systematic comparisons of earthquake source models determined using insar and seismic data abstract robust earthquake source parameters e g location seismic moment fault geometry are essential for reliable seismic hazard assessment and the investigation of large scale tectonics they are routinely estimated using a variety of data and techniques such as seismic data and more recently interferometric synthetic aperture radar insar comparisons between these two datasets are frequently made although not usually in a comprehensive way this review compares source parameters from global and regional seismic catalogues with those from a recent database of insar parameters which has been expanded with 18 additional source models for this study we show that moment magnitude mw estimates agree well between the two datasets with a trend for thrust events modelled using insar to have slightly larger mw estimates earthquake locations determined using insar agree well with those reported in regional catalogues with a median difference of 6 3 km between them which is smaller than for global seismic catalogues we also investigate the consistency of source parameters and source directivity by comparing isc hypocentres with gcmt and icmt centroid locations for earthquakes with mw 6 5 in some cases the source directivity is qualitatively comparable with previous studies especially when comparing isc and icmt locations the average difference between insar determined depths and those in the ehb catalogue is reduced if a layered half space is used in the inversion of insar data overall faulting geometry strike dip and rake angles remain in good agreement with values from the gcmt catalogue and any large discrepancies can be attributed to tradeoffs between parameters with continued investment in satellites for radar interferometry insar is a valuable technique for the estimation of earthquake source parameters the observed trends and discrepancies between insar and seismically determined source parameters are the result of issues with the data different inversion techniques and the assumed earth structure model

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

an active deep marine strike slip basin along the north anatolian fault in turkey the tekirdag depression within the marmara sea in the mediterranean region is an active rhomb shaped strike slip basin along the north anatolian fault with a basin floor at a water depth of 1150 m new multichannel seismic reflection data and on land geological studies indicate that the basin is forming along a releasing bend of the strike slip fault and is filled with syntransform sediments of pliocene quaternary age the basin is bounded on one side by the north anatolian fault and on the other side by a subparallel normal fault which forms the steep submarine slope in cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2 5 km adjacent to the north anatolian fault seismic sections also show that the slope forming normal fault connects at depth to the north anatolian fault implying that the basin is completely detached from its substratum the whole structure can be envisaged as a huge rather flat negative flower structure the releasing bend of the north anatolian fault responsible for the formation of the basin is flanked by a constraining bend along the constraining bend the syntransform strata are being underthrust implying a recent change in the direction of the regional displacement vector this thrusting is responsible for the uplift of the submarine slope to a height of 924 m possibly by a mechanism of elastic rebound regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays the anomalous present depth of the tekirdag depression is due to reduced quaternary sedimentation coupled with high rates of displacement along the north anatolian fault which amounts to 20 mm yr in the marmara sea region

imaging the basin and fault geometry from the multichannel seismic reflection data in the tekirda g basin marmara sea turkey summary determination of the fault geometry in the marmara sea has been a major problem for the researchers after the occurrence of the 1999 august 17 golcuk m 7 4 earthquake to shed a light to the problem we applied the pre stack kirchhoff depth migration technique to the multichannel seismic reflection data of three profiles to investigate the basin and fault geometry in the tekirda g basin in the western marmara sea the boundary of the basin and its sediments were revealed in n s and ne sw directions in depth sections we identify major fault types involving these structures at different locations in tekirdag basin showing that the basin is developed under their movement the north anatolian fault is imaged and interpreted as transtensional character at the centre of the tekirda g basin that is symmetrically divided with a large distributed zone the fault plane is imaged through the depth of 2 km dipping to the north with 90 in the upper 350 m and 82 in the lower part the basin thickness reaches about 2 5 km at that point syn transform sediments of the basin are disturbed by some normal faults dipping to the north these faults are represented by notable displacements of the reflections which prompted us to consider them as a potential tsunami source if they move during a large earthquake along the major fault another major fault is identified at the westernmost of the basin because it shows the same character as ganos fault it might be submarine part of it it has reverse component with the dip angle of 65 to the north and trending along the western flank of the basin a reverse fault is identified appearing in low angle 20 surrounding the edge of the submarine slide at southwest of the basin from its geometry it is interpreted as a local fault formed between two main faults from the sketch of the basin and the fault geometry obtained from the images we suggest that the basin should be formed by a pull apart system

using surface waves recorded by a large mesh of three element arrays to detect and locate disparate seismic sources author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 942 958 doi 10 1093 gji ggy316

joint earthquake source inversions using seismo geodesy and 3 d earth models a joint earthquake source inversion technique is presented that uses insar and long period teleseismic data and for the first time takes 3 d earth structure into account when modelling seismic surface and body waves ten average source parameters moment latitude longitude depth strike dip rake length width and slip are estimated hence the technique is potentially useful for rapid source inversions of moderate magnitude earthquakes using multiple data sets unwrapped interferograms and long period seismic data are jointly inverted for the location fault geometry and seismic moment using a hybrid downhill powell monte carlo algorithm while the insar data are modelled assuming a rectangular dislocation in a homogeneous halfspace seismic data are modelled using the spectral element method for a 3 d earth model the effect of noise and lateral heterogeneity on the inversions is investigated by carrying out realistic synthetic tests for various earthquakes with different faulting mechanisms and magnitude mw 6 0 6 6 synthetic tests highlight the improvement in the constraint of fault geometry strike dip and rake and moment when insar and seismic data are combined tests comparing the effect of using a 1 d or 3 d earth model show that long period surface waves are more sensitive than long period body waves to the change in earth model incorrect source parameters particularly incorrect fault dip angles can compensate for systematic errors in the assumed earth structure leading to an acceptable data fit despite large discrepancies in source parameters three real earthquakes are also investigated eureka valley california 1993 may 17 mw 6 0 aiquile bolivia 1998 february 22 mw 6 6 and zarand iran 2005 may 22 mw 6 5 these events are located in different tectonic environments and show large discrepancies between insar and seismically determined source models despite the 40 50 km discrepancies in location between previous geodetic and seismic estimates for the eureka valley and aiquile earthquakes the seismic data are found to be compatible with the insar location a 30 difference in strike between insar and seismic derived source models is also resolved when taking 3 d earth structure into account in the analysis of the eureka valley earthquake the combination of both insar and seismic data further constrains the dip for the zarand earthquake and in all cases the seismic moment is more robustly constrained in the joint inversions than in the individual data set inversions unmodelled lateral heterogeneities in earth and the models could partly explain some of the observed source parameter discrepancies related to the seismic data the authors 2014 published by oxford university press on behalf of the royal astronomical society

lateral velocity variations in southern california i results for the upper crust from pg waves the plate boundary and major crustal blocks in southern california are imaged by a tomographic backprojection of the pg first arrivals recorded by the southern california array the method formulated specifically for local earthquake arrival times is a fast iterative alternative to direct least squares techniques with it we solve the combined problem of determining refractor velocity perturbations and source and station delays resolution and variance are found empirically by using synthetic examples a map showing lateral velocity variations at a depth of approximately 10 km is presented the results show a strong correlation with surface tectonic features clear velocity contrasts exist across the san andreas the san jacinto and the garlock faults the mojave region has the slowest velocities while the peninsula ranges have the highest the san jacinto block has velocities intermediate between mojave and peninsula range velocities and also has early station delays this may indicate that the san jacinto block has overridden mojave material on a shallow detachment surface no velocity variations are found associated with the transverse ranges which we interpret to mean that the surface batholithic rocks in this area do not extend to pg depths

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

tomographic estimates of sub moho seismic velocities in fennoscandia and structural implications abstract pn and sn velocity estimates are derived for the sub moho structure beneath fennoscandia using a tomographic conjugate gradient scheme observational data stem from local earthquake recordings of crustal phases pg sg lg and the sub crustal phases pn and sn by the fennoscandian seismograph network unknowns are pn and sn velocities and event hypocenter parameters crustal thicknesses are assumed as known and are not estimated whereas velocities are allowed to vary the most prominent p and s velocity anomalies are found in the northwest inland lofoten and southwest more of norway and for shear waves also in central finland there is a good correlation between the velocity anomalies in norway and observed negative bouguer anomalies indicating the presence of low density sub moho material in these areas geologically the pn and sn velocity anomalies appear to be associated with geodynamic processes tied to the opening of the norwegian greenland sea

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

an upper mantle s wave velocity model for northern europe from love and rayleigh group velocities summary a model of upper mantle s wave velocity and transverse anisotropy beneath northwestern europe is presented based on regional surface wave observations group velocities for both love and rayleigh surface waves are measured on waveform data from international and regional data archives including temporary deployments and then inverted for group velocity maps using a method accounting for fresnel zone sensitivity the group velocity variations are larger than in global reference maps and we are able to resolve unprecedented details we then apply a linear inversion scheme to invert for local 1 d shear wave velocity profiles which are consequently assembled to a 3 d model by choosing conservative regularization parameters in the 2 d inversion we ensure the smoothness of the group velocity maps and hence of the resulting 3 d shear wave speed model to account for the different tectonic regimes in the study region and investigate the sensitivity of the 1 d inversions to inaccuracies in crustal parameters we analyse inversions with different reference models of increasing complexity pure 1 d 3 d crust 1 d mantle and pure 3 d we find that all inverted models are very consistent at depths below 70 km at shallower depths the constraints put by the reference models primarily moho depth which we do not invert for remain the main cause for uncertainty in our inversion the final 3 d model shows large variations in s wave velocity of up to 12 per cent we image an intriguing low velocity anomaly in the depth range 70 150 km that extends from the iceland plume beneath the north atlantic and in a more than 400 km wide channel under southern scandinavia beneath southern norway the negative perturbations are around 10 per cent with respect to ak135 and a shallowing of the anomaly is indicated which could be related to the sustained uplift of southern scandinavia in neogene times furthermore our upper mantle model reveals good alignment to ancient plate boundaries and first order crustal fronts around the triple junction of the baltica avalonia laurentia collision in the north sea

seismic event detection and source location using single station three component data the seismic event detection and source location scheme presented in this paper uses single station seismic data to analyze seismic events to detect events the detection scheme combines the signals on the horizontal components in a manner analogous to beam steering once an event is detected the location scheme estimates the location of the source with respect to the receiver by estimating the polarization direction of the pn phase the range estimate is then obtained from the relative timing of different phases

application of the maximum likelihood method mlm for sonic velocity logging modern digital sonic tools can record full waveforms using an array of receivers the recorded waveforms are extremely complicated because wave components overlap in time conventional beamforming approaches such as semblance processing while robust sometimes do not resolve the interfering wave components propagating at similar speeds such as multiple compressional arrivals due to the formation alteration surrounding the borehole here the maximum likelihood method mlm a high resolution array processing algorithm is modified and applied to process borehole array sonic data extensive modifications of the original mlm algorithm were necessary because of the transient character of the sonic data and its effect upon the spectral covariance matrix we applied mlm to several array sonic data sets including laboratory data synthetic waveforms and field data taken by a schlumberger array sonic tool mlm s slowness resolution is demonstrated in resolving a secondary compressional arrival from the prima

earthquake magnitude relationships for the saint peter and saint paul archipelago equatorial atlantic we have investigated several relationships between ml m neic and mw for the earthquakes locally recorded in the saint peter and saint paul archipelago spspa equatorial atlantic because we only have one station in the area we could not derive attenuation relations for events recorded at different distances at different stations our approach was then to compare our ml estimates with magnitudes reported by neic this approach produced acceptable results particularly for epicentral distance smaller than 100 km for distances greater that 100 km there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate q we also investigate the mw m neic relationship we find that mw estimates using s wave produce smaller residuals when compared with both m neic finally we also investigate the ml mw relationship and observe that given the data set we have the 1 1 holds we believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region

regional seismic event location with a sparse network application to eastern kazakhstan ussr three component data from a sparse three station seismic network in eastern kazakhstan surrounding the soviet nuclear test site have been analyzed to determine location estimates for regional events recorded by two or three stations included among these events are the september 1987 chemical explosions whose locations are known locations are calculated using arrival times of p and s phases and arrival azimuths from first p location uncertainties are estimated using a combination of a priori and a posteriori data uncertainties a layered p wave velocity model adapted from soviet deep seismic sounding surveys is employed for calculating travel times and two s models are tried location results for the chemical explosions are excellent even if only two stations are used absolute location errors are less than 10 km and estimated 90 confidence uncertainties are only a few kilometers the data are also adequate to determine correctly their depth i e focus at the surface the other regional events include numerous suspected mine blasts and two earthquakes from the tien shan the calculated locations of the latter events agree well with a teleseismic location for one of them falling within a belt of regular seismic activity nearly all of the presumed blasts can be associated with mapped mines and we have been able to identify the source areas for two sets of blasts in high resolution satellite images before and after photographs allow us to identify specific active mines our location estimates agree quite well with the observed active mines

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

global compilation of interferometric synthetic aperture radar earthquake source models 1 comparisons with seismic catalogs 1 while many earthquakes have now been studied using interferometric synthetic aperture radar insar data a full assessment of the quality and additional value of insar source parameters compared to seismological techniques is still lacking we compile a catalog of source models obtained using insar and estimate the corresponding centroid moment tensor cmt parameters we refer to this compilation as the icmt archive we compare source parameters from over 70 insar studies of 57 global earthquakes with those in the global cmt gcmt international seismological centre isc and engdahl hilst buland ehb seismic catalogs we find an overall good agreement between fault strike dip and rake values in the gcmt and icmt archives likewise the differences in seismic moment between these two archives are relatively small and we do not find support for previously suggested trends of insar leading to larger moments than seismic data however epicentral locations show substantial discrepancies which are larger for the gcmt median differences of 21 km than for the ehb and isc catalogs median differences of 10 km since insar data have a high spatial resolution and thus should map epicentral locations accurately this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs earthquake depths from insar are systematically shallower than those in the ehb catalog with a median of differences of 5 km while this trend may be partly due to unmodeled crustal complexity it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer

global event location with full and sparse data sets using three dimensional models of mantle p wave velocity in order to improve on the accuracy of event locations at teleseismic distances it is necessary to adequately correct for lateral variations in structure along the ray paths either through deterministic model based corrections empirical path station corrections or a combination of both approaches in this paper we investigate the ability of current three dimensional models of mantle p wave velocity to accurately locate teleseismic events we test four recently published models two are parameterized in terms of relatively long wavelength spherical harmonic functions up to degree 12 and two are parameterized in terms of blocks of constant velocity which have a dimension of a few hundreds of km these models together with detailed crustal corrections are used to locate a set of 112 global test events consisting of both earthquakes and explosions with p wave travel time data compiled by the international seismological centre isc the results indicate that the supposedly higher resolution block models do not improve the accuracy of teleseismic event locations over the longer wavelength spherical harmonic models for some source locations the block models do not predict the range of observed travel time residuals as well as the longer wavelength models the accuracy of the locations largely varies randomly with geographic position although events in central asia are particularly well located we also tested the effect of reduced data sets on the locations multiple location iterations using 30 p wave travel times indicate that teleseismic events may be located within an area of 1000 km of the true location 66 of the time with only the model based corrections and increasing to 75 if calibration information is available if as few as 8 phases are available then this is possible only 50 of the time further refinement in models and or procedure such as the addition ofp phases azimuth data and consideration of p wave anisotropy may provide further improvement in the teleseismic location of small events

on upper mantle seismic heterogeneities beneath fennoscandia abstract three dimensional seismic mapping of the upper mantle beneath fennoscandia baltic shield using an ach type of inversion technique in combination with p wave travel time residual observations from the local seismograph network gave the following results the central parts of the baltic shield are characterized by relatively high seismic velocities down to approximately 300 km those parts of the shield most affected by the caledonide orogeny exhibit relatively low velocities particularly in the uppermost 100 km depth interval the lower part of the upper mantle 300 600 km does not exhibit pronounced seismic velocity anomalies and in this respect is in contrast to results from similar studies in regions subjected to neotectonic processes like parts of central and southeastern europe the seismic anomaly pattern in the presumed thickened lithosphere is in quantitative agreement with similar ones derived from surface wave dispersion analysis and inversion of electrical measurements the general orientation of these anomalies coincides with that of the glacial uplift

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

the deep structure of the scandes and its relation to tectonic history and present day topography abstract we review the results of the toposcandiadeep project a component of the topoeurope project in which we have studied the crustal and upper mantle structures of southern norway in relation to its high topography the scandinavian mountain chain the scandes is an intracontinental mountain chain at the western edge of the baltic shield and has its southern part located in southern norway the timing as well as the processes causing the formation of the scandes are disputed we bring new geophysical constraints to this issue by providing crustal and mantle seismic models for the area and by integrated modeling of the lithosphere and its potential deformation new maps of moho depth and crustal seismic velocities have been compiled using data from refraction lines p receiver functions and noise cross correlation these results show a thickening of the crust from southwest to northeast and a small crustal root not directly located below the topographic high p s and surface wave tomography infer seismic mantle velocities lower than in normal shield structure with a possible sharp boundary close to the oslo graben these low velocities are imaged in the lithosphere and in the underlying mantle down to the 410 km discontinuity integrated modeling of seismic models and gravity data shows that the low velocities below southern norway are compatible with a change in lithosphere thickness from c 100 km under southern norway to nearly 200 km under southern sweden with possible additional differences in composition the study also indicates that the topography can be isostatically sustained by the density distribution in the crust and lithospheric mantle we argue that the lithospheric lateral variation has been present for at least 300 my and has had a significant influence on the localization of the topography independently of the mechanism for uplift

the moho depth distribution in fennoscandia and the regional tectonic evolution from archean to permian times abstract from a variety of seismic refraction and reflection profiling results a new detailed moho depth map for the fennoscandian part of the baltic shield has been compiled a complementary crystalline crustal thickness map was compiled for denmark the skagerrak sea offshore western norway and adjacent areas where sedimentary strata reach maximum thicknesses of 10 km and even more these maps are discussed in relation to tectonic evolution and crustal ages of fennoscandia seismic velocities bouguer gravity and seismicity areas deviating from the proposed age thickness relationships are the kola peninsula archean and the oslo rift permian the average crustal thickness in the former area is around 44 km while the latter area is associated with a moho elevation of 3 5 km maximum crustal thicknesses in excess of 50 km have been found in southwestern and central finland and correlate with a crust of proterozoic age the caledonides of western norway do not exhibit as elsewhere a crustal root sub moho p n and s n seismic velocities are relatively small in that area and bouguer gravity values are strongly negative intracrustal p velocity variations do not seem to reflect geological age or specific tectonic features although the seismicity is moderate in fennoscandia most of the earthquake activity and in particular the largest earthquakes are confined to areas where the crustal thinning is most pronounced

meso cenozoic morphotectonic evolution of southern norway neogene domal uplift inferred from apatite fission track thermochronology apatite fission track aft thermochronology of precambrian and paleozoic basement samples from southern norway reveals a post paleozoic exhumation history related to offshore mesozoic and cenozoic extensional basin development the data indicate two major phases of rapid exhumation a first mesozoic phase started in the triassic 220 ma in the east and south of the study area and migrated to the west where jurassic 160 ma ages of exhumation predominate a second event is indicated by thermal history modeling of aft ages and track length distributions it is inferred to be neogene in age initiated at about 30 ma and it produced a domal pattern of aft isochrons which follow present day topographic elevation youngest aft ages 100 ma are encountered at sealevel in the inner fjords near the areas of highest topography ages increase radially outward to the mountain peaks and the coastlines forward modeling of age elevation patterns suggests that mesozoic geothermal gradients were 10 15 c km higher than the present value of 20 c km during the triassic and jurassic a total of 1 3 3 5 km of overburden was removed from the study area assuming a 30 c km geothermal gradient for that period we attribute this to rift margin erosion as a result of erosional base level lowering and flank uplift as evidenced by thick continental clastic sequences deposited in triassic jurassic half grabens in the north sea basins we propose that 1 5 2 5 km of neogene exhumation were a result of late stage domal uplift this is supported by basinward dipping pre neogene strata in the basins surrounding southern norway and the infill of a 1 to 2 km thick neogene sediment wedge containing various internal unconformities domal uplift probably started in the late oligocene may have been amplified in the pliocene and was overprinted by plio pleistocene glacial erosion maximum neogene tectonic uplift is estimated at approximately 1 1 5 km radially decreasing outward to a value 500 m near the shoreline neogene domal uplift is coincident with oligocene and pliocene plate reorganizations in the north atlantic similar neogene domes are found around the norwegian greenland sea i e svalbard and the barents sea northern norway east greenland suggesting a regional tectonic cause the onset of neogene uplift postdates major volcanism and continental breakup by 25 m y and predates plio pleistocene glaciations its origin is possibly a combination of induced mantle convection resulting in thermal erosion of the lithosphere and the operation of intraplate stresses

the northern and southern scandes structural differences revealed by an analysis of gravity anomalies the geoid and regional isostasy abstract we investigate the scandes mountain range by analysing the gravity field the geoid heights and the degree of isostatic compensation of the lithosphere topographically the scandes mountain range can be divided in the northern and southern scandes comparisons between the present topographic expression and the gravity field and the geoid show that the axis of highest elevation in the northern scandes is shifted eastwards compared to the minimum of the bouguer anomaly while the two coincide perfectly in the southern scandes geoid heights reduced by the effect of topographic masses show a large scale minimum in the northern scandes but no anomaly in the southern scandes regional flexural isostatic calculations yield a flexural rigidity of d 1023 nm for the lithosphere of the southern scandes and the isostatic gravity and geoid residuals point to additional isostatic support by low density rocks below the moho on the other side for the lithosphere in the northern scandes no significant flexural rigidity can be resolved here the bouguer anomaly is best modelled with a small flexural rigidity indicating nearly airy isostatic behaviour local subsurface loading and horizontal tectonic forces overprint the isostatic compensations and increase the tectonic complexity of the northern scandes these distinctive features of the scandes cannot be explained by currently existing models of the present and neogene uplift and the isostatic mechanism of the scandes

a new class of equilibrium geotherms in the deep thermal lithosphere of continents abstract equilibrium lithospheric geotherms are generally assumed to have a self similar shape with a nearly linear thermal gradient in the upper portions of the thermal lithosphere and a smoothly decreasing gradient in its lowermost portions large thermal gradient increases are thought to be unsustainable because they would seem to imply a local heat flux imbalance that would be smoothed away over time simulations of mantle convection allowing for continents lead us to suggest that this may not be the case and that kinked geotherms may exist in thermal equilibrium within specific continental regions this new class of geotherms arises from the coexistence of two heat loss modes within the continental lithosphere oceanic heat loss is dominated by convection i e plate creation and subduction continental heat transfer on the other hand is of a conjugate nature with conduction dominating in stable chemically buoyant portions of continental lithosphere and convection operating in its weaker lower portions at the ocean continent boundary horizontal heat transfer occurs within a zone of accommodation where oceanic and continental heat loss are reconciled if continents are underlain by mantle downwellings then this horizontal heat transfer can involve a convective pattern that allows weak lower portions of the thermal lithosphere to flow differentially below a passive continental margin horizontal advection can thus be low in the near surface regions of the margin leading to mild thermal gradients but can outweigh vertical conduction at depth leading to steep gradients this allows inflected i e kinked geotherms to be generated downstream of the margin the thermal structure of the lower lithosphere adjusts to that of the continental interior and inflections decay however within a finite downstream region inflected geotherms can be maintained indefinitely by continued sub continental flow a similar situation can occur when weak lower portions of the continental thermal lithosphere flow from thinner to thicker regions of chemically stabilized upper lithosphere

late mesozoic to early cenozoic components of vertical separation across the more trondelag fault complex norway abstract low temperature apatite fission track aft data from two horizontal transects across the more trondelag fault complex mtfc and along the coast of the fosen peninsula have defined a complicated series of structural blocks whose exhumation to temperatures cooler than the uppermost apatite partial annealing zone paz occurred during a broad mesozoic to cenozoic time span the 100 million year cooling difference between the innermost and outermost blocks indicates they were subjected to very different exhumation pathways track length histograms and inverse model results also suggest that significant differences in thermal histories are present over very short horizontal distances in conjunction with the offshore geological evidence the aft data and models strongly suggest that the innermost zones of the mtfc underwent between 2 and 4 km of structurally controlled net vertical rock column uplift subsidence following latest cretaceous time and potentially much of the tertiary as well the up to the east down to the west relative offset at the norwegian margin is interpreted in terms of a flexed nearly broken lithospheric plate architectural model for late mesozoic and tertiary scandes mountain building whose driving force was likely dominanted by erosionally induced loading unloading at the margin

uppermost mantle pn velocity model for the afar region ethiopia an insight into rifting processes the afar depression ethiopia offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland using traveltime tomography and data from a temporary seismic deployment we describe the first regional study of uppermost mantle p wave velocities vpn we find two separate low vpn zones as low as 7 2 km s 1 beneath regions of localized thinned crust in northern afar indicating the existence of high temperatures and potentially partial melt the zones are beneath and off axis from contemporary crustal magma intrusions in active magmatic segments the dabbahu manda hararo and erta ale segments this suggests that these intrusions can be fed by off axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting thought to characterize segmentation of the uppermost mantle at seafloor spreading centres are initiated during the final stages of break up

improving teleseismic event locations using a three dimensional earth model abstract a comparison is made between seismic event locations derived from standard spherically symmetric earth models jb prem iasp91 and a recent earth model sp and a published data set of 82 well located earthquakes with a more even global distribution iasp91 and prem are shown to offer similar errors in event location and origin time estimates with respect to the jb model the three dimensional 3d model sp for the earthquakes the improvements are smaller corrections for crustal thickness beneath source and receiver are found to be of similar magnitude to the mantle corrections but use of station corrections together with the three dimensional mantle model provide the best locations

western turkey poses exploration challenges on offshore the geologic province known as the aegean region covers the western part of the anatolia district of turkey hydrocarbon exploration in this area focuses on offshore and onshore grabens it is thought that the geologic evolution of the area was primarily due to the extentional tectonic regime which has been the dominant factor since the negogene

upper mantle heterogeneities beneath central europe summary an inversion of isc travel time data from selected earthquakes in the distance range 30 90 to 53 stations in central europe has been used to model velocity down to 600 km depth the model explains 0 1 0 2s of the residuals as for other array studies leaving 0 5 s unexplained as noise the uppermost 100 km of the mantle and crust contains inhomogeneities that correlate remarkably well with the geology this may be due to deep seated thermal anomalies or in some areas to delays introduced by passage of the rays through sedimentary cover the deeper anomalies are smaller and unrelated to those in the lithosphere which suggests that the asthenosphere is decoupled from the rigid lithosphere the structure at 600 km depth is again quite inhomogeneous and might be due to undulations of the 650 km discontinuity the models show some suggestion of a high velocity slab trending from east to west beneath the alps

integrated geophysical modelling of a lateral transition zone in the lithospheric mantle under norway and sweden summary the scandinavian mountain chain the scandes exhibits characteristics that are unusual for an old palaeozoic mountain belt these include renewed neogene uplift in a passive margin setting and the lack of a pronounced crustal root we investigate the influence of present day thermal compositional and geometric structures in the crust and mantle on the topography of the southern scandes and the resulting implications for the tectonic history of fennoscandia a self consistent 3 d subsurface model of southern norway and sweden is constructed from recent geophysical data sets that constrain the crustal architecture lithosphere geometry density distributions and thermal properties recent seismological studies show evidence for a relatively abrupt transition from seismically slower lithospheric mantle underneath southern norway to seismically faster lithospheric mantle underneath southern sweden we find that a transition from thin subcontinental lithospheric mantle sclm underneath southern norway to a significantly thicker sclm beneath southern sweden can explain this velocitytrend adifferenceincompositionbetweenthetwosclmdomains owingtodifferent depletion refertilization is required to satisfy the gravity field and isostatically compensated topography but contributes only slightly to the observed velocity contrast such a lateral transition zone constituting a major change in the lithospheric structure in southwestern fennoscandia can be related to several major proterozoic and phanerozoic tectonic events such as the sveconorwegian orogeny the permian oslo rift and perhaps even the opening of the atlantic

three component analysis of regional seismograms abstract both phased array techniques for single component sensors and vectorial analysis of three component recordings can provide estimates of the azimuth and slowness of seismic phases however a combination of these approaches provides a more powerful tool to estimate the propagation characteristics of different seismic phases at regional distances conventional approaches to the analysis of three component seismic records endeavor to exploit the apparent angles of propagation in horizontal and vertical planes as well as the polarization of the waves the basic assumption is that for a given time window there is a dominant wavetype e g a p wave traveling in a particular direction arriving at the seismic station by testing a range of characteristics of the three component records a set of rules can be established for classifying much of the seismogram in terms of wavetype and direction it is however difficult to recognize sh waves in the presence of other wavetypes problems also arise when more than one signal in either wavetype or direction arrive in the same window the stability and robustness of the classification scheme is much improved when records from an array of three component sensors are combined for a set of three component instruments forming part of a larger array it is possible to estimate the slowness and azimuth of arrivals from the main array and then extract the relative proportions of the current p sv and sh wave contributions to the seismogram this form of wavetype decomposition depends on a model of near surface propagation a convenient choice for hard rock sites is to include just the effect of the free surface which generates a frequency independent operation on the three component seismograms and which is not very sensitive to surface velocities this approach generates good estimates of the character of the s wavefield because the phase distortion of sv induced by the free surface can be removed the method has been successfully applied to regional seismograms recorded at the medium aperture warramunga array in northern australia and the two small arrays noress and arcess in norway which were designed for studies of regional phases the new wavefield decomposition scheme provides results in which the relative proportions of p sv and sh waves as a function of time can be compared without the distortion imposed by free surface amplification such information can provide a useful adjunct to existing measures of signal character used in source discrimination

the nature of particle motion in regional seismograms and its utilization for phase identification summary the particle motion of regional arrivals is frequently treated in automatic phaserecognition schemes as that appropriate to simple p or s waves incident on an elastic laterally homogeneous half space this model implies that the motion in p type phases can be described in terms of a single generalized signal process and s type phases in terms of two independent processes sv and sh and thus all regional arrivals could be fully characterized by three components of motion in this paper we present anlyses of the particle motion patterns of various regional arrivals recorded at the arcess array from closely spaced events in the kola peninsula we have found that only pn particle motion described in terms of two independent signal processes can be reliably characterized by three component recordings on the other hand the various regional arrivals following pn such as pg sn and lg can only be poorly characterized on the basis of three component recordings alone the reason is that these arrivals must be described in terms of more than two independent generalized signal processes at least three for pg and sn and possibly up to five for lg recognition of these phases will thus require the use of more sensors than signal processes in the observing sensor configuration such as three component sensors combined with a small tripartite array we have investigated the feasibility of adaptive automatic recognition of regional arrivials by a wavefield extrapolation scheme utilizing such a mini array the process which appear to be promising adaptively learns the particle motion patterns of individual arrivals including complex site response functions from examples of closely located regional events

a three dimensional integrated density and thermal model of the fennoscandian lithosphere abstract a three dimensional geophysical model of the crust and upper mantle for fennoscandia and adjacent regions is presented seismic results gravity field and heat flow data were used for the construction of the model the layers which were allocated from seismic data and distribution of p wave velocities in these layers served as a basis of the initial seismic model empirical equations of interrelation between velocity heat generation and density were used for transforming the seismic model to thermal and density models the influence of pressure and temperature on physical properties was investigated and taken into account statistical parameters of the interrelation between velocity heat generation and density were used when solving the inverse problems for geothermal and gravity data a brief description of the mathematical principles of integrated interpretation is also given as a result 3 d models of distribution of heat generation temperature and density in the crust and upper mantle were obtained these data are represented in horizontal and vertical cross sections outlining physical parameters for various depth levels finally regional geological data are correlated with the obtained density variations in the crust

event location at any distance using seismic data from a single three component station this paper demonstrates the usefulness of a novel technique for analysis of single site three component seismogram records for reliable epicenter determinations for even small seismic events at any distance parameters that may be extracted by this technique are p phase identifications in terms of x 2 probabilities and the associated slowness vectors using data from short period and broadband seismometers installed in the new noress norway array single site event locations are demonstrated azimuth estimates are found directly from the slowness vector while epicenter distance estimates are derived from differential arrival times between pn pg sn and lg sg simultaneous inversion for crustal model and hypocenter data indicate a crustal thickness beneath noress of 33 5 km if sn and or lg are well recorded focal depth estimates are often accurate to within a few kilometers locating teleseisms is problematic since secondary phases are not fully readily identifiable and hence distance can be estimated only by conversion of the measured apparent phase velocity for distances out to approximately 1000 km event location errors as compared to network solutions seldom exceed 50 km and are due mainly to errors in azimuth estimates with sn phases available focal depth errors appear to be of the order of 4 km for teleseismic p waves short period location errors occasionally exceeded 7 and were due mainly to poor distance estimates using broadband records from relatively strong events location errors were about 1 further refinements seem feasible by using seismicity information and or recognition of stationarity in the p wave decomposition pattern for events within the same region at least in certain cases such approaches reflect genuine location refinements as demonstrated

systematic variation in the depths of slabs beneath arc volcanoes summary the depths to the tops of the zones of intermediate depth seismicity beneath arc volcanoes are determined using the hypocentral locations of engdahl et al these depths are constant to within a few kilometres within individual arc segments but differ by tens of kilometres from one arc segment to another the range in depths is from 65 km to 130 km inconsistent with the common belief that the volcanoes directly overlie the places where the slabs reach a critical depth that is roughly constant for all arcs the depth to the top of the intermediate depth seismicity beneath volcanoes correlates neither with age of the descending ocean floor nor with the thermal parameter of the slab this depth does however exhibit an inverse correlation with the descent speed of the subducting plate which is the controlling factor both for the thermal structure of the wedge of mantle above the slab and for the temperature at the top of the slab we interpret this result as indicating that the location of arc volcanoes is controlled by a process that depends critically upon the temperature at the top of the slab or in the wedge of mantle immediately below the volcanic arc

upper mantle structure in southern norway from beamforming of rayleigh wave data presenting multipathing summary a model for the upper mantle sv wave velocity under southern norway is obtained by depth inversion of the average phase velocity of the rayleigh wave fundamental mode in the area the average dispersion curve is obtained in the period range 22 200 s by beamforming of 190 rayleigh waves recorded by the magnus network a temporary regional network of 41 broad band stations resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the lucy richardson algorithm in addition to an average phase velocity beamforming gives us some information concerning the nature of the incoming wavefield we detect deviations of the wave propagation direction from the great circle paths which commonly reach 10 at a period of 25 s for the teleseismic events the amplitude of the deviations decreases with increasing period and with decreasing epicentral distance as expected the phase velocity measured by beamforming does not show any correlation with the deviation from great circle path suggesting that deviation does not bias phase velocity measurements we detect also significant multipathing with characteristics that vary rapidly with frequency the obtained sv wave velocity profile clearly shows that southern norway is underlain by a low velocity zone in the upper mantle and does not have shield like characteristics despite its location in the baltic shield these findings support the hypothesis that the high topography of southern norway is sustained by anomalous upper mantle material

an introduction to the european geotraverse project first results and present plans abstract the european geotraverse egt is an international multidisciplinary project focused on a north south orientated lithospheric profile 4000 km long and of varying width extending from northernmost scandinavia to north africa this profile consists of three interlinking segments northern central and southern comprising a continuous succession of tectonic provinces ranging from the oldest precambrian areas of the baltic shield to the currently active area of the western mediterranean the broad aim of the egt project is to obtain a better three dimensional picture of the structure state and composition of the continental lithosphere to use as a basis for an understanding of its evolution and dynamics all of the 12 major projects that constitute the egt joint programme have now been initiated and several of these projects are nearing completion along the northern segment data from the fennoscandian long range project fennolora a 2000 km long seismic profile across the precambrian baltic shield show that except beneath southern sweden the shield is characterized by a high velocity 40 50 km thick crust including a 5 10 km thick crust mantle transition zone an alternating series of 4 6 high and low velocity zones is present in the subcrustal lithosphere the base of which increases in depth from ca 110 km to ca 230 km from south to north beneath the shield the top of the mantle transition zone lies at a depth of about 450 km the second major project along this segment the eugeno s european geotraverse northern segment southern part project is a multidisciplinary study of the fennoscandian border zone and was largely completed in 1984 with the realization of a large scale seismic experiment preliminary interpretation of the excellent data obtained indicate the presence of strong lateral variations in internal crustal structure beneath the danish basin field work for a third major project a multidisciplinary transect of the archaean and early proterozoic terrains in the northernmost part of the shield the polar profile was carried out in 1985 a series of deep seismic reflection lines has so far been realized in the area of the central segment in the context of german national programmes first interpretations of the seismic data from a 260 km long profile across the two main intra variscan hercynian lineaments have shown the presence of numerous horizons making up a highly reflective zone in the lowermost 10 km of the crustal section studied and distinct changes in reflectivity between the main variscan tectonic zones in 1986 the entire segment will be investigated in detail in an ambitious international programme of integrated geological and geophysical studies a series of seismic experiments termed egt s have been carried out across the southern segment in 1982 1983 and 1985 interpretation of data from the 1982 and 1983 experiments have led to several interesting results including 1 1 the suggestion that two crust mantle like interfaces exist beneath the po basin at depths of about 35 and 50 km and adjacent tectonic units these interfaces marking a deep contact zone between the adriatic and european plates 2 2 in the area between genoa and corsica the ligurian sea is underlain by a greatly thinned distinctly layered section of continental crust and 3 3 corsica and sardinia are underlain by bowl shaped typically variscan continental crusts the 1985 phase of seismic surveys focused on crustal structure beneath tunisia and the adjacent seas in addition two off traverse projects are being realized first a wide aperture network of autonomously recording seismic stations nars installed along the line gothenburg malaga between 1982 and 1984 is already yielding high quality data on the upper 600 700 km of the mantle second an investigation of lithospheric seismic anisotropy in the area of the iberian peninsula is being organized for 1987 1988 finally of great importance are the systematic compilation of existing data and where needed in critical regions collection of new geophysical and geological data presently being carried out for the entire area encompassed by the egt it is expected that these compilations will be completed by 1987 at about the same time that full results from the main large scale seismic experiments become available enabling the construction of an integrated lithospheric cross section along the egt requiring a final phase of intensive multidisciplinary collaboration

precambrian plate tectonics in northern hudson bay evidence from p and s wave seismic tomography and analysis of source side effects in relative arrival time data sets the geology of northern hudson bay canada documents more than 2 billion years of history including the assembly of precambrian and archean terranes during several paleoproterozoic orogenies culminating in the trans hudson orogen tho 1 8 ga the tho has been hypothesized to be similar in scale and nature to the ongoing himalaya karakoram tibetan orogen but the nature of lithospheric terrane boundaries including potential plate scale underthrusting is poorly understood to address this problem we present new p and s wave tomographic models of the mantle seismic structure using data from recent seismograph networks stretching from northern ontario to nunavut 60 100 w and 50 80 n the large size of our network requires careful mitigation of the influence of source side structure that contaminates our relative arrival time residuals our tomographic models reveal a complicated internal structure in the archean churchill plate however no seismic wave speed distinction is observed across the snowbird tectonic zone which bisects the churchill the mantle lithosphere in the central region of hudson bay is distinct from the tho indicating potential boundaries of microcontinents and lithospheric blocks between the principal colliders slow wave speeds underlie southern baffin island the leading edge of the generally high wave speed churchill plate this is interpreted to be paleoproterozoic material underthrust beneath baffin island in a modern style subduction zone setting

subduction zone calibration and teleseismic relocation of thrust zone events in the central aleutian islands abstract teleseismically determined epicenters for thrust zone earthquakes in the central aleutian islands are systematically mislocated by about 40 km to the north relative to local network solutions we attribute the mislocation to travel time anomalies produced by the higher p wave velocity in the subducting slab these travel time anomalies can be estimated by seismic ray tracing through a thermally modeled velocity structure for the slab observed teleseismic station residuals and slab travel time anomalies computed from local network hypocenters plotted as a function of event distance to the center of curvature of the island arc show good agreement this distance versus residual relationship can be used to validate the local network hypocenters and to constrain the length of subducting lithosphere computed slab source corrections when incorporated in a standard location program reduce teleseismic mislocations to 20 km the addition of empirical station corrections reduces the mislocation to about 10 to 15 km depth and origin time estimates can be further improved through use of better station corrections a local station within 2 and depth phases

hydrocarbon occurrences in the western anatolian aegean grabens turkey is there a working petroleum system western anatolian graben basins are filled with continental sediments and minor carbonates deposited in lacustrine alluvial and fluvial environments individual grabens are composite basins and comprise multiple depocenters or subbasins with sediment thickness rarely exceeding 3000 m 9843 ft a number of hydrocarbon occurrences are reported from the basins regional geologic framework justifies these occurrences by providing a generous heat budget good quality source rock fair reservoir seal sequences and suitable traps although no economically producible reserves have been discovered to date the rich source rock with an average total organic carbon of 2 34 and hydrogen index up to 800 mg g is oil and gas generative at maturation however the composite nature of the grabens controlled the stratigraphic variability and led to sporadic distribution of the lacustrine deposits hosting the source rock facies in the basins the depth of burial is generally insufficient 2000 m 6562 ft for the source rock to effectively generate and expel hydrocarbons this limitation was locally overcome by additional heat input into the system through deep reaching faults volcanism and or after volcanic hydrothermal circulation thermal maturity of organic matter effectively increases in the vicinity of the major border structures volcanic rocks and zones of polymetallic mineralization yet this effect is typically constrained within a narrow zone adjacent to heat source and diminishes within short distances thus the hydrocarbon system remains regionally inefficient exploration success in the region depends on the discovery of deeper neogene depocenters that could provide sufficient source rock burial depths

upper mantle shear velocity beneath eastern australia from inversion of waveforms from skippy portable arrays in 1993 the research school of earth sciences of the australian national university commenced a nationwide seismometry project skippy for a comprehensive study of the upper mantle beneath the australian continent we applied a waveform inversion technique to broad band data recorded while the skippy portable arrays were positioned in eastern australia in order to construct a 3 d model of shear velocity in the upper mantle and transition zone beneath eastern australia and the adjacent oceanic regions the skippy data were augmented by data from the permanent seismological observatories in the region the first step of the waveform inversion used involved the matching of the waveforms of fundamental and higher mode rayleigh waves with waveforms synthesized from radially stratified models in the second stage the linear constraints on radial variations in shear velocity were combined in a tomographic inversion for aspherical variations in shear velocity the preferred model reduces the data variance by 90 per cent owing to the dense data coverage structural features with dimensions larger than 250 km laterally and 50 km vertically are resolved the major structural features inferred from the tomographic images are 1 a substantial increase in the thickness of the high velocity lid from the oceanic region to the phanerozoic continental and proterozoic continental regions 2 a pronounced low velocity zone centred at 140 km depth beneath the part of eastern australia often referred to as the tasman fold belt which confirms previous inferences from rayleigh wave dispersion curves 3 a prominent zone of low wave speeds beneath the eastern margin of the continent that coincides with locations of cenozoic volcanism and regions of enhanced heat flow 4 deep low wave speed anomalies beneath both the coral and tasman seas and 5 localized high wave speed perturbations in the mantle transition zone 410 660 km depth beneath eastern australia in particular beneath the new england fold belt and the mount isa block from the images we infer that the eastern boundary of the precambrian shields does not coincide with a sharp seismic contrast unless this boundary is located further to the east than is commonly assumed the structure of the upper mantle and transition zone beneath eastern australia as inferred from the images is more complex than that beneath the precambrian cratons of central and western australia which could be due to subduction beneath the eastern continental margin prior to opening of the tasman sea if correct this interpretation would imply that part of the upper mantle has moved along laterally with the lithosphere during the relatively fast northward motion of the plane

basement types of the thrace basin and a new approach to the pre eocene tectonic evolution of the northeastern aegean and northwestern anatolia a review of data and concepts in northwestern turkey the pre eocene basement of the thrace basin consists of the strandja rhodope metamorphics in the north northwest the istanbul zonguldak paleozoic sequence in the northeast a tectonic mixture of the fragments from the sakarya continent and pre upper cretaceous ophiolites in the southeast and the uppermost cretaceous paleocene transgressive sediments the ophiolites belong to a dogger early cretaceous oceanic basin the northeastern vardar ocean between the rhodope and sakarya continents the ne trending oceanic branch closed diachronously during the early late malm to the northeast but during latest early cretaceous to late cretaceous time toward the main vardar ocean in the southwest during the final closure the suture zone acted as a strike slip fault zone the latest cretaceous paleocene transpressional to transtensional activities caused the juxtaposition of different basement types and the development of a tectonic mixed zone the biga armutlu ovacik zone between the rhodope and sakarya continents under the regional n s compression on the plate overlying the north northeastward dipping vardar subduction zone the southwestward escape of an area of crust bounding by the wnw trending balkan thrace dextral fault zone to the north and the ne trending biga armutlu ovacik sinistral zone to the southeast caused a triangular shaped and isolated depression area for the deposition of the uppermost cretaceous paleocene transgressive sediments in a transtensional setting the tectonically bounded depression area constitutes also a necessary accommodation space for the deposition of the initial deposits of early eocene age in the thrace basin

asymmetric lithosphere as the cause of rifting and magmatism in the permo carboniferous oslo graben compared to other permo carboniferous rift basins of nw europe the oslo graben has two distinct characteristics first it initiated inside cold and stable precambrian lithosphere whereas most permo carboniferous basins developed in weaker phanerozoic lithosphere and second it is characterized by large volumes of magmatic rocks despite relatively little extension seismic reflection surveys show that the crust thickens from southern norway to southern sweden the most significant moho deepening occurring from the oslo region eastwards deep seismic studies also suggest that the base of the lithosphere deepens markedly eastwards from the oslo region such a long wavelength lithospberic geometry cannot be explained by the permian or post permian evolution of the area hence the oslo graben appears to have evolved at the transition between two lithospheric domains with contrasting thickness numerical thermo mechanical modelling is applied to test if this transitional position can influence the dynamics of rifting different models with varying lithosphere thickness contrast are considered model results show that a crust and lithosphere thickness contrast comparable to the oslo region can explain rifting and focusing of magmatism in a narrow zone with minor thinning of the crust models also account for the major characteristics of the oslo graben in terms of location and strain distributions in the crust the geological society of london 2004

seismicity in subduction zones from local and regional network observations the data provided by local and regional seismograph networks are essential for the solution of many problems of subduction zone seismology the capabilities of such networks are limited by the instrumentation currently in common use and the unfavorable source station geometry often imposed by the regional geography nevertheless important contributions have come from the data gathered in many of the earth s subduction zones the accuracy of hypocenter locations based on regional data is affected by the complex velocity structures characteristic of subduction zones but the problems are now well understood examples of numerous studies of the spatial configurations of the seismicity in subduction zones and consequent interpretations of seismogenesis and subduction processes are reviewed studies of the distributions of earthquakes in time and with magnitude for events down to the microearthquake level have the potential for clarifying the earthquake generating processes and possibly a basis for earthquake prediction other uses of local and regional network data have been for investigations of coda s and the identification of asperities in subduction zones

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

hypocenter constraint with regional seismic data a theoretical analysis for the natural resources defense council network in kazakhstan ussr source depth and epicenter determination remains a simple but key method for discrimination between earthquakes and nuclear explosions at near regional distances a variety of secondary body wave arrivals can be observed that may be useful for constraining source depth and epicenter in this paper we study the source location problem using regional arrival time and arrival azimuth data from a sparse seismic network a theoretical analysis of the source location inverse problem provides estimates of the stability and uncertainty of the solution for a particular suite of data as a function of epicenter and depth as well as evaluating the importance of each datum to the solution an empirical analysis with actual data complements the theoretical analysis our approach is applied to the three station natural resources defense council soviet academy of sciences network in kazakhstan the theoretical analysis indicates that reasonable constraint on depth and epicenter is possible whenever three distinct phases p pn pg pzp and pmp or equivalent s phases are observed at two or three stations our theoretical analysis for two station locations shows that the epicenter constraints are extremely poor for sources along the line passing through the two observing stations the use of arrival azimuth in two station locations results in improvement in epicenter constraint for events occurring in the vicinity of the line connecting the two stations but there is no significant improvement elsewhere an empirical analysis of data from two of the september 1987 chemical explosions and data from an explosion in an active mining area supports the theoretical analysis showing that two station locations both epicenter and depth are quite reliable furthermore the theoretical analysis also indicates that even with data from a single observing station satisfactory results are obtained if three or more phases plus arrival azimuth are available

deep structure of the lofoten vesteralen segment of the mid norwegian continental margin and adjacent areas derived from 3 d density modeling to understand the major structural features of the sedimentary cover and crystalline crust of the lofoten vesteralen margin and the northern part of the voring segment of the mid norwegian continental margin a lithosphere scale 3d structural model has been constructed this model extends from the exposed crystalline rocks of the fennoscandian shield in the east to the cenozoic oceanic domain of the norwegian greenland sea in the west covering the vestfjorden ribban and rost basins and the northern parts of the voring basin and trondelag platform all available published and or released data have been used to set the initial 3d model which has been validated by means of 3d density forward modeling to obtain a gravity consistent 3d structural density model results from the 3d density modeling reveal that relatively thick sedimentary rocks are present in the distal rost basin below the lava flows the presence of a low density more than 20 km thick granitic body has been modeled within the middle upper crystalline crust beneath the eastern part of the vestfjorden basin and the adjacent mainland moreover the results of the 3d density modeling indicate the presence of an atypical low density lithospheric mantle beneath a large part of the lofoten vesteralen margin which is required to fit the regional component of the modeled gravity with the observed one the pronounced crustal feature within the model area is the bivrost lineament that appears to be the deeply seated lithosphere scale boundary that delineates clearly the lofoten vesteralen segment from the voring margin showing contrasting densities and crustal thicknesses

interpretation of ambiguous reflection data by imaging processes an example profile crossing steep submarine valley at the sea bottom abstract the determination of the geometry of a vertical structure is one of the most important problems in the conventional stacking process used as an imaging process the horizontal layers in depths of the earth are easily displayed in the seismic time section but the dipping and folded layers are not correctly displayed in the reflection data the present study addresses the same problem for the data collected from a profile of a steep marine valley and that of an offshore extension of the ganos fault at the westernmost part of the tekirdag basin marmara sea nw turkey in the previous studies the fault was interpreted as a low angle reverse fault juxtaposing between the plio quaternary and the miocene strata in the time migration section however the results of the extensive analyses in this study show that the close position of a newly interpreted miocene anticline to the synformal structure of the sea bottom makes the data ambiguous whereas the subvertical fault and the other events coming away from the fault plane causes complexity to eliminate misinterpretation due to ambiguity and complexity as in the previous analysis the data are reinterpreted by pre stack kirchhoff depth migration in addition to the conventional stacking process the new interpretation is checked through the synthetics data created from the model having appropriate parameters of the data used the results have shown the existence of an anticline that is cored by the miocene strata and overlain by the plio quaternary strata 200 m below the sea bottom the ganos fault is imaged as disturbing all the layers down the way and as having a listric geometry and steeper dip angle 75 n at shallow depths but decreasing downward this study examples the importance of considering the problems of the complex geometry and choosing appropriate imaging technique for analyzing seismic reflection data collected over an area with known vertical fault and related tectonic complexity

upper mantle seismic velocities and anisotropy in china determined through pn and sn tomography 1 we have obtained velocity images of the uppermost mantle beneath china by performing tomographic inversion of both pn and sn traveltimes from the annual bulletin of chinese earthquakes 99 139 pn arrivals and 43 646 sn arrivals were selected pn anisotropy was also obtained simultaneously with pn velocity average pn and sn velocities are 8 05 and 4 55 km s respectively and maximum velocity perturbations are about 3 4 the pn and sn velocities are low in eastern china and high in western china particularly high velocities are associated with old basins for example tarim junggar turpan hami qaidam and sichuan and stable craton for example ordos low sn velocities are found mainly throughout north china in addition velocities are relatively low beneath the central tibetan plateau and the north south seismic zone along 103 e in tarim and central china where we observe strong anisotropy the fast pn velocity directions are consistent with the directions of maximum principal compressive stress as well as directions of crustal movement determined from global positioning system beneath the india eurasia collision zone the pn anisotropy direction is parallel to the collision arc and nearly perpendicular to both the direction of maximum compression and crustal movement resulting from pure shear deformation both the velocity variations and anisotropy indicate that the tibetan plateau was extruded and the mantle material beneath the plateau has flowed around the east himalaya syntax while the remaining material has diverted northwestward beneath the tarim basin

a new three component detector and automatic single station bulletin production a new three component 3c seismic signal detector is introduced that has enabled us to produce a preliminary single station bulletin in an automatic mode we consider automatic station bulletins as very important because in the high frequency range local events mostly chemical explosions like quarry blasts are truly numerous say 20 to 50 per day and cannot be handled efficiently by an analyst in the conventional way a short term average long term average sta lta test statistic is used either alone or in combination with 3c signal polarization for p phases which allows a lowered threshold an added advantage with the polarity estimate is that a corresponding slowness vector estimate is obtained the detector is operated in three consecutive steps 1 the detector is run on a suite of bandpass filtered records 2 the initial detection log is compressed while retaining parameters from the best filter and 3 the detected and identified phases are grouped into event families and epicenter parameters are estimated the 3c detector has been tested on 6 days of recordings from the station c4 in the noress array located in se norway and results were compared to the array bulletin for teleseismic signals the array has an advantage in snr of about 15 db for local and regional events distance 1500 km the 3c snr in the frequency range 5 to 15 hz is about 6 to 8 db below that of the array the 3c detector picks practically all s phases detected by the array but occasionally misses the preceding pn however some new events missed by the array were also found at local and regional distances the 3c azimuth and distance estimates are generally within 20 and 20 km respectively of the noress solution and the origin time estimates are within a few seconds the 3c epicenter solutions are less stable than that of the array mainly due to phase identification problems and pn azimuth errors at low snr naturally the benefit of analyst screening and re processing would improve the 3c bulletin quality although the performance is considered satisfactory at the present stage of development

are the norwegian mountains compensated by a mantle thermal anomaly at depth article i nfo article history the norwegian mountains or scandes represent a long mountain range stretching from southern norway to the arctic and is characterised by a rugged topography and peaks up to 2 5 km high the origin of this mountain chain far away from any plate boundary remains a matter of passionate debates inside the geoscientific community hot mantle fingers originating from the iceland plume impacting the base of the scandinavian lithosphere and creating asthenospheric diapirs is one of the most accepted hypotheses for explaining cenozoic uplift in norway in order to test this hypothesis we conducted integrated gravity and thermal modelling we used the dense ngu gravity grid i e one measurement every 3 km and modelled the depth extent and the mass deficit associated to the compensating loads located below the southern scandes assuming that the density deficit below the scandes is purely thermal in origin thermal modelling allowed for testing the magnitude of the potentially associated temperature anomaly and its impact on surface heat flow recently acquired heat flow data were used in order to constrain the results from the thermal modelling the results of our integrated geophysical modelling rule out the possibility that the present day topography of the southern scandes is compensated by a deep seated asthenospheric diapir however our modelling does not exclude that thermal processes in the deep mantle could have initiated or assisted recent uplift of the southern scandes

sn velocities in western and eastern north america we have investigated the use of the new delay time data set of engdahl et al 1997 for the construction of tomographic images of sn velocity in north america the delays show a significant difference in average delay between paths located west and east of 105 w this difference is larger when paths longer than 10 are included indicating a positive gradient for the s velocity in eastern north america discarding outliers two separate regions in the western and eastern united states and canada where imaged low velocities were found under the colorado plateau extending westwards towards the gulf of california in the eastern u s the michigan basin stands out with low sn velocity and the grenville province is characterized by a positive anomaly

inhomogeneities of the eurasian mantle structure from the traveltimes of the nuclear explosions recorded by the finnish seismic network during 1961 1985 summary during the period 1961 1985 hundreds of nuclear explosions from the area of the soviet union and china were well recorded at finnish seismological stations the seismic waves recorded on the baltic fennoscandian shield penetrated through the mantle of the siberian platform the ural mountains and the east european platform from the known crustal models the functions describing the increase of the average velocities of sedimentary cover and crystalline complex of the crust with thickness were found the corrections for sedimentary cover and crustal thickness were included the large amount of data permitted the calculation of traveltimes of p waves for three sectors up to distances of about 5000 km in all mantle models the boundaries 400 and 700 km were found comparison of the results shows a difference in the traveltimes of the order of 5 s at a distance of about 4000 km which reflects the mantle structure differentiation for depths greater than 700 km lowest velocities for latitudinal direction and highest velocities for longitudinal direction the average s wave velocity model of the mantle was obtained using the traveltimes of s wave first arrivals high values of the vp vs ratio were found in the depth interval 200 400 km while in other depth intervals they were close to 1 73 our 1 d models are compared with and discussed in connection with other models of the east european and siberian platforms as well as with global tomographic solutions

the crustal structure of central east greenland ii from the precambrian shield to the recent mid oceanic ridges we present a 3 d crustal model of the east greenland fjord region between 69 n and 74 n the model covers the precambrian shield and the caledonian orogenic belt the adjoining devonian and mesozoic basins the continent ocean transition and the cenozoic oceanic areas as far as the kolbeinsey and the mohns mid oceanic ridges existing seismic models of the crustal structure are extrapolated into adjacent areas using 3 d gravity modelling for this purpose we compile a new regional scale bouguer anomaly map the precambrian shield west of the caledonian orogen approximately west of 32 w shows a mean thickness of 35 km with only small scale undulations this thickness is at the lower limit of the global range in shield thickness the caledonian orogen exhibits a pronounced mountain root with overall crustal thicknesses up to 51 km beside the urals the east greenland caledonides are one of the two palaeozoic mountain belts where a crustal root has preserved to the present day continuation of the crustal model to the east beyond the continent ocean transition yielded thicknesses of the crystalline oceanic crust from 9 km near the kolbeinsey ridge to 3 km west of the mohns ridge differences in the thermal structures of the old continental and the young oceanic lithosphere are responsible for the low density mantle beneath the oceanic crust which is also demonstrated by 3 d gravity modelling

separated earthquake location we present a practical method of locating earthquakes in laterally varying media the procedure has two distinct phases an estimation phase and an application phase in the estimation phase all existing arrival time residuals relative to some reference one dimensional velocity model for a region are used to estimate a set of path anomalies station corrections that vary as a function of source position this is done by sorting earthquakes into groups localized in space and applying a novel multiple event location algorithm this algorithm uses a pair of complementary projection operators to combine a priori information about the lateral structure that is indeterminate from the available data with the information that can be determined uniquely from the available data having estimated path anomalies as a function of source location we can generate a table of path anomalies that can be accessed and interpolated for future earthquake location this is the application phase of the method we have tested the method on synthetic data designed to study how well earthquakes can be located in the vicinity of the rupture zone of the 1984 morgan hill california earthquake we found precise absolute locations could be obtained provided the a priori information was specified appropriately distortion of relative locations occurred near large lateral velocity gradients and for groups of events spread over large areas because of the inadequacy of fitting a single set of path anomalies to the whole group

tomographical mapping of the lithosphere and asthenosphere beneath southern scandinavia and adjacent areas abstract in this paper we report on a seismic tomographical survey of the lithosphere asthenosphere beneath southern scandinavia and adjacent areas the ach inversion technique has been used and the observational data in the form of p wave travel time residuals have been obtained from seismogram records from networks in denmark southern norway and southern sweden the volume under investigation subdivided into four levels layers of 7 7 knots blocks each for estimation of velocity perturbations covers the area 54 62 n and 7 20 e and depth range 0 600 km major findings are as follows level 1 0 100 km pronounced velocity lows beneath southern jutland zealand the variscan foredeep and the sveco norwegian province of southeastern norway 1500 ma old the svecofennides of southeastern sweden exhibit relatively high velocities while the sveco norwegian province of southwestern sweden 1700 ma old is characterized by moderately high velocities the transition between velocity highs and lows coincides with the tornquist teisseyre line ttl or fennoscundian border zone level 2 100 300 km velocity anomalies are less pronounced at this level although velocity lows are found beneath the northern jutland zealand area and slightly northwestwards of the oslo rift the only velocity high is found beneath the southeasternmost part of sweden the ttl does not appear to have a clear counterpart in the velocity anomaly pattern in this depth range although a clearly unambiguous answer here would require far more extensive observational data a research goal of the future level 3 300 500 km and level 4 500 600 km velocity anomalies are weak which is not unexpected for the upper mantle beneath shield areas

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

model calculations of regional network locations for earthquakes in subduction zones algorithms for locating earthquakes recorded by local networks commonly assume a flat layered velocity structure even in island arc regions where the presence of a dipping lithospheric slab introduces large lateral velocity variations moreover because seismic stations occur along the narrow island arc the resulting linear network geometry degrades earthquake location to model this situation we trace rays in a spherical earth from hypothetical earthquakes through appropriate velocity models to networks of various geometries to isolate the effect of the slab most of the velocity models consist simply of a planar dipping constant velocity region embedded in a sphere with a constant lower seismic velocity we then use the calculated p and s travel times to relocate the hypothetical earthquakes with a flat layered velocity structure we perform calculations of this kind in a variety of models varying the dip of the slab the velocity contrast between the slab and the mantle the station geometry and the distance between the earthquakes and the slab mantle boundary we also perform calculations in more realistic models with geometry closely resembling two seismic networks in alaska these model calculations emphasize the great care that seismologists should exercise when interpreting local network locations in island arc regions in the present study all the relocations incorporate p and s arrivals at all stations and include no random or picking errors nevertheless the relocated hypocenters differ from the actual model hypocenters by up to 100 km or more and produce significant distortions in the wadati benioff zone the most prominent spurious feature is a clear increase in the apparent dip of the wadati benioff zone beneath a certain depth furthermore the relocation reduces the width or apparent thickness of the wadati benioff zone e g they produce an apparent thickness of 5 km or smaller for a zone of earthquakes with an actual thickness of 20 km however if different combinations of stations report different events it is possible to determine an apparent thickness which exceeds the actual thickness for local networks near subduction zones it is useful to estimate the mislocation and rms residual expected for each event recorded and located this can be accomplished by performing model calculations in a simple model with a constant velocity dipping slab embedded in a half space for such a simple model there exists only one ray path from each earthquake within the slab to each station and the travel time for this path can be calculated as a part of the routine network location process a relocation using the routine network location algorithm and these calculated travel times provides an indication of the expected mislocation and rms residual for the actual recorded event

j362d28 a new joint model of compressional and shear velocity in the earth s mantle summary the discrimination between chemical and thermal heterogeneity in the earth s mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics to answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies we describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes complete waveforms and surface wave dispersion measurements a horizontal tessellation consisting of 362 spherical splines is used to parametrize the model which is approximately equivalent to a spherical harmonic of degree 18 in resolution the model contains peak variations from prem of up to 7 per cent in s velocity and 2 5 per cent in p velocity in the upper mantle these variations decrease to 1 5 and 0 6 per cent respectively at 1000 km depth and reach 2 5 and 1 0 per cent respectively in the d region the rms ratio of s to p velocity perturbations is fairly constant between 2 0 and 2 5 in the lower mantle but a local minimum in this ratio occurs at a depth of approximately 1700 km resolution tests show that the recovery of p and s velocity is not geographically uniform but also show that this amplitude ratio is well resolved between 670 and 2700 km depth we also observe a persistent negative correlation between bulk sound and shear velocity throughout the same region of the mantle in addition the model contains a minimum correlation between p and s velocity between 670 and 1100 km this feature is supported by both the favourable outcome of resolution experiments and the poor fit provided by the starting model from the inversion in which the p and s velocities are perfectly correlated to our data set of p wave traveltimes the power spectra of both p and s velocity heterogeneity are similar although we note a slightly larger dominance of degree two in the spectra for p velocity in the mid mantle where resolution is highest

mapping of coda wave attenuation and its frequency dependency over eastern indian shield the study area comprises two tectonic blocks namely the chotanagpur microplate and the singhbhum microplate waveform data of 112 local earthquakes of magnitude mw 2 5 were considered for the present analysis coda q qc for each event at eight different central frequencies 1 14 hz and four different coda windows was estimated using back projection algorithm the average q0 qc at 1 hz and exponent values were regionalized by projecting each value in selected square grid of dimension 0 1 0 1 back projection algorithm was used for inversion of qc and the final values were computed after ten iterations when the residual error was reduced to acceptable level inversion was stabilized by a nine point spatial smoothening gaussian filter to compute the qc values for each frequency and subsequently combined values of q0 and were also computed the final power law equation of the coda wave attenuation for the concerned region was found to be qc 336 38 16 50 f 0 83 0 036 q0 varies from 180 to 255 270 to 360 297 to 386 and 340 to 420 and vary from 0 9 to 1 02 0 79 to 0 89 0 79 to 0 88 and 0 79 to 0 86 for 30 35 40 and 45 s coda windows increase in q0 and decrease in values with increase of coda window length shows the depth dependency of seismic wave attenuation at 1 hz frequency the central part surrounding the receiver lying at the junction of the chotanagpur and the singhbhum tectonic provinces documents lower q0 and higher values and presumably caused by more heterogeneities present in the area the higher concentration of lower magnitude earthquakes in this area support this observation the mapping values of attenuation can be utilized for hazard assessment of the area

timing and mechanisms of north atlantic cenozoic uplift evidence for mantle upwelling postrift domal uplift patterns are a distinct feauture of northern north atlantic margins on the basis of apatite fission track data offshore seismic stratigraphy geomorphology gravity and seismic tomography we argue that southern norway is characterized by predominantly neogene domal uplift currently available data suggest similar processes for other uplifted regions such as spitsbergen northern norway the british isles aad parts of east greenland

systematic biases in subduction zone hypocenters 1 earthquake hypocenters from global datasets commonly have regional biases in their locations due to the use of a one dimensional velocity model in their location to analyze this effect we group intermediate depth earthquakes into forty four 500 km long sections of subduction zone we relocate earthquakes in each group relative to one another and in a three dimensional global velocity model hypocenters shift up to 25 km regionally when these effects are included most earthquakes in circum pacific subduction zones are pulled toward the pacific location uncertainties from the relative relocations are reduced to one fifth of those from single event locations wadati benioff zone thicknesses are reduced to two thirds of their original thickness these biases alter estimates of depth to slab beneath arc volcanoes up to 50 km and alter measurements such as the volume of mantle wedge available for water storage or melt generation and the size of the thrust zone on which large earthquakes can occur

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

the lithosphere asthenosphere system in fennoscandia abstract we present a summary of the available information on rayleigh wave dispersion data for the fennoscandian region the observations have been combined to produce regional dispersion relations which have then been subjected to the hedgehog inversion procedure the results are presented on a map outlining the thickness of the lid and the shear velocities in both the lid and the asthenosphere channel lid thickness up to around 135 km is found in the bothnia north central finland area with if any weak shear velocity contrast to the underlying layer the surrounding areas are characterized by lid thickness up to around 75 km a stronger low velocity zone to lid contrast may be found in the caledonian and baltic sea area 0 25 0 45 km s taking into account moho depth data and the aforementioned results a map of the lithosphere asthenosphere system was derived

automatic seismogram analysis statistical phase picking and locating methods using one station three component data abstract seismic events at local and regional distances are located using data from the vaasa vaf 63 0 n 22 7 e three component station in western finland the analysis is performed off line after pseudo on line detections the continuous data are first recorded on long disk loops these loops can cover 10 days of data the events are picked using murdock hutt detector and after that they are recorded as separate files for further analysis the direction of approach which estimates the polarization state of the signal is determined by the well established maximum likelihood method the difference between the arrival times of p and s phases is used to estimate the distance phases observed up to 185 km distance from the source are assumed to be pg and sg and beyond that pn and sn the onset times of the phases are estimated by a statistical data adaptive method the onsets calculated in this way are very accurate when compared with earlier methods like sta lta epicenter locations are similar to those of finsa network reported in helsinki bulletins the median of the location differences is about 50 km

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

structure of the benioff zone beneath the shumagin islands alaska relocation of local earthquakes using three dimensional ray tracing seismic rays are traced through a prescribed three dimensional inhomogeneity that simulates the subducted slab below the shumagin islands region to calculate local station delays for a given hypocenter and a slab model hypocenters determined by the shumagin seismic network are then relocated using the station delays a flat layered velocity structure and a standard earthquake location computer program station delays are calculated for 12 hypocenters with respect to six different slab models to identify the slab model that is most consistent with the available arrival time and waveform data a set of path corrections that is calculated for each grid point station pair on a preliminary grid of 36 points in the depth range from 60 to 300 km is used to recalculate the hypocenters for all of the 1982 earthquakes with depths greater than 50 km application of this method to data from 1982 for the digitally recording shumagin seismic network shows the following results 1 a previously observed apparent increase in dip of the subducted slab at depths of 100 km disappears 2 the subducted slab can be modeled as a dipping structure that dips at a constant angle of 45 toward north northwest at depths between 80 and 250 300 km and has a 7 higher velocity than the surrounding mantle 3 hypocenters determined from shumagin network data are located only 10 20 km south of high quality hypocenters determined from teleseismic data alone 4 qualitative comparison of digitally recorded seismograms with calculated ray paths shows enrichment of high frequency coda possible converted phases and low amplitudes of first p arrivals for rays that travel mostly along the slab conversely for rays that travel almost vertically through the upper plate the seismograms show a high amplitude of first p arrivals that are followed by an insignificant coda and low amplitude s waves

location performance of a sparse regional network a key element in successful seismic verification of a nuclear test ban treaty is the capability of a sparse network of seismic stations to accurately locate regional events we have investigated the regional location accuracy of the regional seismic test network rstn a five element three component network in eastern north america using 62 events varying in size from magnitude 3 0 to 5 1 applying an algorithm which allows inclusion of back azimuth estimates as well as travel times we determined a median location error of 23 km for the data set relative to the pde locations considering the large station spacing 1500 km and a few data used in the locations 2 to 4 stations the rstn location accuracy is remarkably good the results imply that a widely spaced network of single three component stations could reliably locate regional seismic events copyright american geophysical union 1989

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

wavefield decomposition using ml probabilities in modelling single site 3 component records summary this paper presents a new approach to the analysis of three component digital seismograms earlier approaches used techniques such as principal components to estimate particlemotion using models of p and s waves in this paper the maximum likelihood ml estimator is preferred because this allows the use of x2 probabilities to test whether energy of a specific wave type p s love or rayleigh is present in addition this analysis allows the joint estimation of azimuth of approach and in cases of p and sv waves also apparent angle of incidence and hence information on apparent velocity for a single three component seismogram the covariance matrix provides only six independent observations thus restricting analysis to rather simple wave models the technique works satisfactorily for p waves whereas shear and surface wave models sometimes prove cumbersome to handle due to correlation between radial and transverse components reflecting complex propagation characteristics in inhomogeneous media this technique has been tested on synthetic data and in such cases works perfectly for all wave types an important aspect of this work has been the visual display of the probability and velocity information as functions of time and azimuth displaying the data in this form provides information on the ray path in a manner similar to analysis performed by seismic arrays practical examples on a variety of siesmic data are given to illustrate the viability of the technique the data cover a broad spectrum of frequencies and applications from broad band teleseismic data 1 hz regional seismic data 10 40 hz seismic profiling data 125 hz and vsp 500 hz recordings