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

new moho map for onshore southern norway a recent seismic refraction study across southern norway has revealed that the up to 2469 m high southern scandes mountains are not isostatically compensated by a thick crust rather the moho depths are close to average for continental crust with elevations of similar to 1 km evidence from new seismic data indicate that beneath the highest topography moho depths are around 38 40 km these measurements are similar to 2 km deeper than early estimates interpolated from coarsely spaced refraction profiles but up to 3 km shallower than receiver function estimates for the area moho depth variation beneath the mountains roughly correlates with changes in surface topography indicating that topography is at least to the first order controlled by crustal thickness however the highest mountains do not overlie the thickest crust and additional support for topography for example from flexural strength in the lithosphere low densities in the upper mantle or mantle dynamics is likely the relationship between topography and moho depth breaks down for the oslo graben and the fennoscandian shield to the east and north high density lower crustal rocks below oslo graben and increasing crust and lithospheric thicknesses below the fennoscandian shield may produce a negative correlation between topography and moho depth

empirical observations regarding reverse earthquakes blind thrust faults and quaternary deformation are blind thrust faults truly blind active thrust faults pose a significant seismic hazard worldwide many of these faults include blind thrusts where the propagating fault tip does not reach the earth s surface and buried faults where the geomorphic expression of the fault is obscured by subsequent sedimentation and or erosion this raises the issue of whether conventional geologic geomorphic and paleoseismic methods can be used to identify and characterize thrust faults for the assessment of seismic hazards or whether these faults sometimes are truly blind we compiled a data base of 148 worldwide moderate to large magnitude thrust reverse earthquakes to evaluate whether or not the event occurred on a fault that could have been identified prior to the earthquake on the basis of recognizable quaternary surface deformation i e a pre existing fault or fold analysis of the data shows that interplate reverse earthquakes almost always are associated with pre existing quaternary deformation that was or could have been recognized prior to the earthquake in particular most interplate reverse earthquakes are associated with an active reverse fault at the surface and or an active anticline in contrast intraplate reverse earthquakes seldom occur on faults associated with pre existing recognizable surface deformation we conclude that thrust faults can be detected in interplate regions with careful quaternary geologic and geomorphic mapping furthermore the absence of quaternary surface deformation can be used to infer the absence of an underlying active blind thrust fault in interplate tectonic settings however the data show that quaternary geologic mapping techniques alone likely are insufficient to characterize blind thrusts in intraplate regions in these areas inclusion of a floating or random earthquake may be necessary to assess earthquake hazards

evolution of oceanic crust on the kolbeinsey ridge north of iceland over the past 22 myr the evolution of oceanic crust on the kolbeinsey ridge north of iceland is discussed on the basis of a crustal transect obtained by seismic experiment from the kolbeinsey ridge to the jan mayen basin the crustal model indicates a relatively uniform structure no significant lateral velocity variations are observed especially in the lower crust the uniform velocity structure suggests that the postulated extinct axis does not exist over the oceanic crust formed at the kolbeinsey ridge but supports a model of continuous spreading along the ridge after oceanic spreading started west of the jan mayen basin the oceanic crust formed at kolbeinsey ridge is 1 2 5 km thicker than normal oceanic crust due to hotter than normal mantle from the iceland mantle plume the observed generally uniform thickness throughout the transect might also indicate that the temperatures of the astheno spheric mantle ascending along the kolbeinsey ridge have not changed significantly since the age of magnetic anomaly 6b

active faults in the zagros and central iran abstract active tectonic movements in the northwestern zagros include right lateral slip at the rate of about 10 mm a along the main recent fault which inherits the position of the main thrust now inactive and active thrusting and accompanying folding distributed between several zones southwest of the main recent fault in the southeastern zagros the fars province there are several right lateral faults that extend n s obliquely to the overall trend of the zagros fault and fold belt these may be either branches of the main recent fault or faults accommodating relative broadening of the outer zagros in its southeastern segment the main thrust in the southeastern zagros also remains inactive the ipak north tehran and mosha fault zones and several minor structures in the eastern alborz form the e w trending active fault system with combined reverse and left lateral slip on the ipak and mosha zones lateral movements with the late quaternary mean rate exceeding 1 mm a dominate over vertical fault movements together with right lateral faults stretching northeast of zagros the faults of the alborz may accommodate east directed motion of the iranian microplate

a moderate melting model for the voring margin norway based on structural observations and a thermo kinematical modelling implication for the meaning of the lower crustal bodies high p wave velocities 7 1 7 8 km s lower crustal bodies lcbs imaged along volcanic margins are commonly interpreted as plume and breakup related thick mafic underplating this interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer voring basin norway an exceptional strong amplitude reflection the t reflection is particularly well defined below the north gjallar ridge ngr between 7and 8 s twt the t reflection is located near the volcanic lava flows emplaced during the ne atlantic breakup 55 54 ma ago and coincides with the top of the lcb forming a mid crustal dome based on structural and temporal relationships we show that the dome clearly influences the structural development of the ngr and predates the continental breakup at least by 10 15 ma using a thermo kinematical model we tried also to investigate and quantify the relationships between the extension lcb and the magmatic production modelling suggests that significant paleocene early eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the breakup initiation the conclusion of 2d thermo kinematical parametric analysis is that the magmatic model predicts either little extension 5 with significant melting along the outer voring basin we suggest that the continental part of the lcb could not necessarily be breakup related and so magmatic as has often been stated previously it is concluded here that the continental part of the lcb observed beneath the outer voring basin may be partly or fully attributed to inherited high pressure granulite eclogite lower crustal rocks the real amount of mafic material emplaced along the outer voring basin could be 20 40 less than thought

new models for evolution of magma poor rifted margins based on a review of data and concepts from west iberia and the alps direct observation and extensive sampling in ancient margins exposed in the alps combined with drill hole and geophysical data from the present day iberia margin result in new concepts for the strain evolution and near surface response to lithospheric rupturing at magma poor rifted margins this paper reviews data and tectonic concepts derived from these two margins and proposes that extension leading to thinning and final rupturing of the continental lithosphere is accommodated by three fault systems each of them characterized by a specific temporal and spatial evolution during rifting of the margin by its fault geometry and its surface response the data presented in this paper suggest that margin architecture and distribution of rift structures within the future margin are controlled first by inherited heterogeneities within the lithosphere leading to a contrasting behaviour of the future distal and proximal margins during an initial stage of rifting the place of final break up appears to be determined early in the evolution of the margin and occurs where the crust has been thinned during a first stage to less than 10 kilometres during final break up the rheology of the extending lithosphere is controlled by the thermal structure related to the rise of the asthenosphere and by serpentinization and magmatic processes

crustal taper and topography at passive continental margins terra nova 23 349 361 2011 abstract the long term evolution of kilometre s high seaward facing escarpments at passive margins is linked directly to the crustal thinning gradient the development of post rift faults in the onshore parts of the margin and the associated distribution of drainage patterns landscape types and sediment dispersal patterns reflect this linkage for the seismically well imaged norwegian margin as well as for a number of passive margins worldwide we identify a scaling relationship that correlates escarpment height with the distance to the highly extended distal margin or more specifically the taper break the highest escarpments and the most asymmetric margin topography are found inboard of sharply tapering crystalline crust independent of margin age conversely escarpments are lower where the taper is gentle thus the topography of passive margins does not primarily reflect age magmatism climate or mantle convection but more probably the response to loading of the laterally variable fault controlled architecture of the crystalline crust

vp vs ratio along the voring margin ne atlantic derived from obs data implications on lithology and stress field a total of 13 regional ocean bottom seismograph obs profiles with an accumulated length of 2207 km acquired on the voring margin ne atlantic have been travel time modelled with regards to s waves the vp vs ratios are found to decrease with depth through the tertiary layers which is attributed to increased compaction and consolidation of the rocks the vp vs ratio in the intra campanian to mid campanian layer 1 75 1 8 in the central voring basin is significantly lower than for the layers above and beneath suggesting higher sand shale ratio this layer was confirmed by drilling to represent a layer of sandstone this mid cretaceous anomaly is also present in the northern voring basin as well as on the southern lofoten margin further north the vp vs ratio in the extrusive rocks on the voring plateau is estimated to be 1 85 conformable with mafic basaltic rocks landward of the continent ocean transition cot the vp vs ratio in the layer beneath the volcanics is estimated to be 1 67 1 75 these low values suggest that this layer represents sedimentary rocks and that the sand shale ratio might be relatively high here the vp vs ratio in the crystalline basement is estimated to be 1 67 1 75 in the basin and on the landward part of the voring plateau indicating the presence of granitic granodioritic continental crust in the lower crust the vp vs ratio in the basin decreases uniformly from southwest to northeast from 1 85 1 9 to 1 68 1 73 suggesting a gradual change from mafic gabbroic to felsic granodioritic lower crust significant 3 5 azimuthal s wave anisotropy is observed for several sedimentary layers as well as in the lower crust all these observations can be explained by invoking the presence of liquid filled microcracks aligned vertically along the direction of the present day maximum compressive stress nw se

crustal structure across the more margin mid norway from wide angle seismic and gravity data the more margin in the ne atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore in order to study this transition in detail three ocean bottom seismometer profiles with deep seismic reflection and refraction data were acquired in 2009 two dip profiles which were extended by land stations and one tie profile parallel to the strike of the more trondelag fault complex the modeling of the wide angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3d density model modeling of the geophysical data indicates the presence of a 12 15 km thick accumulation of sedimentary rocks in the more basin the modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south near the coast we observe an intra crustal reflector under the trondelag platform but not under the slorebotn sub basin furthermore two lower crustal high velocity bodies are modeled one located near the more marginal high and one beneath the slorebotn sub basin while the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating the inner body has a density close to mantle density which might suggest an origin as an eclogized body formed by metamorphosis of lower crustal gabbro during the caledonian orogeny the difference in velocity and extent of the lower crustal bodies seems to be controlled by the jan mayen lineament suggesting that the lineament represents a pre caledonian structural feature in the basement

the ocean continent boundary off the western continental margin of iberia crustal structure west of galicia bank a seismic refraction transect across the galicia bank continental margin shows that the original continental crust thins westward from 17 to 2 km immediately east of a margin parallel peridotite ridge pr immediately west of the pr oceanic crust is only 2 5 3 5 km thick but farther west oceanward it thickens to 7 km the pr caps a similar to 60 km wide lens shaped serpentinized peridotite body underlying both thinned continental and thin oceanic crust when superimposed on a reflection time version of the velocity model the s reflector is clearly intracrustal at its east end westward s cuts down to lower crustal levels eventually coinciding with the top of the serpentinized peridotite lens original crust mantle boundary these observations render almost impossible the seafloor exposure of the pr by s acting as a top to the west detachment fault numerical models of melting and borehole subsidence information constrain our rifting model the easternmost continental crust experienced a total stretching factor of 4 3 most likely in two stages it probably occurred over similar to 25 m y with the highest fate of stretching at the beginning of the main earlier rift phase valanginian 141 135 ma the 3 4 7 km thick continental crust depending on whether serpentinized peridotite is assigned to crust or mantle which may include melt products requires stretching factors 6 more than 11 7 and a rift duration of more than 25 13 m y the thin oceanic crust immediately west of the pr is explained by conductive cooling of the mantle during the long prebreakup stretching phase which temporarily caused reduced melting immediately after breakup

initiation of crustal scale thrusts triggered by metamorphic reactions at depth insights from a comparison between the himalayas and scandinavian caledonides active eclogitization has recently been inferred at depth beneath the himalaya from geophysical observations and the mechanical consequences of eclogitization can be observed in the field in the eroded and extended nappe stack of the scandinavian caledonides there proterozoic metastable granulites and igneous protoliths underwent partial eclogitization during the collision of baltica with laurentia the reaction began in pseudotachylites and veins and eventually formed a connected network of eclogite facies shear zones that localized deformation and weakened the lower crust of baltica during the collision with laurentia all these features can be compared with the seismic activity of the indian lower crust its strength loss beneath the himalayan ranges and its delayed density increase regarding its penetration in the eclogite facies the caledonian bergen arc eclogites and the himalayan ama drime eclogites are both derived from continental crust in both cases these eclogites were formed contemporaneously with the activation of the main thrusts responsible for the construction of the orogenic wedges the main central thrust in the himalayas and the main thrust below the jotun nappe complex in the caledonides the similarities in these two orogens which compare both in size and structure highlight the importance of eclogitization at depth as a mechanism for weakening of the lower crust and for decoupling of the crust and lithospheric mantle in collision zones

lower crustal high velocity bodies along north atlantic passive margins and their link to caledonian suture zone eclogites and early cenozoic magmatism abstract in this study we use crustal scale ocean bottom seismic models to infer the presence of two types of lower crustal bodies at north atlantic passive margins type i primarily interpreted as early eocene magmatic intrusions and type ii interpreted as caledonian eclogites we discuss how these eclogites might be related to the main caledonian suture zone and other tectonic features in a conjugate north atlantic setting based on the first order approximation that p wave velocities can be related to rock strength the narrower continental margin at the southern more transect may be explained by stronger lower crust there compared with the northern voring transect this difference in strength possibly resulting in a steeper dip in the subducting baltica plate south of the proto jan mayen lineament may explain the asymmetry in extensional style observed across this lineament our interpretation locates the main suture off mid norway close to the more trondelag fault zone on the more margin along the western boundary of the trondelag platform on the voring margin and further northwards beneath the lofoten ridge the lower crustal body type i is about 60 thicker on the greenland side for both transects and its thickness along the northern transect is more than twice that of the southern transect these differences are consistent with sub lithospheric interaction between the icelandic hotspot and the continental rift oceanic accretion system around the time of continental break up

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

crustal structure of the kolbeinsey ridge north atlantic obtained by use of ocean bottom seismographs we present the results of a seismic survey performed around the kolbeinsey ridge north atlantic the seismic data were acquired along three profiles on the ridge axis ll 12 km off ridge l2 and perpendicular to the ridge axis l3 the models indicate lower velocity beneath the ridge axis than in the off ridge area along l3 we obtain velocities of 2 6 3 6 km s upper crust 4 8 6 0 km s middle crust and 6 6 6 9 km s lower crust beneath the ridge axis while at more than 12 km off ridge the model shows velocities of 3 6 4 6 km s upper crust 5 6 6 4 km s middle crust and 6 9 7 2 km s lower crust the model of l1 also shows significant lateral variation along the axis in the lower crust the velocity in the lower crust decreases to 6 3 km s in the southwestern part of ll where the moho depth decreases to 7 2 km the low velocity structure beneath the ridge axis is interpreted to be due to high porosity in the upper crust and to higher temperatures as well as a few percent porosity in the middle and lower crustal material according to this interpretation the crustal model of l3 implies that the cracks have been sealed and the temperatures have decreased to normal in 1 2 m y old crust the anomalous low velocity structure along ll can be interpreted as related to the most recent injection processes or a thermal influence of the spar fracture zone situated 50 km south of the profile

lower crustal intrusion on the north atlantic continental margin near the faroe islands in the north atlantic the majority of basalt is intruded into the continent ocean transition rather than extruded onto the surface this melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 melt as has often been assumed when continents break apart the rifting is sometimes accompanied by the production of large volumes of molten rock1 2 3 the total melt volume however is uncertain because only part of it has erupted at the surface furthermore the cause of the magmatism is still disputed specifically whether or not it is due to increased mantle temperatures we recorded deep penetration normal incidence and wide angle seismic profiles across the faroe and hatton bank volcanic margins in the northeast atlantic here we show that near the faroe islands for every 1 km along strike 360 400 km3 of basalt is extruded while 540 600 km3 is intruded into the continent ocean transition we find that lower crustal intrusions are focused mainly into a narrow zone 50 km wide on the transition although extruded basalts flow more than 100 km from the rift seismic profiles show that the melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 per cent melt as has often been assumed evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures with no requirement for either significant active small scale mantle convection under the rift or the presence of fertile mantle at the time of continental break up as has previously been suggested for the north atlantic ocean4 5 6

palaeoseismicity and pottery investigating earthquake and archaeological chronologies on the hajiarab alluvial fan iran for millennia humans have lived in locations that are highly vulnerable to large earthquakes often out of strategic or cultural necessity and or the proximity of these locations to resources necessary for survival despite the often catastrophic effects when large earthquakes occur recent history reveals that human nature is to rebuild rather than relocate implying that seismic activity is not a sufficient deterrent of population growth in tectonically vulnerable areas in order to investigate whether this was the case for ancient civilisations and thus perhaps a fundamental tenet of human behaviour a palaeo earthquake history was developed for the active cheskin and ipak faults in northwestern iran and compared with the well resolved archaeological history of the nearby sagzabad cluster settlements of zagheh 7170 6300 bp ghabristan 6215 4950 bp and sagzabad 4050 2350 bp combining new geologic geomorphic and chronologic datasets revealed the presence of a fault propagated anticline formed by large mw 6 5 7 0 earthquakes on a blind thrust fault that projects to seismogenic depth directly beneath the sagzabad cluster settlement sites large earthquakes with a return period of 90 probability under most faulting scenarios that the energy release from these earthquakes would have been of sufficient magnitude to generate peak horizontal acceleration pha values at the sagzabad cluster in excess of likely threshold values for complete settlement destruction poisson modelling assuming a time displacement repeating model for earthquake recurrence indicates a 66 42 probability of one two earthquakes that would generate pha 0 25 g occurring during occupation of zagheh a 79 55 probability for ghabristan and an 88 65 probability for sagzabad despite the near certainty that the residents of these holocene settlements experienced large destructive earthquakes the near continuous history of occupation at this area suggests that early humans were not apt to relocate in response to earthquake activity environmental e g alluviation stream channel avulsion climate change cultural and or political factors may have been more important drivers of settlement shifts and abandonment at the sagzabad cluster of iran

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

the crustal structure of central east greenland results from combined land sea seismic refraction experiments summary we present results from the first combined marine land seismic refraction survey in the area of the east greenland caledonides together with gravimetric measurements the seismic and gravimetric models show a consistent picture of the crustal structures in the western area which is part of the caledonian mountains of east greenland crystalline rocks with p wave velocities of about 5 5 km s 1 occur at the surface seismic velocities increase continuously with depth and reach values of 6 6 km s 1 at 12 km the total thickness of the crust as revealed by the seismic measurements reaches high values of up to 48 km in the southwestern part of the region 28 w gravity data which also cover the region west of the seismic lines indicate a possible further increase of the crustal thickness these high values raise questions about whether they represent a caledonide crustal root which would stand in strong contrast to the findings in the caledonian areas of europe or whether the crustal thickening represents a pre caledonian structure and is affine rather to the older regions west of the caledonides and adjacent to the greenland inland ice towards the east crustal thickness decreases rapidly it reaches a minimum of 22 km under the late palaeozoic mesozoic sedimentary basin of jameson land the crustal thinning is the result of the stretching of east greenland which was produced by a general extensional tectonic regime and the collapse of the caledonian mountain chain from devonian time onwards in the area of transition from thick to thin crust the seismic data indicate a layered structure at the moho this region is interpreted as a zone of extensive intrusion or underplating during the rifting in the tertiary

ephemeral stream response to growing folds the response of ephemeral alluvial streams to active tectonics is not as well established as those documented for perennial alluvial streams this study documents the response of ephemeral streams transverse to growing folds along the north fl ank of the san bernardino mountains in southern california the growing folds emerge amid a broad sloping piedmont mantled by north dipping alluvial fans and underlain by coarse angular gravel and sand of mixed provenance the study area contains fans composed of two distinct lithologies that control the expression of the folds sediment transport processes differ among alluvial perennial and ephemeral channels and play a primary role in defi ning the range of responses that ephemeral streams have to an actively rising fold we fi nd that ephemeral streams respond by 1 changing pattern from a single slightly incised channel with well defi ned banks to a braided channel upstream of the fold axis 2 incising across the fold axis preserving a terrace and braid bars and 3 returning to a single thread less incised channel downstream of the fold axis this channel response is documented for both a topographically obvious anticlinal fold the cougar buttes anticline as well as a suspected but not topographically obvious anticline the pitzer buttes anticline variations from this general model appear to be correlated with locations of slow fold growth and or channel alluvium that is fi ne grained and of low cohesion a growing fold such as the cougar buttes anticline provides a laboratory for the investigation of the development of transverse streams with respect to position along strike with the fold axis some streams crossing the cougar buttes anticline are antecedent whereas others are consequent to the growth of the fold these observations lay the foundation for a conceptual model for ephemeral stream response to active tectonics particularly useful in identifying previously unrecognized actively rising folds in this study the fold axis of the cougar buttes anticline is revealed to extend at least 1 km beyond its current obvious topographic expression because ephemeral streams are sensitive to tectonic deformation they can be used locally in paleoseismological investigations regionally to understand the strain partitioning between the big bear and mojave blocks and conceptually to constrain geodynamic models investigating the interaction between surface processes and the geometry of and slip rates on faults responsible for fold growth

implications of earthquake focal mechanism data for the active tectonics of the south caspian basin and surrounding regions summary the south caspian basin is a relatively aseismic block within the alpine himalayan belt but is surrounded by zones of high seismicity we used the focal mechanisms of 16 earthquakes whose source parameters we determined from inversion of body waves and the mechanisms of 15 other earthquakes to determine the style of faulting in the seismic belts surrounding the south caspian basin earthquakes beneath the talesh mountains of north west iran and immediately off shore in the south west caspian sea have shallow thrust mechanisms showing that the continental crust of north west iran is overthrusting the oceanic like crust of the south caspian basin earthquakes south of the caspian sea in northern iran show a mixture of focal mechanisms both high angle reverse faulting and left lateral strike slip faulting mechanisms are observed in the high alborz mountains farther south on the edge of the central iran plateau oblique left lateral reverse mechanisms are observed it appears that the ne direction of shortening between central iran and the south caspian basin is partitioned into pure left lateral strike slip and thrusting in the wnw trending high alborz but is accommodated by oblique faulting in lower elevations earthquakes in the kopet dag mountains east of the caspian sea also show a mixture of high angle reverse and strike slip faulting mechanisms and may be another example of the partitioning of oblique slip into strike slip and thrust motion normal faulting mechanisms at centroid depths of 35 50 km dominate in the belt of seismicity that extends across the central caspian sea the significance of the normal faulting earthquakes is enigmatic it is improbable that these events represent the motion between the southern caspian basin and eurasia for they imply a sense of motion that is incompatible with the observed topography and folding in the sediments two shallow earthquakes at about 12 km depth in this belt one a small event and the other a large second subevent of a multiple earthquake have thrusting mechanisms suggesting that shortening occurs as the continental crust of the northern caspian sea is thrust over the oceanic like crust of the southern caspian basin shortening is also suggested by the orientations of folds in the sedimentary cover south of the central caspian sea seismic belt we suggest that this shortening does indeed represent a nne motion of the caspian sea relative to eurasia but that the motion is slow and has not produced many earthquakes the deeper normal faulting events may be related to bending or down dip extension of the incipient subducted slab if the motion of the caspian sea relative to eurasia is indeed slow then the motion in the alborz between central iran and the south caspian basin will be almost the same as that between iran and eurasia as has previously been assumed the combined effect of the overthrusting of the south caspian basin by the talesh alborz mountains in the south and by the continental crust of the northern caspian sea in the north will lead to the eventual destruction of the south caspian basin and the possible formation of an intermediate depth dipping seismic zone within the continental interior similar to that presently observed in the hindu kush

structure of the jan mayen microcontinent and implications for its evolution an extensive seismic survey using ocean bottom seismographs obs was performed in the area across the jan mayen basin north atlantic from the jan mayen ridge to the iceland plateau the jan mayen ridge and surrounding area are considered to be a fragment of a continent which was separated from greenland just prior to magnetic anomaly 6 this study presents the crustal structure of the jan mayen microcontinent and the ocean continent transition to the west of the jan mayen ridge the crustal structures from the centre of the jan mayen ridge to the jan mayen basin are characterized by a deep sedimentary basin a thin basaltic layer within the sedimentary section and extreme thinning of the continental crust towards the iceland plateau the obs data indicate that a continental upper crust v p 5 8 6 1 km s 1 and lower crust v p 6 7 6 8 km s 1 underlie the deep sedimentary basin the thickness of the continental lower crust varies significantly from 12 km beneath the jan mayen ridge to almost zero thickness beneath the northwestern part of the jan mayen basin an ocean continent transition zone is found at the western edge of the jan mayen basin within the 10 km wide transition zone crustal velocities increase towards the iceland plateau and approach the velocities of the oceanic crust obtained at the iceland plateau that is 3 8 5 1 km s 1 oceanic layer 2a 5 9 6 5 km s 1 oceanic layer 2b and 6 8 7 3 km s 1 oceanic layer 3 the crustal model indicates very thin oceanic crust 5 km immediately oceanwards of the ocean continent transition zone beneath the iceland plateau the oceanic crust is thicker 9 km than the typical thickness of normal oceanic crust this might imply that the oceanic crust at the iceland plateau has been generated by asthenospheric material slightly hotter than normal from the crustal structure obtained by the present study it is proposed that the western part of the jan mayen ridge may be referred to as a non volcanic continental margin generated by a long duration of rifting even if the asthenospheric material upwelling along the margin were hotter than normal only small amounts of magmatic intrusions and extrusions would have been generated because of significant conductive cooling under the long duration of rifting

effective medium modeling of gas hydrate filled fractures using the sonic log in the krishna godavari basin offshore eastern india 1 indian national gas hydrate program expedition 01 has established that clay rich marine sediment from the krishna godavari kg basin in the eastern indian margin hosts one of the richest gas hydrate deposits in the world resistivity at bit images and pressure cores reveal that the gas hydrate morphology in clay rich sediment varies from complex vein structures grain displacing to invisible pore filling existing rock physics models which relate acoustic data to in situ gas hydrate concentrations generally assume isotropic pore filling gas hydrate which yields misleading concentration estimates for fractured fine grained sediments the anisotropic kg basin sediment presents additional complications here we apply differential effective medium theory to incorporate grain displacing morphologies by which gas hydrate is included as vertical ellipsoids with aspect ratios ranging from those of thin veins up to those of nodules in an elastic anisotropic background we have estimated gas hydrate concentrations from sonic velocities at hole 10d in the kg basin considering three basic gas hydrate morphologies i pore filling ii grain displacing and iii a combination of grain displacing and pore filling average gas hydrate saturations for these three cases are 35 42 27 30 and 33 41 of the total porosity respectively in the depth range 60 140 m below seafloor mbsf saturation is highest at 67 mbsf for any morphology but the values differ between morphologies for the pore filling morphology the maximum gas hydrate saturation of 56 is 18 22 higher than the grain displacing morphology and 2 9 higher than the combined morphology estimates differ by 6 of the sediment volume with rotations of gas hydrate veins from vertical to horizontal

seismic structure and composition of the crust beneath the southern scandes norway abstract new results on p and s wave seismic velocity structure in southern norway indicate that the crust has an average poisson s ratio of 0 25 is predominantly of felsic intermediate composition and lacks a significant mafic lower crust a crustal scale refraction seismic study magnus rex mantle investigations of norwegian uplift structure refraction experiment acquired data along three 300 to 400 km long active source seismic profiles across the southwest scandinavian domain in southern norway the youngest section of the fennoscandian shield moho depths in the domain are 36 40 km thinning towards the continental shelf and oslo graben the high vp lower crust beneath the southwest scandinavian domain vp 7 km s is around 4 km thick crustal structure in the adjacent svecofennian domain differs significantly moho depths reach 50 km and an up to 24 km thick high vp lower crust is present strong p and s wave arrivals are recorded from magnus rex from which poisson s ratio for the crust is calculated the unusually strong s wave arrivals allow rare insight into crustal poisson s ratio structure that is not commonly available from active source data the thinness of the mafic lower crust in southern norway is in significant contrast to other parts of the fennoscandian shield and delamination or convective removal of the lower crust is proposed tectonic events that may have triggered detachment of the lower crust include extensional collapse after the caledonian orogeny and permian extension

magma productivity and early seafloor spreading rate correlation on the northern voring margin norway constraints on mantle melting abstract continental rifting at the voring margin off mid norway was initiated during the earliest eocene 54 ma and large volumes of magmatic rocks were emplaced during and after continental breakup in 2003 a marine survey collecting ocean bottom seismometer single channel reflection and magnetic data was conducted on the norwegian margin to constrain continental breakup and early seafloor spreading processes the profile described here crosses the northern part of the voring plateau and the crustal velocity model was constructed through a combination of ray tracing and forward gravity modeling the latter corrected for the thermal effects remaining from the seafloor spreading we found a maximum igneous crustal thickness of 18 km decreasing to 6 5 km over the first 6 m y after continental breakup both the volume and the duration of excess magmatism are about twice as large as that of the more margin south of the east jan mayen fracture zone which offsets the two margin segments by 170 km a similar reduction in magmatism occurs to the north over an along margin distance of 150 km to the lofoten margin but without a margin offset both the geochemical data and the mean p wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the voring margin the mean p wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production 2 m y after breakup the magnetic data were used to derive plate half spreading rates for the northern voring margin which are very similar to that obtained at the more margin there is a strong correlation between magma productivity and early plate spreading rate suggesting a common cause a model for the breakup related magmatism should be able to explain this correlation but also the magma production peak at breakup the along margin magmatic segmentation and the active mantle upwelling proposed end member hypotheses comprise elevated upper mantle temperatures caused by a hot mantle plume or edge driven small scale convection fluxing mantle rocks through the melt zone edge driven convection does not easily explain these observations but a mantle plume model in which buoyant plume material flows laterally to pond in the rift topography at the base of the lithosphere close to breakup time is promising when the continents break apart the hot and buoyant plume material can flow up into the rift zone from surrounding areas as the rift transits to drift and the excess temperature of this material will then cause excess magmatism which dies off as the rift restricted material is spent the buoyancy of the plume material may in addition cause active upwelling which can increase the melting furthermore and also increase the force on the plate boundaries to enhance plate spreading rate this conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading and thus correlate

hydrate morphology physical properties of sands with patchy hydrate saturation 1 the physical properties of gas hydrate bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase the host sediment grain size and the state of effective stress determine the hydrate morphology in sediments this information can be used to significantly constrain estimates of the physical properties of hydrate bearing sediments including the coarse grained sands subjected to high effective stress that are of interest as potential energy resources reported data and physical analyses suggest hydrate bearing sands contain a heterogeneous patchy hydrate distribution whereby zones with 100 pore space hydrate saturation are embedded in hydrate free sand accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate bearing sands and captures observed physical property dependencies on hydrate saturation for example numerical modeling results of sands with patchy saturation agree with experimental observation showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations the hydrate patch size itself impacts the physical properties of hydrate bearing sediments for example at constant hydrate saturation we find that conductivity electrical hydraulic and thermal increases as the number of hydrate saturated patches increases this increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross section of the specimen

estimation of intact and remoulded undrained shear strengths from penetration tests in soft clays difficulties in obtaining high quality soil samples from deepwater sites have necessitated increasing reliance on piezocone t bar and ball penetration tests to determine soil properties for design purposes this paper reports the results of an international collaborative project in which a worldwide high quality database of lightly overconsolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device the derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics the overall statistics showed similar levels of variability of the resistance factors with low coefficients of variation for all three types of penetrometer however correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stiffness or rigidity inde

continent ocean transition and voluminous magmatic underplating derived from p wave velocity modelling of the east greenland continental margin summary deep seismic refraction data were gathered across the entire east greenland rifted margin north of the jan mayen fracture zone between 72 n and 75 n in 2003 investigations of the deep crustal structure of this continental margin provide constraints on the formation of the margin and its structural evolution during and after late cretaceous early tertiary rifting and continental break up we present here the results along two profiles located in the prolongation of the godthab gulf and the kejser franz joseph fjord regional p wave velocity models were derived from forward traveltime modelling of land stations and ocean bottom hydrophone obh recordings for the first time long deep seismic sounding transects off east greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust a mean result is the identification of voluminous magmatic underplating which is wider and thicker than previously thought p wave velocities of the underplated material range between 7 1 and 7 4 km s 1 and the horizontal extents on the profiles are 225 and 190 km the maximum thickness of the underplated material is 15 16 km furthermore the p wave velocity models reveal a 120 130 km wide continent ocean transition zone cot based on an interpretation of the extent of cretaceous syn rift sediments mixed with basaltic intrusions and the lateral increase of velocities in the crustal layers excess magmatism must have been present during a long term rifting process accompanying the extension of the continental crust and giving rise to the voluminous magmatic underplating a consequence of our interpretation of the seismic refraction data is a likely rift propagation in the greenland sea from north to south additionally a comparison of p wave velocity models of the east greenland margin and voring margin reveals significantly asymmetric crustal architectures the voluminous magmatic underplating and asymmetrical conjugate margins formations are considered as a mirror of complex pre and syn rift processes

gas hydrate distributions in sediments of pockmarks from the nigerian margin results and interpretation from shallow drilling a joint research expedition between the french ifremer and the german marum was conducted in 2011 using the r v pourquoi pas to study gas hydrate distributions in a pockmark field 1141 1199 meters below sea surface at the continental margin of nigeria the sea floor drill rig mebo of marum was used to recover sediments as deep as 56 74 meters below seafloor the presence of gas hydrates in specific core sections was deduced from temperature anomalies recorded during continuous records of infrared thermal scanning and anomalies in pore water chloride concentrations in situ sediment temperature measurements showed elevated geothermal gradients of up to 258 c km in the center of the so called pockmark a which is up to 4 6 times higher than that in the background sediment 72 c km the gas hydrate distribution and thermal regime in the pockmark are largely controlled by the intensity periodicity and direction of fluid flow the joint interaction between fluid flow gas hydrate formation and dissolution and the thermal regime governs pockmark formation and evolution on the nigerian continental margin

the bam iran earthquake of december 26 2003 from an engineering and seismological point of view abstract this paper is devoted to studying the destructive bam earthquake from an engineering seismological point of view on december 26 2003 a large earthquake of magnitude 6 7 m s shook the bam district located in southeastern iran about 80 of buildings totally collapsed several dozen villages were destroyed and tens of them were severely damaged more than 45 000 people were killed and 30 000 were injured according to the macroseismic data focal depth of the event was estimated at 7 2 km the event was associated with a 9 km surface rupture of the bam fault the maximum residual strike slip displacement is 5 cm which is left lateral the highest recorded peak ground acceleration is at bam station 0 98 g vertical and 0 87 g horizontal located about 1 5 km from the surface rupture the macroseismic analyses show that the epicenter of the quake is 1 5 km east of bam all of the masonry buildings totally collapsed in the epicentral area many semi engineered structures were heavily damaged and some of them collapsed engineered structures constructed according to the seismic code of iran have shown very good structural behavior without significant damage finally the earthquake intensity at the epicenter is determined as ix on the msk scale which strongly decreases with distance from the surface ruptures

modelling shear waves in obs data from the voring basin northern norway by 2 d ray tracing three component recordings from an array of five ocean bottom seismographs in the northwestern part of the voring basin have been used to obtain a 2 d shear wave s wave velocity depth model the shear waves are identified by means of travel time differences compared to the compressional p waves and by analyzing their particle motions the model has been obtained by kinematic travel time ray tracing modelling of the obs horizontal components

faulting and folding in quaternary deposits of tehran s piedmont iran abstract tehran lies on the southern flank of the central alborz an active mountain belt characterized by many historical earthquakes some of which have affected tehran itself the border between the alborz mountain and the tehran s piedmont northern part of tehran city is marked by the north tehran fault ntf dividing the eocene rock formation from the alluvial units of different ages early pleistocene to the recent alluvium a detail mapping of the piedmont combined with structural study reveal that two active thrust faults situated south of the ntf are of importance for hazard assessment of the city the geomorphological evidences along the ntf are not in agreement with an active fault indicating that the fault activity may have been shifted southward furthermore differentiation of newly recognized alluvial units and their inferred ages together with the mapped fault pattern permit us to characterize the quaternary deformation the late pleistocene alluvial deposits consist of three alluvial fans among them the youngest one together with the modern alluvial fan defines the holocene deposit the present deformation in the piedmont is accommodated along vertically left lateral strike slip faults and low angle thrust faults trending in range from n070 to n110e

monotonic and dilatory pore pressure decay during piezocone tests in clay during a pause in cone penetration in fine grained soils pore water pressure dissipation tests are performed to evaluate the coefficient of consolidation for standard piezocones with shoulder fil

hydrate dissolution as a potential mechanism for pockmark formation in the niger delta received 17 february 2010 accepted 9 march 2010 published 11 august 2010 1 based on acquired geophysical geological and geotechnical data and modeling we suggest hydrate dissolution to cause sediment collapse and pockmark formation in the niger delta very high resolution bathymetry data acquired from the niger delta reveal the morphology of pockmarks with different shapes and sizes going from a small ring depression surrounding an irregular floor to more typical pockmarks with uniform depression geophysical data in situ piezocone measurements piezometer measurements and sediment cores demonstrate the presence of a common internal architecture of the studied pockmarks inner sediments rich in gas hydrates surrounded by overpressured sediments the temperature pressure and salinity conditions of the studied area have allowed us to exclude the process of gas hydrate dissociation gas hydrate turns into free gas water mixture as a trigger of the observed pockmarks based on numerical modeling we demonstrate that gas hydrate dissolution gas hydrate becomes mixture of water and dissolved gas under a local decrease of the gas concentration at the base of the gas hydrate occurrence zone ghoz can explain the excess pore pressure and fluid flow surrounding the central hydrated area and the sediment collapse at the border of the ghoz the different deformation or development stages of the detected pockmarks confirm that a local process such as the amount of gas flow through faults rather than a regional one is at the origin of those depressions

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

crustal structure and evolution of the southern voring basin and voring transform margin ne atlantic abstract the dominantly passive volcanic voring and more margins ne atlantic are separated by the 200 km long voring transform margin vtm the southern voring basin and the vtm have been studied by use of four regional ocean bottom seismograph obs profiles combined by gravity modelling the models demonstrate a complex pattern of magmatism along the transform margin the distribution of magmatism seems to be related to the existence and trend of a lower crustal 8 km s body interpreted as eclogitized rocks present in the southern voring basin early tertiary breakup related magmatic leakage across the continent ocean transition cot appears to be facilitated where this layer is absent these results support earlier workers who have concluded that the jan mayen fracture zone originated from a caledonian zone of weakness we propose that partly eclogitized rocks were uplifted into the lower crust close to this zone during the caledonian orogeny and that this body acted as a barrier to magma emplacement during the late cretaceous early eocene phase of rifting breakup the eclogitized terrain also appears to have caused northeastward channeling of the late cretaceous early tertiary intrusions within the voring basin an up to 10 km thick pre cretaceous sedimentary basin in the southern voring basin may be genetically related to the ns trending late paleozoic and mesozoic rift basins in north east greenland

rates of continental breakup magmatism and seafloor spreading in the norway basin iceland plume interaction 1 in year 2000 an ocean bottom seismometer obs profile was acquired across the more margin to the aegir ridge an extinct seafloor spreading axis the margin is an early eocene volcanic passive margin located between the faeroe iceland ridge fir and the east jan mayen fracture zone ejmfz the p wave data were modeled by ray tracing to give a crustal transect showing a 10 11 km thick igneous crust created by breakup magmatism tapering off to magma starved seafloor spreading by c23 time 51 4 ma the location of the ejmfz was reinterpreted from a satellite derived gravity map and spreading direction in the norway basin reevaluated no other fracture zones were confirmed and both thin oceanic crust 4 5 km and lack of fracture zones resemble ultraslow spreading on the arctic gakkel ridge magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the obs profile and half spreading rates were derived early seafloor spreading was slow 15 32 mm yr 1 approaching ultraslow 6 8 mm yr 1 by c20 time 42 7 ma a v shaped pattern seen in the gravity field located only around the northern part of the aegir ridge corresponds to increased crustal thickness in the seismic model recording northeast transport 3 6 mm yr 1 of more melt fertile asthenosphere zones the magma starved character of the norwegian basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the iceland plume constructed the fir to the south as the asthenosphere is subsequently transported into the norway basin

the t reflection and the deep crustal structure of the voring margin offshore mid norway seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust we have completed a detailed 2d seismic interpretation of the deep crustal structure of the voring margin offshore mid norway where high quality seismic data allow the identification of high amplitude reflections locally referred to as the t reflection using a dense seismic grid we have mapped the geometry of the t reflection in order to compare it with filtered bouguer gravity anomalies and seismic refraction data the t reflection is identified between 7 and 10 s sometimes it consists of one single smooth reflection however it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries amplitudes and contact relationships the t reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults the spatial correlation between the filtered positive bouguer gravity anomalies and the deep dome shaped reflections indicates that the latter represent a high impedance boundary contrast associated with a high density and velocity body in 50 of the outer voring margin the depth of the mapped t reflection is found to correspond to the depth of the top of the lower crustal body lcb which is characterized by high p wave velocities 7 km s we present a tectonic scenario where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high grade metamorphic rocks deep intrusions into the faulted crustal blocks are responsible for the rough character of the t reflection whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km s the result is a heterogeneous lcb that likely represents a complex mixture of pre to syn breakup mafic and ultramafic rocks cumulates and sills and old metamorphic rocks such as granulites and eclogites an increasing degree of melting towards the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust

holocene slip rate on the sabzevar thrust fault ne iran determined using optically stimulated luminescence osl abstract fault slip rates and the recurrence interval between earthquakes can be determined from reliable dating of deformed sediments we report optically stimulated luminescence osl ages of alluvial gravels fine grained sediments and colluvial deposits associated with the sabzevar thrust fault in northeastern iran six samples of the late quaternary deposits were dated by osl using the single aliquot regenerative dose sar protocol the osl ages indicate deposition of alluvial gravels in the study region between 30 and 9 13 ka followed by a period of fluvial incision which is ongoing at the present day the alluvial deposits have been uplifted by 9 5 m relative to the river level indicating a holocene slip rate of 1 mm yr and a rate of convergence across the fault of 0 4 0 6 mm yr assuming a maximum fault dip of 60 the average interval between large earthquakes on the sabzevar fault will be 3000 years if the fault dips 60 and less if the fault dip is less the last earthquake to destroy sabzevar was in 1052 a d

lower crustal composition and crustal lineaments on the voring margin ne atlantic a review abstract a prominent lower crustal high velocity layer observed in the voring basin ne atlantic has been investigated with regard to composition and spatial link to crustal scale lineaments in the southernmost part of the basin the lower crustal layer is interpreted as eclogites based on anomalously high p wave velocities 8 4 km s in the remainder of the basin the layer is preferably interpreted as mafic intrusions emplaced during the last phase of rifting but it cannot be excluded that the body consists of older caledonian mafic rocks direct link with high grade caledonian rocks to the east and westwards to east greenland cannot be made since these rocks are mainly of felsic composition the crustal scale lineaments inferred from wide angle seismic data appear to represent the oceanward extension of post caledonian detachments the spatial variation in the thickness of the layer is within the late rifting magmatic hypothesis partly interpreted in terms of pre magmatic variations in thickness of the lithosphere in addition lateral variations in extension mantle upwelling and decompressional melting during the last phase of rifting may also have contributed

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

a new assessment of the abundance of serpentinite in the oceanic crust the gabbro model of the composition of the oceanic crust has prevailed for more than two decades but serpentinites are common along much of the mid atlantic ridge and elsewhere leading to renewed debate over the abundance of serpentinites in crust created at slow spreading ridges based on data from both oceanic and ophiolite samples it has also been suggested that serpentinites are not distinguishable from meta gabbros and diabases by their seismic properties we have made new statistical analyses of the relationship between vs and vp in oceanic gabbro and diabase samples and serpentinized peridotites and compared them to in situ s wave and p wave velocities derived from expanding spread profiles esps acquired in the atlantic our findings demonstrate 1 that there is some overlap of the properties of gabbroic samples taken from ophiolites with the properties of serpentinites but 2 over the range of typical layer 3 seismic velocities the seismic properties of oceanic gabbros and diabases are distinctly different from the properties of serpentinites and 3 that in situ seismic velocities are in excellent agreement with the properties of the gabbros while the shear velocities in serpentinites are significantly lower partially serpentinized peridotite is certainly present but not abundant in normal oceanic crust

regional structure and polyphased cretaceous paleocene rift and basin development of the mid norwegian volcanic passive margin abstract the more and voring basins of the mid norwegian volcanic passive margin are characterized by thick accumulations of cretaceous to paleocene sedimentary strata they were formed during a series of late mesozoic early cenozoic extensional events and represent vast underexplored areas with a limited number of wells recently a new generation of long offset 2d seismic reflection lines and 3d seismic data together with new well data has permitted a significant improvement in the regional understanding of the more and voring basins this has enabled much better imaging of the deep cretaceous subbasins and sub basalt structures in light of this significant data improvement we performed a regional tectonostratigraphic synthesis of the pre breakup development of the more and voring basins we have interpreted eight regional cretaceous and paleocene horizons and constructed a series of structural and thickness maps the new interpretations allow us to examine the sequential evolution of the cretaceous to paleocene sedimentary infill and to discuss its relationship to the deep crustal structures and regional tectonic events we conclude that the long and polyphased development of the more and voring basins is partly controlled by deep seated structural highs we show that active deposition in the early cretaceous was mainly focused in the more basin while the main cenomanian and subsequent late cretaceous paleocene depocentres developed principally in the voring basin and migrated sequentially west towards the present continent ocean boundary we argue that the outer more and voring basins are likely underlain by a relatively thick continental crust compared to the inner part of the regional sag basin in this setting our observations do not support evidence for a large zone of exhumed upper mantle which has previously been proposed to have formed before magmatism and breakup

insights from the jan mayen system in the norwegian greenland sea ii architecture of a microcontinent summary we study the formation and evolution of the jan mayen microcontinent jmmc in the framework of conjugate margin evolution in the norwegian greenland sea the jmmc structural map and crustal architecture have been constrained by seismic mapping and potential field modelling supplemented by published seismic refraction transects the sedimentary and basement geometries have been further studied together with their conjugate to refine our knowledge on the less explored microcontinent structurally the jmmc main ridge is characterized by a platform and or terrace architecture flanked by sag type basins similar to those described on the mid norwegian conjugate margin while its southern part is marked by windows exposing crustal and or mantle material that was exhumed during higher degrees of extension the eastern side of the jmmc broke up in a magma rich fashion while the western side is magma poor the limited amount of magma involved in the jmmc formation suggests that changes in far field forces were the driving mechanism to initiate the isolation process and that a mantle plume had a lesser influence but might have helped the final mid ocean ridge establishment between the western jan mayen and greenland margin

seismicity and seismotectonics of madagascar revealed by the 2011 2013 deployment of the island wide macomo broadband seismic array abstract the seismicity and seismotectonics of madagascar have been studied using an island wide distribution of broadband seismic stations the 28 station madagascar comoros mozambique macomo array was deployed for a 23 month period between 2011 and 2013 macomo data were supplemented by seven temporary stations from the seismological signatures in the lithosphere asthenosphere system of southern madagascar selasoma project ten temporary stations from the reunion hotspot and upper mantle reunions unterer mantel project rhum rum and 11 permanent stations a total of 695 earthquakes with magnitudes between ml1 and ml5 3 located within madagascar were recorded a new local magnitude scale was developed and focal mechanisms were determined for 23 well recorded events most of the seismicity is clustered within central madagascar forming nw se trends in the ankaratra region and ne sw trends in the alaotra and ankay regions that roughly align with extensional tectonic features the northern and southern parts of madagascar also show seismicity clusters that align parallel to existing tectonic features primarily precambrian shear zones focal mechanisms exhibit a wide orientation of nodal planes show predominantly normal faulting throughout madagascar and provide no evidence for a sharp east west striking plate boundary between the lwandle and somalian plates in the middle of the island however a diffuse plate boundary cannot be excluded we suggest that topographically generated extensional stresses is the cause of most seismicity given that significantly fewer earthquakes are located in the lower elevation areas of the island compared to regions of higher elevations the frequency magnitude distribution has a b value of 1 2 and indicates that events with magnitude ml5 or greater should occur with an average repeat time of 1 4 years however no earthquake exceeding ml6 has been recorded in the last century suggesting that the frequency magnitude distribution could be truncated

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

mesozoic detachment faulting between greenland and norway inferences from jan mayen fracture zone system and associated alkalic volcanic rocks the spatial relation between the jan mayen fracture zone system and two occurrences of early tertiary mantle derived volcanic rock complexes indicates that an older continental fault system may have had hidden extensions in the deep lithosphere this is taken as indirect evidence that the inferred fracture zone precursor may have acted as a transfer fault system linking rifts formed by opposing simple shear detachment faulting through the lithosphere we infer that this contributed to continental rifting between greenland and norway in mesozoic to paleocene time before sea floor spreading began in the norwegian greenland sea region

long term fault slip rates distributed deformation rates and forecast of seismicity in the iranian plateau in this paper the long term crustal flow of the iranian plateau is computed using a kinematic finite element model neokinema software based on the iterated weighted least squares method the models are fitted to the newest data set of iran including updated fault traces geologic fault offset rates geodetic benchmark velocities principal stress directions and velocity boundary conditions we are successful to find the best kinematic model in which geological slip rates geodetic velocities and interpolated stress directions are fitted at levels of 0 35 1 0 and 1 0 datum standard deviation respectively the best fitted model for the first time provides long term fault slip rates velocity and anelastic strain rate field in the iranian plateau from all available kinematic data in order to verify the model the estimates of fault slip rates are compared to slip rates from merely analyzing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous gps based estimates using the selected model long term average seismicity maps and long term moment rates are produced on the basis of the shift hypothesis and previous global calibrations our kinematic model also provides a new constraint on ratio of seismic deformation to total deformation for different seismic zones of iran the resulting slip rates and the proposed seismic fraction of deformation provide the necessary input data for future time dependent hazard studies in iran moreover spatial distribution and total number of strong m 6 and major m 7 earthquakes which dominate the seismic hazard are all compatible with the regional seismic catalog

the crustal structure of central east greenland i from the caledonian orogen to the tertiary igneous province summary we present a regional crustal model of the east greenland fjord region between 69 n and 74 nw hich spans the caledonian fold belt and the adjoining devonian and mesozoic basins the model is a compilation of existing seismic models that were partly reinterpreted and newly derived results from different modelling approaches remodelling of 33 stations on three deep seismic lines in the southern area yielded consistent p wave velocity models for the entire fjord region seismic velocities between 5 5 km s 1 near the surface and 6 9 km s 1 in the lower crust are typical for regions of palaeozoic age moho depths up to 48 km in the seismic models suggest the existence of a crustal root beneath the caledonian orogen shear wave modelling of 51 stations on six refraction seismic profiles resulted in s wave velocities between 3 2 km s 1 in the upper crust 4 0 km s 1 at the crust mantle boundary and 4 2 km s 1 in the partial magmatic underplating of the lower crust in the northern area calculation of poisson s ratio portrays a fairly homogeneous crust with only slight variations in poisson s ratio of 0 26 0 30 for the uppermost crystalline crust and 0 22 0 24 for the middle crust these values cannot be linked to lithological variations because they are either small scale or span several tectonic provinces finite difference modelling and amplitude analysis confirm models without magmatic underplating in the lower crust of the southern hall bredning scoresby sund area

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

upper cretaceous paleogene stratigraphy and development of the mimir high voring transform margin norwegian sea abstract transform margins represent strike slip type of plate boundaries that form during continental breakup and initial ocean opening they are often characterized by margin parallel highs with exposed pre and syn rift sequences the voring transform margin offshore mid norway initiated in the earliest eocene during the opening of the ne atlantic here 2d seismic reflection data reveal a transform margin high the mimir high the western flank of this undrilled structure is a kilometer high escarpment where seismic reflections of pre breakup age are truncated at the seafloor the aim of this study was to recover seabed rock samples from the outcropping or shallowly buried sedimentary sequences to provide a geological tie to the regional seismic framework thereby constraining the basin history and tectono stratigraphic development seabed samples were successfully collected from 14 gravity core and selcore stations and 10 rov remotely operated vehicle sites along a 750 m high sampling profile recovering clay shales sandstones and glacial dropstones biostratigraphy results revealed that the ages of the sedimentary rocks follow the stratigraphic order predicted by the initial seismic interpretation with upper cretaceous sediments at the base and lower eocene sediments at the top the integrated interpretation shows that the mimir high area including parts of the outer voring and more basins and the proto jan mayen microplate complex were characterized by the deposition of late campanian to early maastrichtian near coastal and shale dominated sequences with poor source rock qualities the early paleocene samples indicate deep marine conditions that abruptly ended by rapid uplift of the mimir high in the earliest eocene finally a reworked pliensbachian palynomorph assemblage in potential early eocene strata indicate the presence of exposed mesozoic sequences in the vicinity of the mimir high we argue that some of the lower eocene sediments where deposited within a hypothetical drainage system sourced from greenland traill o or jameson land and or from the jan mayen ridge prior to continental separation and not the result of recent ice rafting

styles of extension offshore mid norway and implications for mechanisms of crustal thinning at passive margins 1 eocene magmatic breakup along the mid norway rifted margin was preceded by extreme jurassic cretaceous crustal thinning in a magma poor environment along the se borders of the rift top basement detachment faults with heaves on the order of 15 40 km evolved in at least two stages to become the boundaries between moderately thinned 20 30 km thick crust and a 100 200 km wide highly extended area with crustal thicknesses generally between 2 and 12 km under the present day more and voring basins in the footwalls of the basin flank detachments lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults under the most highly thinned areas a more distal set of deep seated basin floor detachments incised and extended remnant crust and probably the upper mantle leaving as little as 5 km of continental crust to be preserved under thick synrift and postrift deposits we suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust thus they prepare the ground for incision by the basin floor detachments which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed

the scattering of shear waves in the crust the two major sources of scattering for shear waves in the crust interactions with the topography at the surface and the effective anisotropy of aligned cracks throughout the rockmass introduce first order changes to the shear wave particle motion at the surface shear waves are scattered by the topography within a wavelength or two of the recording site so that unless the effective incidence angle is less than the critical angle sin 1vs vp the recorded waveforms may bear little relationship to the waveforms of the incident wave within the rockmass shear waves are scattered by extensive dilatancy anisotropy eda the distribution of stress aligned fluid filled cracks microcracks and preferentially oriented pore space pervading most rocks in the crust analysis of this shear wave splitting yields new information about the internal structure of thein situ rockmass which is not otherwise available

contribution of archaeological data to studies of earthquake history in the iranian plateau we use archaeological evidence to identify ancient earthquakes in the vicinity of large 20th century events in the iranian plateau two large earthquakes on the zagros main recent fault were preceded by historical earthquakes in ad 1008 and ad 1107 and by earthquakes in the intervals ad 224 459 and 1650 1600 bc giving return times of 1800 2100 500 800 and 850 950 years the ad 1962 ms 7 2 bo in zahra earthquake on the ipak fault in north central iran was preceded by an earthquake in 2000 1500 bc recorded at the sagzabad mound a return time of 3500 4000 years if there are no missing events the ad 1990 ms 7 3 rudbar tarom earthquake in the western alborz mountains was preceded by an earthquake in 1000 800 bc recorded at the marlik mound a return time of 2800 3000 years the ad 1948 ms 7 2 kopeh dagh earthquake that destroyed ashkabad capital of turkmenistan was preceded by an earthquake in 10 bc ad 10 recorded at mithradatkert nesa mound and by an earthquake in 2000 bc recorded at ak tapeh mound assuming no missing earthquakes this region has an earthquake return time of about 2000 years in khorasan province which was struck by a sequence of large earthquakes from ad 1936 to 1997 a mosque at qa en was destroyed in the mid 11th century ad probably the historical earthquake of ad1066 in the absence of palaeoseismic investigations archaeology offers the promise of recording earthquakes through more than one seismic cycle in different regions of iran q 2001 elsevier science ltd all rights reserved

holocene settlement shifts and palaeoenvironments on the central iranian plateau investigating linked systems for thousands of years humans have inhabited locations that are highly vulnerable to the impacts of climate change earthquakes and floods in order to investigate the extent to which holocene environmental changes may have impacted on cultural evolution we present new geologic geomorphic and chronologic data from the qazvin plain in northwest iran that provides a backdrop of natural environmental changes for the simultaneous cultural dynamics observed on the central iranian plateau well resolved archaeological data from the neighbouring settlements of zagheh 7170 6300 yr bp ghabristan 6215 4950 yr bp and sagzabad 4050 2350 yr bp indicate that holocene occupation of the hajiarab alluvial fan was interrupted by a 900 year settlement hiatus multi proxy climate data from nearby lakes in northwest iran suggest a transition from arid early holocene conditions to more humid middle holocene conditions from ca 7550 6750 yr bp coinciding with the settlement of zagheh and a peak in aridity at ca 4550 yr bp during the settlement hiatus palaeoseismic investigations indicate that large active fault systems in close proximity to the tell sites incurred a series of large mw 7 1 earthquakes with return periods of 500 1000 years during human occupation of the tells mapping and optically stimulated luminescence osl chronology of the alluvial sequences reveals changes in depositional style from coarse grained unconfined sheet flow deposits to proximal channel flow and distally prograding alluvial deposits sometime after ca 8830 yr bp possibly reflecting an increase in moisture following the early holocene arid phase the coincidence of major climate changes earthquake activity and varying sedimentation styles with changing patterns of human occupation on the hajiarab fan indicate links between environmental and anthropogenic systems however temporal coincidence does not necessitate a fundamental causative dependency

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

receiver function analysis of the crust and upper mantle in fennoscandia isostatic implications abstract the mountains across southern norway and other margins of the north atlantic ocean appear conspicuously high in the absence of recent convergent tectonics we investigate this phenomenon with receiver functions calculated for seismometers deployed across southern fennoscandia these are used to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust such parameters are key to understanding crustal isostasy and assessing its role or lack thereof in supporting the observed elevations our study focuses on the southern scandes mountain range that has an average elevation 1 0 km above mean sea level the crust mantle boundary moho is ubiquitously imaged and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal chemical or viscous boundaries in the upper mantle the moho resides at 25 30 km depth below mean sea level in southeastern coastal norway and parts of denmark 35 45 km across the southern scandes and 50 60 km near the norwegian swedish border that section of thickest crust coincides with much of the transscandinavian igneous belt and often exhibits a diffuse conversion at the moho which probably results from the presence of a high wave speed mafic lower crust across inner fennoscandia a zone of thinned crust

crustal composition of the more margin and compilation of a conjugate atlantic margin transect highlights the basement at the mid norwegian more margin is dominantly felsic in composition a lower crustal body is interpreted as a mixture of continental blocks and eclogite the thickness of the outer lower crustal body is twice as thick on the east greenland margin the thinning during this first phase of post caledonian extension was highest for proto norway abstract the inner part of the volcanic passive more margin mid norway expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust previous p wave modeling of wide angle seismic data revealed the presence of a high velocity 7 7 8 0 km s body in the lower crust in this transitional region these velocities are too high to be readily interpreted as early cenozoic intrusions a model often invoked to explain lower crustal high velocity bodies in the region we present a vp vs model derived from the modeling of wide angle seismic data acquired by use of ocean bottom seismograph horizontal components the modeling suggests dominantly felsic composition of the crust an average vp vs value for the lower crustal body is modeled at 1 77 which is compatible with a mixture of continental blocks and caledonian eclogites the results are compiled with earlier results into a transect extending from onshore norway to onshore greenland back stripping of the transect to early cenozoic indicates asymmetric conjugate magmatism related to the continental break up further back stripping to the time when most of the caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25 higher for proto norway than proto greenland

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

archaeological sediments from settlement mounds of the sagzabad cluster central iran human induced deposition on an arid alluvial plain abstract we outline results of a pilot geoarchaeological study of three settlement mounds tepe in the qazvin plain near tehran ca 7350 to 2450 cal bp conducted as part of a wider investigation of the interaction between prehistoric human communities and their environments in western iran the aim of the geoarchaeological study was to assess the potential of settlement sediments as records of past human practices and to guide future systematic sampling for geoarchaeological analyses here we integrate bulk sediment sediment texture organic matter with thin section based thin section micromorphology sem analyses in order to characterize human inputs in settlement deposits and infer human practices that drove sediment deposition plinth degradation and various kinds of burning byproducts and domestic and manufacturing waste furnished distinctive inputs to settlement sediments different types of fuel wood perhaps tamarix straw dung may reflect diverse domestic and manufacturing contexts of fire use

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

the 2002 june 22 changureh avaj earthquake in qazvin province northwest iran epicentral relocation source parameters surface deformation and geomorphology summary the m w 6 4 changureh avaj earthquake occurred on 2002 june 22 in qazvin province northwest iran we use observations from seismology field investigation and analysis of satellite imagery and digital topography to suggest that slip on a previously unrecognized thrust fault herein named the abdarreh fault was responsible for the earthquake inversion of longperiod p and sh body wave seismograms shows rupture on a thrust fault dipping 49 to the southwest and with a centroid depth of 10 km multiple event relocation of the main shock and aftershock epicentres and discontinuous surface ruptures observed after the earthquake are compatible with a northwest propagating rupture on a southwest dipping thrust but maximum recorded displacements are much less than expected from seismology suggesting that much of the slip failed to reach the surface and was accommodated as folding at the surface instead long term folding is difficult to see in the topography of the epicentral region as the abdarreh fold is growing through a relict neogene topography anticlinal uplift can however be inferred from drainage disruption and stream incision the 2002 june 22 changureh earthquake shows the importance of being able to interpret diagnostic features of active faulting in the landscape

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved