IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS013 Poster presentation 2234
Camparison between fault lineaments on satellite images and Riedel
model shear: a case study in Damavand Volcano, Central Alborz Mountains,
Northern Iran
Mrs. Safieh Omidian
Department of Geology MSc. Student of Petrology, Department of Geology IASPEI
Jamshid Hassanzadeh, Mohsen Eliassi, Faribourz Gharib
The Alborz Mountains that fringe southern Caspian have deformed in response to the Arabia-Eurasia
collision since ca. 12 Ma. An estimated shortening of 53 3 km has been accommodated by a
combination of range-parallel, conjugate strike-slip faulting and range-normal thrusting. About 17km of
this shortening has been interpreted to be accommodated by westward relative motion of a crustal
block bounded by conjugate dextral and sinistral strike-slip fault systems. It has also been shown that a
change of dextral component of reverse faults to sinistral ones took place at 52 Ma ago. We have used
remote sensing data in order to investigate the possible correlation between the lineaments pattern and
Riedel model. The study was focused on Damavand volcano and its surrounding highlands; and Landsat
ETM data were utilized to spot fault lineaments. By using several factors 2540 lineaments were
distinguished. We discuss: 1) how comparable the rose diagram of these fault lineaments is with the
Riedel model and 2) how a useful tool is this model to predict geometry of structures that may form in
shallow crustal rocks deformed in a strike-slip regime. A principal displacement zone (PDZ) commonly
forms parallel to the shear couple. Due to the direction of Arabia-Eurasia collision (N010-040), the
prevailing structural trend is WNW-ESE; and 115 was taken as the dominant trend. Normal faults (T)
should form perpendicular to the direction of maximum tensile stress. Riedel shears (R) form at an
angle of (~15-20) with the PDZ, where is the angle of internal friction for the faulted material (we
considered which is typical of the upper crust). R shears will have the same sense of strike-slip motion
as the PDZ, and they typically form a suite of en echelon fractures. Conjugate Riedel shears (R′) can
form at (~60-75) relative to the PDZ. These conjugates have the opposite senses of strike-slip motion
as the main fault. Finally, folds and thrust faults should form with their axes or traces, respectively,
normal to the main compressive stress (P). Fold axes will initially be oriented at about 45 to the PDZ.
Activation of first order phases results in second and third order R, R′, T and P systematic fractures.
Directions of the lineaments spotted on satellite images were tested with directions of the structural
elements predicted by Riedel model for both sinistral and dextral systems. Most lineaments are
compatible with this model. Exercising with Riedel model can provide indications for characteristics that
fit each lineament.
Keywords: alborz, damavand, riedelmodel