فهرست مطالب میثم کوه پیما

The Kopeh Dagh and Binalud-Alla Dagh mountains are important structural elements located in the northeastern boundary of Arabia-Eurasia collision zone. Due to existence of large cities with a long history of civilization, there is a relatively rich body of data on historical seismicity in this area. Nonetheless, little adequate instrumental seismic data were available prior to this study. In this paper, we utilized the temporary China-Iran local seismic network data deployed in the area for 13 months. Based on this data, we determined 37 focal solutions through first motion polarity approach suggesting a combination of strike-slip, reverse and normal mechanisms. There is a significant concentration of epicenters and focal mechanisms around the eastern Alborz - Kopeh Dagh boundary along the Atrak River. The southern and western boundaries of the Binalud Mountains also show relatively high seismic activities. The Local magnitude (ML) of the events ranges from 3.5 to 4.9 with depths of up to 20 km, mostly concentrated at ~10 km. The principal stress axes and slip vectors obtained from the focal mechanisms agree well with kinematic state of main faults and tectonic regime of the area, confirming the seismogenic nature of these faults. In addition, they are consistent with right-lateral component of slip along thrust faults in eastern Kopeh Dagh and Binalud and both laft- and right-lateral motions in the central Kopeh Dagh.

The metamorphic rocks around Mashhad city were suffered by several stages of metamorphism and deformation. Special mineral and structural elements were formed in these stages. Metamorphic grade in the pellitic rocks changes from green schist to amphibole facies. Foliations generally are steep toward northeast. Lineations predominantly have gentel to moderate plunge (less than 30°) toward northwest. Kinematic analysis of ductile structures in outcrop and microscopic scale shows dextral strike slip shearing with reverse component from northwest to southeast in shear zones. Contrasting of kinematic analysis of mesoscopic folds coeval deformation with shear sense obtained from ductile shear zones indicates the strain partitioning in the area. Based on field analysis and microscopic studies, the rocks were deformed by two stages of ductile deformation and followed by brittle-ductile and brittle deformation in later stages. The first and second stages of deformation occurred in a progressive and continuous manner accompanied by the higher grade of metamorphism in the area. The main stage of metamorphism is contemporaneous with early Cimmerian orogenic phase.