A powerful 5.8 magnitude earthquake struck northeast Pakistan on Tuesday, damaging dozens of homes and shops and killing at least 29 people and injuring over 300, officials said.
Our subcontinent has suffered some of the largest earthquakes in the world with more than about 60% of its land area prone to shaking of intensity VII and above on the MMI scale, a seismic intensity scale.
In fact, the entire Himalayan belt is considered prone to great earthquakes of magnitude exceeding 8.0, with Kashmir region among the most susceptible. The region lies on the boundary, where the small Indian plate that underlies most of Pakistan and India and the vast Eurasian tectonic plates that consist of Europe, Russia and most of Middle East, collide.
Yesterday’s earthquake was likely occurred as the result of shallow reverse faulting near the convergent boundary between the Indian and Eurasian plates. It was the same natural phenomenon that triggered the October 8, 2005 earthquake.
A reverse fault is one in which one side of the fault, the hanging wall, moves up and over the other side, the foot wall. This movement is caused by compression and is common at tectonic plate boundaries.
The Indian tectonic plate is located in the north east hemisphere. It is bounded by 4 major tectonic plates. North of the Indian plate is the Eurasian plate, to the south east, the Australian plate, to the south west, the African plate and to the west the Arabian plate.
Shallow east-west striking reverse faulting is consistent with the tectonics of the region. A thrust fault is a reverse fault that is at an incline of less than 45 degrees. Tensional stress is when rock slabs are pulled apart from each other, causing normal faults. With normal faults, the hanging wall slips downward relative to the footwall. This causes reverse faults, which are the reverse of normal faults, because in this case, the hanging wall slides upward relative to the footwall.
Earthquakes occur in the northern part of the Indian plate as it is still active today and drifts at a velocity of about 5 cm per year. Low to 5 magnitude earthquakes were registered in the urban areas of India, the largest recorded earthquake occurred near New Delhi in 1950 and had a magnitude of 8.5. The devastating M 7.6 event on October 8, 2005 occurred 160 km to the north of yesterday’s event, also was a result of shallow reverse faulting. It killed at least 86,000 people and caused extensive damage in northern Pakistan. Few other large events have occurred in recent decades in the immediate vicinity. Further afield, six events M 7 and greater have occurred over the preceding 40 years 400-500 km to the northwest in northeastern Afghanistan, mostly at intermediate depths of 100-250 km. The most recent event, one of the largest, was an M 7.5 earthquake in October 2015 that resulted in at least 395 fatalities, more than 1000 injuries, and the destruction of tens of thousands of buildings.
The epicenter of this earthquake was located near densely populated areas of Punjab and AJK. There are reports of high infrastructural damage including shaken/cracked houses, commercial centers and public offices. USGS estimates that around two million people are at risk of further shakeups in the ground. Local communities need to exercise extreme caution in coming days as there are news of aftershocks coming with regular intervals.
