dc.description.abstract | The September 13, 2021 Nantou earthquake (ML 5.6, depth 46.1 km) occurred within a narrow zone of deep seismicity (35-80 km) beneath central Taiwan. This study aims to enhance our understanding of the seismic distribution within the deep seismic zone, investigate its underlying mechanism, and explore its tectonic implications. Additionally, the study examines variations in the S-wave arrival time from the Nantou earthquake.
To accomplish the first objective, events within the deep seismic zone from the CWBSN catalogue were sorted out and clustered using the density-based spatial clustering of applications with noise (DBSCAN, Kriegel et al., 2011). The two clusters thus derived were relocated using the double-difference algorithm (HypoDD) on a multiple events relocation scheme (Waldhauser and Ellsworth 2000). From a tectonic standpoint, we interpret the western cluster as being associated with the strong lower crust, characterized by mafic granulite and fault weakening induced by fluid. The source of stress is dominated by the slab pull of the South China Sea plate. As for the eastern cluster, two potential scenarios are proposed. First, as the Eurasian plate subducts deeper, the scenario may be similar to that of the western cluster. Secondly, the presence of eclogitization beneath the continental mountain root suggests the detachment of the oceanic lithosphere from the continental lithosphere. The source of stress is dominated by the collision of the Philippine Sea plate.
Regarding the second objective, S-wave waveforms from the Nantou earthquake, recorded by the Formosa Array, were subjected to cross-correlation analysis to determine the relative arrival time of the S-wave. The findings reveal a relatively faster arrival of the S-wave in northern Taiwan, which can be attributed to the H2 structure as indicated by Su et al. (2019). | en_US |