Regions of slow strain often produce swarm-like sequences,characterized by the lack of a clear mainshockaftershock pattern.The comprehension of their underlying physical mechanisms is challenging and still debated.We ...Regions of slow strain often produce swarm-like sequences,characterized by the lack of a clear mainshockaftershock pattern.The comprehension of their underlying physical mechanisms is challenging and still debated.We used seismic recordings from the last Pollino swarm(2010-2014) and nearby to separate and map seismic scattering(from P peak-delays) and absorption(from late-time coda-wave attenuation) at different frequencies in the Pollino range and surroundings.High-scattering and high-absorption anomalies are markers of a fluid-filled fracture volume extending from SE to NW(1.5-6 Hz) across the range.With increasing frequency,these anomalies approximately cover the area where the strongest earthquakes occurred from the sixteenth century until 1998.In our interpretation,the NW fracture propagation ends where carbonates of the Lucanian Apennines begin,as marked by a high-scattering and low-absorption area.At the highest frequency(12 Hz) the anomalies widen southward in the middle of the range,consistently marking the faults active during the recent Pollino swarm.Our results suggest that fracture healing has closed small-scale fractures across the SE faults that were active in the past centuries,and that the propagation of fluids may have played a crucial role in triggering the 2010-2014 Pollino swarm.Assuming that the fluid propagation ended at the carbonates barrier in the NW direction,fractures opened new paths to the South,favoring the nucleation of the last Pollino swarm.Indeed,the recently active faults in the middle of the seismogenic volume are marked by a high-scattering and highabsorption footprints.Our work provides evidence that attenuation parameters may track shape and dynamics of fluid-filled fracture networks in fault areas.展开更多
Seismic data of earthquakes recorded during the last 40 years in southern Calabria have been compared with geological data in order to obtain a seismotectonic picture of the area. We sought for any possible correlatio...Seismic data of earthquakes recorded during the last 40 years in southern Calabria have been compared with geological data in order to obtain a seismotectonic picture of the area. We sought for any possible correlation between the main regional tectonic structures, the distribution of earthquake hypocentres and the focal mechanism of earthquakes with magnitude(Ml)≥3.Studies of historical and recent seismicity and analysis of geological structures allowed to define the main shear strips on a regional scale. More than 2600 earthquakes with 1.5 ≤ Ml ≤ 4.5 have been considered. The focal mechanisms of earthquakes with Ml≥3 have been compared with the kinematics of known faults and used to give insight on the current active stress field. From the analysis carried out it was possible to expand the cognitive framework regarding the activity of the main tectonic structures present in the area. This study also served to identify areas of high seismicity which do not correspond to any evidence of tectonic structures on the surface, and areas where recognized tectonic structures have not shown any seismicity during the last decades. These cases could be the subject of future investigation in order to correctly assess the seismic hazard in Calabria.This task is important in the context of seismic hazard evaluation and mitigation.展开更多
文摘Regions of slow strain often produce swarm-like sequences,characterized by the lack of a clear mainshockaftershock pattern.The comprehension of their underlying physical mechanisms is challenging and still debated.We used seismic recordings from the last Pollino swarm(2010-2014) and nearby to separate and map seismic scattering(from P peak-delays) and absorption(from late-time coda-wave attenuation) at different frequencies in the Pollino range and surroundings.High-scattering and high-absorption anomalies are markers of a fluid-filled fracture volume extending from SE to NW(1.5-6 Hz) across the range.With increasing frequency,these anomalies approximately cover the area where the strongest earthquakes occurred from the sixteenth century until 1998.In our interpretation,the NW fracture propagation ends where carbonates of the Lucanian Apennines begin,as marked by a high-scattering and low-absorption area.At the highest frequency(12 Hz) the anomalies widen southward in the middle of the range,consistently marking the faults active during the recent Pollino swarm.Our results suggest that fracture healing has closed small-scale fractures across the SE faults that were active in the past centuries,and that the propagation of fluids may have played a crucial role in triggering the 2010-2014 Pollino swarm.Assuming that the fluid propagation ended at the carbonates barrier in the NW direction,fractures opened new paths to the South,favoring the nucleation of the last Pollino swarm.Indeed,the recently active faults in the middle of the seismogenic volume are marked by a high-scattering and highabsorption footprints.Our work provides evidence that attenuation parameters may track shape and dynamics of fluid-filled fracture networks in fault areas.
文摘Seismic data of earthquakes recorded during the last 40 years in southern Calabria have been compared with geological data in order to obtain a seismotectonic picture of the area. We sought for any possible correlation between the main regional tectonic structures, the distribution of earthquake hypocentres and the focal mechanism of earthquakes with magnitude(Ml)≥3.Studies of historical and recent seismicity and analysis of geological structures allowed to define the main shear strips on a regional scale. More than 2600 earthquakes with 1.5 ≤ Ml ≤ 4.5 have been considered. The focal mechanisms of earthquakes with Ml≥3 have been compared with the kinematics of known faults and used to give insight on the current active stress field. From the analysis carried out it was possible to expand the cognitive framework regarding the activity of the main tectonic structures present in the area. This study also served to identify areas of high seismicity which do not correspond to any evidence of tectonic structures on the surface, and areas where recognized tectonic structures have not shown any seismicity during the last decades. These cases could be the subject of future investigation in order to correctly assess the seismic hazard in Calabria.This task is important in the context of seismic hazard evaluation and mitigation.
