depositional sequence of argillite diamictite hyaloclastite and lava flows within the franciscan complex northern california an originally conformable sequence of argillite diamictite hyaloclastite pillow breccia pillow basalt exists in a 3 km long up to 200 m thick fault bounded slab among franciscan rocks 6 km south of the klamath river mouth argillite and diamictite grade laterally into one another over short distances diamictite contains clasts of chert and graywacke that exhibit detrital rounding greenstone clasts are irregularly shaped and compositionally similar to overlying volcanic rocks hyaloclastite consists of globules and granules of altered basalt and basaltic glass with plagioclase phenocrysts and minor plagioclase crystals and altered glass the hyaloclastite is complexly interstratified with diamictite and features suggesting soft sediment deformation exist locally tongues of chloritized basaltic glass have intruded diamictite matrix pillow breccia has hyaloclastite matrix breccia fragments and whole pillows are abundant at the top of the sequence trace element geochemical data suggest that the seq

irregular recurrence of paleoearthquakes along the central garlock fault near el paso peaks california 1 new investigations at the el paso peaks paleoseismic site have refined and extended the record of paleoearthquakes for the central garlock fault event evidence in the form of buried fissures scarps folds and upward terminations has allowed us to identify six well resolved earthquakes designated as events w u r q k and f within the last 7000 years the exposures that we excavated did not reveal additional evidence for three poorly resolved events reported by mcgill and rockwell 1998 evidence for event y identified in the previous study was reexamined and found not to be a paleoearthquake radiocarbon dates of detrital charcoal combined with a method of interpolating the event ages with revised sedimentation rates provide our preferred constraints on the timing of faulting events the most recent surface rupturing earthquake event w occurred between a d 1450 and 1640 the penultimate event u occurred between a d 675 and 950 event r which was unrecognized in the previous study occurred between a d 250 and 475 event q occurred relatively shortly before event r between a d 25 and 275 event k occurred between 3340 and 2930 b c the oldest identified paleoearthquake event f occurred between 5300 and 4670 b c the event ages indicate that earthquake recurrence is highly irregular at the el paso peaks site with individual preferred intervals ranging from as little as 215 years to as many as 3300 years the irregular recurrence of surface rupturing earthquakes along the central garlock fault may be related to temporal and spatial clustering of earthquakes proposed for faults in the eastern california shear zone

estimating earthquake rupture rates on a fault or fault system previous approaches used to determine the rates of different earthquakes on a fault have made assumptions regarding segmentation have been difficult to document and reproduce and have lacked the ability to satisfy all available data constraints we present a relatively objective and reproducible inverse methodology for determining the rate of different ruptures on a fault or fault system the data used in the inversion include slip rate event rate and other constraints such as an optional a priori magnitude frequency distribution we demonstrate our methodology by solving for the long term rate of ruptures on the southern san andreas fault our results imply that a gutenberg richter distribution is consistent with the data available for this fault however more work is needed to test the robustness of this assertion more importantly the methodology is extensible to an entire fault system thereby including multifault ruptures and can be used to quantify the relative benefits of collecting additional paleoseismic data at different sites

ages of late holocene earthquakes on the central garlock fault near el paso peaks california a trench across the central garlock fault within a small playa adjacent to el paso mountains revealed buried fissures and fault scarps that provide strong evidence for five surface rupturing earthquakes within the past 5 kyr weaker evidence suggested the possibility of three additional events within this same time period these observations indicate an average recurrence interval of 700 to 1200 years nearly all 28 radiocarbon dates on samples of detrital charcoal wood and shell are in correct stratigraphic order these dates constrain the ages of the individual faulting events and indicate that the recurrence interval is not periodic but is quite irregular individual recurrence intervals range from 190 to 1545 years if all eight events are actual earthquakes or from 190 to 3405 years if only the five well documented events represent earthquakes the two most recent earthquakes occurred within the past 550 years with preferred ages of about a d 1790 and a d 1600 the a d 1790 event ruptured a narrower width of the fault zone and may have been a smaller earthquake than the others the radiocarbon dates from the trench also indicate that the sedimentation rate on the playa has fluctuated within the past 5 kyr low sedimentation rates 0 1 to 0 35 mm yr and infrequent floods 1 per century prevailed from about 2000 b c to a d 100 and from a d 500 to 1300 during the remaining intervals within the past 5 kyr the sedimentation rate averaged 1 0 to 1 7 mm yr and major floods occurred two to four times per century the changes in sedimentation rate and flood frequency may reflect climatic changes or they may simply reflect changes in drainage patterns

the age petrogeneis and tectonic significance of the frontenac formation basalts northern new hampshire and western maine within plate basalts are present across the connecticut valley gaspe trough in new england and canada proposed mechanisms for the extensional magmatism include back arc basin extension slab breakoff and extensional collapse the age and composition of the bimodal frontenac formation of northern new england and southern quebec has bearing on the topic we analyzed zircons from the meta felsic rocks of the formation and determined a silurian age of 432 8 ma we also analyzed the frontenac rocks for major and trace elements and compared their compositions to the other mafic rocks along strike in the connecticut valley gaspe trough these include the comerford intrusive suite and the standing pond volcanic member of the waits river formation of vermont the silurian chaleur group and the early devonian dalhousie group of new brunswick and the gaspe peninsula and to the piscataquis belt rocks of northern maine all these rocks are post taconic within plate tholeiites that span an age range from 432 ma frontenac formation to 419 ma comerford intrusive suite in spite of their similar tectonic setting subtle differences in trace element compositions are evident indicating a multiplicity of sources in the production of the siluro devonian magmas ce yb versus la ta values suggest that the frontenac magmas were derived from spinel peridotite sources in the asthenospheric mantle we suggest that slab rollback and back arc basin extension permitted asthenospheric mantle upwelling to the spinel peridotite stability field causing the frontenac partial melting event at depths as low as 35 km sediments of the frontenac formation were deposited as turbidite successions into a developing trough resulting from extension the coeval influx of sediment and intrusion of basalt produced a sediment sill complex because the upward migration of the basaltic magmas was hindered by the rapidly thickening sediment overburden subsequently slab breakoff may have opened an asthenospheric window generating the younger within plate magmas that occurred from 425 to 418 ma across the connecticut valley gaspe trough

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

paleoseismic interevent times interpreted for an unsegmented earthquake rupture forecast 1 forecasters want to consider an increasingly rich variety of earthquake ruptures past occurrence is captured in part by paloeseismic observations which necessarily see three dimensional ruptures only at a point this has not been a problem before because forecasts have assumed that faults are segmented and that repeated ruptures occur uniformly along them a technique is now required to calculate paleo earthquake rates at points that may be affected by multiple recurrence processes and that is consistent with an all possible ruptures forecast dating uncertainties are addressed by bootstrapping across event time windows and the resulting distributions are transformed into log space as f ln t where t is interevent time this takes advantage of a property of time dependent recurrence distributions in which their logarithms are normally distributed paleoseismic series necessarily have a finite number of observations such that the true long term mean interevent time is hard to estimate however the mode most frequent value is easier to identify since the mode is equal to the mean of a normal distribution can thus be found at the mode m of f ln t as em the point occurs where 32 of a folded half normal distribution is found in the interval between ln t 0 and m the value is identified by symmetry which overcomes the difficulty of absent long intervals in the record tests are conducted with complex synthetic interevent distributions and applications to real data from the hayward and garlock faults in california are shown

magmatic development and tectonomagmatic models for the solund stavfjord ophiolite complex west norwegian caledonides abstract geochemical variation and different extrusion rates of the late ordovician solund stavfjord ophiolite complex ssoc suggest both open and closed magma chambers closed chambers existed off axis and within a transform fault and are indicated by dykes and pillow lavas that evolved from high mgo basalt to ferrobasalt by fractional crystallization of olivine plagioclase and clinopyroxene hybrid magmas with ferrobasaltic composition represent open magmatic systems and are characterized by frequent eruptions of sheet flows the ssoc is interpreted as representing either a normal or a propagating ridge transform intersection rti the propagating rti model is favoured as it explains both the high frequency of ferrobasalt and uplift of ultramafic rocks to above the sea level which is suggested by detrital ultramafics occurring in an ophiolitic melange

interaction between sediments and basalt injections in young gulf of california type spreading centers during the transitional stage from stretching of continental crust to accretion of new oceanic crust the upwelhng basaltic magma in spreading troughs of narrow ocean basins and pull apart basins may form sills in soft sediment the injections of subsequent great magmatic pulses are empla ced next to or on top of the contact zone of the older ones in this manner a distinctive sill sediment complex is built up

modern tectonic cracking near the garlock fault california tectonic strain accumulation along the locked eastern segment of the garlock fault is probably sufficient to cause ground cracking and related fissuring at the naval weapons center china lake california a 7 mm yr slip rate measured along the western segment of the fault apparently is not being relieved along the 155 km long eastern segment by creep and no major earthquakes have occurred along this segment during the past 1 000 500 yr therefore the unrelieved slip available for elastic strain may be between 3 5 and 10 5 m during 1970 a zone of erosion modified fissures was observed near the randsburg wash access road 5 km north of the garlock fault the fissures did not significantly enlarge between 1970 and 1983 following a severe thunderstorm the night of august 18 1983 two new zones of ground cracks appeared the first zone included the earlier fissures but also extended to the north and south for a total length of 732 m the second zone intersected the first near its midpoint at a 30 angle and had a total length of 686 m analysis of the cracks suggests that the first zone resulted from tensional stresses and that the second resulted principally from shear the tectonic stress field assumed responsible for the formation of these zones is consistent with that deduced for the western segment of the garlock fault the morphology of the cracks indicates that they occurred shortly after the rainfall and flash flooding ceased and there was probably no causative relationship between them trenching studies indicate that the cracks and fissures are a part of a long term process and that the new cracks are only the latest of a series of events

architecture of the neoarchaean jaguar vhms deposit western australia implications for prospectivity and the presence of depositional breaks abstract the duration and nature of breaks in archaean volcanosedimentary packages recently re evaluated in the abitibi greenstone belt has been assessed at jaguar an archaean cu zn rich volcanic hosted massive sulphide vhms deposit in the teutonic bore volcanic complex tbvc the eastern goldfields of the yilgarn craton western australia the deposit is hosted by coherent volcanic facies and associated volcaniclastic facies with minor non volcanic facies the hypothesis that vhms ore lies on the intersection of volcanic centres and depositional breaks is found to be valid for the jaguar deposit with the site being an active volcanic complex at footwall time with further dome development close to the final ore location at mineralised package time and then reoccurring volcanic complexes andesitic and basaltic at several points in the hangingwall succession broadly tied into the ore position at jaguar the entire stratigraphic sequence faces west with no major structural complications making it ideal for stratigraphic analysis the footwall evidences prolific volcanism with no intervening sedimentation the mineralised package mp consists of intercalated dacite breccia conglomerate sandstone and mudstone the footwall volcanic rocks and the mp dacite appear to be differentiation products from the same magma chamber a major volcanic geochemical boundary is identified between the footwall mp tholeiitic to transitional affinities and the immediate hangingwall succession calc alkaline the hangingwall package includes four distinct volcanic units intercalated with mass flow deposits and graphitic argillites vhms mineralisation occurred across a distinct change in the geochemistry of erupted volcanic facies at a time of increased volcaniclastic sedimentation and extension this break is comparable to member level hiatuses seen in the abitibi gb i e the most brief of breaks because there is no silicification of sedimentary unit tops by silicic seawater exposure and there is minimal development of black shales a third time sensitive criteria was the development of peperite on the base of hanging wall hw andesite lavas the mp closely resembles breaks within interpreted deeper water domains of the abitibi gb for instance the deloro tisdale assemblage interface south of timmins the recognition of the change in the rate of emplacement of volcanic units and particularly the change in chemistry of volcanic rocks are critical exploration lithologic guides to use in the absence of chemical sediment deposits exhalites although crustal extension and basin subsidence were factors in the shaping of the succession their effects were too subtle to use as an exploration tool a corollary of the recognition of a member level vhms bearing interval in the teutonic bore volcanic complex is that like the kidd munro assemblage stratigraphy abitibi gb where several ore bearing depositional breaks are known below the great kidd creek deposit there is scope for the discovery of further potentially larger deposits on higher formation or group level breaks in the tbvc

petroleum generation an easy and widespread process in hydrothermal systems an overview abstract the conversion of organic matter to petroleum products by hydrothermal activity is an easy process occurring in nature in many types of environments geologically immature organic matter of marine sediments has been shown to be altered to petroleum products by this process in the guaymas basin escanaba trough bransfield strait and atlantis ii deep and this process probably occurs elsewhere in active sedimented rift systems contemporary organic detritus and or viable microorganisms are also converted in part to petroleum like products when they become entrained by turbulent mixing into hydrothermal vent waters resulting in their instantaneous hydrous pyrolysis this latter case occurs in hydrothermal vent fields without a sedimentary cover emanating directly from oceanic ridges as for example on the east pacific rise at 13 n and 21 n and on the mid atlantic ridge at 26 n this process is probably also ubiquitous for all actively venting sediment starved oceanic ridges the hydrocarbon products generated in these areas have been compared in terms of composition organic matter sources and analogy to reservoir petroleum they represent a major carbon source for chemosynthetic assimilation by vent biota and are compositionally similar to normal petroleum

quantitative refinement of calibrated 14c distributions abstract a new method is presented for using known ordering or other relationships between 14c samples to reduce 14c dating uncertainty the order of sample formation is often known from for example stratigraphic superposition dendrochronology or crosscutting field relations constraints such as a minimum time between dates and limits from historical information are also readily included dendrochronologically calibrated calendric date histograms initially represent each date the method uses bayes theorem and the relational constraints to upweight date ranges in each date distribution consistent with the other date distributions and the constraints and downweight unlikely portions the reweighted date distributions retain all dating possibilities present in the initial calibrated date distributions but each date in the result now reflects the extra information such as ordering supplied through the constraints in addition one may add information incrementally and thus analyze systematically its effect on all the date distributions thus the method can be used to assess the consistency of the quantitative data at hand the bayesian approach also uses the empirical calibrated date distributions directly so information is not lost prematurely by summarized dates to a mean and variance or confidence intervals the approach is illustrated with data from two densely sampled paleoseismic sites on the san andreas fault in southern california an average reduction in 14 c date distribution variance of 59 is achieved using ordering information alone and 85 is achieved by also applying sedimentation rate constraints and historical information

iceberg drift and ocean circulation in the northwestern weddell sea antarctica abstract icebergs are distinctive features in the southern ocean and can influence the physicochemical properties of the ocean environment around them their trajectories are influenced by ocean currents sea ice bathymetry and wind action here twenty five icebergs were identified and tracked by applying image classification methods to a series of 142 advanced synthetic aperture radar asar images obtained during 2008 and 2009 tracking these icebergs made it possible to associate the patterns of iceberg drift with the main ocean currents and front systems in this region including the antarctic coastal current the antarctic slope front and the weddell front a case study investigated here revealed the recirculation of a weddell sea iceberg within the bransfield strait in the northern antarctic peninsula as well as its corresponding mass loss starting in the weddell sea and extending throughout the monitoring period the icebergs studied experienced an average disintegration percentage of 21 15 and an average drift speed of 0 22 0 11 km h 1 the icebergs that drifted at least 500 km had an average meltwater injection rate of 62 76 38 27 m3 s 1 in the ocean around the northern antarctic peninsula

variation of seismic slip in the gulf of california and the possible effect on geodetic measurements of pacific north american plate motion the gulf of california is a unique tectonic transition zone which progresses from an oceanic ridge transform system at the mouth of the gulf to a predominantly continental transform system in southern california slip rates estimated from seismic moment data amount to about 17 to 30 of the accumulated tectonic slip in the gulf predicted by the nuvel 1 plate motion model even after accounting for the transition in crustal structure the seismic to tectonic slip ratios also appear to increase slightly from south to north this trend in the seismic moment release may reflect changes in the accommodation of pacific north american plate motion along the gulf which can be examined geodetically on the other hand geodetic measurements of the relative plate motion can be disturbed by short term effects associated with episodic seismicity to assess these effects the surface displacements due to typical transform events in the gulf are estimated using a simple dislocation model the results of this numerical calculation suggest that if a large transform event m0 1 5 1026 dyne cm were to occur within 100 to 200 km of a geodetic baseline for example one comprised in the geomex global positioning system network across the southern gulf the relative distance measurements could be affected by up to 15 mm this is marginally at the error level of a few millimeters plus 2 parts in 108 of baseline length for geomex measurements which thus are sensitive only to the far field displacement along the plate boundary over baselines of a few hundred kilometers in length

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

liquid hydrocarbon bearing inclusions in modern hydrothermal chimmeys and mounds from the southern trough of guaymas basin gulf of california abstract liquid hydrocarbon bearing inclusions of variable shape e g spherical bowling pin rod and highly irregular occur in hydothermal minerals of chimneys and mounds in the southern trough of guaymas basin central gulf of california the inclusions are preferentially trapped in amorphous silica which occurs as spherules and 0 01 mm thick encrustations on sulfides sulfates and carbonates the inclusions are primary and pseudosecondary and were trapped during not after mineral growth the inclusions are both two phase liquid hydrocarbon and vapor gas and three phase liquid hydrocarbon aqueous fluid and vapor and range from 2 to 50 m in diameter the large range in liquid hydrocarbon and acqueous fluid contents indicates that the hydrothermall fluid and liquid hydrocarbon were never a homogeneous solution but that hydrocarbons were transported as immiscible and possibly solvated forms the liquid hydrocarbon varies in color from deep to pale orange brown and fluoresces a yellow color during excitation by u v light indicating a condesate mainly c 1 to c 10 hydrocarbons composition measurable quantities of hydrocarbons from the inclusions could not be isolated by mineral dissolution by pyrolsis and decrepitation analyses suggest that the more volatile components predominate two phase hydrocarbon inclusions homogenized with the liquid at temperatures ranging from 75 to 190 c excluding one high measurement to obtain true trapping temperatures an unknown pressure correction is required however the trapping temperature of these hydrocarbon inclusions was estimated by measuring trapping temperatures for adjacent aqueous inclusions which range from 116 to 226 c geochemical modelling using these trapping temperatures indicates that the amorphous silica precipitated from the hydrothermal fluid due to conductive cooling in addition to mixing with ambient sea water the temperatures required for the formation of petroleum and its transport to the seafloor in the guaymas basin coincide with those necessary for the precipitation of amorphous silica in the guaymas basin hydrothermal system

evidence for a twelfth large earthquake on the southern hayward fault in the past 1900 years we present age and stratigraphic evidence for an additional paleoearth quake at the tyson lagoon site the acquisition of 19 additional radiocarbon dates and the inclusion of this additional event has resolved a large age discrepancy in our earlier earthquake chronology the age of event e10 was previously poorly con strained thus increasing the uncertainty in the mean recurrence interval ri a critical factor in seismic hazard evaluation reinspection of many trench logs revealed sub stantial evidence suggesting that an additional earthquake occurred between e10 and e9 within unit u45 strata in older u45 are faulted in the main fault zone and overlain by scarp colluviums in two locations we conclude that an additional surface rupturing event e9 5 occurred between e9 and e10 since 91 a d 40 yr 1 11 paleoearthquakes preceded the m 6 8 earthquake in 1868 yielding a mean ri of 161 65 yr 1 standard deviation of recurrence intervals however the standard error of the mean sem is well determined at 10 yr since 1300 a d the mean rate has increased slightly but is indistinguishable from the overall rate within the uncertainties recurrence for the 12 event sequence seems fairly regular the coeffi cient of variation is 0 40 and it yields a 30 yr earthquake probability of 29 the apparent regularity in timing implied by this earthquake chronology lends support for the use of time dependent renewal models rather than assuming a random process to forecast earthquakes at least for the southern hayward fault online material twelve event oxcal model for paleoearthquakes of the hayward fault

crustal structure across the coseismic rupture zone of the 1944 tonankai earthquake the central nankai trough seismogenic zone 1 differences in the coseismic rupture process between the 1944 tonankai and the 1946 nankaido earthquakes have been studied by many fault models to understand what factors control coseismic rupture zones it is important to investigate differences in deep crustal structures of the rupture zones between the 1944 and 1946 earthquakes the previously published crustal structure of the rupture zone of the 1946 earthquake shows that the coseismic rupture extends to the neogene quaternary accretionary prism however little is known about the structure of the rupture zone of the 1944 earthquake to obtain a complete image of the seismogenic zone of the 1944 earthquake a wide angle seismic survey was performed across the presumed coseismic rupture zone of the 1944 earthquake from ocean to land our model for the crustal structure is based on ocean bottom seismographic data the crustal structure appears characteristic for subducting oceanic crust and a neogene quaternary accretionary prism bounded by an island arc crust the neogene quaternary accretionary prism reaches a maximum thickness of 7 km at 50 km distance landward from the deformation front the subducting oceanic crust can be traced down to 35 km the subduction angle becomes steeper landward reaching up to 11 beneath the island arc crust the depth of the top of subducting oceanic crust at the downdip limit of the rupture zone is 23 km while the updip limit is located beneath the island arc upper crust similar structures of the updip and downdip limits are also published for several other subduction zones

the valais units in savoy france a key area for understanding the palaeogeography and the tectonic evolution of the western alps the valais units in savoy zone des breches de tarentaise have been re mapped in great detail and are subject of combined stratigraphic structural and petrological investigations summarized in this contribution the sediments and rare relics of basement together with cretaceous age mafic and ultramafic rocks of the valais palaeogeographical domain represent the heavily deformed relics of the former distal european margin external valais units and an ocean continent transition internal valais unit or versoyen unit that formed during rifting this rifting led to the opening of the valais ocean a northern branch of the alpine tethys post rift sediments referred to as valais trilogy stratigraphically overlie both external and internal valais successions above an angular unconformity formed in barremian to aptian times providing robust evidence for the timing of the opening of the valais ocean the valais units in savoy are part of a second and more external mid eocene high pressure belt in the alps that sutured the brianconnais microcontinent to europe top n d1 deformation led to the formation of a nappe stack that emplaced the largely eclogite facies internal valais unit versoyen onto blueschist facies external valais units the latter originally consisted of from internal to external the petit st bernard unit the roc de l enfer unit the moutiers unit and the quermoz unit ongoing top n d2 thrusting and folding substantially modified this nappe stack post 35 ma d3 folding led to relatively minor modifications of the nappe stack within the valais units but was associated with substantial top wnw thrusting of the valais units over the dauphinois units along the roselend thrust during w directed indentation of the adria block contributing to the formation of the arc of the western alps

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

emplacement of sills into wet sediments at grunehogna western dronning maud land antarctica the mid proterozoic ritscherflya supergroup antarctica is intruded by numerous mafic to intermediate sills and small layered bodies contact relations are well exposed where the grunehogna and kullen sills intruded argillaceous and arenaceous sedimentary rocks of the schumacherfjellet and hogfonna formations of the ahlmannryggen group a 3 m thick peripheral zone above the upper contact of the grunehogna sill consists of reconstituted sedimentary rocks which have been fluidized and recrystallized due to the intrusion local melting and crystallization of the sediments under hydrous conditions and pressures below 312 bars have produced zones of granite and granophyre which grade into arenites where primary sedimentary structures are preserved the sedimentary rocks have been deformed into large disharmonic folds where the sill transgresses the schumacherfjellet formation the contact relations suggest that emplacement of the mafic sills and sheets at grunehogna occurred when the sediments were still water saturated and only partially lithified

carbon release by off axis magmatism in a young sedimented spreading centre continental rifting creates narrow ocean basins where coastal ocean upwelling and enhanced silicate weathering remove carbon dioxide from the atmosphere evidence from seismic data sonar backscatter and seafloor images and geochemical water analyses suggest that in young sedimented rifts active magmatism occurs in a broader region than appreciated and releases carbon from the sediments

post rift flood basalt like volcanism on the newfoundland basin nonvolcanic margin the u event mapped with spectral decomposition abstract diabase sills emplaced at less than 5 km depth presently 7 km are imaged throughout the newfoundland basin as an extraordinarily high amplitude package of seismic reflections historically referred to as the u event the sills are extensive covering roughly 20 000 km2 and represent a post rift voluminous magmatic episode along an otherwise nonvolcanic rifted margin spectral decomposition is used to estimate a total magmatic volume at roughly 1000 2000 km3 on an individual basis the major sills are comparable to flows in flood basalt volcanic environments a proposed mechanism for generating these large volumes of magma which are also very limited in time to perhaps only two major intrusive episodes 2 sills is the approach of the canary and madeira hot spots suppressed volcanism while the hot spots traveled under full thickness continental lithosphere of newfoundland resulted in a local accumulation of magma which was suddenly released when the hot spots approached thinned lithosphere at the eastern edge of the grand banks the emplacement of the sills anticipated the arrival of the hot spots geographically

seismicity in a model governed by competing frictional weakening and healing mechanisms summary observations from laboratory field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults the associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms the efficiency of the healing processes depends on local material properties and on rheologic temperature and hydraulic conditions we investigate the relative effects of these competing non linear feedbacks on seismogenesis in the context of evolving frictional properties using a mechanical earthquake model that is governed by slip weakening friction weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable the slip weakening rate r using empirical relationships obtained from laboratory experiments in our model weakening depends on the slip of an earthquake and tends to increase r following the behaviour of real and simulated frictional interfaces healing causes r to decrease and depends on the time passed since the last slip results from models with these competing feedbacks are compared with simulations using non evolving friction compared to fixed r conditions evolving properties result in a significantly increased variability in the system dynamics we find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process such as the healing rate b and a lower cutoff time t c up to which no significant change in the friction parameter is observed for relatively large and small cutoff times the statistics are typical of fixed large and small r values respectively however a wide range of intermediate values leads to significant fluctuations in the internal energy levels the frequency size statistics of earthquake occurrence show corresponding non stationary characteristics on time scales over which negligible fluctuations are observed in the fixed r case the progressive evolution implies that except for extreme weakening and healing rates faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales thus highlighting the essential role of memory and history dependence in seismogenesis the results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability

synthetic earthquake catalogs simulating seismic activity in the corinth gulf greece fault system the characteristic earthquake hypothesis is the basis of time dependent modeling of earthquake recurrence on major faults however the characteristic earthquake hypothesis is not strongly supported by observational data few fault segments have long historical or paleoseismic records of individually dated ruptures and when data and parameter uncertainties are allowed for the form of the recurrence distribution is difficult to establish this is the case for instance of the corinth gulf fault system cgfs for which documents about strong earthquakes exist for at least 2000 years although they can be considered complete for m 6 0 only for the latest 300 years during which only few characteristic earthquakes are reported for individual fault segments the use of a physics based earthquake simulator has allowed the production of catalogs lasting 100 000 years and containing more than 500 000 events of magnitudes 4 0 the main features of our simulation algorithm are 1 an average slip rate released by earthquakes for every single segment in the investigated fault system 2 heuristic procedures for rupture growth and stop leading to a self organized earthquake magnitude distribution 3 the interaction between earthquake sources and 4 the effect of minor earthquakes in redistributing stress the application of our simulation algorithm to the cgfs has shown realistic features in time space and magnitude behavior of the seismicity these features include long term periodicity of strong earthquakes short term clustering of both strong and smaller events and a realistic earthquake magnitude distribution departing from the gutenberg richter distribution in the higher magnitude range

variations in the chemical and stable isotope composition of carbon and sulfur species during organic rich sediment alteration an experimental and theoretical study of hydrothermal activity at guaymas basin gulf of california organic rich diatomaceous ooze was reacted with seawater and a na ca k cl fluid of seawater chlorinity at 325 400 c 400 500 bars and fluid sediment mass ratios of 1 56 2 35 to constrain factors regulating the abundance and stable isotope composition of c and s species during hydrothermal alteration of sediment from guaymas basin gulf of california alteration of inorganic and organic sedimentary components resulted in extensive exchange reactions the release of abundant h2s co2 ch4 and corganic to solution and recrystallization of the sediment to an assemblage containing albitic plagioclase quartz pyrrhotite and calcite the 34scdt values of dissolved h2s varied from 10 9 to 4 3 during seawater sediment interaction at 325 and 400 c and from 16 5 to 9 0 during na ca k cl fluid sediment interaction at 325 and 375 c in the absence of seawater so4 h2s is derived from both the transformation of pyrite to pyrrhotite and s released during the degradation of organic matter in the presence of seawater so4 reduction of so4 contributes directly to h2s production sedimentary organic matter acts as the reducing agent during pyrite and so4 reduction requisite acidity for the reduction of so4 is provided by mg fixation during early stage sediment alteration and by albite and calcite formation in mg free solutions organically derived ch4 was characterized by 13cpdb values ranging between 20 8 and 23 1 whereas 13cpdb values for dissolved corganic ranged between 14 8 and 17 7 mass balance calculations indicate that 13c values for organically derived co2 were 14 8 residual solid sedimentary organic c showed small 0 7 depletions in 13c relative to the starting sediment the experimental results are consistent with the isotopic and chemical composition of natural hydrothermal fluids and minerals at guaymas basin and permit us to better constrain sources and sinks for c and s species in subseafloor hydrothermal systems at sediment covered spreading centers our data show that the sulfur isotope composition of hydrothermal sulfide minerals in guaymas basin can be explained by derivation of s from diagenetic sulfide and seawater sulfate basaltic s may also contribute to hydrothermal sulfide precipitates but is not required to explain their isotopic composition estimates of seawater sediment mass ratios based on sulfur isotopic composition of sulfide minerals and the abundance of dissolved nh3 in vent fluids range from 3 29 during hydrothermal circulation sources of c in guaymas basin hydrothermal fluids include thermal degradation of organic matter bacteriogenic methane production and dissolution of diagenetic carbonate

focal depths and mechanisms of large earthquakes on the arctic mid ocean ridge system as part of a global study of the source characteristics and tectonic implications of large earthquakes on mid ocean ridges we report on the focal depths and mechanisms of the six largest earthquakes that have occurred in the last 20 years on the arctic mid ocean ridge system for each earthquake we invert the long period p and sh waveforms to estimate the parameters of the best fitting point source including seismic moment centroid depth double couple source orientation and source time function three of the earthquakes occurred on the oceanic spreading center in the eurasian basin along ridge segments spreading at half rates of 4 6 mm yr these events have mechanisms very similar to those of ridge crest earthquakes on the mid atlantic ridge almost pure normal faulting on planes that dip at approximately 45 and strike parallel to the rift axis moments of 4 5 1024 dyn cm centroid depths of 1 2 km beneath the seafloor and water depths inferred from the predominant period of water column reverberations appropriate to epicentral locations within the median valley the remaining three earthquakes also characterized by normal faulting are associated with the continuation of the divergent plate boundary 2 3 mm yr half rate onto the continental shelf of the laptev sea where the crust becomes transitional in nature one of the largest known spreading center earthquakes august 25 1964 m0 1 1026 dyn cm occurred where the oceanic ridge intersects the outer edge of the continental slope waveform inversion for this event can resolve unilateral rupture from north to south landward along a fault at least 30 km in length the preferred centroid depth is 5 km beneath the seafloor in crustal material with an unusually low shear velocity but a centroid depth as great as 15 km cannot be ruled out two earthquakes beneath the continental shelf have significantly greater centroid depths 10 20 km than mid ocean ridge earthquakes indicating a thicker brittle regime and a cooler thermal structure than are typical of oceanic spreading centers the tectonic environment of these events is more representative of rifted continental lithosphere than of a mid ocean ridge

random stress and earthquake statistics spatial dependence summary we calculate the 3 d stochastic rotations of focal mechanisms disorientations caused by stresses arising from the presence of many small random point defects that may surround the tip of an earthquake fault these random stresses can be shown to be distributed according to a cauchy distribution as a consequence the next episode of fracture of a fault cannot be planar the disorientation of focal mechanisms of these new rupture episodes is closely approximated by a rotational cauchy distribution as observed previously the geometry of fault systems for natural earthquakes is consistent with these observations since it too can be modelled by the cauchy distribution these observations indicate how the 3 d rupture process in rocks and other materials can be modelled we also calculate distributions of disorientations caused by a uniformly random 3 d rotation of sources these distributions are governed by symmetry properties of earthquake focal mechanisms to take into account the source symmetry we compare the cauchy distribution which is due to influence of random stresses to the distributions caused by random rotations

evidence of a modern deep water magmatic hydrothermal system in the canary basin eastern central atlantic ocean new seismic profiles bathymetric data and sediment rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800 5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the canary basin eastern atlantic ocean 500 km west of the canary islands a complex of sill intrusions is imaged on seismic profiles showing saucer shaped parallel or inclined geometries three main types of structures are related to these intrusions type i consists of cone shaped depressions developed above inclined sills interpreted as hydrothermal vents type ii is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer shaped sills domes are interpreted as seabed expressions of reservoirs of ch4 and co2 rich fluids formed by degassing and contact metamorphism of organic rich sediments around sill intrusions type iii are hydrothermal volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones core and dredges revealed that these volcanoes which must be among the deepest in the world are constituted by oib type basanites with an outer ring of blue green hydrothermal al rich smectite muds magmatic activity is dated based on lava samples at 0 78 0 05 and 1 61 0 09 ma k ar methods and on tephra layers within cores at 25 237 ky the subvent hydrothermal volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity

surficial offsets on the central and eastern garlock fault associated with prehistoric earthquakes geomorphic features offset along the central and eastern garlock fault record the amount of surface slip associated with prehistoric earthquakes along the easternmost 90 km of the fault the smallest offsets cluster around 2 3 m of left lateral slip apparently associated with the most recent earthquake on this portion of the fault larger offsets along this part of the fault especially in pilot knob valley cluster around values consistent with 2 4 m of slip in each of the past several events farther west south of el paso mountains offset geomorphic features suggest that each of the past two earthquakes on this stretch of the garlock fault was produced by about 7 m of slip whereas the third event back was produced by about 4 m of slip vertical displacements of geomorphic features range from 0 to 30 of the left lateral offsets within pilot knob valley along the southern side of the slate range vertical displacements are consistently up on the northern side whereas within the avawatz mountains both north and south side up vertical displacements are present on the basis of the geomorphic offsets the geometry of the garlock fault and the precedents set by historical strike slip earthquakes elsewhere a number of different rupture patterns are plausible these range from rupture of the entire garlock fault in a single event with a maximum magnitude of about mw 7 8 to separate rupture of the western segment and of the central and eastern segments combined with approximate magnitudes mw 1 1 and mw 7 5 respectively to separate rupture of even shorter segments producing earthquakes of magnitudes mw 6 6 to mw 7 5 in conjunction with available slip rates for the garlock fault the geomorphic offsets suggest that average recurrence intervals are probably within the range of 600 1200 years south of el paso mountains about 200 750 years in searles valley about 200 1300 years in pilot knob valley and about 200 3000 years near leach lake and in the avawatz mountains

crustal structure volcanism and opening mode of the ulleung basin east sea sea of japan abstract a study of the ulleung basin in the southwestern east sea sea of japan based on single and multi channel seismic reflection profiles and ocean bottom seismometer obs data suggests that the basin formed largely by pull apart opening and the deep northern basin is underlain by thicker than normal oceanic crust 10 km thick probably formed during the earliest stage of seafloor spreading volcanic activity in association with basin opening occurred over much of the basin but it ceased first in the south while it continued in the north until recently the principal evidence for pull apart opening includes 1 an overall rhomboidal shape of the basin consisting of two basement lows and a median high known to be characteristic of pull apart basins 2 the location and orientation of the major volcanic sources suggesting more or less n s opening and 3 the strike slip fault system along the western basin margin which appears to have guided the pull apart opening the lack of extensional deformation along the western basin margin which would have been prevalent if sw japan had rotated away from the korean peninsula as suggested by paleomagnetic data is also not in favor of the alternative rotational opening of the basin the absence of graben and rift topography in the acoustic basement in the deep northern ulleung basin is indicative of the non brittle or ductile nature of the crust tau p analysis of the obs data reveals that the igneous crust consists of upper and lower layers with velocities typical of oceanic layers the velocity depth profiles with a two gradient velocity structure is also characteristic of oceanic crust however the lower layer is much thicker than oceanic layer 3 and the change of velocity gradient which occurs at around 6 5 km s in typical oceanic crust occurs at about 6 km s suggesting that the crust is not a typical oceanic crust the meager basin size and short opening period may suggest that the basin opening did not lead to the formation of full fledged oceanic crust but instead resulted in embryonic or incipient oceanic crust thickened by upper mantle thermal perturbations evoked by rifting

modern ground failure in the garlock fault zone fremont valley california modern ground failures ranging from renewed displacement on 2 5 km long fault scarps to 1 km long tension cracks occur in fremont valley california most of the failures formed along pre existing holocene fault scarps that are part of the tectonically active garlock fault system the failures began to form in the 1960s and currently affect an area of 17 km 2 that is coincident with ground water level decline induced by pumping for crop irrigation several observations indicate that these failures were caused by water level decline rather than natural tectonism first modern ground failure began after water level started to decline and was restricted to the area affected by decline land subsidence was associated with this decline and appears to be caused by aquifer compaction second geodetic monitoring from 1977 to 1982 of faults near the center of the cone of depression demonstrated that fault creep occurred during periods of seasonal water level decline and stopped during periods of seasonal water level recovery by contrast faults near the margin of the cone of depression where water levels declined at a constant rate moved at a steady rate third surface strain fields near failures suggest that subsurface fault associated deformation was restricted to aquifer level depths and fourth seasonal rebound of the land surface across one fault was caused by elastic expansion of the aquifer system that was induced by large seasonal water level recovery

major cretaceous volcanic province in southern rockall trough abstract a group of three large curvilinear ridges called the barra volcanic ridge system has been mapped in the acoustic basement of southern rockall trough typically each ridge is about 2 km high and 20 km wide at its base a crudely layered acoustic character moderate density but high strength of magnetisation point to a volcanic sedimentary ash composition for the ridges seismic continuity with the acoustic basement of the rest of rockall trough suggests that the trough basement is of similar composition an age for the ridges of lower cretaceous is indicated by well ties and consideration of regional geology volumetrically the ridges are on the scale of hot spot features such as the wyville thomson ridge

contribution of giant icebergs to the southern ocean freshwater flux 1 in the period 1979 2003 the mass of giant icebergs icebergs larger than 18 5 km in length calving from antarctica averaged 1089 300 gt yr 1 of ice under half the snow accumulation over the continent given by the intergovernmental panel on climate change 2246 86 gt yr 1 here we combine a database of iceberg tracks from the national ice center and a model of iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant icebergs by comparing with published modeled meltwater distribution for smaller bergs we show that giant icebergs have a different melting pattern an estimated 35 of giant icebergs mass is exported north of 63 s versus 3 for smaller bergs although giant bergs spend more of the earlier part of their history nearer to the coast we combine both estimates to produce the first iceberg meltwater map that takes into account giant icebergs the average meltwater input is shown to exceed precipitation minus evaporation p e in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the southern ocean the calving of giant icebergs is however episodic this might have implications for their impact on the freshwater budget of the ocean it is estimated that over the period 1987 2003 the meltwater flux in the weddell and ross seas has varied by at least 15 000 m3 s 1 over a month because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget variations in iceberg melt rates of this magnitude might be climatologically significant

tectonic stressing in california modeled from gps observations 1 what happens in the crust as a result of geodetically observed secular motions in this paper we find out by distorting a finite element model of california using gps derived displacements a complex model was constructed using spatially varying crustal thickness geothermal gradient topography and creeping faults gps velocity observations were interpolated and extrapolated across the model and boundary condition areas and the model was loaded according to 5 year displacements results map highest differential stressing rates in a 200 km wide band along the pacific north american plate boundary coinciding with regions of greatest seismic energy release away from the plate boundary gps derived crustal strain reduces modeled differential stress in some places suggesting that some crustal motions are related to topographic collapse calculated stressing rates can be resolved onto fault planes useful for addressing fault interactions and necessary for calculating earthquake advances or delays as an example i examine seismic quiescence on the garlock fault despite a calculated minimum 0 1 0 4 mpa static stress increase from the 1857 m 7 8 fort tejon earthquake results from finite element modeling show very low to negative secular coulomb stress growth on the garlock fault suggesting that the stress state may have been too low for large earthquake triggering thus the garlock fault may only be stressed by san andreas fault slip a loading pattern that could explain its erratic rupture history

earthquake recurrence on the south hayward fault is most consistent with a time dependent renewal process 1 elastic rebound and stress renewal are important components of earthquake forecasting because if large earthquakes can be shown to be periodic then rupture probability is time dependent while renewal models are used in formal forecasts it has not been possible to exclude the alternate view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration here a consistency test between time dependent and time independent recurrence distributions is made using a monte carlo method to replicate the paleoseismic series on the south hayward fault time dependent distributions with recurrence interval of 210 years and coefficient of variation of 0 6 reproduce the event series on the south hayward 5 times more often than any exponential distribution a highly significant difference as determined using a two tailed z test for relative proportions therefore large hayward fault earthquakes are quasi periodic and are most consistent with a stress renewal process

geographical distribution and volume of antarctic icebergs derived from ship observation data information on the occurrence spatial distribution and morphometric characteristics of antarctic icebergs is needed in a large number of applications including navigation heat and freshwater balance calculations biochemistry of the ocean and climatology using over 60 000 ship observations of icebergs in the southern ocean collected since the end of the 1940s we have produced a detailed map of the distribution of antarctic icebergs as well as maps of related statistics including the standard deviation minimum and maximum values of the iceberg concentration and the probability of iceberg free observations the study incorporated small and medium sized icebergs with a length of 2 and 16 893 km 3 with uncertainties of 32 33

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

a 100 year average recurrence interval for the san andreas fault at wrightwood california evidence for five large earthquakes during the past five centuries along the san andreas fault zone 70 kilometers northeast of los angeles california indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought rapid sedimentation during the past 5000 years in a 150 meter wide structural depression has produced a greater than 21 meter thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers fault scarps colluvial wedges fissure infills upward termination of ruptures and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in a d 1857 1812 and about 1700 1610 and 1470

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

surficial structures of the northern red sea axial valley from 23 n to 28 n time and space evolution of neo oceanic structures abstract during recent french cruises in the northern red sea the surficial structures of the axial valley were studied by means of bathymetry magnetics and single channel reflection seismics new compilation maps have been established and comparison of the various data allow different segments of the northern red sea axial valley to the distinguished where only intra evaporitic deformations 24 25 n large volcanic outcrops mabahiss deep 25 30 26 n or several recent isolated volcanic intrusions 26 27 n characterize different stages of evolution this new information allows reconstruction of the evolution of oceanization cells from a simple intra evaporitic deep to a limited oceanic rift zone such as those observed in the central red sea a major characteristic of this evolution also depicted in other young oceanic rifts is a succession of volcanic and tectonic phases the major event in the northern red sea axial valley is a recent episode of voluminous but well localized magmatism it would represent a new stage in the red sea evolution and thus may have some implications on earlier phases

stress interaction effect on the occurrence probability of characteristic earthquakes in central apennines 1 in this study we compute the effect of stress change due to previous historical earthquakes on the probability of occurrence of future earthquakes on neighboring faults following a methodology developed in the last decade we start from the estimate of the probability of occurrence in the next 50 years for a characteristic earthquake on known seismogenic structures based on a time dependent renewal model then a physical model for the coulomb stress change caused by previous earthquakes on these structures is applied the influence of this stress change on the occurrence rate of characteristic earthquakes is computed taking into account both permanent clock advance and temporary rate and state perturbations we apply this method to the computation of earthquake hazard of the main seismogenic structures recognized in the central and southern apennines region for which both historical and paleoseismological data are available this study provides the opportunity of reviewing the problems connected with the estimate of the parameters of a renewal model in case of characteristic earthquakes characterized by return times longer than the time spanned by the available catalogues and the applicability of the concept of characteristic earthquake itself the results show that the estimated effect of earthquake interaction in this region is small compared with the uncertainties affecting the statistical model used for the basic time dependent hazard assessment

paleoseismic event dating and the conditional probability of large earthquakes on the southern san andreas fault california we introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the wrightwood and pallett creek sites on the southern san andreas fault we illustrate how stratigraphic ordering sedimentolog ical and historical data can be used quantitatively in the process of estimating earth quake ages calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation the method does not eliminate subjective judgements in event dating but it does provide a means of systematically and objectively approaching the dating process date dis tributions for the most recent 14 events at wrightwood are based on sample and contextual evidence in fumal et al 2002 and site context and slip history in weldon et al 2002 pallett creek event and dating descriptions are from published sources for the five most recent events at wrightwood our results are consistent with pre viously published estimates with generally comparable or narrower uncertainties for pallett creek our earthquake date estimates generally overlap with previous results but typically have broader uncertainties some event date estimates are very sensitive to details of data interpretation the historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data radiocarbon ages peat accumulation rates and historical constraints at pallett creek for event x yield a date estimate in the earliest 1800s and preclude a date in the late 1600s this event is almost certainly the historical 1812 earthquake as previously concluded by sieh et al 1989 this earthquake also produced ground deformation at wrightwood all events at pallett creek except for event t about a d 1360 and possibly event i about a d 960 have corresponding events at wrightwood with some overlap in age ranges event t falls during a period of low sedimentation at wrightwood when conditions were not favorable for recording earthquake evidence previously pro posed correlations of pallett creek x with wrightwood w3 in the 1690s and pallett creek event v with w5 around 1480 fumal et al 1993 appear unlikely after our dating reevaluation apparent internal inconsistencies among event layer and dating relationships around events r and v identify them as candidates for further inves tigation at the site conditional probabilities of earthquake recurrence were estimated using poisson lognormal and empirical models the presence of 12 or 13 events at wrightwood during the same interval that 10 events are reported at pallett creek is reflected in mean recurrence intervals of 105 and 135 years respectively average poisson model 30 year conditional probabilities are about 20 at pallett creek and 25 at wrightwood the lognormal model conditional probabilities are somewhat higher about 25 for pallett creek and 34 for wrightwood lognormal variance rln estimates of 0 76 and 0 70 respectively imply only weak time predictability conditional probabilities of 29 and 46 respectively were estimated for an em pirical distribution derived from the data alone conditional probability uncertainties are dominated by the brevity of the event series dating uncertainty contributes only secondarily wrightwood and pallett creek event chronologies both suggest varia tions in recurrence interval with time hinting that some form of recurrence rate modulation may be at work but formal testing shows that neither series is more ordered than might be produced by a poisson process

estimating recurrence times and seismic hazard of large earthquakes on an individual fault summary we present a strategy for estimating the recurrence times between large earthquakes and associated seismic hazard on a given fault section the goal of the analysis is to address two fundamental problems 1 the lack of sufficient direct earthquake data and 2 the existence of subgrid processes that can not be accounted for in any model we deal with the first problem by using long simulations some 10 000 yr of a physically motivated coarsegrain model that reproduces the main statistical properties of seismicity on individual faults we address the second problem by adding stochasticity to the macroscopic model parameters a small number n of observational earthquake times 2 n 10 can be used to determine the values of model parameters which are most representative for the fault as an application of the method we consider a model set up that produces the characteristic earthquake distribution and where the stress drops are associated with some uncertainty using several model realizations with different values of stress drops we generate a set of corresponding synthetic earthquake catalogues the recurrence time distributions in the simulated catalogues are fitted approximately by a gamma distribution a superposition of appropriately scaled gamma distributions is then used to construct a distribution of recurrence intervals that incorporates the assumed uncertainty of the stress drops combining such synthetic data with observed recurrence times between the observational m6 earthquakes on the parkfield segment of the san andreas fault allows us to constrain the distribution of recurrence intervals and to estimate the average stress drop of the events based on this procedure we calculate for the parkfield region the expected recurrence time distribution the hazard function and the mean waiting time to the next m6 earthquake using five observational recurrence times from 1857 to 1966 the recurrence time distribution has a maximum at 22 2 yr and decays rapidly for higher intervals the probability for the post 1966 large event to occur on or before 2004 september 28 is 94 per cent the average stress drop of m6 parkfield earthquakes is in the range 3 04 0 27 mpa

the connection between iron ore formations and mud shrimp colonizations around sunken wood debris and hydrothermal sediments in a lower cretaceous continental rift basin mecsek mts hungary in the early cretaceous the continental rift basin of the mecsek mts hungary was situated on the southern edge of the european plate the opening of the north atlantic ocean created a dilatational regime that expanded to the southern edge of the european plate where several extensional basins and submarine volcanoes were formed during the early cretaceous epoch permanent seaquake activity caused high swell events during which a large amount of terrestrial wood fragments entered into submarine canyons from rivers or suspended woods which had sunk into the deep seafloor these fragments created extended wood fall deposits which contributed large scale flourishing of numerous burrowing thalassinid crustaceans twelve different thalassinid coprolite ichnospecies can be found in the berriasian hauterivian volcano sedimentary formations

volcanology carbon below the sea floor magma from the mantle meets the ocean at seafloor spreading centres at young rifts basalt sills may heat overlying sediments and induce natural carbon release basalt flows elsewhere may offer secure reservoirs for sequestration of anthropogenic carbon

oxygen isotopic composition of basalts from young spreading axes in the eastern pacific oxygen isotopic composition data are reported for young oceanic basalts from two different tectonic settings in the eastern pacific 1 the uppermost basement on the galapagos rift 1 ma old and 2 subbasement depths up to 150 m in the gulf of california 3 5 ma old in the galapagos area whole rock 18o values exhibit a narrow range of 5 7 6 6 consistent with minimal to slight low temperature alteration limited alteration probably reflects a combination of young basement age low temperatures for solutions in the uppermost basement and confinement of solutions mainly to discrete fractures in the gulf of california by contrast high whole rock values are found at site 474a near the baja margin where the greatest range in 18o also occurs from 2 5 to 12 5 this indicates considerable variation in both the temperature and degree of alteration at this site probably a consequence of the heterogeneous basement sequence intercalated pillow lavas sills and wet sediments differences in

basaltic sill sediment complexes in young spreading centers genesis and significance in contrast to mature mid oceanic ridges where magmatic activity is little affected by the slow accumulation of sediments in young spreading centers such as that of the guaymas basin in the gulf of california the basaltic magma of great magmatic pulses forms dikes and sills within the uppermost few hundred metres of soft sediments in general younger dikes and sills are injected next to or on top of the contact zone of the older ones in this manner a distinctive sill sediment complex is built up the sediments of which are rather compacted and partly metamorphosed despite the low burial depth the thickness of this transitional zone between the sheeted dike complex seismic layer 2 and younger sediment seismic layer 1 is controlled chiefly by the rates of sedimentation and spreading if the half spreading rate is approximately one order of magnitude greater than the sedimentation rate the sill sediment complex can reach a thickness of only a few hundred metres and the depth of the spreading trough remains approximately constant sedimentation rates approaching or surpassing the spreading rate cause filling up of the basins which probably hampers the injection of magma into sediments sill sediment complexes similar to those in the gulf of california are also expected to occur at the passive margins of older oceanic basins as well as orogenic belts

immense vent complex marks flood basalt eruption in a wet failed rift coombs hills antarctica large lava effusions can have impressive explosive antecedents although our picture of flood basalt is overwhelmingly effusive phreatomagmatic eruptions have preceded quiet effusion of some flood basalts and reflect the same influence of vent architecture and hydrology on eruptive style as seen for small volume eruptions the scale of phreatomagmatic deposits associated with flood basalts can be huge at coombs hills a vast but otherwise typical phreatomagmatic vent complex is exposed over more than 25 km 2 and its features are interpreted to reflect processes of tephra jet eruptions with diatreme development similar vent complexes are probably the source of laharic deposits reported elsewhere in the transantarctic mountains and in the karoo province of south africa

san andreas fault rupture scenarios from multiple paleoseismic records stringing pearls we present a new method to objectively combine paleoseismic event data from multiple sites into rupture scenarios and apply it to the southern san andreas fault ssaf of california first a pool is constructed of all ruptures between sites allowed by fault geometry and available event age probability distribution functions pdfs scenarios constructed by drawing from this pool are evaluated by the average quality of agreement event dating evidence by the degree of misfit of cumulative displacement over all ruptures compared to a prediction from the fault slip rate and elapsed time and by the number of events in the scenario three slip rate models from the 2008 working group on california earthquake probabilities wgcep were considered scenarios with full fault length ruptures tend to be inconsistent with low slip rates through the san bernardino and san gorgonio sections of the ssaf favorable scenarios tend to include 1857 like ruptures for three of the most recent five prehistoric ruptures in the northern half of the ssaf from carrizo to approximately wrightwood they also include one to two ruptures that involve the southern half of the ssaf but most earthquakes there appear shorter and exhibit less consistency from event to event by combining paleoseismic data into ensembles of scenarios and selecting viable scenarios using external constraints our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with those at adjoining sites this opens a way for paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern san andreas