UTILIZING COSEISMIC LANDSLIDES TO ANALYZE THE SOURCE AND RUPTURING PROCESS OF THE 2014 LUDIAN EARTHQUAKE

The 2014 Ludian MS 6.5/MW 6.1 earthquake in Yunnan, China caused significant causalities and serious disasters. It also triggered at least 1024 landslides with areas equal to 100m2 or larger. The purpose of this study is to utilize the spatial distribution and scale-changes of coseismic landslides to analyze the source and rupturing process of the 2014 Ludian earthquake. Base on the northwest strike direction of the long axis of the landslide-distribution area and the regional tectonic distribution of the earthquake affected area, the seismogenic fault of the Ludian earthquake is considered to be the Baogunao-Xiaohe fault. Most of the landslides occurred in the areas southeast to the epicenter, which indicates the rupturing direction is from northwest to southeast. The landslides in the northwest part of the affected area is characterized by more, smaller-scales, and larger distribution area, whereas those of the southeast part are few, larger-scales, and distributed in a smaller area. Landslides triggered by blind-ruptured earthquakes always show more quantity, smaller-scale, and larger distribution-area than those of surface-ruptured earthquakes. It can be inferred that the rupturing plane is relatively deep in the northwest section of the seismogenic fault and probably did not generate surface ruptures. The southeast section of the seismogenic fault should be relatively shallower and rupture the ground surface. These inferences have been validated by field investigations. It is concluded the seismic rupturing started from depth in northwest, then spread upward to the shallow subsurface in the southeast, which produced the surface rupture at the terminal of the rupture plane. Such a rupturing process can also explain the unusually serious disasters caused by the Ludian earthquake.