资源环境科技发展态势分析平台

Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum M-w = 3.69 +/- 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013-2014. The geodetic transient lasted similar to 6 months and produced a NW-SE trending extension of similar to 5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded.

Plain Language Summary Among the open problems in Solid Earth Science the comprehension of earthquakes is one of the most intriguing. In order to understand how earthquakes behave it is of fundamental importance to study the whole spectrum of sizes and magnitudes. Small earthquake study is prevented because of the small deformation signals, usually covered by noise. In this work we present the study of a small seismic swarm activity in the northern Apennines (Italy), and we demonstrate that it produced observable deformation at the surface recorded by a dense geodetic network of continuous GPS. Comparing the total deformation recorded from the geodetic network and the one associated with the seismic events, we are able to determine the relative importance of seismic and aseismic motion for small earthquakes. The results indicate that aseismic deformation is not negligible, and seismic crises like the one documented must be taken into account in order to better evaluate the hazard posed by a fault.