Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal

摘要: We analyze geomorphic evidence of recent crustal deformation in the sub-Himalaya central Nepal, south Kathmandu Basin. The Main Frontal Thrust fault (MFT), which marks southern edge sub-Himalayan fold belt, is only active structure that area. Active bend folding at MFT quantified from structural geology and fluvial terraces along Bagmati Bakeya Rivers. Two major two minor strath are recognized dated to be 9.2, 2.2, 6.2, 3.7 calibrated (cal) kyr old, respectively. Rock uplift up 1.5 cm/yr derived river incision, accounting for sedimentation Gangetic plain channel geometry changes. profiles found correlate with bedding dip angles, as expected folding. It implies thrusting has absorbed 21 ± mm/yr N-S shortening on average over Holocene period. ±1.5 defines 68% confidence interval accounts uncertainties age, elevation measurements, initial deformed terraces, seismic cycle. At longitude Kathmandu, localized must absorb most across Himalaya. By contrast, microseismicity geodetic monitoring last decade suggest interseismic strain accumulating beneath High Himalaya, 50–100 km north zone, where Himalayan (MHT) roots into a ductile decollement Tibet. In period MHT locked, elastic accumulates until being released by large (M_w > 8) earthquakes. These earthquakes break near surface front foothills result incremental activation MFT.