ISLAMABAD: 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 say.
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 such as Malakand and Swat.
Two of the quakes originated in the Hindu Kush region, while the other two were located in the Afghanistan-Tajikistan border region, PMD said on its website. All of them occurred deep under the earth’s crust, with at least three of the quakes measuring over 100km in depth.
Experts say collisions between Indian, Eurasian plates may cause areas like Islamabad to rise over time
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 passed 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 United States 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 200km 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.
However, scientists admit that they do not know a great deal about the forces that are in play at such depths. The USGS has stated that most such earthquakes are caused by tectonic plates rubbing together.
According to a report by the National Geographic Society, the two plates are colliding 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. Or conversely, “Some areas can start sinking too. For example, La Paz, the capital of Bolivia, is sinking lower because mountains around it are rising,” Met Office DG Dr Ghulam Rasul told Dawn.
Anatomy of a quake
Most earthquakes arise along fault zones; the ground first bends and then snaps, and an earthquake is generated to release the energy.
The earthquakes arising out of Hindu Kush region are said to be the result of slow collisions between the Indian subcontinent and the Eurasian tectonic plate.
The massive 2005 Kashmir earthquake was also the result of collisions between these two plates. Even the deadly Nepal earthquake of 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 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.
Deep earthquakes can also be caused by friction; if a small area deep inside a fault moves, it generates heat. The hotter it gets, the more it is able to move, and the more heat is created. This sets off a loop that has the potential to destabilise the whole fault, causing a massive quake.
The 8.1 earthquake that occurred on October 26, 2015 was also part of the same series of tremors. In fact, there have been at least 12 aftershocks of that quake, some of which felt like mini-quakes.
At a recent press conference held to allay the fears of the general public, the Met Office has announced that smaller earthquakes were a good sign as they helped dissipate seismic energy without causing a sudden underground jerk that may cause far more widespread damage.
Dr Ghulam Rasul told Dawn that while most earthquakes were not dangerous, the earthquakes occurring in the Hindu Kush region could prove to be dangerous.
He said that the tectonic plates too are not made of consistent material, rather there are hard rocks and even pockets of ancient water bodies.
Dr Rasul said that there was sufficient evidence of marine life having existed in the Himalayas before the formation of the mountains, as is evidenced by the presence of snails and other creatures that have evolved to survive in the new environment over time.
“Since the Indian Plate is sliding under the Eurasian plate, there could be friction caused by the presence of a massive rock formation, either under the Indian plate or the Eurasian plate,” he said.
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.
Published in Dawn, April 9th, 2016