M Rustaei; M Rustaei; B Zamani; M Nemati
Abstract
In this study, the stress regime governing the Gorgan plain area (NE Iran) is calculated using inversion analysis based on earthquake focal mechanism solutions. In addition, a kinematic model is presented for hidden faults in this area. To gain this goal, the earthquakes occurred in this region and had ...
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In this study, the stress regime governing the Gorgan plain area (NE Iran) is calculated using inversion analysis based on earthquake focal mechanism solutions. In addition, a kinematic model is presented for hidden faults in this area. To gain this goal, the earthquakes occurred in this region and had available focal mechanism solutions were first selected for the inversion analysis. After applying the inverse analysis on the seismic data, the results indicate that there is a NW-SE (N42W)-trending tensional stress regime over the area. This is represented by the dominant local extensional structures such as shallow normal faults. Also the intermediate and minimum stress axes are close to horizontal direction, and indicate structures such as strike slip faults in the region. This is in agreement with most of the seismic dataset involved in the inversion analysis. By examining the previous studies and their results, more attempts were made to provide a kinematic model for this area. The Gharnaveh fault system comprises two sinistral faults (Marave-tappeh and Incheboroun), which are assumed to extend at eastern termination along an E-W direction under the Gorgan plain sediments up close to the Caspian Sea. Movement along these two faults under the sediments cause a clockwise rotation in the zone enclosed between them. Direction of this zone, which is affected by the faults, is consistent with the trend of regional seismicity. The proposed model can be used to account for many of the focal mechanism solutions of the earthquakes occurred, as well as the depth of the events. Most earthquakes occurred in this region are associated with the normal or left-lateral components. On the other hand, superficial structures such as mud volcanoes and fault-related folds (in the north of Aq qala) can be explained by this model, although lack of subsurface geophysical data in this area makes this model somehow speculative.
M Roustaee; B Zamani; P Navabpour; M Moayyed
Abstract
Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected ...
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Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected drainage of large rivers, cutting and displacement of alluvial fans across the segments of the fault zone. The amount of alluvial fans displacement in -Dasht e zurabad- (along the segment of the Kamarkassan fault) was estimated nearly 1.8 km. In this research, the neotectonics and mechanism of the Siah Cheshmeh- Khoy fault zone has been studied by Inversion method, based on the combination of focal mechanisms of earthquakes and different shear- fault planes. In this paper, we utilized all of the focal mechanism solutions of earthquakes existent in this area. Besides, the data measured conclude shear planes whit slickenside and the measured fault planes across the Siah Cheshmeh- Khoy fault zone. These data were gaged in 7 sites and 45 shear planes with slickenside. Initially the main axis were obtained in all sites by Inversion method; then by combination of focal mechanisms of earthquakes and the measured data, the stress state of this region was evaluated. The results obtained of this analysis indicate strike- slip stress with NNW-SSE (N162°) direction of compression component and ESE-WNW (N255°)direction of extension component in this area. It can be stated that the mentioned stress regime was the main factors controlling the recent kinematic movements of faults and strong earthquakes in the region. Also the right- lateral strike- slip motion of the Siah Cheshmeh- Khoy fault segments are affected by this stress (under the influence of this stress). The results of this research are compatible with the results of the geodetic studies and the GPS measurements in the region that were done by other researches.
A Nouri Mokhoori; B Zamani; M Moayyed
Abstract
Tabriz Fault is one of the major faults of Iran that is situated in the northwest of Iran and central part of the Iranian Azerbaijan. The fault has a well-known paleoseismological history, and being situated adjacent to the Tabriz city with two millions ofinhabitants makes ita big seismic hazard. In ...
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Tabriz Fault is one of the major faults of Iran that is situated in the northwest of Iran and central part of the Iranian Azerbaijan. The fault has a well-known paleoseismological history, and being situated adjacent to the Tabriz city with two millions ofinhabitants makes ita big seismic hazard. In this research,a study of instrumental seismic data, remote sensing and field observationsalong the Tabriz Fault Zone from north of Miyaneh to the west of Marand cities helped us to define three main segments along the fault. Fault Movement Potential (FMP) has a close relationship with tectonic stress in and around a given fault zone. Therefore, the stress state was analyzed using direct inversion method to estimate potential movement of each segment of the Tabriz Fault. Results showedthat the middle and southern segments of the Tabriz Fault have a FMP of 0.67-0.73,implying their high potential of reactivation and generating large and destructive earthquakes, assupported bythe richseismic history of these segments. Therefore the results of this research estimatea 70% movement probability for the North Tabriz Fault. In contrast, the northern segment of the Tabriz Fault (western part of the fault close to the Marand city)showsa FMF of 0.3-0.37,indicatingits lower potential of reactivation compared to the middle and southern segments. This is also in agreement with the poor seismic history of the northern segment.
