SEISMIC TOMOGRAPHY AND ITS IMPLICATION STRUCTURES USING REGIONAL SEISMIC PHASE RECORDED IN SYRIAN NATIONAL SEISMIC NETWORK AND SURROUNDING NETWORKS

Abstract

Tomography or production of earth image using seismic waves similar to CAT scan stands for medicine computerized axial tomography using ultrasound, gama rays, or X-rays to produce a focused image of the structures across a specific depth within the body by sending signals through an object in different directions and add the signals to construct a cross section of the object. In this study we focused on Lg attenuation in Syria using the waveforms data recorded at 57 stations for 340 events in Syria and surrounding areas to determine values of Lg Q0 (Q at 1 Hz and its frequency dependence) by using the standard two-station method. These values are used to derive a tomographic model of laterally varying Q0 for Syria and surrounding areas. The Lg Q0 calculated values varies between 60 and 400. The lowest Q values are located in northwestern Syria beneath the triple junction of the Arabian, African, and Eurasian plates. We also observe high Lg attenuation along the northern segments of the Dead Sea fault system, Aleppo plateau, southwestern of Palmyra fold-and-thrust belt, and in eastern region of Syria beneath Rawda and Qamichli Uplifts. We found moderately high Q values along the North-South trending zone that cross the Palmyride fold and thrust belt through central Syria. There are two distinct high Q anomalies: one concentrated beneath Rutbah uplift, and the other in northwestern portion of the Palmyra fold-and-thrust belt and north Euphrates basin. We found that the Lg Q0 tomographic model and its power-law frequency dependence Lg η correlate well with regional tectonic trends within Syria and the surrounding regions. Furthermore, we observe that Lg attenuation is sensitive to the upper crustal structure. As well as in this study we used the Pn Seismic phases velocity for all the enter two stations paths located in Syria and we divided the velocities into two groups of Pn velocity (6.65-7.7), (7.7-8.5) km/sec, and we determined the cross points represents the anisotropic boundaries. The alignments of those anisotropic boundaries in the uppermost part of the mantle showed well correlation with the main tectonic and main structures known in Syria as Palmyra fold-and-thrust belt and we found it limited with the higher group velocity boundaries while the cross points with lower boundaries distributed alignment along Dead Sea fault system. Low velocity zone found trending north west-south east crossing the central Palmyra fold-and-thrust belt and dividing it into two parts the northeastern and the west southern part.