Bimodal seismicity in the Himalaya controlled by fault friction and geometry.

Dal Zilio L; van Dinther Y; Gerya T; Avouac JP

doi:10.1038/s41467-018-07874-8

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Bimodal seismicity in the Himalaya controlled by fault friction and geometry.

Dal Zilio L Geophysical Fluid Dynamics, Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland. luca.dalzilio@erdw.ethz.ch.
van Dinther Y Seismology and Wave Physics, Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
Gerya T Geophysical Fluid Dynamics, Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092, Zürich, Switzerland.
Avouac JP Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA.

2019-01-04

Published in:

Nature communications. - 2019

General Biochemistry, Genetics and Molecular Biology

English There is increasing evidence that the Himalayan seismicity can be bimodal: blind earthquakes (up to Mw ~ 7.8) tend to cluster in the downdip part of the seismogenic zone, whereas infrequent great earthquakes (Mw 8+) propagate up to the Himalayan frontal thrust. To explore the causes of this bimodal seismicity, we developed a two-dimensional, seismic cycle model of the Nepal Himalaya. Our visco-elasto-plastic simulations reproduce important features of the earthquake cycle, including interseismic strain and a bimodal seismicity pattern. Bimodal seismicity emerges as a result of relatively higher friction and a non-planar geometry of the Main Himalayan Thrust fault. This introduces a region of large strength excess that can only be activated once enough stress is transferred upwards by blind earthquakes. This supports the view that most segments of the Himalaya might produce complete ruptures significantly larger than the 2015 Mw 7.8 Gorkha earthquake, which should be accounted for in future seismic hazard assessments.

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