lithospheric dynamics and tectonic stratigraphic evolution of the ebro basin we present analysis of two dimensional modeling of the tectonic subsidence in the ebro basin along three profiles crossing the pyrenees the ebro basin and the catalan coastal range to the east and the iberic cordillera to the west the deformation of the foreland basin during tertiary times is simulated using a lithospheric flexure model incorporating laterally varying elastic thicknesses the deflection of the plate is the combined result of pyrenean loading and the loads exerted by the iberic cordillera and catalan coastal range in the eastern part of the ebro basin no extra driving force on the iberian plate is required the flexural modeling supports the hypothesis that underplating of the iberian plate under the european plate is not associated with subduction of old oceanic lithosphere a good fit with the tertiary basin subsidence data and bouguer anomalies is obtained for an elastic plate with local weakness zones under the ebro basin the inferred lateral variation in the elastic rigidity is consistent with heat flow measurements in northern spain and with major mesozoic extension in the iberic cordillera and valencia trough

the organization of seismicity on fault networks abstract although models of homogeneous faults develop seismicity that has a gutenberg richter distribution this is only a transient state that is followed by events that are strongly influenced by the nature of the boundaries models with geometrical inhomogeneities of fracture thresholds can limit the sizes of earthquakes but now favor the characteristic earthquake model for large earthquakes the character of the seismicity is extremely sensitive to distributions of inhomogeneities suggesting that statistical rules for large earthquakes in one region may not be applicable to large earthquakes in another region model simulations on simple networks of faults with inhomogeneities of threshold develop episodes of lacunarity on all members of the network there is no validity to the popular assumption that the average rate of slip on individual faults is a constant intermediate term precursory activity such as local quiescence and increases in intermediate magnitude activity at long range are simulated well by the assumption that strong weakening of faults by injection of fluids and weakening of asperities on inhomogeneous models of fault networks is the dominant process the heat flow paradox the orientation of the stress field and the low average stress drop in some earthquakes are understood in terms of the asperity model of inhomogeneous faulting

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

the impact of co2 on shallow groundwater chemistry observations at a natural analog site and implications for carbon sequestration in a natural analog study of risks associated with carbon sequestration impacts of co2 on shallow groundwater quality have been measured in a sandstone aquifer in new mexico usa despite relatively high levels of dissolved co2 originating from depth and producing geysering at one well ph depression and consequent trace element mobility are relatively minor effects due to the buffering capacity of the aquifer however local contamination due to influx of brackish waters in a subset of wells is significant geochemical modeling of major ion concentrations suggests that high alkalinity and carbonate mineral dissolution buffers ph changes due to co2 influx analysis of trends in dissolved trace elements chloride and co2 reveal no evidence of in situ trace element mobilization there is clear evidence however that as u and pb are locally co transported into the aquifer with co2 rich brackish water this study illustrates the role that local geochemical conditions will play in determining the effectiveness of monitoring strategies for co2 leakage for example if buffering is significant ph monitoring may not effectively detect co2 leakage this study also highlights potential complications that co2 carrier fluids such as brackish waters pose in monitoring impacts of geologic sequestration

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

a model for repetitive cycles of large earthquakes the theory of the fusion of small cracks into large ones reproduces certain features also observed in the clustering of earthquake sequences by modifying our earlier model to take into account the stress release associated with the occurrence of large earthquakes we obtain repetitive periodic cycles of large earthquakes a preliminary conclusion is that a combination of the stress release or elastic rebound mechanism plus time delays in the fusion process are sufficient to destabilize the crack populations and ultimately give rise to repetitive episodes of seismicity

seismotectonic constraints at the western edge of the pyrenees aftershock series monitoring of the 2002 february 21 4 1 lg earthquake this work was carried out with the support of the marconi ren2001 1734 project from the spanish mcyt mr and cl benefited from a phd grant from the spanish mcyt we would like to thank to the responsible of the ign renass omp and cea databases for sharing the seismological data used in this study

testing self organized criticality by induced seismicity we examine the hypothesis proposed in recent years by several authors that the crust is in a self organized critical soc state this hypothesis has been suggested on the basis of the observation of power law distributions such as the gutenberg richter law for earthquakes and the fault length distribution and of the fractal geometry of sets of earthquake epicenters and of fault patterns these self similar properties are shared by simplified models of the crust exhibiting a spontaneous organization toward a critical point characterized by similar scale invariant properties the term critical is here used in the sense of phase transitions such as the curie point in magnetism the usefulness of a hypothesis is measured by its predictive and explanatory power outside the range of observations that have helped defined it we thus explore how the soc concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity we review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes p and mass transfers m leading to incremental deviatoric stresses of 1 mpa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7 0 in otherwise historically aseismic areas once triggered stress variations of at least 1 order of magnitude less but still larger than the 0 01 mpa tidal stress are enough to sustain seismic activity we argue that these observations are in accord with the soc hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations this property is shared by simplified models of soc not all perturbations however trigger seismic activity this is also compatible with the soc hypothesis which embodies naturally the existence of large heterogeneities in the stress field the induced seismicity is found to obey generally the gutenberg richter law up to a magnitude cutoff which correlates well with the width of the local seismogenic bed ranging in size from that of mine pillars for mining induced seismicity to the thickness of brittle sedimentary beds in the vicinity of dams or depleted hydrocarbon reservoirs in conclusion the properties of induced seismicity and their rationalization in terms of the soc concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

the equivalent strength of geometrical barriers to earthquakes we present a quantitative framework for evaluating the influence of non planar fault geometry on repeated seismic ruptures we model quasistatic ruptures on a non planar fault trace imbedded in a two dimensional elastic medium under in plane strain because of the presence of fault segments that are not parallel to the regional shear stress i e bends the apparent strength at a given point on the fault is not fixed but fluctuates with normal stress compressional features behave as increasingly strong barriers to fracture unless the stored normal stress is released in order to unlock the fault since slip on the fault itself cannot get rid of the normal stress this is achieved through the action of off fault morphological features such as secondary faulting folding and vertical motions that we introduce parametrically in the form of an aseismic relaxation the apparent strength of a fault bend will stabilize in a narrow interval of values after repeated ruptures characterized by a non dimensional hardness parameter whereby the relaxation rate is scaled by the tectonic loading rate on a fault structure having several small widely separated bends three families of events can be identified whose frequency and magnitude depend on the hardness relaxation parameter and the geometry small events that cluster in the tension zones of the bends intermediate size ruptures involving a single interbend segment and large ruptures that break through bends and link on or more interbend segments large multi segment events are most likely to occur for low values of the hardness i e fast relaxation and slow loading rate regions with compressional features act as barriers that stop most ruptures stress is stored at these sites until they themselves break and initiate motion on the smoother long reaches of the fault

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

inverted turtle salt anticlines in the eastern basque cantabrian basin spain abstract halokinetic structures are sometimes masked by subsequent compression in inverted salt related basins making their study difficult the eastern basque cantabrian basin is an outstanding area to study salt tectonics and sedimentation relationships because precursor salt structures have maintained undeformed geometries after the alpine contraction phase based on the interpretation of subsurface data with surface geology a structural model of some of the area s salt structures is proposed according to the model the formation of listric faults and raft tectonics during the first extensional rifting stage resulted in the sinking and collapse of the late jurassic early cretaceous formations giving rise to a turtle back anticline structure with a semicircular geometry the upper triassic keuper salt migrated towards the outer zones of the structure and peripherial troughs were subsequently filled with albian late cretaceous post rift sediments during the eocene alpine contraction the whole area was folded and moved southwards maintaining much of the geometry of the previously formed salt anticlinal structures traditionally the presence of an nne ssw alignment of triassic diapirs in the eastern zone of the basin has been used to place the southern segment of the so called pamplona fault rather than being associated with fault these diapirs are interpreted to rise along the eastern edge of the collapsed extensional turtle structure existing below the eocene urbasa andia synclines no evidence of fault affecting the mesozoic cover series is observed in several composite profiles that cross the pamplona fault alignment it is suggested that the alignement of the triassic diapirs is due to the incidence of the later alpine compression in a previous expulsion rollover rather than the effect of a major alpine strike slip fault

miocene sediment dispersal in the central espanola basin rio grande rift new mexico u s a abstract the central espanola basin in north central new mexico represents one of the best opportunities to examine deposits related to the development of the rio grande rift the miocene tesuque formation represents the bulk of the espanola basin fill it is composed of a 2000 2500 m thick sequence of alluvial fluvial and subordinately lacustrine deposits with numerous interbedded ash fall tuff layers the overall detrital composition of the tesuque formation is very similar throughout the central espanola basin provenance is primarily from basement uplifts composed of precambrian igneous and high grade metamorphic rocks nevertheless the combined use of paleocurrent analysis and sandstone and conglomerate petrology allows a detailed reconstruction of the sediment paleodispersal system two sedimentary provinces are present within the tesuque formation province a present in the eastern central and southern portions of the study area has a predominantly plutoniclastic and metamorphiclastic composition and shows systematic paleocurrents toward the west the sediments were derived from the precambrian cored santa fe block of the sangre de cristo mountains located directly to the east of the study area province b present only in the northwestern portion of the study area is characterized by a minor but significant amount of volcaniclastic and sedimentaclastic detritus and shows consistent ssw directed paleocurrents the source area was possibly located in the area of the taos plateau and latir volcanic fields an intermediate narrow and discontinuous belt province a b represents a hybrid province where directional and compositional parameters are gradational

the ecors deep reflection seismic survey across the pyrenees the pyrenees are an alpine age mountain belt located on the boundary between the iberian and european plates using the same geological and geophysical data earth scientists studying the structure of the pyrenees during the past ten years have not reached a consensus here we report the first results from a nearly continuous 255 km long reflection seismic survey across the pyrenean chain this first deep reflection profile of an entire erogenic belt will help to constrain possible models for the structure and formation of the pyrenean chain

water quality and hydrogeochemistry of a basin and range watershed in a semi arid region of northern new mexico hundreds of domestic wells in northern new mexico have concentrations of u as and no3 that exceed the environmental protection agency s epa maximum contaminant level mcl for drinking water consumption as part of a case study in groundwater quality we collected groundwater samples from 749 domestic wells throughout the eastern half of the espanola basin all water samples were analyzed for major ions trace metals and alkalinity selected samples were also analyzed for stable isotopes of o h and n of the wells we measured 15 173 and 99 had respective no3 u and as concentrations that exceeded the epa s mcl total dissolved solids tds u and hco3 were elevated in the sangre de cristo mountain block and around the town of nambe our findings suggest that roll front u deposits and devitrification of volcanic ash result in elevated u near nambe while weathering of granitic rocks accounts for high u in the mountain block arsenic concentrations were high in much of the study area with the exception of the santa fe metro region and the mountain block elevated as concentrations can be explained by devitrification of volcanic ash anion exchange with clays and mixing with hydrothermal fluids in wells with high no3 concentrations analysis of n isotopes are consistent with contamination from domestic wastewater effluent our findings suggest that the geochemistry of the region is largely influenced by local geology while groundwater contamination from domestic water treatment and wastewater effluent is an emerging issue

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

dynamic simulations of slip on a smooth fault in an elastic solid we report on numerical simulations of slip evolution along a two dimensional slip varies only with depth vertical strike slip fault in an elastic half space using a framework incorporating full inertial elastodynamics the model is a follow up on earlier quasi static and quasi dynamic simulations of deformations along smooth fault systems in elastic continua the fault is driven below a crustal depth of 24 km by a constant plate velocity of 35 mm yr deformation at each fault location in the crustal zone is the sum of slip rate contributions from rate and state dependent friction and power law creep where both processes have temperature dependent and hence depth varying coefficients and both take place locally under the same stress the simulations employ two versions of rate and state dependent friction a slip law which requires nonzero velocity for state evolution and an ageing slowness law which incorporates state evolution and restrengthening in stationary contact the assumed constitutive laws and distribution of frictional parameters are compatible with laboratory experiments the elastodynamic calculations are based on spectral representations of variables and a new algorithm providing a unified computational framework for calculations of long deformational histories containing short periods of rapid instabilities the simulations show dynamic rupture propagation and wave phenomena not accounted for in the previous quasi static and quasi dynamic works however the results are qualitatively similar to those obtained by corresponding quasi static and quasi dynamic calculations slip histories along a smooth fault simulated here with full elastodynamics for various constitutive laws and model parameters consist mostly of quasi periodic large events this finding indicates that inertial dynamics does not provide a generic mechanism for generating spatio temporal complexities of slip on the other hand calculations done for cases representing approximately strongly disordered systems do show rich slip histories with a range of event sizes this result is compatible with our previous conclusions that the origin of observed broad distributions of earthquake sizes is strong fault zone heterogeneities the fully dynamic calculations illustrate the evolution of nucleation phases of instabilities associated with accelerating and expanding creep final slip values of model earthquakes in full elastodynamic calculations are larger than those of corresponding quasi static and quasi dynamic events the dynamic overshoot in simulations with the slip version of friction is larger than in those employing the ageing slowness law

excess area and depth to detachment a plot of the excess area in cross section vs the depth to a reference level for several stratigraphic horizons in a compressional fold produces a curve that gives the depth to detachment the curve is a straight line for detachment folds the slope of the line is the displacement on the lower detachment and the depth intercept where excess area zero is the depth to detachment for a fault bend fold the result is a line that abruptly changes slope at the position corresponding to the upper detachment the difference in slope between the two parts of the line is the displacement on the upper detachment added layer parallel shear produces a curve on the graph tested on detachment folds from the jura mountains the method accurately predicts the depth to detachment he tip top field anticline in the wyoming thrust belt is found to be interpretable as either a detachment anticline with a basal detachment close to the top of the basement or as a fault bend fold with a basal detachment at the base of the triassic the excess area diagram is useful for testing a cross section for balance determining the structural style detachment anticline vs fault bend fold and for examining alternatives in the construction of cross sections

a subsurface stress analysis and its possible relation with seismicity near the itoiz reservoir navarra northern spain abstract we study the effects of surface water loads and moderate magnitude earthquakes on the subsurface state of stress and its relation with seismicity near the newly constructed itoiz reservoir in the western pyrenees northern spain to do this we initially compute the evolution of the stress changes in the subsoil due to the water load distribution during the impounding of the reservoir and relate it with the main seismicity occurred after the beginning of impoundment after this we compute the coseismic and postseismic stress changes produced by the main events of the seismic series and study its influence on the triggering of the aftershocks stress changes due to the water loads are computed by means of the boussinesq solution for a homogeneous elastic half space whereas the coseismic stress changes due to earthquakes are obtained using the equations for an internal elastic dislocation in a half space the effects over the possible seismogenic faults are in both cases accounted by means of the coulomb failure stress criterion cfs we considered different threshold values and apparent friction coefficients of cfs for the effective static triggering then we calculate the pore pressure changes produced by the time evolution of the surface water loads as also the pore pressure changes generated by the elastic dislocations due to the largest earthquake of the series mainshock the fault parameters for the computation of the cfs of the perturbing seismic events were selected from published focal solutions to define the target fault parameters we took into account the focal solutions of the earthquakes and aftershocks themselves the parameters of mapped faults based on the tectonic setting and those of optimally oriented faults due to the absence of reliable estimations for the slip distributions of the main earthquakes we assumed for stress computations a semi elliptical distribution of slips over the fault results show the existence of a mainly positive stress influence of the surface water loads on the main earthquake of the series in two different senses the elastic coulomb failure stress and the change in pore pressure however due to different uncertainties on the possible values of the apparent coefficient of friction for the zone there is not a clear indication of an effective earthquake triggering of the mainshock due to the elastic stress changes by the surface water loads on the other hand a more clear effect is found on the possible triggering of aftershocks due to the largest earthquakes of the series it is also found a positive pore pressure influence of the two largest events on most of the aftershocks

control of lithosphere rheology on subduction polarity at initiation insights from 3d analogue modelling abstract a series of analogue experiments was used to explore how lateral variations in lithosphere rheology may result in a subduction polarity reversal lithosphere models made of sand and silicone putty were designed to represent a plate convergence setting varying laterally from continent continent to ocean continent several experiments were performed to test the effects of strength profile variations in the converging plates the modelling outcomes categorized into models that develop with and without a subduction polarity reversal while a subduction polarity reversal was the most prevalent experiment outcome the results suggest that upper mantle strength is the dominant factor in determining whether a subduction polarity shift occurs or not a weak upper mantle layer promotes obduction of the oceanic lithosphere in the western segment of the model in model iterations where the upper mantle of the continental lithosphere was stronger than the oceanic lithosphere a reversal in subduction polarity from north dipping in the east to south dipping in the west occurred the experiment design was inspired by the iberian eurasian plate convergence and may provide a simple regional scale explanation for the deformation patterns along the pyrenean and cantabrian orogen

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

crustal structure of the north iberian continental margin from seismic refraction wide angle reflection profiles abstract the structure and geodynamics of the southern margin of the bay of biscay have been investigated from a set of 11 multichannel seismic reflection profiles recorded also at wide angle offsets in an onshore offshore network of 24 obs obh and 46 land sites this contribution focuses on the analysis of the wide angle reflection refraction data along representative profiles the results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the iberian peninsula offshore the crust has a typical continental structure in the eastern tip of the bay which disappears smoothly towards the nw to reach crustal thickness close to 10 km at the edge of the studied area 45 n 6 w the analysis of the velocity depth profiles altogether with additional information provided by the multichannel seismic data and magnetic surveys led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic typical oceanic crust has not been imaged in the investigated area onshore the new results are in good agreement with previous results and document the indentation of the bay of biscay crust into the iberian crust forcing its subduction to the north the interpreted profiles show that the extent of the southward indentation is not uniform with an alpine root less developed in the central and western sector of the basque cantabrian basin n s to ne sw transfer structures seem to control those variations in the indentation degree

structural and stratigraphic evolution of the west jaca thrust top basin spanish pyrenees thrust top basins form and fill during their detachment from the foreland margin by active thrust sheets strike normal n s sections from the west jaca thrust top basin southwest pyrenees to the ebro basin show that the pena flexure the local expression of the thrust front can be interpreted as a passive roof duplex the duplex accommodated up to 7 km bulk shortening at the tip of the gavarnie thrust sheet unravelling the timing of uplift and sedimentation in the west jaca basin has revealed that development of the pena flexure represented the climactic phase of deformation lateral e w diachroneity of gross stratigraphy and thrust emergence throughout the southwest pyrenees suggests that the thrust front propagated both toward the foreland and westward parallel to the orogen axis

seismic activity at the western pyrenean edge abstract the present day seismicity at the westernmost part of the pyrenean domain reported from permanent networks is of low to moderate magnitude however it is poorly constrained due to the scarce station coverage of the area we present new seismic data collected from a temporary network deployed there for 17 months that provides an enhanced image of the seismic activity and its tectonic implications our results delineate the westward continuity of the e w pyrenean band of seismicity through the variscan basque massifs along the leiza fault ending up at the hendaya fault this seismicity belt is distributed on a crustal scale dipping northward to almost 30 km depth other relevant seismic events located in the area can be related to the central segment of the pamplona fault and to different e w thrust structures

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

a model of foreshock occurrence summary we have constructed a model for the occurrence of foreshocks and foreshock sequences the foreshocks as well as the main shock are assumed to occur because of the abrupt coalescence of pre existing cracks coalescence occurs if the stress intensity factors at the crack tips exceed a certain critical value in the sub critical state each crack undergoes accelerated extension quasi statically due to stress corrosion until it reaches the critical state at which point growth becomes catastrophic the rate of foreshock occurrence increases as the time of the main shock approaches and is described by a power law function of time the exponent in the power law is independent of the distributions of crack sizes spacings and fracture strengths this universality implies that foreshock patterns should be useful identifiers for the prediction of the occurrence times of large earthquakes however we find that there is considerable diversity in the patterns of energy release nevertheless there is some hope that the magnitudes of large earthquakes can be predicted from the magnitudes of the events in the foreshock sequences if one has a priori information describing the distributions of barrier strengths and geometries

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

potential earthquake triggering in a complex fault network the northern south island new zealand summary a synthetic seismicity computer model of multiple interacting faults has been used to investigate potential earthquake triggering in the alpine marlborough buller fault network northern south island new zealand of particular interest is whether large characteristic earthquakes on the central 300 km long segment of the alpine fault average recurrence time of 240 yr might trigger events to the north and northeast possible temporal clustering of other large events and stress shadows the synthetic seismicity model generates long homogeneous catalogues that sample a wide range of possible stress interactions and stress states allowing statistical analysis the catalogues used here include 1500 central alpine fault events of m 7 8 and approximately 2 000 000 other events of magnitudes down to 4 8 these other events occur on four additional segments of the alpine fault on 30 segments of the major marlborough and buller faults and on 4650 randomly distributed smaller faults the synthetic seismicity model is of the quasi static type governed by the coulomb failure criterion with extensions to better account for rupture propagation and fault healing true rate and state friction and viscoelastic relaxation are not yet included mechanical properties are adjusted so that most events rupture an entire fault segment i e the faults behave characteristically the regional b value of 1 thus arises mainly from the fault size distribution the driving mechanism and fault properties are iteratively adjusted so that the resulting long term slip rates single event displacements and recurrence times match the observed real world values the major results are as follows i large alpine fault earthquakes m 7 8 on the central segment have recurrence times with a broad distribution from 81 to 601 yr average 234 yr ii the regional moment release rate is constant over periods of 1000 yr but is quite variable on scales of a few hundred years iii large events on the central alpine fault will usually propagate at least part way along strike to the northeast past the junctures with the marlborough faults that splay off to the east iv thirty seven per cent of such large alpine fault events lafes will also instantaneously trigger significant activity m 6 5 on one or another of the other major faults here instantaneous means with a 0 to approximately 3 yr delay v characteristic events initiating on other major faults also have a high chance of triggering activity elsewhere vi following the short period of increased risk of triggered events a stress shadow effect predominates probably reflecting the mutually inhibitory nature of parallel strike slip faults and the need for a constant long term moment release rate

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

genesis of arsenic fluoride enriched soda water a case study at datong northern china abstract the high as and f groundwaters from datong basin are mostly soda waters with a na cl so4 meq ratio greater than unity as and f up to 1550 g l and 10 4 mg l respectively and with ph between 7 6 and 9 1 geochemical modeling indicates that the waters are oversaturated with respect to calcite and clay minerals such as kaolinite and undersaturated with respect to primary rock forming minerals such as anorthite and albite the water chemistry also is affected by evapotranspiration the degree of evaporative enrichment is up to 85 in terms of cl results of the hydrogeochemical studies indicate that the occurrence of soda water at datong is the result of incongruent dissolution of aluminosilicates at one stage of their interaction with groundwater when the water is oversaturated with respect to calcite and evapotranspiration related salt accumulation is not too strong studying the genesis of soda waters provides new insights into mechanism of as and f enrichment in the aquifer system due to caf2 solubility control and oh f exchange reactions f can be enriched in soda water and the high ph condition of soda water favors as desorption from oxyhydroxide surfaces thereby increasing the concentration of as in the aqueous phase

switches in subduction direction and the lateral termination of mountain belts pyrenees cantabrian transition spain the switch in subduction polarity at the transition from the pyrenees to the cantabrians implies an abrupt change in the gross direction of plate movement the pyrenees formed in response to the northward subduction of continental crust beneath europe during the palaeogene whereas the cantabrians developed during the southward subduction of biscay oceanic crust beneath spain as yet no attempt has been made to explain the mechanism and geometry of this apparent switch in plate kinematics the transition from northward to southward subduction occurs across a discrete lineament the pamplona fault oriented transversely with respect to the long axis of the adjacent mountain belts regional mapping reveals a 180 switch in the facing direction of thrusts and associated folds across the pamplona fault balanced structural cross sections constructed either side of the pamplona fault exhibit marked contrasts in bulk shortening depth to detachment gross structural geometry and the thickness and completeness of the pre orogenic mesozoic succession the pyrenean cantabrian transition zone is thus envisioned as a fundamental crustal lineament of pre orogenic origin a new model for the cenozoic tectonic evolution of north spain has the pamplona fault separating a series of transtensional basins in the pyrenees from a passive margin in the cantabrians subsequent plate collision between spain and europe reactivated the faults that controlled pre orogenic 9syn rift9 sedimentation in the present pyrenean area in the cantabrians however plate collision signalled a shift from a passive margin to an active margin consuming biscay oceanic crust beneath a northern spain subduction zone an implication of this model is that the foreland crust was affected variably by 9backarc9 heating during the early stages of spain europe collision this is expressed by the changing depth of the ebro basin the foreland basin that developed in response to pyrenean cantabrian orogenesis whose thickness of the tertiary succession varies laterally according to changes in flexural rigidity

fluids migration and dynamics of a blocks and faults system abstract we explore the impact of fluids migrating through a fault network on the dynamics of lithosphere both on slow movements and seismicity for that purpose fluids in the fault zones are incorporated into modelling of blocks and faults systems which takes into account driving forces and the system s geometry simulations have been performed for two dimensional models an idealised brick wall structure and a coarse image of sinai subplate migrating fluids originating in different locations are considered as well as fluids trapped in closed pockets basic features of the modelled and observed seismicity are in good accord as shown by comparison with the earthquake catalog compiled by geophysical institute of israel

the nappe des marbres unit of the basque cantabrian basin the tectono thermal evolution of a fossil hyperextended rift basin the architecture of the pyrenean cantabrian belt results from the inversion of a series of former cretaceous rift basins a ht lp metamorphic event dated at 105 to 85 ma ago is commonly associated with an albo cenomanian episode of hyperextension of the continental crust this metamorphism is well known in the eastern basque cantabrian basin within the nappe des marbres unit nmu that is preserved from intense compressional deformation during the pyrenean orogeny based on a structural study at the scale of the eastern basque cantabrian basin bcb and on a dense sampling for trscm estimates with the rscm method raman spectrometry on carbonaceous material we show following results 1 the nmu has recorded two major phases of deformation related to a localized extensional ductile foliation s1 during the cretaceous rifting and later by the regional n s shortening recorded by a regional cleavage s2 observed only in shale sediments 2 the nmu is affected by early salt tectonics related to several diapirs and salt walls fed by the upper triassic evaporitic layer 3 the nmu recorded maximum temperatures exceeding 550 c which represent some of the highest temperatures along the pyrenees these new data demonstrate that there is no e w lateral metamorphic gradient across the belt and that hyperextension rifting occurred consistently within a high thermal regime 4 metamorphic isograds are oblique in respect of the main structures suggesting that the metamorphic event postdates most of the early salt related deformations prior to or coeval with early stages of rifting as it represents one of the best preserved example of pre orogenic hyperextended basin the eastern bcb record may be used regionally to better understand the rift to orogen evolution of the pyrenean internal metamorphic zone but also more generally as an analog of salt bearing hyper extended rift record

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

basement blocks and tecto sedimentary evolution in the pyrenees during mesozoic times the alpine tectonics in the pyrenean range is controlled by motions of basement blocks high primary range north pyrenean blocks these blocks belong to different tectonic units they are amygdaloid wedge shaped squeezed at their roots upthrust and displaced with their cover detached or not in a convergent shear zone between the european and iberian plates these basement blocks are distributed within isopic isofacial units with diachronous terrigenous prisms the stratigraphical analysis of their mesozo c cover reveals their relative position during the mid cretaceous continental break up which induced the separation of the two previously joined plates

riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain this study presents u and li isotope and major and trace element data for the dissolved load suspended particulates and bedload for icelandic rivers draining predominantly basaltic catchments physical erosion rates range from 920 to 2084 t km2 yr with the higher values associated with glacier fed rivers chemical erosion rates range from 45 to 91 t km2 yr with lower rates being associated with glacier fed rivers uranium activity ratios 234u 238u are close to secular equilibrium in the suspended and bedloads but all dissolved load samples show values greater than unity ranging from 1 13 to 2 41 the highest 234u 238u values are found in glacier fed rivers and can be attributed to recoil effects as grinding by glaciers locally enhances rates of physical weathering activity ratios in glacial rivers decrease with distance from the glacial source due to input from non glacial tributaries which have high levels of dissolved uranium and lower activity ratios in contrast in non glacial rivers uranium activity ratios increase with distance downstream due to continued weathering in soils and of bedrock the 7li value of the suspended load is always lower than that of the bedload due to preferential retention of 6li in secondary minerals during weathering in turn the 7li value of the dissolved load is always greater than that of the bedload ranging from 17 0 to 43 7 7li for the dissolved load decreases with increasing levels of dissolved silicon and the saturation index of secondary minerals which suggests that 7li decreases with increasing chemical weathering there is no correlation between 7li values and uranium activity ratios for the dissolved load for non glacial rivers but for glacier fed rivers there is an increase in 7li with increasing 234u 238u suggesting that where physical comminution of mineral grains by glaciers is high chemical weathering is suppressed and vice versa