Complex Slip Distribution of the 2021 Mw 7.4 Maduo, China, Earthquake: An Event Occurring on the Slowly Slipping Fault

Abstract

The 21 May 2021 Maduo earthquake occurred on the Kunlun Mountain Pass–Jiangcuo fault (KMPJF), a seismogenic fault with no documented large earthquakes. To probe its kinematics, we first estimate the slip rates of the KMPJF and Tuosuo Lake segment (TLS, ∼75 km north of the KMPJF) of the East Kunlun fault (EKLF) based on the secular Global Positioning System (GPS) data using the Markov chain Monte Carlo method. Our model reveals that the slip rates of the KMPJF and TLS are 1.7 ± 0.8 and 7.1 ± 0.3 mm/yr, respectively. Then, we invert high-resolution GPS and Interferometric Synthetic Aperture Radar observations to decipher the fault geometry and detailed coseismic slip distribution associated with the Maduo earthquake. The geometry of the KMPFJ significantly varies along strike, composed of five fault subsegments. The most slip is accommodated by two steeply dipping fault segments, with the patch of large sinistral slip concentrated in the shallow depth on a simple straight structure. The released seismic moment is ∼1.5×1020 N·m, equivalent to an Mw 7.39 event, with a peak slip of ∼9.3 m. Combining the average coseismic slip and slip rate of the main fault, an earthquake recurrence period of ∼1250−400+1120 yr is estimated. The Maduo earthquake reminds us to reevaluate the potential of seismic gaps where slip rates are low. Based on our calculated Coulomb failure stress, the Maduo earthquake imposes positive stress on the Maqin–Maqu segment of the EKLF, a long-recognized seismic gap, implying that it may accelerate the occurrence of the next major event in this region.

Earthquake Cycle Deformation Associated With the 2021 MW 7.4 Maduo (Eastern Tibet) Earthquake: An Intrablock Rupture Event on a Slow‐Slipping Fault From Sentinel‐1 InSAR and Teleseismic Data

“…The crustal rheological structure consists of three layers: a 25 km thick elastic upper crust, a viscous Burgers‐body lower crust with a thickness of 33 km, and a viscous Maxwell‐body upper mantle; the transient and steady‐state viscosities of the Burgers body are 4.0 × 10 17 and 6.3 × 10 18 Pa s, respectively; the viscosity of the Maxwell body is 1.0 × 10 20 Pa s (full details in Hong et al., 2022). Our ΔCFS shows a similar pattern as published results (Guo et al., 2021; K. He, Wen, et al., 2021; Hong et al., 2022). We note that the 2021 Maduo earthquake caused positive stress changes of larger than 0.01 MPa on 2 segments of the KF: east of the Tuosuo Lake segment, and the Maqin segment which has drawn extensive concern of high seismic risk due to few historical earthquakes in the past ∼1,000 years in this seismic gap (X. Wen et al., 2007; Xiong et al., 2010; L. Zhu, Ji, & Liu, 2021); besides, the western Jiuzhi Fault as well as part of the Dari Fault and the Bayan Har Shan Main Peak Fault in the west have experienced comparable increased ΔCFS (Figure 10).…”

“…The crustal rheological structure consists of three layers: a 25 km thick elastic upper crust, a viscous Burgers-body lower crust with a thickness of 33 km, and a viscous Maxwell-body upper mantle; the transient and steady-state viscosities of the Burgers body are 4.0 × 10 17 and 6.3 × 10 18 Pa s, respectively; the viscosity of the Maxwell body is 1.0 × 10 20 Pa s (full details in Hong et al, 2022). Our ΔCFS shows a similar pattern as published results (Guo et al, 2021;K. He, Wen, et al, 2021;Hong et al, 2022).…”

“…To assess the seismic hazard after the Maduo earthquake, we use the PSGRN/PSCMP code (R. Wang et al., 2006) to calculate the Coulomb Failure Stress change (ΔCFS) in surrounding area and on neighboring faults based on our preferred coseismic slip model shown in Section 3.1. We use a friction coefficient of 0.4 as different friction coefficients have little effect on the spatial pattern of ΔCFS (Guo et al., 2021; L. He, Feng, et al., 2021; Hong et al., 2022; Xiong et al., 2010). The crustal rheological structure consists of three layers: a 25 km thick elastic upper crust, a viscous Burgers‐body lower crust with a thickness of 33 km, and a viscous Maxwell‐body upper mantle; the transient and steady‐state viscosities of the Burgers body are 4.0 × 10 17 and 6.3 × 10 18 Pa s, respectively; the viscosity of the Maxwell body is 1.0 × 10 20 Pa s (full details in Hong et al., 2022).…”

“…To assess the seismic hazard after the Maduo earthquake, we use the PSGRN/PSCMP code (R. Wang et al, 2006) to calculate the Coulomb Failure Stress change (ΔCFS) in surrounding area and on neighboring faults based on our preferred coseismic slip model shown in Section 3.1. We use a friction coefficient of 0.4 as different friction coefficients have little effect on the spatial pattern of ΔCFS (Guo et al, 2021;L. He, Feng, et al, 2021;Hong et al, 2022;Xiong et al, 2010).…”

“…Among all the block models of Tibet (Q. Chen et al., 2004; Loveless & Meade, 2011; Thatcher, 2007; W. Wang, Qiao, & Ding, 2021; W. Wang et al., 2017), the Jiangcuo Fault has never been defined as a block boundary, including the most recently published 30‐element block model for Tibet (W. Wang et al., 2017) (Figure 1c). Geodetic observations from GNSS reveal that the fault is slow‐moving, with a maximum slip rate of less than 2 mm/yr (Guo et al., 2021; Y. Zhu, Diao, et al., 2021), exhibiting a relatively low interseismic strain rate either from GNSS (20–30 nanostrain/yr, M. Wang, Shen, et al., 2021; M. Wang, Wang, et al., 2021) or InSAR (<20 nanostrain/yr, Zhao et al., 2021); both show a distributed deformation around the fault. A very slow slip rate of ∼0.6 mm/yr (strike‐slip) has been estimated geologically (Pan et al., 2022).…”