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.

Recent moderate-sized earthquakes (ML≤5.2) that occurred in northern Italy demonstrate that the currently available ground-motion prediction equations (GMPEs) largely underestimate shaking in the Po Plain region at hypocentral distances greater than 70 km. In order to investigate this phenomenon, we collected a set of peak ground acceleration (PGA) observations for weak and moderate earthquakes in the area. Nonparametric regression analysis of PGA observations as a function of magnitude and hypocentral distance shows that PGA is systematically enhanced for distances between 70 and 200 km. An indirect estimation through the analysis of the attenuation of macroseismic intensities suggests that the effect also applies to strong earthquakes (ML>5.5). We performed numerical modeling experiments to investigate the cause of the phenomenon. The characteristics of the computed synthetic seismograms indicate that the enhancement of ground motion is mainly an effect of the reflection of S waves at the Moho (SmS phase). The analysis of both real and synthetic data shows that the Moho reflection effect is maximized at hypocentral distances between 90 and 150 km, where the PGA increases by a factor larger than 2.4

Northeastern Italy (NEI), bordering Slovenia and Austria, consists of the Friuli-Venezia Giulia, Veneto, and Trentino-Alto Adige regions. The area includes the Italian part of the southeastern Alps to the north, and the Veneto and Friuli Plains to the south. Together with its neighboring regions of southern Austria and western Slovenia, this is possibly the most tectonically active area of the Alpine Arc in the present age.

Fluctuations in groundwater content may produce surface deformation and affect the elastic properties of the Earth’s crust. In this study, we evaluate the temporal variations of the Earth’s crust elastic properties (in the form of relative seismic‐velocity variations) in a tectonically active region in Northern Italy characterized by the presence of karst systems. In this area, GPS measurements already revealed hydrologically‐induced deformation, modulated by changes in groundwater storage. We study the relation of our seismological observations with the geodetic and hydrological results and identify the effects of groundwater‐content variations in the seismic‐velocity perturbations. Our results show that hydrologically‐induced changes in karstic media produce significant seismic‐velocity perturbations, therefore its role in tectonic‐stress adjustment studies must not be ignored. Depth sensitivity analysis of our results constrain the crustal perturbations to range between 500 and 3,500 m depth. Results from scattering imaging locate the crustal perturbations along the main local karst systems.