The Sichuan-Yunnan region, located at the southeastern margin of the Qinghai-Xizang Plateau, serves as a key channel for the southeastward extrusion of plateau material. The characteristics of crustal deformation and the mechanisms of deep material flow have been central topics of interest in geoscience research. In this work, a three-dimensional viscoelastic-plastic finite element model including the upper and mid-lower crust was established, constrained by GNSS horizontal crustal velocity observations and incorporating major active faults and geophysical survey data to explore the contribution of mid-lower crustal flow to surface deformation and its coupling with faults. Comparison of modeling experiments shows that relying solely on boundary loading or uniform layering assumptions fails to reproduce the GNSS observed velocities. We introduce a mid-lower crustal low-velocity weak zone, derived from the latest seismic velocity structure models. The new model improves the fit to GNSS observations. Tests of different viscosity coefficients in the low-velocity zone indicate an optimal viscosity range of 7.5 × 10¹⁹–1 × 10²⁰ Pa·s. Vertical profiles reveal that mid-lower crustal material motion is mainly concentrated at depths of 20–40 km, forming localized channelized flow in low-velocity zone with a typical Poiseuille velocity profile which indicates a ductile, fluid-like behavior with the low-velocity zone serving as primary pathways for deep material transport. The results further show that under the geometric constraints of upper-crustal faults, the mid-lower crustal flow contributes approximately 1–3 mm/a to surface deformation, primarily concentrated along major faults. This indicates that faults play a key role in constraining and modulating the transmission of deep-seated dynamics to shallow surface deformation. However, the contribution of mid-lower crustal flow is also significant; neglecting its influence on surface deformation would lead to an incomplete understanding of the deformation pattern and bias the interpretation of block boundaries and crustal kinematic segmentation.

The subsurface fluid injection can cause pressure increase within faults, leading to earthquake occurrences. However, the factors controlling earthquake rupture due to pressure perturbation remain poorly understood. To resolve this problem, we simulate the physical processes of earthquake nucleation and rupture on strike-slip faults perturbated by pressure migration based on the slip-weakening law. Multiple kinds of factors, including background stress, fluid injection rates, the area of the pressurized region, fault geometry, and fault friction coefficients, are considered in our simulations. Our simulation results reveal that the ratio of shear stress to normal stress rather than their absolute values controls the rupture behavior. With the large stress ratios, high injection rates, and large pressurized areas, earthquakes are prone to propagate as runaway ruptures. Additionally, faults with large aspect ratios of length to width are also favorable for causing runaway ruptures. In contrast, the factors of fault strike, dip angles and friction coefficients have minor influence on rupture behavior.

As an important model for explaining the seismic rupture mode, the asperity model plays an important role in studying the stress accumulation of faults and the location of earthquake initiation. Taking Qilian-Haiyuan fault as an example, this paper combines geodetic method and b-value method to propose a multi-source observation data fusion detection method that accurately determines the asperity boundary named dual threshold search method. The method is based on the criterion that the b-value asperity boundary should be most consistent with the slip deficit rate asperity boundary. Then the optimal threshold combination of slip deficit rate and b-value is obtained through threshold search, which can be used to determine the boundary of the asperity. Based on this method, the study finds that there are four potential asperities on the Qilian-Haiyuan fault: two asperities (A1 and A2) are on the Tuolaishan segment and the other two asperities (B and C) are on Lenglongling segment and Jinqianghe segment, respectively. Among them, the lengths of asperities A1 and A2 on Tuolaishan segment are 17.0 km and 64.8 km, respectively. And the lower boundaries are 5.5 km and 15.5 km, respectively; The length of asperity B on Lenglongling segment is 70.7 km, and the lower boundary is 10.2 km. The length of asperity C on Jinqianghe segment is 42.3 km, and the lower boundary is 8.3 km.

The M_W7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_W9.2 great Alaska earthquake in the United States. In this study, high-rate GPS data and near-field broadband seismograms are used in separate and joint inversions by the generalized Cut-and-Paste (gCAP) method to estimate the focal mechanism. In order to investigate the influence of crustal velocity structure on the focal mechanism inversion results, two velocity models (Crust1.0 and Alaska Earthquake Center (AEC)) are used for detailed comparison and analysis. The results show that: (1) The two nodal planes of the optimal double-couple solution are nearly north-south striking, with dip angles of about 30° and 60° respectively, and the centroid focal depth is 54–55 km, which is an intraplate normal fault event. (2) The inversion results for the two types of data and the two velocity models are consistent with some previous studies, which indicates that the results are stable and reliable. The more accurate velocity structure model is helpful for focal mechanism inversion of the complex earthquake. (3) The inclusion of high-rate GPS data in joint inversion provides a more effective constraint on centroid depth.