The Makran subduction zone in southeastern Iran and southern Pakistan is where the oceanic crust of the Arabian plate (Oman Sea) is subducting beneath Eurasia. Compared to other subduction zones in the world, the Makran subduction zone has some unusual features, including different seismicity patterns in its eastern and western parts. Also, the Quaternary volcanoes in the eastern part of Makran are located far from its foreland comparing to the western part of Makran. The very low seismicity of western Makran causes two different viewpoints about its current situation; i.e., whether the subducted plate is undergoing aseismicity or has been locked strongly. The Partitioned Waveform Inversion (PWI) method is used here to image the S-velocity structure of the upper-mantle and Moho-depth variations of Makran subduction zone and explore the relationship of the Makran seismic structure with the seismicity and the volcanic arc in the region. For this purpose, we used the vertical components of the seismograms recorded by the National Iranian Seismic Network with high signal to noise ratio from the earthquakes with magnitudes of 5.5 to 7.7. Despite the limited number of stations around the Makran region, choosing proper earthquakes enables us to improve the azimuthal and path coverage and apply the PWI method in the region. Our tomography data show that the Moho depth across the Makran subduction zone is increasing from the Oman seafloor and Makran forearc setting to the volcanic arc. Generally, the crust in the western Makran is thicker than its eastern part and the maximum crustal thickness in the Makran region reaches to 50±2 km below the Taftan volcano. The Moho map clearly depicts the western edge of the Makran subduction zone, where the Minab fault (representing the eastern edge of the Hormuz Straits) marks the boundary between the thick continental crust of the Arabian plate and the thin oceanic crust of the Oman Sea. Our results show clearly that the high-velocity slab of the Arabian plate subducts northwards beneath the low-velocity overriding lithosphere of Lut block in the western Makran and Helmand block in the eastern Makran. We found that the slab in the western Makran starts with a gentle dip (about 8?) and increases to about 55?, where it plunges into the asthenosphere beneath the volcanic arc. In eastern Makran, the slab is subducting with a low dip angle of about 8? and reaches approximately 20?below the volcanic arc. We found that the bending of the subducted plate occurs with relatively low dip and much farther beneath eastern Makran than in the western part which may explain the different volcanic arc offsets across the Makran subduction zone.

There are two different seismotectonic zones in around of the Zendan- Minab- Palami (ZMP) fault system and the Oman Line, in south of Iran (Makran subduction zone in the east and Zagros collision zone in the west), which led to the complexity of this region. Since studying the stress field is important for accurate perception from elastic features of environment, surveying the exerted the tectonic stresses to the tectonics plates and their magnitude, and description the geodynamic of this region, in this study considerd to assessment of stress field and also, maximum horizontal stress (SH) in around of ZMP fault system. To receive this purpose, amount and direction of stress is calculated by iterative joint inversion of earthquake focal mechanism. From east to west of ZMP fault system, with transition from Makran subduction to Zagros collision, direction of SH is reduced from 5.09º in east to 0.9º. To surveying the strain field, we used Global Positioning System (GPS) data. Maximum variance between velocity vector and direction of SH is determined in Bandar-Abbas (BABS) station, that located in adjacent of ZMP fault system. The friction coefficients which obtained in this study show that friction in Makran zone is more than Zagros zone.

Despite the ambiguous tsunamigenic behavior of the Makran Subduction Zone (MSZ), due to the low level of offshore seismicity, historical evidences and the 1945 tsunami in Makran confirm the potential of the MSZ for generating tsunami events. Possible future tsunamis generated by the MSZ will pose the coastlines of Iran to hazard more than any other country. Probabilistic tsunami hazard assessment (PTHA) is an effective approach to assess hazard from tsunamis and help for planning for the future. In this study, we assess the probabilistic tsunami hazard along the southeastern coast of Iran considering the entire Makran, the western Makran and the eastern Makran tsunamigenic sources. Tsunami scenarios include earthquakes of magnitudes between 7.5-8.9 for the western and eastern Makran and between 7.5-9.1 for the entire Makran. Both seismicity and tsunami numerical simulation are inputs for probabilistic hazard analysis. Assuming that the tsunami sources are capable of generating tsunamigenic earthquakes, estimating the annual rate of these events is required for PTHA. The truncated Gutenberg-Richter relation (Cosentino et al., 1977 and Weichert, 1980) is used in this study to compute the annual number of the earthquakes. We model tsunamis using the COMCOT well-known algorithm (Liu et al., 1998). The distributions of tsunami heights along the coastline of Iran are used in probabilistic tsunami hazard assessment. The results of PTHA show that Konarak and Sirik coastlines are posed to the most and least hazard from tsunamis, respectively. The probability of exceeding (POE) 1 and 3 meters increases with time. The probability that tsunami wave height exceeds 3 meters in 500 years is about 0.63 and 0 near the coastlines of Konarak and Sirik, respectively. The maximum POE for 3 meters belongs to the area between Beris and the west of Kereti. Distributions of probabilistic tsunami height along the coastline of Iran also indicate that Konarak and Sirik are the most and least vulnerable shorelines to tsunami hazard, respectively. The annual probability of exceeding 1, 2 and 3 meters are 1, 0.4 and 0.2, respectively. The results indicate the need of attention to tsunami long-term hazard along the southeastern coast of Iran, especially for the area between Jask and Beris. Our tsunami hazard assessment does not involve the tsunami inundation distances on dry land due to lack of high resolution site-specific bathymetric/topographic maps. Such computations are required in order to estimate the exact impacts of possible future tsunamis on the southeastern coast of Iran. High-resolution hydrographic surveys are required to be done in future for the major ports. Furthermore, future works should consider other possible near-field tsunami sources, such as the Murray Ridge, Minab-Zendan and Sonne faults and far-field tsunami sources, such as the Sumatra-Andaman subduction zone.

Summary For the present two-dimensional (2-D) lithospheric density-temperature distribution modeling, we have selected a north-south geo-transect cut in east of Iran from the Oman Sea to the Lut block with a length of about 800 km. As the structural domains, investigated in this paper, have mainly been created under the effect of the north-south subduction of the Arabian Oceanic Plate under the Eurasia, thus, most of these structures are approximately perpendicular to this direction. As a result, in order to avoid three-dimensional (3-D) structural effects in our 2D modeling, we have selected a profile perpendicular to the strike, which is roughly the north-south direction.
Introduction In order to avoid interpreting isolated anomaly features being located accidentally on the profile of the geoid, free air and topography data, we average the data within a width of 50 km to both sides of the profile and calculate the variance within this stripe using 5 km long steps along the profile. The resulting standard deviation is plotted as uncertainty bars. Since the lateral resolution of our data is of the order of several kilometers, therefore, we cannot reproduce small‐scale details. The generated model consists of a sedimentary layer, the upper, middle and lower crust and a lithospheric mantle layer. In order to constrain the various thicknesses, the results of previous works carried out in the study region have been used.
Methodology and Approaches Modeling carried out in this research is based on the assumption of local isostatic equilibrium and joint interpretation of gravity, geoid and topography data with temperature-dependent density. Bouguer anomaly data are mainly sensitive to crustal density distribution and decrease proportionally to the squared distance (r) from an object, whereas elevation is very sensitive to changes in density and thickness of the lithospheric mantle and the geoid undulations diminish proportionally to r−1. The data different sensitivity on distance from the object can be a good constraint on modeling lithospheric density-temperature distribution.
Results and Conclusions Because of subducting Arabian plate in Makran subduction zone, thickness of the lithosphere increase from the Oman Sea (90 km) to the Taftan-Bazman volcanic arc, with a maximum thickness (290 km) under the volcanic arc. Based on our modeling results, subduction of the oceanic crust of Arabian plate under the Makran belt starts with a very low dip angle and bends under the Taftan-Bazman volcanic arc with a relatively higher dip. There is a logical correlation between the subducted slab and the seismicity of Makran subduction zone. Because of the low dip subducting slab, there is a long distance between volcanic arc and forearc setting (~450 km). Further to the north, lithospheric thickness is reduced to the ~200 km under the Lut block which is in good agreement with earlier studies. Our integrated modelling approach reveals a crustal configuration with the Moho depth varying from ∼21 km beneath the Oman Sea, and ∼47 km beneath the Taftan-Bazman volcanic arc to about 37 km beneath the Lut block. Across the Makran subduction zone, Moho depth is increasing from the Oman seafloor and Makran forearc setting (~21 km) to the volcanic arc (∼45–50 km). Furthermore, we have found that the oceanic crust is a two layered plate and there is a thick sedimentation there to about 8-9 km.

From 2011 to 2013, several major earthquakes occurred in the Makran Seismotectonic zone (Iran and Pakistan). The low event interval of these earthquakes in a tectonic zone may indicate their interaction. In this paper, the interactions between 2011 Dalbandin earthquake of Pakistan, 2013 Saravan and Goharan earthquakes of Makran seismotectonic zone in SE Iran was investigated by calculating the Coulomb stress changes. Maps and cross sections of coseismic stress changes show that Saravan and Goharan earthquakes have occurred in the stress enhanced areas indicating the positive effect of Dalbandin earthquake on trigerring the mentioned events. In order to quantify the seismicity level changes, statistical parameters including b-value, seismicity rate and temporal changes of local standard deviation of gradient (lsd) were calculated over a 10 year period (5 years before and after the Dalbandin earthquake).The results show that the seismicity rate of Makran seismotectonic zone has significantly increased after this event. The temporal variation graph of lsd parameter also decreases at the time of the Dalbandin earthquake event, indicating an increase in seismicity rate in the region. In overall, the results indicate that the Dalbandin earthquake is the beginning of an active seismic period in the Makran subduction zone on which the peak of activity occurred in 2013 with two years delay.

The Makran accretionary prism in southeastern Iran contains extensive Mesozoic melange zones and large intact ophiolites, representing remnants of the Neotethys oceanic crust that was subducted beneath Eurasia. To the north of the Makran accretionary prism, the Jazmurian depression lies which is a subduction-related back-arc basin. The Ganj Complex is one of the ophiolitic complexes, located on the west side of the Makran accretionary prism and Jazmurian depression, and is bounded by the Jiroft fault system in the west. The Ganj Complex with an Upper Cretaceous age is composed mainly of lava flows, pillow lavas, acidic plutonic rocks and sedimentary rocks, which are intruded by northwest-southeast trending dykes and does not ressemble a classical ophiolitic sequence. It lacks the intrusive crustal and mantle sections. The Ganj Complex pillow lavas, mainly olivine basaltic, occur as normal and as mega-sized bodies and are mostly flattened - tubular in shape with bread crust crack surfaces. They show three textural zones from the top glassy (zone 1) through the intermediate (zone 2) to the holocrystaline interior (zone 3), with each characterized by varying assemblages of plagioclase and olivine that form different textures. The Ganj pillow basalts are characterized by variolitic, porphyritic, microlitic-porphyritic, intersertal, intergranular and amigdaloidal textures. Mineralogically, they consist of plagioclase ± olivine ± pyroxene + opaque. The outer glassy surfaces of pillows frequently consist of one, or rarely multiple rind. The rinds consist of three layers, which from surface inwards are: (1) sideromelane, (2) dark tachylyte; and (3) tachylyte with elongated vesicles.

The Makran zone in southeastern Iran and southern Pakistan is the result of subduction of oceanic crust of the Arabian Plate under the Eurasian Plate. From seismic behavior point of view, there is a distinct segmentation between the western and eastern parts of the subduction zone. The western part of the Makran has an abnormally very low level of deep seismicity with lack of recorded great earthquakes, while the eastern part has experienced many great earthquakes. Another difference between the western and eastern parts of the Makran region is that the distance between the Quaternary volcanic arc and fore-arc setting is larger in the east than in the west. Understanding the nature of unusual behaviors of the Makran subduction zone has long been one of the biggest challenges in seismotectonic investigations of this region. The present study aims at producing high-resolution love-wave velocity structure maps of the crust and the upper mantle in the Makran subduction zone using ambient seismic noise. To achieve this purpose, a large dataset has been provided to produce tomographic maps. Empirical Green’s functions were obtained from cross-correlations of broad-band seismic noise records at different stations inside and outside the region. Love-wave velocity dispersion curves were then extracted from the ambient noise, and finally converted into a 2D group velocity image (or tomography map) for crustal and upper mantle structures of the region.

Based on the role of fault segmentation in the deformation, it is necessary to determine the main segments of the Makran fault by transfer faults for the potential risk of earthquake and tsunami. Therefore, in this study, the transfer faults of Makran subduction zone were identified. Our research shows that Makran fault consists of 6 main segments with step- arrangement which most of these segments are separated by NW-SE transfer fault (such as sonne fault). These transfer faults have cuted the Makran fault and caused the displacement in the acceleration zone. According to the effect of the slope of the subduction slab in the seismic risk and the tsunami assessment, we proposed four cross-sections perpendicular to the subduction zone at longitude 58°, 60°, 63°, and 66°. Review of these sections shows that at the subduction wedge, the slab plate does not have a slight slope, so that the slope is horizontal. In these cross-sections, slope of the slab plate in different points are determined.

Kuh-Som, KuhzaBozorg and KuhzaKochak volcanic cones are located in the southeastern of Bam and northwest of Bazman cites. From the perspective geology these cones are belong to the Iranian central zone and south-eastern edge of Lut block. These cones are composed of extrusive igneous rocks such as basalt, olivine basalt, andesite and basaltic andesite, and are predominant trachytic texture. Plagioclase, pyroxene and olivine are main minerals. Pyroclastic deposits, lapilli, tuff, ash and volcanic bombs, along with lava flows are main construction volcanic cones. These volcanoes are monogenitic and limited eruption. Based on type material that construction cone of the volcanoes, it seems they are among between Hawaii to Strambolian volcanoes. These rocks shows enrichment to LILE relative to HREE (Ce / Yb= 33-45) , high ratio Zr / Y (33.4), enrichment to LILE and negative anomaly from Ni, Cr and nearly Eu that reveals these rocks related to Calc-alkaline magmatism. In spider diagrams of trace elements and rare earth elements that normalized to Chondrites and primitive mantle show light rare earth elements enriched more than high rare earth elements and show pattern similar to affiliate subduction zones. Geochemical characteristics such as ratio of La / Yb 8/6 to 7/13, low Rb content with the tectonic setting discrimination diagrams indicate that they are related to subduction environments and low tendency to intapalate zone. Source of magma that formed these volcanoes resulted from melting of a garnet Lherzolite at depth of 100 to 110 Km. Tectonomagmatic diagrams shows these rocks dependence on of continental subduction environments to show slightly into the intraplate zone, so that it seems the volcanic cones of them related to the Makran and Oman subduction and related to Makran- Chaghy magmatic arc.

Summary: Southeastern Iran، in Makran region، due to movement of the Arabian plate toward Eurasia، the oceanic crust is subducted beneath the continental crust forming a subductionzone. This movement and subduction has given a special situation to seismicity and geology of this zone. Covering the lake of seismological studies and the effect of geological structure on seismic wave propagation in this region، we have studied effects of the medium on propagated seismic waves from the source to the receiver using recorded data on stations of International Institute of Earthquake Engineering and Seismology from 2005 to 2011. The coda quality factor، Qc، in addition to engineering applications، could be used and provide remarkable information for seismicity studies and analyzing how the subduction of oceanic crust is treating. Regarding the extent of the studying area، it has been divided into three subareas of Southeastern of Central Iran،Southeastern of Zagros and Makran، then for each، the variation of quality factor with depth is evaluated. The “Single Back-Scattering Method” is used for estimate. The frequency dependence of coda wave quality factor for events up to 100 km epicentral distance at each three subareas is determined. Also، the lateral and depth variation of Qc are computed and discussed. In this study، the Qc values are calculated for 12 lapse times (5 to 60s with a step of 5s) for three regions. The frequency dependent relationships of Qc، for SE Zagros varies from Q  (12 1. 1) f (1. 260. 02) c at 5s to Q  (1251. 1) f (1. 070. 014) c at 60s lapse time windows. Similarly، for SE Central Iran، the relationship varies from Q (17 1. 3) f (1. 130. 051) c at 5s to Q  (147 1. 3) f (0. 890. 038) c at 60s lapse time windows; and for Makran region varies from Q  (12 1. 1) f (1. 30. 015) c at 5s to Q  (137 1. 1) f (1. 030. 018) c at 60s lapse time windows. In all regions، the value of Q is less than 200، which implies، beside a highly tectonically and seismically behavior، a highly heterogeneous medium. The results show an increase in Qc value with increasing lapse time window. Among three studied regions، SE Zagros has the minimum Qc and so is more tectonically active compared with the two others. The North Makran and SE Central Iran are places in thenext ranks، respectively. Estimated Qc at bigger lapse time window indicates less attenuation at bigger depth. In Makran region at a depth of ~97 km the variation rate of Q suddenly increases. Based on available geological cross sections، for the eastern and western Makran، depth of about 100km of oceanic crust is in the northern region of the western Makran، which shows good agreement with our observation that oceanic crust has higher velocity، so attenuation is less than continental crust.