Characterizing seismic rupture scenarios for the Eastern Betic Shear Zone, Spain, using physics-based earthquake simulations: a preliminary approach.

The Eastern Betic Shear Zone (EBSZ) is the main tectonic structure in SE Iberia and is dominated by sinistral strike-slip faults, some of them with reverse component. Many of the largest damaging historical earthquakes occurred in the Betic Cordillera are related to the EBSZ. When estimating rupture scenarios in this fault system, we find some limitations: 1) poorly constrained geometrical parameters; 2) large uncertainties associated with slip rates, which are generally low (< 1 mm/yr); 3) the historical catalog covers short time period compared with the long recurrence interval between major events. Earthquake simulators can solve the limitations of real catalogs and provide interesting information based on fault geometry and its kinematics, which allow us to check different rupture scenarios and evaluate if multi-fault ruptures are potentially possible.

We first constructed a fault model of the 6 major faults, composed of 2.0 km x 2.0 km square cells and associated slip rates and other kinematic data from the Quaternary Active Faults Database of Iberia (QAFI). The first approach has been to implement a boundary element earthquake simulator, Virtual Quake, which performs simulations based on stress interactions between fault elements. We compiled a synthetic seismic catalog lasting 100 kyr that contains more than 15000 events, 4.7 ≤ M≤ 7.2 magnitude; 58 events are M≥7.0 magnitude. We observe that most of those events are associated with a complete rupture of the Carboneras Fault, which implies a 1.5 m mean slip. This is consistent with paleosismological data in the northern section of this fault. The synthetic catalog only includes a M≥7.0 event in Alhama de Murcia Fault, which triggers a joint rupture with Los Tollos, Carrascoy and Bajo Segura Faults. The linking potential seems to be greater from the Alhama de Murcia Fault toward the northeastern faults of the EBSZ.

Further research will consist in comparing the synthetic seismicity with the real seismicity and geological evidences of historical events. Upcoming scenarios will include variations in the fault geometry (dips, strikes, endpoints), rakes and slip rates estimated recently. Implementing physics-based simulators based on the rate- and state- variable friction law would improve the modeling of the physical processes that control earthquake occurrence.