Physics-based modeling of earthquakes in slow deforming areas: a case study from the Eastern Betic Fault System (SE Spain)

<p align="justify">The challenges in the characterization of slow-moving faults and the temporal limitations of the earthquake records in these regions complicate the seismic hazard assessment. The instrumental and historical seismic catalogs cover a short time period compared with the long recurrences between large destructive events in some faults. Paleoseismic evidence allows us to increase the time frame, but when field data is scarce, scattered or difficult to collect, <span lang="en-US">numerical modeling provides us with an excellent tool to </span><span lang="en-US">support the </span><span lang="en-US">characteriz</span><span lang="en-US">ation of</span><span lang="en-US"> a fault system and its associated </span><span lang="en-US">threat</span><span lang="en-US">. </span>Physics-based earthquake simulators overcome the limitations of actual earthquake catalogs and generate long-term synthetic seismicity. Recent numerical codes based on rate- and state-dependent friction allow the modeling of both the long-term seismic cycle deformation and the short-term rupture based on quasi-dynamic physical approximations. We use the RSQSim earthquake simulator to <span lang="en-US">reproduce a 100 kyr synthetic catalog of earthquake ruptures based on</span> a 3D fault model that contains the long-term slip rates, rakes and frictional properties of the main active sources of the Eastern Betic Fault System, a slow deforming area (< 1.5 mm/yr) at southeastern Spain with only one instrumental event greater than M_W5.0: the 2011 Lorca earthquake (M_W 5.1). <span lang="en-US">The resulting </span><span lang="en-US">long-term</span><span lang="en-US"> earthquake statistics </span><span lang="en-US">(more than 77.000 events) </span><span lang="en-US">show that </span><span lang="en-US">only about 10% of the simulated events have a magnitude greater than M</span>_{<span lang="en-US">W</span>}<span lang="en-US"> 5.0, but all faults in the system are capable of generating M</span>_{<span lang="en-US">W</span>}<span lang="en-US"> &#8805; 6.0 earthquakes, supporting paleoseismic observations </span><span lang="en-US">of surface ruptures </span><span lang="en-US">and some historical events (I > VIII) that likely reached magnitudes </span><span lang="en-US">greater than M</span>_{<span lang="en-US">W</span>}<span lang="en-US"> 6.0 </span><span lang="en-US">(e.g., 1522 Alhama de Almeria and 1829 Torrevieja earthquakes)</span><span lang="en-US">. </span><span lang="en-US">C</span><span lang="en-US">omplex ruptures involving </span><span lang="en-US">several fault </span><span lang="en-US">segments </span><span lang="en-US">and spatial-temporal clustering of events </span><span lang="en-US">are physically compatible </span><span lang="en-US">in this system, according to our simulations. </span><span lang="en-US">The largest M</span>_{<span lang="en-US">W</span>}<span lang="en-US"> > 6.5 events are as a result of </span><span lang="en-US">complex</span><span lang="en-US"> ruptures between the </span><span lang="en-US">major</span><span lang="en-US"> faults, with recurrence times of</span> <span lang="en-US">1 kyr</span><span lang="en-US">. </span><span lang="en-US">T</span><span lang="en-US">he occurrence of larger earthquakes, even M</span>_{<span lang="en-US">W</span>}<span lang="en-US"> &#8805; 7.0 </span><span lang="en-US">in the Alhama de Murcia and Carboneras faults</span><span lang="en-US">, cannot be ruled out, contrasting with the low magnitudes </span><span lang="en-US">of</span><span lang="en-US"> the</span> <span lang="en-US">instrumental</span><span lang="en-US"> earthquake catalog. Knowing the characteristics and behavior of these large seismic ruptures, </span><span lang="en-US">with </span><span lang="en-US">no</span><span lang="en-US"> instrumental data available,</span><span lang="en-US"> is crucial for </span><span lang="en-US">the </span><span lang="en-US">estimation of the maximum ground motion that could be reached </span><span lang="en-US">in </span><span lang="en-US">this</span><span lang="en-US"> region. With this contribution, we intend to discuss</span><span lang="en-US"> how</span><span lang="en-US"> physics-based models c</span><span lang="en-US">ould</span><span lang="en-US"> contribute to this task for deterministic and probabilistic seismic hazard assessments (DSHA and PSHA). Funded by Project DT-GEO: A Digital Twin for GEOphysical extremes, project ID 101058129.<br /></span></p>