relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

the southern caspian a compressional depression floored by a trapped modified oceanic crust the south caspian intracontinental depression floored by oceanic basement is a relatively stable block with minor deformation surrounded by active fold thrust belts of arcuate form talesh alborz and kopeh dagh mountains which have undergone intense late cainozoic crustal shortening the basin is interpreted as a neogene quaternary compressional depression bounded by multi role mountain bordering reverse faults and apparently floored by a late paleozoic triassic or late mesozoic early tertiary modified oceanic crust trapped along an old geosuture it may be a relic of an old paleozoic triassic ocean or else a marginal sea developed behind a mesozoic paleogene ocean and analysis of geological and geophysical data enables a scheme to be suggested the general arcuate shape of the alborz and the talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south caspian depression a tectono sedimentary study of the south caspian region coupled w

microseismicity and seismotectonics of the south caspian lowlands ne iran this paper is concerned with the microseismicity and seismotectonics of the eastern south caspian sea region where the east alborz mountains descend to meet the south caspian lowlands of ne iran to better understand the present day tectonics and seismicity of this region which includes the cities of gorgan and gonbad e qabus combined population 500 000 we installed a temporary local seismic network across the area for 6 months between 2009 and 2010 we analysed the seismicity and focal mechanisms together with data from the permanent networks of the institute of geophysics university of tehran igut and the international institute of earthquake engineering and seismology iiees based in tehran microseismicity is focused primarily on the shahrud fault system which bounds the east alborz range to the south relatively few earthquakes are associated with the khazar thrust fault which bounds the north side of the range a cluster of shallow microseismicity 15 km depth occurs 40 km north of the khazar fault within the south caspian lowlands scl an area typically thought to be non deforming this area coincides with the location of three relatively deep thrust earthquakes m w 5 3 5 5 which occurred in 1999 2004 and 2005 inversion of teleseismic body waveforms allows us to constrain the depth of these earthquakes at 26 29 km although significant sedimentation throughout the scl obscures any expression of recent fault activity at the surface focal mechanisms of well located events from the shallow cluster of micro seismicity show a significant component of left lateral strike slip motion assuming slip occurs on ne sw fault planes typical of active faults in the region as well as a small normal component inversion of traveltimes for well located events in our network yields a velocity structure for the region and a moho depth of 41 km the pattern of deep thrust and shallow normal seismicity could be explained by bending of the rigid south caspian crust as it underthrusts the east alborz mountains and central iran late quaternary reorganization of drainage systems in the scl may be the result of shallow normal fault activity within the scl

relocation of the 2006 mw 6 1 silakhour iran earthquake sequence details of fault segmentation on the main recent fault the m w 6 1 silakhour earthquake occurred on 31 march 2006 in the zagros region of iran it was preceded by two relatively large foreshocks of m b 4 8 and 5 2 on 30 march and followed by an extensive aftershock sequence the earthquake sequence occurred along the right lateral strike slip main recent fault mrf to understand the spatial relationship between the mainshock and the high level of foreshock and aftershock activity we have merged all seismic data recorded by iranian seismic networks with data from the global catalogs and relocated the events using a multiple event relocation method we also conducted source studies of the mainshock and larger foreshocks and aftershocks which confirm dominantly right lateral strike slip faulting for the mainshock the two large foreshocks and the largest aftershock the relocated epicenters of the 2006 earthquake sequence lie close to the mrf and spread parallel to the mrf over a distance of 55 km much longer than the 15 20 km rupture length to be expected of a magnitude 6 1 strike slip earthquake the relocated epicenters reveals that the seismic sequence is divided into two parts an eastern patch on the borujerd dorud segment of the mrf that is directly associated with the rupture of the mainshock and a second patch 20 25 km long on the nahavand borujerd segment of the mrf the two patches are offset by 5 km in the same sense as the mrf the pattern of the western patch of seismicity strongly suggests a seismically active lineation that does not correspond closely to the mapped faults of the area we take this as evidence of ongoing evolution of fault geometry on this section of the mrf coulomb stress calculations suggest that the seismicity on the nahavand borujerd segment may be a separate earthquake sequence triggered by static stress changes related to the mainshock rupture

the deep structure of the iranian plateau high resolution structures of the lithosphere asthenosphere system beneath a seismic profile in iran are obtained by the simultaneous inversion of data from receiver functions and fundamental mode rayleigh wave group velocity and validated by modeling bouguer gravity anomaly data the seismic data are gathered over a profile extending across zagros sanandaj sirjan zone ssz urumieh dokhtar magmatic arc udma central iran alborz binalud mountain ranges and kopeh dagh mountain ranges the results confirm the presence of crustal roots at the north and south of iranian plateau where it meets the arabian plate and eurasia the high velocity lithosphere of the arabian plate gently plunges nne ward beneath central iran supporting the subduction of the continental lithosphere responsible for the seismicity of the area the crust and lithosphere are thinner beneath central iran where two low velocity structures are very likely related to magma sources of the udma and in east of iran around lut block where the volcanism shows calcalkaline subduction related geochemistry the crustal lithospheric root to the north of the iranian plateau may represent the relict of a previous cimmeric subduction zone therefore the iranian lithosphere asthenosphere system could be the result of the coalescence of two separate subduction zones

on the nature of regional seismic phases ii on the influence of structural barriers summary the blockage of the lg wave by crustal barriers such as continental margins and graben structures has long been recognized as providing a very useful tool for mapping large scale lateral crustal variations along the propagation path numerical simulation of lg wave propagation in complex anelastic media using the pseudospectral method provides insight into the nature of the propagation process using both snapshots of the wavefield and synthetic seismograms a variety of 2 d structures have been investigated including the influence of sediments crustal thickness and attenuation thick sedimentary basins covering a graben structure can have a major influence since they remove lg energy by generating p conversion and scattering the principal mechanisms for strong lg attenuation across a graben the reduction of the lg energy is reinforced by anelastic attenuation in the sediments as well as the influence of the gradually thinning crustal waveguide associated with an elevated moho the extinction of lg in a sequence of explosions fired across the central graben of the north sea can be simulated by numerical calculations for the structure derived from refraction experiments

geomorphic and structural variations along the doruneh fault system central iran 1 this paper focuses on the analysis of geomorphic structural and behavioral characteristics along the doruneh fault system dfs east of longitude 56 45 e detailed geomorphic and structural analyses of different scale satellite images and digital topographic data accompanied with field surveys allowed us to establish a fault segmentation model in which three discrete fault zones have been recognized 1 the western fault zone wfz characterized by reverse left lateral mechanism with left handed step over geometry 2 the central fault zone cfz which is pure left lateral strike slip and comprises nearly parallel faults and 3 the eastern fault zone efz that is a trailing imbricate fan fault termination characterized by reverse faulting and fault related folding each fault zone shows discrete geometry and kinematics implying that deformation is not uniformly accommodated along the dfs we propose a new kinematic model to explain how the dfs accommodate the arabia eurasia convergence normal to the overall fault orientation according to this model the dfs takes up the northward motion between central iran lut block relative to eurasia by a complex kinematics varying from pure reverse to pure left lateral strike slip faulting the kinematics of the wfz and efz corresponds to the direction of the ne trending regional compression while the partitioning of slip into strike slip and reverse component of faulting on parallel faults strain partitioning allows the cfz to remain pure left lateral strike slip such a model propose a way to explain how large strike slip faults such as the dfs accommodate tectonic block motions perpendicular to strike of the faults

lg coda q variation across eurasia and its relation to crustal evolution an extensive set of broadband and short period seismograms from regional seismic events has been used to derive a tomographic image of broad scale variations of lg coda q for most of eurasia the image indicates that lg coda q at a frequency of 1 hz varies between about 200 and 1000 lowest q values 800 are found in four regions the east european shield the siberian shield the indian shield and the southwestern and oldest portion of the altaid belt the pattern of lg coda q variation across eurasia suggests that crustal q in any region is directly proportional to the length of time that has elapsed since the most recent episode of large scale compressional tectonic activity or upper mantle heating that occurred there we interpret the low q as resulting largely from hydrothermal fluids generated by tectonic activity or heating that now reside in cracks and permeable portions of the eurasian crust crustal q increases with time after that activity as fluids are lost to the surface or absorbed by retrograde metamorphism

lg coda q and its relation to the geology and tectonics of the middle east regional seismograms were collected to image the lateral variations of lg coda q at 1 hz q 0 and its frequency dependence in the middle east using a back projection method the data include 124 vertical component traces recorded at 10 stations during the period 1986 1996 the resulting images reveal lateral variations in both q 0 and in the turkish and iranian plateaus a highly deformed and tectonically active region q 0 ranges between about 150 and 300 with the lowest values occurring in western anatolia where extremely high heat flow has been measured the low q 0 values found in this region agree with those found in other tectonically active regions of the world throughout most of the arabian peninsula a relatively stable region q 0 varies between 350 and 450 being highest in the shield area and lowest in the eastern basins all values are considerably lower than those found in most other stable regions low q values throughout the middle east may be caused by interstitial fluids that have migrated to the crust from the upper mantle where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there low q 0 values about 250 are also found in the oman folded zone a region with thick sedimentary deposits varies inversely with q 0 throughout most of the middle east with lower values 0 4 0 5 in the arabian peninsula and higher values 0 6 0 8 in iran and turkey q 0 and are both low in the oman folded zone and western anatolia

correlation of lg amplitude ratios from peaceful nuclear explosions to crustal structure in northern eurasia because the lg phase is strongly affected by the variations of crustal structure in some areas understanding these factors is important for nuclear test monitoring this study examines the effects of regional tectonic structure on lg propagation by using the peaceful nuclear explosion pne profiles in russia the logarithms of lg sn and lg pcoda pne amplitude ratios within the 0 5 to 3 hz frequency band are measured and correlated with the regional crustal structures both ratios are found to decrease within the areas with thick low velocity sedimentary cover and across tectonic boundaries with abrupt variations of crustal thickness for the offset derivatives of both the logarithmic ratios a linear relationship to the slopes of the moho and the vertical travel times within the sedimentary cover is determined a strong negative slope is observed along both crustal thinning and crustal thickening segments and a positive slope follows the negative slope across a crustal thickening segment therefore crustal thinning appears to affect the lg propagation stronger than crustal thickening which could be due to focusing lg energy within the crustal wave guide the log amplitude regression provided in this article could be useful for predicting lg behavior in areas where amplitude measurements are not available

crustal scale structure of the south caspian basin revealed by deep seismic reflection profiling abstract two deep seismic reflection profiles from the south caspian basin provide the first normal incidence image of possibly the thickest sedimentary basin in the world significant features imaged with these seismic data are 1 a series of high amplitude folds developed within a thick 10 km neogene sedimentary section bounded discordantly below by 2 a gently n dipping intermittent reflection at 14 20 km 8 0 s 3 a prominent deep reflector at 26 28 km depth 12 8 13 0 s with a gentle northward dip 4 an underlying layered interval with discernibly lower frequency reflections down to 36 40 km 16 0 16 5 s and 5 a noticeable decrease in reflectivity below 36 40 km based on the downward termination of fault cored folds and their discordance with subhorizontal underlying reflections the reflection at 14 20 km is interpreted to be the basal detachment for structures associated with the absheron ridge the bright reflection at 26 28 km depth is interpreted as the basement cover contact and the underlying 10 km portion of the section is interpreted as crystalline basement downward diminution of reflectivity at 36 40 km is thought to represent the moho despite the absence of a clearly reflective horizon these interpretations are consistent with previous velocity models from both seismic refraction and teleseismic studies in the south caspian region that suggested a minimum sedimentary thickness of 20 km and a crustal thickness of 35 40 km both the apparent lack of local structural relief on the basement reflector and seismic velocities vp 6 8 km s obtained from earlier studies suggest this crust is not thinned continental material although thicker than typical oceanic crust 6 8 km the apparent 10 km thickness of the south caspian crystalline crust is interpreted to be of oceanic affinity for this part of the basin active seismicity down to mantle depths 80 km and gentle deepening of the crust from south to north suggest northward subduction of the south caspian oceanic lithosphere beneath the continental lithosphere of the central caspian basin

variation of moho depth in the central part of the alborz mountains northern iran summary the alborz mountains of northern iran form a belt of active crustal deformation along the southern side of the caspian sea within the broad arabian eurasia continental collision zone although the range has an average elevation of about 3000 m with the volcanic peak damavand reaching an elevations of 5671 m early gravity studies found that the crust beneath the range is no thicker than that beneath the surrounding region suggesting the range is not supported by a crustal root we determine a model for the crust of the central alborz mountains using teleseismic receiver functions from data recorded on a network of broad band seismographs temporarily deployed across the central part of the range the receiver functions from these recordings have been inverted simultaneously with fundamental mode rayleigh wave group velocity measurements in the 10 100 s period range our analysis shows a thickening of the crust from 48 km beneath the northern part of the central iranian plateau to 55 58 km below the central part of the alborz mountains then a thinning of the crust to 46 km north of the alborz mountains beneath the coastal region of the south caspian sea our seismological results show that the central alborz mountains have a moderate crustal root but of insufficient thickness to compensate the elevation of the range the analysis of free air gravity shows that the elevation of the alborz mountains is largely supported by the elastic strength of the iranian plate the south caspian plate or both

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

structures of the west african craton margin across southern mauritania inferred from a 450 km geoelectrical profile magnetotelluric mt measurements were carried out at 20 sites extending 450 km across southern mauritania in order to study lithospheric structures related to the west african craton wac margin the mt profile starts to the west on the senegal mauritania basin s m basin traverses across the mauritanides orogenic belt and terminates on the western border of the wac taoudeni basin distortion effects due to local shallow inhomogeneities are present in nearly all of the basin data in such a situation the preliminary interpretation of the data was done by using 1d inversions based upon rotationally invariant parameters such distortion is not apparent for the belt and craton sites and 1d inversions were followed by 2d modeling the models produced reveal a clear crustal subdivision into a resistive upper crust underlain by a two layer lower crust with two conductors one at mid crustal depths supposed fluid produced beneath the s m basin and the second at the base of the crust beneath the wac the 14 km thick conductive material below the mauritanides belt is interpreted as large imbricated thrusts representing the deep roots of the mauritanides nappes the models also show that significant contrasts in resistivity extend deep in the lithosphere between the cratonic area and the senegal microplate

precise dielectric profiling of ice cores a new device with improved guarding and its theory dielectric profiling dep a capacitive method for measuring an ice core s electrical conductivity and permittivity has been in use for several years we have built an improved dep instrument with a modified guarded electrode geometry whose capacitance can be determined from potential theory the new instrument can measure an ice core s conductivity and permittivity to within a few per cent error a high enough accuracy to infer its density using well known models

tomographic pn and sn velocity beneath the continental collision zone from alps to himalaya 1 we have obtained vp and vs velocity images of the uppermost mantle beneath the continental collision zone from the alps to the himalaya by performing tomographic inversion using both pn and sn travel times 654 999 pn arrivals and 121 838 sn arrivals were selected from the joint database including isc ehb iran bulletin and the annual bulletin of chinese earthquakes average pn and sn velocities are 8 04 km s and 4 60 km s respectively and maximum velocity perturbations are about 6 pn velocity correlates well with topography in general mountains with high elevations show low velocity while the seas basins and plains with low elevations show high velocity because the mountains are collision zones with strong tectonic activity and the low elevation areas are stable plates the large tectonic lines are boundaries between high and low pn velocity such as plate boundaries sutures and faults between plates and orogens sn velocity shows a very similar pattern to pn velocity a geodynamic cartoon is proposed to show the relationship between velocity and tectonics indicating that the sutures are boundaries with high dip angles and the plate boundaries are low angle reverse faults in the region

the 1994 sefidabeh eastern iran earthquakes revisited new evidence from satellite radar interferometry and carbonate dating about the growth of an active fold above a blind thrust fault in 1994 three shallow earthquakes of mw 6 occurred close together on blind thrusts near sefidabeh in eastern iran in an earlier study of the teleseismic waveforms the geomorphology and the faulting in the epicentral region it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system whose activity could be detected by its effect on the surface drainage in this study we present a sar interferogram that precisely determines the location and amount of coseismic surface displacements showing that the earthquakes in the sefidabeh sequence probably occurred on en echelon fault segments associated with three stepping ridges we also present u th dates of 100 ka for lake deposits uplifted by the growing ridge from the cumulative dated uplift and knowledge of the surface displacements due to an earthquake sequence we estimate that 120 such events have occurred in the past 100 ka with an average recurrence interval of 830 yr and an average convergence rate of 1 5 mm yr 1 on the sefidabeh thrust each estimate has an uncertainty of a factor of two either way we argue that the sefidabeh fault originally formed by coalescence of many small fault segments and has grown in length at about 2 cm yr 1 in the past 100 ka though the coseismic surface deformation observed in the sar interferogram closely resembles folding the overall topography does not because of inherited topography associated with earlier geological deformation in spite of this the activity of the buried thrust fault can easily be detected by its effect on the surface drainage a significant lesson when interpreting landscapes that are not entirely due to the present day deformation

present day kinematics and fault slip rates in eastern iran derived from 11 years of gps data we analyze new gps data spanning 11 years at 92 stations in eastern iran we use these data to analyze the present day kinematics and the slip rates on most seismogenic faults in eastern iran the east lut west lut kuhbanan anar dehshir and doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5 6 0 6 4 4 0 4 3 6 1 3 2 0 0 7 1 4 0 9 and 1 3 0 8 mm yr respectively slip is right lateral on the ns striking east lut west lut kuhbanan anar and dehshir faults and left lateral on the ew doruneh fault the ns faults slice the eastern iranian crust into five blocks that are moving northward at 6 13 mm yr with respect to the stable afghan crust at the eastern edge of the collision zone the collective behavior of the ns faults might thus allow the arabian promontory to impinge northward into the eurasian crust the ns faults achieve additional ns shortening by rotating counterclockwise in the horizontal plane at current rates up to 0 8 ma modeling the gps and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate 1 0 4 ma over the last 12 ma we identify large strains at the tips of the rotating east lut west lut and kuhbanan faults which we suspect to be responsible for the important historical and instrumental seismicity in those zones

thrust tectonics of the binalood region ne iran the binalood region in ne iran which is an eastern segment of the alborz mountains is affected by thin skinned tectonics lower paleozoic jurassic cretaceous and cenozoic rock sequences as well as remnants of the paleo tethys oceanic realm are transported in a southwestward direction by several thrust faults which are of two generations 1 cimmerian and 2 alpine structural units in this region form either single thrust sheets or duplexes they have been displaced sequentially in a piggyback style from the hinterland ne to foreland sw under ductile brittle ductile and brittle conditions geometrically they constitute an antiformal stack breached on its southwestern side by major and minor out of sequence thrusts

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

pn tomographic imaging of mantle lid velocity and anisotropy at the junction of the arabian eurasian and african plates an edited version of this paper was published by blackwell publishing in geophysical journal international copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02355 x http atlas geo cornell edu middleeastnorthafrica publications al lazki2004 htm

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

the crustal structure of the southern caspian region the south caspian basin appears to behave as a relatively rigid aseismic block within the otherwise deforming alpine himalayan orogenic belt this anomalous character suggests that there is a fundamental compositional difference between the crust of the south caspian basin and that of the surrounding region five new estimates of crustal velocity structure beneath the southern caspian region are determined by the teleseismic receiver function method these models show that the crust in turkmenia along the trend of the apshceron balkhan sill kopet dag mountains is 50 km thick in the southwestern part of the caspian basin the crust is 33 km thick and consists of a 13 km thick sedimentary section lying on a high velocity vp 7 1 km s 1 lower crustal section in the southeastern part of the basin the crust is 30 km thick and consists of a 10 km thick sedimentary section overlying a 20 km thick low velocity vp 5 8 km s 1 crystalline crust the receiver function models are combined with velocity models from previous russian deep seismic sounding studies into a 1800 km long ese wnw trending crustal cross section across the kura depression the south caspian basin and the kopet dag mountains the most significant features of this crustal model are the 20 km variation in thickness of cenozoic sedimentary basin deposits the absence of a granitic vp 5 8 6 5 km s 1 crustal layer in the central part of the south caspian basin and 20 km of crustal thinning beneath the central part of the basin the moho beneath the south caspian basin has a broad arch like structure whose western boundary is a relatively narrow zone across which the crust thins rapidly 20 km thinning over a 100 km zone and whose eastern boundary has a more gradual change in crustal thickness 20 km thinning over a 400 km zone the velocity depth profiles derived from the receiver functions are compared to laboratory velocity estimates made at pressures and temperatures appropriate for the lower crust in turkmenia but the seismic p wave data alone do not permit differentiation between the various possible rock types the crustal model developed for the south caspian basin is consistent with the hypothesis that the crystalline crust of the basin is a section of oceanic crust that is being overthrust by the continental crust around much of its margins however we cannot rule out the possibility that the crystalline crust beneath the basin is a section of lower continental crust whose upper crustal section has been removed by erosion or faulting

seismological evidence for crustal scale thrusting in the zagros mountain belt iran summary crustal receiver functions rfs computed from the records of 45 temporary seismological stations installed on a 620 km long profile across central zagros provide the first direct evidence for crustal thickening in this mountain belt due to a rather short 14 km average station spacing the migrated section computed from radial rfs displays the moho depth variations across the belt with good spatial resolution from the coast of the persian gulf to 25 km southwest of the main zagros thrust mzt the moho is almost horizontal with slight depth variations around 45 km crustal thickness then increases abruptly to a maximum of 70 km beneath the sanandaj sirjan metamorphic zone between 50 and 90 km northeast of the surface exposure of the mzt further northeast the moho depth decreases to 42 km beneath the urumiehdokhtar magmatic assemblage and the southern part of the central iranian microcontinent the region of thickest crust is located 75 km to the northeast of the bouguer anomaly low at 220 mgals gravity modelling shows that the measured moho depth variations can be reconciled with gravity observations by assuming that the crust of zagros underthrusts the crust of central iran along the mzt considered as a crustal scale structure this hypothesis is compatible with shortening estimates by balanced cross sections of the zagros folded belt as well as with structural and petrological studies of the metamorphic sanandaj sirjan zone

new constraints on upper mantle s velocity structure and crustal thickness of the iranian plateau using partitioned waveform inversion summary the continental collision between the african and eurasian plates resulted in a tectonically young and complex deformation in the iranian plateau the present day iranian plateau is characterized by diverse tectonic domains including the continental collisions e g zagros and alborz and the oceanic plate subduction e g makran partitioned waveform inversion method is used here to image the s velocity structure of the upper mantle and moho depth variations in the iranian plateau of nearly 3000 waveforms originally selected for the analysis we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper mantle s velocity structure and moho depth for the region our new seismic images show seismically faster upper mantle beneath the zagros and the arabian plate compared to the central iran and alborz this high velocity anomaly has descended beneath the central iran along the main zagros thrust across the zagros collision zone the tomographic images show a slab stagnation in the transition zone at about 410 km depth in the form of a horizontal high velocity zone which does not penetrate the deeper parts of the mantle the lowest s velocities are concentrated beneath the central iran and alborz according to our velocity models a strong high velocity anomaly is resolved beneath the trapped south caspian basin with clear indication of westward underthrusting beneath the talesh and western alborz in makran southeast iran there is a clear evidence of subduction of oceanic crust of the arabian plate beneath the makran belt which is correlated with seismicity pattern across the makran zone also the inverted moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the zagros suture zone in some places to a maximum depth of 65 km which indicates the influence of crustal thickening and shortening beneath arabian eurasian plate boundary a significantly crustal thinning is observable across the south caspian basin compared to its margins

fault identification for buried strike slip earthquakes using insar the 1994 and 2004 al hoceima morocco earthquakes summary the 1994 m w 6 0 and 2004 m w 6 5 al hoceima earthquakes are the largest to have occurred in morocco for 100 yr and give valuable insight into the poorly understood tectonics of the area bodywave modelling indicates the earthquakes occurred on near vertical strike slip faults with the nodal planes oriented nw se and ne sw distinguishing between the primary fault plane and auxiliary planes using either geodetic or seismic data is difficult due to the spatial symmetry in deformation fields and radiation pattern of moderately sized buried strikeslip earthquakes preliminary studies using aftershock locations and surface observations have been unable to identify the orientation of the primary fault plane for either earthquake conclusively we use radar interferometry and aftershock relocation of the earthquake sequence to resolve the ambiguity for the 2004 earthquake inverting the interferograms for a uniform slip model based either of the two potential nodal planes results in similar misfits to the data however the ne sw best fit fault plane has an unrealistically high fault slip to length ratio and we conclude the nw se striking nodal plane is the primary fault plane and slip was right lateral we carry out tests on synthetic data for a buried strike slip earthquake in which the orientation of the fault plane is known a priori independent of geometry missing data and correlated noise models produced assuming the auxiliary plane to be the fault plane have very high fault slip to length ratios the 1994 earthquake had a smaller magnitude and comparisons of model misfits and slip to length ratios do not conclusively indicate which of the nodal planes is the primary fault plane nonetheless the insar data provides valuable information by improving the accuracy of the earthquake location by an order of magnitude we carry out a multiple event relocation of the entire earthquake sequence including aftershocks making use of the absolute locations for the 1994 and 2004 main shocks from our insar study the aftershock locations are consistent with a nw se orientated fault plane in 2004 and suggests that the 1994 earthquake occurred on a ne sw fault perpendicular to the fault which ruptured in 2004 previous tectonic models of the area proposed a bookshelf model of block rotation with nne ssw left lateral faults this model requires modification to accommodate the observation of right lateral slip on a nw se fault plane for the 2004 earthquake and we prefer to interpret the fault orientations as due to a zone of distributed shear with a right lateral fault striking at 115 and conjugate clockwise rotating left lateral faults striking at 25

seismic imaging of the lithospheric structure of the zagros mountain belt iran we present a synthesis and a comparison of the results of two temporary passive seismic experiments installed for a few months across central and northern zagros the receiver function analysis of teleseismic earthquake records gives a high resolution image of the moho beneath the seismic transects on both cross sections the crust has an average thickness of 43 2 km beneath the zagros fold and thrust belt and the central domain the crust is thicker beneath the hanging wall of the main zagros reverse fault mzrf with a larger maximum moho depth in central 69 2 km than in northern zagros 56 2 km the thickening affects a narrower region 170 km beneath the sanandaj sirjan zone of central zagros and a wider region 320 km in northern zagros we propose that this thickening is related to overthrusting of the crust of the arabian margin by the crust of central iran along the mzrf considered as a major thrust fault cross cutting the whole crust the fault is imaged as a lowvelocity layer in the receiver function data of the northern zagros profile moreover the crustal scale thrust model reconciles the imaged seismic moho with the bouguer anomaly data measured on the central zagros transect at upper mantle depth p wave tomography confirms the previously observed strong contrast between the faster velocities of the arabian margin and the lower velocities of the iranian micro blocks our higher resolution tomography combined with surface wave analysis locates the suture in the shallow mantle of the sanandaj sirjan zone beneath central zagros the arabian upper mantle has shield like shear wave velocities while the lower velocities of the iranian upper mantle are likely due to higher temperature but these velocities are not low enough and the low velocity layer not thick enough to conclude on a delamination of the lithospheric mantle lid beneath iran the lack of a high velocity anomaly in the mantle beneath central iran suggests that the neotethyan oceanic lithosphere is probably detached from the arabian margin

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

seismicity in the western coast of the south caspian basin and the talesh mountains summary we have studied the seismicity of the western margin of the south caspian basin scb and the neighbouring talesh fold and thrust belt we have used the hypocentroidal decomposition multiple event location technique to obtain accurate location of events recorded during 2 yr of observation data from a temporary seismic network in northwest iran and other national and regional networks were combined to make an accurate assessment of seismicity in the region significant offshore seismicity is observed in a 50 km wide margin of the scb east of the talesh fault along the caspian coastline the depth of seismicity varies from 20 to 47km this pattern extends inland about 20 25km west of the north talesh fault this pattern of seismicity indicates that the basement slab of the south caspian is undergoing intense seismic deformation as it is underthrusting beneath the northern talesh whereas the sedimentary cover deforms aseismically the seismicity depths and previous focal mechanisms of the larger offshore events are consistent with low angle underthrusting of the south caspian floor withinthetalesh seismicityismostlyconcentratedinthenorthernandsouthernstructuralarcs of the range where deformation is more intense and complicated shallow crustal seismicity in the eastern flank of the talesh is much less intense than in the western flank where it signifies the deformation of the upper continental crust one major observation is the lack of any significant n s alignment of shallow epicentres inside the central talesh to match the observed right lateral shear deformation there this suggests that shear deformation inside the taleshmayhaveadistributednature ratherthanbeingconcentratedonasinglethorough going fault zone as the talesh moves northward relative to the south caspian we have determined a new moment tensor solution in the southwestern talesh with a dominant n s trending right lateral motion the only solution so far confirming along strike shear deformation in the talesh

accommodation of late cenozoic oblique shortening in the alborz range northern iran abstract the alborz range northern iran deforms by strain partitioning of oblique shortening onto range parallel left lateral strike slip and thrust faults deformation is due to the north south arabia eurasia convergence and westward motion of the adjacent south caspian relative to iran roughly north south shortening occurs on thrusts that dip inwards from the range margins precambrian basement is not exposed because of detachment along upper proterozoic evaporites and the thickness of overlying strata 10 km other detachments occur within phanerozoic sediments active left lateral strike slip faults trend ene in the east of the range wnw in the west the eastern mosha fault has a left lateral offset of 30 35 km shortening across the range is 30 km 25 30 at the longitude of tehran this is hard to reconcile with the crustal thickness of 35 km which is similar to adjacent basins percentage shortening across the alborz is similar to the adjacent kopet dagh but because the latter is twice as wide finite shortening is roughly half the difference may be accommodated by subduction of the adjacent south caspian basin northwards under the middle caspian south caspian sediments began folding in the pliocene the present kinematics of the alborz may have begun at this time including a reversal from range parallel right lateral to left lateral strike slip faulting but the regional stratigraphy indicates uplift as early as the mid tertiary

offset on the main recent fault of nw iran and implications for the late cenozoic tectonics of the arabia eurasia collision zone summary we use drainage patterns geological markers and geomorphological features to determine a right lateral offset of 50 km and possibly as much as 70 km on the main recent fault in nw iran this fault trends nw se and forms the ne border of the zagros mountains it accommodates the strike slip component of the n s convergence between arabia and eurasia with the ne sw shortening component being accommodated in the zagros fold belt its 50 km strike slip offset implies a shortening of 50 km in the fold belt and 70 km total n s convergence accommodated in the nw zagros this is a substantial fraction of the 85 140 km overall arabia eurasia convergence expected over the last 3 5 ma if the main recent fault initiated at that time as seems likely from geological arguments it has a horizontal slip rate of at least 10 17 mm yr 1 and should be the source of frequent earthquakes of ms 6 7 as has been seen in the 20th century and the earlier historical record the similarity of the offsets and probable ages of the north anatolian and main recent faults suggests that they have been active as an almost continuous zone of right lateral shear on the north edge of the arabian and anatolian plates since the early pliocene

oblique to orthogonal convergence across the turan block in the post miocene the 2 17 km thick post triassic sediments of the turan continental block accumulated in a south dipping basin characterized by fault controlled facies and thickness variations since the late miocene the thickest part of the basin fill on the southern margin of the turan block has been folded and uplifted as the kopet dag range in response to the iran turan convergence the apsheron sill which separates the northern continental from the southern oceanic caspian sea basins links the kopet dag greater balkan ranges turkmenistan to the caucasus azerbaijan the large scale east west to west northwest east southeast oriented arrays of periclinal folds of the kopet dag range which indicate a north south oriented compression were generated by a fault propagation mechanism the migration and accumulation of hydrocarbons has been controlled by the deformation pattern the 75 km of north south shortening in the western kopet dag greater balkan area can be resolved into 70 km of pure compression orthogonal to the n120 oriented ashgabat fault and 35 km of dextral slip along this fault the north south iran asia relative motion has produced the oblique convergent northwest southeast structures along the dextral ashgabat fault and the pure convergent east west structures in the western kopet dag greater balkan region the orientation of the structures has been controlled by the angular relationship between the relative motion of two blocks and the orientation of their boundaries the ashgabat fault as a major crustal anisotropy has concentrated the deformation into a narrow fold and thrust belt whereas in the west the deformation is distributed over a wider area the pattern of deformation has been controlled by the iran turan boundary conditions

evidence for a missing crustal root and a thin lithosphere beneath the central alborz by receiver function studies summary the alborz mountains build the northern part of the alpine himalayan orogen in western asia they are located south of the caspian sea and form an east west range across the north of iran this region is one of the most active tectonic areas as it undergoes extensive crustal deformation and shortening in the present work we used data from 11 permanent stations of the tehran telemetry seismic network to estimate the thickness of the crust and mantle lithosphere beneath the central alborz region by p and s receiver function methods results of both p and s receiver functions revealed a relatively large crustal thickness beneath this region 51 54 km which can be associated with the shortening process related to the orogenic belt no remarkable crustal thickening has been detected below the high topography of central alborz a thick crust 67 5 km is observed locally in the region beneath the damavand volcano which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region the s receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of 90 km which we interpreted as the base of the lithosphere the missing crustal root and the relatively thin lithosphere beneath the alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the alborz

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models