seismic and aseismic slip indicators in serpentinite gouge structures observed within experimentally deformed serpentinite gouges provide information that may be used to identify the seismic behavior of natural fault zones in laboratory friction experiments serpentinite exhibits two modes of behavior one can only result in stable fault creep and the other may result in stable slip but has the potential for earthquakes the microstructures that form during these experiments reflect the deformation style of the serpentinite distributed deformation results from aseismic fault creep and localized deformation results from conditions favorable for seismic slip distributed deformation produces a crystallographic preferred orientation of the serpentine grains s foliation localized deformation forms riedel shears similar structures occur within a natural serpentinite shear zone from monterey county california and suggest a history of stable fault creep with intermittent seismic events

sedimentology of quaternary perched springline and paludal tufas criteria for recognition with examples from guadalajara province spain outcrop scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model at the field scale four end member models encompass the tufa continuum 1 perched springline 2 paludal 3 fluvial and 4 lacustrine tufas individual bed types can occur with variable dominance within several of these models but one or more beds are characteristically dominant only within a single tufa model so it can be differentiated from relatively isolated outcrop fragments two models perched springline tufas and paludal tufas are known in outline only in the literature despite being present within the quaternary deposits of most karstic regions perched springline tufas generally form lobate fan shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences mature deposits show a subhorizontal top and a steep face on the downflow side the steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle tufa deposits lying downslope of the mounds are usually detrital in nature especially if some dismantling of the mound has occurred the relatively thin subhorizontal lobe top deposits commonly contain organic rich deposits paludal tufas develop predominantly in waterlogged valley bottom situations where line sourced waters emerge from valley side and bottom aquifers lime mud precipitation predominates in these sites mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences tufa spring mounds may form where lesser volumes of water are involved individual tussocks phytoherm cushions of grasses and rushes are the most diagnostic feature of the model but sapropels and peats may be intercalated diagenesis in both models is rapid lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation the resulting highly porous and permeable fabrics remain fresh in holocene tufas but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits dissolution in many perched springline tufas is small scale many large cavities are primary but with later coatings of speleothems early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction

new stratigraphic and geochemical data on the holocene environment and climate from a tufa deposit at direndall mamer valley luxembourg tufa deposits are proven to record high quality palaeoenvironmental and palaeoclimatic information they also appear to be influenced by human activities as indicated by the late holocene tufa decline observed in europe from the atlantic optimum when tufa should be well developed regarding climatic conditions the studied tufa comes from the mamer valley in luxembourg direndall as it covers a broad part of the holocene this deposit offered a great opportunity to discuss modalities and timing of the tufa decline and the human impact on fluvial formations since the early holocene recent fieldwork at direndall allowed the collection of new stratigraphic data and samples for a geochemical study we investigate calcite stable isotopes as records of past temperature and humidity conditions comparisons with the environmental reconstructions from a previous malacological study show strong consistency with the 13c record and suggest humidity might have been the main factor controlling environment evolutio

earthquakes along eltanin transform system se pacific ocean fault segments characterized by strong and poor seismic coupling and implications for long term earthquake prediction summary centroid moment tensor solutions are recomputed for 190 earthquakes from 1976 to 2010 along the heezen tharp and hollister transform faults of the eltanin system using a 3 d seismic velocity model the total length of the three en echelon faults is nearly 1000 km each is characterized by fast long term rates of displacement of about 80 mm yr 1 strike slip faulting with moment magnitudes mw up to 6 4 characterizes most of these events the few involving normal faulting are located up to 40 km on either side of the transforms and involve extension nearly normal to the transforms this partitioning of slip likely results from changes during the last few million years in the euler pole for relative motion between the antarctic and pacific plates some parts of the heezen and tharp transforms exhibit strong seismic coupling but others were aseismic at the resolution of our study mw 5 0 5 5 earthquakes were not found along nearby fast spreading ridges at that resolution we calculate downdip widths of seismic coupling of about 5 km for four strongly coupled segments from observed moment rates and lengths along strike assuming earthquake activity accounts for the entire plate motion major differences in seismic coupling along strike are not in accord with common thermal models of plate cooling but instead are attributed to varying degrees of metamorphism rock type and effective normal stress and possibly to the presence of short intratransform spreading centres one 30 42 km long segment of the heezen transform that appears to be an isolated well coupled asperity has ruptured in eight earthquakes of mw 5 9 6 1 quasi periodically with a coefficient of variation of 0 26 every 4 0 1 0 yr other well coupled fault segments which were sites with earthquakes up to mw 6 39 and fewer events since 1976 have average repeat times of about 7 24 yr the fast rate of plate motion maximum size of events and relatively short repeat times make these fault segments a good laboratory for research on quasi periodic behaviour and earthquake prediction

variations in earthquake rupture properties along the gofar transform fault east pacific rise mid ocean ridge transform faults experience more foreshocks than continental faults yet the mainshock rarely ruptures the entire fault analysis of seismic data from the gofar transform fault at the east pacific rise indicates that the foreshock region has different material properties from the mainshock region and acts as a barrier to rupture propagation on a global scale seismicity on oceanic transform faults that link mid ocean ridge segments is thermally controlled1 2 however temperature cannot be the only control because the largest earthquakes on oceanic transform faults rupture only a small fraction of the area that thermal models predict to be capable of rupture3 4 5 instead most slip occurs without producing large earthquakes3 4 6 when large earthquakes do occur they often repeat quasiperiodically7 8 moreover oceanic transform faults produce an order of magnitude more foreshocks than continental strike slip faults7 9 here we analyse a swarm of about 20 000 foreshocks recorded on an array of ocean bottom seismometers which occurred before a magnitude 6 0 earthquake on the gofar transform fault east pacific rise we find that the week long foreshock sequence was confined to a 10 km long region that subsequently acted as a barrier to rupture during the mainshock the foreshock zone is associated with a high porosity and undergoes a 3 decrease in average shear wave speed during the week preceding the mainshock we conclude that the material properties of fault segments capable of rupturing in large earthquakes differ from those of barrier regions possibly as a result of enhanced fluid circulation within the latter we suggest that along strike variations in fault zone material properties can help explain the abundance of foreshocks and the relative lack of large earthquakes that occur on mid ocean ridge transform faults

time domain observations of a slow precursor to the 1994 romanche transform earthquake low frequency spectral anomalies have indicated that some large earthquakes are preceded by extended episodes of smooth moment release but the reality of these slow precursors has been debated because they have not been directly observed in the time domain high gain seismograms from the 14 march 1994 romanche transform event moment magnitude m w 7 0 show a precursory ramp with a moment of 7 1018 newton meters beginning about 100 seconds before the arrival of the high frequency p waves this precursor was the initial phase of a slow component of slip that released nearly half of the total moment of the earthquake such behavior may be typical for large earthquakes on the oceanic ridge transform system

the geology of earthquake swarms differences between earthquake sequences in the crust and adjacent uppermost mantle at oceanic transform faults are revealed by a seafloor seismic experiment at the blanco transform fault

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

a slow earthquake sequence on the san andreas fault earthquakes typically release stored strain energy on timescales of the order of seconds limited by the velocity of sound in rock over the past 20 years observations1 13 and laboratory experiments14 have indicated that rupture can also occur more slowly with durations up to hours such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones the detection of events with larger timescales requires near field deformation measurements in december 1992 two borehole strainmeters close to the san andreas fault in california recorded a slow strain event of about a week in duration and we show here that the strain changes were produced by a slow earthquake sequence equivalent magnitude 4 8 with complexity similar to that of regular earthquakes the largest earthquakes associated with these slow events were small local magnitude 3 7 and contributed negligible strain release the importance of slow earthquakes in the seismogenic process remains an open question but these observations extend the observed timescale for slow events by two orders of magnitude

back propagating super shear rupture in the 2016 mw7 1 romanche transform fault earthquake how an earthquake rupture propagates strongly influences the potentially destructive ground shaking complex ruptures often involve slip along multiple faults which masks information on the frictional behaviour of fault zones geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics because strain is accommodated along a single wide fault zone that offsets the homogeneous geology here we present an analysis of the 2016 mw 7 1 earthquake on the romanche fracture zone in the equatorial atlantic using data from both nearby seafloor seismometers and global seismic networks we show that this rupture had two phases 1 upward and eastward propagation towards a weaker region where the transform fault intersects the mid ocean ridge and then 2 an unusual back propagation westwards at a supershear speed towards the centre of the fault we suggest that deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones this highlights that even earthquakes along a single distinct fault zone can be highly dynamic observations of back propagating ruptures are sparse and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments in one earthquake an oceanic transform fault ruptured in one direction and then backwards at a speed exceeding that of shear wave propagation according to an analysis of data recorded by nearby seafloor and global seismometers

immediate foreshock sequences of oceanic transform earthquakes on the east pacific rise foreshock sequences provide one of the few windows into the earthquake nucleation process until recently it was impossible to study foreshock sequences of oceanic earthquakes owing to the low detection thresholds of standard seismic catalogs for the regions near spreading ridges in the last few years autonomous hydrophone arrays operated by the national oceanic and atmospheric administration9s pacific marine environmental laboratory have lowered the detection threshold in several oceanic regions to about magnitude 3 we investigate the fore shock sequences of large oceanic transform fault earthquakes using the seismicity catalogs derived from the hydrophone data transforms on the equatorial east pacific rise regularly have foreshocks within 1 hr before a magnitude 5 6 earthquake while those on the juan de fuca and mid atlantic ridges do not the foreshocks typically occur in the period between 100 and 1000 sec before the mainshock suggesting that this timescale is important for large earthquake nucleation in this region

stable isotope record of palaeoclimatic change in a british holocene tufa a 9 5 m long continuous core through holocene tufa deposits in derbyshire uk was analysed for oxygen and carbon stable isotope variations with a view to palaeoclimatic and palaeoenvir onmental interpretation the depositional environment of the tufa is well understood and dated using 14c and biostratigraphy it is argued that smooth variations of up to 1 in 18o of the tufa calcites are caused by changes in the isotopic composition of regional rainfall which in turn were caused mainly by changes in air temperature palaeoclimate in general lower 13c values for calcite correspond with higher 18o values suggesting a stronger component of soil derived carbon during warmer climatic phases a stable isotope approach to reading terrestrial palaeoclimatic records is of widespread application to holocene and older tufa deposits which are common in carbonate bedrock regions

tufas and travertines of the mediterranean region a testing ground for freshwater carbonate concepts and developments actively forming travertine and tufa sites are widespread in temperate and warm climates such as the mediterranean region but also develop in other climatic regimes from the arctic to equatorial latitudes the terms travertine and tufa are sometimes applied indiscriminately today however each has a specific definition most studied deposits are active or of quaternary especially holocene age there are fewer tertiary and even less late mesozoic examples on record in part this is because of a recognition problem as these deposits commonly preserve as fragmentary erosional remnants physico chemical precipitation of calcium carbonate is commonly considered to be the main mechanism contributing to tufa and travertine deposition rapid cooling of waters further aids the process in thermal travertine sites however biomediation of calcium carbonate associated with prokaryote microphyte biofilms is now recognized to be equally important in slow flowing and near static sites much of this precipitation occurs in close association with cyanobacterial heterotrophic bacterial and diatoms the mediterranean region figures significantly in the development of travertine and tufa research consequently this article employs key literature on mediterranean examples to illustrate developments and concepts in freshwater carbonate research modern work started in the 1950s and defined many previously unknown outcrops many such sites became the targets for early radiocarbon dating studies since the late 1970s a number of laboratory based and field based classification schemes have been proposed some schemes were based on associated macrovegetation types others were based on petrological characteristics or on geometry and sedimentary facies characteristics of late the sedimentological modelling has benefited greatly from the use of shallow geophysical techniques in order to better define the internal geometries of the deposits two distinct research strands were developed during the 1990s both aimed at a better understanding of environmental change the first considered biocomponents the research was multifaceted and ranged from exploring the role of micro organisms in cement and lime mud precipitation to biostratigraphic analysis of contained pollen and invertebrate remains these provided proxy environmental information which has helped to define past climate variability in the region the second research strand focussed on geochemical signatures as a proxy tool for defining environmental change this definition was made possible by new petrological studies which have greatly aided the recognition of primary depositional fabrics this improved knowledge has reduced the sampling dangers of diagenetic contamination inherent in earlier geochemical studies lithofacies modelling has also brought to light important early post depositional neomorphic changes which obscure primary fabrics and complex diagenetic histories have been revealed stable isotope signatures of carbon and oxygen have also been used to define palaeo water temperature fine tuning of depositional time frames has also been achieved from absolute dating techniques employing radiocarbon and uranium thorium

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

scaling relations for seismic cycles on mid ocean ridge transform faults 1 mid ocean ridge transform faults rtfs have thermal structures that vary systematically with tectonic parameters resulting in predictable seismic characteristics and clear seismic cycles we develop a scaling relation for repeat time tr of the largest expected earthquake mc tr 1 2 3cmc1 3at1 4v 1 where is the shear modulus is the stress drop cmc is a constant at is the area above 600 c and v is the slip rate we identify repeating mc earthquakes by measuring differential arrival times of first orbit rayleigh waves to determine centroid offsets between pairs of events comparing our observations of tr 5 14 years for earthquakes on gofar and blanco rtfs with predictions from our scaling relation we can constrain rtf stress drops specific tests of this scaling relation are proposed for earthquakes on blanco gofar discovery and clipperton rtfs which are all expected to have large ruptures in the next few years

molluscan successions from the holocene tufa of st germain le vasson normandy france and their biogeographical significance a detailed molluscan succession from a 10 m thick deposit of holocene tufa at st germain le vasson normandy provides the most complete record from northern france and has shed new light on the historical biogeography of several species of land snail the succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal wood and shell the onset of tufa formation occurred after 9700 90 yr bp and persisted until 4213 77 yr bp the tufa appears to have accumulated at a remarkably constant rate 14 4 16 5 cm 100 yr 1 except for the upper levels where the rate increases fourfold the succession has been divided into six local molluscan zones an early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade demanding taxa reflecting the encroachment of woodland shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422 60 yr bp zone 5 a change also reflected in the tufa lithology by the development of silty grey horizons notable species recovered from the tufa include acicula fusca vertigo substriata v alpestris v moulinsiana all rare or unknown living in northern france hygromia limbata a twentieth century introduction to britain was previously thought to be a relatively recent arrival in northern france but its record at st germain shows that it has been present in normandy since 6500 yr bp azeca goodalli another shade demanding species appeared at st germain much later just after 4420 65 yr bp several other species present in the tufa such as pomatias elegans no longer live on the site adding to the evidence for a distributional decline in normandy and elsewhere perhaps the most noteworthy record is that of leiostyla anglica between about 8500 yr bp and 5000 yr bp because this constitutes its only holocene occurrence from mainland europe following this discovery it seems likely that further holocene sites with l anglica may be found along the western seaboard of europe connecting populations in iberia with those of the british isles copyright 2004 john wiley sons ltd

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

classification and environmental models of cool freshwater tufas abstract tufa deposits are common in the quaternary record facies developments are dependent upon localised carbonate precipitation generally these take the form of phytoherm build ups together with associated detrital deposits derived from disagragation of the former phytoherm cements differ from speleothems and floe calcite accumulations in being biologically mediated or modified this paper recognises the following five types perched spring line cascade fluviatile paludal and lacustrine facies each type is composed of distinctive constructional and detrital sediment associations these unique sediment combinations are the product of an interplay between angle of slope water discharge rate standing water bodies phytal and microbial colonization and ambient temperature the proposed models will be of value in the interpretation of ancient and partially exposed tufas

serpentinization faults and their role in the tectonics of slow spreading ridges two major families of faults dominate the tectonics of slow spreading ridges the transform faults paralleling the spreading direction and the gloria faults observed by large scale side scan sonar normal to it the observation of microearthquakes to 8 km depth beneath the mid atlantic ridge axis implies that not only the transform faults but the gloria faults as well penetrate into the mantle since large horizontal temperature gradients are often associated with them both types of fault provide the means of circulating large volumes of sea water through the oceanic mantle under these conditions serpentinization of upper mantle rocks will occur in a predictable way its influence on the tectonic development of slow spreading ridges is discussed

seismic cycles and earthquake predictability on east pacific rise transform faults the concept of a seismic cycle where the stress on a fault repeatedly builds up over a long period of time and then is rapidly released in a large earthquake influences studies of both the basic physics of faulting and applied research aimed at estimating earthquake hazards this hypothesis suggests that large earthquakes might be quasi periodic and that the probability of a particular portion of a fault rupturing twice in quick succession should be low however this basic hypothesis has been difficult to verify owing to the long repeat times of the largest earthquakes on most faults east pacific rise epr transform faults are an advantageous location to evaluate the seismic cycle hypothesis owing to their fast slip rates and the moderate size m w 6 of their largest earthquakes using surface wave based determinations of the relative separations between earthquake centroids i document 16 pairs of m w 5 5 events that had overlapping ruptures the distribution of interevent times for these pairs is tightly clustered around 5 yr with a coefficient of variation 0 2 indicating that quasi periodicity may be prevalent for the largest events on these faults moreover i find no pairs of overlapping m w 5 5 6 2 earthquakes separated by less than 50 cm of elapsed plate motion indicating that the two basic features of the seismic cycle hypothesis are evident in the timing of large epr transform mainshocks i have also confirmed earlier results demonstrating a high degree of short term predictability of epr mainshocks by combining teleseismic and hydroacoustic earthquake catalogs thus there appears to be a high degree of both short and long term predictability on epr transforms

confidence intervals for motion and deformation of the juan de fuca plate finite rotation parameters for 17 isochrons from anomalies 1 4a for the juan de fuca pacific plate pair are reported comparison of confidence intervals for plate rotations derived by different techniques indicates that a single plate misfit criterion significantly underestimates the confidence region defining the confidence interval by a threshold level of misfit determined by an f statistic gives similar results to the technique of bootstrap resampling for internally consistent data bootstrap resampling offers far greater robustness in the case of inconsistent data precision of about 1 km in the direction normal to isochrons is available for the younger anomalies this precision allows confident recognition of 2 5 km of eastward deformation of the pacific plate 50 100 km south of the active sovanco transform slight deformation of the northern juan de fuca plate adjacent to the nootka fault zone is also apparent east of the northern gorda ridge younger 3 ma anomalies do not show measurable deformation near the blanco fracture zone but older anomalies are up to 30 km east of their position predicted by rigid behavior of the juan de fuca plate reconstruction of the overlap geometry of past propagators shows no evidence that the extent of overlap has ever exceeded 70 km even with offset of 75 km in one case and 140 km in another new techniques for testing for intervals of constant plate motion require at least two changes in instantaneous motion at 99 confidence a clockwise change in motion direction at about 5 ma and an increase in the gradient of spreading rate since 2 ma two other changes in gradient since 5 ma are required at 95 confidence

seismic properties of the eltanin transform system south pacific abstract we present a compilation of the seismic properties of the eltanin transform fault tf system compelled by the recent discovery of the hollister ridge and the possibility of a change of plate kinematics pattern in the region the hollister ridge is a major volcanic system located on the western flank of the pacific antarctic ridge par immediately south of the eltanin fracture zones fzs we find or confirm two anomalous characteristics the occurrence of seven normal faulting events on the transform segments expressing extension across the plate boundary in the azimuth n26 w and more than 90 deficiency in the seismic moment released during strike slip events on the transforms as compared to the rate expected from kinematic models other seismic properties are typical of the seismicity of a fast spreading mid ocean ridge mor system in particular we could not document a single teleseismically recorded event on the hollister ridge earthquakes are confined to narrow tfs with no activity present on the ridge segments the transform events have regular frequency moment statistics and we could not document any significantly slow sources these seismic properties generally support conventional plate tectonics models such as nuvel 1 and cannot be reconciled with a proposed reorientation of the pacific plate 4 ma ago

earthquake scaling relations for mid ocean ridge transform faults 1 a mid ocean ridge transform fault rtf of length l slip rate v and moment release rate can be characterized by a seismic coupling coefficient ae at where ae v is an effective seismic area and at l3 2v 1 2 is the area above an isotherm tref a global set of 65 rtfs with a combined length of 16 410 km is well described by a linear scaling relation 1 ae at which yields 0 15 0 05 for tref 600 c therefore about 85 of the slip above the 600 c isotherm must be accommodated by subseismic mechanisms and this slip partitioning does not depend systematically on either v or l rtf seismicity can be fit by a truncated gutenberg richter distribution with a slope 2 3 in which the cumulative number of events n0 and the upper cutoff moment mc dcac depend on at data for the largest events are consistent with a self similar slip scaling dc ac1 2 and a square root areal scaling 2 ac at1 2 if relations 1 and 2 apply then moment balance requires that the dimensionless seismic productivity 0 0 atv should scale as 0 at 1 4 which we confirm using small events hence the frequencies of both small and large earthquakes adjust with at to maintain constant coupling rtf scaling relations appear to violate the single mode hypothesis which states that a fault patch is either fully seismic or fully aseismic and thus implies ac ae the heterogeneities in the stress distribution and fault structure responsible for relation 2 may arise from a thermally regulated dynamic balance between the growth and coalescence of fault segments within a rapidly evolving fault zone

mode of slip and crust mantle interaction at oceanic transform faults oceanic transform faults connecting offset mid ocean spreading centres rupture quasi periodically in earthquakes up to about magnitude m 7 0 that are often preceded by foreshocks in addition to seismic slip a large portion of slip takes place as aseismic creep which likely influences initiation of large earthquakes although oceanic transform faults are one of the major types of plate boundaries the exact mode of slip and interaction between the seismic and aseismic motion remains unclear here we present a detailed model of the mode of slip at oceanic transform faults based on data acquired from a recent temporary deployment of ocean bottom seismometers at the blanco transform fault and existing regional and teleseismic observations in the model the crustal part of the fault is brittle and fully seismically coupled while the fault in the mantle shallower than the depth of the 600 c isotherm creeps partially and episodically the creep activates small asperities in the mantle that produce seismic swarms both mantle and the crustal zones release most of the plate motion strain during large magnitude earthquakes large earthquakes appear to be preceded by a brief episode of shallow mantle creep accompanied by seismic swarms which explains the observation of foreshocks and shows that mantle creep likely influences initiation of large seismic events earthquakes in the crust and mantle at transform faults are distinct yet coupled with seismic swarms in the mantle apparently preceding large earthquakes according to ocean bottom seismic monitoring of the blanco transform fault

methane hydrate recycling offshore of mauritania probably after the last glacial maximum to what extent methane liberated from marine hydrate will enter the ocean during a warmer world is unknown although methane release due to hydrate dissociation has been modelled it is unclear whether or not methane will reach the seafloor during a warmer world and therefore contribute to oceanic and atmospheric budgets here we show using a new three dimensional 3 d seismic dataset that some hydrate deposits surround the gas chimneys passing through the hsz bottom water warming since the last glacial maximum lgm is interpreted to cause hydrate dissociation but critically some of the released methane was not vented to the ocean the released gas caused seal failure and free gas entered the hydrate stability zone hsz through vertical gas chimneys to where new hydrate accumulations formed this process is a new evidence for methane recycling and could account in part for the lack of methane in ice core records that cover warming events during the late quaternary this research provides new insight into how methane could be recycled rather than vented during a warmer world

climatic change recorded by stable isotopes and trace elements in a british holocene tufa combined stable isotope d18o and d13c and trace element mg sr geochemistry from bulk tufa calcite and ostracod shell calcite from an early holocene british tufa reveal clear records of holocene palaeoclimatic change variation in d18o is caused principally by change in the isotopic composition of holocene rainfall recharge itself caused mainly by change in air temperature the d13c variability through much of the deposit reflects increasing influence of soil zone co2 owing to progressive woodland soil development bulk tufa mg ca and sr ca are controlled by their concentrations in the spring water importantly mg ca ratios are not related to d18o values and thus show no temperature dependence first order sympathetic relationships between d13c values and mg ca and sr ca are controlled by aquifer processes residence times co2 degassing and calcite dissolution reprecipitation and probably record intensity of palaeorainfall recharge effects stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data the ostracod isotopic records are markedly spiky because the ostracods record snapshots of relatively short duration years whereas the bulk tufa samples record averages of longer time periods probably decades the d18o record appears to show early holocene warming a thermal maximum at ca 8900 cal yr bp and the global 8200 yr bp cold event combined d13c mg ca and sr ca data suggest that early holocene warming was accompanied by decreasing rainfall intensity the mg ca data suggest that the 8200 yr bp cold event was also dry warmer and wetter conditions were re established after the 8200 yr bp cold event until the top of the preserved tufa sequence at ca 7100 cal yr bp

seismic investigation of an active ocean continent transform margin the interaction between the swan islands fault zone and the ultraslow spreading mid cayman spreading centre

flash weakening of serpentinite at near seismic slip rates 1 to investigate the processes responsible for dynamic frictional weakening in antigorite serpentinite we conducted single velocity and velocity stepping friction experiments at slip rates v from 0 01 to 0 4 m s 1 sliding displacements up to 40 mm and a normal stress of 5 mpa single velocity experiments demonstrate an approximately 1 v dependence of friction on velocity above a characteristic weakening velocity vw 0 1 m s 1 consistent with theoretical predictions for flash heating and subsequent weakening of asperities velocity stepping experiments impose stepwise increases in slip rate show stepwise weakening at slip rates above vw scanning electron microscopy of experimental fault surfaces reveals nanoparticle gouge textures at raised sites 10 m in diameter in tests that exhibit dramatic weakening furthermore x ray diffraction analyses of fault gouge from the sliding surface document the formation of significant talc in these tests indicating that weakening temperatures reached 500 c 700 c in contrast no talc is observed in samples for which v remained significantly below vw the observed value for vw is consistent with published microphysical models for flash weakening when independent constraints on the thermal stability and contact strength of antigorite are considered finally while serpentinite displays velocity strengthening behavior at plate tectonic slip rates our results indicate that seismic ruptures propagating into serpentinized regions in the shallow lithosphere may trigger seismicity or slow earthquakes after limited amounts of displacement

segmentation of the blanco transform fault zone from earthquake analysis complex tectonics of an oceanic transform fault 1 the blanco transform fault zone btfz forms the 350 km long pacific juan de fuca plate boundary between the gorda and juan de fuca ridges nearby broadband seismic networks provide a unique framework for a detailed long term seismotectonic study of an entire oceanic transform fault otf system we use regional waveforms to determine 129 earthquake source parameters combined with 28 harvard moment tensors they represent the largest waveform derived otf source parameter data set joint epicenter determination removes the northeasterly routine location bias projecting seismicity onto the btfz we determine along fault seismic slip rate variations earthquake source parameters and morphology indicate several transform segments separated by extensional step overs the eastern segment from gorda ridge to gorda depression is a pull apart basin the longest transform 150 km following blanco ridge from the gorda to cascadia depression is seismically very active seismically fully coupled has a wider seismic zone 9 km than other btfz transform segments and accommodates the largest mw 6 4 6 5 btfz earthquakes interpretation of cascadia depression as spreading ridge is supported by plate motion parallel normal faulting t axes spreading is currently tectonic 9 km deep earthquakes indicate a deep source for intermittent intrusives and rapid postemplacement cooling a short transform connects to the pull apart surveyor depression widely spread seismicity along the western btfz reflects complex morphology indicating ongoing plate boundary reorganization along short narrow width subparallel faults seismic coupling is low in extensional 15 compared to transform areas 35 100 implying different mechanical properties centroid depth variations are consistent with seismic slip cutoff near 600 c

high potential of calcareous tufas for integrative multidisciplinary studies and prospects for archaeology in europe calcareous tufas are continental carbonates from open air conditions specific to wet and warm periods they contain abundant remains of fauna and flora fossilised in situ and may accumulate regularly over thousands of years offering high stratigraphic resolution for palaeoenvironmental reconstructions as they are mainly comprised of calcite tufas allow direct and precise dating as well as geochemical reconstructions of past climates additionally recent investigations have highlighted their strong potential for archaeology as several studied sequences provided high quality record of in situ prehistoric levels tufas are thus a unique archive in continental areas for development of synergic multidisciplinary investigations of past human societies and associated environmental and climate evolution we emphasise that calcareous tufa are key deposits to investigate human environment climate interactions during interglacial periods from lower palaeolithic to antiquity in europe

olivine friction at the base of oceanic seismogenic zones 1 we investigate the strength and frictional behavior of olivine aggregates at temperatures and effective confining pressures similar to those at the base of the seismogenic zone on a typical ridge transform fault triaxial compression tests were conducted on dry olivine powder grain size 60 m at effective confining pressures between 50 and 300 mpa using argon as a pore fluid temperatures between 600 c and 1000 c and axial displacement rates from 0 06 to 60 m s axial strain rates from 3 10 6 to 3 10 3 s 1 yielding shows a negative pressure dependence consistent with predictions for shear enhanced compaction and with the observation that samples exhibit compaction during the initial stages of the experiments a combination of mechanical data and microstructural observations demonstrate that deformation was accommodated by frictional processes sample strengths were pressure dependent and nearly independent of temperature localized shear zones formed in initially homogeneous aggregates early in the experiments the frictional response to changes in loading rate is well described by rate and state constitutive laws with a transition from velocity weakening to velocity strengthening at 1000 c microstructural observations and physical models indicate that plastic yielding of asperities at high temperatures and low axial strain rates stabilizes frictional sliding extrapolation of our experimental data to geologic strain rates indicates that a transition from velocity weakening to velocity strengthening occurs at approximately 600 c consistent with the focal depths of earthquakes in the oceanic lithosphere

aseismic transient slip on the gofar transform fault east pacific rise oceanic transform faults display a unique combination of seismic and aseismic slip behavior including a large globally averaged seismic deficit and the local occurrence of repeating magnitude m 6 earthquakes with abundant foreshocks and seismic swarms as on the gofar transform of the east pacific rise and the blanco ridge in the northeast pacific ocean however the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults in the model strong dilatancy strengthening supported by seismic imaging that indicates enhanced fluid filled porosity and possible hydrothermal circulation down to the brittle ductile transition effectively stabilizes along strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically the modeled slow slip migrates along the barrier zones at speeds 10 to 600 m h spatiotemporally correlated with the observed migration of seismic swarms on the gofar transform our model thus suggests the possible prevalence of episodic aseismic transients in m 6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip earthquake swarms and fault zone hydromechanical properties