E. Kosari; A. Bahroudi; M. Talebian; A. Chehrazi
Abstract
One of the essential studies in exploration, exploitation and development of hydrocarbon fields is to evaluate the fault and fracture systems and the role that they can play in reservoir quality and geometry. If the hydrocarbon reservoir is a fractured carbonate reservoir, assessing the mentioned properties ...
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One of the essential studies in exploration, exploitation and development of hydrocarbon fields is to evaluate the fault and fracture systems and the role that they can play in reservoir quality and geometry. If the hydrocarbon reservoir is a fractured carbonate reservoir, assessing the mentioned properties is of great importance. Assessment of the structures should be done simultaneously because of their close relations, and the their probable genesis connection should be revealed. In this research, subsurface data including 2D seismic profiles, underground contour maps and FMI log and eventually analogue modeling have been used for evaluation of probable scenarios explaining formation of faults and fractures. The studied area is located at the front of Zagros deformation belt and the Zagros stresses have apparently not affected it. Two sets of faults of different geometry and role have been detected; the first reverse set (N-S trending) was apparently controller of the reservoir geometry in the structure; the second normal set (NW-SE trending) are most likely causative of the main fractures in the field. It is likely that positive inversion tectonic of the basin led to the development of this field in form of a pop-up structure. Based on the interpretations, the internal normal faults have been formed probably by the rise of Hormuz salt or by local stretching due to left-lateral component of the boundary reverse faults. Using interpretation of drilling-induced fractures and break-outs derived from FMI, trends of the Shmax and Shmin are determined. Also it was revealed that the natural fractures and the main set 2 of faults are sub-parallel with the fractures induced by drilling. Therefore, the compatibility between trends of the natural fractures, breakouts and local normal faults can suggest a tectonic origin for the natural fractures.
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. 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.
Arman Heravi; H. Nazari; A. Shahidi; M. Talebian
Abstract
The Garmsar Fault with a length of about 75 km and E-W trend is located in Garmsar.This Fault observed in north of Garmsar and eastern part of central Alborz with slop toward north, continus east of Eyvanakey Fault. Base of the morphotectonical investigation, along the Garmsar Fault this ...
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The Garmsar Fault with a length of about 75 km and E-W trend is located in Garmsar.This Fault observed in north of Garmsar and eastern part of central Alborz with slop toward north, continus east of Eyvanakey Fault. Base of the morphotectonical investigation, along the Garmsar Fault this fault is devided to 5 segments from east (Dehnamak village) to the west (Eyvanakey), with attention to this segmentation we could consider the branch of kuh-e-sorkh Fault at west of Garmsar in kuh-e-sorkh anticline such as separated fault with slop toward north and pressure mechanism with small left-lateral strike slip component. Base on observations and Paleostress measurment along the Garmsar Fault in Bon-e-kuh station and eastern segment of this fault, we could consider that Paleostress direction around Neogen Time, is N-S with pressure component. However, base of data, is gain from morphotectonical investigations, young and overcome mechanism in eastern segment (Fault segment 1) left-lateral with pressure component, on the other side, in kuh-e-sorkh anticline at western part of research area, considered stress direction at quaternary period E-W under the effect of Thrust fault with left-lateral component. Base of this study from geometry point of view, the Garmsar Fault is a fault with slop toward north which is able to devide in to 5 segments that is strike and geometry of each fault segment mechanism is from left-lateral with pressure component until Tension and the Garmsar Fault is considered as an active fault in quaternary period. Maximum and minimum on the left horizontal displacement measured on the fault equal to 220 meters and 4 meters of a fault on the part of the fault system and third segment on the drainages of Garmsar displaced is visible.
A. Fathian Baneh; S. Solaymani Azad; H. Nazari; M. Ghorashi; M. Talebian
Abstract
Tabriz city, the most highly population city of NW Iran, is located close to the North Tabriz Fault (NTF). This 150 km right-lateral strike-slip fault consists of two major fault segments arranged in right-stepping pattern. A pull-apart basin has been formed within the overlap zone of these fault segments ...
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Tabriz city, the most highly population city of NW Iran, is located close to the North Tabriz Fault (NTF). This 150 km right-lateral strike-slip fault consists of two major fault segments arranged in right-stepping pattern. A pull-apart basin has been formed within the overlap zone of these fault segments due to the recent right-lateral motion. The basin margins mark by fault branches and fault splays, which connect these two major segments of NTF. High level historical earthquakes occurrence shows seismic activity of NTF. Among which, NTF is responsible of at least two destructive earthquakes occurred in 1721 A.D. (Ms 7.3) and 1780 A.D. (Ms 7.4). This fault has not experienced any strong seismic events since 1780 A.D. Within past decades, it has been tried to recognize large number of old earthquakes utilizing paleoseismological investigation. Previous paleoseismological studies have been focused on the NW and SE segments of the fault. In the present study, to complete the data sets necessary to assess the seismic hazard related to Tabriz city, we focus on overlap zone of the two main fault segments. Using aerial photos, satellite images and field investigations, a potential site has been recognized within the zone (6 km NW of Tabriz City) to perform paleoseismological studies. Trench opened perpendicular to fault scarp strike and focused paleoseismological investigations in that, show evidences of at least two macroseismic events.
M. Nemati; D. Hatzfeld; M. R. Gheitanchi; M. Talebian; N. Mirzaei; A. Sadidkhouy
Abstract
The Shahroud fault system plays important role in seismotectonic of the eastern Alborz. In this paper we have surveyed the seismicity of the middle-eastern Alborz and its southern area. At this investigation, the data of the Geological Survey of Iran local seismological networks, the seismological networks ...
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The Shahroud fault system plays important role in seismotectonic of the eastern Alborz. In this paper we have surveyed the seismicity of the middle-eastern Alborz and its southern area. At this investigation, the data of the Geological Survey of Iran local seismological networks, the seismological networks of the Institute of Geophysics of the University of Tehran and the International Institute of Earthquake Engineering and Seismology of Iran were used for processing the focal mechanism of micro-earthquakes and the south of Damghan earthquake and its greatest aftershock. Distribution of the micro-earthquakes and the south of Damghan events epicenters indicate intense activity of the Shahroud fault system and the Toroud fault. Focal mechanisms of them shows near vertical dipping of the faults and left lateral mechanism of the western segments of the fault system and the Toroud fault. The focal mechanisms suggest the Astaneh, Chashm and Firouzkuh faults from the system fault behave in a same manner with no deference between them at depth and have seismic potential proportion to their total length. Also due to left lateral mechanism of the south of Damghan earthquakes, Toroud fault treats like of the eastern Alborz seismotectonically and this area could cover Toroud fault.
Z. Hosseinmardi; M. Ghorashi; M. R. Ghassemi; M. Talebian
Abstract
The outcrop of northern part of North Eshtehard Thrust has been selected for study of structural evolution and geological processes. The study area includes folding structures with different scales from regional to outcrop which belong to fault related folding category. Analysis of joints in the region ...
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The outcrop of northern part of North Eshtehard Thrust has been selected for study of structural evolution and geological processes. The study area includes folding structures with different scales from regional to outcrop which belong to fault related folding category. Analysis of joints in the region among upper red formation strata shows two main sets which are usually tensional (j1 & j2). These joints are visible in sandstone units of upper red formation and most of them are filled with gypsum. It is obvious that the j1 joints are younger than j2. j1 and j2 joints are related to folding processes. The local stress field which could be measured from the joint study is σ1=337/75, σ2=189/13 and σ3=077/03 and corresponds with the given paleostress direction for southern part of central Alborz.
T. Majidi Niri; H. Nazari; M. Ghorashi; M. Talebian; A. Kaveh Firooz
Abstract
Pishva fault with about 35km length is located between Alborz and Central Iran structural zones in southeast of Varamin. General trend of the fault is NW-SE (N38W, 33NE) which has reverse mechanism accompanied by sinistral component. Achieved Morphotectonic studies along the Pishva fault reveal its activity. ...
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Pishva fault with about 35km length is located between Alborz and Central Iran structural zones in southeast of Varamin. General trend of the fault is NW-SE (N38W, 33NE) which has reverse mechanism accompanied by sinistral component. Achieved Morphotectonic studies along the Pishva fault reveal its activity. 3-5 seismic events with recurrence time of 3265 years are identified by studying on two Paleoseismic trenchs T1 and T2, The youngest and oldest events are 0.87 Ka and 29 Ka respectively. According to Wells and Coppersmith equations (1994), the biggest and smallest computed earthquake magnitudes are respectively 7.08 and 5.9. It would be possible to assign Shahr-e-Rey 1384 AD earthquake to this fault, since Event 1 is 870 years old.
