No abstract

The eastern Betics shear zone comprises one of the most seismically active areas in Iberia, due to the presence of large active faults loaded by the oblique convergence between Eurasia and Africa plates. We focus our study on the sector of the eastern Betic Cordillera affected by the Alhama de Murcia fault (AMF) and other nearby faults that are the source of large paleoseismic events and some damaging historical earthquakes. This study aims to give more accurate locations to the hypocenters in the region around these faults, using a model that accounts for lateral variations of P-wave velocity. This task was accomplished, developing a new 3D velocity crustal model of the region, by combining recent regional and local geological and geophysical data, such as geological mapping, gravimetry, seismic-wave tomography, and seismic exploration surveys. Afterward, as a preliminary test of performance, we compared the hypocenters obtained with this model against the ones computed with other 1D velocity models, using NonLinLoc with a seismic dataset of the highest possible quality (i.e., filtered by a minimum magnitude) in this area within the period January 2015–December 2018. Then, for comparing the reliability of the new 3D local model against a larger 3D regional model, we carried out a final relocation with all the earthquakes of the Spanish Seismic Catalog in the study area for the period April 2011–October 2019. New locations obtained with the local model, which show better clustering near active structures and lower epicentral uncertainty in comparison with the regional model, allow us to observe possible genetic relation between seismicity and specific faults after the inversion, in particular, the AMF.

The Trans-Alboran Shear Zone is one of the most seismically active areas in the westernmost Mediterranean, where a wide variety of tectonic domains have developed within the context of oblique convergence between Eurasia and Africa plates. In this region, earthquakes occur close to seismogenic structures, some of them large enough to cause damaging events. In addition, the diversity of tectonic domains implies a lateral variation of seismic wave propagation, which could affect the hypocenter reliability if not addressed during the location procedure. In this work, we present mTAB3D, a new 3D P-wave velocity model that accounts for the lateral heterogeneity of our study area. To test this model, we used arrival times from the Spanish Seismic Network catalog and performed two non-linear absolute location inversions: the first comprises all the seismicity detected during 2018-2022 in the Eastern Betics Shear Zone; the second one consists of the earthquakes recorded during the Al-Hoceima seismic sequence (2016). We compare our results against hypocenters computed with a 1D velocity model of the region (mIGN1D) and observe that mTAB3D achieves better clustering near active structures and lower epicentral uncertainties. Moreover, hypocenters obtained with mTAB3D show notable reliability even in scenarios of a low azimuthal gap, such as the 2016 Al-Hoceima sequence. The new catalogs computed with our model help us to infer possible genetic relations between seismicity and source faults within our study area and can be used as an additional tool when looking into prior seismic sequences.