Terrain attributes of earthquake- and rainstorm-induced landslides in orogenic mountain Belt, Taiwan

Landsliding induced by earthquakes and rainstorms in montane regions is not only a sculptor for shaping the landscape, but also a driver for delivering sediments and above-ground biomass downstream. However, the terrain attributes of earthquake- and rainstorm-induced landslides are less discussed comprehensively in Taiwan. As part of an island-wide inventory, we here compare and contrast the landslide terrain attributes resulting from two catastrophic events: the Chi-Chi earthquake (M_w = 7.6, September 1999) and typhoon Morakot (rainfall >2500 mm, August 2009). Results show that the earthquake-induced landslides are relatively small, round-shaped and prone to occur primarily in middle and toe of slopes. In contrast, the rainstorm-induced landslides are larger, horseshoe-shaped and preferentially occurring in slope toes. Also, earthquake-induced landslides, particularly large landslides, are usually found at steeper gradients, whereas rainstorm-induced landslides aggregate at gradients between 25° and 40°. Lithologic control plays a secondary role in landsliding. From an island-wide perspective, high landslide density locates in the region of earthquake intensity ≥ VI or one-day rainfall ≥600 mm day⁻¹. Through the landslide patterns and their terrain attributes, our retrospective approach sheds light on accessing the historical and remote events for close geophysical investigations. Finally, we should bear in mind that the landslide location, size, and terrain attributes varying with triggers may affect the landscape evaluation or biogeochemical processes in landslide-dominated regions.