A Alizadeh; R Safari
Abstract
Seismic values are the main parameters in evaluating the neotectonic activity of a region. In August 11, 2011, two Mb=6.4 and Mb=6.3 earthquakes occurred in Ahar-Varzaghan region within 11 minutes. Seismotectonic investigations imply that the faults generating the events are the young faults of the regions. ...
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Seismic values are the main parameters in evaluating the neotectonic activity of a region. In August 11, 2011, two Mb=6.4 and Mb=6.3 earthquakes occurred in Ahar-Varzaghan region within 11 minutes. Seismotectonic investigations imply that the faults generating the events are the young faults of the regions. Also, distribution of the epicenters represent a pattern consistent with the fault trends in the area. Temporal and spatial distribution of the earthquakes (fractal analysis) as earthquake pre-indicators together with a-b values were used toassessthe neotectonic activity and explore the seismic model of the Ahar area. Results showa sharp decrease in b-value,indicating that the main shock was associated with a zone of high strain rate. The seismic model presented for the Ahar area illustrates three periods after the main shock including: 1) an early quiescence Q1, 2) an aftershock period B, and 3) a late quiescence Q2. The rather increase in b-value during the Q2period is interpreted to indicate stress decrease in the region.
B Zamani G; N Kiyanizadeh; H Parhizgari
Abstract
In this research, the stress state in the Zagros fold and thrust belt is studied using inversion method analysis of focal mechanisms of earthquakes related to active faults of this region. Geological, structural and seismic differences throughout the Zagros fold and thrust belt led us to divide it into ...
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In this research, the stress state in the Zagros fold and thrust belt is studied using inversion method analysis of focal mechanisms of earthquakes related to active faults of this region. Geological, structural and seismic differences throughout the Zagros fold and thrust belt led us to divide it into five structural zones to make the analysis of a homogenous stress state in each zone possible. Stress analysis in the Zagros belt was done using a large body of available earthquake dataset. For this purpose to be achieved, focal mechanism data of the Zagros earthquakes was first collected from different sources, then were integrated in the analysis after doing a process of corrections and controls. The present research uses Dyngli Software to analyze stress separation in the defined structural zones. Results show that different parts of the Zagros fold and thrust belt are characterized by at least three, and in some cases four, separate stress regimes. It is evidently shown that the orientations of the first and third stress regimes in Zones 1 and 2, third and fourth regimes in Zone 3, third regime in Zone 4, and first, second and fourth regimes in Zone 5 are in a good agreement with previous studies particularly GPS geodesy results. Crustal displacement directions already determined by GPS geodesy show that, on the one hand, shortening is not uniform across the whole length of the Zagros ranges, and on the other hand strain field orientations and fault slips are also different. This could be related to multiple stress regimes in the Zagros belt. Furthermore, considering a thin-skinned tectonic model in the Zagros, those stress regimes that are compatible with GPS results seem to occur within the sedimentary cover, causing a relatively continuous seismic response in the form of earthquakes of small magnitude. Therefore, the first, second and fourth stress regimes in Zone 1, second regime in Zone 2, first and second regimes in Zones 3 and 4, and third regime in Zone 5 are suggested to be linked to basement, in which stress concentration causes large magnitude earthquakes in Zagros. Also, results showed that compressional stress orientations are normal to the structural trends in all zones; the second compressional regime in Zones 1, 2, 3 and 5, and first regime in zone 4 are normal to the folded and thrusted structures.
M.A Shokri; M Foroutan; M Nemati; M.J Bolourchi; SH Javadipour; B Oveisi
Abstract
The Touchahi earthquake of Aug 27, 2010 (MN 5.9; IRSC- Mw 5.7; USGS) occurred at 19:23:49 UTC (23:53:49 local time on 5 Shahrivar 1389) in south of Damghan city. No foreshock were reported before this earthquake whereas 85 aftershocks (MN 1-5) were registered by IRSC until 1 month after the mainshock. ...
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The Touchahi earthquake of Aug 27, 2010 (MN 5.9; IRSC- Mw 5.7; USGS) occurred at 19:23:49 UTC (23:53:49 local time on 5 Shahrivar 1389) in south of Damghan city. No foreshock were reported before this earthquake whereas 85 aftershocks (MN 1-5) were registered by IRSC until 1 month after the mainshock. According to our field study after the event, surface rupture of causative fault was not observed but we measured some fractures related to this event with dominant strike of N120º-140º. According to our observations of 32 towns and villages that were damaged in this seismic event, maximum intensity (I0) of VIII+ in MMI scale occurred near the Touchahi village in ~85 km south of Damghan city. Unfortunately in this earthquake 4 people were killed. Focal mechanisms of the Touchahi seismic event and its greatest aftershock is solved using the first P motion method. The fault plane solution show near vertical plane for the causative fault of the earthquake and suggests a left- lateral mechnism. The mechanisms associated with the fault show mainly left-lateral strike–slip motion, on a NE –SW striking fault plane. Based on location of the earthquake epicenter, its aftershocks location, the fault plane solution (left-lateral strike-slip with N039º strike and dip direction toward NW) and field observations, the causative fault of Touchahi earthquake is one of the active fault branches that is situated in north of Darestan mountain and south of Touchahi, Koohzar and Kooshahi villages. This fault with left-lateral strike-slip mechanism by general strike of NE-SW and dip direction toward NW is indicated as Touchahi fault.
U Alladin; M Talebian; M Arian; M.M Ahmadi
Abstract
Earthquake is an undeniable phenomenon that can cause financial and social damage if occur in populated areas. Vulnerability of buildings is not just function of magnitude and distance from the epicenter but also depends on physical properties of soil. In this study we evaluate physical properties ...
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Earthquake is an undeniable phenomenon that can cause financial and social damage if occur in populated areas. Vulnerability of buildings is not just function of magnitude and distance from the epicenter but also depends on physical properties of soil. In this study we evaluate physical properties of alluvium in an area of approximately 100 square kilometers in west of Tehran between longitudes 51 º 15´ to 51º 23´ and latitudes 35º 40´ to 35º 50´. As a first step we collected field data regarding the alluvium deposits as well as location of Quaternary faults. We then combined this information with data from 440 boreholes which were aquired from more than hundred urban development projects. We use sedimentological diagrams of the boreholes to define three zones of coarse-, intermediate- and fine-grained material in the region. We considered physical and mechanical properties of the sediments to produce seismic amplification map of the area which shows three zones of high, moderate and no amplification. Finally, we investigated liquefaction potential of sediments, considering ground water level and structure of the basin and we have concluded that there is no potential of liquefaction in the area of study.
SH Pourbeyranvand; M Tatar
Abstract
Having knowledge of stress variations in the Zagros region, southwest Iran is necessary to study the deformation resulting from oblique collision between the Eurasian & the Arabian plates and to obtain insight into the complicated tectonics of the region. In this study, earthquakes focal mechanism ...
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Having knowledge of stress variations in the Zagros region, southwest Iran is necessary to study the deformation resulting from oblique collision between the Eurasian & the Arabian plates and to obtain insight into the complicated tectonics of the region. In this study, earthquakes focal mechanism data were used to collect information on the state of stress in 12 subdivisions of the data including teleseismic and local events in the Zagros region. The stress axis show noticeable variations in the Zagros region, especially around the Oman Line. The angular difference between the stress & strain axis increases from the southeast to the northwest of the ZagrosMountain. The deformation partitioning due to pre-existing faults and fractures and introducing a weak zone in the NW Zagros under the influence of the Main Recent Fault activity may explain this increasing.
M Nemati; J Hollingsworth; M.R Ghassemi
Abstract
Our research focuses on the seismotectonics of the north of Eastern Alborz and southeast of the Caspian Sea. Eastern part of the Caspian fault, and seismological active plain situated in north of the area have been studied. The seismological data of microearthquakes (ML>4.5) recorded by the local ...
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Our research focuses on the seismotectonics of the north of Eastern Alborz and southeast of the Caspian Sea. Eastern part of the Caspian fault, and seismological active plain situated in north of the area have been studied. The seismological data of microearthquakes (ML>4.5) recorded by the local network of the Geological Survey of Iran (installed during 2009 and 2010) and regional seismicity located by seismological networks of the Geophysics Institute of University of Tehran and International Institute of Earthquake Engineering and Seismology of Iran were used. Also geomorphological evidences in the area and dynamic parameters of the 1985 Gorgan earthquake, MS=6.0, are included for getting a better justification. Although deep thrust mechanisms of the 1999, 2004 and 2005 earthquakes indicate N-S compressional regime at depth and normal component of shallow earthquakes (ML>4.5) shows extensional regime at near surface in southeast of the Caspian Sea. The morphological evidences confirm this normal kinematics. In addition, the dynamical parameters of the 1985 Gorgan earthquake and its focal mechanism introduce the Caspian fault as the source of this thrust earthquake. All evidences confirm probable underthrusting of southeast of the CaspianBasin beneath the Eastern Alborz.
M Agh-Atabai
Abstract
In this paper, the properties of temporal distribution of earthquakes in southeast Zagros were studied using multifractal methods. To describe the multifractal characteristics of the occurrence time of events, the generalized correlation dimensions Dq and the singularity spectrum f(αq) were calculated ...
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In this paper, the properties of temporal distribution of earthquakes in southeast Zagros were studied using multifractal methods. To describe the multifractal characteristics of the occurrence time of events, the generalized correlation dimensions Dq and the singularity spectrum f(αq) were calculated for earthquake sequence with magnitudes equal to or larger than the completeness magnitude (M= 4.5). In order to investigation of the spatial variations of seismicity pattern, the study area is divided into the three subareas and the results of the analyses were compared to each other. The calculated multifractal spectra for all subareas indicate that the pattern of seismic activity in these regions is a heterogeneous multifractal phenomenon. However, the graphs of correlation integral functions of the studied subareas have clear differences. Except the transition zone on which there are three scaling ranges, the other subareas show two scaling ranges: short and long time scales. The properties of short time scale are controlled by the distributions of small earthquakes (e.g. aftershocks) in clusters, whereas the long time scale is related to the distribution of larger main earthquakes and the clusters related to them. In the graph of transition zone, the large time scale is divided into two different ranges with a characteristic break on about 3.6 years. This characteristic length means there is another kind of clusters (main shocks) rather than the small earthquake clusters. The graphs of recurrence time of earthquakes support these results and show the shorter recurrence time of events in the transition zone. In addition, the results show that the transition zone has a more heterogeneous multifractal pattern rather than its surroundings.
M Agh-Atabai
Abstract
The Golestan province lies on one of the seismically active zones of the world. The occurrence of numerous historical and instrumental earthquakes in this area indicates its high seismic activity. Therefore, it is necessary to study its seismicity using different methods. In this research, the mono and ...
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The Golestan province lies on one of the seismically active zones of the world. The occurrence of numerous historical and instrumental earthquakes in this area indicates its high seismic activity. Therefore, it is necessary to study its seismicity using different methods. In this research, the mono and multifractal analyses have been applied for quantification of earthquakes pattern in the GolestanProvince. For this aim, the correlation dimension, generalized multifractal dimensions and singularity spectrum f (αq) have been calculated using the correlation integral and fix-mass methods. The epicentral analyses of earthquakes showed that their distribution has two scaling ranges with two different patterns and mechanisms controlling the earthquake pattern in these scales. It seems that the movements of small faults and fractures, which caused increasing the correlation dimension (1.84) and heterogeneity of multifractal structure, controlled the small scale. However, at large scale, the distribution of earthquakes is mostly controlled by the main structural trends, which in turn results in becoming almost linear their correlation dimension and also more homogeneous multifractal structure.
K. Habibi; M. Behzadfar; A. Meshkini; S. Nazari
Abstract
Due to its geographic position and located on the World earthquake belt; Iran is always under threat from earthquakes and several shakes are recorded every year all over the country. The most recent earthquake with 6.8 degree magnitude on the Richter scale hit the city of Bam in 2003 and caused large ...
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Due to its geographic position and located on the World earthquake belt; Iran is always under threat from earthquakes and several shakes are recorded every year all over the country. The most recent earthquake with 6.8 degree magnitude on the Richter scale hit the city of Bam in 2003 and caused large losses of human life and infrastructure. The 2003 Bam earthquake, with more than 30,000 casualties and 10,000 injuries, was the most Destructive earthquake in the current century in Iran. We aim to recognize the main reasons causing these deterioration problems. To this end, we first conceptualize thirteen physical-spatial factors. These factors are analyzed using fuzzy logic and IHPW (Inverse Hierarchy Process Weight) within Geographical Information System. We also attempt to identify the Correlation coefficient analyses between urban vulnerability and damage using Fuzzy logic and GIS. In statistics, correlation and dependence are any of a broad class of statistical relationships between two or more random variables or observed data values. With respect to the covariance between two variables (urban vulnerability map and damage post earthquake) the correlation coefficient is calculated 0.59. The results of the model as applied to the structures of the city of Bam illustrate that a fuzzy approach is a basic tool that can be used to identify urban vulnerability and damage post earthquake incident. Its application to the problem assists in unifying relevant theories and practices.
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.
M. Talebian; S. H. Tabatabaei; M. Fattahi; M. Ghorashi; A. Beitollahi; A. Ghalandarzadeh; M.A. Riahi
Abstract
The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran ...
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The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran block is relatively stable and thus moves to the north with an average velocity of about 13 mm/y. As the stable Afghanistan block lies to the east, the northward motion of Central Iran produces a right-lateral shear in eastern Iran, which is distributed mainly over a few major faults to the west (~5 mm/yr) and east (~ 8 mm/yr) of the Lut desert. Limited information is available about the slip rates of individual faults in eastern Iran; therefore in this study we try to combine all geological, geodetic and available Quaternary dating results to estimate the fault slip rates and distribution of active deformation in eastern Iran. Finally, we report the results from OSL dating of samples taken from uplifted plain deposits near the south end of the Bam-Baravat fault. These results show that this fault is growing in the vertical direction with at a rate of ~ 0.5 mmy-1. Considering geometric relation between the Bam-Baravat and the south Bam earthquake fault, we estimate a slip rate of about 2 mm/y for the south Bam earthquake fault.
M. Asadi sarshar; A. Bahroudi; M. Qorashi; M. R. Ghassemi
Abstract
Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. In fact, moment rate states rate of energy which exists in deformation system. There are three different approaches ...
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Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. In fact, moment rate states rate of energy which exists in deformation system. There are three different approaches to state moment rate that each one express tectonic motion and movement of a region from a particular view. These three approaches consist of: geodetic (surveying), seismic and geology methods. Geodetic method which is determined on the basis of gained strain rate tensor from geodetic data, shows deformation rate (including seismic and aseismic) that is happening in the region at this moment in time. Moment rate which has gained on the basis of historical and instrumental catalogues, shows the total released seismic energy during quake events which are available in earthquake of region and geologic moment rate which gained with geometric parameters of faults, reveals potential of the faults in releasing stored elastic energy in. Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Central Alborz region. The most moment rate in the study area belongs to geodetic approach (8.83×1019 Nm/yr) and then geologic moment rate (0.12×1019 Nm/yr) and finally the least quantity belongs to seismic moment rate (0.022×1019- 0.046×1019 Nm/yr). Considering, distribution of earthquake epicenters, the most seismic energy is released in the south parts of Central Alborz and considering high geodetic and geologic moment rates in north parts, it seems, north parts of Central Alborz have higher seismic potential.
M. Heidarzadeh; M. Dolatshahi Pirooz; N. Zaker; M. Mokhtari
Abstract
This research attempts to assess the history of tsunami occurrences and potential for tsunami generation at the southern coasts of Iran bordering the Indian Ocean by providing a list of historical tsunamis in this region and also, modeling of phases of tsunami generation and propagation. After the December ...
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This research attempts to assess the history of tsunami occurrences and potential for tsunami generation at the southern coasts of Iran bordering the Indian Ocean by providing a list of historical tsunamis in this region and also, modeling of phases of tsunami generation and propagation. After the December 2004 mega-tsunami in the Indian Ocean, wide efforts were devoted to assess hazard of tsunami, and to develop tsunami warning and mitigation systems in the region. To assess the hazard of tsunami in any particular region, the compilation of historical records of tsunami is always the first primary task. Such a list may lead to useful information about the return period of tsunami events, and most vulnerable coastlines to the impact of possible tsunami. Regarding this fact, in the framework of this study, the first list of Makran historical tsunamis is provided. The Makran zone is located offshore Iran and Pakistan and any tsunami in this region would affect coastlines of Iran, Pakistan, Oman, and India. The last major tsunami in this region was produced following the occurrence of an 8.1 magnitude earthquake which took the lives of at least 4000 people all over the Makran coasts. Also, in this research, the potential for tsunami generation in the Makran subduction zone is quantitatively estimated through modeling of tsunami generation phase. In this regard, based on Mansinha and Smylie (1971) formulas a computer program has been developed to predict the ocean floor deformation due to the occurrence of underwater earthquakes in subduction zones. After the verification of model results, it has been employed to predict possible ocean floor deformation after the occurrence of underwater earthquake in the Makran subduction zone. Tsunami generation analysis shows that the risk of tsunami generation from Makran subduction zone can be classified into three main categories, as follows: (1) very little risk for tsunami generation in the case of occurrence of an earthquake having magnitude up to 7; (2) little to medium risk (Magnitude ranging 7 to 7.5); and (3) high risk (Magnitude greater than 7.5). In the next section of the paper, the tsunami propagation in the Makran zone was modeled. The results of tsunami propagation indicate that in the case of tsunami production in this region, the first tsunami waves will hit the nearest shoreline within 15 to 20 minutes. Finally, considering tsunami hazard assessment performed in this paper, the necessity for the development of a tsunami warning system in southern coasts of Iran was emphasized and its components and orderly sequences of tasks are proposed.
A. Zamani; M. Agh-Atabai
Abstract
The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was ...
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The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was followed by relatively large number of aftershocks. In this research, the aftershock sequence of this earthquake has been studied by measuring quantitative indices of coefficient of variations (CV), the exponent of the power spectral density function, and the generalized multifractal dimensions. The results reveal the presence of fractal structure in the temporal and spatial distribution of aftershock sequence. The multifractal behavior of the aftershock sequence indicates the clustering of the earthquake activity and the degree of the heterogeneity in the seismotectonic and geodynamic processes in the focal region. The results show that the multifractal dimensions of the aftershock sequence decreases and the multifractal dimensions of aftershock epicenters increases with time. It seems that these changes in the multifractal dimensions are related to the activity of secondary and sympathetic faults and changes in the tectonic stress regime of the region. The results also indicate that the multifractal method rather than monofractal approaches is a powerful tool for quantitative analysis of aftershock process's clustering behavior.
A. Kangi; A. Rastgou; F. Ebrahimi; N. Kangi
Abstract
Shadyakh, commonly deemed as the headquarters of NeishabourCity, has so far endured such various events as war, earthquake, and other natural disasters. What has been revealed through recent archeological excavations convincingly depicts a brilliant scientific, cultural, and political manifestation of ...
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Shadyakh, commonly deemed as the headquarters of NeishabourCity, has so far endured such various events as war, earthquake, and other natural disasters. What has been revealed through recent archeological excavations convincingly depicts a brilliant scientific, cultural, and political manifestation of this city in a glorious epoch between 9th to 12th centuries, which must have continued till 1205. Notwithstanding, owing to an unanticipated occurrence, the city was thoroughly devastated. The history of devastating events along with archeological evidence discovered recently indicates that the annihilation of Shadyakh has been an upshot of Genghis Khan's holocaust.
