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Late Quaternary Shortening and Earthquake Chronology of an Active Fault in the Kashmir Basin, Northwest Himalaya

MADDEN, C., Oregon State University, Corvallis, Oregon, USA, madden@earthconsultants.com; TRENCH, D., Oregon State University, Corvallis, Oregon, USA, david.trench@gmail.com; MEIGS, A., Oregon State University, Corvallis, Oregon, USA, meigsa@geo.oregonstate.edu; AHMAD, B., University of Kashmir, Srinagar, J & K, India, shabir79@rediffmail.com; BHAT, M.I., University of Kashmir, Srinagar, J & K, India, bhatmi@hotmail.com; YULE, J.D., CSU Northridge, Northridge, California, USA,

In contrast to the central Himalaya, where shortening from the collision of India with Asia is localized at the Himalayan frontal thrust (HFT), distributed deformation characterizes convergence across the northwest Himalaya (NWH). Evidence for distributed deformation in the NWH includes active shortening on a fault system over 40 km northeast of the HFT that includes the Riasi fault zone (Hebeler et al.; Gavillot et al., this meeting), and the Balakot-Bagh fault, source of the Mw 7.6, 2005 Kashmir earthquake. New mapping and paleoseismic data indicate that active faulting also occurs within the Kashmir Valley (KV), an intermontane basin ~100 km north of the NWH deformation front. The 40-km-long Balapora fault (BF) is the longest of three northeast-dipping reverse faults that cut Quaternary terraces on the southwest side of the KV. Outcrops and artificial trenches demonstrate that the base of overbank deposits in a low fill terrace of the Rambira River exhibits ~13 m of vertical separation across the BF. Weakly developed soils and the lack of loess suggest these deposits postdate the last glacial maximum (22-17 ka) and may be as young as 10-6 ka, the last period of enhanced monsoon and regional aggradation in the NWH. These crude age constraints, 13 m of vertical separation, and a 60 degree average fault dip yield a preliminary shortening rate of 0.3 to 1.3 mm/yr for the BF. Paleoseismic trenches across the BF near Shupiyan reveal growth strata and colluvial wedges that record 2-4 surface rupturing events in the latest Quaternary. These preliminary results indicate that the BF is a low slip rate fault and poses a seismic hazard to the people of the nearby city of Srinagar and the KV. Determining the percentage of Indo-Asian convergence across the KV requires dating of terrace deposits and additional mapping of the BP and other active faults in the KV.

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Last Modified: 2011 Aug 10

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