M Foroutan; H Nazari; B Meyer; M Sébrier; M Fattahi; K Le Dortz; M Ghorashi; Kh Hessami; M. R Ghassemi; M Talebian
Abstract
The Dehshir fault system (DFS) including six fault segments forms the western border of NS-striking active dextral strike-slip fault cutting the Sanandaj-Sirjan, Uromieh-Dokhtar magmatic arc, and Central Iran. This active fault system right-laterally offset Eocene volcanic rocks and Quaternary alluvial ...
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The Dehshir fault system (DFS) including six fault segments forms the western border of NS-striking active dextral strike-slip fault cutting the Sanandaj-Sirjan, Uromieh-Dokhtar magmatic arc, and Central Iran. This active fault system right-laterally offset Eocene volcanic rocks and Quaternary alluvial fans. Geomorphic evidence imply the activity of the DFS in the Late Quaternary, and paleoseismic investigations revealed seismic movements along the Marvast fault segment during the Late Pleistocene and Holocene timescales. In order to unravel the seismic history of the DFS over the intermediate geologic (103 -105 yr) time scale, and based on the morphotectonics and sedimentary-stratigraphic properties, three paleoseismic sites have been selected along the 35-km-long stretch of the Marvast fault segment. The southern site (Harabarjan) shows steep fault branches of N140±10º strike with sub-horizontal striations in dextral component. Another trench has been excavated at the North Marvast site whitin the Late Pleistocene-Holocene alluvial and colluvial deposits. OSL analysis of loose quartz rich deposits yielded an age of ~72 ka for the oldest exposed sediments. Paleoseismic stduies along the Marvast fault segment provide evidence for the occurrence of several large seismic events associated with surface ruptures along the DFS. The chronology of paleoearthquakes on the Marvast segment indicates that at least 7 large (≈Mw > 7) earthquakes occurred in the last 43 ka with an average recurrence time of 3650±150 years. The most recent earthquake, event I, occurred ~2200 years ago, which associated with 2-4 m of dextral slip and >40 km surface rupture along the Marvast fault segment. These investigations are compatible with the lack of destruction in the Marvast historical (~1300 years) castle, located
M. Nemati; B. Oveisi; M. Foroutan; M. J. Bolourchi
Abstract
A MN=5.8 (Institute of Geophysics Seismological Center, University of Tehran) earthquake in 2010 July 20 shook southeastern Zagros, over the active ramp of the Mountain Front Fault (MFF). A body killed during the earthquake and it’s aftershocks have affected hundreds of square kilometers around ...
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A MN=5.8 (Institute of Geophysics Seismological Center, University of Tehran) earthquake in 2010 July 20 shook southeastern Zagros, over the active ramp of the Mountain Front Fault (MFF). A body killed during the earthquake and it’s aftershocks have affected hundreds of square kilometers around the epicenter. The shook area has experienced many moderate to large earthquakes at the historical time and the MFF recognized as their responsible. With the combination of the waveforms of seismological networks for the Institute of Geophysics, University of Tehran, International Institute of Earthquake Engineering and Seismology of Iran and a local network of the Geological Survey of Iran at Fars province, the source parameters of the earthquake were modified. For this event the ML magnitude computed 5.4 and a depth of 10 km were estimated. This event is related to the growing of anticlines neighboring the MFF with a fault propagated through their cores as of the other reverse earthquakes in Zagros. Tilting and uplifting of young alluvial deposits neighboring them are evidences for this growing. The iso-seismal curves elongated along MFF and the maximum intensity in MM and JMA scales was estimated VII. A small conjugate shear zone with maximum 1 km elongation, 150 m width and 10 cm of both vertical and right lateral dislocations with the strike of N45˚E, was mapped. Finally for this earthquake there was not any rupture except this T kind rupture which not merits the earthquake magnitude.
M. Basiri; H. Nazari; M. Foroutan; S. Solaymani Azad; M. A. Shokri; M. Talebian; M. Ghorashi; M. J. Bolourchi; A. Rashidi
Abstract
The Golbaf area in Kerman province (SE Iran) has experienced five earthquake of Mw 5.4-7.1 between 1981 and 1998. Occurrences of these earthquakes in seventeen years time interval indicate that occurrences of earthquakes on the Golbaf (Gowk) fault system have a clustering model. In this study we use ...
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The Golbaf area in Kerman province (SE Iran) has experienced five earthquake of Mw 5.4-7.1 between 1981 and 1998. Occurrences of these earthquakes in seventeen years time interval indicate that occurrences of earthquakes on the Golbaf (Gowk) fault system have a clustering model. In this study we use morphotectonical and paleoseismological evidences to show that seismic behavior of this fault in the past has a clustering model in some time intervals. For this purpose at the first near-field morphotectonical analysis performed using real time kinematics (RTK) GPS survey and digital elevation model and digital topographic map of surface ruptures of past earthquake prepared with high accuracy. Detail analyzing of this model indicate that the rake angle of Golbaf fault is about 10 degree. This result is in agreement with rake angle calculated from seismological methods and also observations of slickenlines on rupture plans that show dominant right lateral strike slip mechanism of the Golbaf fault. According to the paleoseismological investigations which were associated with digging a trench perpendicular to the Golbaf fault indentified four Paleoearthquake with magnitudes of Mw>6.6. By using some of empirical relationship, maximum magnitude of oldest Paleoearthquake calculated about Mw 8.2 that it is unbelievable and show similar to today that occurred five earthquake during short time interval on this fault, occurrence of earthquake in the past on some of time interval have clustering model so that occurred a lot of big earthquake in short time interval that there was not enough opportunity for sedimentation and record of evidences of this earthquake separately.
M Foroutan; H. Nazari; B. Meyer; M. Sébrier; M. Fattahi; K. Le Dortz; M. Ghorashi; Kh. Hessami; M. R. Ghassemi; M. Talebian
Abstract
The evaluation of seismic potential along the Dehshir fault with 550-km length (by count of northern and southern splays) is critical considering that more than 3.5 million people live in cities and towns located at vicinity of the fault. The Dehshir fault is considered as westernmost limit ...
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The evaluation of seismic potential along the Dehshir fault with 550-km length (by count of northern and southern splays) is critical considering that more than 3.5 million people live in cities and towns located at vicinity of the fault. The Dehshir fault is considered as westernmost limit of N-striking dextral strike-slip faults set that slice Central and eastern Iran. Due to the lack of large recorded earthquakes (instrumental and historical) in Central Iran, access to seismic potential of active faults by studying the earthquake catalogs seems to be impossible. No instrumental earthquake has been recorded greater than mb 4.7 around the Dehshir fault and also historical data shows no evidence for occurrence of large earthquake around the fault. No sign of destruction in Marvast historical castle (at a less than 10 km far from the Dehshir fault) built in Islamic period (~700-1250), shows any remarkable seismic activity until 750-1300 years ago. However, several evidence of geomorphologic markers such as drainages, gullies, streams and alluvial fans offsets, represent activity of the Dehshir fault in Late Quaternary. Of Geomorphic evidence at Marvast and Harabarjan sites record dextral - slip on the Dehshir fault during the Late Pleistocene-Holocene as major movement with minor dip - slip component. Rake of the fault movement has been considered for assessing to amount of horizontal and vertical slip rate on the Dehshir fault. This value in the North Marvast site has been calculated ~10 degrees and according to right bank offset on the Marvast river is ~7 degrees with horizontal and vertical displacements of 13 m and 1.5 m, respectively. Combining cumulative offset markers with OSL dating implies the Dehshir fault in Late Pleistocene-Holocene time period slips at horizontal and vertical components about 1±0.3 and 0.1 mm yr-1, respectively. We observed a minimum dextral offset along the Marvast fault segment in west of Harabarjan about 2 m that allow us assuming the related magnitude and date of last large paleoearthquake on the Dehshir fault is about Mw 7 and 2000 years ago, respectively.
