Insights on the Italian Seismic Network from location uncertainties

Abstract

Probabilistic earthquake locations provide confidence intervals for the hypocentre solutions such as errors encountered in the position, the origin time, and in magnitude. If the relationship of the parameters relative to the local arrangement of the seismic network is considered, such as the node distance, the number of stations, the seismic gap, and the quality of phase readings), the uncertainties can then provide insights on the location capability of the network. In this paper, we collect the earthquake data recorded from the Italian Seismic Network for a time span of 5 years. The data pertain to three different catalogues according to the progressive refinement phases of the location procedure: automatic location, revised location, and published location. By means of spatial analysis, we assess the distribution of the location-related and network-related estimators across the study area. These estimators are subsequently combined to assess the existence of spatial correlations at a local scale. The results indicate that the Italian network is generally able to provide robust locations at the national scale and for smaller earthquakes, and the elongated shape of Italy (and of its network) does not cause systematic bias in the locations. However, we highlight the existence of subregions in which the performance of the network is weaker. At present, a unique 2D, 3-layer velocity model is used for the earthquake location procedure, and this could represent the main limitation for the improvement of the locations. Therefore, the assessment of locally optimized velocity models is the priority for the homogenization and the improvement of the Italian Seismic Network performance.

Spatial Relationships Between Coseismic Slip, Aseismic Afterslip, and On‐Fault Aftershock Density in Continental Earthquakes

“…However, analysis of the KOERI catalog is still meaningful following the Izmit earthquake, particularly because the Izmit rupture was so elongate that analysis in the horizontal/along‐strike direction will be less affected. Location uncertainties following the L’Aquila earthquake (INGV catalog) are relatively low (up to a few kilometers), with few default depths assumed (Scudero et al., 2021). Preliminary analysis of seismicity in the approximate space‐time windows of the respective aftershock sequences (within 18 months and within 150 km of the hypocenter following the Izmit earthquake, and within 100 km following the Van and L’Aquila earthquakes) indicates that following the Izmit earthquake M c = 2.7 (by all methods), following the Van earthquake M c = 2.6, 2.5, 2.6 (by different methods, respectively), and following the L’Aquila earthquake: M c = 1.8, 1.9, 2.0 (by different methods, respectively).…”

Urban Seismic Networks: A Worldwide Review

“…This is especially valid for networks designed to detect and locate earthquakes, as the results derive from the combination of observations at several different nodes. For this reason, the geometry plays a critical role in the precision and accuracy of the hypocentre locations as well as in estimation of the the magnitude [171,172]. The relevance of a planned geometry is relatively decreased for networks in which the observations are treated independently on a site-by-site basis (e.g., on-site early warning, assessing site effects, seismic intensity mapping), even though the geometry may affect the later data interpolation or modelling.…”