Locating Rockfalls Using Inter‐Station Ratios of Seismic Energy at Dolomieu Crater, Piton de la Fournaise Volcano

Abstract

Rockfalls generate seismic signals that can be used to detect and monitor rockfall activity.Event locations can be estimated on the basis of arrival times, amplitudes, or polarization of these seismic signals. However, surface topography variations can significantly influence seismic wave propagation and hence compromise results. Here, we specifically use the signature of topography on the seismic signal to better constrain the source location. Seismic impulse responses are predicted using Spectral Element based simulation of three-dimensional wave propagation in realistic geological media. Subsequently, rockfalls are located by minimizing the misfit between simulated and observed inter-station energy ratios. The method is tested on rockfalls at Dolomieu crater, Piton de la Fournaise volcano, Reunion Island. Both single boulder impacts and distributed granular flows are successfully located, tracking the complete rockfall trajectories by analyzing the signals in sliding time windows. Results from the highest frequency band (here 13-17 Hz) yield the best spatial resolution, making it possible to distinguish detachment positions less than 100 m apart. By taking into account surface topography, both vertical and horizontal signal components can be used. Limitations and the noise robustness of the location method are assessed using synthetic signals. Precise representation of the topography controls the location resolution, which is not significantly affected by the assumed impact direction. Tests on the network geometry reveal best resolution when the seismometers triangulate the source. We conclude that this method can improve the monitoring of rockfall activity in real time once a simulated database for the region of interest is created. KUEHNERT ET AL.

Characteristics of the Seismic Signal Generated by Fragmental Rockfalls: Insight From Laboratory Experiments

“…Recent studies have shown that important information related to the failure process and dynamics of rock mass movement can be acquired from seismic signals, such as the detection and differentiation of rock mass movement from seismic sources (Chen et al., 2013; Helmstetter & Garambois, 2010; Norris, 1994; Suriñach et al., 2000, 2005; Weichert et al., 1994; Zhu et al., 2016), precursor of instability (Duranteau et al., 2013; Hu et al., 2018; Schöpa et al., 2018), failure process (Deparis et al., 2008; Dietze et al., 2017), quick locating (Chang et al., 2021; Chen et al., 2013; Dammeier et al., 2015; Esposito et al., 2013; Hibert, Mangeney, et al., 2014; Jolly et al., 2002; Kao et al., 2012; Kuehnert et al., 2021; Yamada et al., 2012), force history (Allstadt, 2013; Ekstrom & Stark, 2013; Hibert, Ekström, & Stark, 2017; Hibert, Mangeney, et al., 2014), volume and velocity (Farin, Mangeney, et al., 2019; Hibert et al., 2011; Le Roy et al., 2019; Marc et al., 2016; Pérez‐Guillén et al., 2016; Yamada et al., 2012), grain interaction (Dammeier et al., 2015; Farin et al., 2018; Farin, Tsai, et al., 2019; Zhang et al., 2021), travel distance (Dammeier et al., 2011; Hibert, Stark, & Ekström, 2014) and other properties (Bottelin et al., 2014; Chang et al., 2021; Chao et al., 2016; Delannay et al., 2017; Farin et al., 2018, Farin, Mangeney, et al., 2019; Farin, Tsai, et al., 2019; Hibert, Ekström, & Stark, 2017, Hibert, Malet, et al., 2017; Vilajosana et al., 2008).…”

“…Despite their small volumes, rockfalls can still be catastrophic and can result in great human and economic losses due to their high frequencies, considerable impact forces, high velocities and unpredictable trajectories (Jaboyedoff et al., 2005, 2012; Rupp & Damm, 2020; Saroglou et al., 2018). Features of continuous seismic signals generated by rockfalls have been proposed as useful quantitative information sources for the real‐time monitoring and study of rockfall dynamics (Allstadt et al., 2018; Bottelin et al., 2014; Feng & Zhuang, 2021; Kuehnert et al., 2021).…”

Acoustic Emissions of Nearly Steady and Uniform Granular Flows: A Proxy for Flow Dynamics and Velocity Fluctuations

“…The high-frequency signal is much more difficult to interpret, due in part to the strong effect of topography and Earth heterogeneity along seismic waves' path from source to receiver (Kuehnert et al, 2020(Kuehnert et al, , 2021. For this reason, mainly empirical relationships have been proposed between high-frequency signals and landslide characteristics (Allstadt et al, 2020;Dammeier et al, 2011;Deparis et al, 2008;Norris, 1994).…”

Review on the Geophysical and UAV-Based Methods Applied to Landslides

“…However, the ambiguities arise in the case where there exist two velocity contrasts and a depth-dependent rise in shear wave velocity; under these conditions, the HVSR curve represents two peaks, and correct peak identification becomes challenging; this multi-peak conundrum has been described elsewhere [23]. Another associated with the interpretation of HVSR results is the influence of geomorphological features as topographic effects such as valleys, hills, basins etc., affect the seismic wave path, polarization and amplitudes [111]. As fluidization leads to change in the solid state, the assumption of a rigid body does not hold, and Newmark's approach doesn't apply in the case of a clayey landslide.…”

“…The force inserted on the ground by the mega landslide was also determined using the force-time inversion approach [108,109]. The landslide event catalog so formed helps in the estimation of the probabilistic occurrence of such an event referred to as landquake (LQ) at a site, as well as an understanding of the triggering mechanism inferred by the correlation of meteorological factors with the so-formed catalogs [110,111].…”