Ground motion analysis in the Dead Sea Basin

In this research we perform a 2-D ground motion analysis in the Dead Sea basin, using the numerical code E3D (Larsen et al., 200 1) capable of simulating seismic wave propagation in a 3-D heterogeneous earth. As seismic waves propagate away from the source they are attenuated by: (i) Geometrical spreading and (ii) material damping. The attenuation of seismic waves is countered by ampliflcation as the waves pass from dense to less-dense
materials when traveling from depth to the surface. Typically, sedimentary basins, exhibit amplifled ground motions, which may cause substantial structural damages. The Dead Sea basin is a deep pull-apart basin formed by the active Dead Sea Transform, along which some of the largest earthquakes in the region have occurred. It is unique because of its great depth, extreme basin-floor geometry and intricate material structure. Thus, wave propagation analysis becomes more complex when compared to flat-bottomed, shallow basins. The Dead Sea basin is divided into two sub-basins: The Northern basin and the Southern basin separated by the Lisan diapir. In this research we will perform a detailed 2-D wave propagation analysis for the Northern and Southern basins. The cross-sections were located so that sites of economical signiflcance, e.g., hotels complexes and industrial facilities are accounted for. The simulations are performed on a SunOS based cluster in the Nevada Seismological Lab in UNR using the E3D code. The code simulates wave propagation by solving the elastodynamic formulation of the full wave equation on a staggered grid. The basin effects are investigated via spectral analysis, PGV examination and visualization of the wave propagation. Ground motion ampliflcation occurs due to a combination of the following: (i) low impedance ratio at the basins floor, (ii) focusing phenomenon where concave or convex material interface at the basins floor acts as a converging or diverging lens respectively and (iii) interference of the trapped waves. The behavior of ground motions with respect to these effects along with the effects contributed by the Sedom formation rock salt are to be studied in detail. Previously studied shallow sedimentary basins, e.g., Los-Angeles basin, typically show ground motion ampliflcation caused by ampliflcation of seismic waves entering the basins sedimentary flll. Preliminary results from this research indicate that in deep and narrow basins, such as the Dead Sea basin, the effects of basin-floor-geometry and depth are more dominant than material properties.