Analysis of historical seismic parameters based on geological hazards from the Xiaonanhai earthquake

[Objective]   As the largest historical seismic event in Chongqing region, the Xiaonanhai Earthquake holds significant scientific value for deciphering seismogenic parameters to inform regional seismic hazard assessment and anti-seismic fortification standards. Addressing the critical challenge of observational data scarcity in historical earthquake research. [Methods]   A novel methodology for inverting seismic parameters through characteristic earthquake relics has been developed, systematically reconstructing the historical seismic parameters of the Xiaonanhai earthquake.. High-precision remote sensing interpretation and field investigations of seismically induced geo-hazards reveal that the landslide clusters triggered by the Xiaonanhai Earthquake exhibit a dominant near-N-S spatial distribution , consistent with the elliptical major axis direction of historically documented felt areas. [Results]   This spatial congruence suggests the NNW-striking Yangtoushan Fault as the seismogenic fault. Detailed remote sensing analyses of landslide orientations, sliding directions, and deposit distributions demonstrate, for the first time, coherent SE-directed motion features across multiple landslide masses, indicating a southeastward coseismic rupture propagation. Comparative analysis with the spatial correlation between geo-hazards and seismogenic structures observed in the Ludian Earthquake, coupled with seismotectonic mechanisms in southeastern Chongqing, further validates the rationality of the derived seismic parameters.  [Conclusion]   The study innovatively identifies a "karst-tectonic" composite mechanism: Under persistent NW-SE tectonic stress, bead-like karst caves developed along the fault zone or dominant joint directions form natural weakening zones, inducing stress concentrationand ultimately triggering left-lateral strike-slip motion with thrust components. This dual mechanism explains the unique seismic characteristics blending tectonic rupture and karst collapse. [Significance]  The proposed "geo-morphodynamic inversion" methodology advances historical earthquake parameter reconstruction and provides critical insights for seismic risk evaluation in karst terrains.