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In this paper we evaluate the local seismic response for thirteen sites located in the municipalities of Arquata del Tronto and Montegallo, two areas which suffered heavy damage during the Mw 6.0 and Mw 5.4 earthquakes which struck Central Italy on August 24, 2016. The input dataset is made by ground motion recordings of 348 events occurred during the sequence. The spectral site response is estimated by the Generalized Inversion Technique and makes use of reference sites. The interpretation is further improved through the information provided by a reference-site independent method (i.e., the so called Receiver-Function Technique) and by the Horizontal-to-Vertical Spectral Ratios of ambient noise recordings. We also provide an independent estimate of the local amplification by comparing the Peak Ground Velocity and the Spectral Amplitudes observed at each site to the value estimated by well-established Ground Motion Prediction Equations for a rock-class site. The results obtained by the adopted methodologies are all highly consistent, and they emphasize the different seismic behavior of several sites at local scale. Thus, sites located on Quaternary deposits overlying the bedrock, such as Castro, Pretare, Spelonga, Pescara del Tronto, and Capodacqua feature some relevant amplifications in a medium (2-10 Hz) frequency range; two sites at Spelonga show amplifications also at low frequencies; three sites located on stiff formations, i.e. Uscerno, Balzo and Colle d'Arquata, respectively, feature either nearly neutral response or low amplification level. A probable topographic effect was identified at the rock site of Rocca di Arquata (MZ80).

In this article, we describe the infrastructure developed and managed by the Italian National Institute of Oceanography and Applied Geophysics – OGS for the seismological and geodetic monitoring of northeastern Italy. The infrastructure was constituted in response to the ML 6.4 Friuli destructive earthquake of 1976, with the main mandate of supporting civil protection emergency activities. The OGS monitoring infrastructure is presently composed of a seismometric and a strong-motion network, complemented by a number of Global Navigation Satellite Systems stations, each delivering observational data in real time, which are collected and processed by the headquarters of the Center for Seismological Research of OGS in Udine. The OGS networks operate in close cooperation with Italian and international networks from neighboring countries, within the framework of the agreements for real-time data exchange, to obtain improved rapid earthquake location and magnitude estimations. Information regarding seismic events is released to the public through a dedicated web portal and, since 2013, through social media. Aside from the standard monitoring activities (>30,000 events have been recorded since 1976), the OGS has progressively increased the number of services to the public and to the Civil Protection of the Friuli Venezia Giulia and Veneto regions. The high availability of good quality data has resulted in the enhancement of scientific products, including advanced seismological studies of the area, spanning broadly from seismic source characterization to engineering seismology. In the future, the OGS networks are expected to further contribute to the development of seismological research and monitoring infrastructures of the Central European region.

Abstract. Thanks to the installation of a temporary seismic network, a microseismicity study has been conducted in the Sulmona area (Abruzzo, Italy) with the aim of increasing the knowledge of seismogenic potential of existing active faults. In this work the first seven months (from 27 May to 31 December 2009) of recorded data have been analysed, over a total period of acquisition of about 30 months. Using a semi-automatic procedure, more than 800 local earthquakes has been detected, which highlight the background seismicity previously unknown. About 70% of these events have been relocated using a 1-D velocity model estimated specifically for the Sulmona area. Phase readings quality is checked and discussed, with respect to weighting schemes used by location algorithms, too. The integration of temporary network data with all the other data available in the region enable us to obtain a statistically more robust dataset of earthquake locations. Both the final hypocentral solutions and phase pickings are released as online Supplement. Local magnitude values of the newly detected events ranges between −1.5 and 3.7 and the completeness magnitude for the Sulmona area during the study period is about 1.1. Duration magnitude coefficients have been estimated as well, for comparison/integration purposes. Local Gutenberg–Richter relationship, estimated from the microseismic data, features low b value, possibly suggesting that the Sulmona area is currently undergoing high stress, in agreement with other recent studies. The time-space distribution of the seismic activity with respect to the known active faults, as well the seismogenic layer thickness, are preliminarily investigated.