资源环境科技发展态势分析平台

Passing seismic waves released by large-magnitude earthquakes may affect geological systems located thousands of miles far from the epicenter. The M9.0 Tohoku earthquake struck on 11 March 2011 in Japan. We detected local seismic activity at the Larderello-Travale geothermal field, Italy, coinciding with the maximum amplitudes of the Rayleigh waves generated by the Tohoku earthquake. We suggest that the earthquakes were triggered by passing Rayleigh waves that induced locally a maximum vertical displacement of approximately 7.5mm (for waves with period of 100s). The estimated dynamic stress was about 8kPa for a measured peak ground velocity of 0.8mm/s. Previous similar observations pointed out local seismicity at the Larderello-Travale Geothermal Field triggered by the 2012 M(w)5.9 Po Plain earthquake. We conducted forward numerical modeling to investigate the effects caused by passing P, S, Love, and Rayleigh waves through the known velocity structure of the geothermal field. Results indicate that maximum displacements focus differently when considering body or surface waves, with displacement values being higher within the first 2km of depth. The focusing of the displacement below 3km seems to be strongly controlled by the velocity structure of the Larderello-Travale geothermal field. We propose that seismic activity triggered by passing seismic waves may be related to a clock-advancing mechanism for local seismic events that may have occurred in any case. Furthermore, our analysis shows that local anisotropies in the velocity structure of the Larderello-Travale geothermal field (possibly linked to compartments of elevated pore pressures) strongly control the reactivation of regions of the geothermal field affected by passing seismic waves.