Spatial distribution of landslides triggered by the 2022 Taitung Earthquakes in relation to active fault systems, topographic effects, and geological conditions

Abstract

In September 2022, eastern Taiwan was shaken by a series of earthquakes, known as the 2022 Taitung earthquakes. A total of 45 landslides were triggered by the earthquakes, and the frequency-area distribution revealed a scarcity of small- and large-scale landslides. Most of the landslides were moderate in scale, with areas ranging from 10³ to 10⁴ m². We examined the relationship between the landslide distribution and earthquake source faults. The distances between landslides and active faults ranged from 0.82 to 17.65 km. The results allowed us to infer parameters of the source faults and the magnitudes of the earthquakes using a model proposed in a previous study, which aligns with the real situation. Furthermore, we analyzed the topographic and geological conditions associated with landslide distribution. We found that most landslides occurred on mid-hillsides or in close proximity to streams, in contrast to the findings of previous studies that highlighted ridge areas as the primary locations of coseismic landslides. As the source fault in this study is situated in a valley, with a flat plain on both sides, only six landslides occurred within 3 km of the fault. Seismic waves transmitted to distant mountains were attenuated and lacked the strength to have amplification on ridges. Because the seismic waves failed to reach higher mountains, the landslides predominantly occurred at lower elevations on steep slopes with more fragile geological conditions. Based on the comprehensive conditions of fault type and surrounding topography and geology, the landslides mostly occurred on mid-hillsides rather than on ridges.