ABSTRACT

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Geodetic deformation across the Himalaya reflects primarily locking of the Main Himalayan Thrust (MHT) fault from the surface to a depth of about 15-20km. Local seismic monitoring has revealed clustered seismicity that is probably driven by stress accumulation near the downdip edge of the locked fault zone. The pattern of geodetic strain and the distribution of seismicity show however lateral variations which could reveal heterogeneous stress build up on the Also both geodetic strain and seismicity show strong seasonal variations. These may be induced by landwater storage variations, mostly in the Gangetic plain, but other causes may also be advocated. We therefore offer to analyze the spatial pattern and temporal evolution of geodetic strain and seismicity in the Nepal Himalaya using data from Continuous GPS (CGPS) from Nepal and southern Tibet, and seismicity recorded by the National Seismic Network of Nepal. The main objectives of this project are to
(1) determine the pattern of locking on the Main Himalayan Thrust (MHT),
(2) assess the relationship between interseismic strain build up and seismicity,
(3) determine the cause of temporal changes of strain,
(4) analyze the relationship between seismicity and strain rates and derive implications for earthquake nucleation.
The project will help constrain the spatio-temporal pattern of stress build up that is preparing future earthquakes in the Nepal Himalaya. It will advance our understanding of the physical parameters that determine whether a fault creeps steadily or has a stick-slip motion producing repeating seismic slip events. It will also advance our understanding of earthquake nucleation.

The project will contribute important information regarding seismic hazard in Nepal and northern India. Indeed, the frequency of large earthquakes in the Himalaya depends critically on the rate at which deficit of slip accumulates in the interseismic period. Also the spatial pattern of deficit of slip is probably heterogeneous and might influence large earthquake ruptures as has been inferred for a number of subduction zones.This project will address most challenging questions in seismotectonics: why does a particular fault portion creeps or produces earthquakes? How does seismicity rate relates to interseismic strain buildup and to other sources of stress fluctuations (earth tides, snow loading, landwater storage.) Finally, the project will foster international scientific collaboration and will constitute the core of a PhD research project.

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