1. Introduction This dataset comprises the relocated earthquake catalog of 7420 earthquakes for the period 2024-01-01 to 2024-04-30 for the Myrtos gulf area north of Kefalonia island, where a swarm-like excitation took place, intensifying during the February - April 2024 period. Phase picking was performed using the Phasenet (Zhu and Beroza, 2019) deep-learning picker and picks were associated using the REAL associator (Zhang et al., 2019). The events were initially located using HYPOINVERSE (Klein, 2002) and relocated using catalog differential times using HypoDD (Waldhauser and Ellsworth, 2000). The seismic velocity model used for the location and relocation procedures is taken from Haslinger et al. (1999). Magnitudes were estimated by applying the relation proposed by Scordilis et al. (2016). 2. Files 2.1 Relocated catalog (catalog_ionio24_swarm.csv, catalog_ionio24_swarm.xlsx and catalog_ionio24_swarm.xml) The dataset consists of the relocated catalog, provided in three different formats (.csv, .xlsx, QuakeML). Arrivals and picks are included within the QuakeML catalog. Field descriptions in the .csv and .xlsx files are as follows: · event_id: Sequential event ID number · latitude: Latitude of relocated epicenter · longitude: Longitude of relocated epicenter · depth: Depth of relocated earthquake · year, month, day, hour, minute, seconds: Temporal origin parameters · magnitude: Earthquake magnitude · magnitude_type: Earthquake magnitude type · RMS: RMS of the travel time residuals of the arrivals used for the origin computation. · ErrH: Horizontal error · ErrZ: Depth error · P_count: Number of defining P phases, i.e., phase observations that were actually used for computing the origin. · S_count: Number of defining P phases, i.e., phase observations that were actually used for computing the origin. · Phases_total: Total number of defining phases The QuakeML catalog follows the modular XML seismological standard schema, extensively described in the QuakeML manuals. 2.2 Phase file (catalog_ionio24_swarm_phases.txt) Standalone phase file used for compiling the relocated catalog in HypoDD format, containing absolute travel time data information for P and S arrivals. File format is described in the HypoDD user guide. 2.3 Stationxml files (Stationxml.tar) Stationxml files used for the preprocessing procedure before phase picking, for the study period.