Seismic Tomographic Modeling of Israel and the Middle East: Improved Resolution Through Optimized Model Parameterization

Abstract:

Accurate regional travel time predictions require us to detect and locate earthquakes at smaller and smaller magnitudes, relying upon regional phases (e.g. Pg, Lg, Pn, Sn) to account for 3-D effects in the crust and upper mantle that are not captured by 1-D models. The Regional Seismic Travel Time (RSTT) prediction model accounts for regional-scale crust and upper mantle structure globally by incorporating regional seismic phases into its travel time calculations. Previous versions of the RSTT model have used a constant grid cell size of 1°; to improve resolution at regional scales down to 0.125° (~14 km), we perform data-driven grid refinement on the RSTT model in pursuit of two main goals: to test the limits of RSTT resolving capability and accuracy through variable grid refinement; and to image smaller, previously unresolved structures in Israel and the Middle East and illuminate crust and upper mantle dynamics operating in this complex tectonic area. We investigate the effects of model parameterization as grid cell size decreases and the tradeoffs between resolution and accuracy. Our data include 5,175 events and 528 stations having 90,051 Pn and 9,269 Pg arrivals. The variable grid refinement method improved resolution and accuracy (reduced residual values) to 0.125° in areas with highest data coverage. At smaller grid cell sizes smoothing and damping need to increase, and longer paths had to be upweighted. Results illuminate tectonic features previously unresolvable: in particular, we observe mantle perturbations related to the subduction zone around the Cyprean arc, crustal anomalies near the Dead Sea Fault and throughout the Anatolian plate.