Seismic Monitoring of an Underground Natural Gas Storage Facility: The Collalto Seismic Network

Online Material: Seismic‐hazard map, figures of event location and waveforms, phase reading distribution, and background seismic noise; and tables of event parameters, 1D regional model, and earthquake catalog. The Collalto Seismic Network (Rete Sismica di Collalto, or RSC) is the infrastructure used to monitor the natural and induced seismicity of the natural gas storage concession known as Collalto Stoccaggio, which is located in northeastern Italy. This network was realized and is currently managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), a public research institute, on behalf of Edison Stoccaggio S.p.A., the storage concession holder. The storage exploits a depleted natural gas reservoir that was converted into a seasonal reservoir in the 1990s. The reservoir is a geologic trap, with porous and permeable rock layers, a few meters thick, sealed by impermeable formations. The production levels are located at 1500–1600 m depth (Picotti, 2007) and extend approximately over a 10  km×4  km wide area (Fig. 1). The gas storage activity affects four municipalities, all of which are located in the province of Treviso: Susegana, Nervesa della Battaglia, S. Pietro di Feletto, and Conegliano. Figure 1. Location of the study area, including the Collalto Seismic Network (RSC). Seismometric stations are indicated by triangles; the 10 RSC stations by white triangles (labels start with ED; all are located within area A); and the stations of the Northeastern Italy Integrated Seismic Network (NEI) by black triangles, respectively. All the stations indicated are managed by the OGS. The two rectangles bordered by thin lines indicate the two target areas, A and B. The irregular area bordered by a thick black line within area A corresponds to the surface projection of the gas storage reservoir. The fault lines indicate the active faults known for the study area according to Poli et al. (2008). Insets (a) and (b) …