Search Results (3)

This research assessed stress regimes and fields in eastern Iran using fault-slip data and the tectonic events associated with these changes. Our stress analysis of the brittle structures in the Shekarab Mountains revealed significant changes in stress regimes from the late Cretaceous to the Quaternary. Reconstructing stress fields using the age and sense of fault movements showed that during the late Cretaceous, the direction of the maximum horizontal stress axes (σ1) under a compressional stress regime was ~N290°. This stress regime led to the uplifting of ophiolites and peridotites in eastern Iran. During the Eocene, the σ1 direction was NE-SW. The late Eocene and Oligocene stress states showed two distinct transpression and transtension stress regimes. This transition from transpression to transtension in the eastern Shekarab Mountains was the consequence of regional variations in stress regimes. The Quaternary stress state indicates that the tectonic regime in the Quaternary is strike-slip and the σ1 direction is ~N046°, which coincides with the current convergence direction of the Arabia–Eurasia plates. Our paleostress analysis revealed that four distinct stress regimes have been recognized in the area, including compressional, transtensional, transpressional, and strike-slip regimes. Our findings indicated that the diversity of the tectonic regimes was responsible for the formation of a variety of geological structures, including folds with different axes, faults with different mechanisms, and the current configuration of the Sistan suture zone. Full article

Seismic bulletin data collected by the Iranian Seismological Center are used to image crust and mantle seismic attenuation, group velocity, and phase velocities for Lg, Pg, Sn, and Pn phases. This is possible because the peak amplitude time is picked, and amplitude measurements can be associated with the phase based on travel time plots. The group velocity is the apparent velocity of the maximum amplitude arrival and represents the combined effect of phase velocity and seismic scattering. Thus, it can be used in combination with the attenuation to identify where scattering attenuation is dominant. The Arabian–Iranian plate boundary separates low-velocity Zagros sediments from central Iran; however, in the mantle, it separates a high-velocity Arabian shield from central Iran. Scattering attenuation is low within the Arabian mantle and crust, and the Zagros sediments do not cause Lg or Pg attenuation. The Eocene Urumieh Dokhtar Magmatic Arc has high attenuation within both the crust and mantle, and while there is no partial melting in the crust, there may be some in the mantle. The northern Eocene Sistan Suture Zone shows particularly high attenuation that is accompanied by high scattering. It represents an incompletely closed ocean basin that has undergone intense alteration. The Alborz Mountains have high attenuation with some scattering. Full article

In this paper, faults, one of the most important causes of geohazards, were investigated from a kinematic and geometric viewpoint in the northern part of the Sistan suture zone (SSZ), which serves as the boundary between the Afghan and Lut blocks. Furthermore, field evidence was analyzed in order to assess the structural type and deformation mechanism of the research area. In the northern Birjand mountain range, several ~E–W striking faults cut through geological units; geometric and kinematic analyses of these faults indicate that almost all faults have main reverse components, which reveals the existing compressional stress in the study area. The northern Birjand mountain range is characterized by four main reverse faults with ~E–W striking: F1–F4. The F1 and F2 reverse faults have southward dips, while the F3 and F4 reverse faults have northward dips. Moreover, the lengths of the F1, F2, F3, and F4 faults are 31, 17, 8, and 38 km, respectively. These faults, with reverse components that have interactive relationships with each other, form high relief structures. The study area’s main reverse faults, including F1 to F4, are extensions of the Nehbandan fault system, while their kinematics and geometry in the northern Birjand mountain range point to an N–S pop-up structure. Full article