[H-TT14] Geographic Information Systems and Cartography

[HTT14-P04] Spatial distribution of landslides induced by the 2022 Taitung earthquakes in eastern Taiwan

★Invited Papers

*Chi-Wen Chen^1,2、Lun-Wei Wei³、Ryuji Yamada⁴、Tomoyuki Iida² (1.Department of Geosciences, National Taiwan University、2.Center for Spatial Information Science, The University of Tokyo、3.Advanced Geological Research Task Force、4.National Research Institute for Earth Science and Disaster Resilience)

キーワード：Landslide, Earthquake, Active fault, Topographic effect, Seismic wave

In September 2022, a series of earthquakes with the largest foreshock of M_W 6.5 and the main shock of M_W 6.9 occurred in eastern Taiwan, known as the 2022 Taitung earthquakes. The Soil and Water Conservation Bureau of Taiwan mapped landslides induced by the 2022 Taitung earthquakes via satellite images before and after the earthquakes. A total of 45 landslides were identified, ranging in area from 1.16×10³ to 2.74×10⁴ m². The frequency-area distribution of the 45 landslides shows that the 2022 Taitung earthquakes induced few small landslides, and there were not too many large-scale landslides. Most of the landslides are with an area of 10³ to10⁴ m². We analyzed the spatial distribution of landslides and explored their relationship with the distribution of earthquake source fault. The distance between landslides and active faults ranges from 0.82 to 17.65 km, with an average of 8.26 km. From this spatial relationship, the parameters of the source fault and the magnitude of the earthquake can be inferred through the model proposed by the previous study, which is very consistent with the real situation with the Central Range fault. In addition, we also analyzed the topographic conditions of landslide distribution and further explored the impact of topographic effects. We found that most of the landslides occurred on the mid-hillside or even closer to the stream. This result is different from the phenomenon that most coseismic landslides occurred near ridges observed by previous studies. The Central Range fault is distributed in the Longitudinal Valley, and the range of about 3 km on both sides of the fault is almost a flat area, resulting in only six landslides distributed within 3 km from the fault. Seismic waves transmitted to distant mountains are weakened by the attenuation effect and are therefore not strong enough to have a significant topographic amplification effect on ridges. Most landslides are mainly distributed at lower elevations, which means that seismic waves cannot reach farther high mountains to induce landslides and most landslides occur on steep slopes, which shows that when seismic waves travel farther away, landslides can only be induced on low stability steep slopes owing to the weakening of seismic waves. In this case, because of comprehensive conditions of fault type and surrounding topography, landslides mostly occur on the mid-hillside rather than on the ridge.