Detection of ground motions using high-rate GPS time-series

Abstract

Monitoring surface deformation in real-time helps at planning and protecting infrastructures and populations, manages sensitive production (i.e. SEVESO-type) and mitigates long-term consequences of modifications implemented.We present RT-SHAKE, an algorithm developed to detect ground motions associated with landslides, subsurface collapses, subsidences, earthquakes or rock falls. RT-SHAKE detects first transient changes in individual GPS time-series before investigating for spatial correlation(s) of observations made at neighbouring GPS sites and eventually issues a motion warning. In order to assess our algorithm on fast (seconds to minute), large (from 1 cm to metres) and spatially consistent surface motions, we use the 1 Hz GEONET GNSS network data of the Tohoku-Oki Mwv 9.0 2011 as a test scenario.We show that the delay of detection of seismic wave arrival by GPS records is of ~10 s with respect to an identical analysis based on strong-motion data and this time delay depends on the level of the time-variable noise. Nevertheless, based on the analysis of the GPS network noise level and ground motion stochastic model, we show that RT-SHAKE can narrow the range of earthquake magnitude, by setting a lower threshold of detected earthquakes to Mw6.5-7, if associated with a real-time automatic earthquake location system.