ALBERT

Description: We investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity (PGV) from moderate to large earthquakes occurring in the southern Apennines (Italy). Simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the PGV, following an evolutionary, probabilistic approach. The system performance is measured through the Effective Lead-Time (ELT), i.e., the time interval between the arrival of the first S-wave and the time at which the probability to observe the true PGV value within one standard deviation becomes stationary, and the Probability of Prediction Error (PPE), which provides a measure of PGV prediction error. The regional maps of ELT and PPE show a significant variability around the fault up to large distances, thus indicating that the system's capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault.

Description: We present the results from a temporary seismic network of 24 stations installed in the urban area of Rome (Italy) from January 10, 2021 until April 08, 2021, with the aim of studying the city's urban subsoil through analysis based on ambient seismic noise. Rome is the largest Italian city (with about three million people) with a history of art, architecture and culture that influenced the world and dating back almost 3000 years ago. The city retains a monumental heritage characterized by a high fragility due to its age. Both the high number of inhabitants and the fragility of its monuments make the city particularly vulnerable to possible earthquakes, even if the seismic hazard of the area is considered as moderate. The continuous recordings from the network allowed the use of ambient seismic noise to derive spectral ratios at sites located in different geological and lithological contexts. Moreover, signals from regional earthquakes were surprisingly well recorded despite the high anthropic noise-level, showing a clear areal variability referable to site effects. In this case, we also benefit from a low-noise period due to the partial lockdown for COVID pandemia. Interferometric analyses based on seismic noise cross-correlation of acquired data, show that it is possible to reconstruct the surface waves at station pairs in the frequency band between 0.2 and 1 Hz. It is then possible to perform a 3D velocity model through Ambient Noise Tomography to characterize shapes, thickness and properties of different geological/lithological units of the subsoil of the city.

Description: We present the activities of EMERSITO, the INGV emergency task force with skills and experience in seismic response studies and in seismic microzonation, in the follow-up to the Mw 5.5 (ML 5.7) earthquake of November 9, 2022 06:07:25 UTC localized in the Costa Marchigiana Pesarese area (Central Italy). Based on geological information and damage estimates in the epicentral areas, EMERSITO focused its intervention in Ancona, the capital of Regione Marche, located at about 40 km south of the epicenter. This city is located in an area characterized by a remarkable seismic hazard, as evidenced by the extensive damage of the 1972 earthquakes (Mw up to 4.7), with part of the urban territory susceptible to landslide phenomena. A temporary seismic network consisting of 11 seismic stations equipped with velocimeter and accelerometer was installed in different urban areas of the city, acquiring data in continuous mode for about 4 months. The analysis of ambient vibrations and aftershock recordings collected by the network suggests a variability of the site response depending on the outcropping lithologies. The peak frequencies from spectral ratio analysis range between 1 and 3 Hz for 6 stations, while other stations are characterized by peak frequencies between 3.5 and 9.5 Hz. The H/V noise spectral ratios do not show peaks with very high amplitudes (〈 3), likely indicating the lack of strong impedance contrasts, at least in the shallow part of the subsoil.