[S08] PM-2

[S08-06] Rupture Dynamics and Fault Characteristics of the Maidan Fault during the 2024 Mw 7.1 Wushi Earthquake in Xinjiang, China

*Hangyu Gao¹, Yuji Yagi¹, Ryo Okuwaki¹ (1. University of Tsukuba)

On January 22, 2024, at 6:09 (UTC), a magnitude (M) 7.1 earthquake struck Wushi County in Xinjiang, China. According to the China Earthquake Network Center (CENC), this large earthquake occurred along the Maidan fault zone on the southwestern side of the Tianshan Mountains. While the southwestern Tianshan fault zone has experienced several earthquakes of magnitude 6.0 and above since 1900, this large earthquake marks the first instance of the M 7-class earthquake since the establishment of the China Earthquake Network. The Maidan fault, which trends southwest, is at the junction of the Tianshan Mountains and the Tarim Basin. Geodetic studies indicate that this fault is affected by the tectonic shortening of the southern Tianshan Mountains. Under north-south compressional stress, the southwestern section of the Maidan fault exhibits distinct left-lateral strike-slip characteristics. Active fault studies classify the Maidan fault as a fold-thrust fault zone, with numerous high-angle segments. A finite-fault inversion has been widely applied to estimate the spatio-temporal distribution of slip-rate. However, this technique requires an assumption of the fault planes, and if the assumed fault planes are inconsistent with the actual fault, the obtained solution will be distorted. In this study, we employed a recently developed Potency Density Tensor Inversion (PDTI) method to analyze the Wushi earthquake using teleseismic P-waves. The PDTI estimates the seismic source process as a spatio-temporal distribution of the potential-rate density tensor along a model plane. The PDTI defines the model plane instead of fault planes, and obtained focal mechanisms are unconstrained by the assumed model plane geometry. To mitigate the overfitting or instability associated with that modeling of high degrees of freedom, modeling errors for the Green's function were introduced into the data covariance matrix and Akaike’s Bayesian Information Criterion was used to determine the strength of smoothing. We selected 44 teleseismic P-waves of the Wushi earthquake and used the CRUST1.0 model to calculate the Green's function for the one-dimensional layered velocity model in the source region.
The results show that the main slip area of this earthquake is concentrated in a triangular region radiating from the initial rupture point toward the surface. This area extends approximately 20 km along the dip direction and has a maximum length of 40 km. The maximum total rupture is located at 7.5 km east and 15 km south from the initial rupture position with a maximum slip of 3.1 m. The total seismic moment is 6.5×10¹⁹ N m (Mw 7.1). The initial rupture with strike of 240° and dip of 40° grows near the hypocenter and continues for about 3 s. The main rupture with strike of 232° and dip of 55° starts about 10 km south of the epicenter at 3.5 s after the origin time and propagates eastward for about 15 km. Subsequently, rupture occurs on the northeast and southwest sides of the main rupture zone, and then rupture becomes faint after 10 s. The southwestern rupture had a strike of 250°–260° with a dip of 50°, while the northeastern rupture had a strike of 230°–240° and a dip of 50°. We will discuss that the discontinuous rupture propagation reflects the complex fault structure of the source region and suggests that multiple faults ruptured in a series.