damped regional scale stress inversions methodology and examples for southern california and the coalinga aftershock sequence 1 we present a new focal mechanism stress inversion technique to produce regional scale models of stress orientation containing the minimum complexity necessary to fit the data current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea this procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor to remove these artifacts while retaining any stress variations that are strongly required by the data we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas this method is conceptually similar to other geophysical inverse techniques that incorporate damping such as seismic tomography in checkerboard tests the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion while resolving sharper true stress rotations than a simple smoothed model or a moving window inversion we show an example of a spatially damped stress field for southern california the methodology can also be used to study temporal stress changes and an example for the coalinga california aftershock sequence is shown we recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field

moment tensor inversion of small earthquakes in southwestern germany for the fault plane solution summary the amplitudes of direct p and s waves as well as p and other deep crustal body wave phases from events in southwestern germany are studied for the effects of the double couple earthquake radiation pattern the direct p and s wave amplitudes for six earthquakes in the southern black forest of west germany with magnitudes between 2 2 and 0 5 were inverted for the source moment tensor and the double couple components were extracted from the solutions and refined by a further inversion the inversion focal mechanisms using both p and s wave amplitudes were quite consistent with those found from a large set of first motion readings even when very different crustal models were used for the events at or above magnitude 1 4 inversions using only direct p wave amplitudes also yielded good focal mechanisms furthermore the vertical component record at a station at p distance from the largest of the events was successfully synthesized using local mechanisms representative of those found from the inversions the phases modelled included p pmp and several free surface reflections the effect of the earthquake radiation pattern was also noted in the amplitudes of the p arrivals of a set of azimuthally distributed stations for two other earthquakes this study confirms that direct p and s amplitudes can be inverted for the source focal mechanism and suggests that deeper crustal phases like p pmp etc are also affected by the earthquake radiation pattern

the northern upper rhine graben basin geometry and early syn rift tectono sedimentary evolution a large scale transfer zone subdivides the northern parts of the upper rhine graben into a northern and a southern sub basin these sub basins display the geometry of asymmetric half grabens with opposing tilt directions the transfer zone connects the western master fault of the northern half graben with the eastern master fault of the southern half graben in the northern upper rhine graben early syn rift sedimentation late priabonian to late rupelian was controlled by the tectonically induced subsidence of these half grabens autogenetic as well as by regional third order sea level variations allogenetic within the graben lateral changes in subsidence rates in dip and strike direction of fault blocks controlled the development of accommodation space and thus sediment thickness and facies furthermore a low displacement segment along the western border fault acted as a sediment entry point tectonics controlled the distribution of early syn rift deposits and the palaeogeography of the northern upper rhine graben

do east australian current anticyclonic eddies leave the tasman sea using satellite altimetry and high resolution model output we analyze the pathway of large long lived anticyclonic eddies that originate near the east australian current eac separation point we show that 25 30 of these eddies propagate southward around tasmania leave the tasman sea and decay in the great australian bight this pathway has not been previously documented owing to poor satellite sampling off eastern tasmania as eddies propagate southward they often stall for several months at near constant latitude along the pathway eddies become increasingly barotropic eddy intensity is primarily influenced by merging with other eddies and a gradual decay otherwise surface temperature anomaly associated with anticyclonic eddies changes as they propagate while surface salinity anomaly tends to remain relatively unchanged as they propagate

generation of a buoyancy driven coastal current by an antarctic polynya descent and spreading of high salinity water generated by salt rejection during sea ice formation in an antarctic coastal polynya is studied using a hydrostatic primitive equation three dimensional ocean model called the proudman oceanographic laboratory coastal ocean modeling system polcoms the shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide and the salinity flux into the polynya at its surface is constant the model has been run at high horizontal spatial resolution 500 m and numerical simulations reveal a buoyancy driven coastal current the coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom variable bottom drag variable vertical turbulent diffusivities higher salinity flux and an offshore position of the polynya it is shown that bottom drag is the main factor determining the current width this coastal current has not been produced with other numerical models of polynyas which may be because these models were run at coarser resolutions the coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast when the polynya is situated offshore an unstable current is produced from its outset owing to the capture of cyclonic eddies the effect of a coastal protrusion and a canyon on the current motion is investigated in particular due to the convex shape of the coastal protrusion the current sheds a dipolar eddy

tectonic implications of transpression and transtension upper rhine graben 1 seismic reflection data from the upper rhine graben urg show a series of synclines along the linear eastern boundary faults from north of karlsruhe to the jura mountains similar structures do not characterize the northern segment of the graben the synclinal shape is portrayed by inversion related to transpression on the linear boundary faults coupled with the conserved easterly dip of the sediments farther inside the tilted hanging block the onset of transpression preceded the known early burdigalian unconformity but was also an early miocene event it suggests that the regional compression axis 1 in early miocene had a trend between 315 and 0 the continuous transtension in the northern segment suggests that at no time during the history of the urg was the regional 1 horizontal with a ne sw trend the lack of transpressional structures in the younger plio pleistocene sediments along the entire eastern boundary of the urg suggests a late change in the regional stress field the main eastern boundary faults and synclines north and south of baden baden are all continuous and have the same trend kinematically they form a single graben segment and respond to the regional stress in the same way

numerical experiments on the movement of a warm core ring with the bottom slope of a western boundary numerical experiments are performed to investigate the effects of the bottom slope of a western boundary on realistic warm core rings using a primitive equation sigma coordinate model warm core rings which initially have baroclinic velocity near a steep bottom slope gradually move northward but those with barotropic velocity do not barotropic velocity on the slope immediately disperses as a topographic rossby wave while baroclinic velocity is retained since the northward movement is caused by an effect very much like the image effect which is originally the effect of a free slip wall the authors term this effect the equivalent image effect the equivalent image effect increases as a slope becomes steeper and bottom friction becomes weaker and vice versa it seems that a steep slope acts like a wall and the bottom friction of a steep slope corresponds to the lateral viscous effect of a wall however the effect of a slope on a warm core ring is different from that of a wall in that ring slope interactions take place at the lower part of the ring because the velocity of a warm core ring is weak in deep layers ring slope interactions are moderate and the leakage of the interior fluid of a ring seen in ring wall interactions is not apparent while the viscous effect is weaker than that of a no slip wall as well these results are applied to the northward movement of kuroshio warm core rings and to warm eddies in the gulf of mexico

eddy train encounters with a continental boundary a south atlantic case study satellite altimetry suggests that large anticyclonic eddies rings originating from the agulhas current retroflection occasionally make their way across the entire south atlantic ocean what happens when these rings encounter a western boundary current in this work interactions between a train of nonlinear lenslike eddies and a southern hemisphere continental boundary are investigated analytically and numerically on a b plane the train of eddies is modeled as a steady double frontal zonal current with the same vorticity and transport as the eddies themselves the continental boundary is represented by a vertical wall which is purely meridional in one case and is tilted with respect to the north in another case it is demonstrated analytically that the eddy wall encounter produces an equatorward flow parallel to the continental wall thus suggesting a weakening of the transport of the associated poleward flowing western boundary current upstream of the encounter zone and unchanged transport downstream a large stationary eddy is established in thecontactzonebecauseitsb inducedforceisnecessarytobalancetheotherforcesalongthewall thesizeof this eddy is directly proportional to the transport of the eddy train and the meridional tilt of the wall these scenarios are in good agreement with results obtained numerically using an isopycnal bleck and boudra model

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

interaction of dipole eddies with the western continental slope of the mozambique channel abstract sea level anomaly sla data were used to track a southward propagating eddy dipole along the western slope of the mozambique channel over some 6 months in april 2005 this dipole with the cyclone to the south was close to the continental slope off southern mozambique the contact zone between the contra rotating vortices and the slope was surveyed by ship using onboard s adcp and ctd lines the data showed strong 1 4 m s 1 southward geostrophic currents over the slope adjacent to the anticyclone with horizontal divergence over the shelf edge significant slope upwelling between the dipole and the shelf was evident concomitant with enhanced nutrient and chlorophyll levels enriching shelf near surface waters satellite observations depicted a 300 km long surface chlorophyll filament extending offshore in the frontal zone between the contra rotating vortices a satellite tracked drifter deployed at the coastal base of this filament confirmed the offshore advection of chlorophyll enriched shelf water which ultimately wrapped around the cyclone and filling its centre the slope upwelling was also clearly evident in hourly temperature data collected by a recorder deployed on a nearby reef zambia reef in a depth of 18 m according to the sla data the dipole took several weeks to pass zambia reef causing prolonged bouts of upwelling that finally ceased when it left the continental slope and moved southwards into the open ocean further analysis showed that lone anticyclones and cyclones against the mozambique continental shelf also induce slope upwelling as a result of horizontal divergence created by the radial circulation of the vortex in the case of cyclones the divergence occurs north of the contact zone overall this case study confirms that eddies moving southwards along the western side of the mozambique channel are the main mechanism for pumping nutrients into the otherwise oligotrophic surface waters and moreover provide a vigorous mechanism for shelf open ocean exchange

stress tensor determination in france and neighbouring regions abstract the tectonic behaviour of different seismic regions of france is inferred from the properties of the local stress tensor obtained from focal mechanisms of regional earthquakes polarities of p wave arrivals for several earthquakes are used in the inversion of the stress tensor and individual focal mechanisms the principal axes and the shape of the tensor are closely related to the forces which generate seismic ruptures on pre existing faults we analyse 142 earthquakes of magnitude above 3 7 which occurred between 1965 and 1989 good results are obtained for some regions the northern alps and the southern end of the upper rhinegraben show a quasi compressive strike slip tectonic regime with a maximum stress axis oriented nw se the tectonic regime changes to an extensional strike slip type in the rhenish massif and the lower rhinegraben the direction of the minimum stress axis being nne ssw the central and western regions of france central and armorican massifs exhibit an extensional tectonic regime combined with strike slip faulting the minimum stress axis strikes in a ne sw direction a strongly non homogeneous stress field seems to be present in the southwestern alps and no unique stress tensor could be obtained for that region this problem is likely to be related to a rapid variation of the stress field in space which could be expected given the arc like geometry of the mountain range the pyrenean domain is unresolved due to lack of data and moreover existing focal mechanisms are globaly inconsistent nevertheless those mechanisms which are well constrained suggest a nnw sse to nw se direction of maximum stress in the western part of the pyrenees thus the stress field in france is fairly homogeneous at a regional scale for most of the territory except for the highly deformed belts

vertical structure of eddies and rossby waves and their effect on the atlantic meridional overturning circulation at 26 5 n the meridional overturning circulation moc at inline image in the atlantic has a standard deviation of 4 9 sv and contains large fluctuations at subannual periods the geostrophic component of the moc is believed to be influenced on subannual time scales by eddies and rossby waves to quantify this effect the vertical structure and surface characteristics of westward propagating signals are studied using altimetric data and full depth mooring measurements from the rapid array at inline image westward propagating features are observed in the western north atlantic in both data sets and have periods of 80 250 days in the first baroclinic mode these features are still observed by the rapid moorings 20 km offshore of the western boundary the western boundary also exhibits deep variability characterized by enhanced energy in higher baroclinic modes the effect of eddies and rossby waves on the geostrophic transport is quantified by representing their vertical structure with the first baroclinic mode in total 42 of the variance of the transbasin thermocline transport inferred from geostrophic calculations at inline image can be attributed to first mode variability which is associated with eddies and rossby waves at periods of 80 250 days the standard deviation of the transbasin thermocline transport due to eddies and rossby waves is estimated to be 2 6 sv

impact of caribbean cyclones on the detachment of loop current anticyclones 1 the western boundary current in the north atlantic is characterized by an intense flow reaching 2 5 ms 1 at the surface that enters the caribbean sea through the lesser antilles passages crosses the entire caribbean and enters the gulf of mexico through the yucatan channel where it is known as the loop current a characteristic feature of the loop current is eddy shedding events i e the detachment of large anticyclonic eddies at irregular intervals moored current measurements between january 2005 and july 2009 in the loop current the yucatan channel and the caribbean coastal waters of mexico i e the western cayman sea along with aviso altimetry are used to evidence the northward propagation of cyclonic anomalies along the caribbean coast of mexico and the marked eastward displacement of the loop current at 23 n latitude just before several anticyclonic eddy shedding events after entering the gulf of mexico these cyclonic anomalies might initiate or enhance existing campeche bank cyclonic eddies which are related to many of the loop current detachment events sixteen of the twenty one detachments that occurred during the study period 76 are related to the cyclonic eddies in the western caribbean sea six of them were not reattached again to the loop current observations thus clearly indicate that cyclonic eddies in the western cayman sea contribute significantly to the loop current eddy shedding process which is complex and in principle not unique

european continuous active tectonic strain stress map this paper shows a new continuous strain stress map for europe obtained from the direct inversion of earthquake focal mechanisms calculated from the centroid tensor method a total of 1608 focal mechanisms have been selected with several quality criteria from different catalogues cmt harvard eth med net i g n and i a g from 1973 to the present day values for the maximum horizontal shortening direction and brittle strain stress regime defined by the k ratio ey ez horizontal maximum vertical strain have been calculated following in europe and pannonian basin the slip model of tri axial deformation the individual results including dey and the shape of the active brittle strain ellipsoid have been interpolated to a final 15 regular grid taking into account the relationship between the tectonic horizontal strain stress value and the vertical load both continuous strain regime and maximum horizontal shortening dey maps show a good correlation with the primary tectonic forces generated along the plate boundaries plate kinematics and also some local perturbations related with main crustal heterogeneities and topography as well as significant spatial variations in integrated crustal strength

evidence for the permutation of stresses σ1 and σ2 in the alpine foreland the example of the rhine graben abstract the orientation of the principal stresses 1 2 and 3 and the ratio r 2 3 1 3 which characterizes the shape of the stress tensor can be calculated using earthquake focal mechanisms in the rhine graben area two types of stress tensor can be determined one of them is an extensional stress state subvertical 1 horizontal 2 n130 in the northern part of the rhine graben the other is a strike slip stress state horizontal 1 n150 in the southern part these results show that the maximum horizontal stress is constant in an approximately n130 150 direction 1 in the south 2 in the north this permutation of the stresses 1 and 2 may be imputed to the interaction between the decrease in alpine pressure and the asthenospheric uprise under the rhenish massif the superficial in situ stresses measured from the alps to the lower rhine embayment showing a decrease in maximum horizontal stress h max support this hypothesis

baroclinic eddy interactions with continental slopes and shelves abstract the evolution and propagation of large anticyclonic eddies similar to the loop current eddies found in the gulf of mexico are studied in a two layer intermediate equation numerical model it is found that the propagation of these eddies is governed primarily by the effect lower layer flow driven by the surface eddies and the image effect as the eddies move westward under the influence of the effect they drive deep circulation that typically includes a cyclone near the eddies trailing edge this cyclone accelerates the eddy southward leading to a path substantially different from that found in reduced gravity models of similar surface eddies when the eddy encounters a continental slope the lower layer flow is dispersed by topographic rossby waves and the eddy loses its southward propagation component if the continental slope is backed by a shelf that is wider than the eddy s radius a deep anticyclone will form over the shelf as the eddy approaches the shelf break this anticyclone w

upper rhine graben role of preexisting structures during rift evolution 1 the evolution of the cenozoic upper rhine graben was controlled by a repeatedly changing stress field and the reactivation of a complex set of crustal discontinuities that had come into evidence during permo carboniferous times a comparison of the spatial and temporal thickness distribution of synrift deposits with preexisting fault patterns permits to infer a sequence of distinct basin subsidence phases that can be related to changes in the ambient stress field reactivation of a system of late palaeozoic fault systems outlining troughs and highs controlled the nucleation of initially separated middle and late eocene basins the depocenters of which coincided with a preexisting wsw ene trend during oligocene crustal extension the individual basins coalesced resulting in the development of the ssw nne striking upper rhine graben during the late oligocene chattian change in stress field the upper rhine graben was probably reactivated as a dextral strike slip system with the central graben segment forming a releasing bend during the early miocene aquitanian a major reorientation of the regional stress field is held responsible for the main subsidence phase of the northern parts of the upper rhine graben this is reflected by a counterclockwise rotation and northeastward shift of the depocenter axis and later by the middle miocene uplift and erosion of the southern parts of the upper rhine graben during the plio quaternary the upper rhine graben was reactivated as a sinistral strike slip system with the central graben segment forming a restraining bend

observed eddy dissipation in the agulhas current analysing eddy characteristics from a global dataset of automatically tracked eddies for the agulhas current in combination with surface drifters as well as geostrophic currents from satellite altimeters it is shown that eddies from the mozambique channel and south of madagascar dissipate as they approach the agulhas current by tracking the offshore position of the current core and its velocity at 30os in relation to eddies it is demonstrated that eddy dissipation occurs through a transfer of momentum where anti cyclones consistently induce positive velocity anomalies and cyclones reduce the velocities and cause offshore meanders composite analyses of the anti cyclonic cyclonic eddy current interaction events demonstrate that the positive negative velocity anomalies propagate downstream in the agulhas current at 44 km day 23 km day many models are unable to represent these eddy dissipation processes affecting our understanding of the agulhas current

modelling the mixing function to constrain coseismic hydrochemical effects an example from the french pyrenees groundwater coseismic transient anomalies are evidenced and characterized by modelling the mixing function f characteristic of the groundwater dynamics in the ogeu western french pyrenees seismic context investigations of water rock interactions at ogeu indicate that these mineral waters from sedimentary environments result from the mixing of deep waters with evaporitic signature with surficial karstic waters a 3 year hydrochemical monitoring of ogeu springwater evidences that using arbitrary thresholds constituted by the mean 1 or 2 as often performed in such studies is not a suitable approach to characterize transient anomalies instead we have used a mixing function f calculated with chemical elements which display a conservative behavior not controlled by the precipitation of a mineral phase f is processed with seismic energy release es and effective rainfalls r linear impulse responses of f to es and r have been calculated rapid responses 10 days to rainwater inputs are evidenced consisting in the recharge of the shallow karstic reservoir by fresh water complex impulse response of f to microseismic activity is also evidenced it consists in a 2 phase hydrologic signal with an inflow of saline water in the shallow reservoir with a response delay of 10 days followed by an inflow of karstic water with a response delay of 70 days the amount being higher than the saline inflow such a process probably results from changes in volumetric strain with subsequent microfracturation transient episodes allowing short inflow of deep salted water in the aquifer this study demonstrates that groundwater systems in such environments are unstable systems that are highly sensitive to both rainfall inputs and microseismic activity impulse responses calculation of f to es is shown to be a powerful tool to identify transient anomalies similar processing is suggested to be potentially efficient to detect precursors of earthquakes when long time series 5 years at least are available in areas with high seismicity

the variscan tectonic inheritance of the upper rhine graben evidence of reactivations in the lias late eocene oligocene up to the recent processing of gravity and magnetic maps shows that the basement of the upper rhine graben area is characterized by a series of ne sw trending discontinuities and elongated structures identified in outcrops in the vosges black forest and the odenwald mountains they form a 40 km wide n30 40 striking sinistral wrench zone that in the visean shifted the variscan and pre variscan structures by at least 43 km to the ne wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340 325 ma the sub vertical ne sw trending discontinuities in the basement acted as zones of weakness susceptible to reactivation by subsequent tectonism the first reactivation marked by mineralizations and palaeomagnetic overprinting along ne sw faults of the vosges mountains results from the liassic nw se extension contemporaneous with the break up of pangea the major reactivation occurred during the late eocene n s compression and the early middle oligocene e w extension the ne sw striking basement discontinuities were successively reactivated as sinistral strike slip faults and as oblique normal faults elongated depocenters appear to form in association with reactivated variscan wrench faults some of the recent earthquakes are located on ne sw striking variscan fault zones and show sinistral strike slip focal mechanisms with the same direction suggesting also present reactivation

a string function for describing the propagation of baroclinic anomalies in the ocean the authors derive a string function that describes the propagation of large scale potentially large amplitude baroclinic energy anomalies in a two layer ocean with variable topography and rotation parameter the generality of the two layer results allows results for the 1 layer 1 5 layer inverted 1 5 layer lens and dome models to be produced as limiting cases the string function is a scalar field that acts as a streamfunction for the propagation velocity in the linear case the string function is simply c2o f where co is the background baroclinic shallow water wave speed and typically describes propagation poleward on the eastern boundaries westward with some topographic steering over the middle ocean and equatorward on the western boundaries in the more general nonlinear case the string function is locally distorted by the anomaly in the fully nonlinear examples of a lens or dome there is no rest or background string function the string function is generated entirely by the disturbance and propagation is due to asymmetric distribution of the anomalous mass over the string function contours it is shown that conventional beta topographic propagation results e g beta drift of eddies the nof speed of cold domes can be obtained as limiting cases of the string function the string function provides however more general propagation velocities that are also usually simpler to derive the first baroclinic mode string function for the global oceans is calculated from hydrographic data the westward propagation speeds in the ocean basins as derived from the meridional gradient of the string function are typically two to five times faster than those expected from standard theory and agree well with the propagation speeds observed for long baroclinic rossby waves in the topex poseidon data

the east madagascar current volume transport and variability based on long term observations abstractthis study provides a long term description of the poleward east madagascar current emc in terms of its observed velocities estimated volume transport and variability based on both 2 5 yr of continuous in situ measurements and 21 yr of satellite altimeter data an array of five moorings was deployed at 23 s off eastern madagascar as part of the indian atlantic exchange in present and past climate inatex observational program on average the emc has a horizontal scale of about 60 100 km and is found from the surface to about 1000 m depth its time averaged core is positioned at the surface at approximately 20 km from the coast with velocity of 79 21 cm s 1 the emc mean volume transport is estimated to be 18 3 8 4 sverdrups sv 1 sv 106 m3 s 1 during the strongest events maximum velocities and transport reach up to 170 cm s 1 and 50 sv respectively a good agreement is found between the in situ transport estimated over the first 8 m of water column 0 32 0 13 sv with the

eddy formation and shedding in a separating boundary current this study deals with the separation of western boundary currents within a reduced gravity framework and it analyzes the formation of eddies in the separation region and the conditions of their shedding into the open ocean it shows that the separation point of the current oscillates along the coast so that the retroflected eastward current develops meanders these meanders grow drift westward under the influence of and finally hit the coastal current which leads to the periodic formation of eddies this study also highlights the impact by the geometrical configurations of the flow and coastline upon the existence or lack of a subsequent shedding of these eddies a shedding occurs when no obstacle hinders the induced westward drift of the eddies this happens when either i the current retroflects far enough beyond the tip of the coast so that because of the eddies can propagate westward without being blocked or ii the tilt of the coast is small enough so that the alongshore component of the induced velocity is enhanced and the eddies can escape from the retroflection region

the destruction of lenses and generation of wodons abstract since midocean eddies migrate westward they eventually reach the western boundaries it is therefore of interest to find out what happens after the eddies collide with the walls an isopycnic two layer primitive equation model on a plane and a simple analytical model on an f plane are constructed to investigate the meridional migration of an oceanic eddy along a western wall on a plane three factors determine the eddy s migration along a western meridional wall first the image effect pushes an anticyclonic cyclonic eddy northward southward second the force resulting from the larger coriolis force on the northern side of the eddy pulls an anticyclonic cyclonic eddy southward northward third after an anticyclonic cyclonic eddy collides with the wall parts of the anticyclonic eddy s interior fluid leak out southward northward along the wall forming a thin jet in an analogy to a rocket this jet pushes the eddy northward southward our aim is to investigate in whi

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

the 2005 heidelberg and speyer earthquakes and their relationship to active tectonics in the central upper rhine graben we determine the source parameters of three minor earthquakes in the upper rhine graben urg a cenozoic rift using waveforms from permanent and temporary seismological stations two shallow thrust faulting events m l 2 4 and 1 5 occurred on the rift shoulder just south of heidelberg in march 2005 they indicate a possible movement along the sediment crystalline interface due to tectonic loading from the near by odenwald in february 2005 an earthquake with a normal faulting mechanism occurred north of speyer this event m l 2 8 had an unusual depth of about 22 km and a similar deep normal faulting event occurred there in 1972 m l 3 2 other lower crustal events without fault plane solutions are known from 1981 and 1983 at such a depth inside the lower crust ductile behaviour instead of brittle faulting is commonly assumed and used for geodynamic modelling based on the newly available fault plane solutions we can confirm the brittle extensional regime in the upper and lower crust in the central to northern urg indicated in earlier studies

seismicity of the northern upper rhine graben constraints on the present day stress field from focal mechanisms abstract we present new results for the microseismic activity in the northern upper rhine graben by analyzing seismogram recordings from two temporary networks of up to 13 broad band stations in combination with data from permanent stations previous studies have mainly focused on the southern and intermediate sections of the upper rhine graben where the station coverage by regional networks is more dense between october 2010 and september 2013 we recorded 56 earthquakes that occurred within the immediate vicinity of the northern upper rhine graben with local magnitudes ranging from 0 5 to 3 2 the majority of the hypocenters are located beneath the eastern graben shoulder and in the graben itself while activity observed along the western graben shoulder is lower a further active region is located along the southern rim of the taunus mountains to the northwest of the study area the seismicity extends to a depth of 25 km the hypocentral depth distribution exhibits a pronounced peak of seismic energy release in the depth range between 12 and 18 km fault plane solutions for a total of 58 earthquakes including data from previous recordings were derived from p polarities and sv p amplitude ratios this new data set more than quadruples the number of available data for regional stress field analysis the majority of the focal mechanisms show predominantly strike slip movements only a few events are of reverse or normal faulting type t axis trends are oriented ne sw the calculated focal mechanisms presented in this study confirm that the area is in transtension however in contrast to previous studies a stronger strike slip component is identified we also derived the azimuths of the principal stress axes by inverting the fault plane solutions and calculated the direction of the maximum horizontal stress which is mainly oriented n135 e

upper slope jets and gulf stream filaments inshore of the charleston bump during winter 2012 abstracta 3 month long field program conducted in winter 2012 inshore of the seaward deflection of the gulf stream at the charleston bump observed several 7 21 day periods of strong 0 5 m s 1 eq