Extracting source characteristics and dynamics of the August 2010 Mount Meager landslide from broadband seismograms

Abstract

[1] Seismic methods can substantially improve the characterization of the dynamics of large and rapid landslides. Such landslides often generate strong long-period seismic waves due to the large-scale acceleration of the entire landslide mass, which, according to theory, can be approximated as a single-force mechanism at long wavelengths. I apply this theory and invert the long-period seismic waves generated by the 48.5 Mm 3 August 2010 Mount Meager rockslide-debris flow in British Columbia. Using data from five broadband seismic stations 70 to 276 km from the source, I obtain a time series of forces the landslide exerted on the Earth, with peak forces of 1.0 × 10 11 N. The direction and amplitude of the forces can be used to determine the timing and occurrence of events and subevents. Using this result, in combination with other field and geospatial evidence, I calculate an average horizontal acceleration of the rockslide of 0.39 m/s 2 and an average apparent coefficient of basal friction of 0.38 ± 0.02, which suggests elevated basal fluid pressures. The direction and timing of the strongest forces are consistent with the centripetal acceleration of the debris flow around corners in its path. I use this correlation to estimate speeds, which peak at 92 m/s. This study demonstrates that the time series recording of forces exerted by a large and rapid landslide derived remotely from seismic records can be used to tie post-slide evidence to what actually occurred during the event and can serve to validate numerical models and theoretical methods.

Seismic and mechanical studies of the artificially triggered rockfall at Mount Néron (French Alps, December 2011)

“…Seismic signal generation processes are related to flow dynamics and trajectory changes (Surinach et al, 2001;Brodsky et al, 2003;Favreau et al, 2010;Schneider et al, 2010;Allstadt, 2013) as well as changes in coupling with topography (Caplan-Auerbach and Huggel, 2007;Mangeney et al, 2007). Thanks to the low-frequency content of the seismograms, the waveform is preserved even for large source-sensor distances allowing the signals to be inverted.…”

“…The seismic source can be modeled as a single horizontal force (Kanamori and Given, 1982;Kanamori et al, 1984;Dahlen, 1993) in which magnitude and direction vary over time and depend on the fallen volume, basal friction and dynamic effects (La Rocca et al, 2004). Sliding mass models (Brodsky et al, 2003;Allstadt, 2013;Yamada et al, 2013) or numerical depth-averaged flows models (Favreau et al, 2010;Schneider et al, 2010;Moretti et al, 2012) showed their ability to reproduce the seismic source characteristics for volcanic, rocky or rock-ice debris flows.…”

Dynamics of the Oso-Steelhead landslide from broadband seismic analysis

“…We use the inversion method developed by Ekström and Stark (2013) to determine the landslide force history (LFH) of the Oso-Steelhead landslide from the long-period waveforms recorded at five broadband stations. The method is based on the approximation that, when considering the longperiod signals, the landslide seismic source can be described as a time-varying, 3D force vector acting at a fixed point (Kanamori and Given, 1982;Fukao, 1995;Brodsky et al, 2003;Ekström and Stark, 2013;Allstadt, 2013). This assumption is justified to the extent that the spatial scale of the slide is small compared to the wavelength of the seismic waves and to the distances to the recording seismic stations.…”

“…The combined analysis of short-period seismic data with the dynamics inferred from long-period waves provides important information on large landslide motion (Schneider et al, 2010;Yamada et al, 2013;Allstadt, 2013;Hibert et al, 2014). While the long-period waves and the force-history (LFH) inversion provide insight into the temporal evolution of the bulk momentum of the whole landslide mass, the shortperiod waves reflect spatially complex momentum exchanges across the basal slide area at shorter length scales.…”

“…In recent years, seismology has proven useful in this regard by offering a way to infer the dynamics of large mass movements (e.g., Brodsky et al, 2003;Favreau et al, 2010;Schneider et al, 2010;Moretti et al, 2012;Yamada et al, 2013;Allstadt, 2013) and estimate important properties such as the mobilized mass (Ekström and Stark, 2013). Additional analysis of the short-period waves provides an extra constraint on source mechanisms and a more complete understanding of the dynamics of slope failures (e.g., Suriñach et al, 2005;Deparis et al, 2008;Vilajosana et al, 2008;Dammeier et al, 2011;Hibert et al, 2011Hibert et al, , 2014.…”