Directional seismic response to the complex topography: A case study of 2013 Lushan Ms 7.0 earthquake

Azimuthal variations in site response can provide a good insight into the site amplification and seismic conditions of geohazard occurrences. In this study, multiple directional site response methods, including D-Arias (Directional-Arias), D-SER (Directional- Shaking energy ratio), D-HVSR (Directional-Horizontal to vertical spectral ratio) and D-SSR (Directional — Standard spectral ratio), are adopted to analyse seismic data of the 2013 Lushan Ms 7.0 earthquake captured by the self-established Lengzhuguan (LZG) station which consists of the complex topography of isolated ridge, large mountain and some typical micro-reliefs. The results show that the isolated ridge could cause stronger site responses than the large mountain, and whose pronounced response direction is roughly perpendicular to its ridgeline. With the growth of elevation, the site resonant frequency decreases. The different microreliefs on the mountain cause different site responses, which present as protruding slope \gt linear slope. The site response mainly exists on the surficial layer of the mountain and shows that with the increase of the distance to mountain surface, the site response gets weaker, the site resonant frequency gets higher, and the pronounced response direction is perpendicular to its ridgeline.