Distribution characteristics of geohazards induced by the Lushan Earthquake and their comparisons with the Wenchuan Earthquake

Abstract

The Lushan Earthquake induced a large number of geohazards. They are widely distributed and caused serious damages. The basic characteristics, formation mechanisms and typical cases of geohazards induced by Lushan Earthquake are described, and compares to the relationships of Lushan and Wenchuan earthquakes between geohazards and earthquake magnitude, geomorphology, slope angle, elevation and seismic intensity in the most affected areas in the article. (1) The numbers and volumes of landslides and rockslides differ significantly between the two earthquakes due to their differing magnitudes. The Lushan Earthquake is associated with fewer and smaller-magnitude geohazards, within the immediate area, which mainly consist of small-and medium-sized shallow landslides and rockslides, and occur on steep slopes and mountain valleys. The largest landslide induced by Lushan Earthquake is the Gangoutou Landslide debris flow with a residual volume of about 2.48×106 m3. The most dangerous debris flow is at Lengmugou gulley in Baoxing County, which has similar geomorphological features and disaster modes as a previous disaster in Zhouqu County, Gansu Province. (2) Geohazards induced by the Lushan Earthquake show four mechanisms: cracking-rockslides-collision-scraping and then debris flows, cracking-rockslides, vibration-rainfall-rockslides-landslide and then debris flow, vibration-throwing or scrolling. (3) There are significant similarities and differences between the geohazards induced by these two earthquakes. The types of geohazards are the same but the volume, quantity and other factors differ: geohazards are concentrated on slope angles of 10°–40° in the Lushan Earthquake area, especially within 10°–20°, and at absolute elevation of 500–2 000 m above sea level (a.s.l.). Geohazards within the Wenchuan Earthquake area are concentrated on steeper slope angles of 30°–40° at higher absolute elevations of 1 500–2 000 m.s.l..