The death toll from Monday鈥檚 magnitude-7.5 earthquake in north-east Afghanistan may end up being less than the 1000 feared because its source was so deep below the surface, say geologists.
Heavily populated areas and cities escaped serious damage, restricting casualties to more remote areas.
Advertisement
By 24 hours after Monday鈥檚 quake near the border with Pakistan, the death toll had reached 311 , with at least 1500 injured.
Most fatalities and casualties were in remote, less densely populated areas, with the worst toll so far in Khyber Pakhtunkhwa, Pakistan聽鈥� an estimated 216 deaths.
But geologists are hopeful that because of the depth and nature of the quake, many fewer will die than the 8000 reported in quakes that hit Nepal in April and May this year, and the massive Kashmir quake that killed tens of thousands in 2005.
Deep down
The US Geological Survey that the quake was of magnitude 7.5, far less than the 7.8-level quake that hit Nepal, and its source was at a depth of 200 kilometres compared with just 8 kilometres for the Nepal quake.
鈥淓arthquakes in the Hindu Kush are deep,鈥� says Gavin Hayes of the US Geological Survey. The reason is the near-vertical dipping of 鈥渄eep old slabs鈥� thought to be the remnants of a former subducting piece of Earth鈥檚 crust that long ago began burrowing down beneath another piece.
The main activity involves the Indian plate pushing northward from the south beneath the Hindu Kush, with the Eurasian plate to the north burrowing beneath the Pamir region where the quake occurred.
鈥淪ome models of what鈥檚 going on suggest the presence of two subduction zones, with the Indian plate being subducted beneath the Hindu Kush region, and the Eurasia plate being subducted beneath the Pamir region,鈥� says Hayes.
鈥淥ther models suggest that just one slab is being conducted but has become contorted and overturned in places,鈥� says Hayes. 鈥淲hatever the model, deep quakes here represent rupture within the core of the subducted 鈥榮lab鈥�.鈥�
Threat of landslides
By contrast, says Hayes, the Nepal quake in April and the huge Kashmir quake in 2005 were both on a much shallower and active plate boundary, where the Indian subcontinent is colliding with and thrusting beneath Eurasia. 鈥淓arthquakes here are thus shallow, [and] are directly related to the accumulation and release of plate boundary strain, and therefore have the potential to be much larger and more damaging than the deep 鈥榠ntraslab鈥� events of the Hindu Kush,鈥� says Hayes.
Nonetheless, reaching and helping casualties could be tricky, says John McCloskey of the University of Ulster, UK. 鈥淚n this region, the topography is very steep, so landslides are likely to pose a particular threat,鈥� he says.
A peak probability is up to 1000 deaths.
鈥淐ommunications appear to have gone down in the worst-affected areas, so it will be some time before we know the full impact,鈥� says Ilan Kelman, a specialist in risk and resilience at University College London.
Image credit: Xinhua News Agency/Rex Shutterstock
