Showing 5 results for البرز
M Mirabedini, M Aghatabay,
Volume 16, Issue 42 (5-2015)
Abstract
Baladeh-Kojour earthquake of May 28th, 2004 is one of the largest earthquakes in vicinity of Tehran, occurred in the northern part of the Alborz range. In this research, spatial variation of fractal parameters has been studied to estimate the seismic pattern of the study area. In order to draw the spatial variation maps, b-value, correlation dimension of epicentral and temporal distribution of earthquakes, De and Dt have been calculated for the data sets of before and after the mainshock, separately. The results show that before the earthquake, these parameters have low values in the eastern side of the mainshock epicenter. It seems that these low values before the earthquake may arise due to clusters of events with larger magnitude and small events after it. Seismic rate has decreased in the surroundings of the mainshock (seismic quiescence). After the mainshock, the lowest values of b-value and Dt is seen in the epicentral and western part of the mainshock. These low values are due to aftershock clustering and stress release, took placed just after the mainshock and during the aftershock sequence. Intensity increasing is observed in the shake map of earthquake. The De parameter is low after the mainshock occurrence. Low b-value and high De indicate high level of seismic activity in the region. The obtained results show the fractal parameters sensitivity to spatial and temporal clustering of earthquakes. Therefore, these parameters can be used as an indicator for seismic precursory patterns of major earthquakes.
Volume 18, Issue 48 (2-2007)
Abstract
A major part of structural studies is the analysis of elements of fold style. In this paper, the elements of main folds style in the Alborz – Central, Iran border zone, were investigated. In this respect, cylindricity, symmetry, style of a folded surface, style of a folded layer and style of a folded multilayer were evaluated. Finally, fold style characteristics and young history of folding in the studied area were indentified. In addition, two main mechanisms (Buckle and Detachment Folding) were distinguished.
Volume 18, Issue 48 (2-2007)
Abstract
Shekarnab intrusion is a part of an extensive magmatism in the Central Alborz Tectonic Zone of Iran. This intrusive body, which is mostly composed of monzonitic, gabbroic and syenitic lithologies, was intruded within green tuffs of the Karaj formation. These plutonic rocks show geochemical alkaline-potassic affinity and in the case of aluminum saturation index, they could be classified as meta-aluminous rocks. These rocks show Nb negative anomaly, enrichment of LILE and are depleted in HFSE. The spider and discrimination diagrams demonstrate that the parent magma of the plutonic intrusion could be related to a subduction zone and have emplaced in an active continental margin. Based on geochemical analysis of trace and major elements, as well as field and petrographical studies, it could be suggested that crystal differentiation has played an important role in lithological diversity of this intrusive body.
Volume 18, Issue 50 (10-2005)
Abstract
Southern flank of the East– Central Alborz Mountain is consisting of several tectonic elements, which were introduced and analyzed, in this paper. This region is including a complex thrust system at north and a widespread foreland basin at south of Alborz– Central Iran border zone. Two significance curvatures at Alborz Mountain belt that have introduced here such as Neyshabur– Esfarayen– Shahrud Syntaxis and Damghan– Semnan– Qazvin Salient, had been created by change in trend of Alborz from NW– SE to NE–SW. According to this research, creative and activities of the fault systems in a sinistral displacement shear zone that had been elongated from south Semnan to north Gonbad–e Kavus was suggested as a cause to forming of above curvatures and thinning of Alborz width at north Bastam. Therefore, deformation in this region is a combination of compressional and left–lateral strike slip components that (Transpression) demonstrated by field evidences and focal mechanism solutions.
Volume 18, Issue 53 (7-2003)
Abstract
A part of Alburz Mountains which is located between Damghan plain (in the south) and Gorgan plain (in the north) structurally is a S-SE vengeance thin-skinned flodthrust belt. Sequential thrusting and related folding during Cimmerian and Alpine orogeny have been the most deformation style since late Triassic. Tectonostratigraphy of Alburz Based on foreland stratigraphical evolution models reveals that structural evolution of Alburz had taken place at three stages: 1) Late Triassic– Early Jurassic duo to Cimmerides 2) Late Cretaceous – Early Paleocene duo to Middle Alpine compress ional movements 3) Neogene duo to Late Alpine compress ional movements. Southward migration of Alburz in each stage accompanied by generation of new thrust faults , uplift and unroofing in fold- thrust belt and caused southward marine transgress-sion and synorogenic classic sedimentation in Foreland basin. Each stage of structural evolution followed by a relaxation period that is characterized by isostasic rebound, reducing of erosion and shallow marine sedimentation in foreland basin duo to north war marine regression.
