New 3D Velocity Model (mTAB3D) for Absolute Hypocenter Location in Southern Iberia and the Westernmost Mediterranean

Abstract

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. We present mTAB3D, a new 3D P-wave velocity created after data collection, geometry modeling and velocity estimation in our study area. To test this model, we used arrival times from the Spanish Seismic Network catalog and performed two non-linear absolute hypocenter 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 (up to 11% lower). 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.