Monitoring Seismotectonic Activity in the Surroundings of the Vuache Fault
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Monitoring seismotectonic activity in the surroundings of the Vuache fault Dr. N. Houlié 1 and Dr. J. Fréchet 2 1 Nicolas Houlie Geologie GmbH, Zurich, CH 2 JFrechet Consulting, Grenoble, FR Introduction The new CERN measurement facility will be more accurate than ever. Like all high-precision instrument, it will be more sensitive to its environment than its predecessor and a wider range of signals resulting from natural or human-driven processes should be considered as noise sources. For instance, the next generation of instruments deployed by CERN will be the first to be disturbed by external processes such as Swiss tectonics and the first effect of climate change on the hydrogeology systems. Fortunately, small amplitudes disturbances of various frequencies have been documented from a wide range of past activities such as seismology, geodesy and space programs. Even though processes are well known by CERN teams, external expertise will be required to characterize the external noise contribution from outside the CERN facilities in both a local and a regional context. Noise contributors New noise contributors are diverse in terms of amplitudes and of durations and periodicity: • Seismic activity (natural or in response to CERN activities or to the geothermal development) • Meteorological effect (troposphere, drying and recharge of natural water reservoirs) • Anthropic activities (trains, planes landing, roadwork, excavations, etc.) • Long-term tectonics (lithosphere deformation, long-term response to earthquakes) • Landslides We show in Figure 1 the variability of the disturbances parameters (Psimoulis et al. 2018). Figure 1: Amplitude versus duration diagram for various geological catastrophic processes. We show detection limits for GPS, dynamic GPS and microgravimetry. In this study, as in any real- time algorithm, we focus on detecting small amplitudes as fast as possible. dynGPS curves are from analyses of dynamic GPS time-series recorded during seismic wave propagations. Static GPS is able to detect motion larger than 1 cm for duration larger than 104 s. From Psimoulis, Houlié et al., GJI, 2019. Proposed work We propose an appropriate monitoring of the Vuache fault which is to our knowledge the best candidate for the generation of seismic and aseismic activity in the area. This monitoring will include: 1. Review of the historical and instrumental seismicity (moment tensors, first motion focal mechanisms, and microseismicity) 2. Installation of supplementary seismic stations (short-period velocity sensors). 3. Characterization of the seismic activity in the area of the Vuache. 4. Characterization of the local surface deformation (triangulation, grids, etc.) using GPS and InSAR. Re-processing of the strain rate field 5. Identification of the most active seismic segments in the area. Beyond the permitting of the stations, there is no bottleneck in this proposal. Drs. Fréchet and Houlié are very experienced in field deployment in France (and abroad), in data processing and reporting. Figure 2: Map of provisory envisaged seismic (red triangles) and GPS networks (blue squares). Existing seismic and GPS are shown using grey symbols. Planning (Gantt chart) The first priority of the project will be to deploy the seismic and the geodetic networks (Figure 2). The exact location of stations will be reevaluated during implementation of the network. From the data gathered various analyses will be carried following approaches previously published in peer-reviewed publications (Fréchet et al., 1989; Houlié et al., 2018; Psimoulis et al., 2018). Reporting will be delivered on a yearly basis and bibliography continuously searched. Y1 Y2 Y3 Y4 Y5 Bibliography Continuous Networks deployment Seismic activity monitoring Surface deformation Most active segment Reporting Deliverables • To Be Defined with CERN (seismicity catalogue, surface vector field, etc.) Bibliography N. Houlié: Houlié, N., Woessner, J., Giardini, D., Rothacher, M., 2018. Lithosphere strain rate and stress field orientations near the Alpine arc in Switzerland. Sci. Rep. Psimoulis, P., Houlié, N., Habboub, M., Michel, C., Rothacher, M., 2018. Detection of ground motions using high-rate GPS time-series. Geoph. J. Int. 214, 1237-1251. J. Fréchet: Poupinet, G., Ellsworth, W. L., Fréchet, J., 1984. Monitoring velocity variations in the crust using earthquake doublets: an application to the Calaveras fault, California. J. Geophys. Res., 89, 7, 5719-5731. Fréchet, J., Martel, L., Nikolla, L., Poupinet, G., 1989. Application of the cross-spectral moving- window technique (CSMWT) to the seismic monitoring of forced fluid migration in a rock mass. Int. J. 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