Paper summaries 2020

Abstract: The strata of the Siwalik Group in the Trijuga area has a total thickness that exceeds 5000m. It is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine Khola Thrust (MKT) and Main Boundary Thrust (MBT) all ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.

Highlights

• 5–8 mm/yr shortening across the Shillong Plateau.

• Discrepancy between geologic and geodetic rates requires underthrusting.

• First Cenozoic example of subduction initiation at a passive margin setting.

• Subduction initiation along the Dauki thrust drives observed shortening.

• The cold and brittle Indian slab increases seismic hazard.

Highlights

• Active-source refraction velocities across the MFT (Nepal) image deformation

• Changes in alluvium thickness of 60–150 m constrain fault throw

• Water table is tied to alluvium thickness, with a 25–100 m step at the faults.

• Subsurface deformation continues 6 km west of the surface expression of one fault.

Highlights

• We study models of multiple seismic cycles on faults with nonplanar geometry

• Our method includes axial surfaces to simulate off-fault deformation associated with fault-bend folding

• Earthquake segmentation can be due to stress heterogeneity caused by friction and fault geometry