experimental constraints on the rheology eruption and emplacement dynamics of analog lavas comparable to mercury s northern volcanic plains we present new viscosity measurements of a synthetic silicate system considered an analogue for the lava erupted on the surface of mercury in particular we focus on the northern volcanic plains nvp which correspond to the largest lava flows on mercury and possibly in the solar system high temperature viscosity measurements were performed at both superliquidus up to 1736 k and subliquidus conditions 1569 1502 k to constrain the viscosity variations as a function of crystallinity from 0 to 28 and shear rate from 0 1 to 5 s 1 melt viscosity shows moderate variations 4 16 pa s in the temperature range 1736 1600 k experiments performed below the liquidus temperature show an increase in viscosity as shear rate increases from 0 1 to 5 s 1 resulting in a shear thinning behaviour with a decrease in viscosity of ca 1 log unit the low viscosity of the studied composition may explain the ability of nvp lavas to cover long distances on the order of hundreds of kilometres in a turbulent flow regime using our experimental data we estimate that lava flows with thickness of 1 5 and 10 m are likely to have velocities of 4 8 6 5 and 7 2 m s respectively on a 5 ground slope numerical modelling incorporating both the heat loss of the lavas and its possible crystallization during emplacement allows us to infer that high effusion rates 10000 m3 s are necessary to cover the large distances indicated by satellite data from the messenger spacecraft

environmental and diagenetic records from trace elements in the mediterranean coral cladocora caespitosa trace element contents in coralline aragonite have long been used as proxies to record environmental growth conditions such as sea surface temperature sst in this study we explored whether trace element contents in modern and fossil corals cladocora caespitosa from the mediterranean could help constrain sst temperature and seasonality of climate in late pleistocene interglacials in modern adriatic c caespitosa the individual corallite sr ca signal captures seasonal variation with up to 68 of the variance related to sst a similar but weaker relationship is shown by mg ca however published equations to quantify absolute water temperature from sr and mg contents in modern c caespitosa did not yield consistent or credible results because each corallite exerts a strong non predictable vital effect with no constant species specific offset from equilibrium temperature trace element relationships become at best colony specific and unsuitable for absolute palaeotemperature reconstruction despite this temperature related cyclicity in sr and mg is preserved in corallites up to at least mis 7 age allowing identification of seasonality in sst in addition unusual trace element anomalies in modern c caespitosa can inform on events such as sediment discharge into the coastal zone partial diagenetic alteration of fossil c caespitosa skeletons from aragonite to calcite destroys original sst driven cyclic trace element signals and is an effective indicator of corallite preservation quality

potential for larger earthquakes in the east san francisco bay area due to the direct connection between the hayward and calaveras faults the hayward and calaveras faults two strike slip faults of the san andreas system located in the east san francisco bay area are commonly considered independent structures for seismic hazard assessment we use interferometric synthetic aperture radar to show that surface creep on the hayward fault continues 15 km farther south than previously known revealing new potential for rupture and damage south of fremont the extended trace of the hayward fault also illuminated by shallow repeating micro earthquakes documents a surface connection with the calaveras fault at depths greater than 3 5 km repeating micro earthquakes located 10 km north of the surface connection highlight the 3 d wedge geometry of the junction our new model of the hayward and calaveras faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7 posing a higher seismic hazard to the east san francisco bay area than previously considered

watching the hayward fault the hayward fault located on the east side of the san francisco bay represents a natural laboratory for seismologists because it does not sleep silently between major earthquakes in his perspective simpson discusses the study by ba rgmann et al who have used powerful new techniques to study the fault the results indicate that major earthquakes cannot originate in the northern part of the fault however surface rupturing earthquakes have occurred in the area suggesting that they originated to the north or south of the segment studied by ba rgmann et al fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the hayward fault

non planar fault models complexities induced by crustal layering in transcurrent faulting processes summary crack models suitable to describe transcurrent faulting in the presence of a softer shallow layer are presented we employ the asymptotic theory of generalized cauchy kernel equations to study the singular behaviour of a strike slip crack crossing the welded interface between two different media if a planar crack cuts vertically across a material discontinuity the dislocation density is bounded at the interface but a stress drop discontinuity condition must be met in which the stress drop is proportional to the local rigidity such a condition cannot be fulfilled in several cases two antiplane strain models are proposed to avoid this difficulty in the first model fault bending model the fault surface is affected by a sharp change of the dip angle at the intersection with the interface an unbounded singularity in the dislocation density distribution and in the stress field appears at the interface and its dependence from model parameters is studied a generalized stress drop condition is obtained which can be interpreted in terms of the interaction of the crack with the welded boundary condition in the second model fault branching model the crack is split into three interacting sections with the lower section vertical and the other two sections inclined with respect to the vertical in this case the order of the singularity at the interface remains undetermined this result may be interpreted in terms of the further degree of freedom introduced by the presence of a second fracture in the upper layer in the case of branching two conditions are obtained for the stress drop on the three sections according to both models the generalized stress drop conditions may account for a stress drop ratio between the soft layer and the hard basement lower than the rigidity ratio

numerical modeling for target water depth estimation of marine target impact craters 1 marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor the geology of this marine target crater is influenced by the layer of water in the upper part of the target the influence increases with increased water depth the target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy the target water depth for a marine target crater is often estimated by facies analysis of sediments related to the impact crater unfortunately often with ambiguous results we propose to combine the conventional methods with numerical modeling of the target water depth based on the special target water related features of the crater we used geological data from the lockne crater as constraints in a simulation with the sova hydrocode the simulations were done for three different target water depths 200 m 500 m and 1000 m within the likely depth range for the middle ordovician sea in which the impact occurred in order to obtain the minimum estimated size of the lockne crater by an asteroid impact at 20 km s the water depth must have been slightly less than 1 km and the impactor radius must have been about 400 m it was not possible to generate a crater with the geological features of lockne for target water depths of less than about 500 m however the ratio may be further constrained by factors such as impactor density impact angle and impact velocity

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

the marine lockne impact structure jamtland sweden a review the lockne impact structure in jamtland 63 00 20 n 14 49 30 e formed in the middle ordovician at approximately 455 ma the structure is a concentric crater with a total diameter of 13 5 km the impact took place in a marine environment seawater played an important role in the cratering process and in crater morphology and the amount of melt remaining in the structure seawater rushed back into the crater in a resurge eroding and redepositing the ejecta among the resurge deposit seawater furthermore facilitated the hydrothermal system which was driven by the residual heat in the structure the lockne structure hosts shocked quartz and an iridium anomaly the rim wall round the crater collapsed in the modification stage of the crater and was annihilated by the resurge the fractured basement and the impact breccia were initially rich in open cavities these became partly filled with dominantly calcite the filling contributed to a low density contrast generating a negative gravity anomaly of 22 gu the gravity model indicates a central uplift and a nw directed tilt of the structure this tilt is also seen in the magnetic models the apparent absence of any impact melt is probably real and related to the environment of impact

regional geological and tectonic structures of the north sea area from potential field modelling the spatial distribution of large scale crustal domains and their boundaries are investigated in the north sea area by combining gravity magnetic and seismic data the north sea is situated on the plates of three continents avalonia laurentia and baltica which collided during the caledonian orogeny in the middle palaeozoic the location and continuation of the collisional sutures are debated we apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures the transformations reveal intrinsic features of crustal transitions between the caledonian plates and their relation to later extensional structures the transformations include the hough transform applied to the gravity field calculation of fractional derivatives and integrals of the gravity and magnetic fields the pseudogravity field and the horizontal gradient field as well as upward continuation the results indicate a fundamental difference between the lithosphere of avalonia laurentia and baltica the location of the mesozoic rift system the central graben and viking graben may have been partly determined by the presence of the sutures between these three plate indicative of extensional reactivation of compressional structures a significant lineament across the entire north sea between scotland and north germany indicates that the lower crust of baltica provenance may extend as far south westward as to this lineament comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties this lineament could represent the suture between lithosphere of caledonian origin avalonia versus lithosphere of precambrian origin baltica in the lower crust and upper mantle if this is the case the lineament is the missing link in the reconstruction of the triple plate collision

shear wave velocity structure of the southern african upper mantle with implications for the uplift of southern africa summary broad band seismic data from the southern african seismic experiment and the africaarray network are used to investigate the seismic velocity structure of the upper mantle beneath southern africa and in particular beneath the kaapvaal craton a two plane approximation method that includes a finite frequency sensitivity kernel is employed to measure rayleigh wave phase velocities which are inverted to obtain a quasi 3 d shear wave velocity model of the upper mantle we find phase velocities for the kaapvaal craton and surrounding mobile belts that are comparable to those reported by previous studies and we find little evidence for variation from east to west across the namaqua natal belt a region not well imaged in previous studies a high velocity upper mantle lid is found beneath the kaapvaal craton and most of southern africa for the kaapvaal craton the thickness of the lid 150 200 km is consistent with the lid thicknesses reported in many previous studies the cratonic lid is underlain by a 100 km thick low velocity zone with a 3 9 per cent maximum velocity reduction by comparing the velocity model to those published for other archean cratons we find few differences and therefore conclude that there is little evidence in the shear wave velocity structure of the mantle to indicate that the southern african plateau is supported by an upper mantle thermal anomaly

the formation and evolution of hule and rio cuarto maars costa rica abstract the hule and rio cuarto maars are respectively located 11 and 18 km northward of the active crater of poas volcano on the caribbean side of the central volcanic range of costa rica they lie on the northern part of poas volcano massif along a n s trending 27 km long volcanic fracture crossing the poas volcano the volcanic products from hule maar 2 3 km 1 8 km area 3 5 km2 are mainly pyroclastic surges poorly vesiculated andesites with very small plagioclases silica rich andesitic pumice flows air fall deposits ballistic blocks and reworked deposits that overlie the regional pleistocene volcanic basement they were produced during three main explosive phases two overlapping pyroclastic cones have developed within the hule maar and at least three lava fields are related to them high al basalt to basaltic andesite another maar pata de gallo 400 m across is located less than 1 km off the se rim of hule rio cuarto is a nearly circular maar 700 850 m across with a surface area of 0 33 km2 rio cuarto products include surges ballistics and air fall tephra produced during three main explosive phases these deposits show a narrow fan oriented westward according to westerly wind direction they indicate a westerly directed surge first 2 km followed by air fall deposits up to 5 km away radiocarbon dating has shown that hule was formed 6 2 ka ago and pata de gallo probably formed 2 8 ka ago while the intra maar products could have ages of 1 7 ka or 0 7 ka indicating that hule is a polygenetic maar there are no radiocarbon ages yet for dating the formation of rio cuarto maar but archaeological data suggest that it erupted between 3 4 ka ago the volume of pyroclastic deposits associated to hule maar is estimated to be 0 51 0 53 km3 from which 20 is juvenile material therefore 0 07 0 08 km3 of new dense rock equivalent dre magma after subtracting 20 30 of porosity the tephra from rio cuarto is estimated to be 4 4 107 m3 of which 0 008 m3 correspond to dre magma the hule and rio cuarto maars are occupied by lakes and in the last decades several lake overturn events have taken place with a repeat cycle of six to seven years the main outcome of these events has been the mass death of fish accompanied by changes in the lake color in these systems the hazard related to the possible occurrence of nyos type gas eruptions can be considered negligible or very local but significant for tourists who camp by the lakes

controls on timing and amount of right lateral offset on the east bay fault system san francisco bay region california the distribution of offset correlated rock units relative position of northward younging volcanic rocks and distribution of units not offset together reveal the history of strike slip deformation along the east bay fault system the system accumulated 175 km of right lateral offset since 12 ma but of this amount only 25 km was accumulated between 12 and 10 ma and only 75 km between 12 and 6 ma the westernmost hayward fault zone is responsible for more than half 100 km of the total and it too has undergone more offset 60 km after 6 ma than before the activity on any single fault zone in the system has been sporadic and alternating periods of activity and inactivity have been recorded on at least some of the fault zones

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

stresses in an overthrust sheet and propagation of thrusting an airy stress function solution an airy stress function solution is derived for the stress field in an elastic wedge shaped overthrust sheet subject to horizontal forces at the rear and at the front from this stress solution the state of stress on the basal thrust lower boundary of the sheet is obtained both normal and shear stresses on the basal thrust are affected by the rear pushing and front buttressing forces and by the slopes of the upper and lower boundaries of the wedge shaped block for 1 nonlinear components of external horizontal forces exerted on the vertical edges of the block and or 2 nonzero slopes of the upper and lower boundaries the normal and shear stresses vary systematically with position along the basal thrust the ratio of shear and normal stresses along this plane the frictional function of the thrust can be compared with the friction coefficient to determine where slippage is likely to occur since the frictional function is a function of position the strength is exceeded only on part of the thrust near the rear for most values of the parameters the assumption of simultaneous displacement of the whole thrust sheet on the basal plane is therefore not realistic even simple static models such as the present one indicate that the motion on thrust faults must be envisaged in terms of progressive consecutive dislocation type slippage

when a cosmic impact strikes the sea bed most bolides that collide with the earth hit the sea limited knowledge about marine target impacts hampers predictions about their perilousness this study presents geological features that are particular to craters formed at sea the features are most likely a result of the influence of the target on the cratering process marine target craters form only if the target sea is shallow enough to admit sufficient kinetic energy into the sea bed when the crater diameter is large compared to the water depth the crater resembles its counterparts that are formed on land craters formed in deeper water are concentric and often lack melt sheets and rim walls but have deposits and radial gullies formed by the resurge of the sea impacts on the deep shelf are probably much more energetic than is suggested by the dimensions of the preserved crater

structure and evolution of cenozoic arc magmatism on the antarctic peninsula a high resolution aeromagnetic perspective structure and evolution of cenozoic arc magmatism on the antarctic peninsula a high resolution aeromagnetic perspective

the mission link between the hayward and calaveras faults the left stepover between the calaveras and hayward faults gives rise to compressive strain that is accommodated by vertical deformation producing the highest hills bordering the east side of san francisco bay monument peak to mission peak the projection of the active trace of the hayward fault is separated 3 5 km from the junction of the northern and southern segments of the calaveras fault at calaveras reservoir for pure strike slip on the hayward and calaveras faults the stepover region is compressed in area at a rate given by the separation times the long term slip rate of 9 mm yr on the hayward fault assuming a seismogenic depth of 10 km the horizontal compression accumulated over 150 years is equivalent to a dip slip seismic moment of 2 8 1018 n m this moment if released in a single event would generate an earthquake of magnitude 6 3 due to dip slip alone dip slip may occur on buried faults throughout the stepover region the base of the southwest face of monument peak suggests a buried thrust or reverse fault dipping northeast the prominent scarp on mission peak has the same strike and sense of slip current microearthquakes between the calaveras and hayward faults align parallel to the mission fault but show only horizontal slip on a vertical fault plane a dipping fault is needed to satisfy the geometric constraint of the convergence therefore the mission fault zone must consist of two or more fault surfaces inclined at different dip angles as is observed in the san andreas fault zone in the loma prieta area horizontal slip is building up stress on the inclined fault which is currently locked growing compressive stress will increasingly impede horizontal slip until a thrust or reverse slip event occurs allowing then more horizontal slip to be transferred from the calaveras to the hayward fault the dip slip fault might be the unstable element governing slip in the larger system

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

formation of resurge gullies at impacts at sea the lockne crater sweden the lockne crater in sweden is a marine target crater formed in a shelf sea approximately 460 ma ago the crater structure consists of an inner crater surrounded by an outer inclined surface that extends to almost 12 km from the center marine craters differ in several respects from craters formed on land one special feature is the formation of resurge gullies excavated by the erosional force of the resurging sea water after the impact the formation of these gullies strongly depends on the ratio crater rim height to water depth as well as on the size of the impact structure such gullies are known from very few marine target craters at the lockne impact site four gullies are identified each of which cuts radially through the rim of the outer crater the rapid collapse of that part of the crater cavity which formed in the seawater resulted in forceful flooding of the crater the resurging seawater not only contained fallback ejecta on its way towards the cavity on the sea bottom it incorporated fractured lithologies from the sea bottom as well this entrained material disintegrated during transport and constitutes today the dominantly monomict lower part of the resurge sequence the resurge flood was highly turbulent highly erosive and developed to a probable hyperconcentrated flow or a possible water flood the erosion in the gullies proceeded as headward erosion down to the transition zone between the brecciated and the less disintegrated crystalline basement

characterisation of fe bearing particles and colloids in the lena river basin ne russia abstract rivers are significant contributors of fe to the ocean however the characteristics of chemically reactive fe remain poorly constrained especially in large arctic rivers which drain landscapes highly susceptible to climate change and carbon cycle alteration the aim of this study was a detailed characterisation size mineralogy and speciation of riverine fe bearing particles 0 22 m and colloids 1 kda 0 22 m and their association with organic carbon oc in the lena river and tributaries which drain a catchment almost entirely underlain by permafrost samples from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in june 2013 and summer baseflow in july 2012 fe bearing particles were identified using transmission electron microscopy as large 200 nm 1 m aggregates of smaller 20 30 nm spherical colloids of chemically reactive ferrihydrite in contrast there were also large 500 nm 1 m aggregates of clay illite particles and smaller 100 200 nm iron oxide particles dominantly hematite that contain poorly reactive fe tem imaging and scanning transmission x ray microscopy stxm indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon poc and attached to the surface of primary produced organic matter and clay particles together these larger particles act as the main carriers of nanoscale ferrihydrite in the lena river basin the chemically reactive ferrihydrite accounts for on average 70 15 of the total suspended fe in the lena river and tributaries these observations place important constraints on fe and oc cycling in the lena river catchment area and fe bearing particle transport to the arctic ocean

shock experiments on pre heated α and β quartz i optical and density data abstract discs of single crystal quartz unheated and pre heated to 275 c and 540 c i e quartz and 630 c i e quartz were experimentally shocked to pressures ranging from 20 to 40 gpa with the shock front propagating parallel to either 10 1 0 or 0001 refractive indices density and the orientation of planar deformation features pdfs were determined on the recovered quartz samples refractive indices of pre heated quartz are unaffected up to 25 gpa but density starts to decrease slightly up to this pressure above 25 gpa pre heating causes drastic variations refractive indices and birefringence of quartz shocked at ambient temperature decrease continuously until complete isotropization is reached at 35 gpa in quartz shocked at 630 c refractivity drops discontinuously in the interval from 25 to 26 gpa and complete transformation to diaplectic glass is reached at 26 gpa density follows the trends demonstrated by the optical parameters with higher pre shock temperatures yielding lower density at a given shock pressure these results indicate that the threshold pressure for the onset of transformation to diaplectic quartz glass is largely temperature invariant lying at 25 gpa whereas the pressure limit for complete transformation decreases with increasing pre shock temperature from 35 to 26 gpa quartz shocked parallel to 0001 always has a higher density and refractivity than that shocked parallel to 10 1 0 indicating a significant influence of the structural anisotropy this is also evident from the distribution of pdf orientations pressures 25 gpa cause in quartz shocked parallel to 10 1 0 pdfs that are predominantly oriented parallel to 10 1 2 while quartz shocked to the same pressures but parallel to 0001 contains almost exclusively pdfs parallel to 10 1 3 pdf orientations in quartz shocked at ambient temperature parallel to 10 1 0 show the following characteristics i the frequency of 10 1 3 is high at 20 gpa declines with increasing pressure and finally is totally absent at 32 gpa ii 10 1 3 begins to occur at 25 gpa increases and finally is the only remaining orientation at 32 gpa and iii 10 1 2 and 11 2 2 are only present at 20 and 25 gpa in contrast quartz shocked at 630 c parallel to 10 1 0 displays a broad pdf distribution with indistinct maxima and 10 1 3 is totally absent the small structural difference between and quartz which is reflected in the pdf distribution should allow in principle evaluation of the pre shock temperature in naturally impacted metamorphic rocks the results substantiate that formation of shock effects in quartz is dependent on i shock pressure ii pre shock temperature and iii shock wave direction so far the latter two parameters have not been considered in the application of experimental results to impact sites

re evaluation of the 1836 hayward fault and the 1838 san andreas fault earthquakes abstract current seismic hazard models include two major earthquakes m 7 in the san francisco bay area that are close in space and time an 1836 event on the northern hayward fault and an 1838 event on the peninsula section of the san andreas fault analysis and interpretation of the available historical accounts indicate that the 1836 event occurred east of monterey bay far from the hayward fault and was of m 6 also the 1838 event was not confined to the 60 km peninsula san andreas as current models indicate instead faulting probably extended from san francisco to san juan bautista 140 km indicating a significantly larger earthquake m 7 than previously thought damaging effects of the 1836 earthquake were reported only from santa clara to carmel and no contemporary effects were reported to the north of santa clara or near the hayward fault the illusion of an 1836 hayward earthquake evolved from a newspaper reminiscence published following the 1868 hayward earthquake stating that the 1868 effects in the east bay were similar to those of an 1836 event the article describes various strong effects in the east bay that differ completely from the effects recorded for the 1836 earthquake but are very similar to those documented for the major 1838 san andreas earthquake that caused extensive damage on both sides of san francisco bay based on this and other evidence we conclude that the reminiscence describes the destructive june 1838 effects but it erroneously indicates the date as june 1836 there is no evidence for any major historical earthquakes in the san francisco bay area before the 1838 earthquake back to the founding of mission san francisco dolores in 1776 during the 1838 san andreas fault earthquake the shaking intensity in monterey was as strong as or stronger than during the great 1906 san andreas fault earthquake this suggests that the 1838 san andreas fault rupture may have extended to san juan bautista as it did in 1906 numerous probable aftershocks were felt in the area south of san juan bautista these damaged carmel and santa cruz in 1840 and alisal 16 km west of the san andreas fault in 1841 the northern end of the 1838 faulting was previously assumed to be 25 km south of san francisco however mission san francisco dolores was damaged in 1838 but not in 1906 suggesting that the 1838 faulting extended to san francisco also the 1838 aftershocks were felt in oakland as frequently and violently as those following the major 1868 hayward earthquake suggesting that the 1838 faulting on the san andreas extended to the latitude of oakland the 1838 fault segment ruptured again 68 years later as part of the overlapping 1906 san andreas fault rupture this and similar evidence from southern california indicates that m 7 san andreas fault earthquakes can recur at intervals of 68 years or less when they are followed by m 8 earthquakes on overlapping segments of the fault

oceanic impacts a growing field of fundamental geoscience the importance of oceanic impacts of collisional events and resulting energy release are briefly described data collection methods from the eltanin a mesosiderite projectile deep water impact are presented

controls on mesopelagic particle fluxes in the sub antarctic and polar frontal zones in the southern ocean south of australia in summer perspectives from free drifting sediment traps the saz sense project examined ecosystem controls on southern ocean carbon export during austral summer january february 2007 at three locations p1 in the low biomass subantarctic zone saz west of tasmania p3 in a region of elevated biomass in the saz east of tasmania fuelled by enhanced iron supply and p2 in high nutrient low chlorophyll hnlc polar frontal zone pfz waters south of p1 and p3 sinking particles were collected using i a cylindrical time series pps3 3 trap for bulk geochemical fluxes ii indented rotating sphere irs traps operated as in situ settling columns to determine the flux distribution across sinking rate fractions and iii cylindrical traps filled with polyacrylamide gels to obtain intact particles for image analysis particulate organic carbon poc flux at 150 m pps3 3 trap was highest at p1 lower at p2 and lowest at p3 3 3 1 8 2 1 0 9 and 0 9 0 4 mmol m 2 d 1 respectively biogenic silica bsi flux was very low in the saz 0 2 0 2 and 0 02 0 005 mmol m 2 d 1 at p1 and p3 respectively and much higher in the pfz 2 3 0 5 mmol m 2 d 1 at p2 hence the high biomass site p3 did not exhibit a correspondingly high flux of either poc or bsi separation of sinking rate fractions with the irs traps at 170 and 320 m depth was only successful at the pfz site p2 where a relatively uniform distribution of flux was observed with 1 3 of the poc sinking faster than 100 m d 1 and 1 3 sinking slower than 10 m d 1 analysis of thousands of particles collected with the gel traps at 140 190 240 and 290 m depth enabled us to identify 5 different categories fluff aggregates low density porous or amorphous aggregates faecal aggregates denser aggregates composed of different types of particles cylindrical and ovoid faecal pellets and isolated phyto cells chains and single cells faecal aggregates dominated the flux at all sites and were larger in size at p1 in comparison to p3 the pfz site p2 differed strongly from both saz sites in having a much higher abundance of diatoms and relatively small sized faecal aggregates overall the particle images suggest that grazing was an important influence on vertical export at all three sites with differences in the extents of large aggregate formation and direct diatom export further influencing the differences among the sites

subsurface geometry of the san andreas calaveras fault junction influence of serpentinite and the coast range ophiolite while an enormous amount of research has been focused on trying to understand the geologic history and neotectonics of the san andreas calaveras fault saf cf junction fundamental questions concerning fault geometry and mechanisms for slip transfer through the junction remain we use potential field geologic geodetic and seismicity data to investigate the 3 d geologic framework of the saf cf junction and identify potential slip transferring structures within the junction geophysical evidence suggests that the san andreas and calaveras fault zones dip away from each other within the northern portion of the junction bounding a triangular shaped wedge of crust in cross section this wedge changes shape to the south as fault geometries change and fault activity shifts between fault strands particularly along the calaveras fault zone cfz potential field modeling and relocated seismicity suggest that the paicines and san benito strands of the cfz dip 65 to 70 ne and form the southwest boundary of a folded 1 to 3 km thick tabular body of coast range ophiolite cro within the vallecitos syncline we identify and characterize two steeply dipping seismically active cross structures within the junction that are associated with serpentinite in the subsurface the architecture of the saf cf junction presented in this study may help explain fault normal motions currently observed in geodetic data and help constrain the seismic hazard the abundance of serpentinite and related cro in the subsurface is a significant discovery that not only helps constrain the geometry of structures but may also help explain fault behavior and the tectonic evolution of the saf cf junction

the effect of fault geometry and minimum shear wavespeed on 3d ground motion simulations for an mw 6 5 hayward fault scenario earthquake san francisco bay area northern californiathe effect of fault geometry and minimum shear wavespeed on 3d ground motion simulations

the target peneplain of the lockne impact the lockne impact crater in central sweden with a diameter of about 7 km formed in the mid ordovician in a marine environment that was deeper than present shelf seas the present dip of the so called sub cambrian peneplain in the target area of the impact is about 0 85 toward the northwest the peneplain is cut by a set of northwest striking nearly vertical faults with a throw of up to just over 100 m collectively the identification of the peneplain and its deformation by faulting allows us to infer that the part of the crater that is exposed to the east of lake locknesjon has been lowered by about 100 m relative to parts exposed to the west of the lake and that it has therefore been spared from significant erosion therefore the preservation of the whole crater is even better than was assumed in previous work the peneplain extends to 600 700 m from the rim of the inner crater hence the structural uplift of the rim is quite subdued compared to the craters that formed on land

response of the tectonically erosive south peruvian forearc to subduction of the nazca ridge analysis of three dimensional analogue experiments 1 the collision zone of the obliquely subducting nazca ridge and the erosive peruvian forearc is characterized by enhanced tectonic erosion normal faulting forearc uplift and a minor indentation we apply two three dimensional sandbox experiments monitored by an optical particle imaging velocimetry system to decipher the spatial and temporal evolution of forearc deformation during oblique convergence the rigid model ridge causes a wave of uplift followed by subsidence to shift along the forearc by varying the strength of the analogue material we demonstrate that the forearc response to ridge subduction in particular the amount and rate of uplift and wedge indentation is controlled by the mechanical strength of the forearc the model using the high strength material yields results more compatible with the geological record of the peruvian forearc first the modeled amount of uplift scales to 1 2 km in nature which agrees with 1 0 km of uplift recorded by marine terraces second the calibrated model uplift rate of 0 9 km myr is similar to the natural rate of 0 7 km myr third the development of normal faults above the model ridge is in accordance with the style of faulting above the nazca ridge finally oversteepening of the uplifted wedge and local slope failure as observed in the experiment has also been identified off southern peru a comparison between the erosive peruvian and accretive margins emphasizes that the style of ridge induced deformation depends on the forearc strength and crustal structure which in turn are controlled by the long term evolution of the margin s mass transfer regime

seasonality in sea surface temperatures from δ18o in cladocora caespitosa modern adriatic to late pleistocene gulf of corinth high resolution stable isotope analysis of coral skeletons is an established method to help reconstruct seawater growth temperatures for palaeoenvironmental reconstructions here we investigated the temperate colonial mediterranean scleractinian coral cladocora caespitosa we first studied modern adriatic corals from mljet croatia where growth temperatures were known a clear sinusoidal cyclicity is present in the d18o of the modern coral skeletons with average cycle minima 3 3 and average maxima 1 6 cyclicity approximately matches the number of seasonal growth band pairs in each sample implying a genetic link between d18o cyclicity and factors that determine seasonal growth band development here mainly water temperature a derived and calibrated species specific d18o temperature relationship was then used to reconstruct growth temperatures from fossil c caespitosa this was applied to well preserved material collected from late pleistocene deposits mis 1 5 and 7 around the gulf of corinth greece clear seasonal d18o signals are seen in all the fossil samples mis 5e was the warmest period studied with a lower than modern seasonal temperature range the early to mid holocene probably experienced the lowest temperatures while conditions in mis 7a c were probably the wettest with most freshwater input into the gulf

ground motion modeling of hayward fault scenario earthquakes part i construction of the suite of scenarios abstract we construct kinematic earthquake rupture models for a suite of 39 m w 6 6 7 2 scenario earthquakes involving the hayward calaveras and rodgers creek faults we use these rupture models in 3d ground motion simulations as discussed in part ii aagaard et al 2010 to provide detailed estimates of the shaking for each scenario we employ both geophysical constraints and empirical relations to provide realistic variation in the rupture dimensions slip heterogeneity hypocenters rupture speeds and rise times the five rupture lengths include portions of the hayward fault as well as combined rupture of the hayward and rodgers creek faults and the hayward and calaveras faults we vary rupture directivity using multiple hypocenters typically three per rupture length yielding north to south rupture bilateral rupture and south to north rupture for each rupture length and hypocenter we consider multiple random distributions of slip we use two approaches to account for how aseismic creep might reduce coseismic slip for one subset of scenarios we follow the slip predictable approach and reduce the nominal slip in creeping regions according to the creep rate and time since the most recent earthquake whereas for another subset of scenarios we apply a vertical gradient to the nominal slip in creeping regions the rupture models include local variations in rupture speed and use a ray tracing algorithm to propagate the rupture front although we are not attempting to simulate the 1868 hayward fault earthquake in detail a few of the scenarios are designed to have source parameters that might be similar to this historical event

geodetic constraints on san francisco bay area fault slip rates and potential seismogenic asperities on the partially creeping hayward fault 1 the hayward fault in the san francisco bay area sfba is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes imaging the spatial variation in interseismic fault creep on the hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the sfba where the relative motion between the pacific plate and the sierra block is partitioned across closely spaced subparallel faults to estimate spatially variable creep on the hayward fault we interpret geodetic observations with a three dimensional kinematically consistent block model of the sfba fault system resolution tests reveal that creep rate variations with a length scale of 15 km are poorly resolved below 7 km depth in addition creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models differential microplate motions result in a slip rate of 6 7 0 8 mm yr on the hayward fault and we image along strike variations in slip deficit rate at 15 km length scales shallower than 7 km depth similar to previous studies we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm yr on the central hayward fault that is spatially correlated with the mapped surface trace of the 1868 mw 6 9 7 0 hayward earthquake and adjacent to gabbroic fault surfaces

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

historic creep rate and potential for seismic slip along the hayward fault california the hayward fault is considered the most likely source of one or more major earthquakes in the san francisco bay area in the next few decades historically at least one and probably two major earthquakes about m 6 8 occurred along the hayward fault one in 1836 and another in 1868 little is known about the 1836 event but the 1868 earthquake was accompanied by a surface rupture that extended as much as 41 km along the southern part of the fault although the amount of surface slip in 1868 is uncertain right slip including afterslip reached at least several centimeters and possibly several decimeters in places this paper documents the spatial variation of creep rate along the hayward fault since the 1868 earthquake creep aseismic fault slip occurs over at least 66 km and may extend over the fault s entire 82 km length of which about 13 km lies underwater creep rate seems nearly constant over decades but short term variations occur we derive creep rate mainly from our own systematic surveying of offset cultural features curbs fences and buildings on each feature we solve directly for accumulated creep by using multiple linear regression creep rate mostly falls in the range of 3 5 6 5 mm yr but systematic variation occurs along strike fault segments with distinctly higher and lower rates generally correspond to parts of the fault most salient from the overall average alinement of the fault most distinctive is a 4 km long section near the south end of the fault that creeps at about 9 mm yr such a high rate has occurred there at least since the 1920s and probably since the 1868 earthquake as indicated by an offset railroad track built in 1869 we suggest that this 9 mm yr slip rate may approach the long term or deep slip rate that controls average recurrence interval between major earthquakes if so assuming an elastic rebound model the potential for slip in large earthquakes below the surficial creeping zone is now 1 1 m in the southern 1868 segment of the fault and 1 4 m in the northern 1836 segment subtracting surface creep rates from a long term slip rate of 9 mm yr gives present potential for surface slip in large earthquakes of up to 0 8 m with an average of 0 6 m in the northern segment and 0 4 m in the southern segment we present a simple hypothesis for rupture potential that is compatible with historic creep rate microseismicity distribution and geodetic data if seismic rupture occurs on segments 41 km long by 10 km deep 7 km fully locked 3 km creeping today s potential for seismic moment release is 1 4 1019 and 1 1 1019 n m for both 1836 and 1868 segments respectively and 2 5 1019 n m for both segments jointly converting moment to magnitude gives ml 6 8 in the northern segment ml 6 7 in the southern segment and ml 7 0 for simultaneous rupture of both

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

long term creep rates on the hayward fault evidence for controls on the size and frequency of large earthquakes the hayward fault hf in california exhibits large m w 6 5 7 1 earthquakes with short recurrence times 161 65 yr probably kept short by a 26 78 aseismic release rate including postseismic its interseismic release rate varies locally over time as we infer from many decades of surface creep data earliest estimates of creep rate primarily from infrequent surveys of offset cultural features revealed distinct spatial variation in rates along the fault but no detectable temporal variation since the 1989 m w 6 9 loma prieta earthquake lpe monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate we now identify significant temporal variations mostly associated with local and regional earthquakes the largest rate change was a 6 yr cessation of creep along a 5 km length near the south end of the hf attributed to a regional stress drop from the lpe ending in 1996 with a 2 cm creep event north of there near union city starting in 1991 rates apparently increased by 25 above pre lpe levels on a 16 km long reach of the fault near oakland in 2007 an m w 4 2 earthquake initiated a 1 2 cm creep event extending 10 15 km along the fault using new better constrained long term creep rates we updated earlier estimates of depth to locking along the hf the locking depths outline a single 50 km long locked or retarded patch with the potential for an m w 6 8 event equaling the 1868 hf earthquake we propose that this inferred patch regulates the size and frequency of large earthquakes on hf online material 2007 event creep models plots of creepmeter data maps and cross sections of relocated microearthquakes and active fault traces and iterative solutions for depth of creep

gravity magnetic and high precision relocated seismicity profiles suggest a connection between the hayward and calaveras faults northern california 1 gravity magnetic and seismicity data profiled across the hayward fault zone were generated as part of ongoing studies to help determine the geologic and tectonic setting of the san francisco bay region these data combined with previous geophysical studies that indicate that the hayward fault zone dips 75 ne near san leandro and follows a preexisting structure reveal a possible direct connection between the seismogenic portion of the hayward and calaveras faults at depth although the relocated seismicity data are regional in nature they suggest that the dip of the hayward fault zone may vary from near vertical in the northwestern part of the fault to about 75 ne at san leandro in the central part of the fault to about 50 ne in the southeastern part of the fault gravity and magnetic data profiled across the hayward fault zone were processed using standard geophysical techniques cross sections of high precision relocated hypocenters were constructed along each profile from the northwestern to the southeastern end of the hayward fault zone profiles and cross sections are referenced to pinole point where the hayward fault enters san pablo bay and are spaced 2 5 km apart topographic profiles shown on the seismicity cross sections were generated using u s geological survey usgs 7 5 min 30 m digital elevation models relocation of seismicity data was accomplished using a regional double difference method the double difference method incorporates ordinary travel time measurements and cross correlation of p and s wave differential travel time measurements relative locations between earthquakes have hypocentral errors of about 100 m horizontally and 250 m vertically absolute location uncertainties were not determined but are probably dramatically improved compared to the usgs s northern california seismic network catalog data

coupled effects of impact and orogeny is the marine lockne crater sweden pristine our current understanding of marine impact cratering processes is partly inferred from the geological structure of the lockne crater we present results of a mapping campaign and structural data indicating that this crater is not pristine in the western part of the crater pre impact impact and post impact rocks are incorporated in caledonian thrust slices and are subjected to folding and faulting a nappe outlier in the central crater depression is a relic of the caledonian nappe cover that reached a thickness of more than 5 km the overthrusted crater is gently deformed strike of strata and trend of fold axes deviate from standard caledonian directions northeast southwest radially oriented crater depressions which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim are interpreted to be open synclines in which resurge deposits were better preserved the presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater i a raised crater brim zone acted as an obstacle during nappe propagation ii the occurrence of a central crater depression caused downward sagging of nappes and iii the lack of an appropriate detachment horizon alum shale within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland preliminary results of 3 danalogue experiments suggest that a circular high friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater crustal shortening is also partitioned into the crater basement and decreases laterally outward deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater strain gradients both vertically and horizontally result in non plane strain deformation in the vicinity of the crater the strain tensors in the hanging and foot walls may deviate up to 90 from each other and rotated by up to 45 with respect to the standard regional orientation the observed deflection of strata and fold axes within the lockne crater area as revealed by field mapping is in agreement with the pattern of strain partitioning shown in the analogue models

the gardnos impact structure norway petrology and geochemistry of target rocks and impactites abstract the gardnos structure norway is an approximately circular area of anomalously fractured and brecciated rock about 4 5 km in diameter emplaced in a metamorphic terrane composed chiefly of granitic gneisses with minor amphibolite and quartzite the original recognition of gardnos as a deeply eroded impact structure between 900 and 400 ma old has been followed up by detailed petrographic and chemical studies of approximately thirty samples of target rocks and various types of shocked rocks impactites deep erosion of the structure has erased the original rim removed much of the crater fill deposits and exposed large areas at or near the original crater floor however a wide variety of distinctive impactites fractured and blackened quartzites in the sub crater basement rocks lithic breccias and melt bearing breccias are still preserved these impactites show petrographic and chemical characteristics that confirm an impact origin distinctive planar deformation features pdfs in quartz and feldspar incipient melting of feldspar clasts in the melt bearing breccias close matches between the chemical composition of the breccias and mixtures of the target lithologies and the detection of an extraterrestrial component a minor extraterrestrial component 0 15 was detected in the melt bearing breccias based on significantly elevated ir and os contents and lower 187os 188os ratios compared to those in the target rocks the gardnos impactites are significantly enriched in c 5 10x over the exposed target rocks this may reflect the presence of a c rich shale overlying the metamorphic basement at the time of impact this idea is supported by 13c values of 28 1 to 31 5 measured in the impactites mixing calculations show that the chemical compositions of the impactites can be reproduced by mixtures of target rocks ranging from approximately 60 90 wt granite gneiss 0 30 wt amphibolite 0 12 wt quartzite and 3 19 wt of a c rich shale component the deeply eroded state of the structure and the preliminary state of detailed geologic mapping make crater reconstruction difficult one possible scenario involves the impact of a 300 m diameter stony meteorite that released 1019 j of energy and formed a transient cavity 3 km in diameter that evolved to a complex crater 5 km in diameter with a central uplift of about 350 m the original crater was filled with at least 0 3 km3 of allochthonous melt matrix breccias containing about 0 06 km3 of impact melt the structure underwent low grade greenschist metamorphism in caledonian time about 400 ma ago and was subsequently eroded to its present appearance the value of the gardnos structure for further cratering studies lies in its easy access to large areas of the original crater floor zone in the preservation of a possibly complete sequence of crater fill breccias beneath a cap of elastic sediments and in the unusual carbon enrichment of its impactites

gravity and magnetic expression of the san leandro gabbro with implications for the geometry and evolution of the hayward fault zone northern california the hayward fault one of the most hazardous faults in northern california trends north northwest and extends for about 90 km along the eastern san francisco bay region at numerous locations along its length distinct and elongate gravity and magnetic anomalies correlate with mapped mafic and ultramafic rocks the most prominent of these anomalies reflects the 16 km long san leandro gabbroic block inversion of magnetic and gravity data constrained with physical property measurements is used to define the subsurface extent of the san leandro gabbro body and to speculate on its origin and relationship to the hayward fault zone modeling indicates that the san leandro gabbro body is about 3 km wide dips about 75 80 northeast and extends to a depth of at least 6 km one of the most striking results of the modeling which was performed independently of seismicity data is that accurately relocated seismicity is concentrated along the western edge or stratigraphically lower bounding surface of the san leandro gabbro the western boundary of the san leandro gabbro block is the base of an incomplete ophiolite sequence and represented at one time a low angle roof thrust related to the tectonic wedging of the franciscan complex after repeated episodes of extension and attenuation the roof thrust of this tectonic wedge was rotated to near vertical and in places the strike slip hayward fault probably reactivated or preferentially followed this preexisting feature because earthquakes concentrate near the edge of the san leandro gabbro but tend to avoid its interior we qualitatively explore mechanical models to explain how this massive igneous block may influence the distribution of stress the microseismicity cluster along the western flank of the san leandro gabbro leads us to suggest that this stressed volume may be the site of future moderate to large earthquakes improved understanding of the three dimensional geometry and physical properties along the hayward fault will provide additional constraints on seismic hazard probability earthquake modeling and fault interactions that are applicable to other major strike slip faults around the world manuscript received 11 january 2002

deformation localization in orogens spatiotemporal expression and thermodynamic constraint abstract orogens are spatiotemporal expressions of instabilities in materials under load constrained by thermodynamics and preserved in the cold outer shell of the planet their pressure temperature time histories are consistent with the predictions of differential grade 2 dg 2 materials in pure shear we place the statistically invariant shear localization mechanism of these materials in a coherent thermodynamic context using an analysis of strained elastic materials this prototype system exhibits non classical thermodynamic symmetry breaking where the potentials are all functions of a single variable and the distinction between heat and work fades from view consequently internal energy must be described by a monotonically decreasing function of the entropy in order for heat capacity and absolute temperature to be positive the entropy itself exhibits an inverse dependence on length these constraints are satisfied by the overall shape and slope of the distributed deformation threshold d for dg 2 materials and its noted 1 length correlation with naturally observed folds as a function of thermomechanical competence we predict that temperature in this non linear elastic material will vary in proportion to the slope of d being high at low competence and low at high competence similar constraints apply to a self gravitating body where the energy function varies inversely with radius assigning zero pressure at the surface of the body we also predict that pressure the tensor trace of its stress energy density will vary inversely with radius thus the body force of gravity will be expressed in this elastic self gravitating system through the interplay of elastic and thermal lengths deformation localization in dg 2 materials arises due to the dynamic rescaling of lengths in response to a spike in the intrinsic energy i at while the intrinsic i and localization l thresholds are monotonically decreasing for they exhibit positive slopes at lower competence signaling a return to classical thermodynamics and joule heating in this transitional domain numerous structural and tectonic observations can be correlated using this remarkably simple model beginning with the thickness and mechanical character of the brittle crust and oceanic lithosphere in effect this model projects the kinematic theory of plate tectonics into four dimensional spacetime

geology of the early palaeozoic lockne impact structure central sweden abstract the diameter of the crater at lockne as seen on topographic maps is 7 8 km the tandsbyn breccia the principal evidence of impact consists of strongly crushed local basement its distribution follows the crater margin on the north margin basement granite rests on an inverted sub cambrian erosion surface on the lowermost middle cambrian tangential faults occur at the periphery of the structure after the impact occurred under the sea during the middle ordovician there was a resurgence of ejecta loaded sea water which deposited a chaotic breccia lockne breccia which has the appearance of a debris flow the lockne breccia together with a less coarsely grained turbidite loftarsten which lies immediately above it predominantly consist of clasts of lower to middle ordovician limestone and mainly subordinate inclusions of tandsbyn breccia and isolated clasts of crystalline basement fragments of impact melt are important components of the turbidite a protective cover of sediments formed after the impact is in turn overlain by an outlier of a caledonian overthrust nappe which occupies the central and topographically deepest part of the crater shocked quartz has been identified in the loftarsten

subsurface structure and kinematics of the calaveras hayward fault stepover from three dimensional vp and seismicity san francisco bay region california the calaveras and hayward faults are major components of the san andreas fault system in the san francisco bay region dextral slip is presumed to transfer from the calaveras fault to the hayward fault in the mission hills region an area of uplift in the contractional stepover between the two faults here the estimated deep slip rates drop from 15 to 6 mm yr on the calaveras fault and slip begins on the hayward fault at an estimated 9 mm yr a lineament of microseismicity near the mission fault links the seismicity on the calaveras and hayward faults and is presumed to be related directly to this slip transfer however geologic and seismologic evidence suggest that the mission fault may not be the source of the seismicity and that the mission fault is not playing a major role in the slip transfer we perform a joint inversion for hypocenters and the 3d p wave velocity structure of the stepover region using 477 earthquakes we find strong velocity contrasts across the calaveras and hayward faults corroborated by geologic gravity and aeromagnetic data detailed examination of two seismic lineaments in conjunction with the velocity model and independent geologic and geophysical evidence suggests that they represent the southern extension of a northeasterly dipping hayward fault that splays off the calaveras fault directly accounting for the deep slip transfer the mission fault appears to be accommodating deformation within the block between the hayward and calaveras faults thus the calaveras and hayward faults need to be considered as a single system for developing rupture scenarios for seismic hazard assessments online material 3d interactive visualizations of the mission and alum rock hypocenters

geodetically inferred coseismic and postseismic slip due to the m 5 4 31 october 2007 alum rock earthquake on 31 october 2007 the m 5 4 alum rock earthquake occurred near the junction between the hayward and calaveras faults in the san francisco bay area producing coseismic and postseismic displacements recorded by 10 continuously operating global positioning system gps instruments the cumulative postseismic displacements over the four months following the earthquake are linearly related to the cumulative number of aftershocks and are comparable in magnitude to the coseismic displacements the postseismic signal suggests that in addition to afterslip at seismogenic depths localized right lateral reverse slip occurred on dipping shallow fault surfaces southwest of the calaveras the spatial distribution of slip inferred by inverting the gps data is compatible with a model in which moderate calaveras fault earthquakes rupture locked patches surrounded by areas of creep afterslip and microseismicity oppenheimer et al 1990 if this model and existing calaveras fault slip rate estimates are correct a slip deficit remains on the 2007 alum rock rupture patch that may be made up by aseismic slip or slip in larger earthquakes recent studies e g manaker et al 2005 suggest that at depth the hayward and central calaveras faults connect via a simple continuous surface illuminated by the mission seismic trend mst implying that a damaging earthquake rupture could involve both faults graymer et al 2008 if this geometry is correct the combined coseismic and postseismic slip we infer for the 2007 alum rock event predicts static coulomb stress increases of 0 6 bar on the mst surface and on the northern calaveras fault 5 km northwest of the alum rock hypocenter

development of san leandro synform and neotectonics of the san francisco bay block california abstract high resolution 24 channel seismic reflection data show a stratified synform beneath south san francisco bay these seismic reflection data reveal an eastward dipping bedrock surface that is about 40 m deep subbottom beneath the western south bay and that reaches a maximum observed depth of 500 800 m subbottom below the eastern half of the south bay an angular unconformity cuts both the synform and underlying bedrock the age of the unconformity is unknown but may be pleistocene when these strata forming the synform were presumably exposed subaerially during lowered sea levels the synformal strata the unconformity and some generally flat lying and overlying strata are folded near the eastern shore of the bay this folding may result from movement on the hayward fault fault interactions and localized strain partitioning or from compressional deformation in the east bay hills related to ne sw fault normal convergence between the pacific and north american plates in general reflections from sediment overlying the unconformity are flat lying except near the eastern shore of the bay whereas reflections beneath the unconformity dip eastward the overlying flat sediment section fills a shallow basin that is coincident with an elliptical residual gravity low this low appears to be related to the deeper sedimentary synformal section based on the spatial correlation between the east dipping reflections and the gravity anomaly projecting the east dipping reflections to the center of the gravity low suggests that the total section of flat lying and dipping reflections in the synform may exceed 1000 m modeling of the gravity low suggests a total low density section about 1 5 km thick at the center of the synform relative to the surrounding bedrock of presumed franciscan complex