DOI: 10.13127/etna_nll_sc_2000-2024
title: NonLinLoc high-precision earthquake location catalog for Mount Etna (2000-2024) (Etna_NLL_SC_2000-2024)
title: Etna_NLL_SC_2000-2024

description: High-precision earthquake locations are indispensable for a wide range of seismological studies, including seismic hazard assessment, fault rupture process analysis and subsurface structural imaging.
Here we present a catalog of high-precision relocated volcano-tectonic earthquakes, recorded by the seismic network managed by Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) from 2000 to 2024 and originating on Etna volcano area. 
To perform hypocentral location we adopt the NLL-SSST-coherence (NLL-SC; Lomax et al., 2022) probabilistic non-linear location method. NLL-SC is an advanced location method designed to improve precision across multiple scales. This is achieved through the correction of seismic wave travel times and the analysis of waveform similarity. 
We produced a 24-year catalog of hypocentral locations for Etna volcano, representing a previously unexplored dataset using high-precision location techniques.
This comprehensive dataset not only will contribute to understanding the seismic behaviour of Etna volcano but also will plays a key role in ongoing monitoring and scientific research related to volcanic activity in the region.
description: The NLL-SC method (Lomax & Savvaidis, 2022; Lomax et al, 2024) improves earthquake location by refining hypocenter accuracy. Based on the NonLinLoc (NLL) algorithm, a probabilistic global search technique, it estimates earthquake hypocenters using three-dimensional probability density functions (PDFs).
A key component of this method is the application of Source-Specific Station Term (SSST) corrections, which iteratively refine travel-time estimates to minimize biases from velocity model inaccuracies. Additionally, Waveform Coherence Relocation utilizes waveform similarities between nearby events to improve relative locations, enhancing the clustering of seismic events.
By integrating these approaches, the NLL-SC method produces a more precise and internally consistent earthquake catalog, providing valuable insights into the seismotectonic processes and structural characteristics of Etna volcano area.
description: The dataset, used as input for the new hypocentral locations consists of approximately 22,000 earthquakes recorded in the Mount Etna region from 2000 to 2024, covering a geographical area defined by latitudes 37.5°N to 37.9°N and longitudes 14.7°E to 15.3°E. 

The seismic network operating during this long time period underwent several technical upgrades. From 2000 to 2024, the network transitioned from a sparse configuration primarily equipped with short-period (1s) analog sensors to a significantly denser network featuring exclusively three-component digital sensors (40s and 120s). This evolution resulted in an enhanced detection capability, enabling a minimum local magnitude (ML) threshold of approximately 0.2 to be achieved in certain areas (Ferrari et al., 2024).
The present new catalog reports, for each earthquake, different parameters as the origin time in Coordinated Universal Time (UTC), the hypocentral coordinates (latitude N and longitude E), the depth of the earthquake in kilometres b.s.l., the local magnitude (ML) and the moment magnitude (MW) as derived from Saraò et al., 2023. Additional parameters such as the number of stations used for location (NO), the root mean square of residuals (RMS), and the horizontal and vertical location errors (ERH and ERZ) are also reported together with P and S- wave arrival times. 
Earthquake location accuracy through the NLL-SC method is directly dependent on the quality of the initial velocity model. For this analysis, we have adopted a smooth, 1D velocity model derived from the 1D model used at INGV-OE for monitoring purposes (see Lomax et al., 2024 and references therein).
The configuration of NLL-SC used here follows closely that of Lomax et al. (2024).
description: Data and Resources
The original dataset, used as input for the new hypocentral locations is available for public access through a dedicated online platform:
https://sismoweb.ct.ingv.it/Etna/catalogs/2000_2010/
https://sismoweb.ct.ingv.it/Etna/catalogs/2011_2013/
https://sismoweb.ct.ingv.it/Etna/catalogs/2014_2016/index.php?17984
https://sismoweb.ct.ingv.it/Etna/catalogs/2017_2019/
http://eqcatalog.ct.ingv.it/etnarsc/

Acknowledgement
We are indebted to the INGV-OE seismic network staff for ensuring the regular operation of seismic stations and to the Seismic Data Analysis Group for earthquake data processing.
This catalog was produced in the frame of the IMPACT PROJECT (INGV Department strategic Projects-2019) WP1. Task 2-Mt. Etna structure, and INGV PROJECT Pianeta Dinamico (NEMESIS)—code CUP D53J19000170001—funded by Italian Ministry MIUR.

References
Alparone, S. C., Maiolino, V., Mostaccio, A., Scaltrito, A., Ursino, A., Barberi, G., et al. (2015). Mt. Etna Seismic Catalog 2000-2010 [Data set]. Istituto Nazionale di Geofisica e Vulcanologia (INGV) - Osservatorio Etneo. https://doi.org/10.13127/etnasc/2000_2010
Alparone, S. C., Barberi, G., Di Grazia, G., Giampiccolo, E., Maiolino, V., Mostaccio, A., Musumeci, C., Scaltrito, A., & Ursino, A. (2020). Mt. Etna Seismic Catalog 2011-2013 (Version 1) [Data set]. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/ETNASC/2011_2013
Alparone, S. C., Barberi, G., Di Grazia, G., Giampiccolo, E., Maiolino, V., Mostaccio, A., Musumeci, C., Scaltrito, A., Tuvè, T., & Ursino, A. (2020). Mt. Etna Seismic Catalog 2014-2016 (Version 1) [Data set]. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/ETNASC/2014_2016
Barberi, G., Di Grazia, G., Ferrari, F., Firetto Carlino, M., Giampiccolo, E., Maiolino, V., Mostaccio, A., Musumeci, C., Scaltrito, A., Sciotto, M., Tusa, G., Tuvè, T., & Ursino, A. (2020). Mt. Etna Revised Seismic Catalog from 2020 (EtnaRSC2020) (Version 1) [Data set]. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/ETNASC/ETNARSC2020
Alparone, S. C., Barberi, G., Di Grazia, G., Giampiccolo, E., Maiolino, V., Mostaccio, A., Musumeci, C., Scaltrito, A., Tuvè, T., & Ursino, A. (2022). Mt. Etna Seismic Catalog 2017-2019 (Version 1) [Data set]. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/ETNASC/2017_2019
Ferrari F., Giampiccolo E., Musumeci C., Tusa G., Tuvè T., Di Grazia G., Mostaccio A., Sciotto M., (2024). La sismicità dell’area etnea nel periodo Gennaio – Dicembre 2021. Quad. Geofis., 192: 132, https://doi.org/10.13127/qdg/192
Lomax, A. and A. Savvaidis (2022). High-Precision Earthquake Location Using Source-Specific Station Terms and Inter-Event Waveform Sirnilarity, J. Geophys. Res., Solid Earth, 127, e202 IJB023190, doi: 10.1029/2021JB0231907
Lomax, A., Tuvè, T., Giampiccolo, E., & Cocina, O. (2024). A new view of seismicity under Mt. Etna volcano, Italy, 2014-2023 from multi-scale high-precision earthquake relocations. Annals of Geophysics, 67. https://doi.org/10.4401/ag-9147
Saraò A., Moratto L., Giampiccolo E., Cocina O. (2023). Moment magnitude for earthquakes in the Etna volcano area, Geophysical Journal International.  Vol. 234, Issue 3, 2519–2533, https://doi.org/10.1093/gji/ggad257