a dense seismological network of 23 stations was installed in the epicentral area of the 2003 December 26 Bam earthquake to study the aftershock seismicity. We select the 331 earthquakes recorded at a minimum of 10 stations, with rms less than 0.1 s and uncertainties less than 1 km, to infer the precise geometry of the seismicity in the fault region. We also process the data with the Double Difference technique to confirm the results. The aftershock cluster is 25 km long, trends north-south, and is located 5 km west of the Bam-Baravat escarpment, exactly beneath the observed surface breaks. At depth, aftershocks are concentrated between 6 and 20 km, beneath the upper layer of relatively low velocity that experienced the maximum slip, and they dip slightly westward. The southernmost part of the aftershock cluster is narrow and defines the rupture zone that is likely the Bam-Baravat fault at depth. However, it is unlikely that it is connected at surface to the Bam-Baravat escarpment but more likely to the co-seismic ruptures south of Bam. On the contrary, the distribution of the northernmost aftershocks spread into a more complex pattern, which is consistent with a northward propagation of the rupture along the fault plane. The focal mechanisms are consistent with right-lateral strike-slip faulting on N-S trending faults, parallel to the Bam-Baravat escarpment.

SUMMARY We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of >54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5–10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10–20 km depth range, we find evidence for a band of high velocities (>4.0 km s–1) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30–50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.

We use a very large seismic data set to provide a comprehensive image of the mantle transition zone (MTZ) beneath the Middle East. We utilized the technique of Common Conversion Point stacking of P wave receiver functions to investigate the topography on the 410‐ and 660‐km discontinuities defining the upper and lower boundaries of the MTZ. Our results show significant topography on the 410‐ and 660‐km discontinuities and corresponding variations in the MTZ thickness. The MTZ topography is broadly consistent with the results of seismic tomography studies, implying the presence of both cold thermal anomalies imparted by detached Tethyan slabs and lithospheric segments and hot thermal anomalies induced by upwelling of lower mantle material. The MTZ topography in the northern Middle East is dominated by the presence of patches of cold material that are intermittently separated by regions of hot to normal MTZ. Our results suggest that instead of a continuous slab, the Tethyan slab in the Middle East is strongly segmented along the strike of the subduction boundary. Furthermore, we find evidence for a significant gap in subduction extending from the eastern edge of the Cyprean arc to NW Iran. The southern Middle East is dominated by the processes related to the mantle upwelling beneath the Afar depression. Our results imply that buoyant lower mantle material enters the MTZ beneath the Afar depression and then spreads laterally to the northeast beneath the western Arabia, flowing within the MTZ and in the upper mantle.

Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.

No abstract

Complex interaction of rheologically contrasting layers within the lithosphere during the collision of continental plates leads to active faulting, which represents a serious hazard to the population and infrastructure. One of the collision scenarios presumes the existence of a middle-lower crustal channel composed of subducted silicic upper crustal rocks, which is thought to exist in the Tibetan-Himalayan system. Based on the results of seismic tomography, we argue that a similar mechanism of crustal channeling takes place beneath the Zagros mountain system in southwestern Iran. The 3D seismic velocity model reveals an inverted crustal architecture of the collision zone, in which the low-velocity felsic (granitic and sedimentary) upper crustal rocks of the Arabian plate form a seismically inactive lower crustal channel below the higher-velocity mafic (basaltic) middle-upper crustal layer of the Iranian crust. Based on existing numerical models, we suggest that the formation of the felsic channel is likely governed by separation (delamination) of the weak felsic upper crust of the subducting Arabian lithosphere and its ductile underplating under rheologically stronger upper-middle crust of the Iranian plate.

No abstract

The concept of urban resilience has drawn more attention in recent years, especially in terms of urban planning. This concept is particularly highlighted when a city or community encounters threats such as natural hazards and rapid population growth. To respond to these threats, a comprehensive resilience assessment is required to identify priority areas for disaster risk management. Resilience is a multi-faced and complex concept, and any effort to evaluate it must take into account its social, economic, physical, and environmental dimensions. The city of Mashhad, as the second-largest city in Iran, is one of the most vulnerable cities due to being surrounded by several active faults, including Toos, Kashfarood, and Shandiz-Sang Bost. Since this city is located in a moderate to high earthquake risk zone, it is very necessary to pay attention to the resilience of this city against the earthquake crisis and implement management measures to increase the resilience capacity of this city. Accordingly, this study aims to evaluate urban resilience's capacity by introducing various indicators that promote resilience. This study focuses on two main domains: resilience dimensions and resilience criteria. This research has integrated three dimensions of resilience: social, cultural, physical, environmental, and economic, with four criteria of a resilient city: resistance, adaptation capacity, redundancy, and recovery to measure resilience capacity. A wide range of indicators covering all dimensions of resilience has been identified, enabling us to understand how resilient an area is structurally and functionally in the face of a natural disaster. Four neighborhoods of Mashhad (Khajeh Rabi, Sajjad, Honarestan, and Hijab) were selected as case studies. To calculate resilience capacity, each indicator of resilience dimensions was scored based on the analysis of statistical data and expert opinions. Findings show that all selected neighborhoods represent a moderate resilience against disasters like an earthquake. However, Sajjad has a higher resilience to face unexpected circumstances like an earthquake than the other three neighborhoods. According to the research findings, more structural and non-structural measures should be taken to improve resilience capacity, especially in the neighborhoods of Khajeh Rabi, Hijab, and Honarestan. This study concludes that urban resiliency in selected neighborhoods is strongly associated with social indicators such as residents' knowledge and awareness, the level of public participation, economic indicators including income and employment, as well as physical-environmental status in terms of urban and health infrastructure. The proposed framework for evaluating urban resiliency using various indicators in this study can be served as a basis for further investigations and development of methodologies that simultaneously consider the temporal and spatial dimensions of resilience.