International Journal of Remote Sensing Applications Volume 3 Issue 4, December 2013 doi: 10.14355/ijrsa.2013.0304.06
www.ijrsa.org
Determination and Structural Analysis of the Lahijan Transverse Fault in Forestall Region of Alborz Mountains, Iran: A Geospatial Application Hojjat Ollah Safari1*, Mohammad Reza Ghassemi2, Raana Razavi-Pash3 *1,3Geology Department, College of Sciences, Golestan University, Gorgan, Iran, 2
Research Institute of Earth Sciences, Geological Survey of Iran, Meraj Avenue, Azadi Square, Tehran, Iran
*1
safari.ho@gmail.com; 2 ghassemi.m.r@gmail.com; 3Ranarazavi@ymail.com
Abstract The Lahijan fault zone (LFZ) is a transverse fault placed in a Forestall area of western Alborz Range, and cuts across this fold-thrust belt along the Sepid-rud valley. The results were later completed with field investigations. Analysis of the results of Geoinformatics Techniques (GiT) helped us to determine the limits and kinematics of the main fault zone and other related faults. The results showed that LFZ with N55E general strike, 90 km length and 30 km width extend from Sepid-rud dam to the Lahijan city. This fault zone, as a transversal fault, truncated and offset the western part of Alborz fold-thrust belt and thus, caused many structural complexities in this region. The results of structural investigations showed that LFZ was established as a leftlateral strike-slip fault zone. Several fault trends are generated by this tectonic regime. Keywords Alborz Fold-thrust belt; GiT, Left-lateral Strike-slip Fault; Geometrical and Kinematic Analyses
Introduction The Alborz Mountain ranges extends between the Talesh Mountains, in the west, to the Kopet-Dagh Mountains in the east (Djamour et al. 2010; Radjaee et al. 2010; Ritz et al. 2006; Allen et al. 2003b; Berberian& Yeats 2001) (Fig. 1). Active faulting, recent volcanism and high surface elevations are important characteristics of this area (Sadid khouy et al. 2006; Safari & Gholami 2011). This Orogenic belt with ~100 km width and ~650 km length is branch of the AlpineHimalayan Orogenic belt, formed as V-shape foldthrust belt due to collision of Eurasian plate with Iranian micro-plate along the several Orogenic phases (Sadid khouy et al. 2006; Allen et al. 2003a; Jackson et al. 2002; Stocklin 1974). The V-shaped pattern of Alborz ranges was formed by activity of numerous
faults with strike mainly parallel to this mountain range (Berberian 1983). A recent global positioning system (GPS) study showed that N-S shortening across the Alborz occurs at 5 ± 2 mm/yr and that the left-lateral shear across the overall belt has a rate of 4 ± 2 mm/yr (Djamour et al. 2010). The N-S convergence of Alborz-central Iran coupled with the south-west ward motion of the South Caspian Basin (respect to central Iran) leads to a NNE-SSW transpression regime in Alborz. The detailed analysis of the geological structures (Allen et al. 2003a; Ritz et al. 2006) showed that the overall oblique left-lateral motion across the Alborz is thought to be partitioned onto separate strike-slip and thrust faults, both parallel to the trend of the belt (Tatar et al. 2007). This fold-thrust belt is divided into three parts, composed of western, central and eastern zones. These zones are separated by major morphotectonic features. Many Tear faults truncate this mountain range. These transverse tear faults, as lateral ramps, facilitated the N-S movements of different thrust bodies in the foldthrust belt. One of these transverse faults is probably the Lahijan fault zone (LFZ) that is located in a Forestall area of Gilan province in Northern Iran. Unfortunately, the large part of this fault zone is covered by forested areas. It seems that this covered fault zone, as a tear fault, truncated the western Alborz along the Sepidrud valley. The Sepid-rud is the only river to cross the Alborz from central Iran to the Caspian (Jackson et al. 2002). LFZ was firstly determined after the Rudbar– Tarom earthquake (20 June 1990 Mw= 7.3) (Berberian et al. 1992; Sarkar et al. 2003) and probably extended from the near of Sepid-rud Dam, (near the 1990 Rudbar–Tarom earthquake epicenter) to the Lahijan
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