Conference abstracts (2000-01)
ASC (Asian Seismological Commission) on "Seismology, earthquake hazard
assessment and earth's interior related topics"- Iran, Tehran; 2000
Block rotation evidences in the simple shear zone between North Tehran and Niavaran
thrusts
Rezaeian, M.; Shahriari, S.
The study area is located in the northernmost part of the Greater Tehran, between North
Tehran Thrust (NTT) and Niavaran Thrust (NT). The NTT is about 100 km long and marks
the tectonic border between the Alborz range to the north and Pliocene-Quaternary alluvium
to the south. NT is about 18 km long and is situated at about 2 km south of NTT. The study of
air-photographs and field work indicated major fault set, suggesting sinistral simple shear
zone between these thrusts. This set is about 2 km long, attitude N40-50E, dextral strike slip
faults and was first developed as T or R fracture within the simple shear zone. Continuation of
deformation caused later dextral displacement of about 150-500 m along this set and its anticlockwise rotation around vertical axis, also there is an evidence of block rotation around
horizontal axis. The mechanism of block rotation in this region conforms to experimental
models of block rotation. There are many minor fractures in this region which correspond to
T, R and P shears in a second order dextral simple shear zone.
31st International Geological Congress- Brazil, Rio de Janeiro; 2001
Neotectonic evidences on activity of North Tehran & Niavaran faults
Rezaeian, M.
The study area is situated between latitudes 35,29 and 35,50 N and longitudes 51,15 and
51,42E. Major part of the study area is within the Greater Tehran. The area is basically is
covered by glacio-fluvial sediments of Quaternary. Mountain front sinuosity and valley floor
ratio indexes indicate that the region is young tectonically, showing an activity of number of
about one. Study of the landforms that contain alluvial fans and those associated with active
faulting indicates that tectonic activity is translated from the North Tehran thrust into the
pediment front. The study also suggests a sinistral strike slip component superimposed on the
predominant reverse component of the fault movement within the area. The Daneshgah
Shahid Beheshti fault set (attitude N50E, 85NW) first developed as T or R fractures in a
simple shear zone between North Tehran Thrust and Niavaran Thrust. These fractures are
resulted from sinistral component along aforementioned thrusts. Continuation of deformation
caused later dextral displacement of about 150-500 m along this set and its anti-clockwise
rotation (4-5 degree). Furher block rotation moved these into the compressive zone of
deformation during the latest stage of activity, and caused reverse dip slip displacement of
about 1km along the faults. That occurred before deposition of upper part of C formation.
Because the activity is related to the movement along North Tehran Thrust therefore, it
suggests the time of latest activity of main structure of North Tehran Thrust.
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