RAINFALL TRIGGERING THRESHOULD FOR LARGE SCALE LANDSLIDES

Abstract:

The study collected the seismic records of the Broadband Array in Taiwan for Seismology (BATS) to identify the ground motion probably triggered by totally 481 large landslides having areas larger than 0.1 km² from 2005-2009. After eliminating the signals from local and teleseismic earthquakes, 45 landslide-triggered seismic signals were interpreted. The landslide-triggered seismic signals provided accurate timing of landslide initiation to assess the rainfall conditions for large landslide.

The analyses of landslide-triggered seismic signals reveal that there is a significantly positive relationship between envelope area of vibration and landslides having area larger than 0.5 km², which means landslide ground-motion signals could reflect the scale of landslides. A similar relationship exists between calculated surface wave magnitude and landslide area as well.

The preliminary results about critical rainfall for large landslides includes (1) the amount of cumulative rainfall is the major factor to trigger large landslide, (2) the I-D rainfall threshold for large landslide is I = 49.3‧D^-0.37 , which is significantly higher than that for shallow landslides, and (3) this study takes antecedent rainfall into consideration, the amount of effective cumulative rainfall for 70% occurrence probability for large landslides should be 1345 mm, and for 90% should be 1600 mm.ABSTRACT

The study collected the seismic records of the Broardband Array in Taiwan for Seismology (BATS) to identify the ground motion probably triggered by totally 481 large landslides having areas larger than 0.1 km² from 2005-2009. After eliminating the signals from local and teleseismic earthquakes, 45 landslide-triggered seismic signals were interpreted. The landslide-triggered seismic signals provided accurate timing of landslide initiation to assess the rainfall conditions for large landslide.

The analyses of landslide-triggered seismic signals reveal that there is a significantly positive relationship between envelope area of vibration and landslides having area larger than 0.5 km², which means landslide ground-motion signals could reflect the scale of landslides. A similar relationship exists between calculated surface wave magnitude and landslide area as well.

 The preliminary results about critical rainfall for large landslides includes (1) the amount of cumulative rainfall is the major factor to trigger large landslide, (2) the I-D rainfall threshold for large landslide is I = 49.3‧D^-0.37 , which is significantly higher than that for shallow landslides, and (3) this study takes antecedent rainfall into consideration, the amount of effective cumulative rainfall for 70% occurrence probability for large landslides should be 1345 mm, and for 90% should be 1600 mm.