Magnitude 8 or greater earthquake predicted near Kathmandu, Nepal

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December 5, 2016: A research paper published in the journal Earth and Planetary Science Letters claims fault near Kathmandu could produce magnitude 8 or greater earthquake.

An international team, including researchers from the University of Nevada, Reno warned Kathmandu and other areas along the Himalayan Frontal Fault could be due for an even more powerful event.  

Researchers dug two deep trenches near the mouths of major rivers at Tribeni and Bagmati and studied soils and fault lines looking back over the past 2,000 years.

In Tribeni, they discovered a scarp of at least 15 feet vertical separation between 1221 and 1262 AD. Similarly, at the Bagmati site, they found a vertical separation of about 30 feet or more, formed between 1031 and 1321 AD.

The research found that the 200 kilometers, extending from Tribeni to Bagmati, could be in the stages leading up to a massive earthquake of magnitude 8 or greater, capable of producing fractures 15-30 feet high.

A massive earthquake of magnitude 7.9 on April 25 last year killed 8,778 people in Nepal. The highest number of fatalities were reported from Sindhupalchowk (3,440) followed by Kathmandu (1,222).

Abstract

The 2015 Gorkha earthquake produced displacement on the lower half of a shallow decollement that extends 100 km south, and upward from beneath the High Himalaya and Kathmandu to where it breaks the surface to form the trace of the Himalayan Frontal Thrust (HFT), leaving unruptured the shallowest ∼50 km of the decollement. To address the potential of future earthquakes along this section of the HFT, we examine structural, stratigraphic, and radiocarbon relationships in exposures created by emplacement of trenches across the HFT where it has produced scarps in young alluvium at the mouths of major rivers at Tribeni and Bagmati. The Bagmati site is located south of Kathmandu and directly up dip from the Gorkha rupture, whereas the Tribeni site is located ∼200 km to the west and outside the up dip projection of the Gorkha earthquake rupture plane. The most recent rupture at Tribeni occurred 1221–1262 AD to produce a scarp of ∼7 m vertical separation. Vertical separation across the scarp at Bagmati registers ∼10 m, possibly greater, and formed between 1031–1321 AD. The temporal constraints and large displacements allow the interpretation that the two sites separated by ∼200 km each ruptured simultaneously, possibly during 1255 AD, the year of a historically reported earthquake that produced damage in Kathmandu. In light of geodetic data that show ∼20 mm/yr of crustal shortening is occurring across the Himalayan front, the sum of observations is interpreted to suggest that the HFT extending from Tribeni to Bagmati may rupture simultaneously, that the next great earthquake near Kathmandu may rupture an area significantly greater than the section of HFT up dip from the Gorkha earthquake, and that it is prudent to consider that the HFT near Kathmandu is well along in a strain accumulation cycle prior to a great thrust earthquake, most likely much greater than occurred in 2015.

1. Steven G. Wesnouskya, 2. Yasuhiro Kumaharab, 3. Deepak Chamlagainc, 1. Ian K. Piercea, 3. Alina Karkic, 4. Dipendra Gautam

1. Center for Neotectonic Studies and Seismological Laboratory, University of Nevada, Reno 89557, USA

2. Graduate School of Education, Hiroshima University, 1-1-1, Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8524, Japan

3. Department of Geology, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu, Nepal

4. Centre for Disaster and Climate Change Studies, Kathmandu, Nepal

Received 18 June 2016, Revised 6 October 2016, Accepted 6 October 2016, Available online 3 November 2016 (published in the journal Earth and Planetary Science Letters)