Abstract
Abstract. Soil and debris slides are prone to rapid and dramatic reactivation. Deformation within the instability is accommodated by sliding, whereby weak seismic energies are released through material deformation. Thus, passive microseismic monitoring provides information that relates to the slope dynamics. In this study, passive microseismic data acquired at Super-Sauze (southeastern France) and Pechgraben (Upper Austria) slow-moving clay-rich debris slides (“clayey landslides”) are investigated. Observations are benchmarked against previous similar case studies to provide a comprehensive and homogenized typology of microseismic signals at clayey landslides. A thorough knowledge of the various microseismic signals generated by slope deformation is crucial for the future development of automatic detection systems to be implemented in landslide early-warning systems. Detected signals range from short-duration (< 2 s) quake-like signals to a wide variety of longer-duration tremor-like radiations (> 2 s – several min). The complexity of seismic velocity structures, the low quantity and low quality of available signal onsets and non-optimal seismic network geometry severely impedes the source location procedure; thus, rendering source processes characterization challenging. Therefore, we constrain sources' locations using the prominent waveform amplitude attenuation pattern characteristic of near-source area (< about 50 m) landslide-induced microseismic events. A local magnitude scale for clayey landslides (ML−LS) is empirically calibrated using calibration shots and hammer blow data. The derived ML−LS returns daily landslide-induced microseismicity rates that positively correlate with higher average daily displacement rates. However, high temporal and spatial resolution analyses of the landslide dynamics and hydrology are required to better decipher the potential relations linking landslide-induced microseismic signals to landslide deformation.
Highlights
Slow-moving soil and debris slides developed in tectonized marl formations are characterized by seasonal dynamics as well as by sudden reactivation and liquefaction phases (Malet et al, 2005; Hungr et al, 2014)
This study aims at proposing a classification of microseismic signal types as recorded by tripartite microseismic arrays deployed at slow-moving clay-rich debris slides (“clayey landslides”)
Based on the literature and searching for consistent observations at Sauze 2010 (SZ10), Pechgraben 2015 (PG15) and Pechgraben 2016 (PG16) we propose a typology of tremor events, where landslide-induced tremor-like signals are distinguished from external sources of tremor-like radiations
Summary
Slow-moving soil and debris slides developed in tectonized marl formations are characterized by seasonal dynamics as well as by sudden (generally rainfall triggered) reactivation and liquefaction phases (Malet et al, 2005; Hungr et al, 2014). The slow deformation of soil and debris slides is expected to generate elastic accumulation and rupture, which releases seismic energy within the landslide body. Passive seismic monitoring is a good approach to monitor and mitigate slope instabilities, as it provides high temporal resolution data (sample rates up to 1000 Hz) in near realtime that relate to the dynamics of the landslide. This means that the transition (and rapid transformation) of the landslide from steady-state sliding into a debris flow may be detected and slope failure anticipated. Examples of case studies carried out at rockslides include, but are not limited to, the following: the Randa rockslide in the Swiss Alps (Eberhardt et al, 2004; Spillmann et al, 2007); the Åknes rockslide in Norway (Roth et al, 2005; Fischer et al, 2014); the Séchilienne rockslide in the southeastern French Alps (Helmstetter and Garambois, 2010; Lacroix and Helmstetter, 2011); and the Gradenbach, Hochmais-Atemskopf and NiedergallmiggMatekopf deep-seated rock slope deformations in the eastern Austrian Alps (Brückl and Mertl, 2006; Mertl and Brückl, 2007; Brückl et al, 2013)
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