The Emersito Task Force activities for site effect studies following the 2016 Mw 6.0 Amatrice Earthquake (Italy)

Following the MW 6.0 earthquake occurred on August 24 2016 close to Amatrice (Central Italy), the Emersito task force has been mobilized by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The aim of Emersito is to carry out and coordinate the monitoring of local site effects, caused by geological and geomorphological settings. Usually, these studies are based on background seismicity and can last several months. A seismic sequence, like the one occurred at Amatrice, is a good chance to record strong events in few days with a rapid installation of temporary stations. During the first days after the mainshock, Emersito installed a temporary seismic network at 4 municipalities (Amandola, Civitella del Tronto, Montereale and Capitignano), using 22 stations equipped with both velocimetric and accelerometric sensors. The selection of the sites was mainly driven by the proximity to the epicentral area (20-40 km), without interfering with the rescue operation, and by peculiar geologic and geomorphologic settings. Considering the morphology of the settlements stroke by the earthquake, we focused on the investigation of site effects related to the topography and to the presence of small intra-mountain basin and fault zones. Preliminary analyses performed on ambient noise and aftershocks signals recorded in Amandola and Montereale villages have shown that directional amplification effects may have occurred at stations installed on the top of topographic irregularities. We also observed the lengthening and amplification of the seismograms and a variability of the peaked frequency across the sedimentary basin between Montereale and Capitignano villages, probably related to a different thickness of the deposits. Finally, we have investigated amplification at 4 stations installed close to an active normal fault in Capitignano village. Further analyses are necessary to assess the correlation with surface geology.