kaneohe acoustic thermometer further validated with rays over 3700 km and the demise of the idea of axially trapped energy the kaneohe acoustic source transmitted 133 hz 60 ms resolution signals over 3709 km from oahu at 183 m depth to a naval receiver at 1433 m depth near northern california ray theory successfully models the acoustic multipaths whose travel times are unambiguously tracked between 1983 89 despite the fact that the sound bounces one or more times from the oahu slope before becoming trapped in the sound channel the eigenrays are inclined at about 15 at the axis of the sound channel the upper turning depths of the eigenrays are insensitive to realistic perturbations along the section this supports the finding that the changes in delay of 0 2 s between 1983 89 are due to temperature and not due to changes in the multipaths compared with transmission through a smoothed representation of the ocean s acoustic waveguide the mesoscale and submesoscale features vertically scatter axially trapped energy about 200 and 800 m respectively the submesoscale structure may be associated with internal waves scatt

where the ocean influences the impulse response and its effect on synchronous changes of acoustic travel time in 1983 sounds at 133 hz 0 06 s resolution were transmitted in the pacific for five days at 2 min intervals over 3709 km between bottom mounted instruments maintained with atomic clocks in 1989 a technique was developed to measure changes in acoustic travel time with an accuracy of 135 microseconds at 2 min intervals for selected windows of travel time within the impulse response the data have short lived 1 to 10 ms oscillations of travel time with periods less than a few days excluding tidal effects different windows exhibited significant synchronized changes in travel time for periods shorter than 10 h in the 1980s this phenomenon was not understood because internal waves have correlation lengths of a few kilometers which are smaller than the way sound was thought to sample the ocean along well separated and distinct rays corresponding to different windows the paradox s resolution comes from modern theories that replace the ray picture with finite wavelength representations that predict sound

strain partitioning and stress perturbation around stepovers and bends of strike slip faults numerical results abstract stepovers and bends along strike slip faults are where push up ranges and pull apart basins are formed they are also commonly where fault ruptures terminate field study and analogue models suggest that the configuration of faults plays a key role in crustal deformation around bends and stepovers but the related mechanics of stress perturbation strain partitioning and fault evolution remains poorly understood here we present results of systematical mechanical models of stress changes and strain partitioning around simple stepovers and bends using three dimensional viscoelasto plastic finite element code our model predicts elevated deviatoric stress around all stepovers and bends with higher stresses around the restraining ones narrow stepovers localize strain between the fault gaps to form connecting faults whereas wide stepovers localize strain on the tips of fault segments so the stepovers may evolve into subparallel faults we explored how various configurations of stepovers and bends change the stress field and strain distribution and show that these results can help explain some key differences between the pull apart basins in the dead sea trough and death valley and the push up ranges along the san andreas fault

inversion of body wave delay times for mantle structure beneath the hawaiian islands results from the pelenet experiment abstract as an experiment to assess the nature of resolvable seismic velocity anomalies in the mantle surrounding the hawaiian islands we operated a temporary network known as pelenet consisting of seven broadband portable seismometers on the islands of kauai molokai maui and hawaii during 1995 1999 here we report the inversion of body wave delay times across the network including arrivals at the global seismic network station kip on oahu and the ocean seismic network pilot experiment south of oahu to determine the three dimensional seismic velocity structure of the upper mantle of the region the consistent feature observed in both p and s wave inversions is a low velocity anomaly beneath maui and molokai which we suggest may reflect a zone of secondary melting in the asthenosphere downstream from the hotspot locus the inversions do not resolve a cylindrical low velocity plume in the upper mantle beneath the island of hawaii but resolution tests indicate that this outcome could be the result of the sparse and nearly linear distribution of stations combined with the incomplete azimuthal coverage of earthquake sources a determination of the detailed three dimensional structure of the upper mantle beneath the hawaiian hotspot will require a simultaneous deployment of both ocean bottom and land seismometers

dynamically modeling fault step overs using various friction laws it is well known that fault step overs can under some circumstances allow through going rupture and under other circumstances cause rupture to terminate however the effects of different friction law formulations on jumping rupture have not been extensively explored in this study we use the 2 d dynamic finite element method to investigate how different frictional parameterizations affect the ability of rupture to jump a step over in both extensional and compressional settings we compare linear slip weakening friction and three forms of rate and state dependent friction the aging law slip law and slip law with strong rate weakening we have found that for friction parameterizations with the same effective slip weakening distance the functional forms of such friction laws can have a significant effect on maximum jump distance with friction laws scaled to have equivalent fracture energies we find that the functional forms of such friction laws have a second order effect on jumping rupture finally with our specific parameterizations we find that delays in rupture across the step over systems can lead to a previously unseen mode of supershear transition once the rupture renucleates on the secondary fault segment even if the initial stress field precludes such a transition studies using multiple friction laws in complex geometries such as fault step overs can lead to better understanding of the dependence of rupture properties on the type of friction law utilized in models and statistical analysis

earthquake rupture through a step over fault system an exploratory numerical study of the leech river fault southern vancouver island the leech river fault lrf zone located on southern vancouver island is a major regional seismic source we investigate potential interactions between earthquake ruptures on the lrf and the neighb

liquidus and solidus temperatures of a fe o s alloy up to the pressures of the outer core implication for the thermal structure of the earth s core abstract the solidus and liquidus temperatures of the fe75o5s20 alloy are determined up to 157 gpa using a laser heated diamond anvil cell combined with in situ x ray diffraction technique fe fcc hcp fe3s2 fe3s and feo b1 b8 rhombohedral phases are stable under subsolidus conditions first fe3s2 or fe3s phase melts at a temperature close to the eutectic point of the fe fe3s system suggesting that the alloying effect of 5 at oxygen on the eutectic temperature in the fe fe3s system is minor then feo melts at several hundreds of degrees kelvin higher than the solidus and fe is a liquidus phase in this system the liquidus temperature is 260 670 k lower than the melting temperature of pure fe because of the alloying effect of s and o on the melting temperature of fe based on our results the temperatures at the core mantle boundary tcmb and at the boundary of the inner outer core ticb are estimated to be 3600 200

geologic inheritance and earthquake rupture processes the 1905 m 8 tsetserleg bulnay strike slip earthquake sequence mongolia in 1905 14 days apart two m 8 continental strike slip earthquakes the tsetserleg and bulnay earthquakes occurred on the bulnay fault system in mongolia together they ruptured four individual faults with a total length of 676 km using submetric optical satellite images pleiades with ground resolution of 0 5 m complemented by field observation we mapped in detail the entire surface rupture associated with this earthquake sequence surface rupture along the main bulnay fault is 388 km in length striking nearly e w the rupture is formed by a series of fault segments that are 29 km long on average separated by geometric discontinuities although there is a difference of about 2 m in the average slip between the western and eastern parts of the bulnay rupture along fault slip variations are overall limited resulting in a smooth slip distribution except for local slip deficit at segment boundaries we show that damage including short branches and secondary faulting associated with the rupture propagation occurred significantly more often along the western part of the bulnay rupture while the eastern part of the rupture appears more localized and thus possibly structurally simpler eventually the difference of slip between the western and eastern parts of the rupture is attributed to this difference of rupture localization associated at first order with a lateral change in the local geology damage associated to rupture branching appears to be located asymmetrically along the extensional side of the strike slip rupture and shows a strong dependence on structural geologic inheritance

the 14 november 2001 kokoxili kunlunshan tibet earthquake rupture transfer through a large extensional step over the 14 november 2001 kokoxili tibet earthquake m w 7 8 ruptured 400 km of the western kunlun fault in northern tibet we apply two inversion methods to p and sh waves recorded by the global seismographic network to recover the spatial and temporal history of the rupture process the observed surface rupture consists of two strike slip segments offset by an extensional step over little surface rupture was observed in the graben system in this step over which is approximately 45 km long and over 10 km wide our results imply that the rupture did not jump this large gap but that the rupture was continuous through the graben the earthquake began with a small strike slip subevent presumably along the westernmost of the two segments this was followed 5 sec later by a subevent of about the same magnitude but having an oblique mechanism with a large normal faulting component the likely location for this subevent is within the graben this oblique slip event probably enabled transfer of the rupture onto the main kunlun fault the main moment release began 18 sec after rupture initiation and propagated over 350 km eastward along the kunlun fault slip on this segment was very heterogeneous averaging 2 m for the first 200 km followed by a sharp increase to a maximum of 7 5 m within the next 50 km and then a rapid decline the average rupture velocity along the main segment was high 3 6 km sec 1 and probably exceeded the local shear wave velocity the m w 7 8 kokoxili earthquake had a longer surface rupture and faster average rupture velocity radiated more energy and probably had a lower average fracture energy than the november 2002 m w 7 9 denali fault alaska earthquake evidence suggests that the velocity of the rupture front dropped significantly after passing the point of maximum slip implying a large difference in frictional strength between the two ends of the fault online material waveform fits to teleseismic body waves

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution a case study of the 2017 mw 6 5 jiuzhaigou earthquake abstract heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes we propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 mw 6 5 jiuzhaigou earthquake which occurred in the intersection area of the minjiang tazang and huya faults in sichuan province china with the slip distributed on two distinct left lateral strike slip faults as shown in previous geodetic and seismic joint inversion we use the seismic efficiency empirical relation to infer the average stress and the average stress drop is estimated using the static stress drop with the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks different principal stresses are calculated with different combinations of average stress and average stress drop the initial normal and residual stresses can be determined using the projection of the principal stresses the initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop which is generated by a set of gaussian random numbers with a given mean and the variance and mapped one by one with the given slip on the fault so that the area with a large slip has a large stress drop by comparing the slip from dynamic rupture simulations and the input joint inversion result we show that the case with a 36 mpa average stress and 2 1 mpa average stress drop provides the best fitting slip snapshots the dynamic coulomb stress change shows that the 2017 mw 6 5 jiuzhaigou earthquake could bring the southeast of the tazang fault and the middle of the minjiang fault closer to failure this work provides a new insight to understand the initial stresses of nature earthquakes

fesi melting curve up to 70 gpa abstract the melting curve of iron monosilicide fesi has been determined in a laser heated diamond anvil cell from 6 up to 70 gpa by direct visual observation of the continuous laser speckle motion in the liquid state at 12 gpa and 1700 k a discontinuous change in the slope of the melting curve indicates the first order phase transition between the fesi b20 and the cscl type fesi structures b2 during the phase transition the coordination number of both fe and si atoms increases from 7 to 8 above this pressure the melting curve rises steeply but shows significant flattening at higher pressures a comparison with the melting curve of fe shows that both curves cross at 32 3 gpa fesi having higher melting temperatures about 100 k at high pressures

electrical investigation of metal olivine systems and application to the deep interior of mercury we report electrical conductivity measurements on metal olivine systems at about 5 and 6 gpa and up to 1 675 c in order to investigate the electrical properties of core mantle boundary cmb systems electrical experiments were conducted in the multianvil apparatus using the impedance spectroscopy technique the samples are composed of one metal layer fe fes fesi2 or fe ni s si and one polycrystalline olivine layer with the metal olivine ratio ranging from 1 0 7 to 1 9 2 for all samples we observe that the bulk electrical conductivity increases with temperature from 10 2 5 to 101 8 s m which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions in some experiments a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase both the metal olivine ratio and the metal phase geometry control the electrical conductivity of the two layer samples by combining electrical results textural analyses of the samples and previous studies of the structure and composition of mercury s interior we propose an electrical profile of the deep interior of the planet that accounts for a layered cmb outer core structure the electrical model agrees with existing conductivity estimates of mercury s lower mantle and cmb using magnetic observations and thermodynamic calculations and thus supports the hypothesis of a layered cmb outermost core structure in the present day interior of mercury we propose that the layered cmb outer core structure is possibly electrically insulating which may influence the planet s structure and cooling history

an updated perspective on basin scale tomography there seems to be little doubt that pulse like acoustic transmissions at 1000 to 5000 km can be used to measure small changes in average temperature in many oceanic regions given the numerous results published by different groups the early experimental results in this field which led to these conclusions have been confirmed by recent experiments our purpose in this letter is to summarize the work in this field in the context of addressing a few reservations expressed about the early experiments

rupture propagation beyond fault discontinuities significance of fault strike and location summary earthquake rupture sometimes occurs on several faults and often decelerates or terminates at fault stepovers factors that control the rupture processes across stepovers are important for an understanding of earthquake growth and termination in this study we investigate such factors by calculating the spontaneous rupture processes of two non coplanar faults in a 3 d model dealing with two extreme models in which two strike slip faults are either parallel or perpendicular we show that the rupture processes beyond fault discontinuities are drastically different for the two models we find three factors influencing rupture processes beyond fault discontinuities depth of the upper edge of the two faults location of the edge of the first fault and geometry of the two faults these factors determine the time and location of rupture jumps to the second fault for rupture propagation to the second fault it is essential for rupture on the first fault to arrive at the edge of the fault in particular whether rupture on the first fault reaches the earth s surface or not controls the difficulty of rupture jumps and the locations where the rupture is triggered which is also related to the step direction of the two faults this is because the stress perturbation at the fault edge is affected by the earth s free surface

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

acoustic signals of underwater explosions near surfaces underwater explosions are conventionally identified and characterized by their seismic and or acoustic signature based on spherical models of explosion bubbles these models can be misleading in cases where the bubble is distorted by proximity to the free surface the bottom or to a solid object an experimental and numerical study of the effects of various nearby surfaces on the bubble s acoustic signature is presented measurements from high speed movie visualizations and acoustic signals are presented which show that the effect of proximity to a rigid surface is to increase the first period weaken the first bubble pulse and affect significantly the second period resulting in a peak value at standoffs of the same order as the maximum bubble radius these results are compared to results under a free surface over a bed of sand and over a cavity in a rigid surface in all cases the first period is increasingly lengthened or shortened as the motion of fluid around the bubble is increasingly or decrea

interdecadal variability in a numerical model of the northeast pacific ocean 1970 89 abstract variations in the thermocline depth of the northeast pacific ocean during 1970 1989 are investigated using a reduced gravity numerical model forced by the local surface wind stress and at the southern land ocean boundary by a coastal kelvin wave signal three experiments are presented with forcings by wind only kelvin wave only and a combination of both the wind forcing generates an anticyclonic gyre circulation with mostly annual variations the kelvin waves along the coast excite rossby waves that propagate into the basin interior producing changes in upper layer thickness related to changes in thermocline depth that last for years after the kelvin signal has passed two sequential upwelling kelvin waves in 1973 and 1975 produce upwelling rossby waves that reduce the mean upper layer thickness by approximately 10 20 m during 1976 this shift is reinforced by later upwelling events lasting until the early 1980s the authors present a new hypothesis that the previously known climate shift o

a decade of acoustic thermometry in the north pacific ocean 1 over the decade 1996 2006 acoustic sources located off central california 1996 1999 and north of kauai 1997 1999 2002 2006 transmitted to receivers distributed throughout the northeast and north central pacific the acoustic travel times are inherently spatially integrating which suppresses mesoscale variability and provides a precise measure of ray averaged temperature daily average travel times at 4 day intervals provide excellent temporal resolution of the large scale thermal field the interannual seasonal and shorter period variability is large with substantial changes sometimes occurring in only a few weeks linear trends estimated over the decade are small compared to the interannual variability and inconsistent from path to path with some acoustic paths warming slightly and others cooling slightly the measured travel times are compared with travel times derived from four independent estimates of the north pacific 1 climatology as represented by the world ocean atlas 2005 woa05 2 objective analysis of the upper ocean temperature field derived from satellite altimetry and in situ profiles 3 an analysis provided by the estimating the circulation and climate of the ocean project as implemented at the jet propulsion laboratory jpl ecco and 4 simulation results from a high resolution configuration of the parallel ocean program pop model the acoustic data show that woa05 is a better estimate of the time mean hydrography than either the jpl ecco or the pop estimates both of which proved incapable of reproducing the observed acoustic arrival patterns the comparisons of time series provide a stringent test of the large scale temperature variability in the models the differences are sometimes substantial indicating that acoustic thermometry data can provide significant additional constraints for numerical ocean models

measurements of gulf stream meandering and evidence of seasonal thermocline development using long range acoustic transmissions abstract phase coded signals with 60 rms resolution were transmitted twice weekly for several months from acoustic sources at 2000 m depth in the sargasso sea to three bottom mounted receives designed as west east and north stations at ranges approximately between 1000 and 2000 km the transmission paths to west and east stations were entirely in the sargasso sea the path to north station crossed the gulf stream and so traversed one of the most time and range dependent environments found anywhere in the ocean arrivals at all three stations were stable and could be identified from range dependent ray traces travel times at west station clearly change is response to the warming of the seasonal thermocline from spring to summer the travel time change with predictions travel time changes at north station primarily respond to the north south meandering of the gulf stream

thermohaline variability in the upper ocean the main goal of this exploratory study is to determine how the temperature salinity relationship changes with horizontal length scale and depth in the ocean temperature and salinity were measured on a range of scales from 4 m to 1000 km towing a seasoar along isobars and isopycnals in the subtropical gyre of the north pacific during the winter of 1997 the wavelet transform technique is used to compute the horizontal density ratio and thermohaline variability as a function of scale and location measurements along an isobar in the mixed layer show that the horizontal density ratio is 1 at all scales observed that is horizontal temperature and salinity gradients tend to cancel each other in their effect on density thermohaline variability at small scales is intermittent and clusters around large scale thermohaline anomalies below the base of the mixed layer horizontal gradients of temperature are only partially opposed by salinity and the density ratio is close to 2 in the thermocline the distribution of thermohaline variability is uniform along isobars but intermittent and colocated at different scales along isopycnals density compensated variability ubiquitous in the mixed layer is reduced along deeper isopycnals compensation of horizontal temperature and salinity gradients supports recent theoretical ideas that mixing in the winter mixed layer depends on horizontal density gradients

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

u s navy sources and receivers for studying acoustic propagation and climate change in the ocean l sounds from a u s navy ssq 110a source are received at high signal to noise ratios at ocean basin scales at two sound surveillance systems in the pacific the sounds have sufficient pulse resolution to study climatic variations of temperature the acoustic data can be understood using ray and parabolic approximations to the wave equation modeled internal waves decrease pulse resolution from 0 01 to 0 1 s consistent with observations

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

mgsio3 phase boundaries measured in the laser heated diamond cell abstract new data on phase equilibria in the mgsio3 system relevant to the stability of mg si perovskite perovskite are obtained in the laser heated diamond cell using improved techniques for accurate pressure measurement and novel heating techniques eliminating temperature gradients the data of the mgsio3 ilmenite akimotoite perovskite phase boundary measured in the range of 19 25 5 gpa and 1800 2350 k are consistent with the pressure and temperature conditions generally assumed at 660 km depth and agree within the experimental uncertainties with earlier multi anvil quench experiments the triple point wadsleyite stishovite akimotoite perovskite is at 21 gpa and 2300 k the slope of the akimotoite perovskite boundary is not well constrained by reversal experiments alone due to large hysteresis but results using glass starting materials yield a value of 0 004 0 002 gpa k the slopes of the phase transitions to mg si perovskite in both olivine and pyroxene systems are less negative than those required to cause layering in mantle convection at the pressure of the 660 km seismic discontinuity 23 8 gpa the phase boundary between akimotoite and perovskite yields a slightly lower temperature than that of the ringwoodite to perovskite periclase transition in the mg2sio4 system 1900 100 k garnet majorite is not observed above 21 gpa

a compositional origin to ultralow velocity zones we analyzed vertical component short period scp waveforms for 26 earthquakes occurring in the tonga fiji trench recorded at the alice springs array in central australia these waveforms show strong precursory and postcursory seismic arrivals consistent with ultralow velocity zone ulvz layering beneath the coral sea we used the viterbi sparse spike detection method to measure differential travel times and amplitudes of the postcursor arrival scsp and the precursor arrival spcp relative to scp we compare our measurements to a database of 340 000 synthetic seismograms finding that these data are best fit by a ulvz model with an s wave velocity reduction of 24 a p wave velocity reduction of 23 a thickness of 8 5 km and a density increase of 6 this 1 1 vs vp velocity decrease is commensurate with a ulvz compositional origin and is most consistent with highly iron enriched ferropericlase

evidence from coseismic slip gradients for dynamic control on rupture propagation and arrest through stepovers received 30 july 2008 revised 14 november 2008 accepted 18 december 2008 published 27 february 2009 1 analysis of historic slip distributions from large magnitude continental strike slip earthquake ruptures reveals a pronounced correlation between the distance over which slip decreases as a rupture approaches a structural step in the fault and the ability of the rupture to propagate through the step our analysis of coseismic slip gradients near these stepovers indicates that in earthquakes in which slip decreases gradually toward a step rupture will not continue on the next segment conversely in earthquakes in which slip decreases abruptly rupture commonly renucleates on the next segment the fact that ruptures that stopped had low slip gradients near stepovers relative to those that continued indicates that rupture dynamics control the propagation of rupture through stepovers these results corroborate dynamic rupture models that show that ruptures in which slip decreases abruptly at a step generate strong seismic waves that serve to renucleate rupture on the opposite side of the structural step there are several potential causes for gradual decrease of displacement as rupture approaches a stepover including transference of deformation onto subsidiary structures rheological contrasts that could dictate favored rupture propagation directions the existence of stress shadows from previous earthquakes within the system or other material or frictional heterogeneities all of these are potentially observable and if mapped systematically could provide the basis for a strong constraint on the likely end points of future earthquakes inasmuch as earthquake magnitude is strongly dependent on the size of the rupture such predictions would be of great utility as a basic component of scenario based earthquake rupture forecasts

phase relations in the fe fesi system at high pressures and temperatures the earth s core is comprised mostly of iron and nickel but it also contains several weight percent of one or more unknown light elements which may include silicon therefore it is important to understand the high pressure high temperature properties and behavior of alloys in the fe fesi system such as their phase diagrams we determined melting temperatures and subsolidus phase relations of fe 9 wt si and stoichiometric fesi using synchrotron x ray diffraction at high pressures and temperatures up to 200 gpa and 145 gpa respectively combining this data with that of previous studies we generated phase diagrams in pressure temperature temperature composition and pressure composition space we find the b2 crystal structure in fe 9si where previous studies reported the less ordered bcc structure and a shallower slope for the hcp b2 to fcc b2 boundary than previously reported in stoichiometric fesi we report a wide b2 b20 two phase field with complete conversion to the b2 structure at 42 gpa the minimum temperature of an fe si outer core is 4380 k based on the eutectic melting point of fe 9si and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur at the highest pressures reached onlymore the hcp and b2 structures are seen in the fe fesi system we predict that alloys containing more than 4 8 wt silicon will convert to an hcp b2 mixture and later to the hcp structure with increasing pressure and that an iron silicon alloy in the earth s inner core would most likely be a mixture of hcp and b2 phases less

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

quantitative analysis of seismicity in iran we use historical and recent major earthquakes and gps geodetic data to compute seismic strain rate geodetic slip deficit static stress drop the parameters of the magnitude frequency distribution and geodetic strain rate in the iranian plateau to identify seismically mature fault segments and regions our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle with the possibility of generating major earthquakes these faults primarily are located in the north and the east of iran four seismically mature regions in southern iran with the potential for damaging strong earthquakes are also identified we also delineate four additional fault segments in iran that can generate major earthquakes without robust clues to their maturity the most important fault segment in this study is the strike slip system near the capital city of tehran with the potential to cause more than one million fatalities

dynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in chinadynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in china

propagation of sound through a spicy ocean the sofar overture using a closely sampled 1000 km hydrographic section in the eastern north pacific the sound speed finestructure is separated into two component fields i isopyncal tilt dominated by internal waves the traditional view and ii spicy cold fresh to hot salty millifronts associated with upper ocean stirring numerical transmission experiments show significant scatter within the mixed layer from the spicy fronts this scattered energy arrives near the start of the sofar sequence and is superimposed on a triplication of the channel dispersion at the transition from reflected to upper ocean refracted energy this sofar overture is totally different from the finale which has been prominent for over 50 years the critical dependence of the overture on mixed layer processes suggests a scheme for acoustically monitoring the upper oceans at surface conjugate depths 3 to 5 km offering some advantages over in situ monitoring

a test of basin scale acoustic thermometry using a large aperture vertical array at 3250 km range in the eastern north pacific ocean broadband acoustic signals were transmitted during november 1994 from a 75 hz source suspended near the depth of the sound channel axis to a 700 m long vertical receiving array approximately 3250 km distant in the eastern north pacific ocean the early part of the arrival pattern consists of raylike wave fronts that are resolvable identifiable and stable the later part of the arrival pattern does not contain identifiable raylike arrivals due to scattering from internal wave induced sound speed fluctuations the observed ray travel times differ from ray predictions based on the sound speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates suggesting that the equation used to compute sound speed requires refinement the range averaged ocean sound speed can be determined with an uncertainty of about 0 05 m s from the observed ray travel times together with the time at which the near axial acoustic reception ends used as a surroga

melting temperature of the earth s mantle and core earth s thermal structure abstract although the temperature at the top of the lower mantle is well constrained by phase equilibrium data for the transformation of transition zone minerals to the denser perovskite polymorphs the temperature distribution in the lower mantle is poorly known models depend strongly on the assumptions of the amount of internal heating and the viscosity profile new melting data on iron to pressures of the outer core 2 mbar and the observed strong decrease of eutectic melting depression in the fe feo fes system with increasing pressure however tightly constrain the temperature at the inner core boundary to slightly less than 5000 k this estimate can be reconciled with all recent static melting measurements on iron and lays within the uncertainty of shock temperature measurements the resulting temperature at the core mantle boundary of about 4000 k then requires a large temperature gradient at the bottom of the lower mantle of about 1500 k recent findings of the very high melting temperatures o

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

dynamics of parallel strike slip faults with pore fluid pressure change and off fault damage we use a 2d finite element program to investigate how effects of time dependent pore pressure and off fault damage in the form of plastic yielding could affect earthquake rupture on parallel strike slip faults with a stepover from single fault tests we find that the positive coulomb stress pcs region at the end of the first fault controls the rupture initiation time and location on the second fault plastic deformation could significantly reduce the effective normal stress and adjust the shear stress in a specific direction resulting in a narrowband with pcs in a dilatational stepover favoring the initiation of rupture for a compressive stepover the effect of plastic deformation is less obvious and the crescent shaped pcs region triggers rupture initiation on the second fault the undrained pore pressure increases the effective normal stress in a dilatational stepover which significantly reduces the jumping ability of rupture when both undrained pore pressure and significant off fault damage are present the effect of undrained pore pressure dominates in the dilatational stepover whereas plastic deformation in the compressive stepover slightly reduces the maximum jumpable width

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

numerical simulation of spontaneous rupture processes on twonon coplanar faults the effect of geometry on fault interaction summary analyses of earthquake sources have revealed that the earthquake rupture process is complex and that the rupture does not occur on a single plane earthquake faults are often composed of several subfaults and rupture propagation tends to decelerate or terminate at places where the fault strike changes these observations imply that fault geometry including fault steps and fault strike change plays an important role in earthquake rupture complexity in this paper we calculate the spontaneous rupture processes of two non coplanar faults in 2 d in plane problems attempting to clarify the eiect of fault geometry we consider two simple modelsmodels in which two faults are either parallel or perpendicular to each other we calculate spontaneous rupture propagation on the faults bya nite diierence method andwe then compare the results in our simulations rupture initially grows on the main fault and stress perturbation from the main rupture then triggers rupture on the secondary fault propagation of the main fault rupture controls a spatio temporal pattern ofstress diierence in the uniform elastic medium which determines the rupture process of the secondary fault the rupture propagation and termination of the secondary fault are signi cantly diierent between the two models the diierence is obvious when rupture of the main fault is arrested and the secondary fault is located near the arrested end of the main fault when the secondary fault is parallel to the main fault rupture can propagate ahead on the secondary fault however when the secondary fault is perpendicular to the main fault rupture is either not triggered on the secondary fault or soon terminates if triggered this variation of the rupture process implies that fault interaction depending on geometry can explain the termination and change of rupture at places where the fault strike varies this shows the importance of the fault geometry in studying spontaneous dynamic rupture processes

dynamic models of earthquakes on the north anatolian fault zone under the sea of marmara effect of hypocenter location 1 we perform three dimensional spontaneous dynamic rupture models of potential earthquakes on the geometrically complex north anatolian fault zone nafz under the marmara sea turkey the nafz south of the city of istanbul consists of a large scale extensional stepover with right lateral strike slip segments linked by an oblique normal segment we find that earthquakes nucleating near the stepover do not propagate across the entire fault system due to the statically unfavorable stress field on the oblique fault and lead to moderate size events only however earthquakes initiating a significant distance from the stepover cause significant dynamic unclamping of the oblique fault and thus generate large through going ruptures dynamic unclamping also produces supershear rupture propagation in the vicinity of fault discontinuities the results emphasize that estimations of earthquake size rupture propagation and slip distribution cannot be decoupled from the location of the hypocenter and the orientation of the geometrically complex fault system within the tectonic stress field

supershear transition due to a free surface in 3 d simulations of spontaneous dynamic rupture on vertical strike slip faults supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments we study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike slip faults we find that locally supershear rupture near the free surface can occur due to i the generalized burridge andrews mechanism that is a supershear loading field between p and sv wave arrivals generated by the main rupture front at depths and ii the phase conversion of sv to p diffracted waves at the free surface weaker supershear slip due to the generalized burridge andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth such global supershear transition which depends on prestress can occur under prestress levels lower than the theoretical estimates for models with no free surface although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors it may play an important role on natural faults at least in those strike slip earthquakes that accumulate significant surface slip

comparison of basin scale acoustic transmissions with rays and further evidence for a structured thermal field in the northeast pacific from may to september of 1987 250 hz 16 ms resolution acoustic signals were transmitted between four sources and nine receivers in the northeast pacific this paper examines the acoustic transmissions across nine of the sections within this group with path lengths ranging from approximately 1700 to 3300 km acoustic multipaths are tracked in the data and ray theory is successfully used to identify the multipaths where the spring and summer levitus climatological databases are used to determine the sound speeds the observed multipaths arrive on the order of 1 s later than the predicted rays travel time differences greater than 0 15 s are due to temperature errors in levitus climatology within the ocean s upper 1 km the resulting corrections to levitus spring and summer oceans are 0 2 and 0 3 c respectively the upper turning depths for all rays are found to vary by less than 50 m from spring to summer variations in the measured travel times over the four month period are about 0 5 s some s

the effects of d0 on rupture propagation on fault stepovers abstract according to the slip weakening friction law andrews 1976a fault friction drops from a static value to a sliding value over some slip weakening distance d 0 laboratory studies of fault friction confirm this weakening but do not settle on a single value for d 0 however this parameter is a critical input in dynamic earthquake models as it affects rupture nucleation and propagation we use the 2d finite element method to test how the specific value of d 0 affects rupture behavior we consider the ability of rupture to jump from segment to segment of a disconnected stepover or to propagate through the double bends of a connected stepover as a way to gauge rupture energy and behavior we find the stepover width or bend angle through which rupture can propagate is affected by the choice of d 0 but it is not a linear relationship this is true regardless of whether the stepover is connected or disconnected compressional or extensional or whether the initial rupture velocity is supershear or subshear we do find however that scaling the intensity of the regional stress field up or down does linearly correspond to scaling d 0 down or up we interpret the nonlinearity of the d 0 scaling results to be related to the area of the secondary fault that intersects the lobe of failure level coulomb stress change induced by rupture of the first fault segment because 1 the d 0 controlled critical patch size for renucleation must be exceeded on the second segment and 2 the area of this overlap also does not change linearly with distance from the first fault

acoustic observations of internal wave strength in the mid pacific in 1989 and 1996 depth diffusion of acoustic energy in the finale of acoustic pulses has been observed for transmissions of 1 mm slice89 mid pacific 3 5 mm atoc california to hawaii and 5 1 mm atoc california to christmas island this depth diffusion is a measure of the strength of internal waves in the main thermocline a measure of the strength of internal waves is defined as the variance of displacement at a reference buoyancy frequency of 3 cph the standard garrett munk spectrum has a strength of 50 m2 in the case of slice89 an internal wave strength of 25 10 m2 was observed july 1989 internal wave strength will be presented for the two atoc location paths for dates beginning in november 1995 information from identifiable time fronts in the early arriving part of the pulse will also be presented work supported by onr and by the strategic environmental research and development program through arpa

coupled seismoacoustic modes on the seafloor 1 wave to wave coupling arises when an acoustic pulse selects a rayleigh mode of the same speed and both travel together swapping energy across an interface ewing et al 1957 a distinctive signal is observed at the hawaii 2 observatory for purely oceanic paths from earthquakes on the blanco and mendocino fracture zones off the coast of north america the signal appears to be a composite of undispersed higher rayleigh modes propagating along the ocean floor both in the sediments and in the water the new coupled modes are identified by their frequency composition and their phase and group velocities seismoacoustic coupling at the seafloor is conditioned on a the presence of a low velocity interface at the ocean floor and b the wavelength of the rayleigh component being shorter than the depth of the water layer

hydroacoustic ray theory based modeling of t wave propagation in the deep ocean basin offshore eastern taiwan t waves are conventionally defined as seismically generated acoustic energy propagating horizontally over long distances within the minimum sound speed layer in the ocean sofar axis minimum however t waves have also been observed by ocean bottom seismometers in ocean basins at depths greater than the sofar axis minimum previously non geometrical processes such as local scattering at rough seafloor and water sediment interface coupling have been proposed as possible mechanisms for deep seafloor detection of t waves here we employ a new t wave modeling approach based on hydroacoustic ray theory to demonstrate that seismoacoustic energy can propagate to reach deep seafloor previously considered as shadow zone of acoustic propagation our new hydroacoustic simulations explain well the observations of t waves on ocean bottom seismometers at deep ocean basins east of taiwan and shed new light on the mechanism for deep ocean t wave propagation

damage in step overs may enable large cascading earthquakes seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults cascading into a larger more devastating event while ruptures are expected to arrest at fault discontinuities larger than 4 5 km scientists are often puzzled by much larger rupture jumps here we show that material properties between faults significantly affect the ability to arrest propagating ruptures earthquake simulations accounting for fault step over zones weakened by accumulated damage provide new insights into rupture propagation revealing that lowered rigidity and material interfaces promote rupture propagation our models show for the first time that step overs as wide as 10 km may not constitute effective earthquake barriers our results call for re evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models

simulated tomographic reconstruction of ocean current profiles in a bottom limited sound channel tomographic reconstruction of the vertical current profile in a bottom limited sound channel requires solving a difficult ray identification problem an approach to deal with this problem is a ray group method in which received arrival pulses are divided into several ray groups according to the characteristics of the arrival patterns the method is validated using numerically simulated reciprocal acoustic transmission in a synthetic ocean in the luzon strait where the kuroshio current has speeds as high as 1 2 m s for both narrowband and broadband signals four ray groups are found for the synthetic data these are chosen based on arrival time the differential travel time is determined by pairing up the reciprocal arrival peaks and then averaging the differential travel times within the selected time windows compared with the narrowband case the estimated broadband differential travel time is more consistent with that computed from the current magnitude in the synthetic ocean the vertical current profile is reconstructed from the broadband differential travel times by a generalized tikhonov regularization approach the data weighting matrix includes observation error in picking and pairing travel times and model parameter error due to path length uncertainty the time series of the reconstructed current agrees with the synthetic ocean current the fractional residual variance is 0 013 for the surface layer and 0 01 for the entire water column the ray group method mitigates the ray identification problem in the bottom limited environment and could offer valuable data regarding the range integrated current velocity

study of a novel range dependent propagation effect with application to the axial injection of signals from the kaneohe source a novel range dependent propagation effect occurs when a source is placed on the seafloor in shallow water with a downward refracting sound speed profile and sound waves propagate down a slope into deep water under these conditions small grazing angle sound waves slide along the bottom downward and outward from the source until they reach the depth of the sound channel axis in deep water where they are detached from the sloping bottom and continue to propagate outward near the sound channel axis this mudslide effect is one of a few robust and predictable acoustic propagation effects that occur in range dependent ocean environments as a consequence of this effect a bottom mounted source in shallow water can inject a significant amount of acoustic energy into the axis of the deep ocean sound channel that can then propagate to very long ranges numerical simulations with a full wave range dependent acoustic model show that the kaneohe experiment had the appropriate source bathymetry and sound speed profiles that allows this effect to operate efficiently this supports the interpretation that some of the near axial acoustic signals received near the coast of california from the bottom mounted source located in shallow water in kaneohe bay oahu hawaii were injected into the sound channel of the deep pacific ocean by this mechanism numerical simulations suggest that the mudslide effect is robust

ocean acoustic tomography travel time biases the travel times of acoustic rays traced through a climatological sound speed profile are compared with travel times computed through the same profile containing an eddy field the exact travel time difference is compared with its constituent terms one of which is linearly related to the deviation of the sound speed referenced to the climatological profile and the others which are nonlinearly related to the deviation at ranges that are much greater than the eddy scale and for eddy fields whose range averaged temperature anomaly is small the numerical results are 1 the values of the nonlinear terms are insensitive to changes in the positions of the eddies and 2 the nonlinear terms are approximately proportional to the range between the source and receiver and to the square of the eddy anomaly at a 1084 km range in the east atlantic at 24 n 36 n the nonlinear terms can account for 17 90 of the exact travel time change where the temperature anomalies associated with the eddies are typicall

stepover rupture of the 2014 mw 7 0 yutian xinjiang earthquake multiple parallel strike slip faults cut through the ashikule basin xinjiang the ashikule basin was struck by an m w 7 0 earthquake on 12 february 2014 to distinguish the causative fault from these parallel faults the rupture process of the earthquake was investigated here we first jointly backprojected teleseismic p wavetrains at alaska european and australian seismic networks to obtain a rupture model next a kinematic finite fault model was derived by inverting teleseismic p waves recorded at the global seismographic network the two rupture models together show that that the earthquake first bilaterally ruptures the northwestward dipping south xiaoerkule fault and then steps over to another parallel xiaoerkule ashikule fault the fault stepover acts as a geometrical barrier during the rupture propagation the rupture at the fault stepover bursts an energy releasing peak in both high and low frequency content the high frequency sources are located at the edge of the shallow low frequency asperity which has an average stress drop of 1 4 mpa the aftershock spatial gap in the northeastern branch of the mainshock indicates that the accumulated strain energy could be all used up inferring that the earthquake has a recurrence period of 160 years electronic supplement 1 figures of waveform comparison and the synthetic test for spatial resolution 1 http www bssaonline org lookup suppl doi 10 1785 0120160099 dc1

effect of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs earthquakes can rupture geometrically complex fault systems by breaching fault step overs quantifying the likelihood of rupture jump across step overs is important to evaluate earthquake hazard and to understand the interactions between dynamic rupture and fault growth processes here we investigate the role of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs our computational and theoretical study is focused on the canonical case of two parallel strike slip faults with large aspect ratio uniform prestress and friction properties we conduct a systematic set of 3 d dynamic rupture simulations with different seismogenic depth step over distance and initial stresses we find that the maximum step over distance h c that a rupture can jump depends on seismogenic depth w and strength excess to stress drop ratio s commonly used to evaluate probable rupture velocity as h c w s n where n 2 when h c w 1 5 and n 1 otherwise the critical nucleation size largely controlled by frictional properties has a second order effect on h c rupture on the secondary fault is mainly triggered by the stopping phase emanated from the rupture end on the primary fault asymptotic analysis of the peak amplitude of stopping phases sheds light on the mechanical origin of the relations between h c w and s and leads to the scaling regime with n 1 in far field and n 2 in near field the results suggest that strike slip earthquakes on faults with large seismogenic depth or operating at high shear stresses can jump wider step overs than observed so far in continental interplate earthquakes

observations of polarized seismoacoustic t waves at and beneath the seafloor in the abyssal pacific ocean combined seismic and hydrophone observations show that the traditional t wave propagates as a seismoacoustic polarized interface wave ti coupled to the seafloor seismoacoustic ti waves propagating at the sound speed of water are routinely observed over megameter distances at the deep 4979m seafloor hawaii 2 observatory h2o between hawaii and california even though the seafloor site is within a shadow zone for acoustic wave propagation ti has also been observed on seismometers 225 km ssw of oahu at the osn1 site at the seafloor and within an odp borehole into the basalt basement analyses of timing apparent velocity energy and polarization of these interface waves are presented at low frequency 5hz ti propagates dominantly in the sediments and is consistent with higher mode rayleigh waves at higher frequencies the observed ti waves dominantly propagate acoustically with characteristics suggesting local scattering the observation of ti from an earthquake in guatemala at osn1 whose path i

scattering from the mixed layer base into the sound shadow long range sound transmissions in the ocean are largely controlled by the sofar wave guide the agreement between the measured and predicted arrival patterns is generally excellent except for an observed extension downward by many hundreds of meters from the lower caustics into the deep sound shadow the deepening of early arrivals is proposed to be associated with the sharp transition zone marking the lower boundary of the surface mixed layer this mixed layer base mlb is distorted by internal waves multiple collisions of the ray like acoustic transmission with the wavy mlb lead to a mean deepening of the lower caustics of 2 a 1 2 35m per collision where a 1 c dc dz 1 13 10 2km 1 is the fractional abyssal adiabatic sound speed gradient and 2 2 10 4 is the variance in mlb slope there are typically 20 such collisions in a 1000km transmission monte carlo numerical experiments yield statistics of ray inclination range travel time and lower turning point the resulting time front includes a dee

seismic ground motions from a bolide shock wave 1 an intensely brilliant bolide accompanied by an audible sonic boom occurred on the night of 3 november 2003 2150 lt or 4 november 2003 0350 ut in northeastern arkansas the sonic boom was well recorded by 22 three component stations of the center for earthquake research and information cooperative seismic network arrival times and wave polarizations were used to reconstruct the acoustic wave front propagating across the network and to estimate trajectory parameters of the bolide a grid search location technique constrains the trajectory and gives a reference height of 50 100 km above the southern edge of the network an azimuth of propagation of 270 290 toward the northwest and a plunge of 38 48 downward the trajectory and date of the bolide event are consistent with a taurid shower meteor transient ground motions from the sonic boom were studied using plane wave cagniard dehoop and propagator matrix theory for an incident pressure pulse impinging on a layered elastic earth model general characteristics of the vertical and radial polarization and wave frequency content require acoustic coupling within a thin 10 m near surface layer with low p wave 0 25 km s and s wave 0 125 km s velocities ground motions are generally confined to this near surface layer are not sensitive to deeper earth structure within the mississippi embayment unconsolidated sediments and display both leaky mode pl a type of dispersed p type seismic wave and locked mode rayleigh wave propagation acoustic wave ground motion coupling studies may be a useful way to analyze near surface site responses to determine velocity structure in earthquake shaking hazard studies

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

elastic parabolic equation solutions for underwater acoustic problems using seismic sources several problems of current interest involve elastic bottom range dependent ocean environments with buried or earthquake type sources specifically oceanic t wave propagation studies and interface wave related analyses additionally observed deep shadow zone arrivals are not predicted by ray theoretic methods and attempts to model them with fluid bottom parabolic equation solutions suggest that it may be necessary to account for elastic bottom interactions in order to study energy conversion between elastic and acoustic waves current elastic parabolic equation solutions must be modified to allow for seismic starting fields for underwater acoustic propagation environments two types of elastic self starter are presented an explosive type source is implemented using a compressional self starter and the resulting acoustic field is consistent with benchmark solutions a shear wave self starter is implemented and shown to generate transmission loss levels consistent with the explosive source source fields can be combined to generate starting fields for source types such as explosions earthquakes or pile driving examples demonstrate the use of source fields for shallow sources or deep ocean bottom earthquake sources where down slope conversion a known t wave generation mechanism is modeled self starters are interpreted in the context of the seismic moment tensor

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

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

influence of releasing step overs on surface fault rupture and fault segmentation examples from the 17 august 1999 izmit earthquake on the north anatolian fault turkey the 17 august 1999 izmit earthquake broke four distinct structural segments of the north anatolian fault from east to west the karadere sakarya sapanca and golcuk fault segments these segments are separated from one another and the adjoining yalova and duzce fault segments to the west and east respectively by distinct right releasing step over and or gaps in the fault trace these include from east to west the eften lake step over 2 4 km wide akyazi gap 6 13 km long sapanca step over 1 2 km wide golcuk step over 1 2 km wide and karamursel step over 4 5 km wide the earthquake nucleated within or near the golcuk step over with bilateral rupture propagation to the west and east to the west about 4 5 5 m of surface rupture up to 7 m of subsurface rupture on the golcuk segment was mostly if not entirely arrested by the 4 to 5 km wide karamursel step over to the east about 3 4 m of surface rupture about 4 m of subsurface rupture propagated through the 1 to 2 km wide sapanca step over triggering up to 4 5 5 5 m of surface rupture up to 5 6 m of subsurface rupture on the sakarya segment rupture on the sakarya segment stepped across the akyazi gap triggering 1 1 5 m of rupture on the karadere segment rupture on the karadere segment was arrested by the 2 to 4 km wide eften lake step over modeling of the transient stress field associated with the rupture propagation agrees well with the field observations the modeled fault rupture of 5 m on the golcuk segment appears to decrease the transient stress on the eastern tip of the adjoining yalova segment across the 4 to 5 km wide karamursel step over even if we allow rupture on the golcuk segment to extend along the entire southern margin of the step over our model shows that regardless of the amount of slip in a generic sense it is difficult to increase stress on the tip of an adjoining fault segment across a 5 km wide step over on the other hand fault rupture of 3 m on the western tip of the sapanca fault segment significantly increases the transient stress on the adjoining sakarya segment across the 1 to 2 km wide sapanca step over allowing rupture propagation across the basin an evaluation of 30 historical strike slip earthquakes involving 59 step over basins supports our field observations and stress modeling of the izmit fault rupture historical strike slip events with small to large displacements usually propagate through step overs less than 1 2 km wide with increasing displacement larger and larger step overs can be ruptured through the empirical data generally show a ratio ranging from 2 1 to 1 1 between step over width in kilometers and strike slip displacement in meters for a through going rupture however step overs of 4 to 5 km width appear to always arrest fault rupture regardless of the amount of displacement these results therefore provide important constraints for evaluating the probability of multisegment ruptures on segmented strike slip faults manuscript received 20 august 2000

full wave simulation of the forward scattering of sound in a structured ocean a comparison with observations the propagation of a 133 16 hz acoustic signal through the eastern north pacific ocean is simulated over basin scale ranges a high angle c0 insensitive parabolic equation model is used for the simulations the ocean environment was constructed using ctd data or climatologically averaged data from the levitus database along the geodesic from kaneohe near oahu to the receiver located 3709 km to the northeast a projection of a three dimensional frozen internal wave field is superposed the stable earlier arrivals measured from experimental data were used as a reference anchor and it is demonstrated that internal wave energy in addition to mesoscale structure is responsible for vertically scattering the late axial acoustic energy over 1 km

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000

acoustic identification of a single transmission at 3115 km from a bottom mounted source at kauai sounds received in the gulf of alaska at 3115 km from the atoc npal source at kauai 75 hz 0 027 s resolution bottom mounted are compared with acoustic and oceanographic models unlike data collected at stationary sosus arrays these data come from a towed horizontal array at 372 m depth of military origin a plausible identification of the acoustic reception is made despite the fact that only one transmission is collected and sound interacts with the bottom near the source the similarity between the modeled and measured impulse response here may be useful for understanding the signals between this same source and the npal array near southern california the plausible identification of sound from the horizontal array here appears to point toward the feasibility of using other military platforms of opportunity besides sosus to study acoustic propagation and possibly map climatic changes in temperature by means of tomography