DOI: 10.5281/zenodo.17936591
title: Machine-Learning derived, NLL-SSST-coherence high-precision relocated earthquake catalog for the 2025 Santorini–Amorgos seismic crisis

description: 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.