plio quaternary uplift of the iberian chain central eastern spain from landscape evolution experiments and river profile modeling abstract the iberian chain central eastern spain is characterized by a dome shaped topography with poorly incised and relatively flat landscape in its interior at an elevation of 1300 m a recent regional tectonic event started during or after the late pliocene inducing deep valley incision on the flanks of the iberian chain the rate and timing of this deformation as well as the magnitude of the uplift induced erosion processes still lack a quantitative validation we used 3d signum and 1 d river profile numerical models to investigate the landscape evolution of the iberian chain from the late pliocene to the present and to study the response of topography and rivers to tectonically induced base level lowering our model results are supported by geological geomorphological and geochronological data the results of the signum experiments show that the iberian chain topography has experienced regional uplift since ca 3 ma with rates between 0 25 and 0 55 mm y 1 in response to this uplift rivers have incised at an average long term incision rate of about 0 22 mm y 1 and have progressively captured drainage areas from the chain interior to further validate the results of landscape evolution modeling we use a 1 d river incision model to explore the incision history of several rivers draining the iberian chain the results constrain the range of values of bedrock erodibility from 5 8 10 5 to 5 0 10 4 m 0 4 y 1 and predict long term incision rates similar to those from the signum experiments

including anisotropy in 3 d velocity inversion and application to marlborough new zealand summary two types of seismic velocity heterogeneity are often observed in a given region pronounced patterns of anisotropy shown by local earthquake shear wave splitting and seismic velocity structure imaged by local earthquake traveltimes we seek to combine these types of observations by including anisotropy in 3 d velocity inversion the fast polarization directions from local earthquake shear wave splitting are used to define an initial anisotropy model the ray paths are estimated for each of the shear wave splitting observations and the 3 d initial model is determined via an averaging process and a coherence analysis the initial magnitude of anisotropy at a node is dependent on the number of adjacent ray paths and the consistency of the shear wave splitting anisotropy measurements the traveltime inversion is parametrized with an isotropic component and two azimuthal anisotropy parameters for each node the ray paths are defined with approximate 3 d ray tracing and for each point along a ray path the velocity is defined as a function of the ray path azimuth at that point a blended approach is used to damp the perturbations to the magnitude of anisotropy and or perturbations to the fast direction tests with synthetic traveltime data show that the anisotropic velocity inversion method is reliable application to the marlborough region shows variations in anisotropy in the brittle crust ductile lower crust mantle and subducted slab the patterns are consistent with the shear wave splitting observations but show some additional features the maximum anisotropy is approximately 12 per cent oriented northeast between the awatere and wairau faults this high anisotropy may reflect deformation and extensive fracturing in a region of high total shear strain in the region of interaction of the ductile lower crust with the shallow subducting slab moderate anisotropy with east west orientation is imaged this is consistent with ductile deformation roughly parallel to the plate velocity

the summit erosion surfaces of the inner betic cordillera their value as tools for reconstructing the chronology of topographic growth in southern spain erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the earth s crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift thereby preserving much of the initial plateau topography as it rises to greater elevations here we analyze a regionally extensive population of mappable planar surfaces which crown several major tectonically active sierras of the inner south eastern betic cordillera se spain based on a synthesis of long term landscape evolution involving landform reconnaissance dem based morphometric analysis structural geology sediment provenance analysis and field stratigraphy we conclude that the summit surfaces are a mosaic of discrete post orogenic erosion surfaces that each developed in relation to mediterranean marine base levels at a time when the sierras formed a series of low elevation islands they are not therefore fragments of a once regionally continuous paleoplain the summit surfaces were partly the result of shallow angle detachment faulting during the middle miocene in response to lithospheric slab detachment where evidence exists that the resulting low relief topography was reworked by marine abrasion during the tortonian sea level rise the terminal age of the surfaces is latest miocene age bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years 8 ma 5 7 ma they were subsequently uplifted to their current elevations 1 7 to 2 km by pliocene to quaternary neotectonics in at least two major pulses

seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault abstract the concud fault is located at the junction between the jiloca and teruel grabens central eastern iberian chain spain the late pleistocene activity of this fault has been well logged from structural and palaeoseismological trench studies but only scattered data of the late pliocene seismic activity exist the late pliocene early pleistocene syn tectonic infill consists of an endorheic continental succession in which a 75 m long continuous well was drilled near the concud fault along the entire well core several types of soft sediment deformation structures with variable morphology size and frequency have occurred including clastic dykes load structures and slumps the rigorous analysis of the deformation structures their relationships with the involved sedimentary facies and the discrimination of possible deformation mechanisms and trigger processes allow us to interpret part of them as seismically induced structures the recognition of 21 deformed beds seismites allow the late pliocene early pleistocene seismic history of the concud fault to be reconstructed therefore 21 seismic events with m 5 and an apparent recurrence period of about 45 ka have been inferred

structural analysis of supracrustal faults in the charlevoix area quebec relation to impact cratering and the st laurent fault system the charlevoix area which is host to an impact structure of devonian age straddles the boundaries among crystalline rocks of the grenville province the cambrian ordovician sedimentary succession of the st lawrence platform and accreted units of the appalachian orogen the area features well developed supracrustal fault systems attributed to impact cratering a major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and less frequently by pseudotachylyte detailed mapping of faults both within and outside the charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact related fault rocks in the charlevoix area the st laurent fault trending to the northeast represents a major structure interpreted as being related to late proterozoic early paleozoic rifting of the iapetus ocean howev

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

charlevoix and sudbury as gravity readjusted impact structures on the basis of detailed field investigations and the study of impact breccias at the charlevoix impact structure quebec a structural analysis is given this analysis shows that the annular arrangement of both topography and lithology can be applied to subdivide the two craters discussed in this review successive rings characterize the central uplift and its collapsed ring graben in the charlevoix structure fault breccias show an annular distribution and indicate diverse directions of movement suggesting progressive readjustment they formed cohesionless products inside fault planes named mylolisthenite and are believed to have acted as lubricants during the modification stage of the formation of the structure listric readjustment by gravity after the formation of the transient crater the sudbury structure ontario shows fault breccias in a concentric arrangement similar to that of charlevoix it may be compared with the charlevoix structure by applying the same mechanical readjustment model with deep listric faults the only difference is the amount of the rise structural uplift that is the height of central uplift which is less important in the larger impact structure

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

anisotropic structure beneath central java from local earthquake tomography 1 in this study we present the new tomographic code anita which provides 3 d anisotropic p and isotropic s velocity distribution based on p and s traveltimes from local seismicity for the p anisotropic model we determine four parameters for each parameterization cell this represents an orthorhombic anisotropy with one predefined direction oriented vertically three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0 60 and 120 and one is a perturbation along the vertical axis the nonlinear iterative inversion procedure is similar to that used in the lotos code we have implemented this algorithm for the updated data set of central java part of which was previously used for the isotropic inversion it was obtained that the crustal and uppermost mantle velocity structure beneath central java is strongly anisotropic with 7 10 of maximal difference between slow and fast velocity in different directions in the forearc area between southern coast and volcanoes the structure of both isotropic and anisotropic structure is strongly heterogeneous variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust beneath volcanoes we observe faster velocities in vertical direction which is probably an indicator for vertically oriented structures channels dykes in the crust beneath the middle part of central java north to merapi and lawu volcanoes we observe a large and very intense anomaly with a velocity decrease of up to 30 and 35 for p and s models respectively inside this anomaly e w orientation of fast velocity takes place probably caused by regional extension stress regime in a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and or penetration of quasi horizontal lenses with molten magma in the mantle trench parallel anisotropy is observed throughout the study area such anisotropy in the slab entrained corner flow may be due to presence of b type olivine having predominant axis parallel to the shear direction which appears in conditions of high water or and melting content

reflectivity and seismic properties of the deep continental crust the recovery of drill core from a section of upper amphibolite facies terrane located in the inner piedmont of south carolina provides a rare opportunity to study in detail the seismic character of rocks which were once part of the deep continental crust seismic reflection profiles over the inner piedmont in the vicinity of the drill hole reveal subhorizontal high amplitude reflections the origin of these reflections has been investigated by measuring compressional wave velocities as a function of confining pressure and densities in 150 samples obtained from 305 m of drill core synthetic seismograms generated from the velocity and density measurements demonstrate that reflections originate from subhorizontal metamotphic layering probably originating from lower crustal ductile flow fine tuning of the metamotphic layering which is temperature and pressure related can produce bright spots in the deep crust anisotropy resulting from preferred mineral orientation is another important propeny of this sectim velocities are low for vertical wave propagatim whereas horizontal velocities are relatively high horizontal velocities show mly a slight variatim with azimuth which is unlikely to be detected using standard refractim techniques reflectivity decreases with increasing anisotropy critical to this study has been the continuous coring of a major section of high grade metamotphic terrane which has provided the necessary stratigraphic and lithologic cmtrol for the generation of accurate synthetic seismograms

earthquake relocation and three dimensional vp and vp vs models along the low angle alto tiberina fault central italy evidence for fluid overpressure summary the active extension in the central portion of the northern apennines is believed to be accommodated by an ene dipping low angle normal fault cutting the upper crust called alto tiberina fault atf the physical properties and mechanics of such a severely misoriented fault are still unknown and debated in this study we constrain the deep geometry of the atf and investigate the material properties of the fault system by using microseismicity recorded by a dense local seismic network the inversion of local earthquake p and s wave arrival times yields high resolution v p and v p v s images of the fault system we find positive v p anomalies that define the eastward verging thrust and fold belt developed in the sedimentary cover which inner bulk consists of triassic evaporites remains of the older compression microseismicity reveals the 20 ne dipping atf nearly planar from 3 to 14 km depth no sharp velocity contrasts are observed across the fault but only a gentle warping of the velocity anomalies and the dislocation of the triassic evaporites top at shallow depth on the fault hangingwall normal v p and strong high v p v s indicate the presence of a fractured high fluid pressure volume within which steep normal fault segments are located this evidence suggests that fluid pressure plays a dominant role in triggering the shallow background seismicity along the atf low v p v s anomalies are observed suggesting a different level of cracking and pore saturation and that the fault acts as impermeable barrier we speculate that the microseismic activity on the atf is favoured by the entrapped and locally overpressured co2 testified by the low v p v s volumes

seismicity and faulting in the charlevoix zone of the st lawrence valley abstract continuous monitoring of the seismically active charlevoix zone since late 1977 has delineated the boundaries of the earthquake zone under the north shore and has enabled an association to be made with surface mapped faults that strike along the st lawrence valley and dip to the southeast within the active zone aseismic volumes are found under parts of the st lawrence river and another elongated zone of activity is found to the southeast on unmapped faults dipping under the river the previous suggestions that the activity is related to old rift faults which have been later weakened by a meteor impact would seem to be upheld

a three dimensional p wave velocity model for the charlevoix seismic zone quebec canada 1 a three dimensional p wave velocity model has been developed for the charlevoix seismic zone csz the csz is located along the st lawrence river 100 km northeast of quebec city canada and is one of the most active seismic zones in eastern north america five earthquakes with magnitudes equal to or exceeding 6 0 have occurred in the csz in historic time and around 200 earthquakes occur annually hypocenters are located in precambrian basement rocks basement rocks have been affected by numerous tectonic events including grenvillian collision iapetan rifting and meteor impact we performed a sequential tomographic inversion for p wave velocity structure based upon 3093 p wave arrivals from 489 earthquakes recorded by 12 stations high velocity is associated with the center of the impact crater the region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks an elongated high velocity region is present at midcrustal depths that trends parallel to the st lawrence river earthquakes avoid the high velocity body and separate into two bands one on either side of the feature larger earthquakes magnitude 4 have occurred along the northern edges of the high velocity region

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

mapping p wave azimuthal anisotropy in the crust and upper mantle beneath the united states abstract much progress has been made on revealing seismic structure and mantle dynamics beneath the united states us with the earthscope usarray project seismic anisotropy revealed by shear wave splitting studies provides important constraints on constructing geodynamic models with regard to the seismic images but the shear wave splitting observations have poor vertical resolution and so their interpretations are often not unique in this work we used a large number of arrival time data from local and distant earthquakes recorded by the usarray to determine the first p wave azimuthal anisotropy tomography of the crust and upper mantle beneath the us our results show that fast velocity directions fvds in the lithosphere under the tectonically active areas correlate well with the surface tectonic features suggesting that the p wave anisotropy mainly reflects the present deformation a circular pattern of the fvds centered in the great basin is revealed which is well consistent with the specific circular shear wave splitting observations there suggesting that the anisotropy occurs in the crust and uppermost mantle in contrast beneath the stable cratonic region the fvds revealed by this study differ from the shear wave splitting observations but consistent with the features of gravity and magnetic anomalies indicating that the p wave fvds mainly reflect the fossil anisotropy in the lithosphere whereas the s wave splitting observations mainly reflect the significant anisotropy in the asthenosphere the present results shed new light on the seismic anisotropy in the crust and upper mantle and provide new constraints on constructing geodynamic models beneath the us

segmentation and increasing activity in the neogene quaternary teruel basin rift spain revealed by morphotectonic approach abstract the nnw sse trending teruel basin rift is the largest late miocene quaternary extensional intracontinental structure located within the central eastern iberian chain spain the structural and morphotectonic study carried out in the central northern part of this half graben basin north of teruel city has allowed us to analyse rift segmentation deformation partitioning and rift evolution results are based on vertical displacement calculations fault throw and bending of the main border and intrabasin fault zones we use two geomorfological stratigraphical markers the intramiocene erosion surface ies 11 2 ma and the fundamental erosion surface fes 3 5 ma while the first marker reveals rift initiation under an e w extension the late marker records vertical displacements associated to a second late pliocene quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ene wsw trending o3 despite the along axis rift segmentation into three structural domains northern central and southern and the distribution of deformation among border and intrabasin faults in the central and southern domains a consistent average slip rate post ies of 0 09 mm a has been calculated on distinct transects across the basin suggesting a homogeneous crustal scale extension process in the region the results also reveal that slip rates during the late pliocene quaternary 0 12 0 16 mm a are higher than the late miocene early pliocene 0 05 0 07 mm a slip rate increase is caused by i a westward propagation of deformation from the valencia through and ii a change in the regional stress field both enhanced by crustal doming affecting central eastern iberia as well as progressive fault linkage throw vs distance graphs suggest that the main faults are in a transient stage towards coalescence less advanced within the southern domain regional late pliocene quaternary uplift concomitant with increasing slip rates in the teruel basin rift has caused the basin to rise so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present day fluvial network

seismicity along st lawrence paleorift faults overprinted by a meteorite impact structure in charlevoix quebec eastern canada abstract the charlevoix seismic zone csz in quebec has the highest number of earthquakes in eastern canada with cataloged events diffusely distributed between the st lawrence paleorift faults in this study we relocate 1242 out of 1639 earthquakes in the csz from 1988 to 2010 using double difference relocations with phase arrivals from manual picks and waveform cross correlations and requiring a strict set of quality control criteria our results show a diffuse distribution of earthquakes beneath the st lawrence river within a meteorite impact structure and clear lineations of event hypocenters outside the inner boundary of the impact structure the diffuse seismicity distribution coupled with a lower cumulative seismic moment within the impact structure despite a higher number of events suggests the presence of highly fractured crust and weakened pre existing faults a lack of m n 4 0 earthquakes and a wide variation of focal mechanism p axis orientations also provide evidence for weakened pre existing faults relocated earthquakes beneath the north shore of the st lawrence river illuminate a broad southeast trending linear structure suggesting the geometry of the gouffre northwest river fault a paucity of seismicity between the north shore and the river may correspond to fault controlled basins of unconsolidated sediments at the surface and volumes of high seismic velocity material at midcrustal depths online material earthquake catalogs

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

emplacement depth and carbon dioxide rich fluid inclusions in intrusion related gold deposits phanerozoic intrusion related gold deposits have many consistent characteristics such as a spatial temporal and geochemical association with moderately reduced predominantly ilmenite series i type intrusions the deposits exhibit a range of characteristics that vary over a wide range of emplacement depths 7 km deposits in shallow crustal settings 5 km have characteristics of mesothermal environments and are hosted by plutons containing sheeted veins greissen and disseminated gold fluid characteristics also vary with depth deposits in shallow environments contain high temperature 350 c immiscible brine 30 wt nacl equiv and low salinity 5 wt nacl equiv vapor that commonly contains carbon dioxide deposits in deeper environments contain abundant low salinity carbon dioxide rich aqueous fluids 10 wt nacl equiv that in some deposits are postdated by moderate to high salinity brines 10 40 wt nacl equiv these contrasting fluid types are interpreted to be magmatic in origin and are the result of the complex interplay between exsolution of different volatiles carbon dioxide water and chlorine from felsic magmas emplaced at different crustal levels experimental studies have shown that carbon dioxide will exsolve from felsic magmas at much higher pressures than water and chlorine due to its lower solubility in the melt thus deposits formed from felsic magmas in deeper environments will contain abundant carbon dioxide rich fluids subsequent fluids released from the magma are likely to be water rich and more saline felsic magmas in shallow environments will contain lower concentrations of carbon dioxide that will partition into the vapor phase during phase separation between brine and vapor

recognition of eroded astroblemes abstract the morphology of lunar craters degrades only slowly by the formation of new impacts and their ejecta it is not the same on earth because of weathering and tectonism generally the typical crater topography has disappeared and the term impact structure or astrobleme is applied on planetary surfaces as on the moon two classes of craters are recognized based on their depth to diameter ratio simple bowl shaped and complex readjusted flat bottomed craters with a sharp transition from simple to complex pike 1977 1980 on earth small simple craters retain some of their typical rimmed pit morphology because they are generally recent many are associated with meteorite fragments large impact structures or astroblemes in addition to their specific circular features are recognized as such only by the presence of shock metamorphism criteria such as dense minerals coesite stishovite diaplectic minerals and glass maskelynite planar deformation features in minerals principaly in quartz and feldspars and shattercones which are commonly used these criteria are abundant in allochthonous breccia particularly in fall back breccia among which there are glass fragments such as tectite or microtectite glass spherules shards droplets rods etc but on the floor of the astroblemes the criteria of shock metamorphism are restricted to the central part which is often covered or eroded using the measurements of nine astroblemes visited a scaling model is presented for two types of craters readjusted along listric slip surfaces a well readjusted model based on data from charlevoix and manicouagan canada and a partly readjusted model based on data from the ries germany both possess a central uplift and a ring graben there is also on the floor of the astrobleme a specific type of breccia mylolisthenite and pseudotachylite associated with the displacement along the autochthonous masses of rocks in very large impact structures the shock metamorphism is able to melt a part of the floor grieve and cintala 1992 the heat resulting from the superheated impact melt destroys a part of the shock metamorphism criteria

intrusions and anomalous vp vs ratios associated with the new madrid seismic zone 1 detailed p wave velocity vp and s wave velocity vs models and vp vs ratios were determined for a major portion of the new madrid seismic zone using arrival times recorded by the new madrid seismic network and portable array for numerical data acquisition panda stations we performed a simultaneous inversion for p and s wave velocities and hypocentral locations yielding the most detailed tomographic image of the upper portion of the crust to date low vp and high vs anomalies resulted in low vp vs ratios that correspond to the major arms of seismicity north of the intersection of the cottonwood grove blytheville arch cg ba fault with the reelfoot fault the unusual low vp vs values can be attributed to the presence of quartz rich rocks two regions contain anomalous vp and vs values and vp vs ratios that cannot be attributed to variations in rock composition and are probably produced by overpressured fluids one region is located on the hanging wall of the northern portion of the reelfoot fault and is aseismic the other region corresponds to a portion of the southern reelfoot fault that experiences swarm activity a distinct velocity contrast exists across the cg ba fault at depths exceeding 4 65 km basement rocks southeast of the fault have vp values that are 4 6 slower than values for rocks located to the northwest the most logical explanation is that the fault follows a preexisting structural feature or lithologic change in basement rocks

velocity models and hypocenter relocations for the charlevoix seismic zone three dimensional p and s wave velocity vp and vs models and hypocenter relocations are determined for the charlevoix seismic zone csz using local arrival time tomography the csz is located along the st lawrence river about 100 km downstream from quebec city canada and is one of the most active seismic zones in eastern north america earthquakes occur in grenvillian basement rocks affected by iapetan ocean rifting and a large devonian meteor impact low vp and vs are associated with the impact structure to a depth of 12 km relocated hypocenters form a semicircle delineating the eastern margin of the impact structure northeast of the impact hypocenters cluster into two groups separated by a region of high vp and vs velocity hypocenters within each group align along planar surfaces suggesting the presence of distinct seismogenic faults the planes trend ne in the same direction as the iapetan rift faults and dip to the se one plane is located beneath the north shore of the st lawrence river and extends to a depth of at least 30 km two other planes with shallower dips are located beneath the river and extend to depths of 12 and 15 km all three planes are disrupted within the impact zone but can be followed suggesting partial preservation of rift parallel fault fabric

a model of rift basin evolution constrained by first order stratigraphic observations the stratigraphy of many nonmarine rift basins records a common sedimentological history consisting of a relatively abrupt increase of water depth followed by a slower shoaling upward trend we explore in this paper the origin of these sequences through a three dimensional physical model that incorporates the affects of fault growth flexure erosion sedimentation and isostasy fault growth is assumed to occur in a self similar manner and is treated as dislocations inducing flexure in a thin elastic plate topography generated by faulting and flexure is allowed to undergo diffusion to simulate erosive and sedimentary processes isostatic response to the redistribution of mass results in additional flexure of the thin plate the model is tested using two models of fault growth and we compare the numerical results with the stratigraphy observed in nonmarine rifts basins generated using a constant lengthening rate mode of fault growth fail to reproduce the stratigraphy of continental rift basins we find that the commonly observed stratigraphic succession of lacustrine to fluvial conditions requires the displacement rate of the bounding fault to decrease with time consistent with opening at a relatively constant areal extension rate

relationship between structures stress and seismicity in the charlevoix seismic zone revealed by 3 d geomechanical models implications for the seismotectonics of continental interiors 1 the charlevoix seismic zone in the st lawrence valley of quebec is the most active in eastern canada the structurally complex region comprises a series of subparallel steeply dipping iapetan rift faults superimposed by a 350 ma meteorite impact structure resulting in a heavily faulted volume the elongate seismic zone runs through the crater parallel to the rift most large events localize outside the crater and are consistent with slip along the rift faults whereas background seismicity primarily occurs within the volume of rock bounded by the rift faults within and beneath the crater the interaction between rift and crater faults is explored using the three dimensional stress analysis code flac3d the rift faults are represented by frictional discontinuities and the crater is represented by a bowl shaped elastic volume of reduced modulus differential stresses are slowly built up from boundary displacements similar to tectonic loading results indicate that weakening the rift faults produces a stress increase in the region of the crater bounded by the faults this causes a decrease in stability of optimally oriented faults and may explain the localization of low level seismicity additionally slip distribution along the rift faults shows that large events localize at the perimeter of the crater and produce focal mechanisms with p axes oblique to the applied stress field consistent with historic large earthquakes it is speculated that similar systematic rotation of focal mechanism p axes may be expected along other intraplate rift zones raising a potential caveat for the use of focal mechanisms for stress estimation in continental interiors

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

a test of the longevity of impact induced faults as preferred sites for later tectonic activity the hypothesis that impact induced faults have been preferred sites for later deformation in response to lithospheric stresses has been suggested for several planets and satellites this hypothesis is investigated on earth by examining whether terrestrial impact structures show higher rates of nearby earthquake activity than do surrounding intraplate regions for 28 of 30 probable impact structures having an original crater 20 km or more in diameter the rates of nearby seismicity have been no higher than the regional background rates for two large probable impact structures vredefort and charlevoix with higher than normal rates of nearby seismicity factors other than slip on impact induced faults appear to control the occurrence of earthquakes it is concluded that impact induced faults at least on earth do not persist as lithospheric weak zones for periods in excess of several million years after the impact event

three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland