laboratory earthquakes the sub rayleigh to supershear rupture transition we report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub rayleigh to supershear rupture transitions in frictionally held interfaces the laboratory experiments mimic natural earthquakes the results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

dynamic rupture processes inferred from laboratory microearthquakes we report macroscopic stick slip events in saw cut westerly granite samples deformed under controlled upper crustal stress conditions in the laboratory experiments were conducted under triaxial loading 1 2 3 at confining pressures 3 ranging from 10 to 100 mpa a high frequency acoustic monitoring array recorded particle acceleration during macroscopic stick slip events allowing us to estimate rupture speed in addition we record the stress drop dynamically and we show that the dynamic stress drop measured locally close to the fault plane is almost total in the breakdown zone for normal stress 75 mpa while the friction f recovers to values of f 0 4 within only a few hundred microseconds enhanced dynamic weakening is observed to be linked to the melting of asperities which can be well explained by flash heating theory in agreement with our post mortem microstructural analysis relationships between initial state of stress rupture velocities stress drop and energy budget suggest that at high normal stress leading to supershear rupture velocities the rupture processes are more dissipative our observations question the current dichotomy between the fracture energy and the frictional energy in terms of rupture processes a power law scaling of the fracture energy with final slip is observed over eight orders of magnitude in slip from a few microns to tens of meters

laboratory earthquakes along inhomogeneous faults directionality and supershear we report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch rupture is always found to be asymmetric bilateral in one direction rupture always propagates at the generalized rayleigh wave speed whereas in the opposite direction it is subshear or it transitions to supershear the lack of a preferred rupture direction and the conditions leading to supershear are discussed in relation to existing theory and to the earthquake sequence in parkfield california and in north anatolia

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

benthic foraminiferal response to changes in bottom water oxygenation and organic carbon flux in the eastern mediterranean during lgm to recent times abstract we present a high resolution study of benthic foraminiferal abundances in 4 cores from the central aegean and ne levantine seas spanning the interval from 30 ka bp to the present the benthic foraminiferal faunas indicate that during lgm times bottom waters were well ventilated while organic flux to the sea floor was significantly higher than today from 30 to 10 2 ka bp faunal density and composition suggest a gradual decrease in organic flux to the sea floor this trend is interrupted by a short return to higher organic flux levels during the younger dryas 12 8 11 5 ka bp the faunas immediately preceding the early to middle holocene organic rich layer sapropel s1 are very similar to late holocene faunas indicating oligotrophic conditions the transition from well ventilated bottom waters to anoxic levantine basin or strongly dysoxic aegean sea bottom waters appears to take place within a time span of only 600 years from 10 8 to 10 2 ka bp sapropel s1 10 2 6 4 ka bp is characterized by extended periods of bottom water anoxia in the levantine basin and by strongly dysoxic conditions punctuated by episodic re ventilation events in the aegean sea re establishment of fully oxygenated bottom water conditions after sapropel s1 was extremely rapid the ensuing late holocene faunas are very similar to recent faunas found in the aegean sea suggesting much lower fluxes of organic matter to the sea floor than during glacial times

middle to upper miocene benthonic foraminiferal palaeoecology of the tap marls alicante province se spain and its palaeoceanographic implications abstract the benthonic foraminiferal faunas of twenty sections have been analysed statistically cluster analysis and interpreted palaeoecologically the analysis shows that oxygenation was the most important factor for the distribution of the faunas in the investigated area the lifting and lowering of the sill to the atlantic ocean gibraltar sill in conjunction with climatic changes and sea level fluctuations led to changes in the current system and to two faunal turnovers at the transition from langhian to serravallian 15 2 15 0 ma and at the end of the serravallian respectively 11 7 11 4 ma the faunas indicate well oxygenated langhian reduced oxygenated serravallian and again well oxygenated tortonian conditions a simplified circulation model for the western mediterranean based on the author s interpretation and additional sources suggests a an estuarine circulation during the langhian b a restricted anti estuarine pattern with sluggish circulation until the end of the serravallian and c an anti estuarine circulation similar to today s situation during the tortonian

photo acoustic study of subshear and supershear ruptures in the laboratory abstract we report supershear ruptures observed in spontaneously nucleating laboratory microearthquakes and describe the signature of the associated mach wavefront radiation transducers detect the wavefield both close and at a distance from the fault the rupture velocities are inferred from either photoelastic high speed imaging or using the acoustic recordings both methods yield compatible estimates of sufficient accuracy to discriminate between sub shear and supershear ruptures the acoustic records allow to characterize the mach wavefront radiated from the supershear rupture front in particular its amplitude and decay velocity functions recovered by integrating high frequency accelerometer signals in the case of supershear ruptures consist in a double pulse function a first pulse traveling at supershear velocity followed by a second pulse traveling at the rayleigh wave velocity conversely the sub shear event is characterized by a single pulse finally we perform numerical simulations of our experiment using a prescribed supershear rupture velocity the synthetic waveforms obtained from these simulations including the mach wave amplitude and phase yield a satisfactory fit to the experimental results

characterization of nucleation during laboratory earthquakes 1 we observe the nucleation phase of in plane ruptures in the laboratory we show that the nucleation is composed of two distinct phases a quasi static and an acceleration stage followed by dynamic propagation we propose an empirical model which describes the rupture length evolution the quasi static phase is described by an exponential growth while the acceleration phase is described by an inverse power law of time the transition from quasi static to accelerating rupture is related to the critical nucleation length which scales inversely with normal stress in accordance with theoretical predictions and to a critical surfacic power which may be an intrinsic property of the interface finally we discuss these results in the frame of previous studies and propose a scaling up to natural earthquake dimensions

characteristic features of local breakdown near a crack tip in the transition zone from nucleation to unstable rupture during stick slip shear failure abstract characteristic features of local breakdown near a propagating crack tip during slip failure nucleation and its transition process to unstable rupture under mode ii conditions are experimentally studied using a rock sample with a simulated fault the size of which is large compared with the size of the breakdown zone in addition distinctive features in the nucleation zone are compared with those in the zone of steady dynamic rupture propagation it is found that the local breakdown stress drop the local dynamic stress drop the local stress increase immediately before the slip weakening process the dimensionless parameter s defined by das and aki and the shear fracture energy are functions of crack length in the transition zone from nucleation to unstable rupture i e they all increase with crack growth in the nucleation zone this is contrasted with the observations in the zone of steady dynamic rupture propagation where these physical parameters do not depend on crack length an increase in the magnitudes of these parameters with crack growth in the nucleation zone results in increasing resistance to crack extension with crack growth in the nucleation zone the reason for the increase in crack growth resistance in this zone is that a slip failure nucleus is formed at a point or zone where the local strength and the shear fracture energy are at a minimum this basic physical information can provide the key to earthquake prediction since the nucleation itself is a precursory phenomenon the ratio of the size of the breakdown zone to the crack length decreases abruptly beyond the critical crack length rupture velocity v accelerates with crack growth and reaches the shear wave velocity or super shear and v is found to be expressed empirically as a function of crack length in the nucleation zone a positive correlation is found between s and v in the nucleation zone v increases with increasing s however no such correlation was observed in the zone of steady dynamic rupture propagation where v seems to have reached the shear wave velocity of super shear for s 0 5 this is consistent with das and aki s numerical result the interrelationships between shear stress slip displacement slip velocity and acceleration near the crack tip during the breakdown in the nucleation zone are revealed and they are compared with those in the zone of dynamic rupture propagation the present experiments suggest that the relationship between shear stress and slip displacement is more fundamental during the breakdown process than the relationship between shear stress and slip velocity a model is presented to describe the breakdown process in the nucleation zone

benthic foraminiferal faunal and isotopic changes as recorded in holocene sediments of the northwest indian ocean 1 historically the holocene has been considered an interval of relatively stable climate however recent studies from the northern arabian sea netherlands indian ocean program 905 suggested high amplitude climate shifts in the early and middle holocene based on faunal and benthic isotopic proxy records we examined benthic foraminiferal faunal and stable isotopic data from ocean drilling program odp site 723 and total organic carbon data from odp site 724 oman margin 808 and 593 m water depths respectively at site 723 the mid holocene shift in 18o values of infaunal benthic species uvigerina peregrina 1 4 is 3 times larger than that of epifaunal benthic species cibicides kullenbergi recorded at site niop 905 off somalia however none of the five other benthic species we measured at hole 723a exhibits such a shift in 18o we speculate that the late holocene 18o decrease in u peregrina represents species specific changes in ecological habitat or food preference in response to changes in surface and deep ocean circulation while the stable isotopic data do not appear to indicate a middle holocene climatic shift our total organic carbon and benthic faunal assemblage data do indicate that the early holocene deep arabian sea was influenced by increased ventilation perhaps by north atlantic deep water and or circumpolar deep water incursions into the indian ocean leading to remineralization of organic matter and a relatively weak early holocene oxygen minimum zone in the northwest arabian sea in spite of strong summer monsoon circulation

latest cretaceous forearc basin development along an accretionary convergent margin south central alaska upper cretaceous sedimentary strata exposed in south central alaska provide insight on tectonic processes that shaped the northern pacific margin following accretion of the wrangellia composite terrane the largest addition of crust to north america over the past 100 m y sedimentologic geochronologic biostratigraphic and petrographic data from the matanuska formation permit reconstruction of the tectono sedimentary history of strata in a forearc basin constructed upon accreted oceanic arc crust the matanuska formation consists of 3 km of sedimentary strata exposed in the northern chugach mountains matanuska valley and southern talkeetna mountains of interior south central alaska measured stratigraphic sections and lithofacies analyses demonstrate that mass slumps and slides debris flows and turbidity currents deposited campanian maastrichtian sandstone conglomerate and mudstone on a gullied trenchward dipping submarine ramp benthic foraminifera inoceramid bivalves and nereites ichnogenera indicate deposition mainly at bathyal water depths sandstone and conglomerate petrofacies are characterized by monocrystalline quartz plagioclase feldspar and volcanic lithic fragments q39f40l21 qm29f40lt32 lm25lv42ls32 and qm42p54k4 jurassic cretaceous arc plutons exposed north of the basin were an important sediment source based on u pb zircon ages of granitoid clasts from conglomerate and detrital zircons from sandstone coeval arc plutons were unroofed relatively quickly judging by the presence of 77 71 ma detrital zircons in sandstone and 79 77 ma granitic clasts in conglomerate together with maastrichtian 71 65 ma ammonite and foraminifera fossils sparse paleozoic triassic detrital zircons indicate minor sediment contribution from inboard sources including the yukon tanana composite terrane and recycled jurassic cretaceous sedimentary strata kahiltna assemblage new data from the upper matanuska formation together with recent studies from age equivalent strata exposed in the alaska range and wrangell mountains provide an exceptional example of basin development along a subduction margin shortly following accretion of an oceanic arc forearc basin development was dominated by subsidence and sediment gravity flow deposits enriched in plutonic and volcanic clasts eroded from both remnant and coeval arc plutons within the arc newly recognized conglomerate in the northern talkeetna mountains records erosion of coeval and remnant arc source terranes to the south and precambrian paleozoic sources to the north farther inboard syndepositional shortening prompted thrust top basin development and accumulation of alluvial lacustrine strata derived from both the former continental margin to the north and accreted oceanic rocks to the south regional subsidence and basin development terminated during late maastrichtian early paleocene time coincident with subduction of progressively younger oceanic lithosphere inboard of an oceanic spreading center

transcritical flows in the coastal marine atmospheric boundary layer abstract numerical solutions of shallow water flow in a variable width channel are computed to model the summertime marine atmospheric boundary layer off the u s west coast using an idealization of the coastline in the vicinity of point arena california as an example several steady state base flows are presented that are hydraulically transcritical these flows are strongly nonlinear weakly rotational and are forced by constant pressure gradients and damped by nonlinear bottom drag at the sea surface the transcritical base flows are supercritical in the vicinity of bends in the coastline but are subcritical to the north upstream and to the south downstream where the coastline is straight within the supercritical region orographic bends in the coastline produce expansion fans and compression jumps the same structures found in globally supercritical flows when the imposed pressure gradient forcing is increased the resulting base flow has a supercritical to subcritical transitional jump that

the west coast thermal trough climatology and synoptic evolution abstractalthough the west coast thermal trough wctt is the most important mesoscale feature over the u s west coast during the warm season its initiation evolution and structure are not well understood originating in the southwest united states this inverted trough can extend northward into oregon washington and british columbia with large impacts on temperature wind humidity and air quality using ncep s north american regional reanalysis narr annual and diurnal climatologies of wctts reaching the northwest united states were constructed for the entire year wctts are most frequent along the coast near the california oregon border with weaker maxima west of the cascade and coastal mountains over the coastal region they occur most often during autumn while east of the cascade mountains the highest frequency is during summer there is strong diurnal variability in wctt frequency during the summer with little diurnal variation in winter though compositing revealed important seasonal d

oxygen minimum expansion in the sulu sea western equatorial pacific during the last glacial low stand of sea level the sulu sea in the western equatorial pacific is presently a shallowly silled dysaerobic deep marine basin deep waters in the sulu sea are ventilated through a single sill at 420 m depth which connects it to the china sea benthic and planktonic foraminiferal oxygen and carbon isotope records benthic and planktonic foraminiferal census data and total organic carbon measurements have been used to evaluate changes in water mass conditions in the sulu sea between the last glacial maximum 18 000 yrs b p and the present day an increase in the abundance of the planktonic foraminiferaneogloboquadrina dutertrei and relatively light planktonic foraminiferal 18o values suggest that during the last glacial maximum surface water salinities were reduced in the sulu sea enhanced isolation of the basin due to glacio eustatic lowering of sea level and reduced surface salinities resulted in stagnation of deep water and an expansion of the mid water oxygen minimum layer increased organic carbon preservation at mid water depths occurs at this time benthic carbon isotope data and an increase in the abundance of benthic foraminiferal species considered to prefer low oxygen environments support the conclusion of an oxygen minimum expansion at mid water depths during the last glacial maximum at water depths greater than 4000 m bottom waters appear to have maintained some degree of oxygenation during the last glacial maximum stronger pacific ocean trade winds at this time may have caused the influx of denser celebes sea surface water into the southern part of the sulu sea the slow sinking of this water would have then ventilated bottom waters in this part of the basin at the transition from glacial to interglacial conditions rising sea level caused denser water to flow over the deepest sill into the sulu sea vertical circulation increased resulting in a greater downward flux of oxygen and a dissipation of the oxygen minimum continued post glacial sea level rise caused periodic ventilation of deep water until the present dysaerobic conditions were established

how fast is rupture during an earthquake new insights from the 1999 turkey earthquakes we report that during the two devastating 1999 earthquakes in turkey rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km s we present observations and modeling which confirm the original inference of supershear rupture during the izmit earthquake and we show that supershear rupture also occurred during the duzce earthquake we show that the rupture velocity measured about 2 times the shear wave velocity is the value predicted by theoretical studies in fracture dynamics we look for clues to explain these observations

small amplitude coastally trapped disturbances and the reduced gravity shallow water approximation solutions are obtained for linear hydrostatic disturbances propagating parallel to the face of an uninterrupted topographic step in an infinitely deep stably stratified fluid on an plane these waves are vertically trapped because their frequencies are smaller than the coriolis parameter and the height of the topographic step is finite these waves are referred to as step trapped kelvin waves because they are dynamically similar to internal kelvin waves throughout the layer of fluid below the top of the topographic step these waves appear to provide an idealized semi analytic model for the coastally trapped disturbances observed to propagate parallel to mountainous coastlines in several parts of the world computations are performed for a basic state with uniform static stability and for a three layer basic state in which the two lowest layers represent the marine boundary layer and a strong capping inversion one might suppose that the linear dynamics of hydrostatic disturbances in the three layer basic state could be well approximated by a reduced gravity shallow water model but this is not the case in particular the reduced gravity shallow water model does not provide reliable estimates for the phase speed of linear step trapped kelvin waves this defect suggests that detailed quantitative comparisons between marine boundary layer flows and the reduced gravity shallow water system may not have any intrinsic physical significance nevertheless these results do not preclude the possibility of constructing useful qualitative analogies between marine boundary layer flows and the reduced gravity shallow water model

supershear mach waves expose the fault breakdown slip abstract mikumo et al 2003 showed that it is possible to estimate the breakdown slip dc as the slip at the time of the peak slip rate for rupture propagation with subshear speeds cruz atienza et al 2009 later attempted to extend this method to extract information about dc as the displacement at the time of the peak particle velocity from seismic strong motion records however a reasonably accurate estimate of dc was only possible in a narrow zone adjacent to the fault typically on the order of hundreds of meters due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process when the rupture propagates with supershear speeds on the other hand this energy is carried much farther away from the fault by mach waves in particular rayleigh mach waves when rupture reaches the earth s surface dunham and bhat 2008 here we present a new approach to estimate dc from strong motion records containing mach waves first we show that the method by mikumo et al is valid for supershear rupture propagation this method is then used to estimate dc via an asymptotic approximation of the slip and slip rate time histories from the mach waves using spontaneous rupture simulations we demonstrate that for a visco elastic half space model dc can be estimated within an error of 40 from mach waves that have propagated a distance of at least 3 km from the fault the method is applied to estimate dc for the 2002 mw7 9 denali alaska earthquake 1 5 m and for the 1999 mw7 6 izmit turkey earthquake 1 7 m

attenuation of radiated ground motion and stresses from three dimensional supershear ruptures 1 radiating shear and rayleigh waves from supershear ruptures form mach waves that transmit large amplitude ground motion and stresses to locations far from the fault we simulate bilateral ruptures on a finite width vertical strike slip fault of width w and half length l with l w breaking the surface of an elastic half space and focus on the wavefield out to distances comparable to l at distances much smaller than w two dimensional plane strain slip pulse models i e models in which the lateral extent of the slip zone is unbounded accurately predict the subsurface wavefield amplitudes in the shear mach wedge of those models are undiminished with distance from the fault when viewed from distances far greater than w rupture is accurately modeled as a moving point source that produces a shear mach cone and on the free surface rayleigh wave mach fronts geometrical spreading of the shear mach cone occurs radially and amplitudes there decrease with the inverse square root of distance the transition between these two asymptotic limits occurs at distances comparable to w similar considerations suggest that rayleigh mach waves suffer no attenuation in the ideally elastic medium studied here the rate at which fault strength weakens at the rupture front exerts a strong influence on the off fault fields only in the immediate vicinity of the fault for both sub rayleigh and supershear ruptures and at the mach fronts of supershear ruptures more rapid weakening generates larger amplitudes at the mach fronts

from sub rayleigh to supershear ruptures during stick slip experiments on crustal rocks supershear earthquake ruptures propagate faster than the shear wave velocity although there is evidence that this occurs in nature it has not been experimentally demonstrated with the use of crustal rocks we performed stick slip experiments with westerly granite under controlled upper crustal stress conditions supershear ruptures systematically occur when the normal stress exceeds 43 megapascals mpa with resulting stress drops on the order of 3 to 25 mpa comparable to the stress drops inferred by seismology for crustal earthquakes in our experiments the sub rayleigh to supershear transition length is a few centimeters at most suggesting that the rupture of asperities along a fault may propagate locally at supershear velocities in turn these sudden accelerations and decelerations could play an important role in the generation of high frequency radiation and the overall rupture energy budget

ducted coastal ridging over s e australia the intense and rapidly established coastal ridging which is a regular occurrence over south eastern australia during the warm seasons is investigated using a detailed case study and mesoscale numerical model simulations we suggest that the ridge is initiated by a forced kelvin type edge wave which forms on the south western edge of the great dividing range and is ducted in an anticlockwise sense around the coast the ridge is then stabilized by inertial modification and decays over a synoptic time scale of a few days our results apply to similar phenomena in other parts of the world notably southern africa and south america

organic carbon distribution in the north atlantic ocean during the last glacial maximum abstract the organic carbon content of eighty two last glacial maximum lgm sediment samples from the north atlantic ocean was determined with a coulometer organic carbon in these sediments averaged about 0 5 by weight slightly higher than in modern sediments factors that control organic carbon distribution were examined in two ways by mapping the spatial distribution of organic carbon during the lgm and by comparing organic carbon content to sediment characteristics in general sediment organic content increases with increasing sedimentation rate increasing clay content and decreasing carbonate content the spatial distribution of lgm organic content is similar in most respects to the mapped modern distribution the primary exception being areas of high organic content one area of high organic content off nortwest africa is situated in the same area geographically but is larger than its modern counterpart perhaps indicating that wind driven upwelling was more intense and or widespread during the lgm the two other areas of high organic carbon content the north american margin and west of the mid atlantic ridge mar at about 40 n have no modern counterpart on the north american margin south of cape cod organic carbon content is generally 0 6 and in several samples is 0 9 the increased organic carbon content of sediment in this area appears to be related to an increase in sedimentation rate and the concomitant increase in inorganic nutrients the area west of the mar is more perplexing and appears to be related to changes in lgm surface circulation

coherence of mach fronts during heterogeneous supershear earthquake rupture propagation simulations and comparison with observations 1 we study how heterogeneous rupture propagation affects the coherence of shear and rayleigh mach wavefronts radiated by supershear earthquakes we address this question using numerical simulations of ruptures on a planar vertical strike slip fault embedded in a three dimensional homogeneous linear elastic half space ruptures propagate spontaneously in accordance with a linear slip weakening friction law through both homogeneous and heterogeneous initial shear stress fields in the 3 d homogeneous case rupture fronts are curved owing to interactions with the free surface and the finite fault width however this curvature does not greatly diminish the coherence of mach fronts relative to cases in which the rupture front is constrained to be straight as studied by dunham and bhat 2008a introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear wave speed calculations of the fourier amplitude spectra fas of ground velocity time histories corroborate the kinematic results of bizzarri and spudich 2008a 1 the ground motion of a supershear rupture is richer in high frequency with respect to a subshear one 2 when a mach pulse is present its high frequency content overwhelms that arising from stress heterogeneity present numerical experiments indicate that a mach pulse causes approximately an 1 7 high frequency falloff in the fas of ground displacement moreover within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the mach fronts ground motion at stations experiencing mach pulses should be richer in high frequencies compared to stations without mach pulses in contrast to the foregoing theoretical results we find no average elevation of 5 damped absolute response spectral accelerations sa in the period band 0 05 0 4 s observed at stations that presumably experienced mach pulses during the 1979 imperial valley 1999 kocaeli and 2002 denali fault earthquakes compared to sa observed at non mach pulse stations in the same earthquakes a 20 amplification of short period sa is seen only at a few of the imperial valley stations closest to the fault this lack of elevated sa suggests that either mach pulses in real earthquakes are even more incoherent that in our simulations or that mach pulses are vulnerable to attenuation through nonlinear soil response in any case this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20 close to the fault to account for mach pulses provided that the existing data are adequately representative of ground motions from supershear earthquakes

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

palynological foraminiferal and aminostratigraphic studies of quaternary sediments from the u s middle atlantic upper continental slope continental shelf and coastal plain abstract a pollen climate index curve provides the basic stratigraphic subdivision of the 305 m cored quaternary section of amcor 6021c located on the upper continental slope off new jersey u s a cold and warm intervals from top to bottom were assigned to marine oxygen isotope stages 1 through 13 at a sub bottom depth of about 220 m foraminiferal data indicate a possible hiatus and if so sediments below this may be as old as isotope stage 16 or older aminostratigraphic studies yielded results that are consistent with either interpretation benthic foraminifers are dominated by elphidium excavatum and islandiella norcrossi the planktic foraminiferal record provided no independent means of subdividing the section the stratigraphic distribution in 6021c of six species of quercus oak and aminozone determinations were applied to dating in terms of presumed oxygen isotope stages of other offshore core hole samples and some onshore quaternary deposits of delaware stratigraphic information from amcor sites 6021 and 6009 correlated to seismic reflection profiles that cross the shelf slope break indicate that the thickest accumulations of terrigenous quaternary sediments are located along the outer continental shelf upper continental slope offshore the northeastern united states

trends in caribbean paleoproductivity related to the neogene closure of the central american seaway abstract this study tests the hypothesis that the late miocene to early pliocene constriction and closure of the central american seaway cas connecting the tropical atlantic and east quatorial pacific eep caused a decrease in productivity in the caribbean due to decreased coastal upwelling and an end to the connection with high productivity tropical pacific waters the present study compared paleoceanographic proxies for the interval between 8 3 and 2 5 ma in 47 samples from south caribbean odp site 999 with published data on eep dsdp site 503 proxies for site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor the ratio of infaunal epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates bfars in addition we calculated resistant planktic foraminifers species and used the previously published sand fraction and benthic carbon isotope values from site 999 during early shoaling of the isthmus 8 3 7 9 ma the caribbean was under mesotrophic conditions with little ventilation of bottom waters and low current velocity the pre closure interval 7 6 4 2 ma saw enhanced seasonal input of phytodetritus with even more reduced ventilation and enhanced dissolution between 6 8 and 4 8 ma during the post closure interval 4 2 2 5 ma in the caribbean paleoproductivity decreased current velocity was reduced and ventilation improved while the seasonality of phytodetrital input was reduced dramatically coinciding with the establishment of the atlantic pacific salinity contrast at 4 2 ma our data support the hypothesis that late miocene constriction of the cas at 7 9 ma and its closure at 4 2 ma caused a gradual decrease in paleoproductivity in the caribbean consistent with decreased current velocity and seasonality of the phytodetrital input

association of bathyal foraminifera with water masses in the northwestern gulf of mexico abstract q mode cluster analysis and r mode factor analysis of benthic foraminiferal data from 120 core tops from the northwestern gulf of mexico 87 1361 m 26 4 29 0 n 88 5 96 4 w distinguish separate thanatotopes and faunal assemblages related to the five water masses present within the depth range of the samples these water masses are the surface mixed layer sml gulf water gw oxygen minimum water omw subantarctic intermediate water saiw and caribbean midwater cmw reussella atlantica bigenerina irregularis and angulogenerina bella are particularly associated with sml bulimina spicata planulina foveolata and cibicidoides umbonatus with gw sphaeroidina bulloides bulimina mexicana and siphonina bradyana with omw epistominella exigua with saiw and gyroidinoides laevis cibicides wuellerstorfi pullenia subsphaerica bulimina aculeata gyroidinoides polius and laticarinina pauperata with cmw cluster analysis also indicates the presence of three faunal groups related to water depth and bottom water oxygen content within the omw assemblage an additional assemblage recognized in the mississippi river delta area may be related to low oxygen conditions above the normal depth for the oxygen minimum the close correspondence between the results of cluster and factor analyses suggests that similar numerical analyses of fossil data should be useful in deciphering ancient bathyal assemblages influenced by water mass properties

fracture in westerly granite under ae feedback and constant strain rate loading nucleation quasi static propagation and the transition to unstable fracture propagation new observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of westerly granite using acoustic emission ae monitoring by conducting the tests under different loading conditions the fracture process is demonstrated for quasi static fracture under ae feedback load a slowly developing unstable fracture loaded at a slow constant strain rate of 2 5 10 6 s and an unstable fracture that develops near instantaneously loaded at a fast constant strain rate of 5 10 5 s by recording a continuous ultrasonic waveform during the critical period of fracture the entire ae catalogue can be captured and the exact time of fracture defined under constant strain loading three stages are observed 1 an initial nucleation or stable growth phase at a rate of 1 3 mm s 2 a sudden increase to a constant or slowly accelerating propagation speed of 18 mm s and 3 unstable accelerating propagation in the 100 ms before rupture the high level of ae activity as seen on the continuous record prevented the location of discrete ae events a lower bound estimate of the average propagation velocity using the time to rupture and the existing fracture length suggests values of a few m s however from a low gain acoustic record we infer that in the final few ms the fracture propagation speed increased to 175 m s these results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments it is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation

the 14 november 2001 kokoxili tibet earthquake high frequency seismic radiation originating from the transitions between sub rayleigh and supershear rupture velocity regimes seismic array based analysis of the major kokoxili earthquake tibet 14 november 2001 yields an unambiguous reconstruction of the seismic rupture history and relates it to the generated seismic radiation we demonstrate that after a classical sub rayleigh velocity stage the rupture speed has jumped to supershear values close to compressional wave velocity over a 175 km long fault segment before abruptly slowing down in the late part of the earthquake the transition locations between these three phases are correlated with the fault geometry and are associated with the most energetic radiation this observation proves that the rupture velocity changes as theoretically predicted are a primary source of high frequency seismic radiation this result requires reconsidering the origins of seismic damage generally attributed to slip variations

pulse like and crack like ruptures in experiments mimicking crustal earthquakes theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws stress conditions on faults energy partition and heat generation during earthquakes scaling laws and spatiotemporal complexity of fault slip early theoretical models treated earthquakes as crack like ruptures but seismic inversions indicate that earthquake ruptures may propagate in a self healing pulse like mode a number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated this study presents experimental observations of spontaneous pulse like ruptures in a homogeneous linear elastic setting that mimics crustal earthquakes reveals how different rupture modes are selected based on the level of fault prestress demonstrates that both rupture modes can transition to supershear speeds and advocates based on comparison with theoretical studies the importance of velocity weakening friction for earthquake dynamics

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

identifying the unique ground motion signatures of supershear earthquakes theory and experiments the near field ground motion signatures associated with sub rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by rosakis and co workers xia et al 2004 2005a lu et al 2007 rosakis et al 2007 heterodyne laser interferometers enable continuous high bandwidth measurements of fault normal fn fault parallel fp and vertical v particle velocity ground motion records at discrete locations on the surface of a homalite 100 test specimen as a sub rayleigh or a supershear rupture sweeps along the frictional fault photoelastic interference fringes acquired using high speed digital photography provide a synchronized spatially resolved whole field view of the advancing rupture tip and surrounding maximum shear stress field the first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures experimental results demonstrate that a shear mach front produced by a stable supershear rupture is characterized by a dominant fp velocity component the situation is shown to reverse in the sub rayleigh rupture speed regime whereby the fn particle velocity component dominates the ground motion record additional distinguishing particle velocity signatures consistent with theoretical and numerical predictions and repeatedly observed in experimental records are 1 a pronounced peak in the fp velocity record induced by the leading dilatational field which sweeps the measurement station in advance of the shear mach front and 2 a pronounced velocity swing in the fn record associated with the arrival of a trailing rayleigh sub rayleigh secondary rupture which follows the arrival of the shear mach front analysis of the particle velocity records also confirms 2d steady state theoretical predictions pertaining to the separation attenuation and radiation partitioning of the shear and dilatational portions of the rupture velocity field components the second phase of our experimental investigations re examine the 2002 mw7 9 denali fault earthquake and the remarkable set of near source ground motion records obtained at ps10 located approximately 85 km east of the epicenter and just 3 km north of the fault along the alaska pipeline motivated by the analysis and interpretation of these records by ellsworth et al 2004 dunham and archuleta 2004 2005 we attempt to mimic the denali strike slip rupture scenario and replicate the ps10 ground motion signatures using a laboratory earthquake experiment the experiments feature a left to right west to east propagating right lateral rupture within a homalite 100 test specimen with particle velocity data collected at a near field station situated just above north of the fault both sub rayleigh and supershear laboratory earthquake experiments are conducted using the denali ps10 configuration in order to compare and contrast the resulting particle velocity signatures supershear laboratory records capture all of the prominent features displayed within the ps10 ground motion records noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time to match the scale of the ps10 ground motion records the strong correlation between the scaled experimental records and the actual ps10 ground motion records support the hypothesis that the denali strike slip fault exhibited a supershear burst finally we present a 2d steady state stress velocity formulation that relates the fp and fn particle velocity records measured close to the fault to the evolution of the stress tensor at the same location a locally steady state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses xx t and t at the near fault station dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration experimental findings are presented which capture the temporal and spatial distributions of xx and evolution of the dynamic friction coefficient and velocity weakening behavior of a supershear slip pulse

self healing pulse like shear ruptures in the laboratory models predict that dynamic shear ruptures during earthquake faulting occur as either sliding cracks where a large section of the interface slides behind a fast moving rupture front or self healing slip pulses where the fault relocks shortly behind the rupture front we report experimental visualizations of crack like pulse like and mixed rupture modes propagating along frictionally held incoherent interfaces separating identical solids and we describe the conditions under which those modes develop a combination of simultaneously performed measurements via dynamic photoelasticity and laser interferometry reveals the rupture mode type the exact point of rupture initiation the sliding velocity history and the rupture propagation speed

effects of supershear rupture speed on the high frequency content of s waves investigated using spontaneous dynamic rupture models and isochrone theory 1 in this paper we achieve three goals 1 we demonstrate that crack tips governed by friction laws including slip weakening rate and state dependent laws and thermal pressurization of pore fluids propagating at supershear speed have slip velocity functions with reduced high frequency content compared to crack tips traveling at subshear speeds this is demonstrated using a fully dynamic spontaneous three dimensional earthquake model in which we calculate fault slip velocity at nine points locations distributed along a quarter circle on the fault where the rupture is traveling at supershear speed in the in plane direction and subshear speed in the antiplane direction this holds for a fault governed by the linear slip weakening constitutive equation by slip weakening with thermal pressurization of pore fluid and by rate and state dependent laws with thermal pressurization the same is also true even assuming a highly heterogeneous initial shear stress field on the fault 2 using isochrone theory we derive a general expression for the spectral characteristics and geometric spreading of two pulses arising from supershear rupture the well known mach wave and a second lesser known pulse caused by rupture acceleration 3 we demonstrate that the mach cone amplification of high frequencies overwhelms the de amplification of high frequency content in the slip velocity functions in supershear ruptures consequently when earthquake ruptures travel at supershear speed a net enhancement of high frequency radiation is expected and the alleged low peak accelerations observed for the 2002 denali and other large earthquakes are probably not caused by diminished high frequency content in the slip velocity function as has been speculated

synoptic scale forcing of coastal lows forced double kelvin waves in the atmosphere gill 1977 has interpreted the coastal lows of southern africa as atmospheric coastal kelvin waves the lows are trapped horizontally next to the steep slopes of the great central plateau by coriolis forces and vertically by a low level inversion this hypothesis is tested and extended using two linear models a barotropic primitive equation analysis on an equatorial beta plane models the generation of these waves an impermeable eastern boundary is included to reflect the blocking of the low level flow below the coastal inversion by the orography results of the linear analysis suggest that the formation of the coastal lows may be explained in terms of the scattering of eastward propagating synoptic scale disturbances at the meridional boundary the boundary response is structurally similar to a kelvin wave at the frequencies of interest no zonally propagating rossby waves are excited further in contrast to the case of a western boundary the equatorial response is negligible a two layer f plane model enables the dynamics of the layer of fluid below the interior inversion to be incorporated at the period of the synoptic forcing six days the boundary response is a maximum along the escarpment and decays exponentially from it the e folding distance is slightly less than the appropriate rossby radius of deformation these results together with observations suggest that the coastal low and its companion low over the interior may be interpreted as forced internal double kelvin waves the possible application of these results to foehn chinook winds and lee cyclogenesis is mentioned

late glacial to recent deep sea benthic foraminifera from the northeastern atlantic cadiz gulf and western mediterranean alboran sea paleooceanographic results abstract deep sea benthic foraminifera of the region of water exchange between the mediterranean and the atlantic ocean at the gibraltar strait show significant water mass relationships for the past 18 000 years cores used in this benthic foraminifera analysis were selected according to the context of the distribution of various deep bottom water masses on each side of the gibraltar strait 1 1 on the atlantic side of the strait two cores ks 8228 ks 8229 are located in the present day nadw and one kc 8221 in the upper part of the present mediterranean outflow water 2 2 on the mediterranean side of gibraltar two cores kc 8241 su 8107 are located in the deep water mass and one ks 8230 in the intermediate water mass in the two deep basins 1500 2800 m depth in the gulf of cadiz 1200 1300 m depth in the alboran sea the paleooceanographic changes appear to be in an opposite way for the past 18 000 years the alboran basin shows a paleooceanographic evolution from a well oxygenated nutrient rich environment at about 18 000 yr b p to a nutrient poor oxygen depleted environment from 13 000 to the present time moreover for the time span synchronous with the well known development of sapropels in the eastern mediterranean basins between 10 000 and 7000 yr b p the faunal assemblage shows most unusual characteristics implying drastic environmental conditions conversely in the gulf of cadiz the environment pass as from a biotope occupied by an oxygen depleted nutrient poor water mass at about 18 000 years b p to a biotope occupied by nadw since the younger dryas this agrees with previous data obtained in the northeastern atlantic ocean caralp 1987 in the epibathyal zones 550 800 m depth on both sides of the gibraltar strait paleohydrographic changes do not seem so important according to the present and very late holocene assemblages which are similar on both sides of the strait with a strong east west flow two other stratigraphic episodes have shown the same conditions of water exchanges the end of the isotopic stage 2 and the younger dryas conversely during the last glacial maximum the bolling allerod and the lower holocene westward water fluxes were probably lower at no time the hypothesis of a reversal or a stop in the east west exchanges between mediterranean and atlantic ocean may be justified

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

earthquake nucleation size evidence of loading rate dependence in laboratory faults recent gps observations of major earthquakes such as the 2014 chile megathrust show a slow pre slip phase releasing a significant portion of the total moment ruiz et al 2014 despite advances from theoretical stability analysis rubin ampuero 2005 ruina 1983 and modeling kaneko carpenter nielsen 2017 it is not fully understood what controls the prevalence and the amount of slip in the nucleation process here we present laboratory observations of slow slip preceding dynamic rupture where we observe a dependence of nucleation size and position on the loading rate laboratory equivalent of tectonic loading rate the setup is composed of two polycarbonate plates under direct shear with a 30 centimeters long slip interface the results of our laboratory experiments are in agreement with the pre slip model outlined by ellsworth and beroza 1995 and observed in laboratory experiments latour schubnel nielsen madariaga vinciguerra 2013 nielsen taddeucci vinciguerra 2010 ohnaka kuwahara 1990 which show a slow slip followed by an acceleration up to dynamic rupture velocity however further complexity arises from the effect of 1 rate of shear loading and 2 inhomogeneities on the fault surface in particular we show that when the loading rate is increased from 10 2 mpa s 1 to 6 mpa s 1 the nucleation length can shrink by a factor of three and the rupture nucleates consistently on higher shear stress areas the nucleation lengths measured fall within the range of the theoretical limits lb and l derived by rubin and ampuero 2005 for rate and state friction laws

latest pliocene through holocene paleoceanography of the eastern indian ocean benthic foraminiferal evidence multivariate analyses of latest pliocene through holocene benthic foraminifera from 61 samples from deep sea drilling project dsdp site 214 eastern indian ocean were carried out the 46 highest ranked species were used in r mode factor analysis which has enabled to the identification of three environmentally significant assemblages at site 214 assemblage 1 is characterized by uvigerina hispido costata osangularia culter gavelinopsis lobatulus cibicides wuellerstorfi and karreriella baccata as principal species this assemblage is inferred to reflect high energy well oxygenated and probably low organic carbon deep sea environment at site 214 assemblage 2 is defined principally by globocassidulina pacifica and u proboscidea and is considered to indicate an organic carbon rich environment which resulted from high surface productivity irrespective of dissolved oxygen content assemblage 3 is marked by oridorsalis umbonatus textularia lythostrota hoeglundina elegans pyrgo murrhina and pullenia quinqueloba as principal species this assemblage is inferred to indicate a low organic carbon environment with high pore water oxygen concentration leading to better preservation of deep sea sediments

spatiotemporal properties of sub rayleigh and supershear ruptures inferred from full field dynamic imaging of laboratory experiments many earthquakes propagate at sub rayleigh speeds earthquakes propagating at supershear speeds though less common are by far more destructive hence it is important to quantify the motion characteristics associated with both types of earthquake ruptures here we report on the spatiotemporal properties of dynamic ruptures measured in our laboratory experiments using the dynamic digital image correlation technique earthquakes are mimicked by the frictional rupture propagating along the interface of two homalite plates digital images of the propagating ruptures are captured by an ultrahigh speed camera and processed with digital image correlation in order to produce sequences of evolving displacement and velocity maps our measurements reveal the full field structure of the velocity components bridge the gap between previous spatially sparse velocimeter measurements available only at two to three locations and enable us to quantify the attenuation patterns away from the interface

benthic foraminiferal response to sea level change in the mixed siliciclastic carbonate system of southern ashmore trough gulf of papua 1 ashmore trough in the western gulf of papua gop represents an outstanding modern example of a tropical mixed siliciclastic carbonate depositional system where significant masses of both river borne silicates and bank derived neritic carbonates accumulate in this study we examine how benthic foraminiferal populations within ashmore trough vary in response to sea level driven paleoenvironmental changes particularly organic matter and sediment supply two 11 3 m long piston cores and a trigger core were collected from the slope of ashmore trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera relative abundances principal component analyses and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time assemblage 1 with high abundances of uvigerina peregrina and bolivina robusta dominated between 83 and 70 ka early regression assemblage 2 with high abundances of globocassidulina subglobosa dominated between 70 and 11 ka late regression through lowstand and early transgression and assemblage 3 with high abundances of neritic benthic species such as planorbulina mediterranensis dominated from 11 ka to the present late transgression through early highstand assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand assemblage 3 signals increased off shelf delivery of neritic carbonates likely when carbonate productivity on the outer shelf great barrier reef increased significantly when it was reflooded benthic foraminiferal assemblages in the sediment sink slopes of ashmore trough likely respond to the amount and type of sediment supplied from the proximal source outer gop shelf

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

experimental observation of stick slip instability fronts summary stick slip dynamic instability is a key mechanism governing frictional processes from microscale physics to earthquake faults and landslides yet challenging questions are still open about its nucleation and propagation dynamics here we present novel observations on laboratory experimental faults where spontaneously nucleating fractures are produced describing 1 an initial quasistatic stable rupture front propagating at about 5 per cent the shear wave velocity vs accelerating to subshear and then to intersonic velocity 2 the arisal of a higher degree of complexity when the friction to prestress ratio is increased on the sliding surface the complex behaviour includes stop and go sequences irregular propagation and rerupturing episodes within short time intervals implying rapid restrengthening of the surface and the formation of self healing pulses reproducing experimentally for the first time a behaviour observed on seismic faults

near source ground motions from simulations of sustained intersonic and supersonic fault ruptures we examine the long period near source ground motions from simulations of m 7 4 events on a strike slip fault using kinematic ruptures with rupture speeds that range from subshear speeds through intersonic speeds to supersonic speeds the strong along strike shear wave directivity present in scenarios with subshear rupture speeds disappears in the scenarios with ruptures propagating faster than the shear wave speed furthermore the maximum horizontal displacements and velocities rotate from generally fault perpendicular orientations at subshear rupture speeds to generally fault parallel orientations at supersonic rupture speeds for rupture speeds just above the shear wave speed the orientations are spatially heterogeneous as a result of the random nature of our assumed slip model at locations within a few kilometers of the rupture the time histories of the polarization of the horizontal motion provide a better diagnostic with which to gauge the rupture speed than the orientation of the peak motion subshear ruptures are associated with significant fault perpendicular motion before fault parallel motion close to the fault supershear ruptures are associated with fault perpendicular motion after significant fault parallel motion consistent with previous studies we do not find evidence for prolonged supershear rupture in the long period 2 sec ground motions from the 1979 imperial valley earthquake however we are unable to resolve the issue of whether a limited portion of the rupture approximately 10 km in length propagated faster than the shear wave speed additionally a recording from the 2002 denali fault earthquake does appear to be qualitatively consistent with locally supershear rupture stronger evidence for supershear rupture in earthquakes may require very dense station coverage in order to capture these potentially distinguishing traits

space and time evolution of rupture and faulting during the 1999 izmit turkey earthquake we use the records of the ground motion obtained at near fault accelerometers to study the space and time evolution of rupture and faulting during the izmit earthquake we find that the rupture propagated at the sub rayleigh speed of about 3 km sec on the western and eastern segments of the fault but that the central segment izmit sapanca lake sakarya nearly 50 km long broke at the supershear speed of about 4 8 km sec this value within the range of uncertainties is the one theoretically predicted sqrt 2 v mathrm s in fracture dynamics for stable shear crack growth at intersonic speed we infer an average fault slip of about 2 9 m over a total rupture length of about 150 km with the largest values of up to 6 m occurring in the golcuk area to the west and in the sakarya region to the east the strong motion data also indicate that the slip diminished gradually to the west beyond the hersek peninsula over about 30 km whereas it stopped abruptly at depth at the termination of the eastern karadere segment the slip duration is between 2 and 4 sec except in the hypocentral area which slipped in about 1 sec the seismic moment inferred is about 2 5 10 20 n m

evolution of b value during the seismic cycle insights from laboratory experiments on simulated faults abstract we investigate the evolution of the frequency magnitude b value during stable and unstable frictional sliding experiments using a biaxial shear configuration we record broadband acoustic emissions ae while shearing layers of simulated granular fault gouge under normal stresses of 2 8 mpa and shearing velocity of 11 m s ae event amplitude ranges over 3 4 orders of magnitude and we find an inverse correlation between b and shear stress the reduction of b occurs systematically as shear stress rises prior to stick slip failure and indicates a greater proportion of large events when faults are more highly stressed for quasi periodic stick slip events the temporal evolution of b has a characteristic saw tooth pattern it slowly drops as shear stress increases and quickly jumps back up at the time of failure the rate of decrease during the inter seismic period is independent of normal stress but the average value of b decreases systematically with normal stress for stable sliding b is roughly constant during shear however it exhibits large variability during irregular stick slip we see a mix of both behaviors b decreases during the interseismic period between events and then remains constant when shear stress stabilizes until the next event where a co seismic increase is observed our results will help improve seismic hazard assessment and ultimately could aid earthquake prediction efforts by providing a process based understanding of temporal changes in b value during the seismic cycle

a new multilayered visco elasto plastic experimental model to study strike slip fault seismic cycle nowadays technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle however the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years to overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters we have developed a new experimental approach allowing for the simulation of strike slip fault earthquakes and analyze in detail hundreds of successive seismic cycle model rheology is made of multilayered visco elasto plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle ductile coupling postseismic deformation phase and far field stress transfers the kinematic evolution of the model surface is monitored using an optical system based on subpixel spectral correlation of high resolution digital images first results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory these results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth along the fault plane our analog modeling approach appears then as an efficient complementary approach to investigate earthquake dynamics

a model for improving the precision of paleobathymetric estimates an example from the northwest gulf of mexico intraspecific variation in test morphology of ten commonly occurring benthic foraminiferal species collected from 47 stations and from water depths ranging from 53 to 3230 m in the northwest gulf of mexico were subjected to canonical discriminant analysis in order to statistically define an a priori bathymetric zonation three species bolivina subspinescens gavelinopsis translucens and uvigerina peregrina had intraspecific variation capable of statistically dividing the bathyal zone into six contiguous 200 m intervals statistical analysis of the remaining seven species bolivina albatrossi b lowmani cassidulina subglobosa cibicidoides pachyderma c robertsonianus epistominella exigua and qridorsalis umbonatus divided the bathyal zone into five contiguous 250 m intervals the statistical differences in morphologic variability found in this study appear to be the organism s physiologic response to biogeochemical changes in sea floor habitat as they transcend various water masses as such the statistical analyses is a direct measure of the effect of those environmental factors allowing better resolution and reliability of paleodepth estimates and geodynamic modelling than that commonly attained through faunal association

on the generation and propagation of the southern african coastal low the time height variability of the lower marine atmosphere during the eastwards propagation of coastal lows around the coast of southern africa is presented these coastal lows are shallow mesoscale disturbances that are trapped vertically by a strong subsidence inversion and horizontally through coriolis effects against the steep escarpment that fringes the subcontinent prior to the event warm offshore flow descending off this escarpment at about the inversion level provides an input of buoyancy which together with the cyclonic vorticity acquired during the descent acts to generate a coastal low rather than a high analysis of the data shows that coastal lows are characterized by a marked lowering of the inversion level a switch in the direction of the winds below the inversion and a drop in the near surface temperature which are all consistent with the hypothesis that the coastal low is an internal kelvin wave propagating in the marine layer good agreement between the observed propagation speed of the coastal low and the theoretical phase speed of such a wave reinforces this hypothesis a model of the vertical buoyancy advection into the marine atmosphere that results from the warm offshore flow is presented it is illustrated that an internal kelvin wave in the form of a coastal low results from this buoyancy advection comparisons are made between coastal low dynamics and those characteristics of other mesoscale coastally trapped disturbances which propagate in the marine layers of california and south eastern australia

distribution patterns of benthic foraminifera across the ypresian lutetian gorrondatxe section northern spain response to sedimentary disturbance article we present a study of benthic foraminiferal assemblages from an ypresian lutetian distal submarine fan system in the lower bathyal gorrondatxe section basque cantabrian basin northern spain the objective of our study is to analyze the benthic foraminiferal distribution patterns and their response to sedimentary disturbance and related factors assemblages contain a high percentage of allochthonous taxa such as asterigerinids and other shallow water taxa which were transported downslope by turbidity currents detailed quantitative analyses supported by r mode cluster and detrended correspondence analyses after removing allochthonous taxa from the foraminiferal counts allowed us to identify 6 assemblages that are divided into two groups related to the turbidite content in the gorrondatxe section assemblages 1 characteristic of the turbidite poor intervals with low sedimentary disturbance include assemblage 1a with highly diverse common middle lower bathyal calcareous taxa assemblage 1b with common agglutinated taxa mainly trochamminids and assemblage 1c characterized by calcareous taxa that are also common in the turbidite rich interval assemblages 2 characterized by a high dominance prevail in the turbidite rich interval and include assemblage 2a characterized by the dominance of infaunal bolivinids and epifaunal cibicids assemblage 2b typified by moderate to low diversity and dominated by deep infaunal globobulimina species and assemblage 2c typified by very abundant suspension feeding astrorhizids the high abundance of bolivinids and globobulimina species may be related to an enhanced input of low quality organic matter transported by turbidity currents to the seafloor representing different stages of recolonisation after disturbance and different energy regimes high current activity was probably responsible for the abundance of cibicids while moderate to low diverse and high dominance assemblages characterize the recolonisation of the substrate after disturbance we conclude that sedimentary disturbance and other related factors such as current activity resuspension of sediments at the seafloor and supply of organic matter and its quality played an important role in the distribution of benthic foraminifera inthe gorrondatxesection the identification of allochthonous taxa emerges as an essential aspect of the study of environments with sedimentary disturbance

off fault damage patterns due to supershear ruptures with application to the 2001 mw 8 1 kokoxili kunlun tibet earthquake 1 we extend a model of a two dimensional self healing slip pulse propagating dynamically in steady state with slip weakening failure criterion to the supershear regime in order to study the off fault stressing induced by such a slip pulse and investigate features unique to the supershear range specifically we show that there exists a nonattenuating stress field behind the mach front that radiates high stresses arbitrarily far from the fault practically this would be limited to distances comparable to the depth of the seismogenic zone thus being capable of creating fresh damage or inducing coulomb failure in known structures at large distances away from the main fault we allow for both strike slip and dip slip failure induced by such a slip pulse we show that off fault damage is controlled by the speed of the slip pulse scaled stress drop and principal stress orientation of the prestress field we apply this model to study damage features induced during the 2001 kokoxili kunlun event in tibet for which it has been suggested that much of the rupture was supershear we argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture however those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault we also make some estimates of fracture energy which for a given net slip and dynamic stress drop is lower than for a sub rayleigh slip pulse because part of the energy fed by the far field stress is radiated back along the mach fronts

relationship of surface sediments and benthic foraminiferal distribution patterns in the norwegian channel northern north sea abstract our study of the distribution of benthic foraminifers in surface sediment samples from the norwegian channel has shown that eight species and five different assemblages are important the assemblages are dominated by uvigerina peregrina bolivina skagerrakensis cassidulina laevigata elphidium excavatum and bulimina marginata respectively hyalinea balthica melonis barleeanum and trifarina angulosa are also abundant the first four assemblages and their dominant species can be related to certain water masses with known characteristics two species are related to certain types of substrate m barleeanum seems to prefer a fine grained substrate while t angulosa occurs most abundantly where the content of silt and clay is low b skagerrakensis and h balthica occur most abundantly in sediments with a high content of organic carbon while t angulosa shows inverse correlation to the organic carbon content

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

rock pulverization at high strain rate near the san andreas fault rocks near the san andreas fault are pervasively crushed at distances of up to 400 m from its core laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates 150 s 1 associated with a supershear rupture a rupture propagating at a velocity equal to greater than that of seismic shear waves

environmental distribution of recent benthic foraminifera on the northeast united states continental slope several bathymetrically consistent recent benthic foraminiferal biofacies have been recognized from the continental slope south east of cape cod faunal assemblages are dominated by globobulimina bulimina upper slope less than 1 000 m and uvigerina peregrina lower slope uppermost rise water depths between 1 000 and 2 500 m the globobulimina bulimina assemblage coincides with the oxygen minimum zone this agrees with the occurrence of globobulimina in mediterranean sapropels organic rich sediments deposited under anoxic conditions previous studies have noted the association of u peregrina with bathyal water depths deep water temperatures of 3 to 4 c and water of low oxygen content however correlations between abundance of u peregrina and water depth or temperature are not the same everywhere and no correlation with dissolved oxygen in the water column is seen on the united states continental slope and rise the highest abundances of u peregrina coincide with maxima of organic carbon and silt within the slope sediments this suggests that the distribution of u peregrina in this region may be influenced more by low oxygen in the sediments rather than by low oxygen content of the overlying water

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

the distribution of recent benthic foraminifera in the polar front region southwest atlantic abstract twenty five core top samples from the maurice ewing bank meb and islas orcadas rise ior were examined to determine the distribution of benthic foraminifera in the vicinity of the polar front in the southwest atlantic ocean the polar front has a subsurface expression that effects the areal and depth distribution of benthic foraminifera in this region three faunal assemblages were identified by q mode factor analysis the shallowest assemblage dominated by bulimina aculeata is present from 1500 to 2600 m on the maurice ewing bank and is associated with potential temperatures of 1 71 0 50 c salinities of 34 74 34 70 and potential density values of 45 84 46 04 sigma 4 a second assemblage dominated by uvigerina peregrina occurs in water depths from 2600 to 3100 m and is associated with potential temperatures of 0 40 0 26 c salinities of 34 70 34 69 and potential density values of 46 05 46 07 sigma 4 the third assemblage is dominated by nuttallides umbonifera ehrenbergina trigona and secondarily by oridorsalis umbonatus and pullenia bulloides the n umbonifera e trigona assemblage is present form 2770 to 3120 m on the islas orcadas rise this assemblage is associated with potential temperatures of 0 36 0 14 c salinities of 34 69 34 68 and potential density values of 46 06 46 09 sigma 4 although the u peregrina assemblage and the n umbonifera e trigona assemblage overlap bathymetrically they are present in waters of slightly different properties the bulimina aculeata assemblage is within the core of the lower circumpolar deep water lcdw while the other two assemblages occur within transition zones between the lcdw and weddell sea deep water wsdw the difference in the benthic foraminiferal assemblages at similar depths on the islas orcadas rise and the maurice ewing bank is the result of different water mass regimes separated by the polar front

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

late glacial holocene paleoclimatic and paleoceanographic evolution of the aegean sea micropaleontological and stable isotopic evidence abstract late glacial to holocene paleoclimatic and paleoceanographic changes are examined using records of calcareous and organic walled marine microfossils pollen and terrestrial spores and oxygen isotope data in cores from the aegean sea basins planktic foraminiferal coccolith and dinoflagellate data show that the late glacial holocene transition in the region was associated with a large warming of surface water mediterranean based paleotransfer functions for planktic foraminifera show a 5 10 c increase in surface water temperature from 14 000 to 9600 yr b p estimates of surface water oxygen isotopic composition 18 o w derived from planktic foraminiferal oxygen isotopic and transfer function data indicate that this warming was associated with a 2 0 to 2 5 reduction in 18 o w transfer function results indicate corresponding 1 0 to 1 5 salinity reductions for this tim ca 6400 9600 yr b p throughout the aegean sea pollen dinoflagellate and isotopic data show that the early holocene excess fresh water originated from rapid melting of the northern european and siberian ice sheets supplied primarily from the black sea by the opening of bosphorus and dardanelles channels during the post glacial sea level rise and supplemented by major rivers entering the aegean sea continuous outflow of fresh water into the aegean sea provided a low salinity surface lid preventing the ventilation of the deep water benthic foraminifera shows a major turn over that indicates low dissolved oxygen however bottom waters were not anoxic sapropel level s1 resulted from a combination of stagnant deep water in isolated depressions increased terrigenous organic matter and periods of high primary productivity as indicated by pollen and dinocysts respectively the surface water temperature and salinity reached present day values at 6400 yr b p with little subsequent change despite the major deforestation onshore