circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

a new geological map of the brabant massif belgium a new geological map mostly subcrop of the brabant massif is presented based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area new interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes a structural model of the western northern and southern parts of the brabant massif is presented the main anticlinal axis plunges towards the west northwest its core comprising upper precambrian to lower cambrian terrigenous rocks which outcrop in the southeast to the north of the main axis younger rocks appear in regular succession but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc

on the subsurface cfc maxima in the subtropical north pacific thermocline and their relation to mode waters and oxygen maxima the spatial structure of the subsurface chlorofluorocarbon cfc concentration maxima in the subtropical north pacific is examined using data from the pacific ocean sector of the world ocean circulation experiment woce hydrographic program collected in the period 1991 1994 comparison with potential vorticity pv sections reveals that the cfc maxima coincide with the pv minimum associated with subtropical mode water stmw in the western pacific as suggested by earlier observations warner et al 1996 in the eastern part of the central pacific the cfc maxima appear to be shallower than the central mode water cmw while they are deeper than the eastern subtropical mode water in the eastern pacific a subsurface oxygen maximum also coincides with stmw and the cfc maxima in the west is located between the cfc maxima and cmw in the central pacific and is absent in the east the collocation in the west is explained by the fact that stmw is the densest water to outcrop in the recirculation to the south of the kuroshio and the kuroshio extension while denser water is not directly ventilated in this region data from two post woce cruises and results from a steady state age model indicate that the cfc maxima are transient and are deepening such that the collocation of the cfc maxima and stmw does not persist in the late 1990s model experiments based on a smooth age profile demonstrate that the deepening of the cfc maxima is closely related to changes in the atmospheric cfc growth rates

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

a new look at belgian aeromagnetic and gravity data through image based display and integrated modelling techniques digital processing and image based display techniques have been used to generate contour and shaded relief maps of belgian aeromagnetic data at a scale of 1 300000 for the whole of belgium these highlight the important anomalies and structural trends particularly over the brabant massif north and vertically illuminated shaded relief plots enhanced structural belts trending west east to northwest southeast in the brabant massif and west east to southwest northeast in the core of the ardennes the principal magnetic lineaments have been identified from the shaded relief plots and tentatively correlated to basement structures most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures magnetic highs within the brabant massif are attributed to folded sediments of the tubize group the magnetic basement in the east of belgium is sinistrally displaced to the north by an inferred deep nnw sse crustal fracture the bouguer anomaly map of belgium identifies the ardennes as a negative area and the brabant massif as a positive area with the exception of a wnw trending gravity low in its western part the southern margin of the brabant massif is defined by a steep gravity gradient coincident with the faille bordiere border fault trial modelling of the gravity and magnetic data carried out along profiles across the brabant and stavelot massifs has identified probable acid igneous intrusions in the western part of the brabant massif and a deep magnetic lower density body underlying the whole ardennes region which is thought to be a distinctive precambrian crustal block

palaeozoic amalgamation of central europe new results from recent geological and geophysical investigations abstract multidisciplinary studies of geotransects across the north european plain and southern north sea and geological reexamination of the variscides of the north bohemian massif permit a new 3 d reassessment of the relationships between the principal crustal blocks abutting baltica along the trans european suture zone tesz accretion was in three stages cambrian accretion of the bruno silesian lysogory and malopolska terranes end ordovician early silurian accretion of avalonia and early carboniferous accretion of the armorican terrane assemblage ata palaeozoic plume influenced metabasite geochemistry in the bohemian massif explains the progressive rifting away of peri gondwanan crustal blocks before their accretion to baltica geophysical data faunal and provenance information from boreholes and dated small inliers and cores confirm that avalonian crust extends beyond the anglo brabant deformation belt eastwards to northwest poland the location and dip of reflectors along the tesz and beneath the north european plain suggest that avalonian crust overrode the baltica passive margin marked by a high velocity lower crustal layer on shallowly southwest dipping thrust planes forming the heligoland pomerania deformation belt the variscan orocline of southwest poland masks two junctions between the armorican terrane assemblage ata and previously accreted crustal blocks to the east is a dextrally transpressive contact with the bruno silesian and malopolska blocks accreted in the cambrian while to the north is a thrust contact with easternmost avalonia deeply buried beneath younger sedimentary cover in the northeast bohemian and rhenohercynian massifs devonian early variscide deformation dominated by wnw and nw directed thrusting records closure of ordovician devonian seaways between detached islands of the ata and avalonia

ventilation of the subtropical north pacific the shallow salinity minimum abstract the shallow salinity minimum of the subtropical north pacific is shown to be a feature of the ventilated wind driven circulation subduction of low salinity surface water in the northeastern subtropical gyre beneath higher salinity water to the south causes the salinity minimum variation of salinity along surface isopycnals causes variations in density and salinity at the minimum a model of ventilated flow is used to demonstrate how the shallow salinity minimum can arise the model is modified to account for nonzonal realistic winds it is also extended to examine the three dimensional structure of the western shadow zone the boundary between the subtropical and subpolar gyres is given by the zero of the zonal integral of ekman pumping the western shadow zone fills the subtropical gyre at the base of the ventilated layers and decreases in extent with decreasing density for parameters appropriate to the north pacific the eastern shadow zone is of very limited extent observations of salini

diapycnal diffusivity at the upper boundary of the tropical north atlantic oxygen minimum zone a deliberate tracer release experiment in 2008 2010 was used to study diapycnal mixing in the tropical northeastern atlantic the tracer cf3sf5 was injected on the isopycnal surface 26 88 kg m 3 which corresponds to about 330 m depth three surveys performed 7 20 and 30 months after the release sampled the vertically and laterally expanding tracer patch the mean diapycnal mixing estimate over the entire region occupied by the tracer and the period of 30 months was found to be 1 19 0 18 10 5 m2 s 1 or alternatively 3 07 0 58 10 11 kg m 3 2 s 1 as computed from the advection diffusion equation in isopycnal coordinates with the thickness weighted averaging the latter method is preferable in the regions of different stratification for it yields local diapycnal mixing estimates varying less with stratification than their cartesian coordinate counterparts results of this study are comparable to the results of the north atlantic tracer release experiment natre however the internal wave wave interaction models predict reduced mixing from the breaking of internal waves at low latitudes thus the diapycnal diffusivity found in this study is higher than parameterized by the low latitude of the site 4 n 12 n

modeling of source rupture characteristics for the saguenay earthquake of november 1988 the magnitude mb 6 0 saguenay earthquake of 25 november 1988 in quebec canada was one of the largest to have occurred in eastern north america during the past half century recorded high frequency ground motions exceeded anticipated values for an event of its size by a factor of 10 on both the regional network and strong motion instruments two proposed explanations for the discrepancy are 1 that the source was a rare high stress drop event and 2 that it was an asymmetrical fractional stress drop rupture involving only normal effective stresses in this article detailed fault slip models are derived to fit characteristics of strong motion displacement velocity and acceleration data the results establish that the effective rupture stress was normal less than 100 bars that the fault rupture was highly asymmetrical with respect to the point of rupture initiation and that the average slip time for points within the rupture area approx 0 2 sec was considerably less than that associated with the standard brune 1970 source spectral model the rupture area developed in a number of episodes each widening or lengthening the previously ruptured area which may explain the short average slip time the results indicate that the widely used assumption in hazard analyses that earthquake spectra are adequately represented by the standard brune 1970 complete stress drop model may be seriously unreliable for prediction of strong ground motion in eastern north america

use of empirical green s functions spectral ratios and kinematic source models for simulating strong ground motion abstract ground motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern north america ena very few direct observations of such ground motions have been obtained however because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available because of the generally large distances between recording stations the main source of useful data comes from lg wave trains observed at relatively large distances for the two largest earthquakes to have occurred near populated regions of southeastern canada during the past decade spectral ratios of the lg wave trains of the mainshocks with respect to those of their aftershocks are found to depend almost entirely upon the source radiation characteristics of the sources alone this result is utilized to derive elastodynamically based kinematic rupture models that are consistent with the empirical spectral ratio data such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region in converse application it is shown that spectral ratios obtained from such models along with empirical seismograms from small earthquakes can be used to accurately simulate strong ground motions at short and moderate as well as large distances as such small event seismograms are relatively plentiful the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models the solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling

interpreting fold and fault geometries from within the lateral to oblique parts of slumps a case study from the anglo brabant deformation belt belgium abstract using a rigorous comparison of as many slump fold based and slump related fault based methods as possible also small complex data sets can be used to deduce a reliable slump transport direction and sense this is exemplified using late early ordovician to middle ordovician slump features of the anglo brabant deformation belt the suggested procedure involves a an analysis of fold data by means of 1 the mean axis method 2 the separation arc method 3 the axial planar intersection method 4 the fold hinge azimuth and interlimb angle method 5 the fold axial surface strike and interlimb angle method and 6 the axial surface dip and dip direction method b an analysis of slump related fault data by means of 1 the mean fault orientation method 2 the fault separation method 3 the fault intersection method and 4 the best fit girdle to fault poles method and finally c a rigorous comparison of the results of the different methods several possible diagnostic criteria are put forward for distinguishing slump deformation features trending at low angles to transport direction oblique to lateral parts of slump sheets or internal lobes or tongues and slump deformation features trending at high angles to transport direction frontal to central parts of slump sheets these criteria include the relationship between fold interlimb angle and axial surface dip the plunge of the fanning axis of the reverse slump related faults and the plunge of the intersection of the reverse and normal slump related faults such criteria greatly facilitate the interpretation of the often confusing results of many classical methods moreover the plunge azimuth of the intersection of the normal and reverse slump related faults and the mismatch between slump transport direction inferred from fold based and fault based methods may both be diagnostic for dextrally deformed or sinistrally deformed slump sheet parts

rupture histories of eastern north american earthquakes abstract digital worldwide records of p and sh waves are used to invert for rupture histories of the recent larger eastern north american earthquakes the data include a broad bandwidth to facilitate recovery of both source details and total moment the following events are studied 9 january 1982 new brunswick 5 october and 23 december 1985 nahanni 25 november 1988 saguenay and 25 december 1989 ungava earthquakes we employ a finite fault waveform inversion scheme that discretizes the slip history as a function of position on the fault this formulation allows estimation of rise time and slip velocity in addition to the spatial distribution of slip static stress drops averaged over the entire rupture surface range from a few tens of bars to just over 100 bars and are similar to values estimated for western united states earthquakes estimates of stress drop for spatially limited asperities are in the range of a few hundred bars with the value for the saguenay earthquake asperity being the largest approaching 1 kbar the variation in stress drop is considerable but no evidence is seen for a scaling relation in which stress drop increases with moment maximum slip velocities on the fault also have a wide range from 50 cm sec to perhaps greater then 200 cm sec with the saguenay and 5 october nahanni earthquakes lying at the upper end of this range of the events studied the saguenay earthquake is unique in terms of its greater depth spatially concentrated source and large asperity stress drop

anatomy of a small intraplate earthquake a dissection of its rupture characteristics using regional data summary the magnitude mblg 5 0 mont laurier earthquake of 1990 october 19 in quebec canada was one of the largest to have occurred in eastern north america during the past decade high frequency ground motions recorded on regional network instruments exceeded values anticipated for an event of its size by a factor of 3 a commonly favoured explanation for the discrepancy is that the source was a rare high stress event in this paper detailed fault slip models are derived to fit waveform and spectral characteristics of the regional data the results establish that the effective rupture stress was normal about 100 bars that the fault rupture developed asymmetrically and that the average slip time for points inside the rupture area approx 0 1 s was significantly less than that associated with the standard brune 1970 source spectral model the rupture area developed in at least four distinct episodes each extending the previously ruptured area taken together with similar results for the mblg 6 5 saguenay earthquake of 1988 november the results indicate that a widely used assumption in hazard analyses that earthquake spectra are adequately represented by the standard brune spectral model is unreliable for the interpretation and prediction of strong ground motion

lower palaeozoic and precambrian igneous rocks from eastern england and their bearing on late ordovician closure of the tornquist sea constraints from u pb and nd isotopes the u pb isotope ages and nd isotope characteristics of asuite of igneous rocks from the basement of eastern england show that ordovician calc alkaline igneous rocks are tectonically interleaved with late precambrian volcanic rocks distinct from precambrian rocks exposed in southern britain new u pb ages for the north creake tuff zircon 449 13 ma moorby microgranite zircon 457 20 ma and the nuneaton lamprophyre zircon and baddeleyite 442 3 ma confirm the presence ofan ordovician magmatic arc tectonically interleaved precambrian volcanic rocks within this arc are verified by new u pb zircon ages for tuffs at glinton 612 21 ma and orton 616 6 ma initial end values for these basement rocks range from 4 to 6 consistent with generation of both c 615 ma and c 450 ma groups of rocksin continental arc settings the u pb and sm nd isotope data support arguments for an ordovician fold thrust belt extending from england to belgium and that the ordovician calc alkaline rocks formed in response to subductionof tornquist sea oceanic crust beneath avalonia

the metamorphic history of the concealed caledonides of eastern england and their foreland white mica illite crystallinity data derived mostly from borehole samples have been used to generate a contoured metamorphic map of the concealed caledonide fold belt of eastern england and the foreland formed by the midlands microcraton the northern subcrop of the fold belt is characterized by epizonal phyllites and quartzites of possible cambrian age whereas anchizonal grades characterize silurian to lower devonian strata of the anglian basin in the southern subcrop of the fold belt regional metamorphism in the anglian basin resulted from deep burial and acadian deformation beneath a possible overburden of 7 km assuming a metamorphic field gradient of 36 c km 1 late proterozoic volcaniclastic rocks forming the basement of the microcraton show anchizonal to epizonal grades that probably developed during late avalonian metamorphism cambrian to tremadoc strata showing late diagenetic alteration rest on the basement with varying degrees of metamorphic discordance during early palaeozoic times much of the microcraton was a region of slow subsidence with overburden thicknesses of 3 3 5 5 km however concealed tremadoc strata in the northeast of the microcraton reach anchizonal grades and may have been buried to depths of 7 km beneath an overburden of uncertain age

the cambrian to devonian odyssey of the brabant massif within avalonia a review with new zircon ages geochemistry sm nd isotopes stratigraphy and palaeogeography abstract this study provides an up to date and comprehensive review of the early palaeozoic evolution of the brabant massif belonging to the anglo brabant deformation belt situated at the southeastern side of avalonia microplate it is the only well known part of the northern passive margin of the rheic ocean the cambrian silurian sedimentary pile is 13 km thick with 9 km for the cambrian only the unraveling of this continuous registration reflects the successive rifting and drifting of avalonia from the gondwana mainland followed by soft collisional processes with baltica and finally the formation of laurussia based on recently established detailed stratigraphy sedimentology and basin development on u pb la icp ms analyses of igneous and detrital zircon grains along with geochemical data including sm nd isotopes a new geodynamic and palaeogeographic evolution is proposed brabant megasequence 1 lower cambrian to lowermost ordovician 9 km thick represents an embayment of the peri gondwanan rift from which the rheic ocean has evolved detrital zircon ages demonstrate that the brabant is a typical peri gondwanan terrane with a major pan african neoproterozoic age and a mixed west african and amazonian source palaeoproterozoic archaean and some mesoproterozoic age the transition towards the avalonia drifting is marked by an unconformity and a short volcanic episode the northward drift of avalonia towards baltica is recorded by the megasequence 2 middle to upper ordovician 1 3 km thick the source for mesoproterozoic zircons vanished as the result of the rheic ocean opening and the isolation from amazonian sources the transition to megasequence 3 is marked by a drastic change in palaeobathymetry and an important sub volcanic episode during a tectonic instability period 460 430 ma reflecting the avalonia baltica soft docking as also shown by the reappearance of mesoproterozoic detrital zircons typical of baltica unradiogenic nd isotope signature end 4 5 and tdm model ages 1 3 1 7 ga for brabant magmatic rocks indicate an old recycled component megasequence 3 uppermost ordovician to lowermost devonian 3 5 km thick includes the onset of a silurian foreland basin that reflects the tectonic inversion of the core of the massif brabantian orogeny in response to the baltica avalonia laurentia collision finally the comparison with the strikingly similar cambrian successions of the harlech dome wales avalonia and the meguma terrane nova scotia peri gondwana allows the construction of a new early cambrian palaeogeographic model for the whole avalonia microplate in which the meguma terrane is included

contractional kink bands formed by stress deflection along pre existing anisotropies examples from the anglo brabant deformation belt belgium and the north dobrogea orogen romania abstract kink bands within two slate belts the anglo brabant deformation belt belgium and the north dobrogea orogen romania reveal similar problems with respect to linking kink band geometries to expected palaeostress directions in the north dobrogea orogen the two opposite kink band sets of two different systems of conjugate kink bands develop for a wide variety of cleavage orientations in the anglo brabant deformation belt the occurrence of the two opposite kink band sets of a conjugate kink band system opposes the expected occurrence in both cases this can be attributed to stress deflection along a pre existing anisotropy moreover the presence of kink bands in the north dobrogea orogen with curving kink axes and curving kink band boundaries also puts doubt on the direct relationship between kink band geometry and stress the idea of stress deflection along a pre existing anisotropy and the strong control of the pre existing anisotropy on the kink band geometry and orientation has important implications for the use of kink bands as regional palaeostress indicators depending on the relative intensity and relative orientation of the pre existing fabrics here bedding and cleavage different mechanisms of kink band development may operate depending on the mechanism different solutions in terms of inferred palaeostress direction may exist

tracer dating and ocean ventilation the interpretation of transient tracer observations depends on difcult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions recent studies have attempted to circumvent this problem by making use of a derived quantity age based on the simultaneous distribution of two complementary tracers such as tritium and its daughter helium 3 the age is defined with reference to the surface such that the boundary condition takes on a constant value of zero we use a two dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms an interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age we define an idealized ventilation age tracer that is conservative with respect to mixing and we explore how its behavior compares with that of the tracer based ages over a range of advective and diffusive parameters transient tracers such as tritium and tritiugenic helium 3 chlorofiuorocarbons especially cfc 11 and cfc 12 and radiocarbon produced by nuclear bomb tests have entered the oceans primarily during the past 30 years the inherent time scale of these tracers matches very well typical time scales for thermocline ventilation as well as other important oceanic processes such as deep water formation they have been used with some success to study the time scales of thermocline ventilation e g sarrniento 1983 jenkins 1987 and oxygen utilization rates our e g jenkins 1977 1980 1982 1987 as well as other processes such as equatorial upwelling rates broecker et al 1978 quay et al 1983 wunsch 1984 and transport of upper north atlantic deep water weiss et al 1985 the problem of coping with the nonsteady state aspect of these tracers has been dealt with in many ways few of them truly satisfactory for example rooth and ostlund 1972 chose to estimate the diapycnic diffusivity in a region where there was some evidence that the tracer distributions were approximately in steady state at the time of their measurements wunsch 1984 used a similar steady state assumption in his study of equatorial upwelling using bomb radiocarbon such an argu ment cannot be applied in most regions of the ocean however indeed one can question whether it applies even in the above situations therefore one generally would expect that it would be necessary to know something about the evolution of the tracer concentration in time as well as the time history of the boundary conditions for that tracer over the same span of time for example sarrniento s 1983 tritium box model of the thermocline solved the conserva tion equation for the period of time between 1952 before nuclear bomb tests had injected a significant amount of tritium into the oceans and 1972 when a single realization of the tracer field was obtained by a series of field studies the surface concentration time history of dreisigacker and roether 1978 was used as a boundary condition such an l now at deutsche forschungs und versuchasanstalt ftir luft

intraplate seismicity of a recently deglaciated shield terrane a case study from northern ontario canada the economy of northern ontario canada is heavily dependent on mining so accurate knowledge of seismicity is important for the safe design and op eration of mines and other critical facilities including a proposed underground repos itory for nuclear waste in this study we analyzed 537 cataloged earthquakes that occurred from 1980 to 2006 seismicity is mainly concentrated in topographically elevated archean terranes northwest of lake superior and in the james bay and ka puskasing regions we analyzed waveforms to determine the focal depth for 331 re corded events using the regional depth phase modeling rdpm method coupled with surface wave relative amplitude analysis the majority of events are shallow 350 m although in the east ern part this pattern breaks down and some deeper earthquakes 12 km are ob served based on a moving window event counting technique we show that distinct spatial clusters of seismicity can be delineated that are statistically significant relative to background seismicity levels a particularly active cluster is located within james bay where focal depths range from a few kilometers to more than 20 km another cluster near kapuskasing contains deep focus events and may occur along a hot spot track that runs through western quebec near dryden a shallow 1 km earthquake swarm concentrated in a 1 1 km region commenced in may 2002 faded and then started up again in february 2003 shallow mining induced events are also common around sudbury a major world center for nickel mining the overall pattern of seis micity appears to correlate with upper mantle p wave velocity anomalies suggesting that lateral variations in mantle rheology may play a significant role in controlling intraplate seismicity of shield areas it is also likely that crustal stresses caused by glacial isostatic adjustment are an important factor although the correlation of seis micity with uplift rate is not as clear online material focal depth solutions for earthquakes in northern ontario canada

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

timing of magmatism foreland basin development metamorphism and inversion in the anglo brabant fold belt new data implying crustal activation of eastern avalonia along the anglo brabant fold belt are presented late ordovician subduction related magmatism in east anglia and the brabant massif coupled with accelerated subsidence in the anglia basin and in the brabant massif during silurian time indicate a foreland basin development final collision resulted in folding cleavage development and thrusting during the mid lochkovian to mid eifelian in the southeast of the anglo brabant fold belt acadian deformation produced basin inversion and the regional antiformal structure of the brabant massif the uplift inferred from the sedimentology petrography and reworked palynomorphs in the lower devonian of the dinant synclinorium is confirmed by illite crystallinity studies the tectonic model discussed implies the presence of two subduction zones in the eastern part of eastern avalonia one along the anglo brabant fold belt and another under the north sea in the prolongation of the north german polish caledonides

a first study of sf6 as a transient tracer in the southern ocean abstract halogenated transient tracers such as the chlorofluorocarbons cfc 11 cfc 12 and cfc 113 are commonly used in oceanographic studies these compounds enter the ocean via the atmosphere and their transient atmospheric concentrations make them valuable as oceanic tracers the trends of rapidly rising atmospheric concentrations of these tracers are however broken and the oceanic signal becomes increasingly more difficult to decipher there is a need for a new transient tracer to complement the existing suit of tracers especially for recently ventilated water masses one compound that looks promising in this respect is sulphur hexafluoride sf 6 an inert gas whose atmospheric concentration is rising rapidly in this paper the use of sf 6 as a transient tracer in recently ventilated waters is discussed and the method for determination of sf 6 in seawater is described tracer data from a section in the atlantic sector of the southern ocean along 6 e from 60 s to 40 s occupied during january 1998 are presented the antarctic polar front found close to 50 s was studied with a densely sampled section down to 400 m depth and sf 6 cfc 12 ratios are used to deduce ventilation ages and dilution factors a comparison of apparent ages derived from a variety of tracers is presented together with the uncertainties in these estimates this work demonstrates that sf 6 is a useful and valuable transient tracer for waters ventilated during the last 20 years

distinguishing syn cleavage folds from pre cleavage folds to which cleavage is virtually axial planar examples from the cambrian core of the lower palaeozoic anglo brabant deformation belt belgium abstract within the cambrian jodoigne formation in the easternmost part of the anglo brabant deformation belt sub horizontal to gently plunging folds occur within the limbs of steeply plunging folds the latter folds are cogenetic with cleavage and are attributed to the brabantian deformation event in contrast although cleavage is also 1 virtually axial planar to the sub horizontal to gently plunging higher order folds shows 2 a well developed divergent fanning across these folds 3 an opposing sense of cleavage refraction on opposite fold limbs and 4 only very small cleavage transection angles an analysis of the cleavage bedding intersection lineation suggests that these higher order folds have a pre cleavage origin on the basis of a comparison of structural and sedimentological features these higher order folds are interpreted as slump folds the seemingly normal cleavage fold relationship across the slump folds within the limbs of the large steeply plunging folds is due to the very small angle between cleavage and bedding as such a normal cleavage fold relationship is no guarantee for a syn cleavage fold origin it is not unlikely that also within undeformed recumbent slump folds a well developed compaction fabric formed parallel to the axial surface of the slump folds may show fanning and contrasting senses of cleavage refraction on opposite fold limbs

pre and synorogenic burial metamorphism in the ardenne and neighbouring areas rhenohercynian zone central european variscides abstract the rhenohercynian zone of the central european variscides contains in the central ardenne eifel brabant campine region of belgium france germany and luxemburg an omnipresent thermal overprint which reaches in places uppermost epizonal conditions because of its distribution and structural relationships this metamorphism cannot be explained by a singular tectonometamorphic event field and microstructural observations new illite crystallinity and other data relating to this metamorphism are presented together with a review of existing petrological illite crystallinity vitrinite reflectance conodont alteration index and fluid inclusion data and their relationship to small and regional scale geological structures three distinct geotectonic situations can be described which overlap and alternate in space and time 1 the oldest metamorphism which reached epizonal conditions can be localized in the pre devonian basement rocks of the brabant massif and with minor evidence of the stavelot massif further south it is clearly related to a pre variscan caledonian deformation event and could be of burial origin 2 the main regional metamorphism affected all devonian and carboniferous rocks and the lower palaeozoic basement highs of the ardenne eifel area it does not exceed diagenetic conditions in some areas but reaches maximal values of 500 c and 400 mpa in the serpont and rocroi massif areas theye and fransolet 1993 robion et al 1995 it is pre to synkinematic to the main variscan contractional penetrative deformation and correlates well with the age and thickness of the sedimentary cover rocks the metamorphism is associated with the pre carboniferous preorogenic rifting stage of the rhenohercynian basin and documents the peak of subsidence and sediment accumulation we interpret it as diastathermal metamorphism it reaches its maximum in the low grade metamorphic zones of the ardenne area which are inverted synsedimentary structures 3 the diastathermal metamorphism is overprinted in the central part of the ardenne eifel area middle devonian to carboniferous rocks of the dinant synclinorium by an anchizonal beginning epizonal metamorphism in the foreland basins north of the midi fault zone it reaches diagenetic to lowermost anchizonal conditions it is the expression of the burial by thick synorogenic mid to upper carboniferous cover rocks which were deposited in piggyback and foreland basins this clastic wedge relates to the carboniferous contraction of the rhenohercynian basin whose metamorphosed rocks were themselves affected by the deformation of the advancing orogenic front

large scale slumping deduced from structural and sedimentary features in the lower palaeozoic anglo brabant fold belt belgium distinguishing slump folds from tectonic folds in poorly exposed areas can be difficult especially when the scale of the slump folds exceeds outcrop scale in the southeastern part of the single phase deformed lower palaeozoic anglo brabant fold belt a comparison of cleavage fold relationships and stratigraphic polarity shows that a 200 m thick interval of middle caradoc fine grained turbidites in the core of a large synform was overturned prior to tectonic deformation this overturning is attributed to large scale slumping which was most likely a result of middle caradoc seismic activity the exposed portion of the large slump sheet contains only a few small slump folds and intraformational breccias making up less than 5 of the exposed thickness if the beds were not overturned large scale slumping would never be suspected and the small slump folds would probably be interpreted as localized features in an overall stable sedimentary pile this may explain why so few ancient large scale slides and slumps have been reported the small amount of internal deformation makes them very difficult to recognize especially when dealing with poorly exposed areas as such large ancient slides and slumps may be more common than suggested by the geological literature

attenuation of strong ground motion in canada from a random vibrations approach abstract theoretical relations are developed for the attenuation of horizontal peak ground acceleration pga and velocity pgv in canada with emphasis on eastern canada the theoretical basis is a composite of several approaches at intermediate epicentral distances results from random vibration theory hanks and mcguire 1981 boore 1983 which can be used to describe pga and pgv in terms of shear radiation implied by brune9s 1970 source model are applied to canadian earthquakes motions are extended into the near source region using arguments concerning magnitude scaling joyner and boore 1981 at distances greater than two crustal thicknesses ground motions are attributed largely to the lg phase and are attenuated accordingly nuttli 1982 the resulting attenuation relations for pga and pgv in eastern canada are in excellent agreement with strong motion data from moderate eastern canadian and central united states earthquakes compared to empirical attenuation relationships based on modified mercalli intensity the theoretical model predicts a stronger dependence of peak ground motions on magnitude in other respects amplitude levels and distance decay empirical and theoretical predictions are similar the model predicts that eastern events will have higher peak accelerations but similar peak velocities in comparison to their western counterparts of the same moment magnitude this arises from the relative enrichment of eastern earthquakes in higher frequencies

waveform modeling of the 17 august 1999 kola peninsula earthquake on the kola peninsula one of the strongest seismic events m s 4 2 in recent years occurred on 17 august 1999 the event was located in the lovozero massif close to the city of revda and the umbozero mining site the revda event was recorded with a temporary broadband network in finnmark masi region northern norway based on high quality three component seismic data from this network we analyzed the event by full waveform modeling using a frequency wavenumber method we systematically varied the source depth the size and orientation of the fault plane and the crustal velocity model and compared the resulting synthetic seismograms with the observed data the spectra could be matched quite well with synthetics for a circular fault plane of radius 1 6 km an effective stress drop of 4 5 mpa and a seismic moment of 6 0 10 15 n m the source depth was estimated to be about 5 km the fault plane solution is mainly characterized by a reverse focal mechanism with strike 240 dip 60 and rake 70 consistent with first motions observed at 28 fennoscandian stations the distinct dispersion of the observed data could be explained by introducing a relatively strong shear wave velocity gradient in the uppermost crust we think that the revda event may have been influenced possibly even triggered by the presence of the mine the lovozero massif has a distinct block structure with a northeast southwest oriented fault system and a conjugated system in the north west southeast direction associated and consistent with the regional north northwest compressional tectonic stress field long term mining can redistribute stress and initiate ruptures along favorably oriented faults and to this end our fault plane solution is in agreement with an event on the major alluaiv fault of the northeast southwest oriented system local inspections revealed that a rockburst occurred in a part of the mine that was abandoned 10 20 years ago this rockburst has also a reverse fault mechanism but with a shear plane striking perpendicular to our solution we therefore consider the observed rockburst as a secondary effect

source spectra for the 1988 saguenay quebec earthquakes abstract source spectra are obtained for the 1988 saguenay quebec earthquake m n 6 5 its foreshock m n 4 8 and largest aftershock m n 4 1 using recordings from analog and digital seismographs on rock sites at epicentral distances from 40 to 700 km the source spectra of the foreshock and the aftershock are well matched by a single corner frequency 2 model with seismic moments of 2 2 10 22 and 2 2 10 21 dyne cm respectively and a stress parameter of 65 bars for both events by contrast the spectrum of the mainshock differs dramatically from this simple shape a stress parameter of 500 bars is required to match the observed high frequency amplitudes using the seismic moment determined from teleseismic observations as a constraint this single corner frequency model however overestimates amplitudes at frequencies near 1 hz by a factor of about 2 the relative radiation of short and long period energy for the mainshock is inconsistent with that from other intraplate earthquakes the fore and aftershocks appear typical in this regard the extraction of source spectra from the regional data required a careful examination of attenuation azimuthal variations were observed with the attenuation being most severe to the southeast normal to the st lawrence valley and the dominant structural grain of the region the st lawrence river coincides in part with the boundary between the grenville and appalachian tectonic provinces and the difference in attenuation may be related to the difference in tectonic province the distribution of data however makes it difficult to obtain good estimates of the attenuation in each province lumping the data from both provinces and the three earthquakes together results in an anelastic attenuation factor given by q 755 f 0 5 for frequencies f from 0 6 to 18 hz using data at distances r beyond 100 km from the sources and assuming 1 r geometrical spreading this attenuation is similar to that obtained in a number of other studies in the general area three component recordings were available at a few stations and from these the following frequency dependent ratio of horizontal to vertical motion was obtained hiv 1 14 0 118 f 0 00638 f 2 for frequencies from 0 2 to 15 hz different methods of correcting observations for attenuation in order to derive source spectra were examined source spectra derived by simple regression analyses of observed data assuming a uniform medium are very similar to those based on a more complicated synthetic seismogram correction which accounts for wave propagation in a layered earth

earthquake source spectra in eastern north america abstract a new model for average earthquake s wave source spectra in eastern north america ena is derived the model is consistent with fundamental elasto dynamic principles as well as the familiar spectral scaling laws appropriate to sources having geometrical and dynamical similarity observed characteristics of s wave spectra in ena are fully explained as simple consequences of directivity effects entailed by the classical crack rupture model kostrov 1964 madariaga 1976 with normal effective stresses of the order of 100 bars and fractional stress drop brune 1970 abnormally high stress drops are not required recognition of the fundamental role of directivity explains most features of observed data that are currently interpreted as anomalous among other things neglect of such effects is shown to be responsible for the conclusion by boatwright and choy 1992 and boore and atkinson 1992 that high frequency spectral levels for the magnitude 6 saguenay earthquake of 1988 are anomalously large other important implications of the new model are that some previously inferred systematic variations in brune stress drop with magnitude are simply artifacts of the invalid use of the standard brune 1970 1971 model assumption and that current estimates of q in ena which depend on this assumption are likely to be significantly too large for high frequencies associated uncertainties allow the possibility that effective stress does not vary significantly with magnitude for earthquakes having magnitudes in the range of 4 to 7 the new model suggests that some currently favored source spectra may under estimate spectral amplitudes of future larger earthquakes in ena by as much as a factor of 6 for some frequencies the proposed new spectra are practically identical with those of the brune standard model for an effective stress of 100 bars for frequencies up to about twice the brune corner frequency but then increase to values 3 times larger over a range of about 4 in frequency as such the high frequency spectral levels are equivalent to standard brune model values for earthquakes of one full magnitude unit larger with consequent important implications for seismic hazard estimates in the region

earthquake source spectra in eastern north america source spectra for earthquakes of 3 m 7 in eastern north america ena are determined from regional seismograph recordings strong motion records teleseismic data and modified mercalli intensity data the inclusion of mmi data is made possible by the finding that the felt area of an earthquake is an accurate measure of its high frequency spectral level at the source current ground motion relations for ena are based on a brune source model with a stress parameter of 100 bars this model is a poor fit to ena source spectra for events of m 4 at high frequencies 5 to 10 hz observed spectral amplitudes are more nearly matched by a brune stress parameter of 200 bars intermediate frequency amplitudes near 1 hz are matched by a stress parameter of approximately 50 bars an empirical two corner source model is proposed to describe ena source spectra for events of 4 m 7

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

tetrafluoromethane in the deep north pacific ocean 1 dissolved tetrafluoromethane cf4 has been measured for the first time in the north pacific ocean surface water collected during calm weather is near equilibrium with the modern atmosphere deep water isolated from atmospheric exchange for centuries is near equilibrium with the preindustrial atmosphere after accounting for an expected 5 addition of this low solubility gas due to air injection during high latitude deep water formation these results strongly suggest that dissolved cf4 is conservative in seawater and that the oceanic imprint of anthropogenic increases in atmospheric cf4 can be used as a time dependent tracer of ocean ventilation and subsurface circulation processes although the continental lithosphere is a source of natural atmospheric cf4 we find no evidence of an oceanic lithospheric cf4 input into deep pacific waters the estimated upper limit of a potential oceanic lithospheric cf4 flux to the global atmosphere is on the order of 4 of that from the continental lithosphere

subsidence analysis of eastern avalonian sequences implications for iapetus closure basin subsidence analysis employing the backstripping method indicates that fundamentally different basin generating mechanisms controlled silurian basin development in northern england and in wales accelerating subsidence with time suggests that the dominant control on basin formation in northern england was flexure of the eastern avalonian lithosphere mid wales however displays dominantly decelerating subsidence suggesting an extensional control the errors involved with the backstripping method particularly concerning lower palaeozoic application have been addressed in conjunction with sedimentological and tectonic data the subsidence patterns for the windermere supergroup indicate deposition in a flexurally loaded foreland basin which migrated southwards with time similar data for the powys supergroup of mid wales imply an extensional control on silurian deposition possibly in a strike slip setting however later poidoli and early devonian welsh sedimentation may represent the onset of foreland basin deposition the new data are consistent with a diachronous closure of the iapetus ocean related to rotational collision of eastern avalonia with laurentia during the early silurian early silurian oblique collision produced transtension in wales subsequent rotation of eastern avalonia produced more orthogonal collision thus continental flexure was felt initially in northern england in late wenlock times followed by migration of the resultant foreland basin to the southeast into wales in early devonian times the versatility of the backstripping method is shown by this application to lower palaeozoic sequences

the spatial distribution and annual cycle of upper ocean thermohaline structure 1 observations of the spatial distribution and persistence of thermohaline structure are presented and show how advection and diffusion affect a passive tracer more than two years of underwater glider observations in the central subtropical north pacific showed thermohaline variability over horizontal scales from 5 to 1300 km thermohaline fluctuations along isopycnals spice fluctuations were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions fluctuations were uncorrelated between the layers but stirred by the same velocity field spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated horizontal wave number spectra of spice had slopes of 2 everywhere in the upper 1000 m submesoscale spice fluctuations had slopes in physical space near the ratio of the coriolis parameter to the buoyancy frequency f n consistent with predictions of quasi geostrophic theory in the mixed layer thermohaline structure had a significant annual cycle with smaller interannual differences thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals horizontal diffusivity estimates in the remnant mixed layer were 0 4 m2 s 1 at 15 28 km wavelengths and 0 9 m2 s 1 at 35 45 km wavelengths

fluid flow alteration and polysulphide mineralisation associated with a low angle reverse shear zone in the lower palaeozoic of the anglo brabant fold belt belgium abstract in the lower palaeozoic rocks of the brabant massif belgium a recently discovered polysulphide mineralisation is related to a low angle reverse shear zone this shear zone has been attributed to the main early devonian deformation event data from boreholes and outcrops allow a detailed investigation of the alteration pattern and palaeofluid flow along this shear zone macroscopic observations of the mineralogy and quantitative changes in the phyllosilicate mineralogy indicate that this shear zone is characterised by an envelope of intense sericitisation and silicification in addition chloritisation is associated with this alteration the alteration zone may reach a thickness of 250 m ore mineralisation occurred synkinematically and is spatially related to the shear zone the mineralisation consists of pyrite marcasite arsenopyrite pyrrhotite chalcopyrite sphalerite galena stibnite and smaller amounts of tetrahedrite and other sulphosalts it is concentrated in quartz sulphide veins or occurs diffusely in the host rock the mineralising fluids have a low salinity h 2 o co 2 ch 4 nacl kcl composition and a minimum temperature of 250 320 c the 18 o values of quartz vary between 12 3 and 14 5 smow and d compositions of the fluid inclusions in the quartz crystals range from 65 to 35 v smow the d and the calculated 18 o values of the mineralising fluids fall in the range typical for metamorphic fluids and partly overlap with that for primary magmatic fluids the 34 s values between 4 7 and 10 6 cdt fall outside the interval typical for i type magmas important migration of likely metamorphic fluids causing a widespread alteration and a polysulphide mineralisation along a low angle shear zone has thus been identified for the first time in the caledonian anglo brabant fold belt

three dimensional finite difference simulation of fault dynamics rectangular faults with fixed rupture velocity we analyze three dimensional finite difference solutions for a simple shear crack model of faulting to determine the effects of fault length and width on the earthquake slip function the fault model is dynamic with only rupture velocity fault dimensions and dynamic stress drop prescribed the numerical solutions are accurate for frequencies up to 5 hz and are combined with asymptotic results for shear cracks in order to characterize the slip function at higher frequencies near the hypocenter the slip velocity exhibits a square root singularity whose intensity increases with hypocentral distance at distances greater than the fault width w growth of the velocity intensity ceases and the slip function becomes nearly invariant with distance along the fault length closed form expressions are developed for the dependence of static slip s slip rise time tr and slip velocity intensity v on fault geometry along the center line of a long narrow fault at hypocentral distances exceeding w these expressions reduce to s w tr 0 5 w vr and v w 2 vr where is the dynamic stress drop the shear modulus and vr the rupture velocity the numerical results imply that uniform dislocation kinematic earthquake models in which slip is represented by a ramp time function will underpredict high frequency ground motion relative to low frequency ground motion a further implication of the numerical solutions is that the nature of inelastic processes at the advancing edge of a long fault will depend on fault width but will be independent of rupture length

influence of slump folds on tectonic folds an example from the lower ordovician of the anglo brabant deformation belt belgium although it is generally accepted that buckle folds will not develop in a perfectly planar layer without the presence of some irregularity or perturbation at which the folds initiate there are very few cases in which individual natural folds can be linked to specific irregularities within the lower ordovician abbaye de villers formation anglo brabant deformation belt metre scale tectonic folds occur of which the position and to a certain extent the geometry appear to be controlled by slump folds and related features the metre scale tectonic folds interpreted as parasitic structures on the limb of a large scale host fold occur only within a stratigraphic level affected by slumping in this level tectonic antiforms tend to form superimposed on antiformal slump folds and on zones of abrupt slump related thickness increase and tectonic synforms on synformal slump folds and on zones of abrupt thickness decrease the rather irregular 3d geometry of sedimentary sequences suggests that many more similar cases should exist in which folds can be linked to specific irregularities however possibly it is also this abundance of irregularities in sedimentary sequences in combination with fold and outcrop scale that makes it difficult to attribute a particular fold to a particular perturbation

arcuate fold and cleavage patterns in the southeastern part of the anglo brabant fold belt belgium tectonic implications abstract the brabant massif belgium is situated at the southeastern extremity of the anglo brabant fold belt the predominantly concealed eastern branch of the british belgian caledonides in contrast to the other parts of this caledonian slate belt the deformation history in the brabant massif has to date never been constrained properly in this paper a synthesis is presented of the structural observations in the limited outcrop area of the brabant massif in particular with respect to cleavage and fold trajectories and mutual cleavage fold relationships arcuate fold and cleavage patterns as well as the presence of cleavage transected folds are demonstrated similar to the other parts of the belt moreover the arcuate trajectories are considered to reflect the trace of the caledonian deformation front once obscured by the variscan ardenne allochthon combined with interpretations of the aeromagnetic and bouguer anomaly maps an overall kinematic model is proposed for the acadian deformation event in the brabant massif with the proposed model calling upon processes of indentation by promontories and lateral escape of lithostructural domains as well as on the control exerted by rigid granitoid basement blocks the strong similarities with the other parts of the british belgian caledonides become apparent by defining an overall shortening direction and proposing a trace for the caledonian deformation front in this southeastern extremity of the anglo brabant fold belt an integrated tectonic image is obtained for the entire british belgian caledonides

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

rupture complexity of a moderate intraplate earthquake in the alps the 1996 m5 epagny annecy earthquake summary the magnitude 5 epagny annecy earthquake of 1996 july 15 is the largest seismic event to have occurred in the alps since the introduction of modern digital instrumentation this strike slip event was located on the vuache fault near the town of annecy in the northern french alps the aim of our work was to retrieve the main parameters of the rupture process of this earthquake from seismograms recorded at local and regional distances 20 300 km to eliminate path and site evects from the seismograms we compared the main shock recordings at each station with those of the largest aftershocks nearby we used a combination of techniques including pulse width measurements and cross correlation of velocity traces comparison of p wave displacement pulses and empirical green s function deconvolution to retrieve the apparent duration of the rupture process as seen at each station our results demonstrate that in the absence of on scale data p wave pulse width measurements on clipped signals can be misleading if the rupture process is complex in the case of the annecy earthquake comparisons of on scale p wave displacement seismograms and the empirical green s function deconvolutions show that the rupture process consisted of at least two subevents separated by 0 2 0 3 s and with a total duration of about 0 5 s the systematic azimuthal dependence of both the shape and duration of the apparent source time function is consistent with a nearly unilateral propagation of the main rupture phase in a southeast direction along the fault plane and parallel to the direction of slip an isochron analysis reveals that the first subevent occurred slightly to the northwest of the nucleation point but that the second subevent was located further to the southeast thus confirming the overall rupture directivity towards the southeast an interpretation of our results in light of the previously documented aftershock distribution and of observations of ground cracks in the epicentral area suggests that the main shock occurred on the vuache fault and that rupture in a northwest direction was inhibited by a right lateral stepover in the fault accordingly the vast majority of the subsequent aftershocks which include several magnitude 3 4 events occurred on a fault segment that is slightly ovset from the inferred surface trace of the vuache fault and that was activated by the main shock

differences between magnetic and mineral fabrics in low grade cleaved siliciclastic pelites a case study from the anglo brabant deformation belt belgium abstract theoretically within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which judging from the ams parameters ams is controlled by the paramagnetic carriers the results of x ray pole figure goniometry should show a qualitative relationship with ams this idea is tested on single phase deformed low grade pelites of the lower palaeozoic brabant massif belgium representing the southeastern part of the anglo brabant deformation belt for the vast majority of the samples investigated the different lf ams parameters suggest a paramagnetic control on lf ams different parameters of lf ams measured at 77 k low t lf ams and a comparison of these with the lf ams parameters indicate that lf ams is controlled virtually entirely by paramagnetic carriers high field torque magnetometry hf ams indicates further that ams is controlled entirely by paramagnetic carriers for the vast majority of the samples two apparent discrepancies are observed however these are 1 a frequent mismatch between the lf ams fabric on the one hand and the paramagnetic fabric indicated by low t lf ams and hf ams on the other hand and 2 a rather common mismatch between the preferred orientation of chlorite and white mica suggested by x ray pole figure goniometry on the one hand and the lf ams fabric low t lf ams fabric and hf ams paramagnetic fabric on the other hand these apparent discrepancies may partly be attributed to the composite nature of both the lf ams fabric and the paramagnetic susceptibility fabric the presence of different populations of paramagnetic carriers possibly in combination with minor traces of ferromagnetic s l carriers which are not picked up by the methods applied may explain some of the mismatches observed and are compatible with the basin evolution history of the brabant massif in addition it is possible that the low temperatures low t lf ams and high fields hf ams are capable of enhancing one of the paramagnetic phases thus leading to discrepancies between methods that define the mineral and the magnetic fabrics the results of this study show that even when the lf ams data suggest that the lf ams of a given pelitic rock in which phyllosilicates form the main paramagnetic carriers is controlled entirely by paramagnetic carriers alternative methods such as phyllosilicate x ray pole figure goniometry will not necessarily reflect the paramagnetic carrier orientation although a number of cases have successfully correlated lf ams with mineral fabric and occasionally even strain this study serves as an example for how methods to define mineral and magnetic fabrics can be sensitive in detecting different paramagnetic phases

sulfur hexafluoride as a transient tracer in the north pacific ocean 1 the atmospheric concentration of sulfur hexafluoride sf6 has increased steadily during the past 30 years making it potentially a valuable transient tracer of oceanic circulation and mixing processes on decadal timescales simultaneous measurements of dissolved sf6 with chlorofluorocarbons cfcs which have longer atmospheric histories but different growth rates provides additional information over the use of each tracer alone concentrations of dissolved sf6 cfc11 and cfc12 were measured at the hawaii ocean time series hot site in 2005 concentrations were highest in the upper water column with pronounced cfc11 and cfc12 maxima at a depth of 400 meters apparent water mass ages calculated from sf6 concentrations tend to be younger than those calculated from cfc12 concentrations an isopycnal pipe model is used to estimate the effects of mixing on sf6 and cfc12 derived ages combining sf6 and cfc12 ages allows improved estimates of ideal ages and oceanic uptake of anthropogenic co2

the mont laurier quebec earthquake of 19 october 1990 and its seismotectonic environment on 19 october 1990 at 07 01 ut a magnitude mblg 5 0 earthquake occurred approximately 9 km southwest of mont laurier quebec canada latitude 46 47 n and longitude 75 59 w this earthquake is the largest to have occurred in the western quebec seismic zone since the 1944 magnitude 5 6 cornwall massena earthquake the mont laurier earthquake was widely felt up to distances of 500 km and caused some minor damage in the epicentral region intensity modified mercalli mm v during the week following the earthquake a field survey recorded 23 aftershocks magnitudes were all less than ml 1 5 analysis of the mainshock and its aftershocks indicates focal depths in the range 10 to 12 km of the two east west oriented nodal planes given by the predominantly thrust mechanism of the mainshock the steep northerly dipping one probably represents the fault plane as indicated by the trend of aftershock hypocenters the last 10 yr of recording have confirmed that most western quebec earthquakes including the mont laurier earthquake occur in a northwest southeast trending zone inside the central metasedimentary cm belt with most focal depths varying between 7 and 25 km although some northwest trending structural features are known correlating these with the epicentral trend is premature the mid crustal hypocentral depths of many earthquakes the east west trend of the fault plane of the mont laurier earthquake and variations in regional focal mechanisms all suggest reactivation of deep structural features which may not have a surface expression inside the central metasedimentary belt most earthquakes occur along the eastern side where the activity seems to correlate with the labelle shear zone and the morin anorthosite body which may act as a stress concentrator the western side of the activity does not end with the central metasedimentary belt a fact that implies that even though the factors controlling seismicity lie predominantly within the central metasedimentary belt the adjacent geologic domains are also seismogenic

subduction related magmatism of late ordovician age in eastern england deep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the caledonian basement in eastern england the isotopic compositions of these rocks reveal that many of them are of late ordovician age 440 460 ma and their geochemical compositions suggest calc alkaline affinities the intermediate diorite tonalite plutonic rocks are associated with a prominent northwest southeast trending belt of aeromagnetic anomalies extending from derby to st ives hunts which is interpreted to work the plutonic core of a calc alkaline magmatic arc it is inferred that this arc was generated by the subduction of oceanic lithosphere possibly from the tornquist sea in a south or southwest direction beneath the midlands microcraton in late ordovician times the age and geochemical composition of concealed ordovician volcanic rocks in eastern england and hypabyssal intrusions of the midlands minor intrusive suite in central england is compatible with such a hypothesis

an investigation into earthquake ground motion characteristics in eastern north america abstract a random vibration model of the hanks mcguire type is used to predict peak ground motions at rock sites in eastern north america the assumed geometric decay and distance dependent duration approximate the propagation of direct body waves at short distances and lg waves at regional distances the model predicts peak acceleration and velocities as well as response spectra and magnitude for a given seismic moment and corner frequency to predict ground motions for a given lg magnitude m lg the model is first used to calculate the seismic moment corresponding to that magnitude assuming a source scaling law then knowing the moment and corner frequency the model is used to calculate peak ground motions available data from strong motion recordings and from the ectn and lrsm networks modified to estimate horizontal ground motions on rock where appropriate are used to verify the model9s assumption and predictions modified mercalli intensity data are also used ground motions predicted by the model with a stress drop of 50 to 200 bars agree with the ground motion data but the m lg values computed by the model for given seismic moments do not agree with nuttli9s 1983 moment versus m lg data for large earthquakes resolution of the latter disagreement awaits the collection of instrumental data from large events in eastern north america

measuring lithospheric stretching on tethyan passive margins preliminary estimates of lithospheric stretching have been made by examining 63 stratigraphic sections from the northern and southern tethyan margins southeast france to bulgaria the study was centred on the italian southern alps the dolomites a portion of the southern margin within the external zones of the alpine orogen sections were decompacted and backstripped using the standard procedure allowing for errors in palaeowater depth estimates theoretical subsidence curves based on the finite duration stretching model were then fitted to the resultant water loaded subsidence curves in an attempt to clarify the pre compressional tectonic history of the region according to our results stretching started in the early to mid triassic and lasted 30 40 ma this conclusion is broadly in agreement with some previously published estimates the stretching factor is generally small 1 1 1 3 especially in southeast france and northern italy larger values of occur in the balkans c 1 5 to our knowledge the finite duration stretching model has not yet been applied to water loaded stratigraphic sections from the tethyan belt theory and observation appear to agree well

transit time distributions in lake issyk kul 1 measurements of sulfur hexafluoride sf6 and chlorofluorocarbons cfcs are used to constrain the timescales for deep water renewal in lake issyk kul as these tracers have different tropospheric histories their combination provides more transport information than one tracer alone in particular from these measurements the mean and standard deviation of the distributions of transit times since water made last contact with the surface can be tightly constrained is older than the age determined from sf6 and younger than the ages from the cfcs and increases from around 4 yrs at 200 m to around 10 5 yrs at the deepest location 655 m also increases with depth and equals around 0 7 to 0 8 which corresponds to large ranges of transit times and implies mixing processes play a major role in the transport the approach used can also be applied to similar tracer measurements in the oceans and groundwaters to constrain transport in these geophysical systems