A Comparative Analysis of the 14 November 1986 ML 6.8, Mw 7.3 and 2 April 2024 ML 7.1, Mw 7.4 Hualien, Taiwan, Earthquakes: Insights into Seismic Characteristics and Regional Impact

ABSTRACT Offshore fault systems near northeastern Taiwan pose a significant seismic hazard, underscored by the damaging 14 November 1986 ML 6.8, Mw 7.3 and 2 April 2024 ML 7.1, Mw 7.4 Hualien earthquakes. Despite occurring nearly four decades apart and with epicenters over 120 km from Taipei, both events caused notable damage in the capital. The 1986 earthquake was recorded by a limited seismic network, leaving rupture details uncertain, whereas the 2024 event (Mw 7.4), Taiwan’s largest since the devastating 1999 Chi-Chi earthquake, benefited from a modern, high-density seismic network, enabling precise relocation and detailed rupture analysis. Despite these differences, both earthquakes exhibited similar focal mechanisms and similar long-period (>1 s) waveforms at Geophysical Data Management System (GDMS)/Incorporated Research Institutions for Seismology stations. Moreover, velocity records from a 1986 local strong-motion station (SMART1-C00) closely align with modern 2024 recordings (Taiwan Strong Motion Implementation Program [TSMIP]-E026), suggesting a shared underlying seismogenic mechanism. By applying analytical methods developed for the well-recorded 2024 earthquake to re-examine the 1986 event, we simulated synthetic waveforms at TSMIP-E026 using the 2024 source model and compared them with synthetics derived from source models of the 1986 earthquake. Although direct comparison using modern inversion standard is challenging, this qualitative agreement highlights a common concentration of energy releases around 30 s with similar duration in both earthquakes. Spectral analysis in both Hualien and the distant Taipei basin indicates comparable, and at times higher, ground motion in the southwestern Taipei basin, correlating with observed structural damage in both earthquake scenarios. Although enhanced building codes implemented post-1999 likely mitigated the impact of the 2024 event, the sustained strong shaking highlights persistent vulnerabilities. The striking similarities in waveforms and spectral characteristics imply that these Hualien earthquakes, despite their temporal separation, share not only comparable magnitudes and focal mechanisms but also a common seismogenic process.