A seismic investigation into the crustal structure in Northwestern Iran, Eastern Turkey and the Caucasus regions

In this study, we investigate the velocity structure of the crust in Northwestern Iran, Eastern Turkey and the Caucasus regions, which form the Northern part of the Eurasia-Arabia collision zone. Fundamental mode Rayleigh wave group velocity maps at different periods can show the main geological features of the study region. Data for this research come from the permanent stations of the Incorporated Research Institution for Seismology (IRIS) in Turkey and the Caucasus, and the temporary seismic networks operated by the Institute for Advanced Studies in Basic Sciences (IASBS) in Iran. In the first step, we obtained fundamental mode Rayleigh waves group velocity dispersion curves in the period range of ۵-۶۰ s from regional earthquakes. To develop a more robust ۱D path-average model, we clustered all group velocity dispersion curves for similar paths. This clustering process reduces redundant paths, eliminates outliers, and measures statistical errors. For each period, ray paths with endpoints (stations and events) within ۴% of the path length from one another were grouped together. We then calculated the mean and standard deviation of group wave-speed measurements within each cluster. Next, we built tomographic dispersion maps for ۱۵ different periods between ۵ and ۶۰ s. A grid with ۰.۵˚×۰.۵˚ spacing was constructed for the whole region of the sources and receivers. We employed the method of Debayle and Sambridge (۲۰۰۴) to invert path-averaged surface wave measurements for both isotropic and anisotropic terms. The Kura Basin and South Caspian Basin are floored by very low upper crustal velocities, which is characteristic of their excessively thick sediments. Also, the Rioni Basin, parts of Eastern Anatolia, the Northeastern and Northern regions of Iraq all exhibit the lowest group velocities at short periods. The Southern Lesser Caucasus, Central Alborz, Northern Iraq, Southeastern Anatolia, and the Zagros foreland basin show the highest group velocities at mid- and long-periods.

کلیدواژه ها:

GROUP VELOCITY ، CRUSTAL STRUCTURE ، SURFACE WAVE TOMOGRAPHY ، DISPERSION CURVES