The refined slip rates of the Haiyuan fault system from GNSS and levelling data

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SUMMARY Constrained by the horizontal velocity field of ∼248 GNSS stations and vertical velocity field of ∼432 levelling sites in the northeastern margin of the Qinghai–Tibet, we utilized an improved screw dislocation model with dip angle considered to invert the slip rate, locking depth and dip angle of each segment of the Haiyuan fault system. Comparative analysis of the inverted results shows that the improved screw dislocation model with dip angle considered has superior data fitting to the classical screw dislocation model, especially for faults with low dip angles. From west to east, strike-slip rates increase from 4.4 mm a−1 on the Lenglongling fault to 6.3 mm a−1 on the Maomaoshan–Laohushan fault and then decrease to 3.0 mm a−1 on the eastern segment of the Haiyuan fault, with dip angles varying between 50$^\circ $ and 65$^\circ $. The Maomaoshan–Laohushan segment exhibits the maximum locking depth of 22.5 km and the highest seismic moment, corresponding to an equivalent moment magnitude of up to 7.1 in the next 100 yr. The locking degree and slip rate deficit are generally decreasing from west to east on the Haiyuan fault system. The Lenglongling and Jinqianghe segments exhibit the highest locking degrees with depths of ∼15 km and slip rate deficits of ∼6 mm a−1. In contrast, the Haiyuan segment in the east has a low locking degree with a shallow depth of less than 8 km and a slip rate deficit of 2–4 mm a−1. The high locking degree and strain accumulation suggest a high seismic hazard on the Maomaoshan–Laohushan, Lenglongling and Jinjianghe faults, where should be paid more attention.

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