The Near Fault Observatory community in Europe: a new resource for faulting and hazard studies

Abstract

The Near Fault Observatories (NFOs) community is one of the European Plate Observing System (EPOS, http://www.epos-eu.org) Thematic Communities, today consisting of six research infrastructures that operate in regions characterised by high seismic hazard originating from different tectonic regimes. Earthquakes respond to complex natural systems whose mechanical properties evolve over time. Thus, in order to understand the multi-scale, physical/chemical processes responsible for the faulting that earthquakes occur on, it is required to consider phenomena that intersect different research fields, i.e., to put in place multidisciplinary monitoring. Hence, NFOs are grounded on modern and multidisciplinary infrastructures, collecting near fault high resolution raw data that allows generation of innovative scientific products. The NFOs usually complement regional backbone networks with a higher density distribution of seismic, geodetic, geochemical and other geophysical sensors, at surface and sometimes below grade. These dense and modern networks of multi-parametric sensors are sited at and around active faults, where moderate to large earthquakes have occurred in the past and are expected in the future. They continuously monitor the underlying Earth instability processes over a broad time interval. Data collected at each NFO results in an exceptionally high degree of knowledge of the geometry and parameters characterizing the local geological faults and their deformation pattern. The novel data produced by the NFO community is aggregated in EPOS and is made available to a diverse set of stakeholders through the NFO Federated Specific Data Gateway (FRIDGE). In the broader domain of the Solid Earth sciences, NFOs meet the growing expectations of the learning and communication sectors by hosting a large variety of scientific information about earthquakes as a natural phenomenon and a societal issue. It represents the EPOS concept and objective of aggregating and harmonising the European research infrastructures capabilities to facilitate broader scientific opportunity. The NFOs are at the cutting edge of network monitoring. They conduct multidisciplinary experiments for testing multi-sensor stations, as well as realise robust and ultra-low latency, transmission systems that can routinely accommodate temporary monitoring densification. The effort to continuously upgrade the technological efficiency of monitoring systems positions the NFO at the centre of marketing opportunities for the European enterprises devoted to new sensor technology. The NFOs constitute ideal test beds for generating expertise on data integration, creating tools for the next generation of multidisciplinary research, routine data analysis and data visualization. In particular focus is often on near-real time tools and triggering alarms at different levels are tested and implemented, strengthening the cooperation with the Agencies for risk management. NFOs have developed innovative operational actions such as the Testing Centre for Earthquake Early Warning and Source Characterisation (CREW) and detailed fast ground shaking and damage characterization. Complementing the recent growth of modern laboratory and computational models, the NFOs can provide interdisciplinary observations of comparable high resolution to describe the behaviour of fault slip over a vast range of spatial and temporal scales and aiding to provide more accurate earthquake hazard characterizations.

Microseismicity Monitoring and Site Characterization With Distributed Acoustic Sensing (DAS): The Case of the Irpinia Fault System (Southern Italy)

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Recent developments of Near Fault Observatories in Europe are focused on dense observation systems to investigate the physical processes occurring along the faults, to track fluid migrations and to discover forcing mechanisms that may evolve into the nucleation of large earthquakes (Chiaraluce et al, 2022). To improve the detection of very small events on faults, seismic regional networks are now complemented with arrays of sensors (e.g., Ben-Zion et al, 2015) sometimes completed by temporary arrays to reveal peculiar features of the fault system (e.g., Bindi et al, 2021).

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Sensing Optical Fibers for Earthquake Source Characterization Using Raw DAS Records

“…The site of the installation was near the emergence of the main segment of the normal fault system that generated the devastating 1980 M 6.9 Irpinia earthquake in the Southern Apennines. The area is nowadays monitored by the INFO (Chiaraluce et al., 2022), that detected several dozens of events during the deployment period.…”

Non-linear elasticity, earthquake triggerring and seasonal hydrological forcing along the Irpinia fault, Southern Italy

“…IFS is monitored since 2007 by the Irpinia Near Fault Observatory (INFO), which includes the Irpinia Seismic Network (ISNet, http://isnet.unina.it, network code IX ; 34 ), composed of a total of 31 co-located tri-axial strong motion accelerometers and three-components short period or broad-band seismometers and 8 INGV seismic stations (https://eida.ingv.it/it/, virtual network _NFOIRPINA, network code IV). The period analyzed in the present study ranges from January 2008 through December 2021.…”

“…In this study we perform a long-term (14 years) pump-probe experiment to assess the nonlinear behavior of the seismogenic volume in the Irpinia Fault Zone (IFZ, Figure 1), which hosted the largest (Ms 6.9) instrumentally recorded earthquake in Italy 33 . The high-quality and spatially dense nature of the IFZ geophysical observational infrastructures (seismological and geodetic networks) has been acknowledged as an EPOS Near-Fault-Observatory 34 . Here we measured δv/v induced by annual strain variations originating from recharging groundwater in karst aquifers 35,36 , that significantly extends the temporal tidal forcing employed in previous works 17,30 .…”