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

a seismic event on august 20 1983 double explosion or a single earthquake abstract an interesting weak seismic event occurred on august 20 1983 in the caspian sea region in southwestern u s s r which produced at gauribidanur array two distinct seismic signals viz the leading p signal and a similar signal after an interval of nearly 12 s preliminary data corresponding to these two signals led to an initial assumption that the event was a double underground nuclear explosion however the focal depth of this event from p arrival time data of 21 stations was found to be 45 km further processing of the gauribidanur array seismograms confirmed that the second signal detected exactly 11 85 s after the first arrival was none other than the surface reflected p pulse which lent excellent support to the source depth estimate by using three discriminants viz signal complexity third moment of frequency and relative efficiency of generation of core reflected p the event was objectively compared with 10 small presumed underground nuclear explosions in southwestern u s s r to conclude that the august 20 1983 event was a shallow focus small earthquake in the caspian sea area

leucogranites of the teton range wyoming a record of archean collisional orogeny abstract leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages this study describes leucogranitic gneisses associated with an archean collisional orogeny preserved in the teton range of northwestern wyoming usa these leucogneisses formed at 2 68 ga and initial nd isotopic compositions suggest they are derived from relatively juvenile sources two distinct groups of leucogneisses both trondhjemitic are identified on the basis of field relations petrology and geochemistry the webb canyon gneiss forms large sheet like bodies of hornblende biotite trondhjemite and granodiorite this gneiss is silica rich sio2 70 80 strongly ferroan comparatively low in alumina and is characterized by high zr and y low sr and high ree contents that define seagull shaped ree patterns the bitch creek gneiss forms small sills dikes and plutons of biotite trondhjemite silica zr y and ree are lower and alumina and sr are higher than in the webb canyon gneiss these differences reflect different melting conditions the webb canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down accounting for the low alumina high feo high silica content and observed trace element characteristics the bitch creek gneiss formed by h2o excess melting in which plagioclase breaks down leaving an amphibole rich restite producing magmas higher in alumina and sr and lower in feo and hree both melt mechanisms are expected in collisional environments dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust and water excess melting may occur when collision places a relatively cool hydrous lower plate beneath a hotter upper plate the archean leucogranitic gneisses of the teton range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites the difference in leucogranite composition reflects the geochemically immature archean crust that partially melted in the teton range compared to the more geochemically evolved rocks typically involved in younger collisional orogens

review of seismic source models for underground nuclear explosions abstract a number of seismic source models for underground nuclear explosions have been developed over the past 2 decades these models include the spherically symmetric compressional source model the wave conversion source model the tectonic strain release source model the spall slapdown source model and the near regional source model these model are reviewed in this study and are shown to be inconsistent with various geophysical data associated with underground nuclear explosions in particular the rayleigh and love wave signals generated by underground nuclear explosions have not been explained satisfactorily by any of these source models to explain the observed explosion data it may be necessary to model the explosion seismic source as a sequence of mechanisms producing seismic signals these mechanisms all act within the first few seconds following the explosion detonation one of the most important of these mechanisms is probably explosion induced thrust faulting

estimating displacement along the brenner fault and orogen parallel extension in the eastern alps the major structure accommodating orogen parallel extension in the eastern alps is inferred to be the brenner fault which forms the western boundary of the tauern window the estimated amount of extension along this fault varies from a minimum of 10 20 km to a maximum of 70 km all investigations that have attempted to constrain this amount of extension have calculated the fault plane parallel displacement required to restore the difference in structural level between footwall and hanging wall as constrained by geobarometry however these calculations neglected the component of exhumation of the footwall resulting from folding and erosion therefore the total amount of extensional displacement was systematically overestimated in the present study we project a tectonic marker surface from the footwall and hanging wall of the brenner fault onto a n s striking cross section this marker surface which is the base of the patscherkofel unit in the footwall and the base of the otztal basement in the hanging wall is inferred to have occupied the same structural level in the hanging wall and footwall of the brenner fault before its activity therefore the difference in height between the marker projected from the footwall and from the hanging wall is a measure of the vertical offset across the brenner fault this construction shows that the vertical offset of the marker horizon on both sides of the brenner fault varies strongly and continuously along strike of the brenner fault attaining a maximum value of 15 km at the hinge of the folded footwall tauern dome the along strike change of vertical offset is explained by large scale upright folding of the footwall that did not affect the hanging wall of the brenner fault therefore the difference in vertical offset of 10 km between the area of the brenner pass and the area immediately south of innsbruck corresponds to the shortening upright folding component of exhumation of the footwall the remaining 5 km of vertical offset must be attributed to extensional deformation the brenner fault itself is barely folded its dip varies between 20 and 70 and it crosscuts the upright folds of the western tauern window given the offset of 5 km the dip of the fault constrains the extensional displacement to be between 2 and 14 km we conclude that the tauern window was exhumed primarily by folding and erosion not by extensional unroofing

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

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

subduction complex of pre jurassic age northern anatolia turkey in northern anatolia a zone of pre liassic orogenic deformation is located mainly between the internal anatolian massifs and the north anatolian fault this belt consists of metamorphic rocks in blueschist greenschist and amphibolite facies and an ophiolitic dynamometa morphic melange the metamorphic rocks represent deformed and metamorphosed oceanic crust and upper mantle whereas the melange rocks originated in diverse environments in abyssal plain trench arc trench gap and forearc environments the evolution of these assemblages is interpreted as a product of subduction probably associated with the closure of the tethys subduction related deformation and meta morphism terminated diachronously from pre late triassic in the west to pre late liassic in the east probably as a result of the diachronous closure of the tethys

geodynamic evolution of the central appalachian orogen geochronology and compositional diversity of magmatism from ordovician through devonian

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

the zandjan fault system morphological and tectonic evidences of a new active fault network in the nw of iran abstract the zandjan province is situated in the nw of iran at the junction between the southern termination of the tabriz right lateral strike slip fault and the western end of the alborz active mountain range despite this key location in terms of active tectonics there is no destructive earthquake reported in available historical seismicity catalogues even if a few low magnitude instrumental earthquakes have been recorded indicating that this area is actively deforming the zandjan region can be considered as a seismic gap based on detailed field investigations digital elevation models dems satellite image and aerial photo interpretations we have identified a major active fault network affecting this regions it is mainly constituted by several west and est verging thrust faults trending nw se to n s that clearly cut late quaternary to holocene deposits evidences in the morphology indicate also that they accommodate some right lateral slip component this fault network can be divided into four major fault zones affecting zandjan city present day population over 500 000 and part of the zandjan mianeh basin more to the west based on fault geometrical characteristics fault length segmentation and kinematics the zandjan fault system is certainly capable to produce moderate to large earthquakes mw 6 5 7 0 and serious damages in the zandjan city and surrounding areas the study of these faults is then of major interest for seismic hazard assessment in zandjan province where total population exceed 1 5 million but also to better understand present day geodynamic of nw iran

a source discrimination study of a chinese seismic event of may 4 1983 abstract a weak seismic event that occurred on may 4 1983 close to the lop nor underground test site in southern sinkiang province china has been studied for source discrimination digital waveforms obtained at gauribidanur array india of this event of six known shallow focus earthquakes from southern sinkiang and of two known underground nuclear explosions in lop nor were processed for further analysis the estimates of signal complexity and tmf third moment of frequency parameters of the may 4 event were found to be quite different from those of the known explosions whereas they were consistent with those of the known earthquakes on this basis the event under investigation appeared to be a crustal focus earthquake

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

k ar dating in the eastern elburz iran abstract forty four potassium argon age determinations on whole rock samples have been done on basaltic flows interbedded with paleozoic and mesozoic sediments in eastern iran a very widespread rejuvenation of 200 250 m y age is shown by most samples this age coincides with the movement of the irano afghan block across the paleo tethyan ocean

the seismic disturbance of 1976 march 20 elast kazakhstan earthquake or explosions summary on 1976 march 20 a seismic disturbance took place near an explosion test site in east kazakhstan ussr on the mb ms criterion this disturbance is identified as an earthquake however it has been suggested that the source may have been one or more explosions it is shown here that the polarities and relative amplitudes of the main arrivals on the short period p wave seismograms of the disturbance can be accounted for by assuming the source was an earthquake in a crust with some lateral variation in structure there is no evidence that the disturbance was anything other than a single earthquake

focal mechanism of the 20 august 1983 caspian sea earthquake abstract the short period array seismogram at gba india of a central caspian sea seismic event on 20 august 1983 was described by some workers as explosion like though they finally favoured an earthquake source on focal depth and p wave complexity spectral criteria we subject gba and other array records to a quantitative test for compatibility with a double couple source the p pp sp relative amplitude method applied in conjunction with a moving depth window process to test separately a wide range of p pp sp times the only sections of coda consistent with being pp and or sp are large amplitude arrivals 12 15 s behind p they indicate a normal fault striking wnw ese and downthrown to the north at a depth of some 30 km in good agreement with the trend of mapped faults and local seismicity and focal depth derived from p onset times

source depth as a useful parameter in the discrimination of earthquakes and underground explosions abstract in order to identify whether observed seismic signals are generated by an underground nuclear explosion or an earthquake it is adequate to rely on one efficient identifier that provides a reasonably good clue in an unambiguous way although it is generally accepted that multi station multi parameter discrimination can provide separation between explosions and earthquakes it has been observed that cases do arise where signal characteristics cannot be established distinctly and satisfactorily in the so called difficult cases which are associated with some ambiguity in deducing the nature of the source using single station seismograms it is shown in this paper that a reliable estimate of source depth proves extremely useful out of the eleven typical examples of not easy to discriminate events recorded at the gauribidanur short period seismic array in southern india seven could be successfully identified as earthquakes and the remaining four as probable underground explosions on the basis of focal depth estimates from multi station data

reply to the comment of fugenschuh et al on the paper estimating displacement along the brenner fault and orogen parallel extension in the eastern alps by rosenberg and garcia int j earth sci geol rundsch 2011 100 1129 1145 fugenschuh et al 2011 question several aspects of our paper rosenberg and garcia 2011 on the estimate of extension along the brenner fault bf first they emphasize the necessity of a two phase extensional model to understand exhumation of the footwall of the bf second they claim that the vertical offsets and extensional displacement calculated by rosenberg and garcia 2011 only refer to the brittle phase of the bf third they follow the new interpretations of tochterle et al 2011 inferring that the continuation of the brenner ductile mylonites is located along the north western border of the tauern window tw fourth they present a new estimate of extension and of exhumation by folding and erosion based on the quantification of tectonic omissions we discuss and reply to these four issues below

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