Nepal: Scientists fear bigger quake could follow to release built up strain

The massive earthquake that has claimed more than 3,200 lives so far in Nepal has most likely not released all the accumulated strain in the Earth's fault line running along the region.

A bigger quake could be expected anytime in the coming decades to the south and west of the present one, say geophysicists.

The latest quake follows the same pattern as earlier big twin tremors that occurred over 700 years ago, with the strain from a quake being transferred to another region along the fault and resulting in a quake a few hundred years later.

In fact, their evidence had led to anticipation of a major earthquake in exactly the location where Saturday's (25 April) big tremor struck. Predicting the time of a quake is difficult.

The present one is believed to be fallout of the 1934 quake which measured eight on the Richter scale and almost destroyed the cities of Kathmandu, Bhaktapur and Patan, reports the BBC.

The historical pattern of quake duos was uncovered by Laurent Bollinger from the CEA research agency in France and his colleagues just last month when studying charcoal fragments buried along the main fault line running 1,000 km from west to east.

What they saw indicated two big tremors that occurred 700 years ago in a domino effect of strain transferred along the fault.

The carbon dating of the fragments showed the fault had not moved since 1344.

But the neighbouring segment of the fault, which lies to the east of Kathmandu, had experienced major quakes in 1255, and then more recently in 1934.

Accumulated stress

Following the 1255 quake to the east, strain accumulated over the following 89 years in the neighbouring westerly segment of fault, finally rupturing in 1344.

Similarly, the 1934 quake in the east has resulted in transfer of strain westwards along the fault, which was finally been released now, 81 years later.

There could be more to come, warns the team.

"Early calculations suggest that Saturday's magnitude-7.8 earthquake is probably not big enough to rupture all the way to the surface, so there is still likely to be more strain stored, and we should probably expect another big earthquake to the west and south of this one in the coming decades," says Bollinger.

"We could see that both Kathmandu and Pokhara would now be particularly exposed to earthquakes rupturing the main fault, where it likely last did in 1344, between the two cities," explains Paul Tapponnier, from the Earth Observatory of Singapore, who was working with Bollinger.

Bollinger presented his findings to the Nepal Geological Society two weeks before the quake.

The present quake occurred at the boundary between the Indian plate and the Eurasian one. The two are converging in the region with the Indian plate moving at 45 millimetres a year under the Eurasian plate.

In fact it is this movement which has given rise to the Himalayas. Massive earthquakes down millions of years have led to the uplift of the mountain range.