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The tomography results reveal not only distinct velocity structures in different tectonic zones but can also provide valuable insights into the geological features of the area. This study presents the results of 2D Rayleigh wave tomographic maps obtained in NE Iran. For this purpose, we used the recorded waveforms of more than 500 earthquakes with M > 4 that occurred between January 2000 and October 2020 at 165 stations. The calculated tomographic maps cover a period range of 3 to 36 s, providing the 3D VS model to analyze crustal structure at depths ranging from 2 to 30 km. At shorter periods, the tomographic maps are primarily influenced by sediment thickness, with the presence of thick sediment layers (~ 10 km) responsible for the observed low VS anomalies (< 3.1 km/s) in the study area. At longer periods, the tomographic maps highlight the structural characteristics of the middle-lower crustal layers and, somewhere, the depth variations of the Moho discontinuity. The VS model also confirms the correlation between tectonic fractures and known faults in the study area as boundaries of seismotectonic provinces. Moreover, a distinct area was observed beneath the Binalud foreland, which we interpreted as a suture zone, as suggested by previous studies. The reliability of the resolved anomalies was supported through a series of tests, including checkerboard and earthquake location uncertainties. These tests demonstrated the robustness of the results and provided confidence in the accuracy of the findings. [ABSTRACT FROM AUTHOR]

Surface wave azimuthal anisotropy in the uppermost crust could be essential to obtain the patterns of the local stress field and shallow Earth's interior structures. We used the micro-earthquakes (M ≤ 4) waveforms recorded by the Tehran Disaster Mitigation and Management Organization (TDMMO) and Iranian Seismological Center (IrSC) networks between 2006 and 2018. We applied the multiple filter analysis, FTAN, to measure Rayleigh wave group velocities and then inverted them to obtain isotropic and fast anisotropic direction maps at periods of 0.5 to 3.0 s. After obtaining the local dispersion curve for each geographic grid point, we applied a 1D VS inversion procedure. We inserted the resulting model into the original grid point to obtain a quasi-3D VS model in the Tehran region. According to these results, we divided the study area into five local fast anisotropic direction sectors. The resulting velocity maps indicate that the Tehran basin, with relatively low velocity, has been filled out by alluvial deposits with thicknesses between 0.4 km (in the north) and 1.2 km (in the south). In contrast, the fast-direction pattern in this basin changes from W-E (sector #2-west) to N-S (sector #4). A low-to-high-velocity anomaly change inside the basin and near-surface depths (up to 3 km) can illustrate the secondary faults, such as the Pardisan fault. The northern Tehran mountains appear with a high velocity in these maps with three different fast anisotropy directions (sectors #1, part of #2-west, and #5). This feature has also been observed in other stress field studies. In general, our tomographic results in the uppermost crust indicate that the azimuthal anisotropy can provide the velocity structure and illustrate the local stress field. [ABSTRACT FROM AUTHOR]

From a joint analysis of fundamental mode Rayleigh wave group velocities and P‐wave receiver functions, we derive a new, high‐resolution 3D shear‐wave velocity (Vs) model for the crust and uppermost mantle of the Iranian Plateau. The thickest crust (>55 km) is located beneath the Sanandaj‐Sirjan Zone and the deforming belts of Alborz‐Binalud‐Kopet Dag Mountains, whereas regions of lower topography/deformation (e.g., central Iran and the Lut Block), and the regions of younger deformation such as the Makran Accretionary Wedge and the Zagros Simply Folded Belt (SFB) have a thinner (<45 km) crust. Our model reveals a low‐Vs tongue‐shaped feature, indicating the underthrusting of the Arabian crust beneath central Iran. In the central Zagros, the underthrusting of the Arabian crust is steeper, resulting in a narrower deforming zone (∼150 km) and a thicker crust (∼60–65 km), compared to the NW or SE Zagros where the deforming zone is broader (∼250 km) and the crust is thinner (∼55–60 km). Regions of low‐Vs in the upper crust correspond to regions of thick sediments; the South Caspian Basin, the Zagros SFB and foreland basin of the Zagros, and the Makran Subduction Wedge. The subcrustal Rayleigh wave azimuthal anisotropy of the Plateau shows a rather uniform and smoothly‐varying pattern. In the NW Zagros the crustal and subcrustal pattern of anisotropy agrees with that previously estimated from the shear‐wave core phases, implying that the whole lithosphere deforms coherently, but for other regions (e.g., the western Alborz and Kopet Dag), the anisotropic pattern does not support a coherent deformational fabric throughout the lithosphere. Plain Language Summary: We use joint analyses of surface and body wave seismic data to investigate the crustal and uppermost mantle wave‐speed structure of the Iranian Plateau, the region of relatively rapid deformation and high‐topography resulting from the collision of the Arabian and Eurasian Plates. The variations in the wave‐speed and thickness of our crustal model reflect the main geological and physical features of the crust. In general, thicker crust (>55 km) underlies the elevated, deforming zones (e.g., the Sanandaj‐Sirjan Zone and the Talesh‐Alborz‐Binalud Mountains), while thinner crust (<45 km) occurs under the lower elevation, more stable regions of the Plateau (e.g., central Iran and the Lut Block). In the Zagros region, our model reveals a low shear wave‐speed, tongue‐shaped feature extending beneath the central Plateau, indicating the underthrusting of the Arabian crust. The low wave‐speed regions in the shallow crust correspond to the thick (∼10–20 km) sedimentary cover (e.g., the South Caspian Basin, the Simply Folded Belt and foreland basin of the Zagros Mountains, and the Makran Subduction). Key Points: Inversion of Rayleigh wave dispersion and P receiver function data result in a shear‐wave velocity model for the lithosphere of the Iranian PlateauThickest crust (>55 km) occurs below the collisional belts; regions of low deformation, or active subduction have thinner crust (<45 km)The crustal model reveals a low‐velocity feature beneath the Zagros and central Iran indicating the Arabian crust underthrusts central Iran [ABSTRACT FROM AUTHOR]

The Neo‐Tethys subduction and subsequent Arabia‐Eurasia continental collision invoked widespread Cenozoic tectono‐magmatism throughout the Iranian Plateau. We herein develop a new method to image the shallow crustal S‐wave velocity (Vs) structure by joint inversion of multifrequency waveforms and horizontal‐to‐vertical ratios around the direct P phase in P‐wave receiver functions. Synthetic tests demonstrate the validity of our method in constraining the absolute Vs values beneath single stations down to ∼12‐km depth. By applying this method to a seismic array of 63 stations with an average spacing of ∼10 km along the main profile, we construct a detailed shallow crustal Vs model across the northwestern Iranian Plateau. The model is characterized by distinct high‐ and low‐velocity anomalies beneath the Iranian hinterland and the Zagros foreland fold‐and‐thrust belt, respectively. In combination with geological observations and laboratory data, the imaged high‐velocity anomalies (with Vs of 3.2–3.9 km/s) may denote arc to intraplate magmatism beneath Central Iran and Alborz to the north, whereas the low‐velocity anomalies (with Vs of ∼1.65 km/s) probably represent the marl/shale layers in Late Cretaceous and Paleocene beneath Zagros. The magmatic rocks at the Iranian hinterland exhibit strong variations in absolute Vs, reflecting different bulk compositions with more mafic inland. The shale/marl layers could have acted as décollements to accommodate crustal deformation. Our observations underline both the key role of lithology‐controlled layering in sedimentary deformation at the Zagros fold‐and‐thrust belt and the change in compositions and forming‐environments of magmatic rocks at the Iranian hinterland. Plain Language Summary: Accurate velocity models of the shallow crust, especially in plate convergence zones, provide constraints on tectonic deformation and related mechanisms at shallow depths. However, existing seismic methods for imaging shallow crustal structures usually require dense and uniform ray‐path coverage, leading to limited application in areas with irregular distribution of stations and/or events. In this study, we propose inverting for shallow crustal velocity structures beneath single stations by using multifrequency signals around the direct P phase in receiver functions. The method is suitable for both the single‐station case and tectonically inactive regions. We applied the method to construct a detailed shallow crustal velocity model in northwestern Iran. The new model provides a more detailed view of the shallow crustal features of this tectonically complex region and helps to elucidate the Cenozoic tectono‐magmatic activities related to the Neo‐Tethys subduction and subsequent continental collision. Key Points: Frequency‐dependent signals around the direct P phase in receiver functions enable a better recovery of shallow crustal Vs structuresThe inland change in compositions of magmatic rocks may reflect a shift from continent arc to intraplate magmatism in northwestern IranThe lithology‐controlled layering plays a key role in sedimentary deformation at the Zagros fold‐and‐thrust belt [ABSTRACT FROM AUTHOR]

Kermanshah province experienced the most recent destructive earthquake in Iran on 12 November 2017 with Mw 7.3. Although this event was recorded by most Iran Strong Motion Network (ISMN) stations in the province, unfortunately, the site conditions of most of these stations were not properly identified. This study investigates seventeen ISMN stations operational in Kermanshah province to characterize them using available geological maps and by analyzing ambient noise recorded at these stations. Ambient noise analyses are efficient and cost-effective methods for identifying resonance frequency and shear wave velocity profiles. Horizontal to vertical spectral ratio of microtremors (mHVSR), time–frequency analysis of horizontal to vertical components (HVTFA), and Random Decrement technique (RayDec) were used in this study. Given the geological lateral variability of ground structure, these ambient noise analyses, along with 1D-linear elastic seismic site response analyses, provide a clearer understanding of site conditions at these stations than the available PS-logs. This study presents site proxies describing the geometry of subsurface layers, mechanical characteristics, and resonance frequencies at these stations. [ABSTRACT FROM AUTHOR]

The study of the dynamic triggering of earthquakes and tremors during large earthquakes at faraway distances is an active area of research. This type of remote dynamic triggering is often found in subduction zones. The Iranian plateau is part of the Alpine–Himalayan orogenic system and hosts different collision styles of deformation and significant strike-slip faults. Using 13 yr (26 December 2004–8 September 2017) of continuous data of Iranian National Seismic Network (INSN) and some dense temporary networks, for the first time we carried a systematic study of dynamic triggering in Iran during 47 recent large earthquakes with magnitude and depth ranges of 6.4–9.1 and 8–90 km, respectively. We explored the local catalogue of 124 805 events with a magnitude of completeness (M c) of 1.8 for the study of dynamic triggering but did not find any convincing evidence of dynamic triggering from the catalogue. The waveform data of 24 hr duration around the main events were analysed to find possible dynamic triggering through manual analysis of the waveform, STA/LTA, and beta statistics and found the triggering. We found dynamic triggering in Iran during Sumatra, 26 December 2004, M w 9.1; Tohoku-Oki, 11 March 2011, M w 9.1; Indian Ocean, 11 April 2012, M w8.6 and Baluchistan, 24 September 2013 earthquakes and also possible triggering during Sumatra, 12 September 2007, M w8.5. Only ∼10 per cent of the analysed earthquakes produced dynamic triggering. The triggering initiates during the passage of high amplitude Love waves and continues through the passage of the Rayleigh waves. We found north, central and eastern regions are more probable for triggering than Zagros and Makran regions. The instances of triggering were not restricted to only a small region, but instead, occurred at multiple locations. We find the onset of tremor correlates with very small stress changes, on the order of 1 kPA. However, the amplitude of the dynamic stresses is not a sufficient condition since some of the areas with considerably larger dynamic stresses are not triggered any seismicity in the region. The backazimuth angle of ∼50° and ∼120° seems to play an important role in the triggering. Teleseismic waves most probable for triggering local earthquakes within NW and central Iran include incoming surface waves with an incident angle of ∼60°–90° with respect to the local fault fabric. [ABSTRACT FROM AUTHOR]

We derived an average shallow shear-wave velocity model for the metropolitan Mashhad city and surrounding region in north-eastern Iran based on ambient noise Rayleigh waves dispersion curves. Phase velocity dispersions, for comparison, came from both beamforming analysis in the frequency domain as finding the average phase velocity within the array, and the spectral method of Bessell function estimations directly from Fourier transform of noise correlation functions provided in the time domain between individual station pairs of known distances across the array. Our results showed a strong agreement between two dispersion measurements. Finally, we inverted the average phase velocity dispersion curves obtained from both the beamforming and Bessel function techniques. Finally, the neighbourhood algorithm was adopted to provide an average 1D shear-wave velocity model. [ABSTRACT FROM AUTHOR]

The interrelation between the local site conditions and the severity of destruction during earthquakes has increased the necessity for more investigations on soil characterization in recent years. In residential areas, where active seismic methods are problematic for defining soil properties, passive seismic methods have attracted considerable attention due to their cost-effective and non-invasive features. Therefore, we have utilized 35 single-station ambient seismic noise recordings in the seismically vulnerable city of Babol, Iran, to evaluate the site response (including azimuthal variation and resonance frequency), estimate the seismic vulnerability index (K g), and classify the soil based on the Vs 30 of the region. To address the aim, we extract Rayleigh wave ellipticities from ambient seismic noise using their polarization features and employ them to define the azimuthal variations, resonance frequencies, and K g values of the region. In each station, the ellipticity curve is inverted with the support of supplementary geotechnical information to obtain a shear velocity profile. The inversion results have good consistency with borehole and downhole test information. The study identifies a low resonance frequency of 0.9 Hz with a NE directivity for the majority of the city and a Vs 30 range of 180 m/s to 350 m/s. Moreover, the seismic bedrock of Babol City is represented by a 3D Vs model at a depth of 60 m. Our results reveal that the city is vulnerable to seismic hazards due to the thick and low-velocity deposits responsible for high amplification affecting the study region, which combines with a high seismic vulnerability index, particularly in the southern part. This work has applications for future structural design, urban development, and seismic hazard reduction. • The results represent that single-station ambient noise analysis is a cost-effective and reliable method for soil characterization. • Polarization methods are effective in extracting Rayleigh wave ellipticities from ambient noise recordings. • · The city is characterized by a low resonance frequency with an almost NE orientation and seismic bedrock at a depth of 60 m • · According to Iran's No. 2800 seismic code, the region classified as ground type III • · The soil characterization, high amplification and k g value make the region's southern part vulnerable to seismic shaking [ABSTRACT FROM AUTHOR]

The evolution of the Eastern Iranian Ranges (EIR) dates back to the Late Cretaceous, coinciding with the closure of the Neotethys and the accretion of the Lut Block to Eurasia. However, controversy remains regarding its orogenic processes due to limited knowledge of the lithospheric structure. To gain a better understanding of the tectonic processes and mountain formation in eastern Iran, we analyzed seismic data from 29 stations in the northern part of the EIR. We initially perform receiver function (RF) analyses on 2160 high-quality RFs, emphasizing single-station analysis and Common Conversion Point (CCP) stacking to examine structural variations. Subsequently, we jointly invert the RFs with Rayleigh wave group velocity dispersion curves to derive a shear-wave velocity (V s) model for each station. Our findings reveal a complex structure with west-dipping interfaces, indicating crustal layering and imbrication. We have identified a significant west-dipping layer, approximately 100 km in length, which could potentially indicate an intra-continental decoupling or shear zone. This decoupling may be responsible for the underthrusting of the Eurasian margin beneath the Lut Block, resulting in a deepening of the Moho depth to over 50 km beneath its footwall, compared to the adjacent Moho depth of around 40 km. Additionally, this process has caused an increase in the topography of approximately 1 km. These findings reflect the potential westward underthrusting of the Eurasian margin. In the deeper parts of the model, we observe a low-velocity anomaly below the crust, shedding light on a weakened lithosphere that facilitates crustal deformation in response to the compressional forces of convergence. [Display omitted] • This study unveils the intricate processes driving mountain building in the Eastern Iranian Ranges. • A significant west-dipping layer, approximately 100 km long, represents Eurasian margin underthrusting below the Lut Block. • The Moho transition, influenced by asthenospheric materials, signifies a mechanically weak zone and lower crustal flow. [ABSTRACT FROM AUTHOR]

The retrieval of stable and reliable empirical Green's functions using ambient seismic noise plays a major role when studying the Earth's structure at various scales. High-resolution noise correlation functions are obtained in the NW of Iran by processing techniques including dividing the continuously recorded raw data into short (i.e., 10 min) overlapping (i.e., 80%) time windows. We compare four stacking methods (i.e., linear, RMS, RMS ratio, and Nth-root stacking methods) to study robust and stable inter-station empirical Green's functions. Our results indicate that the new RMS ratio method of stacking would be the optimal method to stack coherent signals. In other words, this method tackles problems including low signal-to-noise ratio (hereafter SNR) value, distortion of wave shape, and phase instability/unstable polarity treatment. In addition to noise correlation functions, we propose another strategy for the computation of the empirical Green's functions. In this technique, the cross-correlation of scattered coda waves of the calculated noise correlation functions is performed individually. In addition to coda window length, we also investigate another effective parameter, the geometry of various virtual stations to obtain reliable empirical Green's functions from the scattered coda waves of correlation functions with high SNR. The error of the velocities of Rayleigh wave empirical Green's functions is on the order of approximately 0.6%, when compared to ambient seismic noise and scattered coda waves for a period band range of 3–10 s. [ABSTRACT FROM AUTHOR]

We present the most extensive and up-to-date unified GPS velocity field for Iran. We processed the data collected during 10 yr (2006–2015) from the Iranian Permanent GNSS Network (IPGN) and combined them with previously published velocity solutions from the GPS survey measurements during 1997–2013. We analysed this velocity field using a continuum approach to compute a new strain-rate map for this region and we designed a block model based on the main geological, morphological and seismic structures. Comparison between both approaches suggests similar results and allows us to present the first comprehensive first-order fault-slip-rate estimates for the whole of Iran. Our results confirm most of the results from previous geodetic studies. However, we also show a trade-off between the coupling ratio of the Iranian Makran subduction interface and the kinematics of the faults north of the Makran in the Jazmurian depression. Indeed, although too scarce to accurately estimate a coupling ratio, we show that coupling higher than 0.4 on the plate interface down to a depth of 25 km will induce extension on the E–W faults in the Jazmurian region. However, the sites close to the shoreline suggest a low coupling ratio; hence, the coupling on this plate interface is probably more complicated than previously described and the Iranian Makran subduction interface mechanical behaviour might be similar to that on the Hellenic subduction zone. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Obtaining shear wave velocity structure images of the Makran subduction zone, south-east Iran. • Constructing a new model of Moho depth in the Makran region. • Achieving density structure images of the region. Abstract In this study, we developed a method to invert jointly Rayleigh wave group velocities and gravity anomalies for velocity and density structure of the lithosphere. We applied the method to the Makran accretionary prism, SE Iran. The reason for using different data sets is that each of these data sets is sensitive to different parameters. Surface wave group velocities are sensitive mainly to shear wave velocity distribution in depth but do not well resolve density variations. Therefore, joint inversion with gravity data increases the resolution of density distribution. Our approach differs from others mainly in the model parameterization: Instead of subdividing the model into a large number of thin layers, we invert for the properties of only four layers: thickness, P- and S-wave velocities and densities and their vertical gradients in sediments, upper-crust, lower-crust and upper mantle. The method is applied first to synthetic models in order to demonstrate its usefulness. We then applied the method to real data to investigate the lithosphere structure beneath the Makran. The resulting model shows that Moho depth increases from Oman Sea (18–33 km) and Makran fore-arc (33–37 km) to the volcanic-arc (44–46 km). The crustal density is high in the Oman Sea as should be expected for the oceanic crust. We also find a high-velocity anomaly in the upper mantle under the Oman Sea corresponding to the subducting slab. The crust under the fore-arc, volcanic-arc and back-arc settings of Makran subduction zone is characterized by low-velocity zones. [ABSTRACT FROM AUTHOR]

The Zagros fold-and-thrust belt is the principal response to the Arabia–Eurasia continental collision, which generates significant seismic activity in Iran. Surface wave tomography can be a proper tool for crustal structure imaging in this region. We used observed dispersion curves of Rayleigh wave derived from high-quality local-earthquake waveforms to obtain 2D tomographic maps in the period range 1–28 s beneath the Zagros collision zone. Subsequently, local pseudo-dispersion curves for individual grid points are inverted for shear-wave velocity structure, in order to obtain a 3D velocity model of the crust. Our results indicate shallow low-velocity structures near the suture zone. Moreover, a low-velocity flexure shape in the south of the Zagros Mountain Front Fault could be due to the thick sedimentary basin beneath the Dezful embayment. Relatively an uplifting of the deeper structures beneath Sanandaj-Sirjan and the high Zagros might could be led to high-velocity structures at mid-crustal depths. The variation of shear-wave velocity along the Zagros indicates the inhomogeneous structures along this folding and thrust belt. [Display omitted] • A new 3D V S model of the Zagros calculated from Rayleigh waves of local earthquakes. • Low-velocity upper crustal structures are consistent with the location of the suture and thick sedimentary basins. • High-velocity in the middle crust may be associated with an uplifting of the deeper structures. [ABSTRACT FROM AUTHOR]

A 2-D absolute shear wave velocity model has been resolved beneath a seismic profile across the northeastern margin of the Arabian Plate--Central Iran by simultaneously inverting data from P receiver functions and fundamental mode Rayleigh wave phase velocity. The data were gathered by a linear seismic array crossing the Zagros fold and thrust belt, Urmia-Dokhtar magmatic arc and Central Iran block assemblage as three major structural components of the Arabia-Eurasia collision. Our model shows a low-velocity tongue protruding from upper to lower crust which, north of the Zagros suture, indicates the signature of an intracontinent lowstrength shear zone between the underthrusting and overriding continents. The velocity model confirms the presence of a significant crustal root as well as a thick high-velocity lithosphere in footwall of the suture, continuing northwards beneath the overriding continent for at least 200 km. These features are interpreted as underthrusting of Arabia beneath Central Iran. Time to depth migration of P receiver functions reveals an intracrustal flat interface at ~17 km depth south of the suture; we interpret it as a significant decoupling within the upper crust. All these crustal scale structural features coherently explain different styles and kinematics of deformation in northern Zagros (Lorestan zone) with respect to its southern part (Fars zone). [ABSTRACT FROM AUTHOR]

By analyzing Rayleigh and Love wave empirical Green's functions extracted from ambient seismic noise and earthquake data, we obtained near surface radial anisotropy structure beneath the hidden part of the Kahurak fault in the Rigan region, in the southeast of Iran. The deduced seismic radial anisotropy within the hidden part of the Kahurak fault can reveal record of shallow crustal deformation caused by the Rigan earthquake (M W 6.5) occurred on 20 December 2010. Significant radial anisotropy with positive magnitude (V SH > V SV ) appears in the shallow subsurface of the upper part of the crust. The magnitude of radial anisotropy varies from predominantly positive (V SH > V SV ) to mostly negative (V SH < V SV ) values with increasing depth which is correlated with a known sedimentary layer. The sedimentary layer is observed with prominent positive radial anisotropy (V SH > V SV ). The thickness of the sedimentary layer varies between 1 and 3 km from the south to the north beneath the study area with an average radial anisotropy of about 5%. However, cross-section profiles indicate that negative anomaly stretches inside a thick sedimentary layer where the aftershocks occurred. Also, the investigation of cross-section profiles reveals that a dipping angle of the hidden part of Kahurak fault is resolved at approximately 85° using the anisotropy pattern. Moreover, the aftershocks generally occurred in the transitional zones where signs of radial anisotropy anomalies change. Our study indicates that the influence of different resolving powers and path coverage density of Rayleigh and Love waves, which can be artificially interpreted as radial anisotropy, have minor effect on calculated radial anisotropy and they are estimated in the range of − 2% to + 2%. [ABSTRACT FROM AUTHOR]

Surface wave tomography is considered an efficient method to reveal the physical properties of subsurface geological structures, particularly beneath geologically complex areas where conventional active seismic methods are problematic. The salt-rich DehDasht structural basin, in the SW of Iran, is an example of this area, which is characterized by high seismicity. Despite the complex geology and the great thickness of evaporitic deposits in this region, surface wave tomography can retrieve high-resolution images by applying a dense network of stations. Therefore, >11,000 micro-earthquakes (M ≤ 3.0) recorded by 116 broadband stations in 9 months were processed to detect geological structures and a crustal model beneath the DehDasht region. After selecting strict data selection criteria, the observed dispersion curves of Rayleigh waves were then measured using the multiple filter analysis method, and the 2D tomography was done for periods of 0.3 to 5.0 s. A non-linear iterative damped least-squares inversion procedure was then applied to each local dispersion curve to obtain the 1D V S model of the uppermost 5 km, and the results were inserted into the original cells to construct a quasi-3D V S model. Although our resulted V S model has high correlations with known geological units and tectonic features of the study area, we validated it by inverting the observed gravity data independently and consequently recovering the location of the anomalies at the basin and/or around faults, anticlines, and synclines. Generally, the observed low-and high-velocity anomalies are associated with the sedimentary materials. [Display omitted] • Obtaining High-resolution images via surface wave tomography in the presence of evaporitic deposits. • A quasi-3D shear velocity model beneath DehDasht region using micro-earthquake data. • The observed low and high-velocity anomalies are associated with the sedimentary materials. • The high-velocity structures related to the shallow underlying structures of the competent layer. • The V S profiles show that the Gachsaran Formation thickness varies between 0.6 km and 4 km beneath the DehDasht basin. [ABSTRACT FROM AUTHOR]

The lithosphere beneath the Zagros and central Iran has sustained long-lasting Neo-Tethyan subduction and subsequent collisional orogenesis, leading to the complicated crustal and lithospheric structure beneath the Iranian plateau. To better understand the geotectonic and geodynamic evolution of the Iranian plateau, we estimate the shear-wave velocity structure along profiles perpendicular to the Zagros using a self-parameterized Bayesian inversion of the Rayleigh wave group velocity dispersion curves in the period range of 5 to 120 s. Our velocity models, in line with a segmented slab model, show that different geodynamic processes have dominated along the Zagros. In the northern Zagros, the thick and high-velocity lithosphere beneath the Sanandaj-Sirjan Zone (SSZ) and Urumieh-Dokhtar Magmatic Arc (UDMA) is abruptly separated from the low-velocity lithosphere beneath central Iran, while the high-velocity anomaly underlies the UDMA and central Iran in the central and southern Zagros. We propose that the Arabian lithosphere near the suture has probably experienced a distributed thickening in the northern Zagros, and it underthrusts beneath central Iran in the central and southern Zagros. In the central and southern Zagros, a high-velocity anomaly elongates at a depth of 80–120 km between the low-velocity lithospheres of the UDMA and Lut block. This suggests that flat-slab subduction has not extended to the east of the Iranian plateau, therefore, the Eocene-Oligocene flare-up magmatism in the Lut block may be directly independent of the Neo-Tethys subduction. This study suggests that lateral tearing might be responsible for the slab detachment beneath the central and southern Zagros. The slab lithosphere may have started to tear from beneath the central UDMA and have propagated to the edges since ~10 Ma. Furthermore, the southeasternmost Zagros in the vicinity of the Makran zone, as a corner continental collision, has probably experienced slab tearing and break off during the Middle-Late Miocene. • Velocity structure along the profiles perpendicular to the Zagros was explored. • Estimated results support the slab break-off idea along the Zagros. • In line with the support of the segmented slab, results show different geodynamic processes. • Different geodynamic processes have dominated in south to north of Zagros. [ABSTRACT FROM AUTHOR]

The Bam earthquake (Mw 6.5) occurred on 26 December 2003 in southeastern Iran, causing a major disaster in the city of Bam. A remarkable vertical peak ground acceleration value of 988 cm/s2 and two horizontal pulses were recorded inside the damaged city. Previous analyses showed that the earthquake was caused by a subsurface rupture on an unknown strike-slip fault. In this study, we attempt to determine the precise fault location and source process of the 2003 Bam earthquake by performing a multiple-time-window linear waveform inversion of teleseismic and strong-motion data, both individually and jointly. We examined the general features of the fault location and the source process by analyzing the teleseismic displacement waveforms and determined the precise features and fault geometry by inverting the three components of strong-motion velocity records. The final estimate of the source process of the 2003 Bam earthquake was determined by joint inversion of the dataseis. Our results show that a single fault model, characterized by the appropriate location of the hypocenter, rake angle variations, and the Rayleigh-like speed of the rupture front can satisfactorily explain the three components of the strong-motion records at BAM station. [ABSTRACT FROM AUTHOR]

The spatial autocorrelation (SPAC) method is a useful tool for interpreting ambient noise, and several theoretical tools based on this method are available for data collection, processing, and analysis. The method uses the three components of seismic microtremors recorded simultaneously with arrays of different configurations and yields dispersion curves of Rayleigh and Love waves. Existing theories of the SPAC method are based on an idealized circular array with an infinite number of stations (the continuous model). Errors due to the use of a finite number of stations have been derived theoretically for vertically polarized ambient noise. This paper presents an extension of that error theory to horizontally polarized ambient noise so that it is valid for a circular array with M uniformly spaced stations. The quantities that are obtained as the output of the SPAC method, however, depend on the ratio of the power spectral densities (PSDs) of Rayleigh and Love waves, which are difficult to identify beforehand. Instead we introduce a quantity, n, that does not depend on the PSD ratio and therefore is more convenient for separating the properties of Rayleigh and Love waves. We derive an expression of n for a finite, M-station circular array (κM) and compare it with what it should be in the continuous model (κT). We illustrate κM and κT using field data from a site in Tehran and discuss their discrepancies. Finally, we demonstrate how we have estimated Love-wave phase velocities using the calculated κM. [ABSTRACT FROM AUTHOR]

Abstract: Inversion of local earthquake travel times and joint inversion of receiver functions and Rayleigh wave group velocity measurements were used to derive a simple model for the velocity crustal structure beneath the southern edge of the Central Alborz (Iran), including the seismically active area around the megacity of Tehran. The P and S travel times from 115 well-located earthquakes recorded by a dense local seismic network, operated from June to November 2006, were inverted to determine a 1D velocity model of the upper crust. The limited range of earthquake depths (between 2km and 26km) prevents us determining any velocity interfaces deeper than 25km. The velocity of the lower crust and the depth of the Moho were found by joint inversion of receiver functions and Rayleigh wave group velocity data. The resulting P-wave velocity model comprises an upper crust with 3km and 4km thick sedimentary layers with P wave velocities (V p) of ∼5.4 and ∼5.8kms−1, respectively, above 9km and 8km thick layers of upper crystalline crust (V p ∼6.1 and ∼6.25kms−1 respectively). The lower crystalline crust is ∼34km thick (V p ∼6.40kms−1). The total crustal thickness beneath this part of the Central Alborz is 58±2km. [Copyright &y& Elsevier]

Abstract: The shear wave velocity Vs as a function of depth z can be obtained from surface wave tomography, using the phase velocities of fundamental and higher mode Rayleigh waves. Since Vs is principally controlled by temperature, rather than by composition, it can be used to map the lithospheric thickness. Extensive regions of thick lithosphere underlie some, but not all, cratons. Conversely, thick lithosphere underlies some platforms and belts of active deformation. Because of this lack of correspondence, and because their age cannot be determined from seismology, we refer to regions of thick lithosphere as ‘cores’ rather than ‘cratons’. The shape of such cores has controlled the geometry of continental deformation and the distribution of diamond-bearing kimberlites. The strength of the cores resides in the dry crust, which is insulated from the hot convecting mantle by the thick buoyant lithosphere. The most surprising feature is the presence of thick lithosphere beneath Tibet and Iran, whose velocity structure closely resembles that of the cores beneath cratons, though they have a thicker hotter crust. Tibet and Iran appear to be places where cratons are now being formed. [Copyright &y& Elsevier]

• AVTs are performed on eight historical masonry mosques. • Natural periods of the mosques are calculated and numerical models are calibrated. • Fundamental frequency and dynamic characteristics of the ground are identified. • Empirical relation is presented for the natural periods of the mosques. Eight historical mosques of Kermanshah constructed in 18th or 19th century CE are investigated with ambient vibration tests on their sites and buildings. Conventional peak picking technique is used for determination of structures' fundamental frequencies and spectral ratio of horizontal to vertical components along with ellipticity inversion of Rayleigh waves are considered to identify the natural frequency of ground and shear wave velocity profile to define the site conditions according to the national codes of Iran and Italy. The recorded motions on the buildings are used to calculate the fundamental frequencies of the structure. Afterward, buildings are modeled by macro-element method and material properties are tuned in the way that the fundamental frequencies from the modal analyses match with the measured values from AVTs. Finally, more modal analyses are performed by the calibrated models to present an empirical relation between the natural period of the mosques, the geometrical characteristics of the buildings, and the mechanical properties of the construction materials. The results show that the natural periods of the masonry buildings of the mosques are different from the values of empirical relations in the national codes. Meanwhile, the proposed empirical relation presents the natural periods of the buildings of this study reasonably well and can be used for other masonry buildings of similar architecture and materials. [ABSTRACT FROM AUTHOR]

The complexity of the NE Iran region in which the 2014 Nargeschal landslide occurred, increased the necessity of detailed survey on the site response properties of this region. New investigations expanded the set of ambient noise measurements acquired in a previous work on the area affected by mass movement. The outcome of electrical resistivity and geotechnical studies were used to provide a comprehensive model of the landslide in addition to the substratum geology. The ambient noise recordings were analysed using the well-established Nakamura's method and a recently devised approach based on the analysis of the Rayleigh wave ellipticity to provide more detailed information on site resonance properties characterized by directional variations. The outputs, which were compared with the results of electrical resistivity tomography and geotechnical investigations, showed the better performance of the latter method in terms of stability and reliability of the results. Indeed, it allowed to detect site resonance characteristics that were unrecognizable by the Nakamura's method. Conclusively, the ambient noise analysis reveals that the directional resonance on different parts are due to the landslide and structural features of the site. The information obtained in this work is relevant for seismic hazard assessment in the study area. • The polarization analysis has more advantages than the Nakamura's method. • The analysis of the Rayleigh wave ellipticity provide more information on site resonance properties. • The outputs are more stable and reliable of the results. • The electrical resistivity and geotechnical studies used for a comprehensive model of the landslide. • The geological and structural features of the site are responsible for the directional resonance. [ABSTRACT FROM AUTHOR]

The Qeshm earthquake with magnitude Mw 6.0 occurred on November 27, 2005, on a southern island in Iran and was followed by many aftershocks. We analyzed the aftershock waveforms and the first arrival traveltimes to calculate the 3D velocity model. The tomographic procedure was conducted in three different depth ranges from the subsurface to a depth of 17 km beneath Qeshm Island. The subsurface was probed by the Rayleigh wave tomographic method. The waveforms were filtered in the period range of 0.6 to 6 s, the dispersion curves were calculated for the selected signals, and a 2D tomography procedure was then performed. The resulting group dispersion measurement maps were inverted to obtain the shear wave velocity model to a depth of 5 km. However, the first arrival traveltimes were applied to obtain the V P and V P /V S models using the SIMULPS program in the depth range of 5 to 14 km, while depths ranging from 14 to 17 km were considered by the event interferometric approach. All appropriate interevent empirical Green's functions (EGFs) were extracted in the 4 different slices/depths, and the Rayleigh wave tomography processing was then repeated for these layers at the period of 1.2 s. Our results demonstrate that analysis of the interevent EGFs can yield useful information from depths for which a velocity model cannot be obtained via classic techniques. In addition to the Qeshm Fault, which appears as a stretched low-velocity anomaly, the Hormuz salt and evaporites may be other sources with low velocity. Although finding a direct relation between faulting and folding and/or any other mechanism of folding is difficult on Qeshm Island, the role of the Hormuz salt in generating them is undeniable. The rise of the Hormuz salt and evaporites, which appear as a low-velocity (weak) zone, can directly affect crustal layering (lower sedimentary cover and basement), fault dip and anticline formation and deformation at depths to 14 km. According to the effect of these tectonic features, folding and secondary faults, the soft sedimentary thickness varies between 2 and 3 km. • A 3D velocity model of Qeshm Island was calculated from aftershock waveforms. • Different depths were investigated by different tomographic methods. • The Hormuz salt and evaporites contribute to faulting and folding on Qeshm Island. [ABSTRACT FROM AUTHOR]

The continental collision between the Arabian and Eurasian plates plays an important role in the geodynamical evolution of the Zagros and Iranian plateau. In order to investigate the upper mantle structure across the collision zone, we calculated the absolute and relative shear-wave velocity structure along a dense and long temporary seismic profile in NW Iran. The probabilistic 1-D absolute shear-wave velocity (Vs) depth profiles beneath 23 seismic stations were calculated using a trans-dimensional joint inversion approach of P -wave coda together with the Rayleigh wave phase and group velocity dispersion data. These 1-D models are then interpolated to obtain a 2-D Vs model along the profile. In addition, we used a nonlinear teleseismic tomography method to determine shear wave velocity variations beneath 44 seismic stations. Both the absolute and relative velocity models, obtained by different data sets and methods, show a thick (>150 km) high-velocity anomaly beneath the northern part of the Zagros, which could be the thickened Zagros lithosphere associated with continental shortening. A relatively thin lithosphere (~80 km) and lower S -wave velocity beneath Central Iran may suggest a weakened Iranian mantle lithosphere by upwelling of the hot asthenosphere following slab break-off. The presence of a thickened lithosphere beneath the Zagros implies that the Arabian-Eurasian convergence is accommodated mainly as shortening in the mantle lithosphere beneath the Zagros, rather than underthrusting beneath Central Iran. A narrow low-velocity corridor between the Zagros lithosphere and overriding plate (Central Iran), south of the Sanandaj-Sirjan Zone (SSZ), probably due to delamination of the subducting Arabian lithosphere from the Zagros lower crust, likely prohibits transferring stress from the Zagros lithosphere to Central Iran, causing less deformation in the SSZ which is the edge of the overriding plate. • A thick lithosphere (>150 km) is observed beneath the Zagros associated with active continental shortening. • The presence of a narrow low-velocity corridor between the Zagros lithosphere and overriding plate (Central Iran) is probably due to delamination, which prohibits transferring stress from the Zagros lithosphere to Central Iran. • There is no evidence of any attached oceanic slab to the Zagros lithosphere. [ABSTRACT FROM AUTHOR]