Development of Seismic Velocity Combining Tomographic Inversion and Forward Modeling by Ray Tracing: Technique and Application

A Vp velocity model of the sediments, crust and upper mantle of the Dodecanese area, Greece, was obtained by evaluating wide angle reflection refraction seismic (WARRS) data, using Ocean Bottom Seismographs and land stations along a 140 km line. Seismic energy was generated by air gun shots spaced at 120 m intervals fired by a tuned air gun array of 49 l volume. Velocity modeling by seismic tomography combined with forward modeling by ray tracing revealed the structure of the crust and sediments. Four sedimentary layers were mapped with velocities ranging from 1.7 to 5.4 km/s. Lateral velocity variations and existence of several faults indicate intense fragmentation and the development of several individual basins. Sediments are only 2 to 2.5 km thick. The upper crust is 6.5 km thick with Vp velocities between 5.8 to 6.5 km/s. The lower crust is 10 to 12 km thick with Vp velocities between 6.8 to 7.2 km/s. Moho discontinuity is identified at 20 to 22 km depth. A low velocity zone of 7.8 km/s in the uppermost part of the mantle is probably high temperature asthenosphere that was uplifted below the southern Aegean Sea due to the subduction of the Ionian oceanic lithosphere.