friday, the region was shaken by at least four distinct tremors, ranging in intensity from 3.3 to 5.3, according to the Pakistan Meteorological Department (PMD), the strongest of which was felt in parts of Khyber-Pakhtunkhwa.

Two of the quakes originated in the Hindu Kush region, while the other two were located in the Afghanistan-Tajikistan border region, Dawn cited PMD as saying on its website.

All of the quakes occurred deep under the earth's crust, with at least three of the quakes measuring over 100 km in depth.

Over 100 seismic events have been recorded in the region over the past six months alone. Some rocked the earth like a boat, while most of them went unnoticed.Like the four on Friday, the vast majority of these events originated in parts of the Hindu Kush range located in Afghanistan and Tajikistan and were felt as far afield as Islamabad and Lahore.

The region is roughly located on top of the meeting point for the Indian and Eurasian tectonic plates.

The US Geological Survey (USGS) has termed the Hindu Kush "one of the most seismically hazardous regions on earth."

However, nearly all of the recent tremors felt in the region originated deep in the earth's crust, nearly 200 km below the surface.

In a report on earthquakes in this region, the USGS noted that "the Hindu Kush shares this high-stress configuration with a seismically active area in Colombia, South America." These two regions have some of the world's highest rates of deep earthquakes.

According to a report by the National Geographic Society, the two plates collide at a rate of about 1.5 inches a year, pushing up the Himalayan mountain range in the process.

Due to friction along the plate boundaries, the collisions are not smooth or even. When the rocks finally give way under the strain, the plates jerk rapidly, releasing the energy that causes an earthquake.

With the collision of plates pushing land upwards, nearby regions including Islamabad may gradually end up gaining altitude.

"Some areas can start sinking too. For example, La Paz, the capital of Bolivia, is sinking lower because mountains around it are rising," a Met official said.

The massive 2005 Kashmir earthquake was also the result of collisions between these two tectonic plates.

The deadly Nepal earthquake on April 25, 2015, that triggered a massive avalanche on Mount Everest, was caused by a sudden release of built-up stress along the same fault line, USGS reported.

Experiments conducted at the Stanford University mimicking pressures at such depths indicate that rocks should deform and not break rapidly enough to generate seismic waves.

It is suspected that rocks at such depths may chemically rearrange themselves into denser forms to cope with the tremendous pressure. In doing so, they may release water that can lubricate the movement of the fault.

The 8.1 earthquake that occurred on October 26, 2015 was also part of the series of tremors. In fact, there have been at least 12 aftershocks of that quake, some of which felt like mini-quakes.

Pakistan's Met Office has said that small quakes are a good sign as they help dissipate seismic energy without causing a sudden underground jerk that may cause far more widespread damage.

There is a downside; once the plates break through the rocks, there may be a valley or empty space in the earth's crust, which will cause the plates to shift and could trigger a massive tremor.
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