Himalayan strain reservoir inferred from limited afterslip following the Gorkha earthquake

This is the abstract of a letter whcih appeared in Nature Geoscience.

Authors:
David Mencin1, Rebecca Bendick2, Bishal Nath Upreti3, Danda Pani Adhikari4,
Ananta Prasad Gajurel4, Roshan Raj Bhattarai4, Hari Ram Shrestha3, Tara Nidhi Bhattarai4,
Niraj Manandhar5, John Galetzka6, Ellen Knappe2, Beth Pratt-Sitaula7, Abdelkrim Aoudia8
and Roger Bilham1*

The magnitude 7.8 Gorkha earthquake in April 2015 ruptured
a 150-km-long section of the Himalayan décollement terminating
close to Kathmandu1–4. The earthquake failed to rupture
the surface Himalayan frontal thrusts and raised concern that a
futureMw 7.3 earthquake could break the unruptured region
to the south and west of Kathmandu. Here we use GPS records
of surface motions to show that no aseismic slip occurred
on the ruptured fault plane in the six months immediately
following the earthquake. We find that although 70mm of
afterslip occurred locally north of the rupture, fewer than
25mmof afterslip occurred in a narrowzone to the south. Rapid
initial afterslip north of the rupture was largely complete in
six months, releasing aseismic-moment equivalent to a Mw 7.1
earthquake. Historical earthquakes in 1803, 1833, 1905 and
1947 also failed to rupture the Himalayan frontal faults, and
were not followed by large earthquakes to their south. This
implies that significant relict heterogeneous strain prevails
throughout the Main Himalayan Thrust. The considerable slip
during great Himalayanearthquakesmaybeduein part togreat
earthquakes tapping reservoirs of residual strain inherited
from former partial ruptures of the Main Himalayan Thrust.

FROM: Nature Geoscience

(2016)

doi:10.1038/ngeo2734