GNGTS 2018 - 37° Convegno Nazionale

708 GNGTS 2018 S essione 3.2 selective filters is absolutely necessary to detect the events since high frequency noise (above 100Hz), and in some instances harmonic noise, strongly disturb the records. Since there is no velocity model available for the studied rock cliff, the event location exercise was carried out using a constant velocity model. Although the grid spacing affects the accuracy of location, the result is still satisfactory and the error is limited to one grid spacing. However, the results cannot be considered as a prediction of the expected accuracy since the position of the source was very close to one of the geophones, but, to some extent, the test shows that the location algorithm is robust. The research is still in progress and a triggering test with a modified seismic gun is planned in the near future to take a final decision on the source to be used for the tomographic survey. During tomographic survey, 24 to 48 additional 1C geophones will be deployed on the top of the rock cliff and the source point will be moved to several different positions to explore the unstable rock mass from different directions in order to constrain as much as possible the reconstruction of the 3D velocity model. References Colombero C.; 2017: Microseismic strategies for characterization and monitoring of an unstable rock mass , PhD Thesis. Hardy Jr, Reginald H.; 2005: Acoustic emission/microseismic activity: volume 1: principles, techniques and geotechnical applications . Vol. 1. CRC Press. Helmstetter A., and Garambois S.; 2010: Seismic monitoring of Séchilienne rockslide (French Alps): Analysis of seismic signals and their correlation with rainfalls , J. Geophys. Res. Earth Surf., 115(F3), F03016. Lomax A., Virieux J., Volant P. and Berge C.; 2000: Probabilistic earthquake location in 3D and layered models: Introduction of a Metropolis-Gibbs method and comparison with linear locations, in Advances in Seismic Event Location , edited by C. H. Thurber and N. Rabinowitz, Kluwer, Amsterdam, 101-134. Lomax A. and Curtis A.; 2001: Fast, probabilistic earthquake location in 3D models using oct-tree importance sampling . Geophys Res Abstr 3:955. Lomax A., Michelini A., Curtis A.; 2009: Earthquake Location, Direct, Global-Search Methods, in Complexity In Encyclopedia of Complexity and System Science , Part 5, Springer, New York, 2449-2473, doi:10.1007/978-0- 387-30440-3. Spillmann T., Maurer H., Green A. G., Heincke B., Willenberg H. and Husen S.; 2007: Microseismic investigation of an unstable mountain slope in the Swiss Alps , J. Geophys. Res., 112(B7), B07301.