ALBERT

Beschreibung: We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in the 10-100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fundamental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband stations, was identified by applying the frequency time analysis (FTAN) to each epicenter-station path which simultaneously satisfies the two-station method conditions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this procedure, 243 group and phase velocity dispersion curves were processed to obtain tomographic maps by applying the Yanovskaya-Ditmar formulation for periods in the 10-100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully nonlinear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to produce images that have substantially higher lateral resolution compared to images currently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well correlated with the shield-like lithosphere structure in Zagros. A low-velocity zone (LVZ) is not detected in Alborz or the south Caspian basin, which can imply thrusting of the oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh.

Beschreibung: Coda quality factor (Q (sub c) ) estimates for the Faryb region in the southeast Zagros have been obtained by using aftershock data of the Tiab earthquake of 28 February 2006, recorded within an epicentral distance of 100 km. More than 394 earthquakes were recorded by a local temporary network consisting of 9 short-period stations installed for one month after 28 February 2006. Q (sub c) was estimated using the single-backscattering model in frequency bands of 0.5-24 Hz. In this research, the spatial and temporal variation of Q (sub c) in the Sanandaj-Sirjan zone is studied. To explore the lateral variation, Q (sub c) is calculated for nine stations and in different parts of the covered area. The lowest values are derived in KALI station in the southern part and the higher value in BAGA station in the northern part, but generally there is an absence of significant lateral variation in coda Q (sub c) in the Faryab region. To investigate the attenuation variation with depth, Q (sub c) value was calculated for eight lapse times. The average frequency relation for this region is Q (sub c) =(28+ or -1.1)f (super (1.14+ or -0.01)) at 5 s lapse time window length and Q (sub c) =(105+ or -1.3)f (super (0.98+ or -0.047)) at 30 s lapse time window length. Q (sub c) increases with depth; however, the rate of increase of Q (sub c) is not uniform with depth in the study area. Beneath the Faryab region, the rate of increase of Q (sub c) is greater at depths less than 49 km (compared to larger depths), indicating a low attenuation structure at less than approximately 49 km depth, which is the Moho depth in this region.