1. Introduction

This dataset comprises an ML-derived relocated earthquake catalog of 34653 earthquakes covering the period 2025-01-01 to 2025-02-28, during which the Santorini-Amorgos seismovolcanic area seismic crisis occured. Phase picking was performed using Phasenet (Zhu and Beroza, 2019) a machine learning, deep-neural-network-based arrival-time picker, setting the probability threshold for both P and S picking at 0.3. Picks are then associated using the REAL associator (Zhang et al., 2019). From the associated picks, we obtained multiscale high-precision seismicity following the NLL-SSST-coherence relocation methodology, combining source-specific, station traveltime corrections (SSST) and stacking of probabilistic locations for nearby earthquakes based on inter-event waveform coherence (Lomax and Savvaidis, 2022; Lomax and Henry, 2023). A smooth seismic P and S wave velocity model for the Santorini area was constructed, based on the model of Brüstle (2013) below 2.5km depth and the model of Hooft (2019) above 2.5km depth. Magnitudes were initially estimated by applying the relation proposed by Scordilis et al. (2016), followed by the magnitude correction and refinement procedure described by Leptokaropoulos et al. (2013). For a more in-depth description of the followed procedures, one may refer to the Materials and Methods section of Lomax et al., 2025.

2. Files

2.1 Relocated catalog (Full_relocated_catalog.csv and Filtered_relocated_catalog.csv)

The dataset consists of the full relocated catalog (Full_relocated_catalog.csv) and a subset of this catalog that was used for the analysis done in Lomax et al., 2025, filtered to include only events with ellipsoid semi-major axis length (Len3) below 4km. Field descriptions are as follows:

• date-time: Maximum likelihood hypocenter origin time
• latitude: Maximum likelihood hypocenter latitude (deg)
• longitude: Maximum likelihood hypocenter longitude (deg)
• depth: Maximum likelihood hypocenter depth (km below zero level (e.g. sea-level))
• RMS: Root-mean-square of phase residuals at hypocenter
• Nphs: Number of phase readings used for location
• Gap: Maximum azimuth gap (deg) between stations used for location
• Dist: Distance of closest station to maxium likelihood or expectation hypocenter (NonLinLoc Non-GLOBAL mode: kilometers, GLOBAL mode: degrees)
• errH: Horizontal error (semi-major axis of 68% confidence error ellipse)
• errZ: Depth error (68% confidence: sqrt(2.30 * covariance(zz)))
• Mamp: Amplitude magnitude
• Mdur: Duration magnitude
• expect_lat: Expectation hypocenter latitude (deg)
• expect_lon: Expectation hypocenter longitude (deg)
• expect_z: Expectation hypocenter depth (km below zero level (e.g. sea-level))
• EllipsoidAz1: Azimuth of semi-minor-axis of 68% confidence ellipsoid
• EllipsoidDip1: Dip of semi-minor-axis of 68% confidence ellipsoid
• EllipsoidLen1: Length of semi-minor-axis of 68% confidence ellipsoid
• EllipsoidAz2: Azimuth of semi-intermediate-axis of 68% confidence ellipsoid
• EllipsoidDip2: Dip of semi-intermediate-axis of 68% confidence ellipsoid
• EllipsoidLen2: Length of semi-intermediate-axis of 68% confidence ellipsoid
• EllipsoidLen3: Length of semi-major-axis of 68% confidence ellipsoid
• minHorUnc: Semi-minor axis of 68% confidence ellipse
• maxHorUnc: Semi-major axis of 68% confidence ellipse
• azMaxHorUnc: Azimuth of major axis of 68% confidence ellipse
• pdfVolume: Integral over octree cells of volume * cell probability
• mech_strike: Strike of double-couple mechanism
• mech_dip: Dip of double-couple mechanism
• mech_rake: Rake of double-couple mechanism
• mech_misfit: Misfit of double-couple mechanism determination
• mech_Nobs: Number of first motion observations used in mechanism determination
• publicID: Event ID

2.2 Phase file (Santorini_2025_phases.txt)

Raw phase file used for compiling the relocated catalog, in HypoDD format. Contains absolute travel time data information for P and S arrivals, initial locations and depths as obtained from the phase association process. Header field descriptions are as follows:

• YR: Origin Year
• MO: Origin month
• DY: Origin day
• HR: Origin hour
• MN: Origin minutes
• SC: Origin seconds
• LAT: Origin latitude (deg)
• LON: Origin longitude (deg)
• DEP: Origin depth (km)
• MAG: Magnitude
• EH: Horizontal error (km)
• EZ: Depth error (km)
• RMS: Root-mean-square of phase residuals at hypocenter
• ID: Event ID

Followed by lines equal to the number of P and S observations per station, described as follows:

• STA: Station code
• TT: Absolute travel time from event to station 
• WGHT: Weight assigned to the pick
• PHA: Phase type (P or S)

Phase file format is described in-depth in the HypoDD user guide.