Abstract:
[Objective] To determine the rupture mode of the M
S7.3 earthquake in Hualien, Taiwan, China on April 3, 2024 and its triggering effect on subsequent seismic events in the surrounding area, by inverting the geometric structure and sliding characteristics of the seismogenic fault, the co-seismic displacement field and the induced areal strain response were analyzed. To evaluate the static Coulomb Failure Stress (CFS) triggering effect of the main earthquake event on the two earthquake events M
S6.2 and M
S6.3 that occurred on April 23, 2024, and thereby clarify the promoting effect of this earthquake on its seismic activity and its influence on the stress field of the adjacent area. [Methods] The two possible seismogenic nodes of the main earthquake and its subsequent earthquakes are determined by using the method of "central focal mechanism"; Based on the homogeneous elastic half-space theoretical model, the co-seismic displacement field and areal strain field under seismic action are established; Analyze the co-seismic displacement field results of the vertical fault direction of the main shock and determine its sliding characteristics; Calculate the CFS variation of the main shock in subsequent seismic events and evaluate its promoting effect on subsequent earthquakes; The method of facet clustering is adopted to determine the seismogenic fault plane of the earthquake event; Project the stress field of the study area onto the seismogenic fault plane and analyze its causes of occurrence. [Results] The co-seismic displacement analysis of the April 3, 2024 M
S7.3 Hualien Earthquake in eastern Taiwan reveals distinct patterns in both horizontal and vertical displacement fields, consistent with its reverse fault mechanism. Based on the focal mechanism solution, this seismic event is identified as a typical reverse fault-type earthquake, aligning with the tectonic compression between the Eurasian Plate and the Pacific Plate. The horizontal displacement field demonstrates a complex material flow pattern: substantial crustal materials converged towards the seismogenic fault along its southeastern and northwestern flanks, followed by outward migration in northeastern and southwestern directions. This kinematic pattern reflects the intense plate convergence where the Pacific Plate subducts westward beneath the Eurasian Plate along the eastern margin of Taiwan Island. Vertical displacement measurements show significant differential movements across the fault. The southeastern block (upper plate) experienced remarkable uplift reaching 48.4 cm, while the northwestern block (lower plate) underwent subsidence up to 11.4 cm. This vertical displacement configuration, characteristic of thrust faulting, is further confirmed by cross-sectional observations perpendicular to the fault strike. The interface between the upper and lower plates exhibits sharp kinematic contrasts, with the upper plate displaying predominant upward motion components and the lower plate showing downward movements. Along-strike displacements reached approximately 22 cm, significantly exceeding the maximum perpendicular displacement of ~5 cm, indicating thrust-dominated rupture with minor strike-slip components. The strain field distribution presents a compressive belt parallel to the fault trace near the epicenter, flanked by extensional zones to the immediate east and west. Stress field analysis reveals significant shear stress concentrations (relative shear stress >0.7) and negative normal stresses on the fault planes of three major earthquakes in the sequence, consistent with the compressional regime generated by plate convergence. The westward subduction of the Pacific Plate beneath Taiwan Island creates optimal conditions for thrust faulting along the Longitudinal Valley Fault system, where accumulated shear stress ultimately exceeds the fault strength threshold. Notably, The Coulomb Failure Stress (CFS) calculations demonstrate that the April 3 mainshock significantly promoted subsequent seismic activity. The April 23 M
S6.3 and M
S6.2 events occurred in regions where the calculated CFS changes reached 0.020 MPa and 0.3 MPa respectively, both exceeding the 0.01 MPa threshold for earthquake triggering. This earthquake sequence represents a normal release process of accumulated tectonic stress in the plate convergence zone. The spatial-temporal evolution of co-seismic deformation, strain redistribution, and stress interactions fully aligns with the regional tectonic framework dominated by the ongoing collision between the Eurasian and Pacific Plates. [Conclusion] Research shows that the M
S7.3 earthquake in Hualien, Taiwan, exhibited a reverse thrust of thrust. This earthquake event, along with the two subsequent M
S6.2 and M
S6.3 earthquake events that occurred on April 23, 2024, were all normal releases of local stress accumulation. Moreover, the CFS generated by the M
S7.3 earthquake in Hualien, Taiwan, has a significant impact on the surrounding seismic activities and has an obvious promoting effect on the occurrence of the subsequent two earthquakes. [Significance] This study not only evaluates the impact of the M
S 7.3 earthquake in Hualien, Taiwan, on subsequent earthquakes, but also provides a fundamental dataset for geodynamic studies in the region. Strengthening the capacity of earthquake monitoring and forecasting and disaster mitigation promotes the formulation of relevant policies and safeguards people's lives and properties.