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

tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

imaging crustal discontinuities and the downgoing slab beneath western crete the migration of teleseismic receiver functions yields high resolution images of the crustal structure of western crete data were collected during two field campaigns in 1996 and 1997 by networks of six and 47 short period three component seismic stations respectively a total of 1288 seismograms from 97 teleseismic events were restituted to true ground displacement within a period range from 0 5 to 7 s the application of a noise adaptive deconvolution filter and a new polarization analysis technique helped to overcome problems with local coda and noise conditions the computation and migration of receiver functions results in images of local crustal structures with unprecedented spatial resolution for this region the crust under crete consists of a continental top layer of 15 20 km thickness above a 20 30 km thick subducted fossil accretionary wedge with a characteristic en echelon fault sequence the downgoing oceanic moho lies at a depth of 40 60 km and shows a topography or undulation with an amplitude of several kilometres as a consequence of slab depth and distribution of local seismicity the mediterranean ridge is interpreted as the recent accretionary wedge

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

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

the zagros folded belt fars iran constraints from topography and critical wedge modelling summary the late miocene tectonics of the zagros folded belt fars province has for long been related solely to folding of the cover controlled by a ductile decollement between basement and the sedimentary cover however geological constraints topography analysis and seismotectonic studies reveal that basement thrusting may produce locally significant deformation in the cover to determine how the deep seated deformation in the basement may contribute to the overall topography we first examine the filtered large and short wavelengths of the topography we find that the short wavelength component of the topography 20 25 km including the zagros folds is superimposed on the differential uplift at the regional scale in other words the regional base level of folded marker horizons remains parallel to the regional topography of interest modelling reveals that the salt based wedge model alone is not able to reproduce the large wavelength component of the topography of the zagros folded belt this reveals that when a thick relatively to its overburden layer of salt forms the basal decollement it is generally too weak and cannot support the growth of significant topography we then test an alternative thick skinned crustal wedge model involving the crust of the arabian margin which is decoupled above a viscous lower crust this model satisfactorily reproduces the observed topography and is consistent with present day basement thrusting topography analyses and geological constraints we conclude that basement involved thickening and shortening is mechanically required to produce the shape of the zagros folded belt since at least 10 ma finally the involvement of the basement provides mechanical and kinematic constraints that should be accounted for cross sections balancing and further assessing the evolution of zagros at crustal or lithospheric scales

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

neonereites uniserialis from c 600 ma year old rocks in western scotland and the emergence of animals a chain of pellets neonereites uniserialis usually attributed to a coelomate or pseudocoelomate metazoan is described from the middle dalradian bonahaven formation of western scotland in sandstones not far above the port askaig tillite this trail lies more than 8 km below u pb zircon dated tayvallich lavas 595 4 ma and predates early deformation plus intrusion by granites at ben vuirich dated at 597 11 and 590 2 ma u pb zircon chronology for early metazoan evolution suggests that this is the earliest putative evidence for coelomates or pseudocoelomate discovered so far with a minimum interglacial age of c 600 ma bp it is from about this time that a fall takes place in the maximum 13 c of carbonates suggestive of a decline in the long term rate of carbon burial one explanation for this decline is the increasing impact of metazoan bioturbation through the late neoproterozoic to cambrian interval

slip rate of the kazerun fault and main recent fault zagros iran from 3d mechanical modeling abstract the aim of this work is using gps velocities and 3d mechanical modeling including preexisting faults with frictional properties that obey coulomb failure process to explore the long term slip rates of the mrf fault and kazerun faults in the zagros mountain of iran a model was constructed using spatially varying crustal thickness geothermal gradient and two major faults structural boundaries are derived from the several deep seismic soundings carried out in the area far field gps velocities and late quaternary fault slip rates are used to compare the model results rheological tests show that effective fault friction lower than 0 05 leads to high slip rates that fit with geologically and geodetically determined slip rates of mrf and kazerun fault these results suggest that mrf and kazerun fault are weak faults like san andreas and north anatolian fault

seismotectonics of the zagros continental collision zone and a comparison with the himalayas accurate focal depths of 16 medium to large zagros earthquakes were determined from identification of surface reflected phases by comparing observed long period p waves with synthetic seismograms all events are shallow 6 12 km and show no tendency to deepen toward the main zagros thrust geological and geophysical evidence suggests that most of these earthquakes probably occurred within the uppermost precambrian basement because the focal mechanisms of these events indicate high angle reverse faulting the events do not occur on a single detachment surface but rather reflect horizontal shortening of the basement on numerous short segmented 8 probably occurred along this detachment a comparative study of the zagros with the himalayas suggests that the active tectonics of the zagros continental collision zone and the iranian blocks arc similar to those of the himalayas and the tibetan terranes in oligocene time

seismic structure of iran from surface and body wave data summary an investigation of the lithospheric structure of the iranian plateau has been undertaken in order to find complementary information bearing on the tectonic evolution of the plateau the phase velocity dispersion of the fundamental mode rayleigh waves between the wwssn stations shiraz tabriz and mashad and between the sites of the iranian long period array and maio sro have been obtained from well dispersed wavetrains generated by eight great circle earthquakes the aftershocks of the destructive tabas earthquake in central iran which were accurately located by a field survey recorded clear p and s phases at maio providing supplementary travel time information for the interpretation of the phase velocity data the uppermost mantle p wave velocities beneath iran obtained in a previous study asudeh were also used in the analysis an alpine type crust was found for the iranian plateau while uppermost mantle velocities ranging from low velocity mantle in eastern iran to a high velocity shield like structure in the west of the country

tertiary sequence of deformation in a thin skinned thick skinned collision belt the zagros folded belt fars iran 1 we describe how thin skinned thick skinned deformation in the zagros folded belt interacted in time and space homogeneous fold wavelengths 15 8 5 3 km tectono sedimentary evidence for simultaneous fold growth in the past 5 5 2 5 ma drainage network organization and homogeneous peak differential stresses 40 15 mpa together point to buckling as the dominant process responsible for cover folding basin analysis reveals that basement inversion occurred 20 ma ago as the arabia eurasian plate convergence reduced and accumulation of neogene siliciclastics in foreland basin started by 10 ma ongoing contraction occurred by underplating of arabian crustal units beneath the iranian plate this process represents 75 of the total shortening it is not before 5 ma that the zagros foreland was incorporated into the southward propagating basement thrust wedge folds rejuvenated by 3 2 ma because of uplift driven by basement shortening and erosion since then folds grew at 0 3 0 6 mm yr and forced the rivers to flow axially a total shortening of 65 78 km 16 19 is estimated across the zagros this corresponds to shortening rates of 6 5 8 km ma consistent with current geodetic surveys we point out that although thin skinned deformation in the sedimentary cover may be important basement involved shortening should not be neglected as it requires far less shortening moreover for such foreland folded belts involving basement shortening underplating may be an efficient process accommodating a significant part of the plate convergence

brittle ductile transition zone case study zagros iran abstract a three dimensional lithosphere model with horizontal dimensions of 1500 km 600 km and a depth extent of 70 km is constructed from available geophysical data to find out strength as the maximum deviatoric stress the lithosphere supports at a given depth in arabia eurasia plate boundary zone the constructed model is first used in the calculation of thermal initial condition and then strength envelopes were calculated using the obtained geotherm and rheological flow laws numerical models are run for initial temperature distributions representing cold and hot lithosphere with two different rheology wet and dry the obtained mechanical structures were analyzed and compared with other geophysical data e g seismicity depth and isotherm depth distributions model results for wet and dry rheology indicate that the depth of the brittle ductile transition is about 8 km and 11 km for hot geotherm and 10 5 km to14 km and 21 28 for cold geotherm the results are in good agreement with focal depth in the zagros that most earthquakes occur in 8 15 km depth i e the long term strength of the continental lithosphere resided only in its upper part which was contained wholly within the crust the ilss integrated lithospheric strengths values for a wet crustal rheology have high range of 1 4 10 1012 n m 1 which is mainly the result of a low heat flow cold geotherm and 0 1 1012 n m 1 for wet rheology and hot geotherm

zagros phantom earthquakes reassessed the interplay of seismicity and deep salt flow in the simply folded belt unraveling the contributions of main shock slip aftershocks aseismic afterslip and postseismic relaxation to the deformation observed in earthquake sequences heightens our understanding of crustal rheology triggering phenomena and seismic hazard here we revisit two recent earthquakes in the zagros mountains iran which exhibited unusual and contentious aftereffects the mw 6 earthquakes at qeshm 2005 and fin 2006 are both associated with large interferometric synthetic aperture radar insar signals consistent with slip on steep reverse faults in carbonate rocks of the middle sedimentary cover but small aftershocks detected with local seismic networks were concentrated at significantly greater depths this discrepancy can be interpreted in one of two ways either 1 there is a genuine vertical separation between main shock and aftershocks reflecting a complex stress state near the basement cover interface or 2 the aftershocks delimit the main shock slip and the insar signals were caused by shallow updip afterslip phantom earthquakes with very similar magnitudes mechanisms and geographical positions as the original earthquakes here we show that main shock centroid depths obtained from body waveform modeling which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered strongly support the first interpretation at qeshm microseismic aftershock depths are centered at the level of the hormuz formation an infracambrian sequence of intercalated evaporitic and nonevaporitic sediments these aftershocks may reflect the breaking up of harder hormuz sediments and adjacent strata as the salt flows in response to main shock strain at the base of the cover this work bolsters recent suggestions that most large earthquakes in the zagros are contained within carbonate rocks in the midlower sedimentary cover and that the crystalline basement shortens mostly aseismically

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation

measuring lithospheric stretching on tethyan passive margins preliminary estimates of lithospheric stretching have been made by examining 63 stratigraphic sections from the northern and southern tethyan margins southeast france to bulgaria the study was centred on the italian southern alps the dolomites a portion of the southern margin within the external zones of the alpine orogen sections were decompacted and backstripped using the standard procedure allowing for errors in palaeowater depth estimates theoretical subsidence curves based on the finite duration stretching model were then fitted to the resultant water loaded subsidence curves in an attempt to clarify the pre compressional tectonic history of the region according to our results stretching started in the early to mid triassic and lasted 30 40 ma this conclusion is broadly in agreement with some previously published estimates the stretching factor is generally small 1 1 1 3 especially in southeast france and northern italy larger values of occur in the balkans c 1 5 to our knowledge the finite duration stretching model has not yet been applied to water loaded stratigraphic sections from the tethyan belt theory and observation appear to agree well

a combined magnetometry and gravity study across zagros orogeny in iran abstract in this work the structural geology and the tectonic conditions of the zagros orogeny along the route of qom to kermanshah cities were investigated using the combined geophysical methods of the airborne magnetometry and the ground based gravity data airborne magnetometry data of iran with a line space of survey 7 5 km were used to model the magnetic susceptibility property along the route at first the airborne magnetic data were stably 500 m downward continued to the ground surface in order to enhance minor changes of the earth s magnetic field over the studied region afterward 3d inverse modeling of the magnetic data was implemented to the downward continued data and subsequently the section of magnetic susceptibility variation along the desired route was extracted and imaged at depth the acquired model could appropriately predict the observed magnetic data showing low misfit values between the observation and the predicted data the analytic signal filter was applied to the reduced to pole rtp magnetic data leading to the determination of the active and probable hidden faults in the structural zones of the zagros such as sanandaj sirjan central domain cd and urumieh dokhtar based upon the generated peaks along the profile of analytic signal filter in addition the density variations of the subsurface geological layers were determined by 3d inverting of the ground based gravity data over the whole study area and extracting this property along the route the joint models of magnetic susceptibility and density variation could appropriately localize the traces of faults along with the geologically and tectonically structural boundaries in the region the locations of faults correspond well to the variation of geophysical parameters on the inverted sections probable direction slope and extension at depth of these faults were also determined on the sections indicating a high tectonized zone of the sanandaj sirjan zone ssz parallel to the zone of the urumieh dokhtar magmatic assemblage udma the udma zone increases the magnetic and the bouguer anomalies by intruding into the cd zone as well

presence of a layered lithosphere beneath the zagros collision zone abstract the continental collision between the arabian and eurasian plates following the subduction of the neo tethys ocean beneath eurasia resulted in a complex deformation across the zagros mountains we used more than 700 s receiver functions obtained from 61 permanent stations to provide a detailed image of the lithospheric interaction between the eurasian and arabian plates our results suggest the existence of two different lithospheric blocks a 200 km thick lithosphere was observed beneath the zagros collision zone and most likely represents the arabian lithosphere which has been strongly deformed thickened and depleted based on our results shortening due to the collisional process is differently accommodated by the crust and mantle lithosphere of the zagros collision zone we localized the thick arabian lithosphere beneath the zagros sanandaj sirjan zone ssz and urumieh dokhtar magmatic assemblage udma whereas the crustal thickening 70 km seems to be concentrated just beneath the ssz furthermore we found a thin lithosphere of about 80 90 km that we interpret here as the iranian lithosphere beneath central iran and alborz additionally our results suggest the presence of remnants of the fossil neo tethys subduction at depths ranging between 80 and 150 km within the arabian lithosphere this dipping structure can be seen beneath the zagros ssz and udma and seems to disappear towards the northeast beneath central iran and alborz these findings may support the idea of a breakoff of the oceanic neo tethyan slab beneath central iran which results in an asthenospheric upwelling and thinning of the iranian lithosphere beneath central iran and alborz the boundary between the arabian and iranian plates seems to be located northeast of the udma in the northwest of zagros and southwest of the udma in the central zagros region

a re assessment of focal depth distributions in southern iran the tien shan and northern india do earthquakes really occur in the continental mantle summary we investigate the depth distribution of earthquakes within the continental lithosphere of southern iran the tien shan and northern india by using synthetic seismograms to analyse p and sh body waveforms in the zagros mountains of southern iran earthquakes are apparently restricted to the upper crust depths of 20 km whereas in the tien shan and northern india they occur throughout the thickness of the continental crust to depths of 40 45 km we find no convincing evidence for earthquakes in the continental mantle of these regions in spite of previous suggestions to the contrary and question whether seismicity in the continental mantle is important in any part of the world in some regions such as iran the aegean tibet and california seismicity is virtually restricted to the upper continental crust whereas in others including parts of east africa the tien shan and northern india the lower crust is also seismically active although usually less so than the upper crust such variations cannot reliably be demonstrated from published catalogue or bulletin locations even from ones in which depth resolution is generally improved in contrast to the oceanic mantle lithosphere in which earthquakes certainly occur the continental mantle lithosphere is we suggest virtually aseismic and may not be significantly stronger than the lower continental crust these variations in continental seismogenic thickness are broadly correlated with variations in effective elastic thickness suggesting that the strength of the continental lithosphere resides in the crust and require some modification to prevalent views of lithosphere rheology

high resolution image of uppermost mantle beneath ne iran continental collision zone we invert 3775 relative p wave arrival times using the ach damped least square method of aki et al 1977 to study upper mantle structure beneath the ne iran continental collision zone the data for this study were recorded by 17 three component broad band stations operated from august 2006 to february 2008 along a profile from the center of iranian plateau near yazd to the northeastern part of iran on the turan platform just north of the kopeh dagh mountains the results confirm the previously known low velocity upper mantle beneath central iran our tomographic model reveals a deep high velocity anomaly the surficial expressions of this anomaly are between the ashkabad and doruneh faults where the resolution and ray coverage are good a transition zone in uppermost mantle is recognized under the binalud foreland that we interpreted as suture zone between iran and turan platform our results indicate that atrak valley which is the boundary between the binalud and kopeh dagh mountains can be considered as the northeastern suture of the iranian plateau where eurasia and turan platform under thrust beneath the binalud range and central iran

the crustal and upper mantle structure of the interior arabian platform summary the crustal and upper mantle velocity structure of the interior arabian platform is derived using the spectral analysis of long period p wave amplitude ratios the ratio of the vertical to the horizontal component is utilized to obtain crustal transfer functions using the thomson haskell matrix formulation for horizontally layered crustal models 20 earthquakes recorded at the long period station ryd between azimuths n20 w and n150 e were selected for the analysis based on the following criteria focal depths in the range 5 to 215 km body wave magnitudes greater than 5 0 and epicentral distances in the range 7 to 97 a careful quality check of the data left us with six events out of 29 that had short epicentral distances 20 to be analysed the selection criterion for the final model in the forward modelling process was based on the correlation coeycient between observed and theoretical transfer function the model suggested that the crust consists of five distinct layers the upper crustal layer has a p wave velocity of about 5 6 km s 1 and is about 3 km thick the second layer has a velocity of about 6 3 km s 1 and is 10 km thick the third layer has a velocity of 6 6 km s 1 and is 8 km thick the fourth layer has a velocity of 6 9 km s 1 and is 15 km thick the lower layer has a velocity of about 7 6 km s 1 and is 10 km thick for the mohorovicic discontinuity a velocity of 8 3 km s 1 for the upper mantle and 46 km depth are indicated

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

lithospheric structure of the arabian shield and platform from complete regional waveform modelling and surface wave group velocities summary regional seismic waveforms reveal significant differences in the structure of the arabian shield and the arabian platform we estimate lithospheric velocity structure by modelling regional waveforms recorded by the 1995 1997 saudi arabian temporary broadband deployment using a grid search scheme we employ a new method whereby we narrow the waveform modelling grid search by first fitting the fundamental mode love and rayleigh wave group velocities the group velocities constrain the average crustal thickness and velocities as well as the crustal velocity gradients because the group velocity fitting is computationally much faster than the synthetic seismogram calculation this method allows us to determine good average starting models quickly waveform fits of the jon and sn body wave arrivals constrain the mantle velocities the resulting lithospheric structures indicate that the arabian platform has an average crustal thickness of 40 km with relatively low crustal velocities average crustal p and s wave velocities of 6 07 and 3 50 km s 1 respectively without a strong velocity gradient the moho is shallower 36 km and crustal velocities are 6 per cent higher with a velocity increase with depth for the arabian shield fast crustal velocities of the arabian shield result from a predominantly mafic composition in the lower crust lower velocities in the arabian platform crust indicate a bulk felsic composition consistent with orogenesis of this former active margin p and s wave velocities immediately below the moho are slower in the arabian shield than in the arabian platform 7 9 and 4 30 km s 1 and 8 10 and 4 55 km s respectively this indicates that the poisson s ratios for the uppermost mantle of the arabian shield and platform are 0 29 and 0 27 respectively the lower mantle velocities and higher poisson s ratio beneath the arabian shield probably arise from a partially molten mantle associated with red sea spreading and continental volcanism although we cannot constrain the lateral extent of a zone of partially molten mantle

pn velocities beneath iran abstract in active tectonic areas like iran where the coverage of seismograph stations is inadequate but earthquakes occur frequently uppermost mantle body wave velocities are conventionally determined by using a single station and an array of earthquake sources this method fails when earthquakes are mislocated or source areas have varied structures an extension of the traditional surface wave two station method is developed for body waves and shown to be independent of mislocation errors it thus gives accurate estimates of body wave velocities along two station paths with greatly reduced errors uppermost mantle p wave p n velocities are determined along several paths in iran using this method and show zones of low velocity corresponding to zones of high attenuation and quaternary volcanic activity in the country a remarkably high p n velocity of 8 30 km s is found for the zagros area of western iran more typical of shield like structures than that of tectonic areas

ramp flat basement structures of the zagros mountains inferred from co seismic slip and afterslip of the 2017 mw7 3 darbandikhan iran iraq earthquake abstract the november 2017 mw7 3 darbandikhan earthquake in the northern zagros mountains of iran iraq was the largest instrumentally recorded earthquake to date in this mountain belt despite extensive research in this region the nature of active faults in the arabian basement beneath the zagros mountains is largely unresolved additionally there is active debate regarding the interaction of thin and thick skin shortening of the zagros and whether these processes are accommodated seismogenically here we use interferometric synthetic aperture radar insar of co and post seismic surface displacements to document the source of the darbandikhan earthquake and the first 120 days of afterslip following the earthquake we apply a fault inversion approach that finds permissible geometries locations and slip depths as a means to image subsurface structure with remote sensing geodesy we find that the darbandikhan earthquake ruptured the shallowly dipping 14 19 mountain front fault within the arabian crystalline basement 12 22 km deep we additionally find that afterslip propagated up dip of the earthquake onto the nearly horizontal dip 1 5 basal decollement of the zagros mountains indicating that the earthquake and its initial afterslip activated a ramp flat structure we also inverted co seismic insar displacements of the january 11 2018 mandali earthquake sequence that occurred 80 km south of the darbandikhan earthquake and find that these moderate magnitude events mw5 0 5 5 ruptured the lower phanerozoic cover of the zagros together the darbandikhan and mandali sequences demonstrate that the zagros mountains actively shorten via both thin and thick skin styles and that these modes of shortening are accommodated in part by earthquakes moreover the darbandikhan earthquake and afterslip highlight the presence of seismically active low angle thrust faults beneath the zagros that were not previously recognized highlighting sources for potential future large earthquakes we compare these results to the 2015 gorkha nepal earthquake to argue that frictional characteristics of decollement govern spatial relationships between seismic and aseismic slip in ramp flat geometries

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

microearthquake seismicity at the intersection between the kazerun fault and the main recent fault zagros iran summary seismicity and fault plane solutions of earthquakes at the intersection between the main recent fault a right lateral strike slip fault that bounds the zagros to the ne and the kazerun fault system another right lateral zone that crosses the zagros show slip to be partitioned into nearly pure strike slip at shallow depths and nearly pure thrust slip below 12 km such slip partitioning is commonly observed where oblique convergence occurs but in general faults of different styles lie adjacent to one another not at different depths with one below the other we provide evidence for this partitioning in a microearthquake study in which we deployed a temporary network of 29 seismographs for 7 weeks we located no activity north of the main zagros reverse fault mzrf which separates the zagros fold belt from central iran most earthquakes occurred between the northern termination of the kazerun fault and the mzrf but not near to known major faults activity is limited to the upper crust between 2 and 16 km most of the focal mechanisms show strike slip faulting dextral if the ns striking plane is the active plane but a few for the deepest events show reverse faulting distributed between the kazerun fault and the mzrf with p axis trending consistently ns this partitioning of the deformation with depth suggests that the brittle upper crust deforms by slip on pre existing faults that strike obliquely but that the lower crust accommodates the shortening by reverse faulting we infer that the deformation in the upper part of the crust reflects a stiffer medium in which pre existing faults localize the deformation the largest event recorded during this experiment located at the same place as the destructive 1977 naghan earthquake mw 5 9 348 victims shows reverse faulting likely related to the dopolan high zagros fault the crustal thickness deduced from receiver function analysis does not show a marked difference across the kazerun fault which suggests a pure strike slip motion on the fault

the geology of the persian gulf gulf of oman region a synthesis during the mesozoic most of the arabian peninsula persian gulf south western iran and eastern iraq constituted the arabian platform deformation of the musandam peninsula in the late cretaceous and mid tertiary by compression subduction from the east and southwest collision of the arabian platform and eurasian plate along the zagros crush zone during the oligocene or early miocene and emplacement of the zagros mountains by gravitational sliding during the neogene and pleistocene have reduced the platform area to the persian gulf other factors that contributed to the reduction of the arabian platform include the uplift of the arabian peninsula during the opening of the red sea in the tertiary tectonism of the infracambrian hormuz salt upwarp of the platform sediment cover by basement uplift and or salt tectonics and a 600 to 400 m drop in sea level since the cretaceous at present tectonism in the region is restricted to the northern edge of the gulf of oman where the arabian plate is subducting the eurasian plate from the south and to the zagros crush zone where the arabian and eurasian plates are colliding with one another

saudi arabian seismic refraction profile a traveltime interpretation of crustal and upper mantle structure abstract the crustal and upper mantle compressional wave velocity structure across the southwestern arabian shield has been investigated by a 1000 km long seismic refraction profile the profile begins in mesozoic cover rocks near riyadh on the arabian platform trends southwesterly across three major precambrian tectonic provinces traverses cenozoic rocks of the coastal plain near jizan and terminates at the outer edge of the farasan bank in the southern red sea more than 500 surveyed recording sites were occupied and six shot points were used including one in the red sea two dimensional ray tracing techniques used to analyze amplitude normalized record sections indicate that the arabian shield is composed to first order of two layers each about 20 km thick with average velocities of about 6 3 km s and 7 0 km s respectively west of the shield red sea margin the crust thins to a total thickness of less than 20 km beyond which the red sea shelf and coastal plain are interpreted to be underlain by oceanic crust a major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition elsewhere along the profile several high velocity anomalies in the upper crust correlate with mapped gneiss domes the most prominent of which is the khamis mushayt gneiss based on their velocities these domes may constitute areas where lower crustal rocks have been raised some 20 km two intracrustal reflectors in the center of the shield at 13 km depth probably represent the tops of mafic intrusives the mohorovicic discontinuity beneath the shield varies from a depth of 43 km and mantle velocity of 8 2 km s in the northeast to a depth of 38 km and mantle velocity of 8 0 km s depth in the southwest near the shield red sea transition two velocity discontinuities occur in the upper mantle at 59 and 70 km depth the crustal and upper mantle velocity structure of the arabian shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the precarnbrian the shield is currently flanked by the active spreading boundary in the red sea

perceptible earthquakes in the broad aegean area abstract a probabilistic estimate of seismic hazard can be obtained from the spatial distribution of earthquake sources their frequency magnitude distribution and the rate of attenuation of strong ground motion with distance we calculate the earthquake perceptibility i e the annual probability that a particular level of ground shaking will be generated by earthquakes of particular magnitude by weighting frequency magnitude data with the predicted felt area for a given level of ground shaking at a particular magnitude this provides an earthquake selection criterion that can be used in the anti seismic design of non critical structures we calculate the perceptibility at a particular value of isoseismal intensity peak ground acceleration and velocity as a function of source magnitude and frequency for the broad aegean area using local attenuation laws we use frequency magnitude distributions that were previously obtained by combining short term catalogue data with tectonic moment rate data for 14 tectonic zones in greece with sufficient earthquake data and where contemporary strain rates are available from satellite data many of the zones show a characteristic earthquake distribution with the most perceptible earthquake equal to the maximum magnitude earthquake but a relatively flat perceptibility between magnitudes 6 and 7 the maximum perceptible magnitude is in the fastest deforming region in the middle of the aegean sea and tends to be systematically low on the west in comparison to the east of the aegean sea the tectonic data strongly constrain the long term recurrence rates and lead to low error estimates 0 2 in the most perceptible magnitudes

comparisons of downhole geophones and hydrophones receiver tests were conducted to compare the responses of downhole geophones and hydrophones commercial receiver tools use a maximum of eight geophone levels however we use hydrophones because we can record 48 levels simultaneously for frequencies above 300 hz signal to background noise ratios for hydrophones and geophones in a prototype tool were comparable this prototype tool is a lightweight large clamping force device that can record higher frequencies than commercial geophone tools for frequencies below 300 hz signal to noise ratios were greater for the geophones than for the hydrophones a commercial geophone tool had lower low frequency signal to background noise ratios than the prototype tool but greater than those of the hydrophones further analysis was performed to determine why the signal to background noise ratios for geophones were greater than those for hydrophones at low frequencies the measured signal level for a hydrophone was 2 4 times that for a geophone compared with a t

source parameters for moderate earthquakes in the zagros mountains with implications for the depth extent of seismicity six earthquakes within the zagros mountains with magnitudes between 4 9 and 5 7 have been studied to determine their source parameters these events were selected for study because they were reported in open catalogs to have lower crustal or upper mantle source depths and because they occurred within an area of the zagros mountains where crustal velocity structure has been constrained by previous studies moment tensor inversion of regional broadband waveforms has been combined with forward modeling of depth phases on short period teleseismic waveforms to constrain source depths and moment tensors our results show that all six events nucleated within the upper crust 11 km depth and have thrust mechanisms this finding supports other studies that call into question the existence of lower crustal or mantle events beneath the zagros mountains

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

the southern zagros collisional orogen new insights from transdimensional trees inversion of seismic noise the natural environmental research council nerc grant ne r013500 1 and from the european union s horizon 2020 research and innovation program under marie sklodowska curie grant agreement 790203

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

basement faulting and the focal depths of the larger earthquakes in the zagros mountains iran summary the present day seismicity of the zagros seems to occur on high angle reverse faults distributed across the whole width of the belt it does not indicate activity on a single inclined thrust surface and there do not seem to have been any well located events at intermediate depths modelling of the long period teleseismic body waves of seven large earthquakes presented here shows their focal depths to be in the range 8 15 km this is thought to indicate faulting in the uppermost basement beneath the sedimentary cover though the absence of published seismic refraction results renders the sediment thickness uncertain faulting of this type and depth may occur on inherited normal faults which have subsequently been reactivated as thrusts such reactivation allows considerable shortening to take place in the early stages of continental collision without the subduction or excessive thickening of continental crust

active accommodation of plate convergence in southern iran earthquake locations triggered aseismic slip and regional strain rates 1 we present a catalog of interferometric synthetic aperture radar insar constraints on deformation that occurred during earthquake sequences in southern iran between 1992 and 2011 and explore the implications on the accommodation of large scale continental convergence between saudi arabia and eurasia within the zagros mountains the zagros mountains a salt laden fold and thrust belt involving 10 km of sedimentary rocks overlying precambrian basement rocks have formed as a result of ongoing continental collision since 10 20 ma that is currently occurring at a rate of 3 cm yr we first demonstrate that there is a biased misfit in earthquake locations in global catalogs that likely results from neglect of 3 d velocity structure previous work involving two m 6 earthquakes with well recorded aftershocks has shown that the deformation observed with insar may represent triggered slip on faults much shallower than the primary earthquake which likely occurred within the basement rocks 10 km depth we explore the hypothesis that most of the deformation observed with insar spanning earthquake sequences is also due to shallow triggered slip above a deeper earthquake effectively doubling the moment release for each event we quantify the effects that this extra moment release would have on the discrepancy between seismically and geodetically constrained moment rates in the region finding that even with the extra triggered fault slip significant aseismic deformation during the interseismic period is necessary to fully explain the convergence between eurasia and saudi arabia

the distribution of moho depths beneath the arabian plate and margins abstract in this study three new maps of moho depths beneath the arabian plate and margins are presented the first map is based on the combined gravity model eigen 06c which includes data from satellite missions and ground based studies and thus covers the whole region between 31 e and 60 e and between 12 n and 36 n the second map is based on seismological and ground based gravity data while the third map is based only on seismological data both these maps show gaps due to lack of data coverage especially in the interior of the arabian plate beneath the interior of the arabian plate the moho lies between 32 and 45 km depth below sea level there is a tendency for higher pn and sn velocities beneath the northeastern parts of the plate interior with respect to the southwestern parts of the plate interior across the northern destructive margin with the eurasian plate the moho depths increase to over 50 km beneath the zagros mountains across the conservative western margin the dead sea transform dst moho depths decrease from almost 40 km beneath the highlands east of the dst to about 21 23 km under the southeastern mediterranean sea this decrease seems to be modulated by a slight depression in the moho beneath the southern dst the constructive southwestern and southeastern margins of the arabian plate also show the moho shallowing from the plate interior towards the plate boundaries a comparison of the abruptness of the moho shallowing between the margins of the arabian plate the conjugate african margin at 26 n and several atlantic margins shows a complex picture and suggests that the abruptness of the moho shallowing may reflect fundamental differences in the original structure of the margins

earthquakes on the kazerun line in the zagros mountains of iran strike slip faulting within a fold and thrust belt summary the kazerun line is a transverse valley of about 200 km long that obliquely crosses the regular anticlines of the zagros fold belt in sw iran at its northern end it is a clear fault which can be mapped on the surface anticline axes die out or bend towards this valley but do not cross it six moderate sized earthquakes that occurred close the the kazerun line and within a 25 km area involved right lateral strike slip motion parallel to the strike of the valley they indicate that the kazerun line is the surface expression of a buried strike slip fault slip vectors in these strike slip earthquakes are different from those of neighbouring reverse fault earthquakes suggesting that the kazerun line accommodates some of the shortening between arabia and central iran by an elongation of the zagros mountains parallel to strike the centroid depths and the source dimensions of these earthquakes combined with the lack of seismogenic surface faulting in the zagros suggest to us that all these earthquakes involve faulting in the metamorphic basement beneath the sedimentary cover the sedimentary cover is almost certainly decoupled from the basement by several thick evaporite horizons the seismicity of the kazerun line thus demonstrates how lateral interruptions to the regularity of a fold belt can arise from faulting in the basement and not just from lateral ramps between the thrust sheets that deform the sedimentary cover

seismological constraints on the crustal structure beneath the zagros mountain belt iran summary the zagros mountain belt of western iran results from the collision of the arabian and central iran continental blocks the stage of the collision is unclear and the crustal structure of the zagros is rather poorly known in this study we investigate the velocity structure of the crust and upper mantle beneath the ghir region located in the central zagros using data collected by a temporary local seismological network including a broad band instrument the structures of the sedimentary cover and the upper crystalline crust are estimated from the inversion of p and s traveltimes of local earthquakes recorded on a dense seismological network the upper crust consists of an 11 km thick sedimentary layer v p 4 70 km s 1 above a 8 km thick upper crystalline crust v p 5 85 km s 1 the velocity of the lower crust and the depth of the moho are found using receiver function analysis of teleseismic earthquakes the lower crystalline crust is unusually slow v p 6 5 km s 1 and 27 km thick the upper bound for the total crustal thickness beneath the ghir region is 46 2 km a comparison of the thickness of the crystalline crust of the zagros with available information for the thickness of the crystalline crust of the arabian platform shows that at present the zagros has a thinner crust the current crustal thickness beneath the zagros is comparable to the pre collision crustal thickness of the arabian platform suggesting that the zagros is now in a very early stage of continental collision

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

attenuation of high frequency p and s waves in the crust of the east central iran summary we simultaneously estimated qp 1 and qs 1 by applying the extended coda normalization method at 39 stations of three local networks in the east central iran we measured frequencydependent attenuation of both p and s waves for the frequency range of 1 5 3 0 6 0 12 and 24 hz we have analysed 266 three component seismograms of 53 local earthquakes having focal depths less than 25 km which occurred from 2003 december 28 to 2005 april 11 by fitting power law frequency dependence to the estimated values over the whole stations we obtained qp 1 25 3 10 3 f 0 99 0 04 and qs 1 19 2 10 3 f 1 02 0 06 in the upper crust of the east central iran where f is frequency in hz our results are in the range of those estimated for qp 1 and qs 1 of the other seismically active regions

towards a reliable seismic microzonation in tehran iran abstract a hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous anelastic media has been used to model the ground motion in tehran city the synthetic records compare reasonably well with the observed ground motion due to the 2004 firozabad kojor earthquake located 60 km north of tehran the ratio between the response spectrum for the signals calculated along a laterally varying structure sa 2d and that for the signals at the bedrock regional reference structure sa 1d shows a high amplification of seismic waves in tehran the procedure can be readily implemented for the entire tehran city which experienced large historical earthquakes in the past simply by extending the analysis made so far in space and to different scenario earthquakes consistent with the local and regional tectonics