SEISMIC REFLECTION IMAGING OF THE HIMALAYAN SEISMOGENIC ZONE: PAST EXPERIENCE AND FUTURE STRATEGIES

The Himalayan seismogenic zone stands as perhaps the world's exemplar of the intracontinental equivalent of the oceanic subduction zones that host the vast majority of the world's great earthquakes. Just as marine seismic reflection profiling has proven to be a key methodology for detailing variations in structure and physical properties across and along these submarine rupture zones, land reflection profiling is essential to mapping past and future rupture zones of thrust earthquakes in the Himalayas. Although reflection seismics on land in terrane as rugged as the Himalayas presents challenges not present in the marine environment, a number of previous efforts suggest that reflection surveying is not only a viable, but an essential, tool for understanding earthquake hazards in this region. Among these previous reflection surveys are (1) INDEPTH's imaging of the Main Himalayan Thrust (MHT) beneath southern Tibet, which successfully detailed the geometry and physical properties of the roots of active Himalayan thrusting near Nepal, and (2) HIMPROBE's surveys across the Sub-Himalaya fold-thrust belt in Northwest India, which suggest that changes in sedimentary thickness-not lateral ramps in abasal decollement- control rupture in this area. In addition to these deeper seismic efforts, recent high-resolution reflection surveys in Nepal have successfully traced the subsurface geometry of shallow thrust faults, linking rupture to lateral structures at depth. Reflection imagery of the Asian collision zone has proven especially useful when linked with complementary observations, particularly MT and receiver functions. However, no other geophysical technique provides the structural resolution achievable by reflection profiling. We propose a systematic program of reflection profiling, and targeted 3D reflection imaging, that spans both past and potential future rupture zones in the Himalayas. This effort should build upon both existing resources in the region and new technologies (e.g. nodal recording) that can greatly reduce the cost of reflection surveys in the area. Special attention should be given to surveys to identify those structures which control rupture segmentation and to those which can serve as the base for time lapse imaging of rupture zone reflectivity in the future.