Seismological Evidence for Lithospheric Low-Velocity Anomalies beneath the Eastern Mediterranean: Impact of Tectonics

Аннотация

Being a part of the eastern Mediterranean, northern Lebanon and northwestern Syria is a seismotectonically active region due to the juxtaposition of several plate boundaries, the existence of many active faults, and the intense seismicity generated along rifting, transform, and convergent plate boundaries. We applied a tomographic inversion on seismic body wave arrivals recorded at 12 seismic stations distributed in the northern part of Lebanon and northwestern Syria to study the P- and S-wave velocity (Vp, and Vs) structures and the seismogenic behavior of the upper portion of the lithosphere. The seismic data comprise 4855 and 2950 P- and S-wave arrivals, respectively, generated by 605 local crustal earthquakes which occurred mainly along the Yammouneh Fault and splays in the Eastern Mediterranean. The crustal structure is highly heterogeneous down to the upper mantle depths. Low-velocity (low-V) anomalies are widely distributed especially along the active faults delimiting the boundary between the Arabian and African plates and areas of thick sedimentary deposits and Cenozoic volcanics. Results of the checkerboard resolution test and hit count coverage indicate that the mapped velocity anomalies are reliable features. Furthermore, they are generally consistent with many geological and geophysical investigations which have been detected beneath the study area by other researchers including the emplacement of ophiolite rocks, Cenozoic volcanics, inefficient Sn propagation, low Lg Q values, and low seismic wave velocities.