Offshore Fault Geometry Revealed from Earthquake Locations Using New State-of-Art Techniques: The Case of the 2022 Adriatic Sea Earthquake Sequence

Abstract

Abstract Precise hypocenter locations are critical for properly interpreting earthquake occurrence processes. However, when the coverage with seismic stations is unfavorable or sparse, locating precisely earthquake hypocenters, in particular their depth, is challenging. Here we apply a newly developed approach, which uses only two land stations, to the recently occurred 2022 Adriatic Sea offshore earthquake sequence (mainshock of magnitude Mw 5.5) and achieve location results that are comparable to the catalog locations obtained using dozens of stations. First, six events with magnitudes M ≥3.0 were relocated using a travel-time stacking method. Next, using these six earthquakes as reference events, we applied a two-station differential travel-time method to reconstruct the earthquake cluster geometry and locate the remaining events, including the mainshock. The obtained earthquake distribution shows a dipping direction that varies from south to southwest, depending on the choice of the input parameters. Our preferred result shows a cluster dipping at an angle of ∼30° toward the south-southwest. This solution was chosen because the depth of the mainshock hypocenter obtained using the differential-time procedure agrees well with the depth constrained using depth phases. Moreover, the relatively sharp earthquake cluster geometry is in general consistent with the thrust fault structures revealed by a local seismic reflection survey and focal mechanism solutions.