Kinematic significance of fold- and fault-related fracture systems in the Zagros mountains, southern Iran

Initiation and formation of folds and the Kazerun high-angle fault zone, in the Zagros fold-and-thrust belt, were related to the continuing SW–NE oriented contraction that probably initiated in the Late Cretaceous, and intensified, starting in Miocene, when the Arabian and Eurasian plates collided. The contraction that led to folding and thrusting of the Phanerozoic sequence in the belt has led to the strike–slip reactivation of basement faults that formed during the Precambrian. Two major systems of fractures have developed, under the same regional state of contraction, during the folding and strike–slip faulting processes. Folding led to the formation of a system of fold-related fractures that comprises four sets of fractures, which include an axial and a cross-axial set that trend parallel and perpendicular to the confining fold axial trace, respectively, and two oblique sets that trend at moderate angles to the axial trace. Slip along high-angle, strike–slip faults formed a system of fractures in the damage zone of the faults (e.g., Kazerun), and deformed folds that existed in the shear zone by rotating their axial plane. This fault-related fracture system is made of five sets of fractures, which include the two sets of Riedel shear fractures (R and R′), P- and Y-shear fractures, and an extensional set.

Remote sensing analysis of both fracture systems, in a GIS environment, reveals a related kinematic history for folding outside of the Kazerun shear zone and faulting and deformation (fracturing and rotation of folds) within the Kazerun fault zone. Rotation of the folds and formation of the five sets of the fault-related fractures in the Kazerun shear zone are consistent with a dextral motion along the fault. The mean trends of the shortening directions, independently calculated for the fold- and fault-related fracture systems, are remarkably close (N53 ± 4°E and N50 ± 5°E, respectively), and are perpendicular to the general NW–SE trend of the Zagros fold-and-thrust belt. Although segments of the Kazerun fault are variably oriented within a narrow range, the angular relationships between sets of fault-related fractures and these segments remain constant.     

Verification of a new method for evaluation of liquefaction potential analysis

The seismic response of existing earth dams in Iran is important after an earthquake both to provide emergency supplies and to society as well as to ensure structural safety in engineering terms. Better seismic capacity of earth dam results in less structural damage and reduced impacts following an earthquake disaster. Indirect as well as direct costs following earthquakes have gained much attention from both the engineering and socioec onomic research communities in the last few decades. This study is a valuable tool used to study the response of geotechnical structures to infrequent or extreme events such as earthquakes. The Avaj earthquake (2002, Iran) was applied to a series of model tests which was conducted to study the response of soil profiles under seismic loading. The acceleration records at different locations within the soil bed and at its surface along with the settlement records at the surface were used to analyze the soil seismic response. A combination of several software packages with a generated visual user interface computer code by authors named as “Abbas Converter” were employed to evaluate the variation of shear modulus and damping ratio with shear strain amplitude to assess their effects on site response. The proposed method was applied to the Korzan earth dam of Hamedan province in Iran. Site response analysis using the measured shear wave velocity, estimated modulus reduction, and damping ratio as input parameters produced good agreement with the computed site response in this study.