seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

decadal changes in the south pacific western boundary current system revealed in observations and ocean state estimates observations and ocean state estimates are used to investigate the nature and mechanism of decadal variability in the east australian current eac system and south pacific subtropical gyre a 62 year record on the tasmanian continental shelf shows decadal variations of temperature and salinity as well as a long term trend which has been related to wind driven variations in the poleward extension of the eac repeat expendable bathythermograph lines spanning the last 15 years suggest that low frequency variations in the transport of the eac extension and tasman front are anticorrelated but the time series are too short to draw firm conclusions here we use two ocean state estimates spanning the past 50 years to diagnose the physical mechanisms and spatial structure of the decadal variability of the south pacific subtropical gyre the observations and state estimates paint a consistent picture of the decadal variability of the gyre and eac system strengthening of the basin wide wind stress curl drives a southward expansion of the subtropical gyre as the gyre shifts south the eac extension pathway is favored at the expense of the tasman front resulting in the observed anticorrelation of the these two major currents the results suggest that the subtropical gyre and western boundary current respond to decadal variability in basin scale wind stress curl consistent with island rule dynamics that strong decadal variability of the south pacific gyre complicates efforts to infer trends from short term records and that wind stress curl changes over the south pacific basin drive changes in the eac system that are likely to have implications for marine ecosystems and regional climate

biogeography of the lord howe rise region tasman sea abstract the two principal aims of this study were to synthesise physical and biological information to characterise the lord howe rise lhr region and to use recent survey collections of benthic invertebrates mostly large benthic epifauna to describe its biogeography at regional and sub regional scales the lhr region is large 1 95 million km2 spans tropical and cool temperate latitudes 18 4 to 40 3 s and is influenced by several ocean currents notably the east australian current and the tasman front our analyses revealed that biological patterns were related to two groups of geomorphic morphotypes found in this topographically complex region subdued bathymetric features expansive soft sediment basins and plateaus and raised bathymetric features scattered seamounts guyots knolls and pinnacles raised bathymetric features in the lhr region were more likely to support richer and more abundant epifaunal assemblages dominated by suspension feeding invertebrates on hard substrata compared to subdued features which were dominated by infauna and detritivores in soft sediments however this trend does not apply to all raised bathymetric features e g gifford guyot with variations in depth elevation latitude and particularly substrata affected the composition of biological assemblages in addition some demersal fishes ophiuroids and other benthic invertebrates showed distinct north south delineations that coincide with the influence of the tasman front and thermal gradients while the lack of spatially and temporally replicated data in the region limits our interpretation of survey data paleo environmental processes and examples from other regions provide some indication of how dispersal influences migration speciation and endemism in the lhr region although our current knowledge is limited it is hoped that this review will help inform future studies in the area as equitable examination of biological geological and oceanographic characteristics will facilitate future assessments of lhr biogeography and permit the inclusion of this region in biogeographic studies with a national or global context

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

investigations into the applicability of adaptive finite element methods to two dimensional infinite prandtl number thermal and thermochemical convection an adaptive finite element procedure is presented for improving the quality of solutions to convection dominated problems in geodynamics the method adapts the mesh automatically around regions of high solution gradient yielding enhanced resolution of the associated flow features the approach requires the coupling of an automatic mesh generator a finite element flow solver and an error estimator in this study the procedure is implemented in conjunction with the well known geodynamical finite element code conman an unstructured quadrilateral mesh generator is utilized with mesh adaptation accomplished through regeneration this regeneration employs information provided by an interpolation based local error estimator obtained from the computed solution on an existing mesh the technique is validated by solving thermal and thermochemical problems with well established benchmark solutions in a purely thermal context results illustrate that the method is highly successful improving solution accuracy while increasing computational efficiency for thermochemical simulations the same conclusions can be drawn however results also demonstrate that the grid based methods employed for simulating the compositional field are not competitive with the other methods tracer particle and marker chain currently employed in this field even at the higher spatial resolutions allowed by the adaptive grid strategies

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

aftershocks of microearthquakes as probes of the mechanics of rupture 1 using a waveform cross correlation technique rubin and gillard 2000 obtained precise relative locations for 4300 0 5 m 3 5 earthquakes occurring along 50 km of the san andreas fault this study adds to that another 5000 earthquakes distributed along 10 km of the san andreas fault and 20 km of the calaveras fault errors in relative location are typically tens of meters for earthquakes separated by hundreds of meters and after correcting for time dependent station delays meters for earthquakes separated by tens of meters along both faults the minimum separation between consecutive earthquakes scales with magnitude in a manner consistent with a magnitude independent stress drop by treating each earthquake on the san andreas as if it were a main shock scaling the distances to all subsequent earthquakes by main shock size and stacking the results a composite aftershock sequence is produced that has many of the characteristics predicted by rate and state friction models projected onto the fault surface these aftershocks outline a quasi elliptical roughly 4 mpa stress drop main shock elongate in the slip parallel direction by 40 at the ends of the major axes of this ellipse over twice as many aftershocks occur to the nw than to the se an asymmetry attributed to the contrast in material properties across the fault unlike the san andreas the calaveras fault exhibits little p wave velocity contrast and no discernible aftershock asymmetry however the earliest part of the aftershock sequence on the calaveras might be truncated by the 30 s blind time of the network following a triggering event

east australian current volume transports at 30 s estimates from the world ocean circulation experiment hydrographic sections pr11 p6 and the pcm3 current meter array between september 1991 and march 1994 the oceanic region off the east coast of australia at 30 s was the subject of an intense observational program part of the world ocean circulation experiment the objective was to improve our understanding of the dynamics of the east australian current eac and to measure its volume and energy flux the two main components were the pacific current meter array 3 pcm3 with six moorings spanning a total distance of 120 km and repeat high resolution hydrographic surveys the long term average frompcm3 shows the eac as a narrow swift and highly variable current centered at 40 km from the coast with strong shear in the upper 1000 m and mean southward velocities of 0 6 m s 1 in the core the measurements also revealed a thick countercurrent underneath the poleward flow the mean volume transport for the entire section covered by the array between the coast and 154 4 e was 22 1 4 6 sv toward the south with an rms variability of 30 sv combining the data from the pcm3 array with the hydrographic sections generated nine detailed snapshots of the absolute geostrophic current field the snapshots were used to evaluate the reliability of the pcm3 data for determining volume transports the rms difference between transports derived from direct current observations and from hydrographie data was 3 8 sv indicating that the pcm3 array can be used to describe the current variability despite the sparse spatial distribution of velocity measurements transport variability was dominated by periods between 90 and 140 days which are attributed to eddy shedding in the region occasional intense northward flow events were observed where total transports reached up to 50 sv northward on those occasions the southward boundary current changed from being surface intensified and mainly baroclinic to northward and more barotropic related to the northward migration past the array of the eac coastal separation point

sea surface temperatures of the southwest pacific ocean during the last glacial maximum the southwest pacific ocean covers a broad range of surface water conditions ranging from warm salty water in the subtropical east australian current to fresher cold water in the circumpolar current using a new database of planktonic foraminifera assemblages ausmat f2 we demonstrate that the modern analog technique can be used to accurately reconstruct the magnitude of sea surfacetemperature sst in this region we apply this technique to data from 29 deep sea cores along a meridional transect of the southwest pacific ocean to estimate the magnitude of sst cooling during the last glacial maximum we find minimal cooling in the tropics 0 2 c moderate cooling in the subtropical midlatitudes 2 6 c and maximum cooling to the southeast of new zealand 6 10 c the magnitude of cooling at the sea surface from the tropics to the temperate latitudes is found to generally be less than cooling at the surface of adjacent land masses

fluidity a fully unstructured anisotropic adaptive mesh computational modeling framework for geodynamics we present a new computational modeling framework fluidity for application to a range of two and three dimensional geodynamic problems with the focus here on mantle convection the approach centers upon a finite element discretization on unstructured simplex meshes which represent complex geometries in a straightforward manner throughout a simulation the mesh is dynamically adapted to optimize the representation of evolving solution structures the adaptive algorithm makes use of anisotropic measures of solution complexity to vary resolution and allow long thin elements to align with features such as boundary layers the modeling framework presented differs from the majority of current mantle convection codes which are typically based upon fixed structured grids this necessitates a thorough and detailed validation which is a focus of this paper benchmark comparisons are undertaken with a range of two and three dimensional isoviscous and variable viscosity cases in addition model predictions are compared to experimental results such comparisons highlight not only the robustness and accuracy of fluidity but also the advantages of anisotropic adaptive unstructured meshes significantly reducing computational requirements when compared to a fixed mesh simulation

delineation of large localized damage structures forming ahead of an active mining front by using advanced acoustic emission mapping techniques abstract we applied advanced mapping techniques to 291 230 acoustic emission ae events as small as around m 4 that were recorded over 50 days by an ultra high resolution network close to the active front of a tabular mining stope being advanced northward at 1 km depth in the cooke 4 gold mine in south africa we first applied joint hypocenter determination jhd to improve absolute locations and then applied the double difference relative location algorithm to the jhd output these steps resolved the seemingly continuous dense cloud of aes that extend about 20 m ahead of the stope front into several discrete steeply dipping tabular clusters a few meters thick and 10 30 m in dip extent separated by quiet intervals a few meters thick the clusters have a strike parallel to the stope face and a dip of about 65 resembling commonly observed large shear fractures along the plane of maximum shear ortlepp shears in general the activity of the clusters changed in similar ways as the stope face advanced but each cluster remained stationary and the gaps between clusters were impressively quiet this study demonstrates that high resolution ae mapping can delineate the formation of large structures of localized damage in the highly stressed intact rock mass ahead of the stope face a process that may culminate in hazardous seismic events

emergence and disappearance of very small repeating earthquakes on a geological fault in a gold mine in south africa abstract we investigated the activities of very small 5 10 mw 2 35 repeating earthquakes that occurred during 14 months on a geological fault at a 1 km depth in the cooke 4 gold mine in south africa out of 4214 acoustic emissions occurring on the fault 1785 42 36 of the total were identified as repeaters on the basis of the waveform similarity and the proximity of hypocenters quite a few large groups having up to 57 members were recognized activities of some groups certainly continued throughout the 14 months but we also found some repeater groups that newly emerged or disappeared during this period both types often coexisted within a distance as small as 0 5 m within which background fault creep should be coherent some disappearing groups showed a decrease in the event magnitude with time these temporal changes of repeater activities may imply the formation and dissipation of topographical asperity contacts on the fault our results suggest that ultrasensitive observation of acoustic emissions can reveal the physical evolution of asperities

seismicity in deep gold mines of south africa implications for tectonic earthquakes we have studied induced seismicity associated with five deep gold mines located in the far west rand district republic of south africa focusing on the digital data recorded from january 1994 until february 2000 by in mine arrays of three component geophones the observed seismicity which exceeds 1 000 events per day can be divided into two kinds of events designated as types a and b type a events are tightly clustered in time and space and generally occur within 100 m of an active mining face or development tunnel their spectra are comparatively enriched in high frequencies and they have an upper moment magnitude cutoff at mmax 1 we associate these events with the fracture dominated rupture of com petent rock induced by dynamic stresses during blasting and quasi static stress per turbations from the excavation and closure of individual stopes in contrast type b events are temporally and spatially distributed throughout the active mining region they represent friction dominated slip in existing shear zones such as faults or dikes and have source scaling properties that agree well with extrapolations from tectonic earthquakes in the far west rand region type b events can have large magnitudes m 3 but they show a distinct lower magnitude cutoff at mmin 0 we interpret this cutoff in terms of a critical patch size for nucleation of shear failure and we show that the data are consistent with a rate and state dependent friction model in which the critical slip distance d c 10 4 m both the spectral predictions of this model and accelerograms of type b events agree that f max 200 hz

low strength of earth s uppermost mantle inferred from tri axial deformation experiments on dry olivine crystals abstract we have performed tri axial compression experiments on single crystals of san carlos olivine with various orientations at temperatures relevant for the uppermost mantle between 800 and 1090 c the experiments were carried out at a confining pressure of 300 mpa in a high resolution gas medium mechanical testing apparatus at various constant strain rates from 7 10 6 s 1 to 1 10 4 s 1 they yield differential stresses ranging from 88 to 754 mpa unpolarized infrared spectroscopy analyses indicate that hydrogen concentration in the olivine lattice is very low e 1 0 2 10 6 exp 450 60 10 3 rt 1 15 4 1 2 2 where t is the absolute temperature r is the gas constant and is the differential stress in gpa subsequently small fractions of melt or incorporation of hydrogen in olivine may not be required to reconcile natural observations indicating a limited strength of earth s uppermost mantle lithosphere

southward shifting of the tasman front at 4 4 ma early pliocene paleobiogeographic and oxygen isotopic evidence abstract the tasman front represents a thermal boundary across the north tasman sea located between 31 s and 35 s over the tasman sea ridge system in the south west pacific census data of planktic foraminiferal assemblages and oxygen isotopic variations of planktic and benthic foraminifera obtained from three dsdp sites 284 590a and 588 were used to investigate the pliocene history of the tasman front the results indicate that at about 4 4 ma the tasman front shifted to the south of 31 s as reflected by a major change in the biogeographic distribution of planktic foraminifera this change caused warming of the sea surface particularly in the area of dsdp site 590a temperature gradients between surface water and intermediate water indicated by 18 o planktic benthic at dsdp590a also increased suggesting that the site has been subsequently located beneath a more vertically stratified water column than prior to 4 4 ma the southward shifting of the tasman front might have been a response to the intensification of the east australian current and the enlargement of the west pacific warm pool in the western equatorial pacific both of these oceanographic developments may have been caused by the curtailing of the westerly flowing south equatorial current due to tectonic closure of the new guinea seaway involving northward motion of the australian plate and an associated pliocene orogeny in central new guinea

fluid induced earthquakes with variable stress drop the static stress drop of an earthquake which quantifies the ratio of seismic slip to the size of the rupture is almost constant over several orders of magnitudes although variations are often observed it is difficult however to attribute these variations either to a well defined phenomenon or simply to measurement uncertainty in this study we analyze the static stress drop of earthquakes that occurred during a water circulation test in the soultz sous forets france geothermal reservoir in 2010 during this circulation test 411 earthquakes were recorded the largest event having a magnitude md2 3 we show that several earthquakes in the reservoir can be combined into groups of closely located similar repeating waveforms we infer that the amplitudes and hence magnitudes vary between the repeaters although the waveforms and spectra are both similar in shape we measure similar corner frequencies for these events despite their different magnitudes suggesting a similar rupture size our results imply that events at the same location may exhibit stress drop variations by as much as a factor of 300 we interpret that this variation in stress drop is caused by fluid pressure at the interface reducing the normal stress we also hypothesize that the observed variations reflect a transition from stable to unstable slip on the imaged asperities

in situ monitoring and 3d geomechanical numerical modelling to evaluate seismic and aseismic rock deformation in response to deep mining abstract in this work we investigated seismic and aseismic rock mass behaviors in response to deep underground mining for this purpose an area under production of the metal mine of garpenberg sweden was instrumented with a geophysical and geotechnical monitoring network in situ monitoring data were analyzed and interpreted considering mining operations and the local geological setting in addition a 3d elasto plastic numerical model was built to better understand the interactions between quasi static stress changes due to mining and the generation of the induced seismicity results of this multiparameter approach show a complex rock mass response we observed two main types of seismic behaviors one local and temporally short directly induced by production the other long lasting over time and remote from excavations being mainly controlled by geological heterogeneities in addition to seismicity we also observed creep like phenomena induced by mining in turn these time dependent strains appear to be a third mechanism driving seismicity all these findings underline the importance of considering both seismic and aseismic deformations when one wants to characterize the rock mass response to mining this significantly enhances our understanding of the phenomena involved as well as their interactions for an improved hazard assessment in deep mining operations

the tasman front a study using satellite infrared imagery abstract monthly charts of the approximately zonal tasman front between the australian coast near 152 e and 164 e and between latitudes 31 to 37 s have been constructed from infrared satellite imagery for 29 months from march 1982 to april 1985 from these it was found that one to three meanders but usually two are present between 152 and 164 e and that the second meander pinches off at times to form a warm core ring in the same manner as is known to occur for the first meander both second meander and ring tend to propagate westwards the mean zonal widths of the first and second meander are similar and are 3 6 to 3 7 longitude 330 345 km the average and the most likely modal positions of the tasman front were determined and the two positions are most different when the front meanders northward the zonal length scale of frontal perturbations increases eastward from 140 near 155 e to 300 km near 161 e and perturbations propagate westward at approximately 0 1 m s 1

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

the preservation of seismic anisotropy in the earth s mantle during diffusion creep summary seismic anisotropy in the earth particularly in the mantle is commonly interpreted as the result of solid state deformation by dislocation creep that induces a lattice preferred orientation lpo diffusion creep operates where stress levels are lower and or grain sizes smaller it is often assumed that diffusion creep induces grain rotations that eventually destroy any existing lpo a new numerical test of this assumption shows that it is not necessarily the case diffusion creep will create some relative grain rotations but rotation rates decrease through time hence when microstructural change due to diffusion creep dominates that due to grain growth defined here as type p behaviour the converse being type o behaviour the model indicates that lpo will be weakened but preserved for a variety of strain paths including both pure and simple shear one measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors avs a model olivine microstructure with equant grains and initial maximum avs of 10 0 percent has this value reduced to 6 7 per cent when rotational steady state is attained other models with different initial maximum avs values exhibit final maximum avs values more than half the initial values if the grains are initially elongate by a factor of 2 maximum avs is reduced just slightly to 8 5 per cent thus when grain growth plays a subordinate role to the deformation diffusion creep weakens seismic anisotropy by a factor of less than 2 using maximum avs as a measure and olivine as an example consequently the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal regions with lpo may comprise material which once deformed by dislocation creep but is now deforming by diffusion creep in a rotational steady state

south tasman sea alkenone palaeothermometry over the last four glacial interglacial cycles alkenone palaeothermometry has demonstrated a wide spatial and temporal applicability for the reconstruction of sea surface temperatures sst some oceanic realms however remain poorly studied we document u37 index data for two sediment cores retrieved from the south tasman sea one west of new zealand so136 gc3 and the other southeast of tasmania fr1 94 gc3 extending back 280 kyr bp for the former and 460 kyr bp for the latter high climatic sensitivity on orbital time scales is observed at both locations particularly west of new zealand where typical glacial interglacial sst amplitudes always span more than 7 c southeast of tasmania sst amplitudes are lower in amplitude 4 3 to 6 9 c with the exception of termination iv which involved a sst change over 8 c the evolution of maximum glacial cooling through time is different at each location offshore new zealand maximum cooling during glacial stages increases with time whereas south of tasmania maximum cooling decreases with time in addition our data suggest heterogeneity in the spatial expression of sst during the penultimate and last glacial stages these glacial periods are recorded differently in both areas with marine isotopic stage 6 being warmer than marine isotopic stage 2 west of new zealand but slightly colder southeast of tasmania the area southwest of new zealand appears susceptible to expansions and contractions of the western pacific warm pool and or meridional migrations and changes in intensity of currents associated with the tasman front the region southeast of tasmania seems more sensitive to thermal changes as seen at high southern latitudes

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

geodynamic inversion to constrain the non linear rheology of the lithosphere a common method to determine the strength of the lithosphere is through estimating its effective elastic thickness from the coherence between gravity and topography this method assumes a priori that the lithosphere is a thin elastic plate floating on a viscous mantle whereas this seems to work well with oceanic plates it has given controversial results in continental collision zones usually continental collisions zones are well studied areas for which additional geophysical datasets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex yet lithospheric geometry by itself is insufficient to understand the dynamics of the lithosphere as this also requires knowledge of the rheology of the lithosphere experimental results show significant variability between various rock types and there are large uncertainties in extrapolating laboratory values to nature which leaves room for speculation

numerical investigation of the development of the excavation damaged zone around a deep polymetallic ore mine abstract this paper deals with the development of a non linear constitutive model of a rock mass and its application to predict the extension of the excavation damaged zone edz around openings a comparison of the model results with the simulations of triaxial compression tests shows a good agreement between predictions and theoretical values of peak and residual strengths as well as a good reproduction of the transition between brittle failure and ductile response the relevance of the proposed model to evaluate the potential failure around stopes of the garpenberg mine was examined the comparison of the results proved satisfactory and highlighted the interest of considering a more realistic mechanical behavior of hard rock masses in rock engineering compared with the elastic perfectly plastic models generally used in numerical modeling of underground deep mines finally a 3d simulation of the complete mine geometry was carried out in order to model the first phases of stope mining operations the predicted stresses were compared with the continuous measurements of induced in situ stresses recorded by stress cells at different points around the stope the predictions of the proposed constitutive model provided a much better agreement with stress measurements than those obtained with elastic perfectly plastic models

coupled productivity and carbon isotope records in the southwest pacific ocean during the late miocene early pliocene biogenic bloom biogenic components of sediment accumulated at high rates beneath frontal zones of the indian and pacific oceans during the late miocene and early pliocene the 13c of bulk and foraminiferal carbonate also decreased during this time interval although the two observations may be causally linked and signify a major perturbation in global biogeochemical cycling no site beneath a frontal zone has independent records of export production and 13c on multiple carbonate phases across the critical interval of interest deep sea drilling project dsdp site 590 lies beneath the tasman front tf an eddy generating jetstream in the southwest pacific ocean to complement previous 13c records of planktic and benthic foraminifera at this location late neogene records of caco3 mass accumulation rate mar ca ti ba ti al ti and of bulk carbonate and foraminiferal 13c were constructed at site 590 the 13c records include bulk sediment bulk sediment fractions 63 m and 5 25 m and the planktic foraminifera globigerina bulloides globigerinoides sacculifer with and without sac and orbulina universa using current time scales caco3 mars ca ti al ti and ba ti ratios are two to three times higher in upper miocene and lower pliocene sediment relative to overlying and underlying units a significant decrease also occurs in all 13c records all evidence indicates that enhanced export production the biogenic bloom extended to the southwest pacific ocean between ca 9 and 3 8 ma and this phenomenon is coupled with changes in 13c the chron c3ar carbon shift however caco3 mars peak ca 5 ma whereas elemental ratios are highest ca 6 5 ma foraminiferal 13c starts to decrease ca 8 ma whereas bulk carbonate 13c begins to drop ca 5 6 ma temporal discrepancies between the records can be explained by changes in the upwelling regime at the tf perhaps signifying a link between changes in ocean atmosphere circulation change and widespread primary productivity

three types of south pacific subtropical mode waters their relation to the large scale circulation of the south pacific subtropical gyre and their temporal variability a detailed spatial distribution of south pacific subtropical mode water spstmw and its temporal variation were investigated using the world ocean atlas woa 2001 climatology and high resolution expendable bathythermograph hrx line data in the woa 2001 climatology spstmw can be classified into western and eastern parts a detailed examination of spatial distributions using hrx px06 line data revealed that the eastern part can be further divided into two types by the tasman front tf extension consequently spstmw can be classified into three types referred to in the present study as the west north and south types the west type situated in the recirculation region of the east australia current eac has a core layer temperature clt of about 19 1 c the north type in the region north of the tf extension has a clt of about 17 6 c and the south type in the region south of the tf extension has a clt of about 16 0 c the long term 6 yr variations in the inventories of the three types were dissimilar to each other the short term 6 yr and long term variations in the mean clt of the north and south types were greater than that of the west type winter cooling in the previous year may have influenced the short term variation in the south type clt moreover the strength of the eac may have influenced long term variation in the west type inventory and thickness and in the north type thickness and clt

dynamics of microseismicity and its relationship with the active structures in the western corinth rift greece we analyse the complete earthquake archive of the western corinth rift using both cross correlations between pairs of event waveforms and accurate differential traveltimes observed at common stations in order to identify small scale fault structures at depth the waveform database was generated by the dense corinth rift laboratory network and includes about 205 000 events between 2000 and 2015 half of them are accurately relocated using double difference techniques the novelty of this relocated catalogue is the integration of the recent westernmost earthquakes due to the extension of the network in 2010 to the western extremity of the corinth rift and the consideration of the whole database over more than 15 yr the total relocated seismicity exhibits well defined clusters at the root of the main normal faults mainly between 5 and 10 km depth in the middle of the gulf and illuminates thin active structure planes dipping north about 20 under the northern coast some seismicity is observed in the footwall of the main active faults along the west and east helike faults we also built a multiplet database based on waveform similarity taking into account cross correlation coefficients weighted by signal to noise ratios short term multiplets are concentrated in the middle of the gulf along the kamarai fault system in a 1 2 km thick layer at 6 8 km depth interpreted as a highly fractured geological layer they are often associated to slow seismic migration velocities occurring in this zone during strong swarm episodes and are thus likely to be triggered by pore pressure variations on the other hand most long term and regular multiplets are located deeper 7 10 km under the northern coast within a layer less than 0 3 km thick they occur at the border of nearly planar structures with low seismicity rate which we identify as fault planes and they may be explained by aseismic slip on the fault surface around them this supports the existence of an immature structure growing downdip towards the north at the base of the active geological layer which possibly connects to the ductile middle crust around 15 km depth as suggested by the occurrence of deeper events in the continuity of the 1995 fault plane the different migration velocities from 0 05 km d 1 to several km d 1 highlighted during the western 2014 swarms indicate that both pore pressure and creep diffusion are operating in the fault zone the fast migrations observed in the psathopyrgos fault zone where a slow slip event was detected by dilatometers in 2002 compare with that for creeping faults to the west from spatial distribution of events we show that the rion patras fault connecting the western extremity of the corinth rift fault system to the patras rift is dipping around 60 north west with a rake angle of 115 finally we identified two new areas within the central active zone which may correspond to large scale locked asperities on active fault surfaces similar in size to the main asperity broken during the 1995 mw 6 3 aigion earthquake

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

glacial interglacial changes in the east australian current the east australian current eac is the western boundary current of the south pacific gyre transporting warm tropical waters to higher southern latitudes recent modelling shows that the partial separation of the eac 32 s and the coupled formation of the tasman front 34 s are caused by a steep gradient in the zonally integrated wind stress curl analysis of oxygen isotope ratios 18o in the planktonic foraminifer globigerinoides ruber from sediment cores from the coral sea and tasman sea indicates that the eac separation shifted northward to between 23 and 26 s during the last glacial we suggest these results indicate a significant change in the pacific wind stress curl during the glacial given recent evidence for el nino like conditions in the pacific during the last glacial with a reduction in the east west sea surface temperature sst gradient we suggest that weaker trade winds combined with more northerly stronger westerlies were associated with a change to the wind stress curl which repositioned the eac separation and tasman front in contrast by 11 ka bp the eac separation was forced south of 26 s this southward shift was synchronous with a rapid warming of tropical ssts and the onset of a la nina like sst configuration across the tropical pacific it appears that the south pacific trade winds strengthened accordingly causing the eac to readjust its flow this readjustment of the eac marks the onset of modern surface ocean circulation in the southwest pacific but the present eac transport was only achieved in the late holocene after 5 ka bp

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

the earthquake cycle in subduction zones lithospheric plates are subducted episodically a few meters at a time during earthquakes these earthquakes recur over intervals ranging from decades to centuries within weeks to perhaps years after such an earthquake elastic stresses induced in the asthenosphere relax allowing displacement and stress to propagate away from the subduction zone into the adjacent plates finite element modelling of this process has shown that the propagation is asymmetric the subducted slab serves to buffer the subducting plate against extensive motion we have constructed a simple analytic model which incorporates the effect of he subducted slab in a fundamental way the slab s effect is modelled by a maxwell viscoelastic element which is attached to the subducting plate both plates obey elsasser s displacement propagation equations the elastic response of the maxwell element at first restrains the motion of the subducted plate the plate eventually moves on the timescale of stress relaxation in the mesosphere hundreds to thousands of years the model predicts that the trench moves toward the subducting plate at an average speed of one half of the convergence rate a strong extensional pulse is propagated into the overthrust plate shortly after the earthquake whereas the stress pulse is small in the subducting plate although this extension changes into compression before the next earthquake in the cycle the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back arc region

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

management of post mining large scale ground failures blast swarms field experiment for calibration of permanent microseismic early warning systems in france decades of coal and iron ore mining have left extensive underground cavities beneath or in the vicinity of urban areas this poses an environmental challenge for society to ensure post mining risk management and public safety wherever remediation is not possible numerous real time microseismic monitoring systems are being installed the objective is to detect remote rock mass fracturing processes precursory events and acceleration phases for appropriate and timely action although no consistent collapse has occurred in any of the monitored areas yet single 3 d probes record many microseismic events of very low amplitude which create difficulties in the quantitative data analysis the development of specific quantitative processing has therefore become a major issue in our research work for that purpose a field experiment was carried out on six of the instrumented sites it consisted of sequences of small blasts in mine pillars which were accurately controlled in terms of the location orientation and energy of the explosive source the data analysis was used to calibrate parameters velocity model 3 d sensor orientation etc for reliable 3 d localization and to develop an empirical law to estimate the source energy from the sensor energy this work now enables us to analyze real microseismic events with a considerably better level of accuracy and to obtain enough information and confidence to discuss these data in terms of site stability

evidence for coupled seismic and aseismic fault slip during water injection in the geothermal site of soultz france and implications for seismogenic transients summary we analysed the triggered seismicity recorded near 3 km in depth within granite during the 1993 water injection experiment at soultz france we selected all large multiplets associated with the largest dislocated fault identified on the borehole logging 4 3 cm slip and showed that each one consisted of the repeated rupture of a single asperity these asperities were forced to rupture due to fault creep around them so that their growing cumulative slip history reveals the creep history on the fault with a mean slip rate and a seismicity rate both decaying approximately as 1 t this is consistent with a rate strengthening friction law on the creeping faults and differs from the interpretation of omori type 1 t seismicity rates in terms of a weakening friction control of the unstable fault surfaces this model of asperity rupture forced by relaxation creep is easily generalized in seismogenic regions even for single ruptures of asperities on small creeping faults showing that a significant part of aftershock rates can be controlled by the strengthening friction properties and the creep of faults at all scales this lead us to introduce the concept of a critical asperity density above which dynamic interaction between neighbouring asperities can initiate large seismic ruptures at soultz the asperity density is subcritical but the neighbouring asperities nonetheless interact at distances up to a few source dimensions as revealed by their delayed cross triggering considering the seismic cloud in soultz at a global scale the strain produced by the injection experiment was mostly aseismic related to creep on major faults and causing large permeability changes influencing in turn the pore pressure diffusion and the creeping process our observations demonstrate that the identification and analysis of multiplets can provide accurate images of the geometry and kinematics of transient slip patches and indirectly detect pore pressure changes which should contribute to a better understanding of the coupling between transient fluid flow creep and microseismic activity in seismogenic regions

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

long lasting seismic repeaters in the central basin of the main marmara fault the main marmara fault mmf which crosses the whole marmara sea is a significant seismic gap along the north anatolian fault here we show that nine long lasting strike slip seismic repeaters exist below the central basin within the seismogenic zone in a 10 km region where deep creep was previously suggested from the analysis of the local seismicity the typical recurrence time is 8 months during the 2008 2015 period the cumulative slip of the repeating sequence appears to be compatible with the regional geodetic slip rate if they are assumed to be part of a large single asperity 10 km the repeaters also exhibit short term crises and are possibly related to bursts of creep

characteristic small earthquake sequence off sanriku northeastern honshu japan 1 we found eight similar earthquakes of m4 8 regularly occurring from 1957 to 1995 on the plate boundary off sanriku northeastern japan the mean recurrence interval of the events is 5 35 years and its standard deviation is only 0 53 years these events have the same focal mechanisms of low angle thrust fault type and their source sizes are estimated to be around 1 km the slip of each event is comparable to the cumulative amount of relative plate motion in the inter seismic period thus these events are probably caused by repeating slip at a small but strong asperity surrounded by creeping zone on the plate boundary the next event was expected to occur by the end of november 2001 with 99 probability and actually m4 7 event occurred on november 13 2001

frequency magnitude distribution of 3 7 mw 1 mining induced earthquakes around a mining front and b value invariance with post blast time we investigated frequency magnitude distribution fmd of acoustic emissions ae occurring near an active mining front in a south african gold mine using a catalog developed from an ae network which is capable of detecting aes down to m w 5 when records of blasts were removed fmds of aes obeyed a gutenberg richter law with similar b values not depending on post blasting time from the initial 1 min interval through more than 30 h this result denies a suggestion in a previous study richardson and jordan bull seismol soc am 92 1766 1782 2002 that new fractures generated by blasting disturb the size distribution of background events which they interpreted as slip events on existing weak planes our ae catalog showed that the gr law with b 1 2 was valid between m w 3 7 and 0 for aes around the mining front further using the mine s seismic catalog which covers a longer time period of the same area we could extend the validity range of the gr law with the same b value up to m w 1

multiband array detection and location of seismic sources recorded by dense seismic networks we present a new methodology for detection and space time location of seismic sources based on multiscale frequency selective coherence of the wave field recorded by dense large scale seismic networks and local antennas the method is designed to enhance coherence of the signal statistical features across the array of sensors and consists of three steps signal processing space time imaging and detection and location the first step provides for each station a simplified representation of seismic signal by extracting multiscale non stationary statistical characteristics through multiband higher order statistics or envelopes this signal processing scheme is designed to account for a priori unknown transients potentially associated with a variety of sources e g earthquakes tremors and to prepare data for a better performance in posterior steps following space time imaging is carried through 3 d spatial mapping and summation of station pair time delay estimate functions this step produces time series of 3 d spatial images representing the likelihood that each pixel makes part of a source detection and location is performed in the final step by extracting the local maxima from the 3 d spatial images we demonstrate the efficiency of the method in detecting and locating seismic sources associated with low signal to noise ratio on an example of the aftershock earthquake records from local stations of international maule aftershock deployment in central chile the performance and potential of the method to detect locate and characterize the energy release associated with possibly mixed seismic radiation from earthquakes and low frequency tectonic tremors is further tested on continuous data from southwestern japan

pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper mantle the mineral olivine dominates the composition of the earth s upper mantle and hence controls its mechanical behaviour and seismic anisotropy experiments at high temperature and moderate pressure and extensive data on naturally deformed mantle rocks have led to the conclusion that olivine at upper mantle conditions deforms essentially by dislocation creep with dominant 100 slip the resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth the rapid decrease of anisotropy below this depth has been interpreted as marking the transition from dislocation to diffusion creep in the upper mantle but new high pressure experiments suggest that dislocation creep also dominates in the lower part of the upper mantle but with a different slip direction here we show that this high pressure dislocation creep produces crystal preferred orientations resulting in extremely low seismic anisotropy consistent with seismological observations below 250 km depth these results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers both above and below

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

investigating uncertainties in empirical green s function analysis of earthquake source parameters i use a well recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical green s function egf approach the earthquakes in the largest m 2 1 repeating sequence targeted by the san andreas observatory at depth safod parkfield california are recorded by multiple borehole stations and have simple sources well constrained stress drops and abundant smaller earthquakes to use as egfs i perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings i use egf earthquakes with a range of cross correlation values and separation distances from the main earthquakes the stress drop measurements decrease by a factor of 3 as the quality of the egf assumption decreases a good egf must be located within approximately one source dimension of the large earthquake with high cross correlation i subsample the large number of measurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or egfs are available if only one measurement is available the uncertainties are likely to be at least 50 the uncertainties decrease to 20 with five or more measurements using multiple egfs is a good alternative to multiple stations to investigate the effects of limited frequency bandwidth i recalculate the corner frequencies after progressively decimating the sample rate decreasing the high frequency limit of the bandwidth decreases the estimate of the corner frequency and stress drop the corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal

modern tasman sea surface reservoir ages from deep sea black corals abstract marine reservoir ages are a key element in calculating and constraining uncertainty in radiocarbon age estimates and are also essential to better understand regional ocean circulation in this study we present a new method to reconstruct long term high resolution sea surface reservoir ages based on analysis of the organic skeleton of deep sea 560 m black coral anthozoa antipatharia our results confirm that antipatharians are extremely slow growing typical radial growth rate for a south pacific specimen around 0 03 mm yr coupled uranium series and radiocarbon measurements were made on black coral collected live from the norfolk ridge north tasman sea to provide the first modern reservoir ages for this region at the norfolk ridge the average reservoir age between 1790 ad and 1900 ad was 330 years this was followed by a steep decrease over time of about 70 years to 1950 ad our most modern value this indicates an increase in surface ocean ventilation of water masses in this region these results are consistent with observational studies for the early twentieth century which suggest significant changes in regional circulation of the southwest pacific

impact of geological heterogeneities on induced seismicity in a deep sublevel stoping mine with the aim of understanding the nature of mining induced seismicity microseismic activity in the deep metal mine of garpenberg sweden has been recorded during 2 years of excavations the studied area of the mine is operated using sublevel stoping method with backfilling between depths of around 1000 and 1300 meters spatiotemporal analysis of microseismic activity is presented and correlated with the occurrence of mining blasts a clear dependence is observed between blasts and seismic sequences even if the rock mass response to mining appears to be very variable across space and time two main clusters are observed one located in the major production area central cluster while the second right cluster is located at some distance from the excavations in a zone characterized by a heterogeneous distribution of weak materials and stiff rock masses by analyzing seismic source parameters we demonstrate that the two clusters are characterized by different dynamics in addition we show how right cluster events are mainly controlled by geological heterogeneities which impose high stress concentrations in the stiff rock masses surrounding weak lenses high apparent stresses and corner frequencies associated with the right cluster events agree with our proposed model this suggests elevated stresses in the seismic source region and small source dimensions indeed fractures cannot propagate along great distances due to the presence of weak lenses interbedded with the breaking stiff rock mass

mesoscale structure of the mean east australian current system and its relationship with topography abstract we document the mean circulation of the east australian current eac system which is the major western boundary current in the southwest pacific ocean a new high resolution climatology of the region csiro atlas of regional seas cars is used to produce regional fields of steric height and sections of geostrophic velocity the realism of these fields has been enhanced by the high spatial resolution allowance for bathymetric control and the influence of land barriers the increased detail in the maps and sections reveal the major influence that the complex regional topography has on the circulation the results also provide the appropriate resolution for comparison with recent model studies of the region we have been able to both resolve well known features with greater detail and identify previously unrecognized aspects of the circulation important results include 1 the zonal inflow north of 30 s breaks into a series of individual jets after flowing through the island chains as suggested by recent model results 2 the interaction of the zonal inflow with the local topography as it undergoes bifurcation is documented 3 a detailed picture of the evolution of the eac at the western boundary is presented including surface currents and transports 4 separation and recirculation of the eac within the tasman abyssal basin are shown to occur as a double cell structure constrained by bathymetry 5 the eac outflow is resolved as a series of eastward and northeastward currents 6 the path of the tasman front is defined as it interacts with the tasman ridge systems 7 a quasi permanent eddy is identified for the first time adjacent to the norfolk ridge northwest of new zealand

quasi static slip patch growth to 20 m on a geological fault inferred from acoustic emissions in a south african gold mine three months of acoustic emission ae monitoring in a south african gold mine down to mw 5 revealed a newly emergent planar cluster of 7557 events 3 9 mw 1 8 typical rupture radius of 6 70 cm that expanded with time to reach a size of 20 m on a preexisting geological fault near an active mining front 1 km beneath the ground it had a sharply defined planar configuration with hypocenters aggregated within a thickness of only several decimeters we infer that the zone defines an aseismic slip patch on the fault wherein the individual aes represent failures of very small asperities being loaded by the aseismic slip additional support for the interpretation was obtained by analyzing composite focal mechanisms and repeating events the patch expansion over 2 months was likely quasistatic because all individual aes ruptured much smaller areas than the cluster size at the corresponding time the b values dropped gradually from 2 6 to 1 4 consistent with a significant increase in shear stress expected of the mining style another cluster with similar characteristics emerged later on a neighboring part of the same fault and grew to a 10 m extent in the last weeks of the study period the quasi static expansion of inferred localized slow slip patches to sizes of 10 20 m suggests that the critical crack length on natural faults can be at least as large much exceeding the decimeter range derived from laboratory stick slip experiments on saw cut rocks

postseismic response of repeating aftershocks the recurrence intervals of repeating earthquakes on the san andreas fault in the loma prieta aftershock zone follow the characteristic 1 t decay of omori s law a model in which these earthquakes occur on isolated patches of the fault that fail in stick slip with creep around them can explain this observation in this model the recurrence interval is inversely proportional to the loading rate due to creep logarithmic velocity strengthening friction predicts 1 t decay in creep rate following the mainshock the time dependence of recurrence is inconsistent with a simple viscous constitutive relationship which predicts an exponential decay of loading rate thus our observations imply postseismic slip at seismogenic depth under a power law rheology the time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths

on the use of high resolution satellite data to describe the spatial and temporal variability of sea surface temperatures in the new zealand region a new high resolution 1 1 km regional data set of satellite derived sea surface temperatures sst is developed and validated against drifting and moored buoy data analysis of 5 years of monthly means and related statistics suggests that there is often a coherent relationship between the sst patterns and oceanographic features identifiable relationships are detailed then used to indicate the temporal and spatial characteristics of watermasses fronts and currents for example a gradient analysis suggests that the subtropical front east of new zealand and west of 177 w is bathymetrically locked to the southern flank of the chatham rise near 44 s beyond 177 w it loops southward to a mean position close to 47 s on the northern edge of the bounty plateau adjacent to the subantarctic front near 48 s harmonic analysis of the 60 months of data suggests that spatial variability in the amplitude of the sst annual cycle is related to circulation water mass features and varies from less than 1 c in subantarctic waters to more than 4 c in new zealand nearshore neritic waters the antarctic circumpolar east auckland and east cape currents also display coherent annual cycle amplitude signatures that differ from adjacent water masses however the amplitude of the annual cycle in subantarctic waters south of the chatham rise and north of the pukaki rise and bounty plateau is significantly different from that of this water mass at other similar latitudes an empirical orthogonal function eof analysis of seasonal anomalies shows that 90 of sst variance can be associated with the annual cycle however four eofs are required to explain 50 of the variance in sst monthly anomalies the first of these 25 4 of the variance indicates that anomalies north and east of new zealand are negatively correlated with those in the subantarctic the second eof represents a tasman sea mode and suggests that the tasman sea has been in a warming phase since december 1996 to at least april 1998 this might explain the exceptional size and sign of the sst anomaly in new zealand waters during the 1998 el nino where in february 1998 it reached 3 5 c in northern new zealand waters similar to the amplitude of the annual cycle

inferring the coseismic and postseismic stress changes caused by the 2004 mw 6 parkfield earthquake from variations of recurrence times of microearthquakes 1 kinematic models of coseismic stress inverted from ground motion data do not usually find good correlation between the location of aftershocks and high stress patches in particular numerous earthquakes are recorded in areas of the fault where the stress decreases however most of coseismic slip distributions have limited spatial resolution typically not better than 1 km here we investigate the stress changes produced by the 2004 mw 6 parkfield earthquake on and near its rupture zone at the scale of magnitude 2 earthquake asperities approximately tens of meters after relocating earthquakes in this zone between 1984 and 2007 we form repeating highly similar earthquake sequences and study how the quasiperiodicity of occurrence at each sequence observed during the 20 years preceding the 2004 main shock is perturbed by this event we apply a simple model of the seismic cycle to infer the coseismic and postseismic stresses experienced by the repeatedly failing asperities despite being spatially sparse these stress distributions have resolutions only limited by the typical scale of an asperity we propose that the high spatial variability of the seismicity patterns following the mw 6 earthquake results from an heterogeneous coseismic stress field the emergence of the omori utsu law observed at large scale greater than kilometers at parkfield is simply the outcome of averaging such quasi deterministic patterns over many sequences the fact that the coseismic stress can significantly change over distances of the order of 100 m adds credence to the hypothesis that earthquake rupture is intrinsically very heterogeneous

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

unexpectedly frequent occurrence of very small repeating earthquakes 5 1 mw 3 6 in a south african gold mine implications for monitoring intraplate faults we observed very small repeating earthquakes with 5 1 mw 3 6 on a geological fault at 1 km depth in a gold mine in south africa of the 851 acoustic emissions that occurred on the fault during the 2 month analysis period 45 were identified as repeaters on the basis of waveform similarity and relative locations they occurred steadily at the same location with similar magnitudes analogous to repeaters at plate boundaries suggesting that they are repeat ruptures of the same asperity loaded by the surrounding aseismic slip background creep application of the nadeau and johnson 1998 empirical formula nj formula which relates the amount of background creep and repeater activity and is well established for plate boundary faults to the present case yielded an impossibly large estimate of the background creep this means that the presently studied repeaters were produced more efficiently for a given amount of background creep than expected from the nj formula when combined with an independently estimated average stress drop of 16 mpa which is not particularly high it suggests that the small asperities of the presently studied repeaters had a high seismic coupling almost unity in contrast to one physical interpretation of the plate boundary repeaters the productivity of such repeaters per unit background creep is expected to increase strongly as smaller repeaters are considered mo 1 3 as opposed to mo 1 6 of the nj formula which may be usable to estimate very slow creep that may occur on intraplate faults

parameters that control lithospheric scale thermal localization on terrestrial planets 1 shear heating induced localization has been suggested as a potentially important mechanism for breaking the lithosphere yet the physical parameters that control the onset of this instability remain unclear we therefore performed systematic 2 d simulations of visco elasto plastic lithospheric deformation in which we addressed the effects of various parameters and we found that a sharp transition exists between localizing and non localizing regimes in a next step we develop a semi analytical model that combines scaling laws with a 1 d lithospheric deformation model we show that the 1 d model successfully predicts the occurrence of shear localization in 2 d models if the thickness of the plastically deforming part of the lower lithosphere is employed as characteristic length scale an application of the 1 d model to the terrestrial planets shows that this type of shear localization is expected to occur most readily on earth

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake

using thermo mechanical models of subduction to constrain effective mantle viscosity mantle convection and plate dynamics transfer and deform solid material on scales of hundreds to thousands of km however viscoplastic deformation of rocks arises from motions of defects at sub crystal scale such as vacancies or dislocations in this study results from numerical experiments of dislocation dynamics in olivine for temperatures and stresses relevant for both lithospheric and asthenospheric mantle 800 1700 k and 50 500 mpa gouriet et al 2019 are used to derive three sigmoid parameterizations erf tanh algebraic which express stress evolution as a function of temperature and strain rate the three parameterizations fit well the results of dislocation dynamics models and may be easily incorporated into geodynamical models here they are used in an upper mantle thermo mechanical model of subduction in association with diffusion creep and pseudo brittle flow laws simulations using different dislocation creep parameterizations exhibit distinct dynamics from unrealistically fast sinking slabs in the erf case to very slowly sinking slabs in the algebraic case these differences could not have been predicted a priori from comparison with experimentally determined mechanical data since they principally arise from feedbacks between slab sinking velocity temperature drag and buoyancy which are controlled by the strain rate dependence of the effective asthenosphere viscosity comparison of model predictions to geophysical observations and to upper mantle viscosity inferred from glacial isostatic adjustment shows that the tanh parameterization best fits both crystal scale and earth scale constraints however the parameterization of diffusion creep is also important for subduction bulk dynamics since it sets the viscosity of slowly deforming domains in the convecting mantle within the range of uncertainties of experimental data and most importantly of the actual rheological parameters prevailing in the upper mantle e g grain size chemistry viscosity enabling realistic mantle properties and plate dynamics may be reproduced by several combinations of parameterizations for different deformation mechanisms deriving mantle rheology cannot therefore rely solely on the extrapolation of semi empirical flow laws the present study shows that thermo mechanical models of plate and mantle dynamics can be used to constrain the effective rheology of earth s mantle in the presence of multiple deformation mechanisms