rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

sm nd chronology and petrogenesis of mesosiderites we have obtained sm nd data from four mesosiderite silicate clasts including three clasts with a variety of textures from the vaca muerta type 1a mesosiderite and one gabbroic clast from the mt padbury mesosiderite the gabbroic vaca muerta pebble 12 and basaltic pebble 16 yield identical 147 sm 143 nd ages of 4 48 0 19 ae and 4 48 0 09 ae respectively while the highly recrystallized pebble 5 gives an age of 4 42 0 02 ae mt padbury yields an age of 4 52 0 04 ae all clasts show a correlation of 142 nd 144 nd with 147 sm 144 nd and provide unequivocal evidence for the presence of live 146 sm at the time of their formation calculated initial 146 sm 144 sm values range from 0 004 pebble 5 to 0 006 pebbles 12 16 and mt padbury and are generally consistent with the 147 sm 143 nd ages however discordance of whole rock leach and residue data and some disagreement between 146 sm 142 nd relative ages and 147 sm 143 nd absolute ages indicate small but significant disturbances to the sm nd systematics the ranges of ages and initial 146 sm 144 sm and 143 nd 144 nd values suggest that each of these silicate clasts underwent a separate protracted evolution on its parent body prior to mixing with metal textural and trace element criteria indicate that individual clasts from the same mesosiderite often had very different igneous sources and thermal histories prior to their incorporation in the meteorite pebble 12 is extremely lree depleted probably a result of several melt extraction events whereas pebbles 5 and 16 and mt padbury have nearly chondritic sm nd with bulk ree concentrations higher than chondrites by factors of 5 to 15 in general the sm nd systematics of mesosiderite silicates require formation of the silicates on a parent planet which underwent relatively early and extreme differentiation preservation of diverse old ages and the presence of 146 sm imply that metal silicate mixing did not seriously alter the sm nd isotopic memories of these clasts we present a model for metal silicate mixing which combines the cooling history with isotopic reequilibration for the case of thermal blanketing we show that the total amount of isotopic reequilibration in a sample can be related to the initial temperature depth of burial grain size and diffusion parameters application of this model to the silicate clasts measured in this study indicates that if the metal and silicate were thermally equilibrated above the metal solidus temperature during mixing then the clasts must have been buried no deeper than 1 10 m in regolith during the initial high temperature cooling phase in order to prevent the sm nd systems from being extensively reset in order to reconcile these results with the slow cooling rates at lower temperatures determined from studies of exsolution in the metal phase we infer that heat was transferred rapidly from hot metal to cold silicate material during initial metal silicate mixing and that the deeply buried portions of the mixture then cooled slowly after reaching thermal equilibrium at 600 700 c the data from this study point to the following history for the mesosiderite parent body 1 differentiation of a silicate parent body within the first 50 m y of solar system history to form diverse parent magmas 2 emplacement of primitive and differentiated mafic magmas near the planetary surface and extensive differentiation in the near surface environment 3 formation and reworking of regolith breccias through impact gardening at the near surface of the body 4 mixing of molten fe ni metal with the regolith followed by rapid cooling 100 150 m y after the origin of the solar system 5 slow cooling from temperatures of 700 c to produce the observed nickel diffusion profiles in the iron phase 6 mild impact metamorphism and brecciation to obtain the much younger k ar ages and 7 recent collisions or perturbations sending mesosiderite fragments into earth crossing trajectories

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

formation of mesosiderites by low velocity impacts as a natural consequence of planet formation mesosiderites are an enigmatic class of stony iron meteorites composed of roughly equal amounts of pyroxenitic and basaltic silicates and metallic iron nickel olivine is rare we suggest here that during the period of planet formation mesosiderites originated by the low velocity collisions of large metallic core fragments with the surface of a differentiated asteroid size body relative velocities of the asteroids native to this region were low 1 km s 1 because it was distant from massive protoplanets however a few differentiated asteroids were destroyed by high velocity collisions with interlopers perturbed by protoplanets into highly eccentric orbits these collisions reduced mantles and crusts to small silicate fragments but left cores in the form of large durable metal fragments mesosiderite like pyroxenite basalt metal mixtures were formed when large core fragments accreted at low velocities to the regolith of an intact asteroid the metal contents of other regolithic regions remained low most of the olivine in mesosiderite and howardite breccias we attribute to the mantles of the disrupted parent bodies the low 12 20 mg g 1 olivine contents indicate that the amount of debris accreted from disrupted asteroids was small relative to the volumes of the regoliths

rapid source mechanism analysis of the april 29 1993 cataract creek mw 5 3 northern arizona earthquake abstract the source mechanism of two moderate size normal faulting earthquakes located slightly south of the grand canyon in arizona are studied using several near real time seismic wave analysis procedures the events are found to have source depths near 10 to 15 km and the smaller of the two events m b 4 8 is used to provide empirical green9s functions to analyze the rupture directivity of the larger m w 5 3 mainshock these events indicate complexity in the crustal stress environment on the western margin of the colorado plateau

39ar40ar age and petrology of chico large scale impact melting on the l chondrite parent body our studies of the 105 kg chico l chondrite show that it contains 60 impact melt and the largest volume of impact melt recognized in stony meteorites we suggest that it is part of a much larger dike complex that formed when chondritic impact melt was intruded into host chondrite during a large if not catastrophic impact on the l chondrite parent body at about 0 5 ga petrologic and 39ar 40ar dating studies were made on several lithologies including the massive melt zone host chondrite and melt chondrite boundaries for the purpose of studying the melting and thermal histories associated with impacts on small bodies and their effects on the k ar chronometer the chondritic host is shocked to stage s6 and contains pockets and veins of melt there are no unmelted clasts in the interior of the melt coalesced metal troilite nodules reach up to 2 cm in size melt near the contact with the host chondrite contains numerous clasts and quenched more rapidly metal troilite textures suggest cooling rates of 0 1 c s in the interior of the melt dike during crystallization secondary kamacite rims indicate cooling at 0 01 1 c y over the range of 700 500 c consistent with an impact heated volume of up to a kilometer in thickness compositions of olivines and pyroxenes are generally similar in melt and chondritic host reflecting rapid crystallization not metamorphic equilibration the interior melt shows an overall depletion in k whereas the melt near the boundary is enriched in k the 39ar 40ar release spectra during stepwise heating of both melt and chondrite samples can be divided into two parts based on ar diffusion properties and k ca ratios the low temperature high k ca phase of both melt and host chondrite show ages of 0 54 0 78 ga ages of the high temperature low k ca phase of the melt are comparable or higher 0 61 1 35 ga whereas those of the host chondrite are even higher 0 87 1 86 ga due to lesser degrees of degassing isochron plots for several melt samples suggest an age of 0 53 ga and the presence of variable amounts of excess 40ar not completely degassed by the impact even this age however is significantly higher than the previously reported rb sr isochron age of 0 467 015 ga the apparent retention of radiogenic 40ar in the chico impact melt in spite of its relatively large size absence of clasts and moderately slow cooling rate below 700 c raises questions as to the reliability of using melts for 39ar 40ar dating of meteoritic impact events

39ar 40ar ages and thermal history of mesosiderites determinations of 39ar 40ar ages for plagioclase separates of three clasts from the vaca muerta and mount padbury mesosiderites give similar results ages increase monotonically by 0 2 0 3 ga when plotted against increasing 39ar release from the samples and give average values of 3 95 ga when combined with revised ages for mesosiderite analyses previously reported nineteen analyses of thirteen mesosiderites give an average ar ar age of 3 94 0 10 ga the average age at 90 39ar release is 4 13 0 14 ga and the ages at 10 39ar release range over 3 32 3 97 ga it seems unlikely that the 39ar 40ar ages were produced by direct impact heating but they probably are independent evidence for slow cooling deep within the mesosiderite parent body we conclude that the sloped age plateaus and the significant range in ar ar closure temperatures calculated for these mesosiderites 75 340 c are due to significant differences in ar diffusion properties among samples from the ar diffusion data we estimate an approximate mesosiderite cooling rate of 0 2 c ma which is similar to the preferred cooling rate of 0 1 0 5 c ma derived by others from ni diffusion and metal textures the 39ar 40ar ages seem incompatible with very slow cooling rates of 0 2 c ma unless the closure temperatures for ar diffusion and formation of metal cooling textures on the parent body substantially overlap any possible role of fragmentation of the mesosiderite parent body in producing the younger ar ar ages and the very slow cooling rates is unclear

determining source parameters of moderate size earthquakes from regional waveforms abstract waveform modeling of the teleseismic long period body wave phases of shallow earthquakes has proven quite effective in determining source parameters for events of magnitude larger than six unfortunately these teleseismic phases become too weak for smaller events and regional data must be used which are generally much more complicated this is because the crust mantle system acts as a leaky waveguide and a large number of rays are required to model the observations in this report we review a procedure for the systematic determination of source parameters from regional body waves a least squares inversion technique is used which is based on a cross correlation of the data and a synthetic seismogram the synthetic waveforms are a linear combination of those for the three fundamental types of fault a set of profiles of the synthetic waveforms is presented although the synthetic waveforms are generated for a model developed for the western united states this model seems to be adequate for most continental regions the inversion is parameterized in terms of fault strike dip and rake these parameters are relatively insensitive to small changes in crustal structure several examples are presented

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

thermal and shock history of mesosiderites and their large parent asteroid to elucidate the geological evolution of the mesosiderite stony iron meteorites and their 3 4 3 8 gy 40ar 39ar ages we have investigated their shock and thermal histories we have studied shock metamorphism in sixteen mesosiderites and find that none have been shocked to more than 10 gpa shock stage s1 s2 three mesosiderites contain a tiny fraction 0 1 overall of mineral fragments that were shocked to shock stage s3 s6 levels the uniformity of shock features within all fragments shows that these fragments were not shocked in situ our shock data for mesosiderites the absence of evidence of 3 6 3 9 gy impact melt the shock history of impact heated ordinary chondrites and the difficulty in quantitatively removing ar in an impact event all suggest that the mesosiderite parent body did not suffer a major impact event 3 6 3 9 gy ago metallographic cooling rates of 0 03 c my at 400 c were estimated from taenite lamellae in four mesosiderites using the latest diffusion coefficients and fe ni p phase diagram cooling rates of 0 01 c my at 425 325 c were estimated from published compositional data for kamacite grains in four mesosiderites these two techniques and four other semiquantitative metallographic cooling rate indicators show that the mesosiderites cooled slower than any iron meteorite we infer that cooling rates at 400 c were 0 02 0 03 c my and certainly less than 0 5 c my the inferred cooling rate is too slow to allow ar closure before 4 gy all of the shock thermal and age data for mesosiderites are consistent with slow cooling at depth 1 my after metal and silicate were mixed around 4 4 gy ago thermal models indicate that the mesosiderites probably cooled in an asteroid some 200 400 km in radius

seismic source characterization using a neighbourhood algorithm the full characterization of a seismic source requires the specification of the hypocentre location and the source mechanism the non linear inversion is accomplished in two stages using the neighbourhood algorithm na a direct search method in parameter space which is able to preferentially sample those regions with least data misfit there are just two control parameters and no differentiation is employed the first step is hypocentre location using a 4 d search space and a focussed search strategy the second step is waveform inversion of the early part of p and s wavetrains to refine source depth and extract the source mechanism with a moment tensor representation this second stage explores an 8 d parameter space for both the hypocentre and source mechanism inversion the na method provides rapid and effective results with information from just a few stations as illustrated with an event in southern xinjiang

analysis of the trade off between hypocentral depth and source time function focal depth determination for shallow 60 km intermediate size ms 6 5 to 7 5 earthquakes continues to be problematic for these events the depth phases i e pp and sp are not distinctly separated in time and thus synthetic modeling of wave shapes becomes necessary unfortunately the uniqueness of the solution is not easily determined because of the trade off between various focal parameters we have investigated the trade off between depth and source function both theoretically and experimentally the changes in the green s function caused by an incorrect assumed depth can almost always be compensated by changes in the source function producing the same observed seismogram thus there is considerable trade off between depth and the source function perturbing the depth from the true depth leads to a more complicated source function the simplest source function then pinpoints the true depth we have used two different measures of simplicity the varimax norm v max and the half absolute moment time t 1 2 both measures successfully characterize the complications that appear in the source functions for incorrect assumed depths the true depth of an event can be interpreted from the resultant v max versus depth and t 1 2 versus depth curves thus we have a technique that determines the depth range of faulting in a systematic quantitative fashion our observations from the synthetic study have been applied to an outer rise event off the coast of central chile 16 october 1981 ms 7 2 to an event in southern mexico 24 october 1980 ms 7 0 and to the borrego mountain event in southern california 9 april 1968 ms 6 4 resulting in faulting depth ranges of 0 to 20 5 km 60 to 70 5 km and 10 to 14 5 km respectively

inversion of far regional broadband p waves for the estimation of source parameters from shallow depth earthquakes 1 attempts in separating the earthquake source effect from complex upper mantle wave propagation effects have been unsuccessful due to band limited world wide standardized seismograph network data and limitations in the computation of accurate seismograms in this study we examine the potential for estimating source parameters using broadband p waves observed between distances of 10 and 30 we used the reflectivity method which retains all of the rays to compute synthetic green s functions from the earth flattened global ak135 and regional t7 isotropic velocity models we applied the moment tensor inversion and iterative dislocation grid search methods to estimate seismic moment moment tensor focal mechanism and focal depth for three example seismic events the 1995 m w 5 7 west texas 1999 m w 5 6 scotty s junction nevada and 1999 southern iran m w 4 8 earthquakes the west texas and scotty s junction earthquakes were well recorded and they had independently established source parameters independent estimates from different data sets and agencies were used to validate the inversion results we selected the southern iran earthquake to show the utility of the method at lower magnitudes selected vertical and radial component seismograms were windowed about the p wave arrival corrected for instrument response and converted to velocity preserving the absolute amplitudes and periods within approximately 0 5 to 100 s both inverse methods were successful in separating the source effect with the use of the ak135 velocity model the inversion results using the t7 model appear slightly biased and had worse waveform fits compared to ak135 more importantly the use of two different velocity models resulted in biases in focal depths that were less than 2 km thereby providing a robust inverse method for focal depth utilizing far regional p waves would be most useful for remote earthquakes not adequately recorded locally and too small in magnitude to be recorded beyond epicentral distances of 30 for teleseismic analysis

thermal history of mesosiderites quantitative constraints from compositional zoning and fe mg ordering in orthopyroxenes abstract we have derived mathematical relations to calculate cooling rates from the extent of compositional zoning developed during cooling across the interface of a natural diffusion couple these relations were used to calculate the high temperature cooling rates of the mesosiderites lowicz and clover springs from the available data on compositional zoning across core overgrowth interface of orthopyroxene grains we have also determined the cation ordering in four selected orthopyroxene crystals from bondoc and estherville mesosiderites with very high precision and used these data to calculate their low temperature cooling rates the compositional zoning of orthopyroxene crystals reflects extremely rapid cooling rates at least 1 c 100 years in the temperature range 850 1150 c however simultaneous consideration of both metallographic and cation ordering data for estherville within the framework of either an asymptotic or an exponential cooling model requires a cooling rate of l c ma near 250 c the cation ordering data for bondoc for which no metallographic data are yet available are suggestive of even slower cooling rate which implies excavation from a somewhat greater depth in the parent body however within the limits of their uncertainties the measured site occupancies of the orthopyroxene crystals from bondoc can be reconciled with a cooling rate similar to that of estherville the calculated cooling rates at both high and low temperatures have been used to develop a thermal evolution model of mesosiderites the suggested model is not incompatible with an asteroidal parent body for these meteorites further it is shown that the closure temperature of ar ar age must be tied to the slow cooling rate below 500 c

fast and accurate depth and source mechanism estimation using p waveform modeling a tool for special event analysis event screening and regional calibration we have developed validated and applied a fast and accurate interactive easy to use tool for estimating seismic event depth and mechanism by modeling the initial p wave bundle significant features of this tool include its applicability over a broad band of frequencies f 2 hz and magnitudes mb 4 5 its ability to provide accurate high resolution depth estimates and its ability to provide constraints on event mechanism including isotropic contributions it also provides estimates of random and model errors and can be used to test hypotheses and investigate sensitivity to and trade offs between model parameters we validated this tool and its algorithms by showing that our estimated depths and mechanisms are in excellent agreement with ground truth depths and mechanisms based on local and regional data we find that depth can usually be estimated to an accuracy of a few km with a small number of stations although complete mechanisms are sometimes poorly resolved we find that two out of three of the mechanism parameters strike dip rake are usually well constrained we illustrate the potential of this technique for regional calibration special event analysis and event screening by comparing estimated depths and mechanisms of events in the middle east and north africa with those of the national earthquake information center neic and by comparing our depth and mechanism estimates for the may 11 1998 india nuclear explosion and a november 8 1991 earthquake that occurred in the same region

focal depth estimation using pn coda phases including pp sp and pmp abstract we address a classic problem in observational seismology namely the precise estimation of the focal depth of small to moderate earthquakes the data available are three component records including pn onsets and their coda we believe that the pn coda contains p type phases that originate in the source area and lag behind due to longer travel paths phases such as pp and sp are generally not included in seismic bulletins and even cepstrum and array f k techniques have not been successful in extracting such arrivals we use recent developments in polarization analysis roberts and christoffersson 1990 fedorenko et al 2008 to extract secondary p phases in local and regional records from five earthquakes phase characteristics are typically slowness and lag time relative to the preceding pn phase however information is incomplete for confidently deciding whether an arriving wavelet should be classed as pp sp or something else this validation problem is resolved by picking several coda arrivals that can uniquely be fitted to travel time curves for suites of pn coda waves focal depth estimates even for ground truth 05 events are seldom more accurate than to 5 km and therefore we compared our results with those from moment tensor analysis differences in depth estimates were less than 5 km and for h pn arrival is generally spn the dt pn ppn lag time for shallow events is 2 0 s or less and hence difficult to detect in the coda most techniques for focal depth estimation are not user friendly in contrast the polarization schemes tested are easy to use and depth estimates are more accurate than those derived from ground truth studies based exclusively on p wave arrivals

diverse eucritic pebbles in the vaca muerta mesosiderite abstract seven 5 cm basaltic pebbles from the vaca muerta mesosiderite were analyzed by instrumental neutron activation analysis and electron microprobe three additional pebbles were only examined petrographically two pebbles are impact melt breccias four are similar texturally to main group eucrites or some clasts in polymict eucrites three are similar to cumulate eucrites and one is a fragmental breccia similar to certain polymict eucrites cumulate pebbles have extremely low ree concentrations and high eu sm ratios reflecting the virtual absence of intercumulus liquid siderophile interelement ratios in the pebbles are similar to those in vaca muerta metal except for anomalously low ir higher silica and merrillite in the pebbles relative to eucrites may reflect reduction of feo in the silicates by p from mesosiderite metal pebbles were annealed following incorporation into the vaca muerta host impacts were the dominant heat source the occurrence of 20 impact melt breccias among the pebbles and 35 40 melt breccias among mesosiderite whole rocks indicate that mesosiderites were more extensively impact melted than howardites we suggest three alternative models to account for this 1 mesosiderites were derived from a separate parent body that experienced a higher meteoroid fluence than the basaltic achondrite parent body 2 the low velocity accretion of large metallic core fragments from disrupted differentiated asteroids led to metal enrichment of a few regions of the regolith and heat retention in these mesosideritic regions and 3 mesosideritic regolith regions were less likely to be reduced to fine particles by extensive shock than howarditic regions

focal depth determination for moderate and small earthquakes by modeling regional depth phases spg spmp and spn there are three usable regional depth phases spg spmp and spn and their corresponding reference phases pg pmp and pn the differential time between each depth phase and its reference phase can be used to estimate earthquake focal depth we have developed a method to determine focal depth for moderate and small earthquakes by using a regional depth phase modeling rdpm method we used a default focal mechanism to generate the differential times for all earthquakes to estimate the reliability of the modeled focal depths we compared our solutions with those obtained by other methods and found the consistency is good because the focal depths estimated by rdpm are model dependent we tested the extent of the dependency and found that a 10 error in the crustal model may generate a 10 15 error in the modeled depth the absolute error is determined by the error in the crustal model and the focal depth itself we found that earthquake location errors have only a small effect on the modeled focal depths by analyzing synthetic and observed waveforms we found a distance window within which spmp and pmp are well developed and within the window the p portion of the waveform is relatively simple and spmp and pmp are easy to identify we also demonstrated that the assumptions of spmp and pmp are correct that regional depth phases are not developed or not discernible in some regions and that regional depth phases have special features that can be used to identify those phases

carbonate sediment production transport and supply to a coral cay at raine reef northern great barrier reef australia a facies approach abstract coral cays are low lying typically 2 mm grain size and the relative abundances of foraminifera and coral grains gravelly coral dominated sediment is concentrated at the reef margins whereas facies on and around the leeward cay are dominated by the sand size tests of benthic foraminifera mud is absent in reef sediments and reflects the prevailing high energy wave dominated setting as well as a paucity of mud producers benthic foraminifera tests are the major sediment component constituting an average proportion of 39 range 2 77 sediment derived from the skeletal remains of corals 24 1 65 mollusks 15 3 30 halimeda 14 4 36 and coralline algae 6 0 20 are present in lesser volumes foraminifera content is highest 40 on tidally emergent algal pavement where they live in greatest abundance and on the cay shorelines where their tests are deposited and comprise the bulk of beach sand 36 63 a comparison of the raine island data with other exposed modern reefs and platforms of the central and western pacific shows that occurrence and distribution of facies types is broadly consistent beyond these sedimentological data the taphonomy of foraminifera at raine island indicates that tests are vulnerable to destruction due to abrasion when transport and reworking is prolonged therefore the foraminifera rich facies adjacent to and on the cay disjunct from the source zones as well as taphonomic evidence imply that transport from the outer reef flat to the cay must be relatively quick these short temporal links between ecological source zones and depositional landforms are likely to have important ramifications for the contemporary management of reef associated landforms e g cays in the future

scardec a new technique for the rapid determination of seismic moment magnitude focal mechanism and source time functions for large earthquakes using body wave deconvolution accurate and fast magnitude determination for large shallow earthquakes is of key importance for post seismic response and tsumami alert purposes when no local real time data are available which is today the case for most subduction earthquakes the first information comes from teleseismic body waves standard body wave methods give accurate magnitudes for earthquakes up to mw 7 7 5 for larger earthquakes the analysis is more complex because of the non validity of the point source approximation and of the interaction between direct and surface reflected phases the latter effect acts as a strong high pass filter which complicates the magnitude determination we here propose an automated deconvolutive approach which does not impose any simplifying assumptions about the rupture process thus being well adapted to large earthquakes we first determine the source duration based on the length of the high frequency 1 3 hz signal content the deconvolution of synthetic double couple point source signals depending on the four earthquake parameters strike dip rake and depth from the windowed real data body wave signals including p pcp pp sh and scs waves gives the apparent source time function stf we search the optimal combination of these four parameters that respects the physical features of any stf causality positivity and stability of the seismic moment at all stations once this combination is retrieved the integration of the stfs gives directly the moment magnitude we apply this new approach referred as the scardec method to most of the major subduction earthquakes in the period 1990 2010 magnitude differences between the global centroid moment tensor cmt and the scardec method may reach 0 2 but values are found consistent if we take into account that the global cmt solutions for large shallow earthquakes suffer from a known trade off between dip and seismic moment we show by modelling long period surface waves of these events that the source parameters retrieved using the scardec method explain the observed surface waves as well as the global cmt parameters thus confirming the existing trade off for some well instrumented earthquakes our results are also supported by independent studies based on local geodetic or strong motion data this study is mainly focused on moment determination however the scardec method also informs us about the focal mechanism and source depth and can be a starting point to study systematically the complexity of the stf

lg wave cross correlation and double difference location application to the 1999 xiuyan china sequence a surprising discovery has been made that in some cases the complex highly scattered lg wave is found to be similar for clusters of events we analyze in detail a subset of 28 out of 90 events from the 1999 xiuyan sequence cross correlations provide highly accurate differential travel time measurements their error estimated from the internal consistency is about 7 msec these travel time differences are then inverted by the double difference technique to obtain epicenter estimates that have location precision on the order of 150 m the locations are computed with waveform data from four to five regional stations 500 to 1000 km away the epicenter estimates are not substantially affected by the sparseness of stations or large azimuthal gaps comparison with a surface trace a few kilometers away and location estimates based on much more dense networks led us to conclude that the absolute positions are accurate to the 5 km level regional event locations must often be based on a small number of phases and stations due to weak signal to noise ratios and sparse station coverage this is especially true for monitoring work that seeks to locate smaller magnitude seismic events with a handful of regional stations two primary advantages of using lg for detection and location are that it is commonly the largest amplitude regional wave enabling detection of smaller events and it propagates more slowly than p waves or sn resulting in smaller uncertainty in distance for a given uncertainty in travel time

an experiment in the retrieval of depth and source mechanism of large earthquakes using very long period rayleigh wave data abstract the possibility of obtaining an estimate of depth for large earthquakes from low frequency mantle wave data alone is investigated using moment tensor formalism after illustrating the sensitivity to depth of the eigenfunctions in the period range of 160 to 350 sec we give several examples of application of the two step inversion procedure proposed earlier for shorter period rayleigh wave data romanowicz 1982 we find that for earthquakes below a depth of about 50 km we are able to resolve depth even when a spherically symmetric average earth model is used for propagation corrections this is particularly interesting in the case of large subduction zone earthquakes for which an estimate of the vertical extent of faulting can thus be obtained independently of aftershock studies in a very fast and simple manner which does not involve any synthetic seismogram calculations or lateral heterogeneity modeling for shallower earthquakes especially those with one steeply dipping nodal plane the resolution of depth is less precise taking lateral heterogeneity into account by using available regionalized phase velocities improves the results marginally we anticipate that accounting more accurately for the low order harmonics in the worldwide phase velocity distribution should prove most helpful since these interfere the most with the theoretical radiation patterns of earthquakes the determination of depth depends more critically on the source process time which has to be accounted for especially for horizontally propagating faults