relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

region specific key seismic parameters for earthquakes in northern iran strong motion accelerograms recorded within northern iran are used to examine the propagation characteristics of shear wave including geometric spreading behavior q value j 0 and horizontal to vertical h v ratio these region specific key seismic parameters are estimated from 259 three component records of 22 earth quakes with magnitude ranging from m 4 9 to m 7 4 in northern iran the geometric spreading follows a trilinear behavior with a strong postcritical reflection from the moho the first and second hinges of the trilinear behavior are at 75 and 150 km respectively the associated q value based on the vertical component is q 87 f 1 46 j0 value for vertical and horizontal components are 0 03 and 0 05 respec tively because of lack of station specific site information the h v ratio is considered to be a rough estimation of generic site amplification the obtained region specific parameters are used to estimate the average stress drop based on three stochastic modeling approaches stochastic point source modeling suggests a brune stress drop of 125 bars whereas stochastic finite fault modeling based on static and dynamic corner frequency approaches suggests a stress drop of 68 bars

a ground motion predictive model for iran and turkey for horizontal pga pgv and 5 damped response spectrum investigation of possible regional effects we present a ground motion prediction equation gmpe for turkey and iran to investigate the possible regional effects on ground motion amplitudes in shallow active crustal earthquakes the proposed gmpe is developed from a subset of the recently compiled strong motion database of the earthquake model of the middle east region project see data and resources 1 a total of 670 turkish and 528 iranian accelerograms with depths down to 35 km are used to estimate peak ground acceleration peak ground velocity and 5 damped elastic pseudospectral acceleration ordinates of 0 01 s t 4 s the moment magnitude range of the model is 4 m w 8 and the maximum joyner boore distance is r jb 200 km the functional form considers three major fault mechanisms strike slip normal and reverse the nonlinear soil behavior is a function of v s 30 average shear wave velocity in the upper 30 m of soil profile our observations from empirical and estimated ground motion trends advocate regional differences in the territories covered by iran and turkey that originate from the differences in q factors kappa and near surface velocity profiles these factors eventually affect the magnitude and distance dependent scaling of spectral amplitudes in iran and turkey in essence the ground motion amplitudes of these two neighboring countries would draw patterns different than the ground motion estimates of gmpes developed from the strong motion databases of shallow active crustal earthquakes from multiple countries online material matlab code and regression coefficients for computing the response spectrum and distance scaling 1 sec 7

stochastic simulation of strong motion records from the 2012 ahar varzaghan dual earthquakes northwest of iran here the generalized inversion of s wave amplitude spectra is employed for deriving the site response and s wave attenuation quality factor in the northwest region of iran a total of 279 strong motion accelerograms recorded at distances below 200 km from 41 earthquakes with moment magnitudes ranging from m w 3 8 to 6 5 are used to determine the region speci c attenuation model the site responses have been determined for all 54 stations individually the bulk of strong motion data i e 184 records comes from the 2012 ahar varzaghan dual earthquakes in northwest iran and their aftershocks also the modified finite fault method which is able to model nonuniform stress distribution on the fault plane is employed to investigate the coseismic stress parameter for the first and second ahar varzaghan dual earthquakes by minimizing the difference between the synthesized and observed pseudospectral accelerations for 5 damping results denote a concentration of stress drops on the northwestern part of the first event s fault and on the central and eastern part of the second fault stochastic simulations using the calibrated stress distribution have been performed on a regular grid covering the study area for both rock and soil site conditions in total 651 points the results show that the maximum of peak ground accelerations pgas during the ahar varzaghan dual earthquakes for the rock site condition reached 557 cm s s and the largest peak ground velocities pgvs were estimated around 76 cm s in general comparisons between simulated data and empirical ground motion prediction equations gmpes show that the stochastic predictions pgas and pgvs are higher than those predicted by the empirical gmpes for distances less than 30 km and are smaller for distances more than 30 km the simulated data are also consistent with the modi ed mercalli intensity observations and show reasonable agreement this can be considered as another validation of the method

a crustal seismic velocity model for the uk ireland and surrounding seas summary a regional model of the 3 d variation in seismic p wave velocity structure in the crust of nw europe has been compiled from wide angle reflection refraction profiles along each 2 d profile a velocity depth function has been digitised at 5 km intervals these 1 d velocity functions were mapped into three dimensions using ordinary kriging with weights determined to minimise the difference between digitised and interpolated values an analysis of variograms of the digitised data suggested a radial isotropic weighting scheme was most appropriate horizontal dimensions of the model cells are optimised at 40 40 km and the vertical dimension at 1 km the resulting model provides a higher resolution image of the 3 d variation in seismic velocity structure of the uk ireland and surrounding areas than existing models the construction of the model through kriging allows the uncertainty in the velocity structure to be assessed this uncertainty indicates the high density of data required to confidently interpolate the crustal velocity structure and shows that for this region the velocity is poorly constrained for large areas away from the input data

seismic velocity model of the crust and upper mantle along profile pancake across the carpathians between the pannonian basin and the east european craton abstract results are presented of a seismic wide angle reflection refraction survey along a profile between the pannonian basin pb and the east european craton eec called pancake the p and s wave velocity model derived can be divided into three sectors the pb the carpathians including the transcarpathian depression and the carpathian foredeep and the south western part of the eec including the trans european suture zone tesz seismic data support a robust model of the vp velocity structure of the crust in the pb the 22 23 km thick crust consists of a 2 5 km thick sedimentary layer vp 2 4 3 7 km s 17 20 km thick upper crystalline crust 5 9 6 3 km s and an up to 3 km thick lower crustal layer vp 6 4 km s in the central part of the carpathians a 10 24 km thick uppermost part of the crust with vp 6 0 km s may correspond to sedimentary rocks of different ages several high velocity bodies vp 5 35 5 95 and 6 05 km s within the sedimentary flysch sequences may represent volcanic sequences the moho depth changes from 25 km to 45 km over ca 100 km distance beneath the carpathians west of tesz the cratonic crust has a typical three layer structure with a pronounced thickening of the lower crust towards the ukrainian shield where a high velocity lower crust vp 7 2 km s is observed two low velocity lenses in the upper crust of the eec are interpreted beneath major sedimentary troughs lviv and volyn podolsk mantle reflectors are observed at depths of 45 km and 75 km below the pb and 10 20 km below the moho in the eec sub moho pn velocities increase from 8 0 km s beneath the pb to 8 1 km s beneath the carpathians and to 8 3 km s beneath the eec s waves of acceptable quality are recorded in the eec their signal to noise ratios increase towards the ukrainian shield

the flux and mixing rates of antarctic bottom water within the north atlantic calculation was made of the northward flow of antarctic bottom water into the western north atlantic basin through a passageway approximately 300 km wide between the ceara rise and the mid atlantic ridge at about 4 n two moorings carrying four current meters each were placed in the region where currents were expected to be the greatest and were left for 360 days the current was not steady but exhibited large surges with approximately a 60 day time scale whose cause is unknown current meters in the fastest flowing region all exhibited a net northward flow it is estimated that approximately 0 8 106 m3 s 1 of water colder than 1 9 c potential temperature flowed on the average into the north atlantic with this number possibly being too small by 0 3 106 m3 s 1 or too big by 0 1 106 m3 s 1 depending upon estimates of the width of the region which the current meters sample however these numbers differ from geostrophic estimates of 1 98 106 m3 s 1 the disagreement coming almost entirely from the fact that the geostrophic estimates give a sizeable flux of water colder than 1 2 c while the current meters do not based upon the two different flux rates residence times and mixing coefficients are calculated for antarctic bottom water for each 0 1 c potential temperature interval from 1 0 c to 1 9 c finally some comments on the dynamics of the northward flow are made

seismic constraints on a large mafic intrusion with implications for the subsidence history of the danish basin 1 seismic refraction data from the estrid 1 profile are used for seismic velocity modeling along the strike of a large mafic intrusion in the norwegian danish basin central denmark the p wave velocity structure identifies a 8 km thick sedimentary succession with velocities between 1 8 and 5 7 km s the top basement is defined by a step to vp 6 2 km s in the middle to lower crust a high velocity body vp 6 7 km s with its top located at about 10 12 km depth is interpreted as a high velocity and high density gabbroic intrusion of permian age this high velocity body explains the large 50 mgal positive gravity anomaly known as silkeborg gravity high the intrusion has a minimum volume of 40 000 km3 which implies that the magma influx and the consequent cooling of the lithosphere from high temperature could have had profound effects on the subsidence of the danish basin in particular because the magma probably intruded during only a few events and other similar structures cover much of the basin an anomalously high velocity gradient from 7 0 km s in the middle crust to 7 7 km s at 30 32 km depth in the central part of the intrusion coincides with an interval without moho reflections indicative of a gradual transition zone between the crust and the mantle this feature may show the location of the feeder dykes of the intrusion

sea99 a revised ground motion prediction relation for use in extensional tectonic regimes we present sea99 a revised predictive relation for geometric mean horizontal peak ground acceleration and 5 damped pseudovelocity response spec trum appropriate for estimating earthquake ground motions in extensional tectonic regimes which we demonstrate to have lower ground motions than other tectonic regimes sea99 replaces sea96 a relation originally derived by spudich et al 1996 1997 the data set used to develop sea99 is larger than that for sea96 and minor errors in the sea96 data set have been corrected in addition a one step regression method described by joyner and boore 1993 1994 was used rather than the two step method of joyner and boore 1981 sea99 has motions that are as much as 20 higher than those of sea96 at short distances 5 30 km and sea99 s motions are about 20 lower than sea96 at longer periods 1 0 2 0 sec and larger distance 40 100 km sea99 dispersions are significantly less than those of sea96 sea99 rock motions are on the average 20 lower than motions predicted by boore et al 1994 except for short distances at periods around 1 0 sec where sea99 motions exceed those predicted by boore et al 1994 by as much as 10 com parison of ground motions from normal faulting and strike slip events in our data set indicates that normal faulting horizontal ground motions are not significantly different from extensional regime strike slip ground motions

sveconorwegian igneous complexes beneath the norwegian danish basin abstract gravity and magnetic anomalies have previously been interpreted to indicate strongly magnetic permian or even tertiary intrusive bodies beneath the skagerrak waterway such as the skagerrak volcano and beneath silkeborg in denmark our combined modelling of the magnetic and gravity anomalies over these rock bodies indicates that a steep upward magnetisation is required to explain the magnetic anomalies at the surface reminiscent of the magnetic direction in the sveconorwegian rocks of the rogaland igneous province in southern norway the younger rocks of the permian oslo rift region have intermediate and flat magnetisation that is inadequate to explain the observed magnetic field the positive part of the skagerrak aeromagnetic anomaly is continuous with the induced anomalies associated with the eastward extension of the rogaland igneous province this relation also suggests that rocks of the rogaland igneous province and its offshore extension are responsible for the skagerrak anomalies both the negative remanence dominated aeromagnetic anomaly and the positive gravity anomaly can be modelled using constraints from seismic reflection lines and available density data and rock magnetic properties a 7 km thick complex of ultramafic mafic intrusions is located below a southward dipping 1 4 km thick section of mesozoic sediments and 1 2 km of palaeozoic sediments the enormous body of dense ultramafic mafic rocks implied by the modelling could be the residue of the parental magma that produced the voluminous rogaland anorthosites the application of similar petrophysical properties in the forward modelling of the silkeborg source body provides an improved explanation of the observed gravity and magnetic anomalies compared with earlier studies the new model is constrained by magnetic depth estimates from the located euler method ranging between 6 and 8 km forward modelling shows that a model with a reverse magnetic body anorthosite situated above a dense mafic ultramafic body may account for the silkeborg anomalies the anorthosites may have formed by differentiation of the underlying mafic intrusion similar to the intrusive relations in the rogaland igneous province we conclude that there is strong evidence for a sveconorwegian age for both the skagerrak and the silkeborg anomalous rock bodies

an observation of the horizontal and vertical diffusion of a passive tracer in the deep ocean an experiment to measure the dispersion of a passive tracer injected at 300 and 1000 m depth in the pacific 600 miles southwest of san diego is described rhodamine dye was released as a very nearly point source and the subsequent growth of the patch was mapped at various times up to 66 2 hours after release using a self propelled underwater research vehicle spurv which carried temperature conductivity pressure and dye sensors on a depth cycling trajectory through the patch the analysis shows that the horizontal diffusion rates decrease with depth that it is difficult to resolve the mixing in terms of a constant diffusion parameter based on any one of a number of models that the 300 m results agree with those obtained by schuert 1970 and that the patch growth began to develop eddy behavior at 66 2 hours when the rms second moment of the dye distribution was r2 l 2 210 m for the purpose of predicting horizontal mixing the results indicate that eddy diffusivities of 1150 and 360 cm2 s at 300 and 1000 m respectively are the best fit values for spatial scales 200 m horizontally although we have focused on horizontal isopycnal diffusion a few aspects of the vertical diapycnal characteristics of the patch are also discussed

aftershock decay rates in the iranian plateau motivated by the desire to have more information following the occurrence of damaging events the main purpose of this article is to study aftershock sequence parameters in the iranian plateau to this end the catalogue of the iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates for different tectonic provinces the completeness magnitudes mc of the earthquake catalogue have been calculated in different time intervals also the mc variability in spatial and temporal windows has been determined for each selected event for major iranian earthquakes catalogue of aftershocks has been collected thanks to three declustering methods first the classical windowing method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 second a modified version of this using spatial windowing based on the wells and coppersmith bull seismol soc am 84 974 1002 1994 relations and third the burkhard and grunthal swiss j geosci 102 149 188 2009 scheme effects of the temporal windows also have been investigated using the time periods of 1 month 100 days and 1 year in the declustering method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 in the next step the modified omori law coefficients have been calculated for the 15 selected earthquakes the calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time dependent seismic hazard forecasts the regional characteristics of the aftershock decay rates have been studied for the selected iranian earthquakes in the alborz zagros and central iran regions considering their different seismotectonics regimes however due to the lack of sufficient data no results have been reported for the kopeh dagh and makran seismotectonic regions

seismic velocity structure of crustal intrusions in the danish basin abstract we image the east and westward extent of a crustal high velocity body the thickness of a layered sequence around the moho at the flank of the body and the uppermost mantle velocity along the 320 km long refraction and wide angle reflection seismic profile estrid 2007 in the danish basin ray tracing modelling of the seismic data reveals a high velocity body 6 7 7 7 km s between 10 and 30 km depth with a lateral extent of at least 110 km it is interpreted as an intrusive body of gabbroic composition moho depth is variable between 30 and 35 km along the profile the crust is thin in a 180 km wide zone approximately below the western part of the intrusive body and further westward in the basin area the pn velocity in the uppermost mantle is relatively low 7 8 km s beneath the thin crust whereas higher pn velocities 8 0 km s are observed outside this zone the pmp reflection is characterized by reverberations ringing in the seismic signal in the zone with low pn velocity by 2d full waveform modelling these reverberations are explained by a layered transition zone around the moho consisting of intermixed crustal and mantle material the layering may be explained by magmatic intrusion along the moho over a lateral distance of 130 km away from the magmatic source which is located in the middle of the intrusive body these intrusive features may be related to extensional transtensional tectonism in the tornquist fan during the late carboniferous and early permian our new findings suggest a minimum volume of the intrusive body in the danish basin of about 60 000 km3 which is 20 000 km3 larger than interpreted from earlier data such a large intrusion must have affected the temperature field substantially and may have initiated the subsidence of the post permian danish norwegian basin

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

regional geological and tectonic structures of the north sea area from potential field modelling the spatial distribution of large scale crustal domains and their boundaries are investigated in the north sea area by combining gravity magnetic and seismic data the north sea is situated on the plates of three continents avalonia laurentia and baltica which collided during the caledonian orogeny in the middle palaeozoic the location and continuation of the collisional sutures are debated we apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures the transformations reveal intrinsic features of crustal transitions between the caledonian plates and their relation to later extensional structures the transformations include the hough transform applied to the gravity field calculation of fractional derivatives and integrals of the gravity and magnetic fields the pseudogravity field and the horizontal gradient field as well as upward continuation the results indicate a fundamental difference between the lithosphere of avalonia laurentia and baltica the location of the mesozoic rift system the central graben and viking graben may have been partly determined by the presence of the sutures between these three plate indicative of extensional reactivation of compressional structures a significant lineament across the entire north sea between scotland and north germany indicates that the lower crust of baltica provenance may extend as far south westward as to this lineament comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties this lineament could represent the suture between lithosphere of caledonian origin avalonia versus lithosphere of precambrian origin baltica in the lower crust and upper mantle if this is the case the lineament is the missing link in the reconstruction of the triple plate collision

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

summary of project tor delineation of a stepwise sharp deep lithosphere transition across germany denmark sweden project tor teleseismic tomography across the tornquist zone in germany denmark sweden is now producing results we are able to detect very significant deep lithosphere differences and we can now discuss the sharpness laterally in 1996 1997 our 120 seismographs constituted the largest seismic antenna ever in europe the tor area was chosen along a well studied crustal profile of an earlier project and the inversion efforts are concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km the tor investigation can be called two and a half dimensional as it has a 900 km profile length with 100 km width plus a few seismographs off the profile the tor data have been subjected to p wave travel time tomography surface wave and receiver function analysis as well as anisotropy and scattering measurements through ray tracing in a compiled crustal model and subtraction of the modelled travel time anomalies the influence of the lower lithosphere asthenosphere on the seismic rays from distant earthquakes is being established travel time tomography results confirm very large lateral lithosphere differences of 4 6 in p wave velocity for several events of the large data base it is demonstrated that the observed p wave travel time anomalies of 1 2 s can be divided almost equally between known crustal effects and lower lithosphere asthenosphere differences which then must account for about 1 s of the travel time differences the transition is interpreted to be sharp and steep in two places it goes all the way through the lithosphere at the northern rim of the tornquist zone near the border between sweden and denmark and here the lithosphere difference is large a smaller lithosphere difference is found near the southern edge of the ringkobing fyn high just north of the border between denmark and germany also this transition is sharp and steep and goes all through the lithosphere these two sharp transitions divide the tor region into three different lithosphere structures distinguishable in p wave travel time tomography surface wave dispersion p and s wave anisotropy and partly in p wave scattering

on two characteristic frequencies of acceleration spectra patch corner frequency and fmax abstract we examine two issues related to the radiation of tectonic earthquake sources i the complexity of the shape of observed source spectra and ii the effect of recording site characteristics on the cut off frequency f max of acceleration spectra beyond which spectral amplitudes diminish sharply we compute the far field spectra of the 1979 imperial valley and the 1984 morgan hill earthquakes from the slip functions that were inferred from detailed inversion studies of strong motion and teleseismic data of these two california strike slip events these spectra along with data from the 1983 central japan sea earthquake sequence main shock and aftershocks demonstrate the existence of the so called patch corner frequency which is related to the scale length of heterogeneities of the fault plane such a frequency is a distinct feature of the source spectrum of the specific barrier model of papageorgiou and aki by analyzing accelerograms of the san fernando earthquake of 1971 we found that f max determined from records at soil stations is nearly the same as that determined from records at hard rock stations

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

flow through discovery gap abstract a narrow gap discovery gap in the east azores fracture zone at 37 n in the eastern atlantic provides a channel for the exchange of bottom water between the madeira and iberian abyssal basins a detailed survey defines its length 150 km width 10 50 km depth of sills near 4800 m and sediment thickness 0 500 m year long measurements of deep flow are made from six moorings and ten current meters mean flows are about 5 cm s 1 these data are supplemented by 10 days of float tracking near 4700 m and numerous density profiles within and around the gap a persistent southwest northeast flow of dense water is found in discovery gap and the flux of water colder than a potential temperature of 2 05 c is measured to be 0 21 04 106 m3 s 1 this discharge spreads over an area of about 1011 m2 beyond the gap exit where it is warmed both by geothermal heating and by mixing with overlying water an estimate of 1 5 to 4 cm2 s 1 is derived for the diapycnal diffusivity similar to values dete

the santa monica basin tracer experiment a study of diapycnal and isopycnal mixing we have studied cross isopycnal diapycnal and lateral mixing and stirring below the sill of santa monica basin by releasing two tracers sulfur hexafluoride and perfluorodecalin as close as possible to an isopycnal surface and measuring their subsequent dispersion the target for the release was a potential temperature surface at about 790 m depth roughly 100 m above the bottom and 50 m below the sill three surveys performed immediately after about 7 weeks after and about 6 months after the release showed that the time scales for lateral stirring and mixing in the basin were between 2 and 5 months the diapycnal diffusivity for the whole period was found to be 0 29 0 06cm2 s near the injection surface where the buoyancy frequency was about 1 1 cph this estimate may include some mixing in the turbulent boundary layer near the walls of the basin our best estimate for the diapycnal diffusivity in the basin interior is 0 25 0 08 cm2 s

test of goodness of the nga ground motion equations to predict the strong motions of the 2012 ahar varzaghan dual earthquakes in northwestern iran in the first part of this study a set of 87 ground motion records with closest distance to the rupture plane r rup less than 200 km and averaged shear wave velocity over the top 30 m of the subsurface v s 30 between 175 and 1400 m s recorded during the 2012 ahar varzaghan dual earthquakes m w1 6 4 m w2 6 3 were taken into account to examine the predictive capabilities of the next generation attenuation nga ground motion prediction equations gmpes via a set of comparative analyses and tests the first applied method to assess the performance of the nga gmpes is based on the intraevent residual analysis the primary database i e 87 records was also used to develop an event specific gmpe in the case of the ahar varzaghan dual earthquakes by means of regression analyses the derived event specific gmpe has been compared with the nga gmpes for two different site conditions that is v s 30 375 m s rock site and v s 30 375 m s soil site the residual analysis results indicate that the nga gmpes perform better in predicting data recorded at rock sites compared to soil sites for soil sites and at large periods t 2 0 s the observed spectral accelerations are overpredicted by the nga gmpes furthermore as the second part of this study to select the most adequate gmpes 14 strong motion records from the 1997 ardebil earthquake m w 6 1 were added to the primary database the implementation of the likelihood lh and log likelihood methods as modern lh based ranking assessment techniques as well as the nash sutcliffe index reveal that the nga gmpes show good compatibility at short medium periods t 1 0 s on the basis of the data recorded during the 2012 ahar varzaghan dual and 1997 ardebil earthquakes i e 101 records however in the long period range the dispersion in the data does not allow the authors to draw a comprehensible conclusion

a new tectonic model for the laurentia avalonia baltica sutures in the north sea a case study along mona lisa profile 3 abstract we present a new model for the lithospheric structure of the transitions between laurentia avalonia and baltica in the north sea northwestern europe based on 2 d potential field modelling of mona lisa profile 3 across the central graben with constraints from seismic p wave velocity models and the crustal normal incidence reflection section along the profile the model shows evidence for the presence of upper and lower palaeozoic sedimentary rocks as well as differences in crustal structure between the palaeo continents laurentia avalonia and baltica our new model together with previous results from transformations of the gravity and magnetic fields demonstrates correlation between crustal magnetic domains along the profile and the terrane affinity of the crust this integrated interpretation indicates that a 150 km wide zone characterized by low grade metamorphosis and oblique thrusting of avalonia crust over baltica lower crust is characteristic for the central north sea area the magnetic susceptibility and the density across the coffee soil fault range from almost zero and 2715 kg m3 in avalonia crust to 0 05 si and 2775 kg m3 in baltica crust the model of mona lisa profile 3 indicates that the transition between avalonia and baltica is located beneath the central graben with a ramp flat ramp geometry our results indicate that the initial rifting of the central graben and the viking graben was controlled by the location of the caledonian collisional suture located at the coffee soil fault and that the deep crustal part of baltica extends further to the west than hitherto believed

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

seismic model of the crust and upper mantle in the scythian platform the dobre 5 profile across the north western black sea and the crimean peninsula the scythian platform scp with a heterogeneous basement of baikalian variscan cimmerian age is located between the east european craton eec on the north and the crimean caucasus orogenic belt and the black sea bs basin on the south in order to get new constrains on the basin architecture and crustal structure of the scp and a better understanding of the tectonic processes and evolution of the southern margin of the eec during mesozoic and cenozoic time a 630 km long seismic wide angle refraction and reflection warr profile dobre 5 was acquired in 2011 october it crosses in a w e direction the fore dobrudja trough the odessa shelf of the bs and the crimean plain the field acquisition included eight chemical shot points located every 50 km and recorded by 215 stations placed every 2 0 km on the land in addition the offshore data from existing profile 26 placed in the odessa shelf were used the obtained seismic model shows clear lateral segmentation of the crust within the study region on four domains the fore dobrudja domain km 20 160 an offshore domain of the karkinit trough at the odessa shelf of the bs km 160 360 an onshore domain of the central crimean uplift crimean plain km 360 520 and the indolo kuban trough at the kerch peninsula km 520 620 that is the easternmost part of the crimea two contrasting domains of the scp within the central part of the dobre 5 profile the karkinit trough and the central crimean uplift may represent different stages of the scp formation a deep karkinit trough with an underlying high velocity 7 16 km s 1 lower crust body suggests its rifting related origin during early cretaceous time the central crimean uplift represents a thick up to 47 km crustal domain consisting of three layers with velocities 5 8 6 4 6 5 6 6 and 6 7 7 0 km s 1 which could be evidence of this part of the scp originating on the crust of precambrian craton eec the thick heterogeneous basement of the central crimean uplift shows inclusions of granitic bodies associated with magmatic activity related with variscan orogeny within the scp general bending and crustal scale buckling of the central crimean uplift with a wavelength of 230 km could be an effect of the alpine compressional tectonics in the adjacent crimean mountains the extended rifted continental margin of the scp eec at the odessa shelf and buckling uplifted domain of the central crimean uplift affected by compressional tectonics are separated by the n s oriented western crimean fault the crust of the southern margin of the eec is separated from the scp which originated on the eec crust tectonised and reworked during the palaeozoic mesozoic by the crustal fault of w e orientation which corresponds with the golitsyn fault observed at the surface between the eec and the scp the fore dobrudja domain with a thick 10 km heterogeneous basement and two subhorizontal layers in the crystalline crust with velocities 6 2 6 3 and 6 4 6 65 km s 1 differs from the scp crust and its origin could be very similar to that of the trans european suture zone and palaeozoic west european platform

uniqueness of modeling results from teleseismic p wave tomography in project tor within project tor which is about teleseismic tomography across the tomquist zone in germany denmark sweden we have confirmed very significant deep lithosphere differences and modeling is substantiated via completely independent methods in 1996 1997 our 130 seismographs constituted the largest seismic antenna ever in europe the tor area was chosen along a well studied crustal profile of an earlier project and the modeling efforts were concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km the tor data have been subjected to p wave travel time tomography surface wave and receiver function analysis as well as anisotropy and scattering measurements an important goal of the project was to make several independent inversions of the tomography data and compare the results in an attempt to evaluate uniqueness resolution and accuracy of these inversions the comparisons of this paper involve more diversity in methods than any previous comparison the geological outcome is a substantiation of earlier statements that the transition is interpreted to be sharp and steep in two places it goes all through the lithosphere at the northern rim of the tornquist zone near the border between sweden and denmark and here the lithosphere difference is large to depths more than 200 km the other lithosphere difference of smaller scale is found near the southern edge of the ringkobing fyn high near the border between denmark and germany also this transition is sharp and steep and goes all through the lithosphere to depths around 120 km these two sharp transitions divide the tor region into 3 different lithosphere structures distinguishable in p wave travel time tomography surface wave dispersion p and s wave anisotropy and partly in p wave scattering the mentioned broad scale features are judged to be unambiguously determined with well described resolution and accuracy unfortunately a detail like the slope of the subcrustal lithosphere transition right under the tronquist zone cannot be constrained even if this is where the resolution is best and the curiosity largest c 2009 elsevier b v all rights reserved

3d lithosphere scale density model of the central european basin system and adjacent areas abstract to analyze the first order structural features characterizing the crust and the lithospheric mantle below the central european basin system and adjacent areas a new lithosphere scale 3d structural density model has been derived that integrates published knowledge with 3d gravity modeling with this study we aim to integrate previous results on sub domains of the study area and regional results of limited resolution in conjunction with 3d gravity analysis to derive the configuration of the lower crust and lithospheric mantle that is consistent with the known density distribution of the sediment fill and with observed deep seismic data as well as with observed gravity the derived 3d density model resolves the internal configuration of the crystalline crust below the central european basin system and adjacent areas at the regional scale and shows that the crystalline crust is characterized by a layered structure the upper to middle crystalline crust is characterized by relatively low seismic p wave velocities and densities it shows strong variations in thickness across the study area that partly correlate spatially with the inherited segmentation in response to crustal amalgamation this upper to middle crystalline crust is underlain by a continuous high density high velocity lower crustal layer locally more than 30 km thick beneath the east european craton and generally decreasing in thickness from the older to the younger tectonic domains though the thickness of this high density lower crust is generally small below the permo cenozoic central european basin system it can reach locally more than 18 km below the northeast german and the norwegian danish basins the derived depth to the lithosphere asthenosphere boundary confirms previously proposed geometries and is up to 230 km deep beneath the precambrian domain but less than 100 km deep beneath the phanerozoic domains implying that the average thermal gradient is higher in the phanerozoic lithosphere than in the precambrian part

simultaneous study of the source path and site effects on strong ground motion during the 1989 loma prieta earthquake a preliminary result on pervasive nonlinear site effects we considered the effects of source propagation path and local site conditions on strong ground motion from the loma prieta earthquake in the following steps first the local site effect was removed from the strong motion records applying the weak motion amplification factors estimated from nearby stations of usgs regional network using the coda method then we confirmed the approximate validity of the 1 r law of geometrical spreading factor for the crustal model applicable to the region and we determined the attenuation parameter q f and source spectrum s f empirically from the site effect corrected spectral amplitude both q f and s f are consistent with the results obtained earlier for major california earthquakes we then synthesized the time history of ground acceleration by applying the stochastic simulation technique the agreement between the observed and predicted records was good for duration and spectral content we found however a strong systematic discrepancy with regard to peak acceleration namely for distances less than 50 km the predicted peak acceleration consistently overestimated the observed for sediment sites and underestimated it for the franciscan formation sites since the above systematic discrepancy applies to all the available stations within about 50 km from the hypocenter it is unlikely that the effect is due to the radiation pattern near source structure or topography it appears that the strong difference in the amplification factor between the franciscan and the sediment sites observed for weak motion disappears at acceleration levels higher than about 0 1 to 0 3 g if this is due to the nonlinear response of the sediment sites it is in the range expected from geotechnical engineering studies

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

seismic tomographic interpretation of paleozoic sedimentary sequences in the southeastern north sea seismic wide angle data were recorded to more than 300 km offset from powerful airgun sources during the mona lisa experiments in 1993 and 1995 to determine the seismic velocity structure of the crust and uppermost mantle along three lines in the southeastern north sea with a total length of 850 km we use the first arrivals observed out to an offset of 90 km to obtain high resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust seismic tomographic traveltime inversion reveals 2 8 km thick paleozoic sedimentary sequences with p wave velocities of 4 5 5 2 km s these sedimentary rocks are situated below a mesozoic cenozoic sequence with variable thickness 2 3 km on the basement highs 2 4 km in the horn graben and the north german basin and 6 7 km in the central graben the thicknesses of the paleozoic sedimentary sequences are 3 5 km in the central graben more than 4 km in the horn graben up to 4 km on the basement highs and up to 8 km i

a predictive equation for vertical to horizontal response spectral ratios in northern iran abstract the importance of the vertical component of ground motion in damage infliction on a variety of structural systems has been shown in recent years however the available models for ground motion prediction equations gmpes for this component of earthquakes are limited and most of the existing gmpes have been specifically developed for the horizontal component of ground motion alternatively in some cases it is proposed to scale the horizontal spectrum of the earthquake to the vertical one using vertical to horizontal response spectral ratios vhsrs in this work the applicability of some global and regional vhsr models for northern iran are evaluated using several existing statistical approaches the results of these evaluations show inadequate correlation between these models and the observed vhsrs in this region consequently a new vhsr model has been proposed to convert the horizontal earthquake spectrum to the vertical one in the studied region in order to determine the regression coefficients for the proposed vhsr model some 712 three component records with distances less than 300 km from the source from 79 earthquakes with the magnitude ranging from m w 4 1 to 7 3 were used regression coefficients for peak ground acceleration and pseudospectral acceleration for 5 damped systems are determined using a random effect approach a series of comparative studies on the proposed model with respect to the existing vhsrs was performed using the median residuals for the spectral periods in the 0 1 3 s range the results of such investigation show significant reduction of the variability for the proposed model at least 50 compared with the other vhsrs online material database of strong motion records

seismic velocity structure of a large mafic intrusion in the crust of central denmark from project estrid abstract the origin of regional sedimentary basins is being investigated by the estrid project explosion seismic transects around a rift in denmark this project investigates the mechanisms of the formation of wide regional basins and their interrelation to previous rifting processes in the danish norwegian basin in the north sea region in may 2004 a 143 km long refraction seismic profile was acquired along the strike direction of a suspected major mafic intrusion in the crust in central denmark the data confirms the presence of a body with high seismic velocity 6 5 km s extending from a depth of 10 12 km depth into the lower crust there is a remarkable moho relief between 27 and 34 km depth along this new along strike profile as based on ray tracing modelling of pmp reflections the lack of pmp reflections at a zone of very high velocity in the lowest crust 7 3 7 5 km s suggests a possible location of a feeder channel to the batholith the presence of volcanic rocks of carboniferous permian age above the intrusion mafic batholith suggests a similar age of the intrusion an older obliquely crossing profile and two new fan profiles deployed perpendicular to the main estrid profile show that the batholith is about 30 40 km wide the existence of this large mafic batholith supports the hypothesis that the origin of the danish norwegian basin is related to cooling and contraction after intrusion of large amounts of mafic melts into the crust during the late carboniferous and early permian the data and interpretations from project estrid will form the basis for subsidence modelling tentatively we interpret the formation of the danish norwegian basin as a thermal subsidence basin which developed after widespread rifting of the region

the flushing of two deep sea basins southern california borderland a time series of water temperature salinity and nutrient measurements has been made in san pedro and san nicolas basins of the southern california borderland between i977 and 1988 these basins exhibit temporally coincident changes in temperature and nutrient content defining a period of basin flushing 1982 1984 and a period of stagnation 1984 1987 during the flushing period cooler oxygenand no rich water replaces warmer oxygenand no depleted bottom water flushing produces a decrease of 0 2 c in the average temperature of san pedro basin bottom water 790 900 m and an increase in the average oxygen content by 12 pm these values are 0 i and 3 for san nicolas basin 1 400 l 800 m the residence time of water in san pedro basin during the flushing period is 12 6 months and j t2 months in san nicolas basin a box model approach constrained by the time series data for the stagnation period was used to determine values of the effective vertical eddy diffusivities for the 790 m horizon in san pedro basin and 1 400 m horizon in san nicolas basin 1 3 0 4 and 9 9k3 4 cm sk respectively

deep seismic investigation of crustal extensional structures in the danish basin along the estrid 2 profile summary the crust and uppermost mantle in the danish basin are investigated by modelling the p wave velocity distribution along the north south trending seismic profile estrid 2 seismic tomography and ray inversion modelling demonstrate a variable depth to the top of the crystalline crust from 10 km in the northern part of the profile to 2 km depth in the southernmost part the crystalline crust shows very high p wave velocity in the central part of the profile with 6 7 km s 1 at depths as shallow as 12 km and 7 3 7 5 km s 1 in the lowermost crust these values confirm previous results obtained along the orthogonal estrid 1 profile and the eugeno s profile 2 this high velocity zone in the middle to lower crust is interpreted as a mafic intrusion which explains a positive gravity anomaly of 50 mgal silkeborg gravity high the total length of the intrusion is at least 80 km in the east west direction and 25 35 km in the north south direction the estimated thickness of the intrusion from its top to the moho level is 18 20 km which gives a total minimum volume of 40 50 000 km3 the reflectivity properties of the moho discontinuity are variable along the profile below the intrusion the pmp signal is very weak due to the small velocity contrast between the lowermost crust 7 4 km s 1 and uppermost mantle 7 6 7 7 km s 1 the main moho reflection has a reverberative character to the south of the intrusion this feature is interpreted by layering at the moho level possibly due to magmatic underplating the occurrence of a large crustal mafic intrusion associated with magmatic underplating may be related to extensional transtensional tectonism in the tornquist fan area in the late palaeozoic the extensional event probably caused the opening of a plumbing system for intrusion of mantle derived magma into the crust the ascending magma may have been injected at upper middle crustal levels and during the late phases of the development squeezed laterally along the moho

magmatic underplating beneath the emeishan large igneous province south china revealed by the comgra elip experiment abstract because of the abundant geological geochemical and geophysical studies conducted on the emeishan large igneous province elip in south china the permian mantle plume model associated with this region is widely accepted furthermore the dome shaped structure related with this plume has been determined with success by sedimentological data and gravity stripping although the sediment thickness upper crust moho depth and the lithosphere asthenosphere boundary lab are well constrained by active and passive source seismological results the density anomaly in elip is still a poorly constrained issue that needs further attention with the aim especially to understand the impact on surface of the magmatic processes that originated in the deep mantle we performed the comgra elip gravity experiment across this region using a stripping method we determined the residual gravity in elip and surrounding areas the residual gravity reaches a maximum value of 150 mgal in the inner zone of elip and its strength decreases gradually when measuring from the inner zone to the middle and outer zones combining active and passive seismic results and the least squares variance analysis method we propose a strong density contrast of 0 2 g cm3 density of 3 14 g cm3 for the 15 to 20 km thick igneous layer accreted at the base of the crust as evidence of crustal underplating in elip to explain the present day residual gravity anomaly

geophysical characteristics of the tornquist fan area northwest trans european suture zone indication of late carboniferous to early permian dextral transtension

a late paleozoic sill complex and related paleo topography in the eastern north sea analyzed using 3d seismic data abstract in this paper we utilize large igneous intrusions as a key to a detailed analysis and understanding of the late paleozoic evolution of the ringkobing fyn high an important structural element in the north west european craton the study takes advantage of high quality 3d seismic data and boreholes to map the geometry and lateral distribution of intrusive sills cross cutting the sedimentary strata at a low angle transgressive sills our analysis shows that the transgressive sills most likely sourced the vast extrusion of volcanics which covered most of the early permian northern basin and which is associated to the skagerak centered large igneous province sclip furthermore a geometrical analysis of the sills demonstrates that the magmatic source for the sills was located se of the studied area suggesting a correlation with geophysically inferred lower crust intrusions hence we are in this study able to constrain the full magmatic system from the lower crust intrusions to the surface volcanics intrusion of the sills occurred prior to an early permian faulting event which created rotated fault blocks outlining the present ringkobing fyn high the sills exposed for erosion at the crest of the footwall in turn controlled the late permian paleo topography and the distribution of the zechstein evaporites due to the fact that they are harder to erode hence we are able to demonstrate a topography controlled thickness variation of the zechstein evaporites the study furthermore emphasizes that an understanding of the deepest parts of the north sea basin is crucial when evaluating the potential for yet unrecognized hydrocarbon plays

the oslo rift a review the tectonomagmatic history of the oslo rift may be subdivided into 5 main periods stage 1 300 ma development of a shallow depression stage 2 300 295 ma roughly simultaneous onset of widespread basalt volcanism b1 and vertical movement along nnw sse to n s trending faults stage 3 295 275 ma main rifting period accompanied by volcanism dominated by rhomb porphyry lavas latites stage 4 275 240 ma change of magmatic style from basaltic shield volcanism to central volcanoes of mixed compositions many of which went through caldera collapses intrusion of composite batholiths of intermediate to granitic compositions stage 5 240 ma dike intrusions may have continued into triassic time both the crust and total lithosphere under the rift are thinned relative to the precambrian basement on both sides a 12 km thick high density and high velocity body occupies the lower crust along the rift axis and extends under the eastern and western rift shoulder petrological and geochemical data imply that this massive layer represents dense cumulates and gabbroic rocks formed from mantle derived magmas in deep crustal magma chambers two mantle sources one nearly undepleted age corrected nd of about 1 and sr of 10 to 15 the other mildly depleted nd of about 4 sr of 10 contributed melts to the oslo rift magmatism the two sources are interpreted as different parts of a heterogeneous upper mantle which before the rifting event belonged to the subcontinental lithosphere on their way to the surface the mantle derived magmas were retained in deep crustal magma chambers where they underwent extensive fractional crystallization some also suffered moderate contamination anatectic melts and melts formed by mixing between mantle derived and anatectic melts gave rise to syenitic and granitic intrusions

layered crust mantle transition zone below a large crustal intrusion in the norwegian danish basin abstract the crust and uppermost mantle below the large positive gravity anomaly in the central part of the norwegian danish basin the silkeborg gravity high sgh is investigated using controlled source seismic data a more than 80 km long and 20 km thick intrusion is interpreted the seismic velocity within the intrusion varies from 6 8 km s at the top 12 km depth to 7 2 7 7 km s at the moho level 30 31 km depth the characteristics of the moho reflectivity vary along the profile below the central part of the intrusion the moho reflectivity is very weak due to a small velocity contrast between the lowermost crust 7 7 km s and the uppermost mantle 7 9 8 0 km s the seismic data show a ringing moho below the western part of the intrusion the coda trailing the main pmp reflection is about 1 0 s long and is composed of 4 5 wavelets we demonstrate that this feature may be explained by a layered transition zone between 30 and 35 km depth where high velocity layers of mantle affinity 7 9 8 05 km s alternate with layers of typical lower crustal velocity 6 7 7 3 km s the characteristics of this layering which causes the pmp coda are modelled by matching synthetic seismograms to the observed data synthetic seismograms calculated using the reflectivity method for 1d models constrain the nominal layer thickness to 100 500 m waveform modelling in 2d constrains the layered internal structure of the transition zone and the length of the heterogeneous zone along the profile we interpret the layered crust mantle transition zone as solidified melts of mantle affinity which were intruded into the lowermost crust the layered zone is proposed to be associated with the extensional tectonism that occurred in the area in late carboniferous early permian which also caused the large crustal intrusion the subsequent cooling may have initiated the formation of the danish basin

simulation of strong ground motion in northern iran using the specific barrier model summary in this study based upon the calibrated specific barrier model sbm against the latest available strong motion data ground motion prediction equations for soil and rock sites in northern iran are developed the sbm may provide the most complete simple and self consistent description of the faulting process which is applicable in both near fault and far field regions consequently the sbm may provide consistent ground motion simulations over the entire necessary frequency range and for all distances of engineering interests to determine source parameters in this study we used 163 three component records of 32 earthquakes with magnitude ranging from mw 4 9 to 7 4 in northern iran in the database records with hypocentral distances less than 200 km are chosen and only earthquakes whose moment magnitude estimates are available have been used furthermore using the best available information recording sites are classified into two main geologic categories rock and soil because of the lack of site amplification information in the most regions of the world including iran we used the h v ratio method for estimating the site amplification moreover the kappa factor that shows diminishing the high frequency amplitude is determined in this study two data sets are considered for determining the source parameters g and l and the h v ratio and the kappa factor only s wave part of signals is used in each analysis regression analysis is performed using random effects method that considers both interseismic event to event and coseismic within event variabilities to effectively deal with the problem of weighting observations from different earthquakes the residuals are controlled against available northern iranian strong ground motion data to verify that the model predictions are unbiased and that there are no significant residual trends with magnitude and distance at first it is assumed that no sign of self similarity breakdown is observed between the source radius and its seismic moment after controlling the results the modified sbm should be used as some deviations have been observed to verify the robustness of the results the number of observations is changed by removing various randomly selected data sets from the original database which results in unchanged results of the model stochastic simulations are then implemented to predict peak ground motion and response spectra parameters the stochastic sbm predictions are in relatively good agreement with other available attenuation relationships proposed for iran europe and middle east it has been shown that the proposed sbm of this study provides unbiased ground motion estimates over the entire frequency range of most engineering applications it provides a reliable and physically realistic yet computationally efficient way to model strong ground motions

crustal structure along the egt profile across the tornquist fan interpreted from seismic gravity and magnetic data abstract the tornquist fan is a northwestward widening splay of late carboniferous to early permian fault zones in the danish area which emanates from the teisseyre tornquist zone in the baltic sea it is located over an area of deep sedimentary basins around denmark in the southwestern corner of the former baltica plate this paper presents an integrated model of seismic velocity density and magnetic properties along the egt profile across the tornquist fan between southern sweden and northern germany the model shows distinct features that may be related to the main tectonic events in the area the caledonian crustal suture between baltica and eastern avalonia is interpreted from changes in physical parameters at all crustal levels most noticeable as an abrupt lateral change in seismic velocity in the lowest crust at moho level from 6 9 km s in baltica to only 6 4 km s in eastern avalonia thick sedimentary successions beneath the mesozoic sequence are interpreted as palaeozoic sedimentary rocks which may have been deposited on the southern margin of the baltica plate in a deep caledonian foreland basin and in late carboniferous early permian rifts and extensional basins rift related magmatism is indicated by the presence of zones of high velocity density and magnetic susceptibility as well as strong remanent magnetization thermal subsidence following the emplacement of these bodies may be the origin of regional subsidence of the danish and north german basins of late paleozoic and mesozoic age late cretaceous to early cenozoic inversion of basin structures is detected at the sorgenfrei tornquist zone stz in the transition between shield and basin areas the stz coincides with a pronounced change in crustal thickness and the southwestern edge of a major magmatic intra crustal body significant abrupt changes in moho depth exist along the profile 26 30 km beneath the deep basins ca 35 km beneath the ringkobing fyn basement high and 48 km beneath the baltic shield around the sorgenfrei tornquist inversion zone the basement in the tornquist fan area is of proterozoic age the moho topography indicates strong thinning of the crust during its phanerozoic evolution the model supports the hypothesis that existing tectonic structures and weakness zones are continuously being reactivated during subsequent tectonic activity

moho topography and lower crustal wide angle reflectivity around the tesz in southern scandinavia and northeastern europe abstract the moho topography is strongly undulating in southern scandinavia and northeastern europe a map of the depth to moho shows similarities between the areas of the teisseyre tornquist zone ttz in poland and the fennoscandian border zone fbz which is partly coinciding with the sorgenfrei tornquist zone stz in denmark the moho is steeply dipping at these zones from a crustal thickness of approximately 32 km in the young palaeozoic platform and basin areas to approximately 45 km in the old precambrian platform and baltic shield the moho reflectivity pmp waveform in the polonaise 97 refraction wide angle seismic data from poland and lithuania is variable ranging from sharp to strongly reverberating signals of up to 2 s duration there is little or no lower crustal wide angle reflectivity in the thick precambrian platform whereas lower crustal reflectivity in the thin palaeozoic platform is strongly reverberating suggesting that the reflective lower crust and upper mantle is a young phenomena from stochastic reflectivity modelling we conclude that alternating high and low velocity layers with average thicknesses of 50 300 m and p wave velocity variations of 3 4 of the background velocity can explain the lower crustal reflectivity sedimentary layering affects the reflectivity of deeper layers significantly and must be considered in reflectivity studies although the reverberations from the deeper crust cannot be explained by the sedimentary layering only the reflective lower crust and upper mantle may correspond to a zone that has been intruded by mafic melts from the mantle during crustal extension and volcanism

interpretation in statu nascendi of seismic wide angle reflections based on eugeno s data abstract in a new interpretation approach seismic wide angle data are analysed in statu nascendi i e in the state where the interpretational characteristics of the signals are born the approach is complementary to other interpretation methods such as kinematic interpretation of velocity models seismogram sections are qualitatively compared and classified in order to perform the analysis as close as possible to the seismic wavefield correlation of seismic phases and selection of representative reflection characteristics of the phases are required for the analysis the approach has been tested on the methodologically homogeneous eugeno s data set from the danish and surrounding areas together with other data the classifications of intra crustal and pmp reflections show clear regionalizations which correlate with the main geological tectonic and orogenic units the reflection characteristics of the thin crust below the deep basins in denmark the tornquist fan are different from the thick crust of the baltic shield and the ringkobing fyn high the character of moho reflections is ringing in the basin area as opposed to sharp in the latter areas and intra crustal reflections are stronger and more consistent in the basin area than in the latter areas

seismic images of caledonian lithosphere scale collision structures in the southeastern north sea along mona lisa profile 2 abstract the unexposed suture between baltica and eastern avalonia is imaged by coincident normal incidence reflection and wide angle reflection refraction seismic data of the mona lisa project we present new results of the upper lithospheric seismic structure from the n s striking profile 2 across the caledonian deformation front which represents the crustal collision suture between baltica and eastern avalonia that formed after closure of the tornquist sea during the caledonian orogeny in late ordovician times three different crustal types are identified with great similarities to the nearby profile 1 1 a three layered crust typical of shields to the north 2 a transitional crust suture zone in the central part and 3 a two layered crust of caledonian origin to the south characterized by very low velocities throughout the crust the crustal thickness varies from 38 35 km under the northern margin of the ringkobing fyn high baltica crust to 28 27 km beneath the north german basin in the caledonian crust to the south the suture zone is imaged by s dipping crustal reflections from 1 9 to 10 6 s two way travel time twt over a horizontal distance of 70 km within the transitional crust the reflection suture zone terminates in a 60 km wide reflective lens with velocities of 6 6 6 8 km s in the lowermost crust the reflective lens may be interpreted as a remnant of oceanic or island arc crust that was accreted to the leading edge of baltica during closure of the tornquist sea alternatively the reflective lens may represent an indentor of baltica crust into the avalonian terrane the change in lower crustal reflectivity and the abrupt transition from a three to a two layered crust further south suggest that the trans european fault and the elbe lineament continue into the north sea the upper mantle reflectivity is dominated by bands of strong amplitude s dipping reflections from 13 5 to 21 8 s twt and a weaker band of n dipping reflections from 12 to 16 s twt reversed wide angle refractions and reflections indicate the presence of a s dipping high velocity layer 8 65 8 8 km s in the uppermost mantle the sub moho high velocity layer partially coincides with the strong s dipping normal incidence mantle reflections we propose that the s dipping mantle structure may represent a late caledonian or late carboniferous to early permian mantle shear zone

lower crustal intrusions beneath the southern baikal rift zone evidence from full waveform modelling of wide angle seismic data abstract the cenozoic baikal rift zone brz is situated in south central siberia in the suture between the precambrian siberian platform and the amurian plate this more than 2000 km long rift zone is composed of several individual basement depressions and half grabens with the deep lake baikal at its centre the best baikal explosion seismic transect project acquired a 360 km long deep seismic refraction wide angle reflection profile in 2002 across southern lake baikal the data from this project is used for identification of large scale crustal structures and modelling of the seismic velocities of the crust and uppermost mantle previous interpretation and velocity modelling of p wave arrivals in the best data has revealed a multi layered crust with smooth variation in moho depth between the siberian platform 41 km and the sayan baikal fold belt 46 km the lower crust exhibits normal seismic velocities around the rift structure except for beneath the rift axis where a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s is observed reverberant or ringing reflections with strong amplitude and low frequency originate from this zone whereas the lower crust is non reflective outside the rift zone synthetic full waveform reflectivity modelling of the high velocity anomaly suggests the presence of a layered sequence with a typical layer thickness of 300 500 m coinciding with the velocity anomaly the p wave velocity of the individual layers is modelled to range between 7 4 km s and 7 9 km s we interpret this feature as resulting from mafic to ultra mafic intrusions in the form of sills petrological interpretation of the velocity values suggests that the intrusions are sorted by fractional crystallization into plagioclase rich low velocity layers and pyroxene and olivine rich high velocity layers the mafic intrusions were probably intruded into the ductile lower crust during the main rift phase in the late pliocene as such the intrusive material has thickened the lower crust during rifting which may explain the lack of moho uplift across southern brz

boundary versus internal diapycnal mixing in stratified natural waters using the fluorescent dye uranin tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in lake alpnach central switzerland during 1992 1995 a first experiment involved injecting the tracer from a point source into the center of the hypolimnion that part of the lake below the surface mixed layer an in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud allowing rates of diapycnal diffusivity to be determined as long as the tracer was confined to the interior water region the diapycnal diffusivity was relatively small however after the tracer cloud had reached the lake boundary the diapycnal diffusivity increased by approximately one order of magnitude in a second experiment the tracer was released near the sediment water interface in this case the dynamics of vertical tracer spreading were opposite during the first few hours after tracer release diapycnal diffusivities were large subsequently decreasing as the tracer cloud drifted away from the lake boundary basin wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity temperature depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization the results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region

global comparisons of earthquake source spectra a key question in earthquake seismology is whether earthquake sources in different tectonic regions are functionally equivalent in terms of radiated ground motion this article compares the apparent earthquake source radiation for six different regions japan mexico turkey california british columbia b c western canada and eastern north america ena the source path and site effects were consistently separated to the extent possible to allow interregional comparisons of apparent source radiation large fourier spectra databases were created for both horizontal and vertical components for earthquakes with magnitude between 2 5 and 7 5 regional parameters characterizing source path and site properties including crustal and near surface site amplifications were investigated to isolate apparent source spectra based on the vertical component spectra at a reference distance of 1 km a new magnitude scale m 1 was defined from the spectral level at 1 hz the magnitude scale m 1 is a natural complement to existing magnitude scales that measure the low frequency and high frequency spectral amplitudes moment magnitude m and high frequency m hf respectively in all regions the apparent source spectra for small to moderate earthquakes m 6 show good agreement with the single corner brune 1970 1971 point source model 2 spectrum suggesting a stress parameter of about 100 bars 10 mpa a two corner source model better matches the spectra for large magnitude earthquakes m 6 especially at intermediate frequencies for small to moderate events the two source models are nearly equal apparent source spectra from small to moderate earthquakes e g m 1 3 5 6 5 suggest a general similarity between the different tectonic regions studied although minor discrepancies appear in some cases there are no noticeable regional characteristics no evident depth effects were found on the apparent source spectra manuscript received 1 april 2001

calibration of the specific barrier model to earthquakes of different tectonic regions the specific barrier model proposed and developed by papageorgiou and aki 1983a b 1985 provides the most complete yet parsimonious self consis tent description of the faulting process it applies both in the near fault and in the far field region thus allowing for consistent ground motion simulations over the entire frequency range and for all distances of engineering interest the model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions mainly east ern north america events interplate regions and regions of tectonic extension spu dich et al 1999 database the ensemble average value of a key parameter of the specific barrier model the local stress drop dr l i s 161 bars for interplate earth quakes 114 bars for extensional regime earthquakes and 180 bars for intraplate earthquakes the high frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self similar scaling the deviation is most likely caused by the effective source area and or irregularities in the rupture kinematics we account for their overall effects through a high frequency source complexity factor f in the source spectrum of the specific barrier model as a result inter and intraplate source spectra show similar high frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger mag nitudes the interplate soil residuals show clear signs of nonlinear site response whereas only slight signs of such nonlinearity are observed for the extensional data set the regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic yet computationally efficient way to model strong ground motions with implications for seismic hazard and risk analysis online material strong motion station and event station pair information

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

what we can and cannot learn about earthquake sources from the spectra of seismic waves earthquake sources are commonly viewed as shear dislocations this imposes distinct limitations on what source parameters can be realistically determined from radiated shear wave spectra first the slip velocity on the fault is the real parameter that controls the strength of the high frequency radiation it can be directly determined from acceleration spectra by fitting their high frequency level second the relationship between corner frequency of the spectrum and the radius of the source is fundamentally unclear as a result the source dimensions cannot be accurately determined from the spectra such an estimate would be as accurate as any other informed guess third the stress drop only serves as a proxy for the source radius in the relationship between the radius and the corner frequency it thus cannot be reliably determined from the spectra the quantity usually obtained from the spectra and referred to as the stress drop is a poorly defined parameter that may bear little relevance to the actual stresses acting on faults this parameter has little meaning unless converted to the maximum slip velocity which is the only quantity that can be accurately determined from the spectra the typical value of stress drop of 100 bars established from the spectra of california events may imply that the typical slip velocities have been on the order of 0 5 m sec although it is more accurate to determine slip velocities directly from the spectra

a deliberate tracer experiment in santa monica basin the mixing of heat and chemical constituents across density strata in the ocean plays a major role in ocean circulation and in the response of the climate to thermal and chemical perturbations we are developing a tracer technique which in conjunction with fluid dynamical measurements promises to improve our understanding and our estimates of such diapycnal mixing in a prototype tracer experiment in santa monica basin 50km west of los angeles two tracers sulphur hexafluoride sf6 and per fluorodecalin pfd have been injected on an isopycnal surface near the centre of the basin after 50 days the tracers had mixed along the isopycnal surface to nearly every part of the basin although relatively little had penetrated to the basin walls the diapycnal spreading of the tracer distributions during this first stage of the experiment yielded an apparent eddy diffusivity of 0 33 0 08 cm2s 1 at the ambient density gradient of 4 0 0 5 10 9g cm 4

seismicity parameters and spatially smoothed seismicity model for iran abstract in the present study seismicity parameters seismic activity value and maximum regional magnitude of the iranian plateau are computed for sites equally distributed all over the country on a grid of 1 1 decimal degree the most complete available catalog including historical and instrumental earthquakes of the plateau from 734 b c to a d 2011 is first prepared from numerous resources earthquakes within a 200 km buffer surrounding each grid point are selected and historical and instrumental parts are more accurately specified based on the completeness test of stepp 1972 the instrumental part is also analyzed to identify the various completeness intervals and the minimum completeness magnitude for each interval is determined by the maximum curvature method next the seismicity parameters are calculated from uncertain and incomplete data by the maximum likelihood procedure of kijko and sellevoll 1989 1992 and kijko 2004 after removing aftershocks and foreshocks the spatial variation of seismicity parameters is illustrated in the form of contour maps over the whole iranian plateau for the first time the value corresponding to the magnitudes m w 4 varies over the plateau from 0 7 to 23 4 and the highest values are located in the zagros and alborz mountains confirming that a large portion of the seismic deformation in the plateau is accommodated in these regions the estimated values for all points lie between 1 3 and 2 9 this spatial distribution of values demonstrates the crustal heterogeneity over the plateau low values in northeast and east iran also indicate high probability of large earthquake occurrence it is observed that the estimated m max is between m w 6 5 and 8 and hence most of that part of the country may experience large earthquakes the obtained results are important for two aspects 1 new seismotectonic models could be proposed by combining the presented maps with geological geodetic and tectonic data and 2 these results together with a detailed geological data describing potential seismogenic sources can be used directly to evaluate ground motion hazard for engineering design and generate seismic hazard maps an approximate and gross estimate of peak ground acceleration pga level at bedrock for 2 and 10 probabilities of exceedance in a 50 year period is also computed using an area source model characterized by the presented seismicity parameters the regional distribution of the estimated pga sheds a new light on facilitating risk management and allocating national resources for mitigating potential losses at a country based level online material table of completeness magnitude and seismicity parameters

geophysical evidence for early permian igneous activity in a transtensional environment denmark abstract integrated interpretation of gravity magnetic and seismic data in the area of the strong silkeborg gravity high in central denmark has led to a structural geological model involving a transtensional rift feature which probably formed in connection with permo carboniferous wrench faulting and the development of the oslo horn graben system reinterpretation of the deep seismic data from profile 2 of the eugeno s project in the area of the silkeborg gravity high detected a new thin high velocity layer 6 25 km s at about 7 km deep within the palaeozoic sedimentary sequence in the crystalline basement a separate body of high velocity 6 9 7 0 km s was found at 11 km deep beneath this body the moho reaches its shallowest position in the area the seismic results compare well with an interpretation based on magnetism of a shallow volcanic or subvolcanic layer at a depth of 6 8 km this layer shows strong remanent and induced magnetization with a southward inclination of about 10 gravity reinterpretation of the area allows the separation of an upper body of density contrast 0 1 g cm3 from a lower body of density contrast 0 2 g cm3 the upper body roughly coincides with the magnetic body the lower body the major one coincides with the deep seismic body and it is responsible for the main gravity anomaly in the area

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

variability in two deep coastal basins santa monica and san pedro off southern california time series of midbasin hydrographic samples and of an array of moored temperature velocity sensors are used to examine subtidal to interannual scale variability in two 900 m deep basins off the southern california coast the deepest sill that allows entry into the basins is at 740 m and the two basins santa monica and san pedro are separated by a sill about 40 m high the mean flow 40 m above and 60 m below the 740 m sill depth is in the counterclockwise direction and the magnitude is 0 5 1 0 cm s 1 the data indicate that the waters at deeper levels of the basins are neither quiescent at one extreme nor are they filled with random noise at the other extreme rather at all scales examined the variability is significant and much of it is spatially coherent the amplitude of the subtidal velocity fluctuations is 4 cm s 1 almost an order of magnitude greater than that of the mean flow the amplitude of the subtidal temperature fluctuations is 0 1 c at 700 m and 0 05 c at 800 m the temperature variance is roughly a factor of 2 smaller at midbasin than on the basin perimeter this is not the case with the velocity variance which is generally greatest at midbasin and on the coastal edges of both basins much of the subtidal variability in both temperature and velocity appears to be associated with topographic waves that travel counterclockwise around the pair of basins the observed period of the waves 10 20 days is roughly consistent with that predicted by a barotropic model of free waves in an elliptical basin mysak 1985 comparison of time series of currents in the upper 200 m water column with those in the lower water column suggests that the waves are forced by the circulation in the upper water column which is directed over rather than around the basins seasonal variability was observed in both temperature and velocity fields as deep as 800 m i e below the depth of the deepest sill along the perimeters of both basins and at midbasin in santa monica but not in san pedro temperature increases and salinity and density decrease from spring to fall consistent with the seasonal development of the poleward flowing california countercurrent in the upper water column the seasonal cycle of water properties has significant spatial variability over the basins the amplitude is a factor of 2 greater on the seaward side of santa monica basin than at midbasin and on its coastal edges and on the edges of san pedro basin the variance of the subtidal velocity and temperature fields also exhibit a seasonal signal maximum variance occurs during fall minimum variance occurs during spring interannual variability dominates the 4 year time series of water properties of the near bottom water in each basin and differs somewhat between the two basins the interannual variability is dominated by events associated with renewal of basin bottom water two such events were identified a minor one in 1987 and a major one in 1988 each beginning in may of that year in both cases the actual renewal occurs in less than a month and the most rapid return to near normal conditions occurs over a period of about 3 5 months

three dimensional crustal structure beneath the tor array and effects on teleseismic wavefronts abstract the temporary seismic station array tor was designed to study the lithosphere asthenosphere system across the northwestern part of the trans european suture zone tesz by teleseismic tomography teleseismic wavefronts when propagating through complex crustal structure undergo severe distortion that may result in travel time residual anomalies of significant amplitude the inversion of teleseismic travel time residuals for deep structures without accounting for such crustal related anomalies may erroneously map these travel time anomalies into features at greater depth in this study we apply a three dimensional 3 d technique to estimate effects of a priori known 3 d crustal structure on travel times of teleseismic waves observed at the tor seismic array across the tesz to correct for these effects in future tomographic studies a uniform 3 d crustal model is developed by use of published two dimensional crustal models from previous active seismic surveys the parameterization of this 3 d crustal model is designed to adequately represent those crustal structures that mostly influence the propagation of teleseismic wavefronts the 3 d model includes lateral variation in velocity structure moho topography and large and deep sedimentary basins the teleseismic forward problem for this local 3 d model is solved by calculation of travel times to the base of the model using a standard whole earth model and by subsequent propagation of spherical wavefronts using finite difference methods travel time calculations for an event near japan reveal significant lateral variations in the range between 0 3 s and 0 5 s due to crustal structures being able to obtain the full travel time field at the surface of the model has the additional advantage of improving the identification and timing of seismic phases observed at the tor seismic array

danish basin subsidence by triassic rifting on a lithosphere cooling background i report here the first quantitative study of the entire post palaeozoic subsidence history in the ensemble of north west european sedimentary basins data obtained from wells suggests that the late permian through mesozoic subsidence of the danish basin is a result of lithosphere wide cooling following an igneous event of late carboniferous to early permian age this cooling subsidence was superposed by major triassic rifting and minor mid jurassic uplift both events apparently not having significant thermal consequences the danish basin did not experience the late jurassic to early cretaceous rifting and subsequent cooling which were so important in the development of the central north sea rifts this result suggests that a reappraisal of north sea tectonics should look for pre jurassic subsidence

integrating samplers for the deep sea two new types of mechanical integrating samplers have been tried in the deep sea one driven by a constant force spring the other by a spring driven hydraulic system the samplers are triggered simultaneously with the niskin bottle to which they are attached and fill in about 90 min they are useful for sampling poorly mixed tracers and have been used successfully in tracer release experiments at 800 m depth in santa monica basin in 1985 and to depths of 1900 m in santa cruz basin in 1988

potential field modelling of the baltica avalonia thor tornquist suture beneath the southern north sea magnetic anomaly maps of the trans european suture zone tesz highlight the contrast between the highly magnetic crust of baltica and the less magnetic terranes to the sw of the suture although the tesz is imaged on gravity maps anomalies related to postcollisional rifting and reactivated rift structures tend to dominate seismic and potential field data have been used to construct 212 d crustal models along three profiles crossing the baltica avalonia suture in the southern north sea sns the first of these models lies along a transect assembled from reflection line geco snst 83 07 and refraction profile eugeno s 2 the other two models are coincident with mona lisa profiles 1 and 2 additional structural information and density information for the cover sequence is available from released wells while magnetic susceptibility values are compatible with values measured from borehole core samples magnetic anomalies related to the suture are interpreted as due to magnetic baltican basement of the ringkobing fyn high dipping sw beneath nonmagnetic avalonian basement underlying the western part of the sns low amplitude long wavelength magnetic anomalies occurring outboard of the suture are interpreted as due to a mid crustal magnetic body possibly a buried magmatic complex this might represent the missing arc related to inferred southward subduction of the tornquist sea or an exotic element emplaced during the collision between avalonia and baltica the present model supports an imbricated structure within baltica as indicated by the latest reprocessing of the mona lisa seismic data

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

simulation of ground motion in the zagros region of iran using the specific barrier model and the stochastic method abstract physically based ground motion prediction equations for soil and rock sites in the zagros region have been developed based on the specific barrier model sbm used within the context of the stochastic model instead of direct time domain simulation random vibration theory was used to estimate measures of peak motion in terms of the pseudospectral velocity of anelastic harmonic oscillator with 5 viscous damping to avoid the uncertainties calibration of the source model uses a database of carefully selected strong motion data without ambiguity about the site condition therefore only rock sites are selected for determining source parameters also to avoid any inconsistencies caused by magnitude conversion formulas we restricted the dataset only to events with available moment magnitudes regression analysis is performed using the random effects model that considers both interevent and intraevent variabilities to effectively deal with the problem of an unequal number of records from different earthquakes no sign of self similarity breakdown is observed between the source radius and its seismic moment the local and global stress drops derived for the zagros region 39 and 116 bars respectively are more consistent with the values obtained by other authors for an interplate regime than the values for an intraplate region however from the viewpoint of source heterogeneity as the ratio of the stress drops is an indicator of the complexity of the source and heterogeneity of slip on the fault the zagros events which have a stress drop ratio of about three are more homogeneous than other interplate events stochastic simulations are then implemented to predict peak ground motion and response spectra parameters for rock and soil site conditions online material catalog tables of earthquakes and attenuation tables

seismic structure across the caledonian deformation front along mona lisa profile 1 in the southeastern north sea abstract seismic data from the mona lisa marine and onshore north sea acquisition for lithospheric seismic analysis project in the southeastern north sea image the caledonian deformation front cdf which is the collisional suture between baltica to the north and east and avalonia to the south and west the n s trending mona lisa normal incidence reflection profile 1 was recorded to 26 s twt coincident wide angle data were acquired on nine ocean bottom hydrophones and several onshore mobile seismographs along and off the profile the model of compressional seismic velocity shows three different crustal types a a typical three layered shield type crust below the ringkobing fyn high to the north b a highly complex transitional crust in the central part and c a two layered crust of caledonian origin to the south sharp and strong normal incidence and wide angle reflections from moho were recorded south of the caledonian deformation front in contrast to less distinct reflections further north s dipping crustal reflections from 4 to 11 s twt over 70 km horizontal distance terminate at moho and coincide with a change in the seismic velocity structure this indicates northward obduction of avalonian crust non migrated normal incidence seismic sections show crossing weak n dipping and stronger s dipping reflections to 20 s twt from the uppermost mantle we propose a tectonic model where the closure of the tornquist sea took place along a n dipping subduction zone which was later overprinted by a late or post caledonian s dipping shear zone sub moho velocities are 7 8 7 9 km s under 34 35 km thick baltica crust and 8 1 8 3 km s under 25 26 km thick caledonian crust the sub horizontal moho across the caledonian collision zone implies late or post caledonian re equilibration of the seismological moho we interpret the low velocity upper mantle 7 8 8 1 km s to the north as former baltica lower crust in eclogite facies after pressure induced metamorphism as a result of lithospheric flexure during the caledonian orogeny these rocks today appear as upper mantle that was uplifted to their present position during the middle devonian collapse of the north german polish caledonides