Seismic characterization of a clay-block rupture in Harmalière landslide, French Western Alps

B Vial,D Jongmans,G Bièvre,G Chambon,L Baillet,S Fiolleau

doi:10.1093/gji/ggaa050

Abstract

SUMMARYIn late June 2016, the Harmalière clayey landslide (located 30 km south of the city of Grenoble, French Alps) was dramatically reactivated at the headscarp after a 35-yr-long period of continuous but limited activity. The total involved volume, which moved as sliding blocks of various sizes, was estimated to be about 2 × 10 6 m3. Two seismometers were installed at the rear of the main headscarp in August 2016, on both sides of a developing fracture delineating a block with a volume of a few hundred cubic metres. For 4 months, they continuously recorded seismic ambient vibrations and microearthquakes until the block broke. Five seismic parameters were derived from the monitoring: the cumulative number of microearthquakes (CNe), the seismic energy (SE), the block resonance frequency (fB), the relative variation in Rayleigh wave velocity (dV/V) deduced from noise cross-correlations between the two sensors and the associated correlation coefficient (CC). All parameters showed a significant precursory signal before the rupture, but at very different times, which indicates the complexity of the rupture mechanism in this clay material.

Highlights

Numerous regions of the world are exposed to landslides in clay deposits, which pose problems for land management and population safety (Panizza et al 1996; Guzzetti 2000; Picarelli et al 2005; Hungr et al 2014)
The objective of this paper is to evaluate the relevance of five seismic parameters as predictors before the slip of a block that occurred at the head of a major landslide (Harmaliere slide in the French Alps)
The cumulative number of events cumulative number of microearthquakes (CNe) at HAR0, the cumulative seismic energy SE at HAR0 and HAR1, and the cumulative rainfall and temperature evolutions are presented in Figs 3(a)–(c), respectively

Summary

Introduction

Numerous regions of the world are exposed to landslides in clay deposits, which pose problems for land management and population safety (Panizza et al 1996; Guzzetti 2000; Picarelli et al 2005; Hungr et al 2014). Pre-failure slope deformation usually generates numerous microruptures within the landslide body, which emit seismic signals called slide-quakes (Amitrano et al 2005), slopequakes (Provost et al 2018) or microearthquakes (Spillmann et al 2007; Levy et al 2011). Amitrano et al (2005) monitored microearthquakes before the collapse of a 2000 m3 chalk cliff, using a sensor located 5 m from the rupture plane They showed that the seismic energy increased significantly 2 hr before the failure. Cases of increased induced seismicity before rupture have been largely referenced in rocks (Amitrano et al 2005; Senfaute et al 2009; Levy et al 2011; Tonnellier et al 2013)

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Discussion

Conclusion