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

• Published in: Earth and space science (Hoboken, N.J.) Vol. 11; no. 10
• Main Authors: Sánchez‐Roldán, José Luis, Álvarez‐Gómez, José A., Martínez‐Díaz, José J., Herrero‐Barbero, Paula, Perea, Hector, Cantavella, Juan V., Lozano, Lucía
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01-10-2024; American Geophysical Union (AGU)
• Subjects: absolute location; Alboran sea; Basins; Data collection; earthquake location; Earthquakes; Fault lines; Plate tectonics; Sediments; Seismic activity; Seismic waves; Tomography; Trans‐Alboran shear zone; Velocity; Wave propagation; Wave velocity
• ISSN: 2333-5084; 2333-5084
• DOI: 10.1029/2023EA002993

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.
Plain Language Summary
The convergence between Africa and Eurasia plates developed the Trans‐Alboran Shear Zone, where earthquakes are quite frequent. Here, seismicity is controlled by the main active structures, and some of them can trigger large earthquakes (M ≥ 6.0). The tectonic complexity of the study area implies that seismic waves after an earthquake do not propagate equally in every direction, which may produce mislocations when a laterally homogeneous model is used. Due to this, we have developed a new 3D velocity model (mTAB3D) that accounts for this heterogeneity. We tested mTAB3D by locating earthquakes from two catalogs from the Spanish Seismic Network that occurred in our study area and compared the results to those obtained using a 1D model. Broadly, our results show lower uncertainties and locations closer to the possible fault sources, even in scenarios of unfavorable distribution of seismic stations. We conclude that mTAB3D can be used to obtain reliable hypocenters for seismotectonic studies within the westernmost Mediterranean.
Key Points
New 3D velocity model for southern Iberia and the westernmost Mediterranean
Relocation of hypocenters in the Trans‐Alboran Shear Zone and seismotectonic analysis
Seismotectonic analysis of a continuous catalog in Eastern Betics Shear Zone, and the Al‐Hoceima seismic sequence (2016)