geochemical and isotopic study of a norite eclogite transition in the european variscan belt implications for upb zircon systematics in metabasic rocks abstract three different geochronological techniques u pb conventional multigrain single zircon stepwise pb evaporation and sm nd on minerals were applied to rocks from a norite eclogite transition observed in the west european variscan belt and combined with major and trace element including ree geochemistry the studied rocks belong to a cogenetic tholeiitic suite which originated in an immature back arc basin or within plate magmatic environment the initial ndt 480 ma values around 1 2 imply that the noritic protoliths were emplaced in a geotectonic setting in close association with the continental crust u pb mulfgrain and the sm nd dating of a norite sample indicate an age of 481 ma for the basic magmatism sm nd dating on two whole rock garnet pairs yields an age of 408 ma for the eclogite facies metamorphism these two ages are consistent with the present understanding of the european variscan belt finally the single zircon pb evaporation study of an eclogite sample demonstrates the co existence of several types of zircons each zircon population yields a particular type of geochronological information related to the contrasting behaviours of the u pb isotopic system during the eclogite facies tectonometamorphic event these analytical results suggest that complex and heterogeneous behaviour within the u pb zircon system may also be recorded in numerous other samples this last point raises the question of the significance of results obtained by u pb conventional multigrain dating in metabasic rocks

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

alaska crustal deformation finite element modeling constrained by geologic and very long baseline interferometry data we compute crustal motions in alaska by calculating the finite element solution for an elastic spherical shell problem the method we use allows the finite element mesh to include faults and very long baseline interferometry vlbi baseline rates of change boundary conditions include pacific north american pa na plate motions the solution is constrained by the oblique orientation of the fairweather queen charlotte strike slip faults relative to the pa na relative motion direction and the oblique orientation from normal convergence of the eastern aleutian trench fault systems as well as strike slip motion along the denali and totschunda fault systems we explore the effects that a range of fault slip constraints and weighting of vlbi rates of change has on the solution this allows us to test the motion on faults such as the denali fault where there are conflicting reports on its present day slip rate we find a pattern of displacements which produce fault motions generally consistent with geologic observations the motion of the continuum has the general pattern of radial movement of crust to the ne away from the fairweather queen charlotte fault systems in se alaska and canada this pattern of crustal motion is absorbed across the mackenzie mountains in nw canada with strike slip motion constrained along the denali and tintina fault systems in south central alaska and the alaska forearc oblique convergence at the eastern aleutian trench and the strike slip motion of the denali fault system produce a counterclockwise pattern of motion which is partially absorbed along the contact and related fault systems in southern alaska and is partially extruded into the bering sea and into the forearc parallel the aleutian trench from the alaska peninsula westward rates of motion and fault slip are small in western and northern alaska but the motions we compute are consistent with the senses of strike slip motion inferred geologically along the kaltag kobuk trench and thompson creek faults and with the normal faulting observed in nw alaska near nome the nonrigid behavior of our finite element solution produces patterns of motion that would not have been expected from rigid block models strike slip faults can exist in a continuum that has motion mostly perpendicular to their strikes and faults can exhibit along strike differences in magnitudes and directions

u pb zircon and sm nd model ages of high grade moldanubian metasediments bohemian massif czechoslovakia we report single grain u pb ion microprobe as well as conventional bulk size fraction ages for zircons from 3 metasediment samples of the moldanubian complex bohemian massif one of the largest crystalline complexes of the hercynian foldbelt in europe these are complemented by whole rock sm nd model ages the metasediments are of upper amphibolite to granulite grade and come from the bory massif in moravia nw of brno sample aa 1 and from the varied group aa 2 and monotonous group aa 3 in the ceske budejovice region of sw bohemia

kinematic setting and structural control of arc volcanism abstract the evaluation of the kinematic setting and the structural control of volcanic arcs are important in defining the tectono magmatic processes along convergent plate boundaries however our knowledge is fragmented and the available data highlight different behaviours this study analyzes the kinematic setting the structural control and the volcanic productivity of 16 arcs these arcs are characterized by predominant extensional compressional strike slip or oblique motions there is an overall coupling between the normal vs parallel motions along the arc and those of the underlying slab therefore the higher the trench normal or parallel component of the subduction rate the higher is the amount of arc normal or parallel motion this relation confirms that strain partitioning is in general feasible at many convergent settings involving also the volcanic arc portion the arc normal motion may be characterized by extension or compression as a function of the increase in the trench normal convergence or subduction velocity the lack of an evident relation between the subduction rate or convergence rate and the volcanic productivity of the arc is partly inconsistent with previous studies which highlight a relation between the subduction rate and melt production below arcs this discrepancy mainly suggests that different processes control the generation rise and eruption of magma at different depths varying the intrusive extrusive ratio along arcs the structure of the arc does not control the distribution of the volcanoes however it does control the volcanic output through different processes even though regional or local extension associated with strike slip or compressive structures is the ultimate requisite in any setting in general the higher the amount of extension the higher is the output rate along the arc

model for late mesozoic early tertiary tectonics of coastal california and western mexico and speculations on the origin of the san andreas fault cretaceous and early tertiary arc and forearc rocks found along the coast in southern california and baja california have been shown by paleomagnetic measurements to have originated many hundreds or even several thousands of kilometers south of their current locations northward transport also is found in cretaceous batholithic rocks near the edge of the continent in washington and british columbia the consistency of this pattern suggests that slices of arc and forearc rock originating on the western edge of north america have been translated along the coast by strike slip faulting strike slip faults are shown to be an expected response to north oblique subduction of the farallon and or kula plates faulting and subduction probably were concurrent activities i e the arc and forearc grew and were displaced simultaneously because displacement was dominantly parallel to subduction related lithic belts arc and forearc rocks may have traveled large distances without producing either significant hiatuses in the rock record or conspicuous disruptions in the distribution of lithic belts subduction related strike slip faulting is shown to be favored by high angles of oblique convergence shallow dip of the subducting slab relatively easy slip on potential faults within the arc or forearc and the existence of a place for the moving sliver to go it is suggested that these conditions are not difficult to satisfy and that subduction related strike slip faulting may thus be a common feature of convergent orogens the location of the san andreas fault inboard from the continental margin may be attributable to localization of the pacific north american transform by a system of precollision subduction related faults

characteristics of regional stresses in alaska and neighboring areas earthquake focal mechanisms for a selected group of crustal earthquakes located in alaska and neighboring areas have been compiled from various sources and regional characteristics of the horizontal stress have been deduced for the region from the mechanism solutions the results show that the compressional stress regime of southern coastal areas continues inland through central alaska and extends in a northeast direction the western part of alaska including chukotka and the bering sea adjoining alaska and the aleutian island chain constitute a tensional stress regime

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

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

a rare earthquake sequence in the kobuk trench northwestern alaska abstract four moderate earthquakes in the magnitude of 4 to 5 range occurred in the kobuk trench of northwestern alaska during october 1980 this is a characteristically aseismic area all foci were of shallow depth and focal mechanism solutions from the three largest events are consistent in indicating right lateral displacement on a fault trending wnw ese this would be in agreement with mapped faults of quaternary age in the area

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

strain accumulation along the denali fault at the nenana river and delta river crossings alaska surveys of trilateration networks across the denali fault at the nenana river in 1982 1984 and 1988 and at the delta river in 1975 1979 1982 and 1984 indicate a minor 0 10 0 04 strain yr northeastward uniaxial extension the component of right lateral shear strain accumulation across the fault is not significant at the two standard deviation level at the delta river network the strain accumulation rate decreases rapidly with distance from the fault but evidence for a similar decrease with distance from the fault is lacking at the nenana river network the strain accumulation rates inferred from trilateration are consistent with the very long baseline interferometry vlbi measurement reported by ma et al 1990 and support their contention that significant right lateral shear is not accumulating along the denali fault at the present time savage et al 1981 had earlier concluded erroneously that preliminary geodetic measurements at the delta river network demonstrated right lateral shear strain accumulation the absence of significant right lateral deformation across the denali fault in the 1975 1988 interval is in marked contrast with the abundant geomorphic evidence for holocene right lateral secular slip at the rate of 10 20 mm yr on the denali fault in this sector

liδ18osio2 systematics in volcanic rocks and mafic lower crustal granulite xenoliths abstract li 18 o sio 2 relationships have been examined for suites of spilitized basaltic rocks dsdp 504b xigaze ophiolite blanco fracture zone greater caucasus rhenohercynian fold belt and intra plate evolved tholeiites northern hessian depression and vogelsberg w germany mount falla transantarctic mountains relative to unaltered morb and intra plate primary olivine tholeiites both the spilitic rocks and the evolved tholeiites are characterized by li and 18 o enrichment for the spilitic rocks li and 18 o enrichment is accompanied by a loss of sio 2 as a result of seawater hydrothermal alteration whereas the evolved tholeiites have gained sio 2 li and 18 o from fractionation of mafic phases and assimilation of crustal rocks on li vs sio 2 and 18 o vs sio 2 diagrams the two rock groups plot largely in distinct fields suggesting the possibility of so distinguishing between such lithologies in the ancient rock record mafic granulite xenoliths from the northern hessian depression have elevated li and 18 o abundances at low sio 2 contents even after correction for extraction of felsic components their li 18 o sio 2 signatures plot within the field of spilitic protoliths suggesting that the lower crust in this region contains relics of spilitic rocks from a former oceanic crust

sutton alaska earthquake of 1984 evidence for activity on the talkeetna segment of the castle mountain fault system a magnitude 5 7 mb 5 2 ms earthquake occurred on 14 august 1984 14 km north of sutton in the vicinity of the mapped trace of the talkeetna segment of the castle mountain fault system the focal mechanism of the earthquake and the spatial distribution of well controlled aftershock hypocenters indicate that the shock involved dextral slip at 13 to 20 km depth on the talkeetna fault segment the depth of the shocks is consistent with the lack of observed surface breakage the sutton earthquake sequence plus recent small shocks recorded by the southern alaska seismograph network provide definitive evidence that the talkeetna segment of the fault system is active

the transition from strike slip to oblique subduction in southeastern alaska from seismological studies abstract body waveform modeling of 11 moderate to large earthquakes within southeastern alaska has been incorporated with earthquake relocations and the results of previous seismicity studies to examine the transition from strike slip to oblique subduction in southeastern alaska in the sitka region of extreme southeastern alaska earthquakes indicate seismic slip is parallel to the direction of motion between north america and the pacific plate as the plate margin begins to bend to the west near cross sound and encounters the southeastern edge of the yakutat block partitioning of seismic slip is evident both onshore and offshore although the largest earthquakes magnitude 6 0 in this region have slip parallel to plate motion most moderate sized events have slip vectors rotated clockwise from plate motion offshore the 1973 cross sound sequence indicates that the southern end of the transition zone is seismogenic with the pacific plate being thrust beneath the yakutat block while onshore strike slip faulting has occurred along the fairweather border ranges and denali faults in the st elias region thrust faulting is occurring along and above the plate interface moderate sized events in the st elias show a mix of slip vector orientations in the pamplona zone slip vectors of offshore earthquakes and deformation directions determined onshore from gps studies show a counter clockwise rotation relative to plate motion suggesting that a change in strain field occurs just west of the st elias region

nonlinear dynamics granular media and dynamic earthquake triggering the landers earthquake of 1992 triggered a series of earthquakes in other parts of california focusing attention on the mechanism of remote triggering laboratory experiments on granular material under pressure suggest that triggering is a result of seismic waves impinging on a fault and inducing elastic nonlinear behaviour of the fault core accompanied by instantaneous weakening and failure the resulting softening to weakening model fits in well with field observations of real earthquakes the 1992 magnitude 7 3 landers earthquake triggered an exceptional number of additional earthquakes within california and as far north as yellowstone and montana1 2 3 since this observation other large earthquakes have been shown to induce dynamic triggering at remote distances for example after the 1999 magnitude 7 1 hector mine1 and the 2002 magnitude 7 9 denali4 earthquakes and in the near field as aftershocks5 the physical origin of dynamic triggering however remains one of the least understood aspects of earthquake nucleation1 2 3 4 5 the dynamic strain amplitudes from a large earthquake are exceedingly small once the waves have propagated more than several fault radii for example a strain wave amplitude of 10 6 and wavelength 1 m corresponds to a displacement amplitude of about 10 7 m here we show that the dynamic elastic nonlinear behaviour of fault gouge perturbed by a seismic wave may trigger earthquakes even with such small strains we base our hypothesis on recent laboratory dynamic experiments conducted in granular media a fault gouge surrogate6 7 from these we infer that if the fault is weak8 9 10 seismic waves cause the fault core modulus to decrease abruptly and weaken further if the fault is already near failure this process could therefore induce fault slip

tectonic drivers of the wrangell block insights on fore arc sliver processes from 3 d geodynamic models of alaska intracontinental shear zones can play a key role in understanding how plate convergence is manifested in the upper plate in regions of oblique subduction however the relative role of the driving forces from the subducting plate and the resisting force from within intracontinental shear zones is not well understood results from high resolution geographically referenced instantaneous 3d geodynamic models of flat slab subduction at the oblique convergent margin of alaska are presented these models investigate how viscosity and length of the denali fault intracontinental shear zone as well as coupling along the plate boundary interface modulate motion of the wrangell block forearc sliver and slip across the denali fault models with a weak denali fault 1017 pa s and strong plate coupling 1021 pa s were found to produce the fastest motions of the wrangell block 10 mm yr the 3d models predict along strike variation in offs et along the denali fault changing from dextral strike slip motion in the eastern segment to oblique convergence towards the fault apex models further show that the flat slab drives oblique motion of the wrangell block and contributes to 20 models with a short fault and 28 models with a long fault of the observed quaternary slip rates along the denali fault the 3d models provide insight into the general processes of forearc sliver mechanics and also offer a 3d framework for interpreting hazards in regions of flat slab subduction

finite element modeling of crustal deformation in the north america caribbean plate boundary zone we have developed two dimensional spherical shell finite element models of elastic displacements in the north america caribbean na ca plate boundary zone pbz in order to quantify crust and fault motions in the pbz the models we derive are dependent on both the internal fault constraints and the na ca euler pole we used since the location and magnitude of the na ca euler pole are still matters of much debate we consider three euler poles demets et al 1990 calais and mercier de lepinay 1993 and deng and sykes 1995 we compare the resulting finite element model displacements to recent seismicity and to geological and geophysical field observations the model of demets et al 1990 nuvel 1 features an na ca relative velocity across the pbz which is less than the observed cayman spreading axis rate and thus the finite element model based on it produces fault motions which are inconsistent with observation the calais and mercier de lepinay 1993 c m and deng and sykes 1995 d s models both yield far field rates across the pbz at the point of the cayman spreading center of approximately 20 mm yr a value greater than the observed rate the greatest differences in the latter two models lie in the motion calculated for the area around puerto rico both models feature a counterclockwise rotation of the pbz around puerto rico with opening of the anegada passage and compression at the muertos trough south of eastern hispaniola the c m based model produces normal opening of the anegada passage fault system while the d s based model produces left lateral transtension across the anegada passage fault system the result of continuum crustal motions which are nearly orthogonal between the two models in the area ne of puerto rico we conclude that the c m based model better matches geological observations of pbz fault motions and deformation primarily on the basis of the anegada passage results because of this rotation of the pbz from hispaniola to the anegada passage fault system the puerto rico trench includes highly oblique compression in its eastern portion changing to pure left lateral strike slip nw of puerto rico the c m based finite element model agrees with preliminary gps results from hispaniola and puerto rico if the central septentrional fault is constrained to strike slip motion

tectonic motion and deformation from satellite laser ranging to lageos satellite laser ranging slr to lageos acquired during the period 1978 1988 has been analyzed to yield estimates of tectonic motion for 22 laser tracking stations situated on seven major plates the analysis is based on the precise modeling of the orbit dynamics of lageos and includes the determination of other geodynamic and nonconservative force model parameters involved in the orbit determination problem at the centimeter level site velocities were recovered from station positions determined each calendar quarter using a network adjustment procedure which maintains the reference frame within the stable interior of tectonic plates the recovered motions indicate good agreement with existing estimates of stress fields particularly across northern europe the eastern pacific and in the basin and range province of north america a comparison of the intersite motions for stations centrally located on separate plates between slr and those implied by the nuvel 1 geologic motion model yield a strong positive correlation of 0 989 and a 3 7 scale difference which may be attributable to recent changes in relative velocities or geologic time scale uncertainties sites located at or within 250 km of convergent plate boundaries have additional components of motion indicating a need for further tectonic modeling beyond that provided by simple rigid plate motions for lines crossing the north atlantic the san andreas fault and within the basin and range province the geodesic rates determined by slr are in good agreement with those determined by very long baseline interferometry an alternative space geodetic technique

thermo tectono stratigraphic forward modelling of the upper rhine graben in reference to geometric balancing brittle crustal extension on a highly viscous mantle abstract four structural cross sections through the central segment of the upper rhine graben urg were balanced by means of thermo tectono stratigraphic forward modelling ttsf modelling results were compared to geometric retro deformation of pre rift reference horizons applying line length and area balancing methods ttsf modelling with a deep necking level 20 km and or a high effective elastic thickness te 15 km yielded extension values similar to those of geometric balancing while modelling with shallower necking depths and or lower te yielded unrealistic high extension values a best fit of geometric balancing indicating 5 km rift orthogonal extension was reached by ttsf modelling with a te of 15 km and a pre rift necking depth of 29 km coinciding with the moho discontinuity this is compatible with a the geophysically mapped moho that does not shallow significantly beneath the central segment of the urg and its shoulders b seismicity indicating brittle elastic deformation of the entire crust and a seismic ductile deformation of the lithospheric mantle c compensation of crustal faults and shear zones in the crust mantle transition zone modelled time extension paths imply rifting during the middle eocene to early miocene a late miocene post rift stage and renewed rifting during the pliocene to recent apparent northward migration of extension in time is an effect of uplift processes which are not related to rifting correcting for these the extension history for the four cross sections becomes very similar suggesting plane strain deformation and rifting at very low strain rates of about 1 7 10 16 s 1 involving brittle elastic deformation of the crust and ductile deformation of the highly viscous high strength upper mantle that controls the position of the lithospheric necking level

examination of scaling between proposed early signals in p waveforms and earthquake magnitudes summary we examine seismic waveforms generated by clusters of similar earthquakes and additional events located on the karadere duzce branch of the north anatolian fault to investigate possible scaling between proposed early signals in the p waveforms and magnitudes the employed signals can be divided into two classes the first is associated with ellsworth beroza and iio type signals that are assumed to reflect signatures of seismic nucleation phases the second are associated with nakamura type period and wu zhao type maximum displacement in the early waveforms that are related to measures of the corner frequency and local magnitude respectively the impact on each signal of artefacts generated by the finite impulse response fir filter is also examined the use of repeating event clusters reduces considerably the variability of path and site effects compared to previous regional and global studies this allows us to focus more accurately on variations of the potential scaling parameters with the source magnitude however the magnitude range of the employed events is limited to about 4 units the fir filter artefacts can generate spurious signals prior to the p wave arrival potentially affecting the ellsworth beroza type signals but are not a significant influence on any of the other measurements the results indicate that candidates for the ellsworth beroza signals associated with identification of a weak arrival before the main p phase exist in less than 20 per cent of the cases the iio type signals can be determined by definition on all waveforms both of these potential signatures of nucleation phases show little or no scaling with the final event size in the examined data in contrast the nakamura and wu zhao type signals in the first few seconds which can also be determined by definition on all waveforms appear to scale with the final event magnitude albeit with large scatter the relatively large time windows used in the analysis compared to the rupture time of the employed events implies that the results provide little if any information on the physical process of the rupture initiation the scaling of the nakamura and wu zhao type early signals with the final event size may be explained by statistical tendency of stronger initial rupture phases to propagate larger distances

exhumation along the fairweather fault southeastern alaska based on low temperature thermochronometry 1 the southern alaskan syntaxis marks the spectacular junction between the 1000 km long pacific north america transform margin and the chugach st elias belt where subduction and terrane accretion drive rapid convergent deformation and rock uplift new low temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral fairweather fault apatite and zircon u th he ages as young as 0 9 and 2 0 ma suggest maximum exhumation rates of nearly 2 mm a in close proximity 0 5 mm a along the entire plate margin we estimate that long term rock uplift accommodates 3 mm a of fault normal convergence in this area this suggests that the fairweather fault is slightly transpressive and highly partitioned analogous to the central san andreas fault this convergence only accounts for 1 5 of the obliquity between pacific plate motion and the continental margin however implying the deficit is taken up by 1 2 cm a thrust sinistral motion along the offshore transition fault additionally thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation similar to what has been observed in other parts of the pacific northwest the tectonically active fairweather corridor is distinguished however by the magnitude of the acceleration and the depth of exhumation since pliocene climate change

ground motion simulation and validation of the 2008 chino hills california earthquake we present a simulation of the 2008 m w 5 4 chino hills earthquake for a maximum frequency up to 4 hz and a minimum shear wave velocity down to 200 m s and perform a validation study comparing data obtained from seismic networks with simulation synthetics on more than 300 recording stations the simulation was done using a parallel computing code for earthquake simulations that implements a finite element solution to anelastic wave propagation in heterogeneous media the source model corresponds to that of an independent inversion study and the material model used is a community velocity model cvm developed by the southern california earthquake center scec our results for the goodness of fit measure of the synthetics indicate that from a regional perspective the simulation starts to deviate from the data at frequencies above 1 and 2 hz at particular locations or station clusters however the synthetics yield very good results even at frequencies between 2 and 4 hz the best results are obtained between 0 1 and 0 25 hz over the entire region and up to 1 hz within the major basins these and other results from comparisons at boreholes biases of the peak surface response and the differences in the strong phase duration of the waveforms and the arrival time of p waves suggest a strong sensitivity to seismic velocities in particular the cvm used seems to misrepresent the shallow soil deposits and overestimate seismic velocities in the upper layers outside the basins these observations are helpful in identifying regions where the velocity model may need to be revised overall this study shows that extending the maximum frequency for deterministic earthquake simulations beyond 1 hz is an effort worth pursuing

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

origin of granulite terranes and the formation of the lowermost continental crust differences in composition and pressures of equilibration between exposed regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust as had been thought but rather middle and lower middle crustal levels application of well calibrated barometers indicate that exposed granulites record equilibration pressures of 0 6 to 0 8 gigapascal 20 to 30 kilometers depth of burial whereas granulite xenoliths which also tend to be more mafic record pressures of at least 1 0 to 1 5 gigapascals 35 to 50 kilometers depth of burial thickening of the crust by the crystallization of mafic magmas at the crust mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep seated mafic crust represented by many xenolith suites

the composition and petrogenesis of the lower crust a xenolith study granulite facies lower crustal xenoliths from a single basaltic vent hill 32 in the mcbride volcanic province north queensland australia illustrate the extreme lithologic diversity of the deep crust these xenoliths are dominantly mafic but intermediate and felsic granulites represent a significant proportion 20 of the xenolith population all xenoliths have high grade mineralogies and generally well equilibrated textures as well as decompression features which are indicative of derivation from deep crustal levels 0 7 1 0 gpa major and trace element chemistry for 12 xenoliths chosen to span the observed lithologic range are used to constrain the petrogenesis of these rocks in the smaller layered samples metamorphic differentiation may lead to nonrepresentative sampling however in most instances such secondary processes can be identified and the original chemical characteristics delineated the mafic xenoliths formed through a variety of processes including crystallization of mafic magma crystal accumulation from mafic and felsic magmas and partial melting of intermediate compositions to yield a mafic residuum the two analyzed intermediate xenoliths are metasediments based upon high alumina to alkali ratios and rare earth element patterns whereas the two felsic xenoliths have compositions similar to igneous rocks comparisons of noncumulate and or restite xenoliths with unmetamorphosed rock types show that k and rb are variably depleted whereas th and u are strongly depleted in all rock types the large ion lithophile element depletion patterns for xenoliths are similar to those of rocks from granulite facies terrains suggesting similar processes were operative suggestions of an anomalously ba and sr rich lower crust are not supported by the data by using the observed lithologic proportions of xenoliths at hill 32 and the chemical analyses presented here a weighted mean composition of the lower crust can be obtained and compared with recently proposed lower crustal compositions the weighted mean composition is mafic and formed through a combination of basaltic underplating crystal accumulation tectonic underplating and partial melting no simple model of lower crust formation through basaltic or andesitic underplating nor intracrustal melting is sufficient to explain lower crust formation in phanerozoic continental margin settings

evolution of the petrological and seismic moho implications for the continental crust mantle boundary the chemical and petrological composition of mafic rocks from the lower continental crust are discussed by comparing mafic granulites and meta gabbroic rocks from the ivrea zone and the northern hessian depression nhd xenolith suite both regions contain contrasting types of meta mafic lithologies i former basaltic rocks with trace element patterns ranging from morb iike to subduction related or intra plate tholeutes and u ca and al enriched plagiodase dominated gabbroic rocks showing positive eu anomalies generated by complex deep crustal magmatic processes such as fractionation accumulation of plagiodase and pyroxene and crustal contamination the absence of typical garnet omphadte parageneses in these rocks indicates that the eclogite stability field was not reached during palaeozoic orogenic processes a compilation of experimentally determined p wave velocities and densities for mafic granulites gabbroic rocks eclogites and peridotites is used to evaluate key physical properties of lower crustal mafic rocks during crystal thickening caused by continent continent collision in a step by step scenario it is demonstrated that the position of the seismic moho defined as a first order velocity discontinuity and the petrological moho defined as the boundary between non peridotitic crustal rocks and olivine dominated rocks is not identical for the case that mafic rocks are transformed into edogites at the base of orogenically thickened crust p wave velocities of eclogites largely overlap with those of peridotites although their densities are significantly higher than common upper mantle rocks as a consequence refraction seismic field studies may not detect edogites as crustal rocks this means that the seismic moho detected by refraction seismic field studies appears at the upper boundary between edogites and overlying crustal units since edogites generally have higher densities than peridotites they might be recycled into the deeper lithosphere thereby transferring excess eu into the upper mantle this process could be a due for understanding the negative euanomaly in the upper continental crust which is apparently not balanced quantitatively by the abundance of common mafic crustal rocks

evidence for shear wave anisotropy in the mantle wedge beneath south central alaska we investigate shear wave polarization and splitting for more than 200 earthquakes with hypocentral depths ranging from 20 to 180 km beneath southcentral alaska data were recorded at three sites stations skn aui and red a preferred polarization parallel to the strike of the wadati benioff zone wbz n25 e is found for a majority of events however some regions show systematic differences in polarization for a subset of nine events we compute focal mechanisms and find no correlation between the theoretical shear wave polarization caused by the fault plane orientation and the observed polarization delays of the slow versus the fast s wave range from less than 0 05 to 0 25 sec for station skn and up to 0 4 sec for stations aui and red a statistically significant correlation of delay with depth is found r 0 78 with the largest delays corresponding to the deepest events this indicates that the source of the anisotropy cannot be located in the crust based on the ray path geometry the source cannot be solely located in the subducting slab either and must therefore originate in the mantle wedge our results for the subduction zone beneath alaska are consistent with similar studies in other subduction zones that describe slab parallel anisotropy in the mantle wedge

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

calbuco volcano and minor eruptive centers distributed along the liquine ofqui fault zone chile 41 42 s contrasting origin of andesitic and basaltic magma in the southern volcanic zone of the andes calbuco volcano is a late pleistocene holocene composite stratovolcano located at 41 20 s in the southern region of the southern volcanic zone of the andes ssvz 37 46 s in contrast to basalt and basaltic andesite which are the dominant lava types on the volcanic front from 37 to 42 s calbuco lavas are porphyritic andesites which contain a wide variety of crustal xenoliths they have sio2 contents in the 55 60 range and have comparatively low k2o rb ba th and lref abundances relative to other ssvz centers incompatible element abundance ratios are similar to those of most ssvz volcanics but 87sr 86sr and 143nd 144nd are respectively higher and lower than those of adjacent volcanic centers basalts from nearby osorno stratovolcano 25 km to the northeast are similar to other basaltic ssvz volcanoes however basalts from several minor eruptive centers mec located east of calbuco and osorno volcano along the liquine ofqui fault zone lofz are enriched in ba nb th and lree and have higher la yb and lower ba la k la and rb la 87sr 86sr and 143nd 144nd in mec basalts are respectively lower and higher than those of osorno and calbuco lavas we suggest that mec basalts were produced by lower extents of mantle melting than basalts from osorno and other ssvz stratovolcanoes probably as a result of lower water content in the source of mec basalts calbuco andesites formed from basaltic parents similar to osorno basalts by moderate pressure crystallization of a hornblende bearing assemblage accompanied by crustal assimilation hornblende stability in the calbuco andesites was promoted by the assimilation of hydrous metasedimentary crustal rocks which are also an appropriate endmember for isotopic trends together with magma storage at mid crustal depths the unique characteristics of calbuco volcano i e the stability of hornblende at andesitic sio2 contents low 143nd 144nd and high 87sr 86sr and abundant crustal xenoliths provide evidence for crustal assimilation that is not apparent at more northerly volcanoes in the ssvz

preliminary determination of pacfic north america relative motion in the southern gulf of calfornia using the global positioning system global positioning system gps data from experiments conducted in 1985 and 1989 in the southern gulf of california mexico allow a determination of relative motion between the pacific and north american plates the data indicate motion of cabo san lucas on the pacific plate relative to north america at a rate of 47 7 mrn yr and azimuth of 57 6 west of north 1 errors equivalent within uncertainties to the nuvel 1 global plate motion model

stress distribution along the fairweather queen charlotte transform fault system tectonic loading and coulomb stress transfer are modeled along the right lateral fairweather queen charlotte transform fault system using a three dimensional boundary element program the loading model includes slip below 12 km along the transform as well as motion of the pacific plate and it is consistent with most available global positioning system gps displacement rate data coulomb stress transfer is shown to have been a weak contributing factor in the failure of the southeastern sitka segment of the fairweather fault in 1972 hastening the occurrence of the earthquake by only about 8 months failure of the sitka segment was enhanced by a combination of cumulative loading from below 95 by slip of about 5 cm yr since 1848 by stress transfer about 1 from major earthquakes on straddling segments of the queen charlotte fault m 8 1 in 1949 and the fairweather fault m 7 8 in 1958 and by viscoelastic relaxation about 4 following the great 1964 alaska earthquake modeled by pollitz et al 1998 cumulative stress increases in excess of 7 mpa at a depth of 8 km are projected prior to the m 7 6 earthquake coulomb stress transferred by the rupture of the great m 9 2 alaska earthquake in 1964 bufe 2004a also hastened the occurrence of the 1972 event but only by a month or two continued tectonic loading over the last half century and stress transfer from the m 7 6 sitka event has resulted in restressing of the adjacent segments by about 3 mpa at 8 km depth the occurrence of a m 6 8 earthquake on the northwestern part of the queen charlotte fault on 28 june 2004 the largest since 1949 also suggests increased stress the cape st james segment of the fault immediately southeast of the 1949 queen charlotte rupture has accumulated about 6 mpa at 8 km through loading since 1900 and stress transfer in 1949 a continued rise in earthquake hazard is indicated for the alaska panhandle and queen charlotte islands region in the decades ahead as the potential for damaging earthquakes increases

strain accumulation across the fairweather and totschunda faults alaska deformation across the fairweather and totschunda faults is estimated from repeated surveys of geodetic networks that span those faults surveys in 1967 1983 and 1986 of networks crossing the fairweather fault indicate that right lateral engineering shear strain is accumulating across the 1958 earthquake rupture at a rate of 1 6 0 2 rad yr this rate of deformation is one of the highest observed across a strike slip fault system and it is several times greater than the secular rate of deformation across locked parts of the san andreas fault the rate of strain accumulation across the fairweather fault was the same in the two intervals 1967 1983 and 1983 1986 and is thus believed to be a secular rate rather than a transient associated with the 1958 earthquake the 1983 1986 line length changes are best fit by a model fault that is locked from the surface to a depth of 7 to 9 km and is slipping in a right lateral sense at a rate of 41 to 51 mm yr below that depth models with the fault locked to any depth of 4 km fit the data almost equally well the best fitting models indicate a slip rate comparable to the 48 to 58 mm yr average late holocene slip rate indicated by offset glacial moraines and to the 54 mm yr component of relative motion between the pacific and north american plates that is parallel to the fairweather fault no significant contraction was measured across the fairweather fault only a small part of the relative plate motion is transferred across the saint elias mountains to the colinear totschunda fault surveys in 1909 1912 and 1985 of a geodetic network that extends for 72 km across the totschunda fault indicate right lateral shear strain is accumulating at a rate of 0 11 0 06 rad yr this rate of strain accumulation suggests a slip rate of about 10 mm yr on the totschunda fault a value at the lower end of the average holocene slip rate of 10 to 20 mm yr

the san andreas fault revisited through seismic noise and surface wave tomography 1 we present here surface wave tomography results for the san andreas fault in the parkfield area california usa that were extracted from microseismic noise in the 0 15 hz to 0 35 hz frequency band using passive seismic correlation techniques using directive noise incoming from the pacific ocean passive seismic noise tomography was performed using three component sensors from a dense seismic network a rotation algorithm was applied to the nine component noise correlation tensor that optimally forced each station pair to re align in the noise direction a necessary condition to extract unbiased travel times from passive seismic processing after the rotation was performed an optimal surface wave tensor is obtained from which love waves were extracted for tomography inversion dispersion curves were then inverted to obtain a three dimensional shear velocity map showing vertical geological structures and a 1 3 km wide low seismic velocity dip which are in agreement with previous tomography studies in the same area

chronology of late paleozoic tectonothermal activity in the southeastern bohemian massif austria moldanubian and moravo silesian zones 40ar 39ar mineral age controls abstract new 40ar 39ar hornblende and muscovite ages from the moldanubian and moravian zones of the southeastern bohemian massif indicate rapid cooling associated with continental underplating during early carboniferous plate collision and closure of the moravo silesian foredeep 40ar 39ar ages have been determined for hornblende concentrates from 1 amphibolite from the moldanubian nappe complex including the dobra gneiss rehberg amphibolite and loosdorf complex all part of the variegated unit 2 micaschist structurally overlying the bittesch gneiss and 3 amphibolite within the bittesch gneiss moravian zone the five hornblende concentrates display variably discordant 40ar 39ar age spectra because of contamination with extraneous argon components however 36ar 40ar vs 39ar 40ar isotope correlations are well defined for the five hornblende concentrates mswd the hornblende and muscovite ages are interpreted to date post variscan metamorphic cooling through ca 500 c and ca 400 c respectively no record of pre variscan thermal events is preserved in either the hornblende or muscovite argon systems however the widespread occurrence of extraneous argon components suggest a pre variscan stage of tectonothermal development the near concordancy of the hornblende and muscovite cooling ages suggest relatively rapid cooling through the contrasting argon closure temperatures and indicate that relatively high crustal levels had likely been attained during the early carboniferous

opposing gradients of permanent strain in the aseismic zone and elastic strain across the seismogenic zone of the kodiak shelf and slope alaska an industry acquired seismic reflection line from the aleutian arc to the alaska trench was prestack depth migrated and further constrained with wide angle ocean bottom hydrophone seismic velocity data and swath mapping from the seismic reflection image individual thrust slices the backstop and the forearc basin were resolved sufficiently well to balance the section tectonic shortening and age estimates provided rates of permanent contraction in five discrete segments over 150 km during the past 3 myr about 70 of the plate convergence is measured as contraction across the 40 km wide neogene accretionary prism which composes less than 10 of the forearc permanent contraction is minimal above the 1964 alaska earthquake aftershock zone indicating dominently elastic strain since elastic strain is poorly recorded in the geological record it was approximated from the historical record of the 1964 alaska earthquake the 1964 coseismic vertical deformation displays an inverse pattern to the permanent strain consistent with the earthquake cycle concept elastic deformation is dominant beneath the shelf and upper slope rapid permanent deformation is concentrated beneath the lower slope and a transition between them occurs beneath the middle slope

lack of spatiotemporal localization of foreshocks before the 1999 mw 7 1 duzce turkey earthquake we use a matched filter technique to detect small seismic events before the m w 7 1 duzce earthquake that are not included in the regular catalog the study employs extensive waveform dataset recorded by a 10 station fault zone array near the epicenter of the duzce earthquake deployed about three months before the event we use 3134 earthquakes within 20 km of the duzce epicenter listed in the local catalog as templates to scan through waveforms recorded within 65 hours before the duzce earthquake the analysis reveals 262 newly detected events in this time interval which is 5 times more than the 55 events listed in the original catalog most of the events occur to the west of the duzce epicenter which was initiated between a more active western and relatively quite eastern fault segments the results do not indicate a localizing foreshock process that accelerates in time and or involves progressive concentration of activity around the mainshock hypocenter during the preceding 65 hour period instead we find that the duzce source region becomes less active during the 20 hours immediately before the mainshock our results together with other recent studies suggest that progressive acceleration and localization of foreshocks around the mainshock epicenter is not a general phenomenon online material figures of timing of recorded waveforms peak ground velocities foreshock activity seismicity rate and temporal evolution of earthquake activity vertical waveforms and distribution of template events

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

present day geodynamics of the northern north american cordillera abstract diffuse continental deformation results from interactions at plate boundaries buoyancy forces generated by gradients in gravitational potential energy and loads applied to the base of the lithosphere using finite element models we calculate a deviatoric stress field associated with buoyancy forces and then perform an iterative inversion to calculate deviatoric stress fields associated with boundary forces in the northern north american cordillera our results reveal the presence of two distinct geodynamic domains in the outboard domain approximately equal magnitudes of boundary and buoyancy forces can account for the observed deformation along the aleutian megathrust in contrast large boundary forces related to subduction of the pacific and yakutat slabs dominate the force balance in south central alaska and combine with relatively small buoyancy forces to reproduce the observed kinematic indicators in the inboard domain encompassed by interior and northern alaska and western canada boundary and buoyancy forces alone cannot reproduce the observed deformation therefore we infer that deviatoric stresses due to basal tractions from a deeper mantle convection cell contribute to surface deformation in the inboard domain low effective lithospheric viscosity in south central alaska and the balancing effect of an independent geodynamic system driven by basal tractions in northern alaska combine to confine the anomalously large yakutat related boundary deviatoric stresses to south central alaska deviatoric stresses associated with flat slab subduction of the yakutat microplate are a factor of two greater than boundary force estimates for the andean and indian eurasian convergent margins where buoyancy and boundary forces are roughly equal in magnitude and dominate the force balance

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

neotectonics and intraplate continental topography of the northern alpine foreland research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues the accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years which on geological time scales is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity more reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on going intraplate deformation the alpine orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that deformation of the northern alpine foreland is still on going and will continue in the future this has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area we examine relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland and their implications for tectonically induced topography for the environmental tectonics project entec the upper and lower rhine graben urg and lrg and the vienna basin vb were selected as natural laboratories the vienna basin developed during the middle miocene as a sinistral pull apart structure on top of the east alpine nappe stack whereas the upper and lower rhine grabens are typical intracontinental rifts the upper rhine graben opened during its late eocene and oligocene initial rifting phase by nearly orthogonal crustal extension whereas its neogene evolution was controlled by oblique extension seismic tomography suggests that during extension the mantle lithosphere was partially decoupled from the upper crust at the level of the lower crust however whole lithospheric folding controlled the mid miocene to pliocene uplift of the vosges black forest arch whereas thermal thinning of the mantle lithosphere above a mantle plume contributed substantially to the past and present uplift of the rhenish massif by contrast oblique crustal extension controlling the late oligocene initial subsidence stage of the lower rhine graben gave way to orthogonal extension at the transition to the neogene the entec project integrated geological geophysical geomorphologic geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations the response of europe s intraplate lithosphere to late neogene compressional stresses depends largely on its thermo mechanical structure which in turn controls vertical motions topography evolution and related surface processes

3 d viscoelastic fem modeling of crustal deformation in northeast japan as a first step toward establishing a standard earthquake cycle model in japan we simulate the crustal deformation during the past 100 years in northeast japan using a 3 d fem based on the kinematic model then we compare the computed results with the observed long term leveling data and the recent gps data on the whole although the effect of the subducting pac is dominant coseismic deformation of the interplate earthquakes can be clearly seen in the inland moreover the postseismic deformation of the earthquakes due to the viscoelastic upper mantle seriously affects the inland movements and continues for a few decades our modeling including the effects of the interplate earthquakes and the three dimensional viscoelastic inhomogeneity reasonably explains the observed movement finally we stress that the viscoelastic effect should be taken into consideration in the analyses even if no earthquakes occur in the analyzed period

refined thresholds for non linear ground motion and temporal changes of site response associated with medium size earthquakes summary we systematically analyse non linear effects and temporal changes of site response associated with medium size earthquakes using seismic data recorded by the japanese strong motion network kik net we apply a sliding window spectral ratio technique to surface and borehole strong motion records at six sites and stack results associated with different earthquakes that produce similar peak ground acceleration pga in some cases we observe a weak coseismic drop in the peak frequency when the pga is as small as 20 30 gal and near instantaneous recovery after the passage of the direct s waves the percentage of drop in the peak frequency starts to increase with increasing pga values we also observe a coseismic drop in the peak spectral ratio for two sites when the pga is larger than 60 gal to more than 100 gal we observe considerably stronger drops of the peak frequencies followed by logarithmic recovery with time the observed weak reductions of peak frequencies with near instantaneous recovery likely reflect non linear response with essentially fixed level of damage while the larger drops followed by logarithmic recovery reflect the generation and then recovery of additional rock damage the results indicate clearly that non linear site response may occur during medium size earthquakes and that the pga threshold for in situ non linear behaviour is lower than the previously thought value of 100 200 gal

seismic velocity reductions caused by the 2003 tokachi oki earthquake 1 we use four repeating earthquake sequences located near hokkaido to identify velocity changes caused by the mw 8 0 2003 tokachi oki earthquake using a moving window cross correlation technique we identify delays in the arrival time of seismic waves that accumulate linearly with time into the seismogram this behavior is indicative of multiple scattering within a medium where the seismic velocity has been reduced for all of our earthquake receiver geometries we find evidence of significant velocity reductions close to the receiver the correlation of the size of the velocity reductions with both strong shaking and site characteristics suggests that these velocity reductions are caused by damage to near surface materials created by nonlinear strong ground motion for earthquake receiver geometries where the seismic waves cross the tokachi oki rupture zone we identify particularly large reductions in velocity as a result of the earthquake for these geometries we believe that the rupture zone of the tokachi oki earthquake or the shallow crust above it represents a second region where seismic velocities are reduced as a result of the main shock

new gps constraints on the motion of the yakutat block global positioning system gps measurements were made at yakutat on the yakutat terrane of southern alaska to investigate the motion of the yakutat block with respect to the north american plate and to help constrain motion along the fairweather fault the velocity of yakutat derived from the gps data is 44 1 1 9 mm yr toward n37 4 w relative to stable north america the magnitude of this velocity is similar to that of the pacific plate predicted by nuvel1a although there is a significant difference in the azimuth of these two vectors the motion of yakutat relative to north america is almost exactly parallel to the strike of the fairweather fault suggesting that most deformation inboard of yakutat is right lateral strike slip on the fairweather fault or faults parallel to it and that significant motion normal to the fairweather fault occurs offshore of yakutat the gps velocity at yakutat is also used to help constrain the slip rate and locking depth of the fairweather fault

terrane motion by strike slip faulting of forearc slivers forearc slivers bounded by a trench and an active strike slip fault occur in about 50 of modern subduction zones analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1 2 cm yr tertiary transport of some forearc slivers by 1000 km or more is therefore expected as a consequence of normal subduction active arc parallel strike slip faulting occurs whenever interplate coupling is strong and convergence is somewhat oblique strike slip rate increases with greater convergence obliquity

granulite facies lower crustal xenoliths from the eifel west germany petrological and geochemical aspects petrographic petrological and geochemical data for 16 mafic meta igneous granulite facies lower crustal xenoliths from the east eifel were collected in order to develop a model for the lower crustal history for this region the xenoliths consist of plagioclase amphibole clinopyroxene garnet orthopyroxene scapolite opaque minerals apatite rutile zircon garnet has reacted to a variable extent with plagioclase and clinopyroxene to form a corona of plagioclaseii amphibole orthopyroxeneii pyroxenes and plagioclases show complex zoning patterns with regard to al and ca which can be interpreted in terms of p t history decreasing temperature and pressure conditions are recorded by decreasing al in clinopyroxene rims coexisting with increasing anorthite contents in plagioclase rims and the breakdown of garnet in addition a young heating event that affected the granulites to different degrees is inferred from the complementary ca zoning patterns in clino and orthopyroxenes rare earth element ree patterns of whole rocks together with the trends displayed and fractionated liquids ree analyses of the mineral separates display equilibrium partitioning patterns for amphibole and clinopyroxene although isotopic data show that amphibole contains externally derived sr and nd components not recognized in other minerals at least a 4 stage history for the granulites is recorded 1 intrusion and crystal fractionation of basaltic magmas in the lower crust probably accompanied by crustal assimilation 2 granulite facies metamorphism 3 a decrease in temperature and pressure and 4 a later heating event the complicated thermal history is reflected in sm nd mineral isochron ages which range from about 170 ma down to about 100 ma and cannot be assigned to distinct geological events these ages correlate with inferred temperatures the low ages are measured for xenoliths with the highest temperatures in some cases the young heating event is likely to be responsible for partial resetting of the mineral isochrons

primary positive eu anomaly in clinopyroxenes of low crust gabbroic rocks abstract positive eu and sr anomalies have been found in whole rocks and clinopyroxenes as well as feldspars in gabbros of the deep crustal mafic intrusion of the ivrea zone northwestern italy these anomalies are particularly pronounced at one stratigraphie level of the intrusion the upper part of the upper zone of the layered series huz the eu eu ratios range from 19 to 40 in plagioclases and from 3 to 14 in the coexisting clinopyroxenes mass balance calculations show that metamorphic redistribution of eu from plagioclase cannot account for the positive eu anomalies of the clinopyroxenes and that a corresponding anomaly in the parent melt is required speculatively this feature is attributed to mixing of a mantle component with crustal highly polymerized melts deriving from advanced anatexis of granulite facies metasediments the existence in the deep crust of hybrid melts having a positive eu anomaly may be important for the eu balance between the lower and upper crust

a model of reverse differentiation at dikii greben volcano kamchatka progressive basic magma vesiculation in a silicic magma chamber dikii greben volcano is the largest modern volcano with silicic rocks in the kurile kamchatka island arc it consists of many domes and lava flows of rhyodacite dacite and andesite which were erupted in a reverse differentiation sequence non equilibrium phenocryst assemblages quartz mg rich olivine an rich an poor plagioclase etc abundance of chilled mafic pillows in the dacites and andesites and linear variations of rock compositions in binary plots are considered as mineralogical textural and geochemical evidence for mixing mafic pillows in volcanics have a lower density because of high porosity and contain the same non equilibrium phenocryst assemblages as the host rocks their groundmass contains skeletal microlites of plagioclase and amphibole proving that the groundmass as well as the pillows themselves formed from a water rich basaltic magma at depth they are considered as supercooled vesiculated floating drops of a hot hybrid layer in the magma chamber which formed after refilling the lower density of the inclusions allows them to float in the host magma and to concentrate at the top of the chamber prior to eruption magma mingling was effected by mechanical disintegration of the inclusions in the host magma during eruption the rhyodacitic and basic end members of the mixing series cannot be linked by low p fractionation though high p amphibole rich fractionation is not excluded

earthquakes in the pamplona zone yakutat block south central alaska the pamplona zone is a region of complex deformation and moderate seismicity located within the yakutat block a region that has been relatively aseismic since a series of large m 7 8 earthquakes in 1899 in 1970 a sequence of moderate to large sized earthquakes occurred within the pamplona zone largest event of mw 6 7 together with a mw 6 1 event in 1958 these events are the only m 5 5 events known to have occurred in the pamplona region since 1900 thus these events give important information on internal deformational processes within the yakutat block waveform modeling of three earthquakes in april 1970 showed rupture complexity along low angle thrust faults focal depths indicate that two of the events occurred above the wrangell aleutian megathrust while the largest event may have occurred on the megathrust events in 1958 and february 1970 indicate that deformation within the western pamplona zone is occurring along high angle 60 faults with reverse oblique motion we believe the pamplona spur the easternmost part of the pamplona zone may have behaved as an asperity during the 1899 sequence the location of the spur may be influenced by a north south trending fault zone in the subducting pacific plate that appears to be responsible for the 1987 1992 gulf of alaska sequence occurring 50 to 200 km south of the pamplona zone

u pb zircon and sm nd dating of moldanubian hp ht granulites from south ohemia czech republic conventional multigrain u pb systematics of zircon and single grain evaporation data of zircons in combination with nd model ages are presented for pyroxene free felsic garnetiferous granulites and orthopyroxene bearing granulites of felsic mafic and intermediate composition from the blansky les mountains granulite complex s bohemia zircons from mafic and intermediate granulites yield concordia intercept ages between 346 5 and 351 6 ma as well as a single grain evaporation age of 346 12 ma these ages define the time of variscan high grade metamorphism in s bohemia and are supported by an internal sm nd garnet zircon plagioclase whole rock isochron age of 343 21 ma euhedral zircons from felsic granulites of probable granitic derivation yield u pb ages of 366 5 ma and 373 12 ma interpreted as intrusion ages of the granitic precursor an inherited proterozoic crustal component is documented by poorly defined concordia upper intercept ages around 1700 ma and nd model ages between 1 3 and 2 1 ga

mineralogy geochemistry and petrogenesis of kurile island arc basalts whole rock major and trace element and mineral chemical data are presented for basaltic rocks from the main evolutionary stages of the kurile island arc nw pacific an outer inactive arc contains a cretaceous lower tertiary sequence of tholeiitic calcalkaline and shoshonitic basalts the main arc miocene quaternary is dominated by weakly tholeiitic with lesser alkalic basalts the mineralogy of kuriles basalts is characterised by an rich plagioclases a continuous transition from chromites to titanomagnetites pyroxenes with low fe3 contents and without strong fe enrichment abundance of groundmass pigeonites and the absence of amphiboles there is an increase in k2o contents both along arc northwards and towards the reararc side the basalts show an exceptionally wide but continuous range of k2o contents 0 1 4 7 which correlate with other lil element contents tholeiitic basalts with low lil element contents la yb and th u but high k rb p2o5 la and zr nb were derived from depleted lherzolitic mantle which had suffered fluid metasomatism by k rb cs sr ba pb and h2o only alkali basalts are also thought to be derived from depleted mantle but melt metasomatism involved addition of all lil elements to a garnet lherzolite mantle the kuriles basalts and their mantle sources range continuously between these two end member compositions the metasomatic fluids melts were probably released by early dehydration and later melting within subducted oceanic lithosphere though the process is not adequately constrained

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

mechanics of graben formation in crustal rocks a finite element analysis small 1 10 km wide grabens are ubiquitous tectonic structures that have been observed on the surfaces of all the terrestrial planets and satellites in spite of their frequent occurrence there is no fundamental understanding of how they form other than that they are characteristic of extensional terranes this paper examines the mechanics of the initial stages of graben formation and demonstrates that the configuration of a pair of antithetically dipping normal faults a graben is the energetically most favorable fault configuration in elastic brittle rocks subjected to pure extension a corollary to this hypothesis is that the occurrence of synthetic normal faults is indicative of a stress field other than purely extensional or of nonhomogeneous characteristics of the rock the analysis proceeds by computing the stress field in the vicinity of a single initial normal fault using a two dimensional finite element model it is shown that slip on this fault substantially lowers the proximity to failure of the surrounding rocks except for two small regions one near the surface of the downthrown block and the other near the fault tip the region on the downthrown block is located a horizontal distance from the initial fault slightly less than the fault s depth the proximity to failure actually increases here and a secondary fault develops an antithetic secondary fault would link this region with the other failure zone near the fault tip to demonstrate the preference for antithetic secondary faults more rigorously we show that this fault configuration results in a smaller total strain energy than the synthetic configuration in addition a two layer model is used to show that the graben s width is only weakly dependent upon the presence of mechanically distinct layers in the crust both weak over strong and strong over weak configurations are investigated the depth of the initial fault and the thickness of the top layer are varied and the width of the resulting graben is evaluated by computing the distance between the initial fault and the region of highest proximity to failure near the surface this analysis indicates that the depth of the initial fault is the major factor controlling graben width

crustal xenoliths from tertiary volcanics of the northern hessian depression a suite of crustal xenoliths from tertiary basaltic tuffs of the northern hessian depression nhd volcanic field comprises abundant meta igneous pyroxene granulites of mafic noritic to anorthositic iat and tonalitic composition less abundant are granitic tonalitic and leucogranitic gneisses and metasedimentary xenoliths a total of 49 samples were analyzed for modal compositions for major and trace elements including li rb sr ba cs v sc cr co ni y zr nb ta hf th and ree and oxygen isotopes two pyroxene thermometry yields temperatures between 700 and 900 c for mafic and noritic granulites feldspar thermometry indicates temperatures of 660 710 c for tonalitic granulites and 470 520 c for granitic and tonalitic gneisses one highly depleted sillimanite rich metasediment contains cordierite and garnet which have equilibrated at temperatures of 780 c the general lack of garnet in the mafic and noritic granulites and the presence of sillimanite in felsic xenoliths indicates that metamorphic pressures have not exceeded 10 kb major and trace element data and oxygen isotope compositions of the mafic granulites are compatible with an origin from spilitized enriched type morb rocks enrichment in 18o to 11 and in li to 34 ppm at average sio2 contents of 44 1 wt these low t spilites were transformed into amphibolites and then pyroxene granulites during subsequent high temperature metamorphic events low si al k and rb concentrations along with an contents in plagioclase ranging from near 50 to 98 mole percent suggest that amphibolite facies protoliths have generated tonalitic melts during partial melting at temperatures above 700 c the mafic granulite xenoliths are interpreted as restites whereas the tonalitic samples probably represent the extracted partial melts derived by 20 to 30 percent degree of melting metasedimentary xenoliths strongly depleted in granitic component could represent restites from which granitic s type partial melts have been extracted tonalitic and leucogranitic gneisses including one trondhjemite xenolith have many chemical characteristics e g ree distribution in common with tonalite trondhjemite granodiorite suites of the north atlantic region but cannot be accounted for a more specific origin estimated elastic properties of the main types of nhd xenoliths yield p wave velocities of 6 0 6 4 km 1 for granitic tonalitic and trondhjemite gneisses including tonalitic granulites and 6 5 7 0 for the more mafic xenoliths when compared with two seismic depths vp profiles these data are in accordance with a model where the mafic andesitic noritic and tonalitic granulites comprise abundant rock types at depths between 29 km moho and 20 km which mainly consists of old oceanic crust including subduction related volcanic products the more felsic xenoliths probably represent material from depths between 12 and 20 km

a geodynamic framework for eastern mediterranean kinematics we use a finite element model incorporating plate motion boundary conditions fault constraints and space geodetic velocities to calculate eastern mediterranean plate kinematics and to estimate the motion of the region s major faults we then use subsets of these constraints to generate models testing different scenarios of driving forces slab roll back at the hellenic arc arabian plate push gravitational collapse of w anatolia to match the expected pattern of deformation we find that models combining only trench rollback and arabian push are unable to provide a good match to the observed deformation across western anatolia and the aegean and that we need to introduce the effects of mantle corner flow and gravitational collapse to fit observations

improving temporal resolution in ambient noise monitoring of seismic wave speed 1 the use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales besides passive tomography passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the san andreas fault in parkfield california one of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal to noise ratio snr for the phase fluctuations to be measured accurately for the application to passive monitoring one wants the possibility of following short term velocity variations 1 day or less using noise correlation functions calculated on short time windows another difficulty may then appear when the spatial distribution of noise sources also evolves with time the aim of this paper is to introduce an adaptive filter to the parkfield data set in order to improve the snr output of the ambient noise correlation functions when applied to passive monitoring the temporal resolution can be increased from 30 days up to 1 day with this improved temporal resolution the velocity drop observed at parkfield is shown to be cosesimic with the 24 september 2004 mw 6 0 event the relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated finally the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation

measurement of horizontal motions in alaska using very long baseline interferometry we have analyzed 6 years of very long baseline interferometry vlbi data beginning in 1984 from a network of sites in alaska the yukon and the conterminous united states the analysis of these 53 data sets includes constrained continuous piecewise linear estimation of the site atmospheres and clocks application of values and correlations from a self consistent earth orientation series derived from other vlbi data and simultaneous estimation of site positions and velocities from a solution that includes 21 007 observations with a fit of 40 ps in delay and 64 fs s in delay rate we have determined the horizontal velocities of seven sites with precisions of 0 5 2 mm yr 1 standard deviation the three vlbi sites within the alaska aleutian subduction boundary zone yakataga kodiak and sand point have higher instantaneous velocities relative to eastern north america than the interior sites of alaska fairbanks and sourdough the estimated velocity of yakataga relative to fairbanks is 37 8 1 3 mm yr at n27 w 2 modeling of the yakataga data suggests that the observed motion is the result of elastic straining of the overriding plate due to a locked main thrust zone with a component of oblique slip the estimated velocity of kodiak relative to fairbanks is 13 6 0 8 mm yr at n41 w 3 this result is lower than the rate predicted on the basis of simple elastic dislocation models the estimated velocity of sand point relative to fairbanks is 6 4 0 9 mm yr at n65 w 8 the component of this velocity in the plate direction 3 5 1 1 mm yr is not consistent with either an aseismic slip model i e no strain accumulation in the overriding plate or a model in which the site is undergoing compressional strain 10 9 mm yr at n28 w due to simple subduction at the predicted orientation of pacific plate convergence in a north america fixed reference frame the estimated velocities of fairbanks 1 5 0 5 mm yr at s12 e 20 and sourdough 3 9 1 0 mm yr at s13 w 13 are both southward these results may imply motion of this region relative to stable north america but more observations are required to reduce the uncertainties in the azimuths the time evolution of the estimated site positions from vlbi in alaska are in general consistent with constant velocity however in 1988 the yakataga site showed a significant departure from the position predicted from a constant velocity model obtained from the previously estimated position this departure may be static displacement associated with two major strike slip earthquakes that occurred in the gulf of alaska between the 1987 and 1988 measurement sessions

crustal xenoliths from cenozoic volcanic fields of west germany implications for structure and composition of the continental crust crustal xenoliths in three cenozoic volcanic fields of west germany the northern hessian depression nhd the eifel and the urach hegau include medium to high grade meta sedimentary and felsic to mafic meta igneous rocks also present in all three suites are pyroxenites and hornblendites for each volcanic field a model crustal profile is proposed based on calculated or measured p wave velocities of xenoliths and depth vp relationships egt central segment and rhenish massif traverses the xenolith lithologies from the nhd and the eifel show some similarities the middle crust between the depths of about 10 and 25 km consists mainly of meta sediments felsic gneisses and granulites meta sedimentary rock types are particularly abundant in the eifel at depths of between about 5 and 15 km but are less common within the nhd xenolith collection the felsic gneisses range from meta granites to meta tonalites i and s type eifel meta sediments range from meta pelites to meta greywackes and meta quartzites the nhd xenolith suite contains a few highly depleted granulite facies meta sedimentary fragments at depths between 24 and 26 km the increase in vp from about 6 8 to 8 km s 1 28 34 km is correlated with the presence of mafic granulites intercalated with eclogites pyroxenites and hornblendites beneath north hessia the granulite layer problably grades into a composite eclogite peridotite layer at the lower part of this transition zone the crust beneath the urach hegau consists largely of meta sediments with subordinate felsic meta igneous rocks most of the meta sedimentary samples seem to be depleted in felsic components suggesting intra crustal differentiation by partial melting the urach crust contains lithologies which are similar to the outcropping moldanubian type para gneisses of the black forest mafic and ultramafic xenoliths from the urach hegau differ in their mineralogy and chemical composition from the eifel and nhd mafic granulites they represent meta cumulates derived from alkaline magmas which intruded the base of the crust and underwent deformation and recrystallization petrographic and chemical differences between urach hegau and eifel nhd are believed to reflect the contrasting styles of crustal evolution in the rhenohercynian and the moldanubian belts of the variscan orogen

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

mid pleistocene lavas from the seguam volcanic center central aleutian arc closed system fractional crystallization of a basalt to rhyodacite eruptive suite in contrast to adjacent volcanic centers of the modern central aleutian arc seguam island developed on strongly extended arc crust k ar dates indicate that mid pleistocene late pleistocene and holocene eruptive phases constitute seguam this study focuses on the petrology of the mid pleistocene 1 07 07 ma turf point formation tpf which is dominated by an unusual suite of porphyritic basalt and basaltic andesite lavas with subordinate phenocryst poor andesite to rhyodacite lavas increasing whole rock feo mgo from basalt to dacite the anhydrous plag ol cpx opx mt phenocryst assemblage groundmass pigeonite and the reaction ol liq opx preserved in the mafic lavas indicate a tholeiitic affinity thermometry and comparison to published phase equilibria suggests that most tpf basalts crystallized plag ol cpx mt at 1160 c between about 3 5 kb 1 2 h2o andesites crystallized plag cpx opx mt at 1000 c between 3 4 kb with 3 5 h2o and dacites crystallized plag cpx opx mt at 1000 c between 1 2 kb with 2 3 h2o all lavas crystallized at f o 2 close to the nno buffer mineral compositions and textures indicate equilibrium crystallization of the evolved lavas petrographic evidence of open system mixing or assimilation is rare mgo cao al2o3 cr ni and sr abundances decrease and k2o na2o rb ba zr and pb increase with increasing sio2 50 71 lree enrichment ce yb n 1 7 0 2 characterizes most tpf lavas total ree contents increase and eu anomalies become more negative with increasing sio2 relative to other aleutian volcanic centers tpf basalts and basaltic andesites have lower k2o na2o tio2 rb ba sr zr y and lree abundances 87sr 86sr ratios 0 70361 0 70375 and ratios of 206pb 204pb 18 88 18 97 207pb 204pb 15 58 15 62 208pb 204pb 38 46 38 55 are the highest measured for any suite of lavas in the oceanic portion of the aleutian arc conversely end values 5 8 to 6 7 are among the lowest from the aleutians sr nd and pb ratios are virtually constant from basalt through rhyodacite whereas detectable isotopic heterogenity is observed at most other aleutian volcanic centers major and trace element ree and sr nd and pb isotopic compositions are consistent with the basaltic andesitic andesitic dacitic and rhyodacitic liquids evolving from tpf basaltic magma via closed system fractional crystallization alone fractionation models suggest that removal of 80 wt cumulate 61 plag 17 cpx 12 opx 7 ol and 3 mt can produce 20 wt rhyodacitic residual liquid per unit mass of parental basaltic liquid petrologic and physical constraints favor segregation of small batches of basalt from a larger mid crustal reservoir trapped below a low density upper crustal lid in these small magma batches the degree of cooling crystallization and fractionation are functions of the initial mass of basaltic magma segregated the thermal state of the upper crust and the magnitude of extension tholeiitic magmas erupted at seguam evolved by substantially different mechanisms than did calc alkaline lavas erupted at the adjacent volcanic centers of kanaga and adak on unextended arc crust these variable differentiation mechanisms and liquid lines of descent reflect contrasting thermal and mechanical conditions imposed by the different tectonic environments in which these centers grew at seguam intra arc extension promoted eruption of voluminous basalt and its differentiates unmodified by interaction with lower crustal or upper mantle wallrocks

temporal change in site response caused by earthquake strong motion as revealed from coda spectral ratio measurement 1 the spectral ratios of coda waves of local earthquakes have been often used as measures of relative amplification factors of different sites applying this method to coda waves registered by seismometers installed on the surface and at the bottom of a borehole we succeeded in stably measuring the temporal change in site response associated with the occurrence of a large earthquake strong motion a remarkable drop of coda spectral ratio and a shift of the peak frequency were observed during strong shake at two sites by the 2000 western tottori earthquake and at a site by the 2003 tokachi oki earthquake in japan the reduction of the peak frequency reached 30 70 at all the sites after that the peak frequency logarithmically recovered to the value before the strong motions for a few years at two sites whereas the other one quickly recovered in a few tens of minutes

nd sr systematics of the setouchi volcanic rocks southwest japan a clue to the origin of orogenic andesite abstract twenty three volcanic rocks from the setouchi volcanic belt southwest japan were analyzed for nd and sr isotopic compositions for the purpose of examining the genetic relationships among the basalt high magnesium andesite hma and evolved porphyritic andesite the andesites have higher 87 sr 86 sr 0 70487 0 70537 and lower 143 nd 144 nd 0 512509 0 512731 than the basalts i e 0 70408 0 70468 and 0 512691 0 512830 respectively this result confirms earlier conclusions obtained from petrologic study that the andesites cannot be fractionation products of basaltic magma but that the andesitic and basaltic magmas were generated independently on the basis of melting experiments for hma and basalt it is inferred that there is an isotopically stratified mantle beneath southwest japan evolved porphyritic andesites have essentially identical sr and nd isotopic ratios to hma and can be derived by fractionation of primary andesitic magma a model to produce orogenic andesite is proposed on petrologic experimental and isotopic bases

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

seismic potential of southern italy abstract to improve estimates of the long term average seismic potential of the slowly straining south central mediterranean plate boundary zone we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs we express seismic potential long term average earthquake recurrence rates as a function of magnitude in the form of truncated gutenberg richter distributions for seven seismotectonic source zones seismic coupling seems to be large or even complete in most zones an exception is the southern tyrrhenian thrust zone where most of the african european convergence is accommodated here aseismic deformation is estimated to range from at least 25 along the western part to almost 100 aseismic slip around the aeolian islands even so seismic potential of this zone has previously been significantly underestimated due to the low levels of recorded past seismicity by contrast the series of 19 m6 7 earthquakes that hit calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration and seismic potential is revised downward the southern tyrrhenian thrust zone and the extensional calabrian faults as well as the northeastern sicilian transtensional zone between them which includes the messina straits where a destructive m7 event occurred in 1908 all have a similar seismic potential with minimum recurrence times of m 6 5 of 150 220 years this potential is lower than that of the southern apennines m 6 5 recurring every 60 to 140 years but higher than that of southeastern sicily minimum m 6 5 recurrence times of 400 years the high seismicity levels recorded in southeastern sicily indicate some clustering and are most compatible with a tectonic scenario where the ionian deforms internally and motions at the calabrian trench are small the estimated seismic potential for the calabrian trench and central and western sicily are the lowest minimum m 6 5 recurrence times of 550 800 years most zones are probably capable of generating earthquakes up to magnitudes 7 7 5 with the exception of central and western sicily where maximum events sizes most likely do not exceed 7

new 42 ma cratonic north american paleomagnetic pole from the yukon underscores another cordilleran paleomagnetism geology conundrum eocene posttectonic plutons of the beaver river alkalic complex in southeastern yukon intruded devonian mississippian and triassic sandstones in the foothills of the canadian cordillera a paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods the a component characteristic remanent magnetization chrm resides in magnetite with normal polarity in the 42 6 0 8 ma beaver river pluton reversed polarity in the 42 1 0 7 ma larson creek east pluton and both polarities in the 41 3 0 4 ma larson creek west pluton corresponding with magnetic polarity chrons 20n 19r and the boundary between chron 19r and 18n respectively the chrms of the plutons are indistinguishable 2 with a mean for the 42 0 0 5 ma complex of d 158 8 i 73 1 n 21 sites 95 3 0 k 116 8 a positive paleomagnetic contact test shows the a component to be primary and the poorly isolated b component

post rift compressional reactivation potential of passive margins and extensional basins poly phase deformation of a compressional nature is a common feature in the post rift evolution of passive margins and rifts the compressional mode of deformation in these sedimentary basins originally formed by extension in an intraplate setting is characterized by a spectrum of spatial wavelengths spanning several tens of kilometres up to several hundreds of kilometres the actual mode of compressional deformation appears to be strongly affected by the rheological structure of the underlying lithosphere the level of the regional intraplate stress field and the geometry of the rifted basin configuration prior to late stage compressional reactivation the interplay of plumes and intraplate compressional deformation can lead to temporal transitions from basin inversion to lithospheric folding these modes of deformation lead to substantial differential vertical motions late stage anomalies in subsidence and uplift patterns the development of innovative combinations of numerical and analogue modelling techniques is the key to differentiating different modes of compressional deformation of passive margins and extensional basins the geological society of london 2008

3 d electromagnetic imaging of a palaeozoic plate tectonic boundary segment in sw iberian variscides s alentejo portugal abstract in sw iberian variscides the boundary between the south portuguese zone spz and the ossa morena zone omz corresponds to a major tectonic suture that includes the beja acebuches ophiolite complex baoc and the pulo do lobo antiform terrane plat three sub parallel and approximately equidistant mt profiles were performed covering a critical area of this palaeozoic plate tectonic boundary in portugal the profiles running roughly along an ne sw direction are sub perpendicular to the main variscan tectonic features results of the three dimensional 3 d modelling of mt data allow to generate for the first time a 3 d electromagnetic imaging of the omz spz boundary which reveals different conductive and resistive domains that display morphological variations in depth and are intersected by two major sub vertical corridors these corridors coincide roughly with the ne sw messejana strike slip fault zone and with the wnw ese ferreira ficalho thrust fault zone the distribution of the shallow resistive domains is consistent with the lithological and structural features observed and mapped integrating the expected electrical features produced by igneous intrusions and metamorphic sequences of variable nature and age the development in depth of these resistive domains suggests that 1 a significant vertical displacement along an early tectonic structure subsequently re taken by the messejana fault zone in late variscan times has to be considered to explain differences in deepness of the base of the precambrian cambrian metamorphic pile 2 hidden syn to late collision igneous bodies intrude the meta sedimentary sequences of plat 3 the roots of baoc are inferred from 12 km depth onwards forming a moderate resistive band located between two middle crust conductive layers extended to the north in omz and to the south in spz these conductive layers overlap the iberian reflective body evidenced by the available seismic reflection data and are interpreted as part of an important middle crust decollement developed immediately above or coinciding with the top of a graphite bearing granulitic basement

global tectonics and space geodesy much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries m 1 to 60 kilometers wide nonetheless many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide wide plate boundary zones cover m 15 percent of earth s surface area space geodesy which includes very long baseline radio interferometry satellite laser ranging and the global positioning system is providing the accurate long distance measurements needed to estimate the present motion across and within wide plate boundary zones space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years