Seismic Response of a Mountain Ridge Prone to Landsliding

Abstract

During an earthquake, site effects can play an important role in triggering landslides. To document the seismic response of steep hillslopes, we deployed broadband seismometers across a mountain ridge in Taiwan, in an area with a high earthquake-induced landslide hazard. The ridge has a simple, representative shape, and landslides have previously occurred there. Our seismometer array has recorded continuously during more than 1 yr, with both ambient-noise and regional moderate earthquakes as sources. Processing horizontal and vertical signal components, we show that the ridge has a complex response, which we attribute to the combined effects of the subsurface geology and the topographic geometry. Amplification and directionality of ground motion are observed both high and low on the ridge, giving rise to localized, elevated, earthquake-induced landslide hazard. Our database contains earthquakes with mostly similar locations, making it difficult to determine the effect of earthquake back azimuth on the ridge response. A part of the ridge response, possibly due to topographic effects, seems to be explained by a model derived from a frequency scale curvature proxy at low frequency. If correct, this would be a promising first step toward improving local ground-motion estimation in mountain areas. However, the definition of appropriate scaling parameters of site effects based on geophysical measurements, for use in regional and global landslide hazard equations applicable to mountain areas with substantial regolith thickness, remains a significant challenge.

How water, temperature and seismicity control the preparation of massive rock slope failure (Hochvogel, DE/AT)

“…S42). It is often complex to distinguish between topographic resonance effects and interacting localized site effects (Rault et al, 2020;Weber et al, 2022) but landslide appearance and rockfall volume correlate with high peak ground accelerations (Meunier et al, 2007;Massey et al, 2022). During earthquakes, the stability of slopes relies on the magnitude of ground motion and its frequency content (e.g.…”

“…In steep topography it is furthermore important to consider frequencydependent seismic wave amplification due to topographic site effects (Harp and Jibson, 2002;Sepúlveda et al, 2005;Lee et al, 2009a, b;Khan et al, 2020). Through topographic resonance and refraction of waves, seismic amplification can reach factors of 2-14 in the horizontal component at specific frequencies, predominantly triggering landslides at mountain tops and ridge crests facing away from the epicenter (Meunier et al, 2008;Bakun-Mazor et al, 2013;Rault et al, 2020;Weber et al, 2022).…”

Controls on Post‐Seismic Landslide Behavior in Brittle Rocks

“…Based on our initial estimations of equivalent horizontal ground accelerations that cause dynamic shear stress amplitudes of ± 20 kPa and ± 40 kPa (section 3.3.3), we note the potential existence of a threshold ground acceleration between ~0.33 g and ~0.66 g that may be sufficient to cause divergent, path-dependent post-seismic landslide behaviour in shallow landslides. Where both sufficiently dense seismometer networks and detailed landslide inventories are available, it may therefore be possible to identify local to regional differences in postseismic hillslope stability in zones of varying coseismic ground accelerations for different hillslope configurations (Buech et al, 2010;Meunier et al, 2007;Rault et al, 2020).…”

Topographic Control on Ground Motions and Landslides From the 2015 Gorkha Earthquake

“…Ridges, in particular, tend to focus seismic energy through the interactions of scattered waves, a phenomenon known as topographic amplification (Asimaki & Mohammadi, 2018; Hartzell et al., 2017; Lee et al., 2009; Maufroy et al., 2015). Previous studies have investigated the distribution of earthquake‐induced landslides, either coseismic or post‐seismic landslides, with respect to ridge tops with various lithologies and rock strengths (Rault et al., 2019), as well as general relationships between the shapes of ridges and seismic amplification (Rault et al., 2020). However, the lack of dense instrumentation in regions of rugged topography, such as the Himalaya, has hindered progress in understanding the relationships between the characteristics of coseismic landslides and the seismic wavefields from the large earthquakes that promoted these landslides.…”