Fault locking and slip rate deficit of the Haiyuan-Liupanshan fault zone in the northeastern margin of the Tibetan Plateau

GPS-derived horizontal velocities, geologic fault slip rates and earthquake-derived fault slip vector azimuths are inverted simultaneously for fault coupling and slip rate deficit on the Haiyuan-Liupanshan fault in the northeastern margin of the Tibetan Plateau. Along the Haiyuan fault, the results show 3.2-6.2 mm/yr of left-lateral strike-slip, and the strike-slip transformed into thrusting deformation (2.8-3.5 mm/yr) along the Liupanshan fault. The results suggest full coupling down to ∼10 km along the Haiyuan fault. Significant portions from the Jinqianghe fault to the Maomaoshan fault, however, are locked to ∼23 km depth. The abrupt change in fault coupling coincides with the Tianzhu seismic gap. High slip rate deficit (3.0-4.5 mm/yr) and seismic moment accumulation rate are also interpreted along the seismic gap. The Liupanshan fault is locked to 15-20 km depth. A high seismic moment accumulation rate, low slip rate deficit (2.0-3.2 mm/yr) and scarcity of large seismic event over the last 1400 years may imply high strain accumulation on the fault. The results demonstrate that crustal deformation in the northeastern Tibetan Plateau is dominated by elastic block rotation. We also conclude that deformation due to fault coupling is limited along the near-field (less than 50 km with velocities less than 2 mm/yr) of the Haiyuan-Liupanshan fault.