Source parameters of earthquakes and intraplate deformation beneath the Shillong Plateau and the Northern Indoburman Ranges

摘要: We determined the fault plane solutions and focal depths of 17 earthquakes beneath Shillong Plateau northern Indoburman ranges by combining results from inversion long-period P SH waveforms amplitudes, polarities first motions, identification pP sP phases on short-period seismograms. Fault 15 show mixtures thrust strike-slip faulting, but axes for these events are nearly horizontal consistently oriented north-northeast–south-southwest. All occurred at greater than 29 km. Beneath Plateau, one event a depth 52 The relatively large in an intraplate setting suggest that Indian lithosphere this area is especially cold. Earthquakes define gently east-southeast dipping zone 30 to 45 km Bengal basin 40 90 ranges. This seems steepen connect with intermediate seismicity dips eastward Burma. These cannot have along interface between subducting plate overriding lithosphere, because axes, not nodal planes, parallel north-south trending seismic zone. Although couple might within most plate, recently currently being subducted consistent north-northeast trend implies orientation maximum compressional strain throughout its northeastern pan perpendicular responsible roughly folds Thus, either geologic time (since 1 Ma) compression changed dramatically, or, more likely, deformation decoupled underlying plate. Meanwhile, seemingly identical northward displacement India respect south China must be accommodated farther east, Sagaing other faults.