Abstract
The 21 May 2021 Maduo earthquake was the largest event to occur on a secondary fault in the interior of the active Bayanhar block on the north-central Tibetan plateau in the last twenty years. A detailed kinematic study of the Maduo earthquake helps us to better understand the seismogenic environments of the secondary faults within the block, and its relationship with the block-bounding faults. In this study, firstly, SAR images are used to obtain the coseismic deformation fields. Secondly, we use a strain model-based method and steepest descent method (SDM) to resolve the three-dimensional displacement components and to invert the coseismic slip distribution constrained by coseismic displacement fields, respectively. The three-dimensional displacement fields reveal a dominant left-lateral strike-slip motion, local horizontal displacement variations and widely distributed near-fault subsidence/uplift deformation. We prefer a five-segment fault slip model, with well constrained fault geometry featuring different dip angles and striking, constrained by InSAR observations. The peak coseismic slip is estimated to be ~5 m near longitude 98.9°E at a depth of ~4–7 km. Overall, the distribution of the coseismic slip on the fault is highly correlated to the measured surface displacement offsets along the entire rupture. We observe the moderate shallow slip deficit and limited afterslip deformation following the Maduo earthquake, it may indicate the effects of off-fault deformation during the earthquake and stable interseismic creep on the fault. The occurrence of the Maduo earthquake on a subsidiary fault updates the importance and the traditional estimate of the seismic hazards for the Kunlun fault.
Highlights
InSAR deformation maps clearly show that the whole displacement field covers an area of approximately 200 km × 70 km
The occurrence of the Maduo earthquake challenges the common view that the Bayanhar block largely behaves like a block as inferred from the generally constant fault slip rate distribution of the Kunlun fault along sections between longitude 92◦ E and 98◦ E
We use the geodetic measurements on the surface to investigate the fault geometry and rupture kinematics of the seismogenic fault to understand their relationship
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Due to ongoing continental collision of the Eurasian and Indian plates, the Tibetan plateau is one of the regions globally with intense seismicity resulting from significant tectonic loading and crustal deformation. A series of large-scale active strike-slip faults and active sub-blocks are widely distributed across the Tibetan plateau. The Bayanhar block (Figure 1a), on the northern Tibetan plateau, is demonstrated to be the most seismically active sub-block in recent years. A series of major earthquake sequences occurred at the boundary of the Bayanhar block, including the 1997 Ms7.5 Manyi earthquake, the 2001 Ms8.1 Kokoxili earthquake, the 2008 Ms8.0 Wenchuan earthquake, the 2010
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