estimation of coda wave attenuation for nw himalayan region using local earthquakes abstract the attenuation of seismic wave energy in nw himalayas has been estimated using local earthquakes most of the analyzed events are from the vicinity of the main boundary thrust mbt and the main central thrust mct which are well defined tectonic discontinuities in the himalayas the time domain coda decay method of a single back scattering model is employed to calculate frequency dependent values of coda q qc a total of 36 local earthquakes of magnitude range 2 1 4 8 have been used for q c estimation at central frequencies 1 5 3 0 6 0 9 0 12 0 and 18 0 hz through eight lapse time windows from 25 to 60 s starting at double the time of the primary s wave from the origin time the estimated average frequency dependence quality factor gives the relation q c 158 f 1 05 while the average q c values vary from 210 at 1 5 hz to 2861 at 18 hz central frequencies the observed coda quality factor is strongly dependent on frequency which indicates that the region is seismic and tectonically active with high heterogeneities the variation of the quality factor q c has been estimated at different lapse times to observe its effect with depth the estimated average frequency dependent relations of q c vary from 85 f 1 16 to 216 f 0 91 at 25 to 60 s lapse window length respectively for 25 s lapse time window the average q c value of the region varies from 131 36 at 1 5 hz to 2298 397 at 18 hz while for 60 s lapse time window its variation is from 285 95 at 1 5 hz to 2868 336 at 18 hz of central frequency the variation of q c with frequency and lapse time shows that the upper crustal layers are seismically more active compared to the lower lithosphere the decreasing value of the frequency parameter with increasing lapse time shows that the lithosphere acquires homogeneity with depth

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

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

the rudbār mw 7 3 earthquake of 1990 june 20 seismotectonics coseismic and geomorphic displacements and historic earthquakes of the western high alborz iran summary the rudb r earthquake of 1990 june 20 the first large magnitude earthquake with 80 km left lateral strike slip motion in the western high alborz fold thrust mountain belt was one of the largest and most destructive earthquakes to have occurred in iran during the instrumental period we bring together new and existing data on macroseismic effects the rupture characteristics of the mainshock field data and the distribution of aftershocks to provide a better description of the earthquake source its surface ruptures and active tectonic characteristics of the western high alborz the rudb r earthquake is one of three large magnitude events to have occurred in this part of the alborz during recorded history the damage distribution of the 1485 august 15 upper polrud earthquake suggests the east west kelishom left lateral fault which is situated east of the rudb r earthquake fault as a possible source the 1608 april 20 alamutrud earthquake may have occurred on the alamutrud fault farther east analysis of satellite imagery suggests that total left lateral displacements on the rudb r fault are a maximum of 1 km apparent left lateral river displacements of 200 m on the kashach l fault and up to 1 5 km of the kelishom fault which are situated at the eastern end of the rudb r earthquake fault also appear to indicate rather small cumulative displacements given the relatively small displacements the presently active left lateral strike slip faults of the western high alborz fold thrust belt may be younger than onset of deformation within the alborz mountains as a whole

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

crustal thickness of iran inferred from converted waves the iranian plate is part of the alpine himalayan orogenic belt which has been formed by the continental collision between the arabian and eurasian plates the present day iranian plate is characterized by diverse tectonic domains including mountain belts e g zagros and alborz kopeh dagh and oceanic plate subduction e g makran here we present the lateral variations of the moho discontinuity beneath iran using a detailed p receiver function study our results allow for more precise estimations of the crustal thickness and enable us to provide a detailed moho depth map for all of iran for the first time we used the teleseismic events recorded from 1995 to 2011 at 77 national permanent stations 24 broadband and 53 short period stations our results show significant variations in the crustal thickness which are related to the different geological features within iran in general the average crustal thickness beneath iran is about 40 45 km a relatively thick crust of about 54 2 km due to the shortening is observed beneath the alborz mountain ranges the crust beneath the alborz zone shows a thickness changing from 47 2 to 45 2 km from west to east and reaches a thickness of about 50 2 km beneath the kopeh dagh mountain range we find the thinnest crust of about 33 2 km beneath the makran subduction zone in southeast iran showing a normal continental crust which has not been influenced by collisional processes the thickest crust 66 2 km is locally observed beneath the sanandaj sirjan zone which is considered the suture zone of the collision between the arabian and eurasian plates

thermal structure of the mantle wedge beneath northeastern japan magmatism in an island arc from the combined data of seismic anelasticity and velocity and heat flow abstract the thermal structure of the mantle wedge beneath northeastern japan is investigated from seismic anelasticity q 1 laboratory measurements in dry peridotite at high pressures show a strong temperature dependence of anelasticity this may be used to determine the detailed thermal structure of the subduction zone since however water or hydrous minerals may exist in the mantle wedge the laboratory q results for dry peridotite may not be readily applicable to the region we here compare temperatures derived from the dry peridotite q with those from heat flow the comparison yields a correction factor that is used to correct for the unknown water effect on temperatures derived from the seismic q the results show that no temperature corrections are necessary in the back arc side of the volcanoes whereas corrections of as much as 250 660 c are necessary in the fore arc side we then determine the corrected temperatures in the mantle wedge and study the role ofthe wedge and the descending slab in island arc magmatism in the uppermost mantle wedge the temperature decreases from 1000 c beneath the japan sea coast to 200 300 c in the apex of the mantle wedge in good agreement with the location of the volcanoes and the cold slab beneath the volcanic front and to the japan sea temperatures lie between the dry and wet solidus thus partial melting should occur only if water is present in the mantle wedge the seismic structure and the temperature profile indicate that melting as well as volatiles may exist only locally in regions less than 25 km in width possibly forming a plume or a diapir beneath volcano therefore an uprising of hot material from deep mantle appears to produce magmatism and high heat flow in the back arc region the low velocity and low q in this region is generally not due to the occurrence of localized melt but due to the grain boundary weakening of mantle rocks by high subsolidus temperatures on the other hand the derived temperatures are well below the wet solidus and no melting should occur even under water saturated conditions in the fore arc region the temperature profile is thus consistent with the site of the volcanic front some low velocity regions observed in the fore arc mantle wedge are due to the presence of hydrous minerals or free water seismic structure also shows some low velocity zones in the mantle wedge adjacent to or near the slab this could be again produced by volatiles derived from the subducted oceanic crust the high velocity and high q of the slab indicate a fairly low temperature of the region therefore we infer that the slab itself will not melt but instead provides water to the overlying mantle wedge for generating island arc magmas

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

high frequency earthquake ground motion scaling in utah and yellowstone velocity seismograms from the university of utah seismograph stations are used to quantify high frequency ground motion scaling for the yellowstone region and the wasatch front in utah this study uses a data set consisting of over 3000 waveforms from 93 stations and 506 regional earthquakes and mining associated seismic events that occurred in the years 1995 2001 all events lie within the upper crust with magnitudes less than 5 5 the signals were processed to examine the peak ground velocity and fourier velocity spectra in the frequency range of 1 0 16 0 hz regression results for utah are characterized by rapid decreases of amplitude at short distances which requires low q and a rapid geometrical spreading g r for the forward modeling q f 160 f 0 75 eff 0 05 sec and 300 bars are selected to predict the excitation terms when combined with the derived geometrical spreading the frequency dependent excitation of mining associated events differs significantly from that of earthquakes because of either an additional attenuation due to shallow source depth or apparent low stress drops associated with the slow collapse of long tunnels a q f 140 f 0 70 and geometrical spreading less rapid than r 1 0 at short distance ranges are used to describe the wave propagation distance dependence in the yellowstone region the yellowstone attenuation functional d r f is very different from that of utah perhaps because a shallow wave guide in the caldera traps more energy the yellowstone excitation spectra were modeled using 30 bars and eff 0 04 sec manuscript received 24 october 2003

delamination of southern puna lithosphere revealed by body wave attenuation tomography the southern puna plateau has been proposed to result from a major pliocene delamination event that has previously been inferred from geochemical geological and some preliminary geophysical data seventy five seismic stations were deployed across the southern puna plateau in 2007 2009 by scientists from the u s germany chile and argentina to test the delamination model for the region the puna passive seismic stations were located between 25 and 28 s using the seismic waveform data collected from the puna experiment we employ attenuation tomography methods to resolve both compressional and shear quality factors qp and qs respectively in the crust and uppermost mantle the images clearly show a high q nazca slab subducting eastward beneath the puna plateau and another high q block with a westward dip beneath the eastern cordillera we suggest that the latter is a piece of delaminated south american lithosphere a significant low q zone lies between the nazca slab and the south american lithosphere and extends southward from the northern margin of the seismic array at 25 s before vanishing around 27 5 s this low q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array the low q zone reaches 100 km depth beneath the northern part of the array but only 50 km depth in the south lateral variations of the low q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration the depth of the nazca slab as defined by q images decreases from north to south beneath the plateau which is consistent with the steep flat transition of the angle of the subducting slab as defined by previous earthquake studies

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

coda q for the state of washington abstract frequency dependent coda q values for subregions of the state of washington have been determined using a time domain coda decay method a total of 95 earthquakes digitally recorded on a regional seismograph network of over 100 short period stations were selected to obtain 206 on scale high signal to noise ratio traces for analysis grouping the data by structural regions of the state showed only small variations in coda q by region other than in a very localized area at mount st helens at mount st helens coda q was significantly lower than for all other areas an average of all of the data except that from the local mount st helens area results in a q relationship of q c 63 f 0 97 for the frequency band 2 to 16 hz there is little variation of this coda q relationship when using sources down to 50 km depth and thereby uniformly sampling the top 50 to 100 km of the crust and upper mantle

attenuation parameters for friuli region from strong motion accelerogram spectra abstract by using the accelerometric data obtained during the heaviest earthquakes that occurred in friuli in 1976 an attempt was made to obtain a law of attenuation in the northeastern po river area as dependence on the frequency the study was carried out by comparison of power spectra of entire accelerograms at different distances in the frequency range of 0 1 to 10 hz a q value was found which was proportionally dependent on the frequency as f n with n 1 1 this result can be considered valid for that region and for distances of up to about 200 km from the epicentral area

high vp vs ratio saturated cracks or anisotropy effects 1 we measured vp vs ratios of thermally cracked westerly granite thermally cracked carrara marble and 4 porosity fontainebleau sandstone for an effective mean pressure ranging from 2 to 95 mpa samples were fluidsaturated alternatively with argon gas and water 5 mpa constant pore pressure the experimental results show that at ultrasonic frequencies vp vs ratio of water saturated specimen never exceeded 2 15 even at effective mean pressure as low as 2 mpa or for a lithology for which the poisson s ratio of minerals is as high as 0 3 calcite in order to check these results against theoretical models we examine first a randomly oriented cracked medium with dispersion but without anisotropy and second a medium with horizontally aligned cracks with anisotropy but without dispersion the numerical results show that experimental data agree well with the first model at high frequency vp vs ratios range from 1 6 to 1 8 in the dry case and from 1 6 to 2 2 in the saturated case the second model predicts both vp sv and vp sh to vary from 1 2 to 3 5 depending on the raypath angle relative to the crack fabric in addition perpendicular to the crack fabric a high vp vs ratio is predicted in the absence of shear wave splitting from these results we argue the possibility that high vp vs ratio 2 2 as recently imaged by seismic tomography in subduction zones may come from zones presenting important crack anisotropy the cumulative effects of crack anisotropy and high pore fluid pressure are required to get vp vs ratios above 2 2 citation wang x q a schubnel j fortin e c david y gueguen and h k ge 2012 high vp vs ratio saturated cracks or anisotropy effects geophys res lett 39 l11307 doi 10 1029 2012gl051742

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

lithospheric structure beneath nw iran using regional and teleseismic travel time tomography we compute a 2 d tomogram using the p wave arrival time readings from a temporary seismic experiment to study the seismic structure of the crust and upper mantle in nw iran the study area includes the western margins of the south caspian basin scb and the sahand and sabalan post collisional volcanoes in nw iran we invert 2780 regional and teleseismic relative p wave arrival times recorded by 23 stations along the seismic profile extending from the western shoreline of the caspian sea to lake urumieh our tomographic results show a higher velocity region beneath the scb the observed higher velocities strongly correlate with the observed positive gravity anomalies over the southwestern margins of the caspian sea suggesting an oceanic like nature for the scb lithosphere the tomographic results also show several lower velocity anomalies in the crust the sabalan volcano is underlain by a low velocity zone in the lower crust which is most likely thermal in nature in the sahand region the lower velocities are considerably shallower in depth and might be controlled by shallow sedimentary structures as well as an anomalously warm upper crust the shallow low velocity regions are connected with deeper low velocity zones 60 100 km deep in the upper mantle this pattern points to a possible mantle source of post collisional volcanism in nw iran i e the melting of a subducted slab

deciphering oblique shortening of central alborz in iran using geodetic data the alborz is a narrow 100 km and elevated 3000 m mountain belt which accommodates the differential motion between the sanandaj sirjan zone in central iran and the south caspian basin gps measurements of 12 geodetic sites in central alborz between 2000 and 2002 allow to constrain the motion of the belt with respect to western eurasia one site velocity on the caspian shoreline suggests that the south caspian basin moves northwest at a rate of 6 2 mm year with respect to western eurasia north south shortening across the alborz occurs at 5 2 mm year to the south deformation seems to extend beyond the piedmont area probably due to active thrusting on the pishva fault we also observe a left lateral shear of the overall belt at a rate of 4 2 mm year consistent with the geological motion observed along e w active strike slip faults inside the belt e g the mosha fault

crust and uppermost mantle structure of tehran region from analysis of teleseismic p waveform receiver functions crust and uppermost mantle structure of tehran region from analysis of teleseismic p waveform receiver functions

late pleistocene palaeocenography of the tasman sea implications for the dynamics of the warm pool in the western pacific quantitative analyses of planktonic foraminifera from 47 core top samples spatially distributed through the tasman sea and cores rc12 113 e36 23 dsdp sites 588 592 593 and odp site 828a from a n s transect supplemented with stable isotope analyses indicate that three planktonic foraminiferal assemblages defined by factor analysis on core top material correlated with three hydrographic modes defined on the basis of sea surface temperatures temperature profiles seasonal changes in temperature and mixed layer depth similar assemblages were found in down core material along the tasman sea transect that combined with semi quantitative analyses of foraminiferal assemblages provinces and the coiling ratio of globorotalia truncatulinoides allows reconstruction of the position of the tasman front or the subtropical divergence during the late brunhes chron the results indicate that the tasman front migrated from its present position at 30 s to 26 s during the last glacial maximum the northward migration of the tasman front may indicate a reduction in volume of the equatorial warm pool and or an increase in the strength of cool subtropical water masses the late pleistocene distribution of g truncatulinoides left coiling from appears to be related to the formation of subantarctic mode water thermostads this relationship may explain the evolutionary origin of this species in the southwest pacific at 2 4 ma simultaneously with the onset of late pliocene glaciations the past position of the subtropical convergence is reconstructed by means of coilingv directions in neogloboquadrina pachyderma the convergence apparently migrated slightly north of 43 s core e36 23 during glacial stages 6 10 and 12

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

modeling some empirical vertical component lg relations abstract higher mode surface wave theory is used to model the vertical component lg wave observed in eastern north america at regional distances tests of the model are made to determine whether it is capable of describing empirical spectral scaling laws spatial attenuation and peak time domain lg amplitudes it is found that a simple crustal model and a rough estimate of crustal qb are all that are required to accomplish this good results are obtained if the average crustal qp is equated to the coda q of the same frequency introduction the lg wave is a wave observed on short period seismograms of local and regional seismic events which travels with a group velocity of approximately 3 5 km sec in the central united states it is usually the largest arrival on the seismogram which makes it suitable for defining a magnitude scale nuttli 1973 herrmann and nuttli 1982 as part of developing the magnitude scale there have been many studies on the spatial attenuation of the lg wave nuttli 1973 street 1976 bollinger 1979 singh and herrmann 1982 the lg wave is usually thought of as a superposition of higher mode surface waves propagating within the crustal wave guide herrmann and nuttli 1975a b attempted to deterministically model observed lg amplitudes in terms of focal mechanism focal depth and seismic moment using surface wave techniques they were limited by their inability to compute surface wave eigenfunctions at frequencies greater than 0 5 hz however their results were encouraging harkrider 1979 drawing upon the work of apsel 1979 discovered a way to compute surface wave energy integrals of the higher modes very precisely bache

partitioning of strike slip and convergent motion between eurasia and arabia in eastern turkey and the caucasus the plate motion model nuvel 1 de mets et al 1990 predicts a strongly oblique component to the convergence between arabia and eurasia at the longitude of the caucasus earthquake focal mechanisms suggest that this oblique convergence is partitioned into pure right lateral strike slip motion in eastern turkey and pure shortening by thrusting in the greater caucasus such partitioning offers an explanation for the apparent eastward continuation of the right lateral faulting of the north anatolian fault from turkey into iran from a summation of seismic moment tensors between 1911 and 1991 it appears that most of the right lateral strike slip motion in eastern turkey is accommodated by faulting in large earthquakes while most of the shortening in the caucasus appears to occur aseismically

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

attenuation of short period seismic waves at mt vesuvius italy we analysed short period seismograms from about 250 very local events recorded by a network of high dynamic range short period seismic stations deployed on mt vesuvius to estimate the site corrected short period seismic attenuation we calculated qc 1 the inverse of the quality factor for coda waves for short lapse times 12 s and qp 1 and qs 1 the inverse of the direct body wave quality factors for p and s waves follow ing shallow ray paths we used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands obtaining a qc 1 slowly varying with frequency similar to values measured for other volcanoes at the same lapse time site corrected qp 1 and qs 1 were estimated using the frequency decay method for both p and s waves in two frequency bands 1 6 hz and 15 24 hz results show that qp 1 is 0 028 in both frequency bands and qs 1 is 0 015 and 0 017 at low and high frequencies respectively almost independent of the frequency and that the value of qp 1 is about twice that of qs 1 as measured worldwide a check was made by measuring the broadening of the first p wave pulse with station source distance finding qp 1 0 024 using the independent estimates of qc 1 and qs 1 we separated the intrinsic from the scattering quality factor at mt vesuvius obtaining a high scattering and a low intrinsi c q 1 as already observed for other volcanoes this result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes

ocean tide loading displacements in western europe 2 gps observed anelastic dispersion in the asthenosphere gps observed vertical ocean tide loading displacements show in cornwall southwest england and in brittany northwest france discrepancies of 2 3 mm with predicted values based on the isotropic preliminary reference earth model for the main tidal harmonic m2 yet in central europe the agreement is better than 0 5 mm by comparison of ocean tide models and validation with tide gauge observations we demonstrate that the uncertainties in the former are too small to cause this disagreement furthermore we find that different local models of the crust and different global elastic reference models derived from seismological observations can only reduce the observed discrepancies to 1 2 mm which still exceeds the gps observational uncertainty of 0 2 0 4 mm it is customary to use the elastic properties of the earth as given by seismic models previously there has been insufficient evidence to determine how to modify these properties during the transformation from seismic to tidal frequencies to account for possible anelastic dispersion in the asthenosphere and so this effect has been ignored if we include this effect then our discrepancies reduce further to 0 2 0 4 mm this value is of the same order as the sum of the remaining errors due to uncertainties in the ocean tide models and in the gps observations themselves this research provides evidence in western europe of a reduction of around 8 10 of the seismic shear modulus in the asthenosphere at tidal frequencies in addition we find that the asthenosphere absorption band frequencies can be represented by a constant quality factor q

microseismicity and seismotectonics of the north tabriz fault iran abstract we present the results of a microearthquake study conducted in 2004 with 31 portable stations around the city of tabriz which is crossed by an active fault and has experienced several destructive earthquakes in the recent history from april 24 until july 24 we recorded 80 earthquakes by more than 4 stations we complement these data with earthquakes recorded by the 8 permanent seismological stations of the tabriz network operated by institute of geophysics of the university of tehran from august 1995 until march 2008 among a total of 6377 events only 394 earthquakes were recorded by more than 5 stations and located with statistical uncertainties erz and erh less than 5 km and a gap less than 270 most of these earthquakes are located along the tabriz fault at a depth ranging from the surface to 20 km comparable to other studies conducted in central alborz we computed 22 focal mechanisms most of which show right lateral strike slip motion along east southeast planes consistent with the geologic evidence for quaternary slip we do not see any peculiar pattern near the tabriz pull apart basin or at both ends of the north tabriz fault where it terminates in ew trending reverse faults this suggests that the fault is simpler more mature at depth than at the surface

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

three dimensional compressional wave attenuation tomography for the crust and uppermost mantle of northern and central california i present a frequency independent three dimensional 3 d compressional wave attenuation model indicated by quality factor qp for the crust and uppermost mantle of northern and central california the tomographic inversion used t values measured from amplitude spectra of 80 988 p wave arrivals of 3247 events recorded by 463 network stations through a 3 d seismic velocity model the model has a uniform horizontal grid spacing of 15 km and the vertical node intervals range between 2 and 10 km down to 45 km depth in general the resulting qp values increase with depth and agree with the surface geology at shallow depth layers the most significant features observed in the qp model are the high qp values in the sierra nevada mountains and low qp anomalies in the western fault zones low qp values are also imaged in owens valley and long valley at shallow depths and the cape mendocino region in the lower crust 25 km depth an overall contrast of qp values across the fault is observed in the creeping parkfield and cholame carrizo sections of the san andreas fault the new 3 d qp model provides an important complement to the existing regional scale velocity models for interpreting structural heterogeneity and fluid saturation of rocks in the study area

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

space weighted seismic attenuation mapping of the aseismic source of campi flegrei 1983 1984 unrest coda wave attenuation imaging is able to detect fluid melt accumulation and ancient magmatic bodies in volcanoes here we use recently developed space weighting sensitivity functions to invert for the spatial distributions of multifrequency coda wave attenuation qc 1 measured during the largest monitored unrest at campi flegrei caldera 1983 1984 high attenuation anomalies are spatially correlated with the regions of highest structural complexities and cross faulting they characterize deep fluid circulation in and around the aseismic roots of the 1534 a d mount nuovo eruption and fluid accumulation in the areas of highest hydrothermal hazard just offshore pozzuoli and at the highest frequency wavelengths of 150 m the main cause of ground deformation and seismicity during the unrest is an aseismic low attenuation circular anomaly similar in shape and nature to those produced by ancient magmatic reservoirs and active sills at other volcanoes

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

depth dependent intrinsic and scattering seismic attenuation in north central italy summary in this study the attenuation mechanism of seismic wave energy in north central italy is estimated using low magnitude earthquake local data recorded at six stations managed by ingv most of the analysed events are located along the alpine chain in the zone of iseo and garda lakes while a minor part in the po valley the zone investigated is characterized by the occurrence of significantly intense earthquakes magnitude up to 6 6 the most recent occurred in 2004 close to the city of salo on the coast of the garda lake mw 5 0 due to the high population density and presence of industrial activity the investigated area is characterized by a high seismic risk first the ordinary multiple lapse time window analysis mltwa method is applied in the assumption of uniform velocity and scattering and the couple of b0 the seismic albedo and le 1 the extinction length inverse corresponding to the total attenuation coefficient is calculated in the frequency bands of 1 5 3 6 and 12 hz to retrieve more realistic estimates the obtained values of b0 and le 1 are corrected taking into account the effects of a depth dependent earth model consisting of an earth structure characterized by a transparent upper mantle and a heterogeneous crust we find that the corrected intrinsic and scattering attenuation parameters which are proportional to the inverse of the intrinsic scattering quality factors q 1i and q 1s are strongly frequency dependent with a prevalence of scattering attenuation over the intrinsic dissipation the corrected and uncorrected values of total q are in agreement with the total q values obtained with different approaches for the same area

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

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

strong lg wave attenuation in the middle east continental collision orogenic belt abstract using lg wave q tomography we construct a broadband crustal attenuation model for the middle east the q lg images reveal a relationship between attenuation and geological structures strong attenuation is found in the continental collision orogenic belt that extends from the turkish and iranian plateau to the pamir plateau we investigate the frequency dependence of q lg in different geologic formations the results illustrate that q lg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions an average q lg value between 0 2 and 2 0 hz q lg 0 2 2 0 hz may be a critical index for crustal attenuation and is used to infer the regional geology low q lg anomalies are present in the eastern turkish plateau and correlate well with low pn velocities and cenozoic volcanic activity thus indicating possible partial melting within the crust in this region very strong attenuation is also observed in central iran the afghanistan block and the southern caspian sea this in line with the previously observed high crustal temperature high conductivity layers and thick marine sediments in these areas suggests the high lg attenuation is caused by abnormally high tectonic and thermal activities

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering 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

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

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 tectonics of the turkish iranian plateau 1 this paper examines how active faulting in the turkey iran caucasus region accommodates the arabia eurasia collision and the velocity field observed by gps the overall shortening across the zone is in general spatially separated partitioned into right lateral strike slip in the turkish iranian plateau and thrusting in the greater caucasus a band of counterclockwise rotating nw se right lateral strike slip faults accommodates a nw se gradient in ne directed velocity relative to eurasia between the black and caspian seas a nnw sse band of previously unrecognized oblique normal faults is present on the turkey iran border we estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 2 ma at present rates this implies a reorganization of deformation in the collision zone at that time after the initial collision at 12 ma probably in response to mantle induced dynamic uplift

estimation of coda wave attenuation in the central and eastern alborz iran the quality factor of coda q c waves has been estimated by using single backscattering and single isotropic scattering models the earthquakes used were recorded by three permanent and one temporary network located in the central and eastern alborz iran the database was composed of 746 local earthquakes with local magnitude from 1 1 to 5 7 the estimated q c has been found to be similar for lapse times greater than twice the s wave travel time 2 t s for both methods the estimated q c for central frequencies 1 0 hz shows less frequency dependency compared with the higher frequencies by using a q f n relation the average frequency dependence of q c for the whole area has been estimated as 59 f 1 03 69 f 0 97 78 f 0 97 105 f 0 93 123 f 0 89 159 f 0 79 and 203 f 0 68 for central lapse times 30 40 50 65 85 110 and 155 s respectively we found the value of q decreases at an average depth of 78 km which may be the result of high dissipating media at this depth the average q c values estimated for central and eastern alborz and their frequency dependent relationships are similar to those of tectonically active regions

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies

attenuation of high frequency p and s waves in garhwal himalaya india abstract tectonics of a region plays important role on the attenuation characteristics of the region attenuation characteristics have been estimated to understand the effect of the heterogeneity of the region in a tectonically active garhwal region of himalaya seismic body wave attenuation characteristics in the region is studied using 234 short period seismic observations from local events the p wave attenuation qp 1 and s wave attenuation qs 1 were estimated by applying the state of the art extended coda normalization method for the frequency range from 1 5 to 24 hz estimates of qp 1 and qs 1 decrease from 15 86 0 90 10 3 and 5 35 0 51 10 3 at 1 5 hz to 0 54 0 11 10 3 and 0 34 0 06 10 3 at 24 hz respectively the values of qp 1 and qs 1 show strong frequency dependence and fit the power law relation qp 1 f 27 43 3 15 10 3f 1 16 0 06 and qs 1 f 8 05 0 74 10 3f 0 93 0 05 respectively obtained results are in the range of those reported for qp 1 and qs 1 of the other seismically active regions the ratio of qp 1 qs 1 is larger than unity in the entire analyzed frequency range and may suggest high degree of heterogeneity in the region

separation of intrinsic and scattering attenuation in the crust of central and eastern alborz region iran abstract in this study more than 380 local earthquakes 2 m l q d coda q c intrinsic q i and scattering quality factor q sc in the crust of central and eastern alborz region the events were recorded by one temporary and two permanent networks the quality factors of shear and coda waves have been individually estimated at different frequency bands by using coda normalization cnm method and single backscattering sbs method respectively average frequency dependent relationships have been estimated for q d and q c as 111 4 f 0 85 0 04 and 112 8 f 1 02 0 06 respectively the intrinsic quality factor q i has been separated from the scattering quality factor q sc by using individually estimated q c and q d values the average frequency dependent relationships of q i and q sc have been calculated in the form of 108 f 1 00 and 784 f 0 56 respectively the results of this study suggest that s wave s attenuation q d 1 is dominated by the intrinsic attenuation the attenuation of coda waves has been observed similar to the intrinsic attenuation which indicates the coda decay is mostly caused by the intrinsic attenuation it has been observed that the scattering mean free path is frequency independent at frequencies greater than 6 hz the results of this study are similar to the tectonically active regions

three dimensional qp and qs tomography beneath taiwan orogenic belt implications for tectonic and thermal structure summary we determined the 3 d qp and qs structure of the taiwan orogenic belt to enhance understanding of the related tectonic and thermal structure beneath the collision zone the inversion used t values measured from the spectra of p and s waves from the dense taiwan strong motion network for moderate size earthquakes ml 4 5 5 5 to avoid source complexity the time period 1991 2007 includes the aftershock sequence of the 1999 chi chi earthquake that provides good ray coverage in central taiwan over 18 000 velocity spectra from 883 earthquakes were analysed a non linear least square technique is applied to the spectra for t determination by assuming a 2 source model for the frequency band of 1 30 hz a frequency independent q was assumed in this study the corner frequency of a specific event was fixed for the corresponding stations and a quality index was defined to assure good quality data for the inversion the results reveal the sharp variation of qp and qs across the recently ruptured chelungpu fault and the kaoping and chaochou faults in pingtung plain the q values in the hangingwall are smaller by about 85 and 110 for qp and qs respectively relative to the footwall the fault geometry is distinctly delineated by the contour of qp qs of 1 2 that extends to the depth of the geologically identified decollement structure beneath the central range the low qp low qs and high qp qs features coincide well with the aseismic zone comparison to the recent thermomechanical numerical models of taiwan shows that the low q zone corresponds to the exhumation of the lower crust the low qs regime high attenuation beneath the central ranges at the depth of 5 22 km coincides with predicted temperatures of 400 600 c the qs comparison with the major tectonic and thermal mechanical models of taiwan reveals that the shear wave attenuation model contains comprehensive rheological and thermal information of relevance to understanding mountain building processes this technique appears particularly useful for distinguishing strong and weak crustal regions in the absence of other constraints

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