Crustal and uppermost mantel structure study of N-NE Iraq Using Rayleigh wave Analyses

Abstract

The crust and uppermost mantle structure of N/NE of Iraq between lat. (34 ̊12 ̒ - 37 ̊ 12 ̒) and long. (41 ̊36 ̒ – 46 ̊ 04 ̒) are investigated using Rayleigh surface wave analysis and inversion. Data sets of several regional Earthquakes occurred over the period between 1998 and 2000, were recorded by two broad-band seismic stations (HITJ and RUWJ) that were located in Jordan. Multiple filter analysis in the frequency range (0.02-0.25) Hz have been employed to determine fundamental mode Rayleigh group velocities dispersion. Inversion method is performed to find the average structure along seventy ray paths for fifty one recorded events located around Zagros-Taurus plateau which produced a good coverage of the study area. One dimensional crustal velocity models with theoretical group velocity dispersion curve that best fits and match the observed dispersion are considered as representative crustal structure of the event-station path. The thickness of the upper crust ranges between (6-14 Km) low-velocity layers, its primary wave velocity (Vp) varies between 5 and 6 km/s. Mid crustal layer has a P-wave velocity from 6 to 6.5 km/s down to around 28 km depth. A P-wave velocity from 6.4 to around 7.5 km/s characterizes the lower crust. In general the crustal structure revealed lateral and vertical variations in shear wave velocity within the crust, the resulting models display the average S-wave velocities range between 3 to 4 km / s in Earth's crustal layer. The high P-wave velocities greater than 7.8 km/s and about 4.5 km/s for S-wave used to identify the Earth's uppermost mantle.The crustal thickness was found to increase towards the Zagros thrust zone and the interplate seismicity is significantly more dominant than the intraplate activity. Those observations, the variation in crustal thickness and the seismic activity are related to the collision of the Arabian plate with Eurasia.