a geochemical multi proxy approach for anthropogenic processes in a middle upper pleistocene endokarstic deposit abstract deciphering human activities in archaeological sites is a priority issue in archaeological studies nevertheless its geochemical fingerprints on sediments are poorly known in sites belonging to the recent prehistory these geochemical signals have been taken into account but in oldest sites this subject has not been studied sufficiently the aim of this paper consists on tracking geochemical proxies that can be attributed to anthropogenic processes in endokarstic pleistocene deposits recognize these elements can be a key factor in order to explore the potential of non excavated archeological levels and find out activities performed in those sediments more accurately for that purpose a middle upper pleistocene endokarstic deposit cueva del angel belonging to the iberian peninsula has been chosen this site provides numerous evidences of human activities as butchering and cooking of predated animals or the habitual use of fire throughout its main stratigraphic sequence this geochemical archaeological approach highlights that the upper units consist of anthropogenic influenced sediments while the lower unit shows a greater percentage of geogenic inputs based on p and zn cu sr several levels with higher anthropogenic inputs have been identified these two attributes can be suggested as proxies of human activities for this site high values of p appear to be linked with butchering highly occupied levels and high levels of zn cu sr seem to be related with fires this geochemical information has been compared and tested with previous archeological information

validation and joint inversion of teleseismic waveforms for earthquake source models using deep ocean bottom pressure records a case study of the 2006 kuril megathrust earthquake the importance of accurate tsunami simulation has increased since the 2004 sumatra andaman earthquake and the indian ocean tsunami that followed it because it is an important tool for inundation mapping and potentially tsunami warning an important source of uncertainty in tsunami simulations is the source model which is often estimated from some combination of seismic geodetic or geological data a magnitude 8 3 earthquake that occurred in the kuril subduction zone on 15 november 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern pacific ocean because these recordings were unaffected by shallow complicated bathymetry near the coast this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami in this study we estimated the rupture model of the 2006 kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source the tsunami propagation was then calculated by solving the linear long wave equations we found that the simulated 2006 kuril tsunami compared very well to the ocean bottom recordings when simultaneously using p and long period surface waves in the earthquake source process inversion

teleseismic waveform complexities caused by near trench structures and their impacts on earthquake source study application to the 2015 illapel aftershocks central chile

soil variability in the area of an archaeological site near sparta greece results are analysed from a late roman site one of 20 studied in the laconia rural sites project the aim was to consider the extent to which effects of human activity at the time the site was inhabited were still evident in the soil and the exent to which these could be distinguished from natural soil variations the site has not been excavated patterns of soil properties of artefacts on the ground surface and of those encountered in the topsoil whilst sampling are analysed for a 5 m interval grid soil samples from 20 cm depth were analysed for total p pb cu zn fe mn ni ca mg k and organic c mass specific and volume magnetic susceptibility secondary crystalline and amorphous fe ph caco3 particle size distribution and colour all variables are mapped and data are further analysed using cluster regression and principal components analyses relatively high values for soil p cu pb ca organic c magnetic susceptibility and clay content and low ph and darker soil colour are associated with areas of the grid where artefact counts were highest the distinctive character of the soil in these areas reinforced by cluster and principal components analyses is attributed to a combination of inherent soil and anthropogenic effects

location of shallow subduction zone earthquakes inferred from teleseismic body waveforms this article proposes to use the teleseismic waveform of body waves to locate shallow subduction zone earthquakes when the laterally heterogeneous structure near the trench axis is incorporated in calculating synthetic body waveforms not only source depth but also horizontal distance from the source to the trench axis can be well constrained by comparing the synthetic and observed waveforms this analysis is possible because the waveforms are highly sensitive to the shift of the source position an example of this waveform method for an interplate thrust earthquake will be described and gives a well constrained and reasonable location

source parameters of some large earthquakes in northern aegean determined by body waveform inversion average source parameters for three large north aegean events are obtained from body wave inversion for the moment tensor the parameters for the events are as follows

earthquakes in the davie ridge madagascar region and the southern nubian somalian plate boundary the largest earthquake sequence mb up to 6 4 and m0 up to 5 1018 nm to have struck eastern africa within the past 60 years occurred in may and june of 1985 off the coast of the tanzania mozambique border the epicenters are located on the northern extension of the davie ridge a prominent north south trending bathymetrie feature accompanied by distinct gravity anomalies a joint hypocenter location of the 14 largest events in this sequence appears as a cluster of epicenters with no apparent lineation al teleseismic distances p and sh waves generated by the two largest events of this sequence have nearly identical waveforms on the long period records of the worldwide standard seismograph network a formal inversion of the data shows a pure normal faulting mechanism on nodal planes striking slightly west of north at least two point sources are necessary to model each event one at a depth of 40 10 km and the other at about 20 5 km on a regional scale normal faulting seems to characterize the scattered seismicity throughout the region between madagascar and the eastern arm of the east african rift zone even though oceanic lithosphere dominates part of the region and no topographic expression of a rift system can be identified since normal faulting events of up to 25 5 km deep also characterize the scattered seismicity west of the topographic expression of the western arm of the rift zone at about the same latitude we propose that the southern termination of the nubian somalian plate boundary consists of a diffuse zone of east west extension up to 2000 km wide

sourcing ceramics with portable xrf spectrometers a comparison with inaa using mimbres pottery from the american southwest seventy five intact mimbres and jornada pottery sherds from the american southwest were analyzed by portable xrf and instrumental neutron activation analysis inaa examination of the data demonstrates that inaa and portable xrf results for elements common to both analyses can be used to construct similar compositional groups when individual compositional groups are compared to one another it is apparent that unambiguous separation of compositional groups is challenging by portable xrf given 1 the limited number of key discriminating elements that can be measured relative to inaa and 2 the relative analytical precision and accuracy of portable xrf for measurements of intact heterogeneous ceramics we conclude that sourcing intact ceramics by portable xrf is challenging and that bulk analytical measurements such as inaa remain a better approach for sourcing archaeological pottery

magnetic susceptibility of soils along a lithotoposequence in southeast iran abstract magnetic susceptibility is a simple and quick technique to determine soil properties and to describe soil forming processes knowledge about factors affecting data helps better interpretation magnetic susceptibility of soils along a lithotoposequence was studied in this research in order to investigate the effects of soil forming factors parent material and relief and processes on the content and its vertical distribution the study area is a transect from jiroft to kahnooj area south kerman province iran rock pediment mantled pediment inselberg alluvial fan alluvial plain and flood plain landforms with igneous parent materials gabbro diorite and granite were selected in the area thirteen representative pedons on different geomorphic positions were studied low frequency lf values ranged from 193 1 10 8 m3 kg 1 to 2704 2 10 8 m3 kg 1 in studied soils and decreased with increasing diamagnetic material contents mean lf values in soils formed on gabbro diorite and granite parent rock were 1700 10 8 m3 kg 1 515 22 10 8 m3 kg 1 and 352 53 10 8 m3 kg 1 respectively frequency dependent of soils in the range of 0 06 to 1 05 showed that coarse multi domain grains inherited from igneous parent material were the main source of lf in the area under study both increasing and decreasing trends of lf with depth were observed decreasing trend of lf with depth was due to illuviation of diamagnetic material into subsurface layers on the other hand increasing lf with depth was attributed to the primary ferrimagnetic material inherited from igneous parent material alluvial plain 320 44 10 8 m3 kg 1 and mantled pediment 328 50 10 8 m3 kg 1 showed low values of lf due to high amounts of soluble salts anhydrite and calcium carbonate investigated in these geomorphic positions a positive significant relationship r2 0 018 r 0 27 p

intraplate seismicity and stresses in young oceanic lithosphere we have conducted a systematic study of oceanic intraplate seismicity in the period 1964 1983 occurring in lithosphere younger than 35 million years focal mechanisms determined for 26 events using first motions p wave modeling and surface wave amplitude radiation patterns along with 13 previously determined mechanisms indicate a diversity of faulting styles and stress orientations in young oceanic lithosphere there is no evidence for a worldwide transition from extension to compression at a specific lithospheric age tensional axes of normal faulting events are oriented oblique to the spreading direction and do not show extension in the spreading direction congressional axes of thrust events show a weak preferred orientation in the spreading direction presumably due to ridge push stresses however stress axes of thrust events in very young lithosphere age 9 ma do not show a correlation with the spreading direction suggesting that the ridge push force is small near the ridge these observations indicate that tensional stress in the spreading direction is concentrated in a very narrow zone at the ridge axis in agreement with models which assume that the axial region has very little tensile strength normal faulting events occur at greater depths and temperatures than thrust events possibly because rocks under tensional stress have strength maxima at higher temperatures alternatively the depths of the normal faulting events may be a result of the higher thermal gradients at depth in young lithosphere if thermoelastic stresses are important in generating this seismicity differential thermal contraction along fracture zones does not seem to be a significant source of near ridge intraplate seismicity high seismicity rates in young lithosphere noted previously on a global scale seem characteristic of all three major ocean basins additionally most of the total oceanic intraplate moment release takes place in young lithosphere however most of the events and more than 96 of the total moment release of the near ridge intraplate seismicity are contained in five areas two zones in the indian ocean one near chagos bank and the other in the amsterdam st paul region indicate tension parallel to the trend of the plate boundary a region of high seismicity near the east pacific rise between 3 and 7 n shows both normal and thrust faulting while another region on the cocos plate west of the panama fracture zone is characterized by strike slip faulting thrust strike slip and normal faulting events are found in a small seismically active zone of the south central pacific the extremely uneven distribution of seismicity if not a result of the relatively short time period studied 20 years indicates local perturbations strongly affect near ridge seismicity

transform fault earthquakes in the north atlantic source mechanisms and depth of faulting we have determined the centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern mid atlantic ridge from an inversion of long period body waveforms the earthquakes occurred on the gibbs oceanographer hayes kane 15 20 and vema transforms we have also estimated the depth extent of faulting during each earthquake from the centroid depth and the fault width for five of the transforms earthquake centroid depths lie in the range 7 10 km beneath the seafloor and the maximum depth of seismic faulting is 14 20 km on the basis of a comparison with a simple thermal model for transform faults this maximum depth of seismic behavior corresponds to a nominal temperature of 900 100 c in contrast the nominal temperature limiting the maximum depth of faulting during oceanic intraplate earthquakes with strike slip mechanisms is 700 100 c the difference in these limiting temperatures may be attributed to the different strain rates characterizing intraplate and transform fault environments three large earthquakes on the 15 20 transform have shallower centroid depths of 4 5 km and a maximum depth of seismic faulting of 10 km corresponding to a limiting temperature of 600 c the shallower extent of seismic behavior along the 15 20 transform may be related to a recent episode of extension across the transform associated with the northward migration of the triple junction among north american south american and african plates to its present position near the transform the source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes slip vector azimuths agree to within 2 3 of the local strike of the zone of active faulting the only anomalies in mechanism were for two earthquakes near the western end of the vema transform which occurred on significantly nonvertical fault planes secondary faulting occurring either precursory to or near the end of the main episode of strike slip rupture was observed for five of the 12 earthquakes for three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform in all three cases the site of secondary reverse faulting is near a compressional jog in the current trace of the active transform fault zone we find no evidence to support the conclusions of engeln wiens and stein that oceanic transform faults in general are either hotter than expected from simple thermal models or weaker than normal oceanic lithosphere

transition from interplate slip to double seismic zone along the kuril kamchatka arc during subduction the downgoing slab interacts with a strong overriding plate at shallow depths and with the surrounding asthenosphere at intermediate depths thus the transition from earthquakes representing interplate slip to those reflecting intraplate deformation within subducting lithosphere is important for understanding how the mechanics of subduction varies with depth to characterize this transition we studied 44 large to moderate sized earthquakes that occurred between 1964 and 1990 in two regions along the central portion of the kuril kamchatka arc precise earthquake source parameters are determined by analyzing body waveforms recorded at teleseismic distances at depths of 30 50 km our results delineate a transitional thrust zone characterized by earthquakes showing thrust faulting on moderately dipping nodal planes the northwesterly dipping nodal plane dips approximately 40 some 10 15 steeper than the dip of low angle earthquake faulting along the interplate thrust zone at depths shallower than 30 km for earthquakes along the transitional thrust zone secondary features in observed waveforms suggest that either a thick layer of sediments is present in the forearc region or the sources are embedded in materials with crustal seismic wave speeds in the former case the transitional thrust zone is interpreted as the deep seated portion of the plate interface whose dip increases with depth the alternative implies that the transitional thrust zone occurrs below the plate interface within subducted crust of the pacific plate and that the occurrence of earthquakes along the transitional zone may indicate a locked plate interface between depths of 30 and 50 km the inference of a locked plate interface is consistent with the occurrence of compressional earthquakes beneath the outer rise region however a locked interface does not seem to affect the state of strain in the double seismic zone the upper compressional layer of the double seismic zone abuts the transitional thrust zone at a depth of approximately 50 km at this depth the two layers of seismicity in the double seismic zone are separated by as much as 30 40 km too large a distance to be accommodated by models of seismogenesis invoking either the gabbro eclogite transition or dehydration of subducted oceanic crust

an investigation of soil phosphorus distribution within occupation deposits from a romano british hut group abstract a simple scheme for soil sampling and subsequent analysis for total soil phosphorus using perchloric acid digestion is described and its application illustrated by samples from the native farmstead of the roman period at cefn graeanog in north wales the floor deposits of three distinctive buildings were analysed and the data obtained enhanced by trend surface analysis to produce generalized maps of the phosphorus distribution together with levels of significance of such distribution patterns these were then used to clarify the details of the interpretation of the usage of the various types of building data for soil phosphorus concentration clearly reveal the pattern of erosion of constructed floors the presence of features such as hearths and drains and can be used to reveal patterns not otherwise discernible by excavation techniques

overlooked earthquakes on and around the antarctica plate identification and location of 1999 shallow depth events abstract as a contribution to the study of high latitude seismicity on the antarctica plate we have developed a procedure to identify and locate previously unnoticed earthquakes by using broadband records of 29 stations operating in the southern hemisphere a first approach of the method consists of visually examining continuous records from geoscope and gsn stations for rayleigh waves associated with earthquakes missing in the neic monthly catalogue two hundred ten earthquakes were identified that had no corresponding locations in the 1999 neic catalogue among them 88 events with magnitude ranging from 3 7 to 5 2 and identified on at least four stations have been located by using an epicenter location algorithm based on regional rayleigh wave propagation models the precision of the location depending both on the selected propagation model and the phase picking accuracy is around 100 km most of the reported earthquakes occurred on the plate boundaries principally along the south indian and pacific ridges a few epicenters have been located inside the antarctica plate far from the plate limits among them only two earthquakes occurring on the continent itself are reported about half of the events located in our study are reported by the pidc prototype international data center three earthquakes with magnitudes ranging from 4 7 to 5 2 reported neither by neic nor by pidc are sufficiently energetic to be recorded in most broad band stations operating around the world considerations concerning the local crustal structure and the physical processes at the source are involved in interpreting these observations

importance of model parameterization in finite fault inversions application to the 1974 mw 8 0 peru earthquake the spatial and temporal slip distributions for the october 3 1974 mw 8 0 peru subduction zone earthquake and its largest aftershock on november 9 ms 7 1 are calculated and analyzed in terms of the inversion parameterization and tectonic significance teleseismic long period world wide standard seismograph network p and sh waveforms are inverted to obtain the rupture histories we demonstrate that erroneous results are obtained if a parameterization is used that does not allow for a sufficiently complex source involving spatial variation in slip amplitude risetime and rupture time the inversion method utilizes a parameterization of the fault that allows for a discretized source risetime and rupture time well located aftershocks recorded on a local network have the same general pattern as teleseismically determined hypocenters and help to constrain the geometry of the subduction zone for the main shock a hinged fault is preferred having a shallow plane with a dip of 11 and a deeper landward plane with a dip of 30 the preferred nucleation depth lies between 11 and 15 km a bilateral rupture is obtained with two major concentrations of slip one 60 to 70 km to the northwest of the epicenter and a second 80 to 100 km to the south and southeast of the epicenter for these source regions risetimes vary from 6 to 18 s our estimates of risetimes are consistent with the time for the rupture to traverse the dominant local asperity the slip distribution for the november 9 aftershock falls within a conspicuous hole in the main shock rupture pattern near the hypocenter of the main shock the november 9 event has a simple risetime function with a duration of 2 s aftershocks recorded by the local network are shown to cluster near the hypocenter of the impending november 9 event and downdip from the largest main shock source region slip during the main shock is concentrated at shallow depths above 15 km and extends updip from the hypocenter to near the plate boundary at the trench axis the large amount of slip at shallow depths is attributed to the absence of any significant accretionary wedge of sediments and the relatively young age and high convergence rate of the subducted plate which results in good seismic coupling near the trench axis

focal mechanisms of large earthquakes in the north island of new zealand slip partitioning at an oblique active margin we have used body wave modelling to determine the source parameters of 22 moderate to large earthquakes that have occurred along the hikurangi subduction margin and elsewhere in the north island of new zealand since 1964 we have also included events from the harvard cmt catalogue since 1977 as that catalogue contains smaller events than can be modelled with body waves we have found that shallow earthquakes occurring in the back arc taupo volcanic zone and its extension to the north show predominantly normal faulting with nodal planes parallel to the regional fabric and t axes indicating extension in a direction in agreement with geodetic measurements a normal faulting solution for the 1974 opunake earthquake is compatible with the mapping of active faults in the offshore taranaki region and the initiation depth of 17 km is close to the expected brittle ductile transition for that area earthquakes within the subducted plate at the southwestern end of the margin are dominated by down dip tension that is rotated towards the deepest part of the subducting plate further north the events in the upper part of the wadati benioff zone 200 km show pure down dip tension while this association is less obvious for the deeper events suggesting that the aseismic part of the subducting slab inferred from plate reconstructions has reached the 670 km discontinuity normal faulting earthquakes associated with plate bending below the region of interplate contact occur along the length of the margin while shallow normal faulting events also occur in the trench indicating that some slab pull propagates to that region we infer that large interplate earthquakes are not imminent because in other similar areas they are preceded by outer rise compressional events that have not been recorded in the region in historical times slip vectors of interplate thrust earthquakes indicate that the oblique plate motion across the margin is fully partitioned that is the plate interface accommodates very little transcurrent motion which is instead accommodated by faults in the overlying australian plate extensional geodetic strain has been measured across the margin in the northeast which has been regarded as unusual in view of the plate convergence we suggest that the topography at this part of the margin is too steep to be supported by the current horizontal forces due to friction on the plate interface this may have occurred due to a reduction in friction because of the subduction of seamounts and the subsequent entrapment of sediments this also being consistent with the idea of underplating at this part of the margin or due to the subduction of less buoyant crust other margins such as japan and mid america where there is known to be subduction of sediments also show extension in the forearc compressional strain observed across the margin in the southwest is more usual for a convergent margin but it does not show the partitioning we see in focal mechanisms these data might only agree after the long term compressional strain accumulation has been averaged over a complete seismic cycle large historical and palaeo earthquakes have occurred along the length of the margin associated with deformation in both the axial and the coastal ranges in addition along the length of the margin the rate of recent interplate thrust activity is low compared to margins that have a high proportion of aseismic slip these factors indicate that the entire length of this margin is capable of producing large earthquakes

integrating geoarchaeology and magnetic susceptibility at three shell mounds a pilot study from mornington island gulf of carpentaria australia in coastal areas of the globe open shell matrix sites are commonly used to establish regional chronologies of human occupation and identify patterns of cultural change particularly for the holocene post sea level stabilisation period despite this many basic sedimentary analyses that are routinely applied to rockshelter deposits e g geophysical characterisation particle size etc are rarely applied to these sites magnetic susceptibility occasionally used in rockshelters has never been used to investigate shell matrix sites in australia despite several international studies identifying its efficacy for other types of open sites this paper reports a pilot project applying a range of conventional sedimentary and archaeological analyses as well as magnetic susceptibility at three anthropogenic shell mounds on mornington island gulf of carpentaria australia results are compared to firstly assess site integrity and secondly to ascertain whether magnetic signatures are related to cultural or natural site formation processes the results establish that the mounds were repeatedly visited despite the archaeological evidence including radiocarbon ages suggesting effectively instantaneous deposition this has important implications for studies of other shell mounds where the limitations of radiocarbon dating precision may also mask multiple deposition events

focal mechanisms of large earthquakes in the south island of new zealand implications for the accommodation of pacific australia plate motion b the plate motion model nuvel 1 predicts oblique convergence between the pacific and australian plates in the south island of new zealand we used p and sh body waveform analysis to constrain the focal mechanisms of the 15 largest earthquakes ms 5 8 that have occurred in this region since 1964 in order to see how the plate motion is accommodated at the southern end of the alpine fault convergence is achieved by oblique slip movement along a concentrated zone of deformation in the southern offshore region one event may be related to thrusting of the australian plate beneath the pacific plate and another strike slip event probably demonstrates movement on an active strike slip fault system parallel to but offset from the southern limit of the alpine fault this geometry provides a possible mechanism for the rapid uplift of the fiordland region deformation in the northern south island is more distributed in the south west marlborough region partitioning occurs between strike slip faulting in the se and reverse faulting farther nw in the buller region we suggest that the partitioning developed as a consequence of an increasing component of shortening that was accommodated by slip on reactivated pre existing normal faults in the buller region shortening in the buller region may have deflected the ne end of the alpine fault towards the nw forming the prominent bend the marlborough fault system with its youngest and most active faults to the se probably developed in an attempt to maintain a through going strike slip structure as each of the strike slip faults was transported towards the north west partitioning of the opposite polarity with reverse faulting se of the strike slip faulting occurs in north east marlborough the boundary between the two different styles of partitioning in ne and sw marlborough appears to coincide with a change in the nature of the downgoing slab and a change in strike of faults of the marlborough fault system a normal faulting earthquake on the northern edge of the chatham rise probably results from a complex interaction of the buoyant continental crust in that region with the subduction zone and the overlying marlborough fault system

intraplate seismicity of the pacific basin 1913 1988 we establish here a comprehensive database of intraplate seismicity in the pacific basin relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913 1988 these numbers do not include earthquake swarms which account for another 838 events most of the remainder 304 events are actually plate boundary earthquakes that have been erroneously located in intraplate regions a significant number occur in recent years when location capabilities should have guarded against this situation relocations involve a careful linear inversion of p and s arrivals accompanied by a monte carlo statistical analysis we have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

on isc pp and pp data and their use in delay time tomography of the caribbean region summary a major problem in p delay time tomography is the inhomogeneous sampling of mantle structure by the p wave ray paths resulting in low resolution in images of large regions of the upper mantle incorporation of pp and pp phases can improve the quality and reliability of tomographic images because they 1 sample earth structure not ordinarily sampled by direct p phases 2 add rays that are oblique to rays of direct phases which is especially important where the latter sample mantle structure in selected directions and 3 pp data better constrain the earthquake focal depths pp traveltimes have often been used in combination with p data in differential traveltime studies we show that the assumptions and approximations necessary for this approach are problematic and that they can be avoided when the p pp and p data are used in tomographic inversion we investigated the applicability of pp and pp delay times to the tomographic study of the aspherical mantle structure below the caribbean region the success of the application of data of the later arriving reflected waves depends critically on the quality of these data we examined possible sources of error in the isc pp and pp data and assessed the contribution to the delay times used in this study for the caribbean region analyses of the isc pp and pp delay times do not reveal biases due to effects of pp waveform distortions the asymmetry of the reflections or due to misidentifications of phases that reflect at a surface other than that assumed the noise level of pp and pp data is high with respect to data of the direct p wave this is accommodated by weighting with the inverse of the variance of the data of each of the three phases the independent information that is revealed from the pp and pp data results in modifications of tomographic images based solely on p data these modifications are important if the tomographic images are being used to understand the geodynamical history of convergent margins in the caribbean region we investigated the effect of adding data of later arriving phases to the isc p data with sensitivity tests we inverted synthetic delay times to which we added gaussian noise with a standard error typical for the data of the three seismic phases these tests demonstrate that the image resolution of shallow mantle structure is enhanced significantly by the incorporation of later arriving phases due to the absence of seismicity below 200 km the resolution improved less at deeper levels below the caribbean region in some poorly constrained parts of the solution the test results even indicate an apparent decrease of resolution this is explained by changes in the rate of convergence of the inversion algorithm in mantle regions where the effective sampling of structure improved by the addition of pp and pp wave ray paths the convergence was speeded up at the expense of the convergence rate in regions where fewer or no pp or pp wave ray paths were added a shortcoming of the resolution tests used in our study is that some specific problems of reported delay times are not reflected in synthetic data we observe that isc delay times of later arriving phases are not necessarily consistent with the reported hypocentral parameters as most isc reported earthquake locations are computed from direct p wave data for the pp data the inconsistency with event location not only results in a decrease of focal depths during relocation but in a bias of the imaged velocity perturbations as well this property of reported data is not modelled in resolution tests

environmental evolution of the paliouras coastal lagoon in the eastern thermaikos gulf greece during holocene the integration of lithology determination micropaleontological and molluscan analyses scanning electron microscopy magnetic susceptibility measurement and radiocarbon dating contributed to the interpretation of a sedimentary succession recovered from a 870 cm long borehole drilled at the paliouras coastal lagoon in the eastern thermaikos gulf greece in this way the reconstruction of the creation and evolution of the lagoon during the last 8000 years was accomplished four main evolutionary phases are identified 1 initially the pre holocene basement of the study area was inundated during the early holocene marine transgression 2 since 8000 7900 cal yr bp an inner lagoon had been formed in the paliouras coastal plain within a rather restricted environment characterized by a haynesina germanica cerastoderma glaucum and hydrobia sp assemblage relatively high sediment magnetic susceptibility and an intense presence of abnormal foraminiferal tests and lenticular gypsum crystals 3 during 7600 6900 cal yr bp the inner lagoon presented a transition to an open system clearly connected to the sea and characterized by an ammonia beccarii aubignyna perlucida and miliolids assemblage more diversified molluscan fauna minimum sediment magnetic susceptibility and the occurrence of lenticular gypsum aggregates and finally 4 since 5900 cal yr bp to the present time the lagoon water body appears isolated from the marine environment except of occasional seawater intrusions the proposed evolutionary scenario for the paliouras coastal lagoon is in accordance with the existing models of the sea level rise in the aegean coastal areas concerning the time span before 4000 yr bp and the mid late holocene climate events

interpretation of p seismograms from shallow undersea earthquakes the time between direct p and the surface reflections pp and or sp on teleseismic p seismograms is one of the most reliable methods of estimating the depth of a seismic source however correctly interpreting the p seismogram in terms of p pp and or sp is critical to the success of the method using observations from the north pacific intraplate earthquake of 7 march 1988 npe we show that the interpretation of p seismograms from shallow undersea earthquakes can be far from straight forward even in the absence of strong bathymetry gradients above the source the effect of an unconsolidated sedimentary layer on the seafloor and interference between the water reverberations pnwp and snwp where n indicates the n th reverberation can give apparently anomalous polarities on seismograms recorded by narrow band seismograph systems for cross correlation type analyses care must be taken when choosing the reference pulse because the pulse shape due to the water reverberations depends on the acoustic impedance contrast at the seafloor as well as on the relative amplitudes of upward radiated p and s

seismotectonics and relative plate motions in the scotia sea region source parameter inversion of p and sh waveforms and amplitudes for 20 shallow earthquakes using a singular value decomposition technique provides important constraints on the tectonics and relative plate motions of the scotia sea region the derived focal mechanisms show both thrust and strike slip faulting along the north scotia ridge and normal and strike slip faulting along the south scotia ridge two thrust faulting mechanisms south of tierra del fuego indicate diffuse convergence of the antarctic plate along the western margin of the scotia plate earthquakes are consistent with active subduction and back arc spreading along the south shetland trench and bransfield strait the depths of two earthquakes 35 km and 55 km and one shallow thrust faulting event suggest continued subduction along the south shetland trench but the underthrusting is largely aseismic due to the young plate age and slow subduction rate the magnitude and depth of normal faulting earthquakes along bransfield strait and the south scotia ridge are suggestive of diffuse extension rather than typical organized mid ocean spreading which is generally associated with smaller and shallower earthquakes eight strike slip and thrust faulting events provide well constrained slip vectors showing scotia plate motion relative to the surrounding larger plates using a four plate model scotia sc south sandwich ss antarctica an and south america sa and a fixed sa an euler vector we inverted these data together with published centroid moment tensor slip vectors along the south sandwich trench and published marine magnetic data from the ss back arc spreading center to derive the first quantitative plate motion model for the scotia region the sc sa euler pole is located in the south atlantic and shows large latitudinal uncertainties the sc an pole is better constrained and located in the weddell sea these results predict left lateral strike slip motion with a component of compression along the north scotia ridge left lateral strike slip with a component of extension along the south scotia ridge and east west compression in drake passage although no rate data have been published connecting the scotia plate with the global plate system euler vector magnitudes are obtained through closure the results though poorly constrained suggest relative motion rates of 0 5 cm yr along the north scotia ridge and 1 0 cm yr along the south scotia ridge and in drake passage

large earthquakes and crustal deformation near taiwan source parameters of 15 large mb 6 earthquakes which occurred near taiwan during the last 25 years are determined by synthetic seismogram analysis of teleseismic p and s waveforms source depths range from 13 to 88 km three earthquakes of intermediate depth are located within the southernmost limit of the ryukyu arc and show thrust type mechanisms with t axes subparallel to a northward dipping wadati benioff zone shallow earthquakes 30 km are distributed over a broad region along and off the east coast of taiwan and show both high angle reverse and strike slip mechanisms the p axes of the shallow events located off the east coast of northern taiwan are oriented near horizontal trend south to southwest and may reflect relative motion between the okinawa platelet and taiwan or complex deformation at the southwest limit of the ryukyu trench in contrast p axes of shallow earthquakes both onshore and off the east coast of central and southern taiwan consistently trend northwest and are interpreted to reflect relative convergence between the philippine sea and eurasian plates summation of the seismic moment tensors of eight large shallow earthquakes that occurred along and off the central and southern coast of taiwan shows that relative plate motion between the eurasian and philippine sea plates when averaged over the last 25 years has been accommodated by crustal contraction at a rate of 2 6 5 4 cm yr along an azimuth of about 290 o

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

modelling of depth phases and source processes of some central aleutian earthquakes abstract short period synthetic seismograms are computed to determine the relative amplitudes and arrival times of p pp pwp water surface reflection and sp phases except along nodal planes of upgoing p pwp is of greater amplitude than sp for central aleutian earthquakes pwp dominates over sp and pp at north american stations for thrust mechanisms and modelled crustal structures the pwp phase is clearly identified in three aleutian events and can be used to constrain focal depths complex fracturing processes are identified in two of the events in simple events smaller phases which are consistent from station to station can be identified as sub surface reflections and used for modelling the structure of the forearc

a conceptual model for the enhancement of magnetic susceptibility in soils abstract mineral magnetic properties of soils can be strongly influenced by soil forming factors understanding how climate influences magnetic transformations in soils may offer insight into paleoclimate and the pedologic history of landscapes based on our experience with soils in california and hawaii we have developed a conceptual model of the pathways that can lead to enhancement of the magnetic susceptibility in soils we base our model on three sources of iron in soils magnetite maghemite and other iron bearing minerals we find that preferential accumulation transformation diagenesis lessivage neoformation authigenesis and solubilization are the main processes that convert the primary lithogenic minerals inherited from soil parent material to the secondary pedogenic minerals found in the solum biosynthesis is included in the model but does not appear to be an important process in aerobic soil environments our model shows that a major process in the enhancement of eluvial and illuvial horizons is neoformation of secondary magnetite and maghemite resulting from precipitation of iron from the soil solution the processes and products in the model are independent of whether the parent material is transported alluvium or loess or residuum for the soils that we have studied the rates of susceptibility enhancement are shown to be dependent on climate and parent material

element concentrations and magnetic susceptibility of anthrosols indicators of prehistoric human occupation in the inland pilbara western australia the study of archaeological sediments is an important source of information on how humans lived at a site attributes of human site use such as frequency of visits and duration of stay can be explored by measuring changes in phosphorus determined using x ray fluorescence and carbon concentrations in sediments and magnetic susceptibility of sediments in combination with analysis of other sediment attributes stone artefacts and faunal remains this study concludes that increases in phosphorus and carbon concentrations and the discard rate of stone artefacts at marillana a rockshelter in the inland pilbara western australia indicate an increase in the frequency of site use with no change in the function of the site this is interpreted as representative of an increase in regional population density 2005 elsevier ltd all rights reserved

seismic rupture associated with subduction of the cocos ridge the april 3 1983 costa rica earthquake mw 7 4 ms 7 3 occurred where the aseismic cocos ridge has been partially subducting beneath the caribbean plate the epicenter is at the eastern edge of the 70 110 km initial aftershock area which later shows considerable expansion p wave directivity analysis indicates that the rupture front propagated westward 63 km from the epicenter to where the major moment release was truncated the source time history of the 1941 event ms 7 5 which occurred in the same epicentral area appears to be similar to the 1983 event but with more complexity and a slower initiation of moment release the low stress drop of the 1983 event 2 3 bar and low ratio of seismic slip to tectonic slip 0 15 for the 1983 event suggest that the coupling between the descending slab and the overlying plate is weak yet a recurrence time for large events mag 7 0 in this zone of about 40 years is implied by the 1904 1941 and 1983 events suggesting that the cocos ridge causes increased partial coupling compared with that in the adjacent subduction zone the slow source rupture process may reflect the nature of the contact area between the costa rica arc and the subducting plate in the vicinity of the bouyant cocos ridge the normal faulting event of july 1 1979 mb 5 3 is consistent with present day uplift of the burica peninsula which previous studies suggest is related to the subduction of the cocos ridge the burica and osa peninsulas may behave as detached blocks which influence the distribution of partial coupling reflected in the aftershock expansion pattern

seismic moment tensors and source depths determined by the simultaneous inversion of body and surface waves we present a linear moment tensor inversion method that incorporates both body and surface wave data the source coordinates are fixed during the inversion and the source depth is determined by applying the inversion at several depths and taking the depth that produces the minimum residual the inversion is carried out in the time domain for body wave data and in the frequency domain for surface wave data the fundamental rayleigh waves at the period of 256 s from ida stations and the long period p waves from wwssn and gdsn stations whose angular distances are from 30 to 90 are used as the data the simultaneous inversion of both body and surface wave data sets has several merits because of the body wave constraints the present method gives reasonable solutions at shallow depths 30 km where long period surface wave inversions become unstable although the inversion using only body wave data is unstable in the sense that it allows for a variety of solutions with a slight change in the assumed depth probably because of the noise present and poor coverage of body wave data to determine the source mechanisms the inclusion of surface wave data makes the solution stable this is because the surface wave data constrain nodal plane strikes we may also expect better resolution in source depth by including the body wave data because the local crustal structure above the source can be taken into account to generate the green s function we applied our method to two large earthquakes one occurring at the triple junction off boso peninsula central honshu on 18 september 1984 and another at the outer rise area off the chile trench on 16 october 1981 the scalar moments of the boso oki and chile earthquakes are estimated to be 3 2 1026 dyn cm and 6 3 1026 dyn cm respectively the ratio of the minimum absolute eigenvalue of the moment tensor to the maximum which may measure the non double couple component is less than 10 for both earthquakes this suggests that their sources are essentially a double couple the source depths of both events are determined as 30 km the boso oki event is indicative of hinge faulting within the pacific slab at the triple junction the chile event is consistent with compressional bending stress in the deeper part of the lithosphere at the trench outer rise area off chile

examination of slow and late moment release of the 1988 spitak and 1991 racha caucasus earthquakes summary two large shallow earthquakes occurred in the caucasus part of the collisional belt caused by the northward movement of the arabian plate with respect to the eurasian plate the 1988 december 7 spitak armenian m 6 7 and 1991 april 29 racha m 6 9 earthquakes in the present study slow and late moment releases of the earthquakes which were previously proposed based on the body wave analyses are examined using long period surface waves results from spectral inversions using fundamental mode surface waves show that the source durations of both earthquakes are about 20 s although additional investigations utilizing the long period surface waves which are optimized to detect slow and late moment release were employed no evidence of slow and late moment release was found for either earthquake for the racha earthquake the obtained source duration is consistent with the result from body wave analyses within the resolution of the body wave data the simple p and sh waveforms are well modelled by a source time history model with a duration of 20 s however for the spitak earthquake the source duration obtained from the surface waves is about 30 s shorter than the source model suggested in the body wave analysis this discrepancy is attributed to a slow and late thrust fault slip in the body wave source model which was proposed in order to interpret the late arrivals of p waves as the result of source complexity numerical experiments predict that rayleigh wave radiation is sensitive to the radiation from the proposed slow and late slip a comparison between the observed and predicted rayleigh wave radiation patterns however provides no indication of the surface wave radiation from the slow and late slip it is unlikely that the discrepancy in the source model is only due to errors in modelling the propagation of long period surface waves because for the racha earthquake the source models obtained from body and surface waves are consistent the present results thus indicate that the late arrivals of p waves are probably caused by something other than source complexity for example complex local structure near the earthquake source in the continental collisional belt for the spitak earthquake a large non double couple component is observed in the moment tensor solution obtained at long periods if the non double couple component is due to source complexity it should be produced within the 20 s rupture process

high resolution paleoclimatic trends for the holocene identified using magnetic susceptibility data from archaeological excavations in caves abstract a proxy paleoclimatic curve has been produced for the holocene c 9000 3500 bp from magnetic susceptibility ms measurements of sediment samples collected from two dated archaeological excavation trenches in konispol cave albania the resulting ms data provide paleoclimate estimates that are in excellent agreement with independently published paleoclimatic trends for early middle holocene time basically ms variations are attributed to variations in climate controlled pedogenesis and the production of magnetic mineral phases including maghemite outside the cave these soils are then washed blown or tracked into the cave where they accumulate creating the ms changes observed in the samples recovered low ms magnitudes indicate times of cooler drier climate resulting from reduced pedogenesis while warmer wetter times yield higher pedogenetic rates and thus higher ms magnitudes it is clear from the konispol cave results that some caves provide ideal protected environments from which high resolution paleoclimatic records can be extracted composite sections from excavations within a single region can yield a relatively continuous long term climatic proxy that can be routinely correlated to artefacts recovered from these or other protected excavations within the same region

standardised recording of sediments in the excavation of the sabaean town of sirwah yemen abstract the application of sediment description in excavations helps to interpret sedimentary archives on archaeological sites although there are a few standardised approaches for describing deposits in excavations stratigraphic records carried out by archaeologists can differ significantly from those carried out by geoscientists in order to compare the results of both types of records anthropogenic deposits of the sabaean town of sirwah yemen were investigated with regard to sedimentological criteria apart from field description and radiocarbon dating the texture structure and chemical data were studied in order to demonstrate whether or not they are suitable for determining post sedimentary modifications and for refining stratigraphy as developed by archaeologists the comparison of sediment units and cultural layers of a selected part of an archaeological section demonstrates that a stratigraphic record carried out according to a soil manual substantiates depositional history in addition the paper gives some new insights into the occupation and building history of the unique sabaean culture at the ramlat as sab atayn desert margin of yemen in the first millennium bc

a reassessment of the rupture characteristics of oceanic transform earthquakes 1 we investigate the long period source spectra of oceanic transform earthquakes and find that previously proposed slow rupture components can be explained as artifacts generated by the modeling procedure we use low frequency 20 mhz rayleigh and love waves to calculate the amplitude spectra of five earthquakes on the romanche and chain transform faults in the equatorial mid atlantic ocean we find that errors and approximations in the centroid depth focal mechanism and earth structure at the source have significant effects on the shape of the source spectra if global catalog values and an average crustal model are assumed the spectra exhibit apparent anomalous energy at long periods which has previously been interpreted as a result of slow rupture we recalculate the source spectra using precise independently determined depths and moment tensors and a more realistic oceanic crustal structure in the source region the resulting source spectra are flat at long periods with no indication of anomalous long period energy our results imply that oceanic transform earthquakes do not commonly have detectable slow rupture components

multi element analysis of soils from scottish historical sites interpreting land use history through the physical and geochemical analysis of soil arable farming in the highlands and islands of scotland by the 18th century was characterized by labour intensive techniques of husbandry and the transfer of fertilizing resources from their extensive non arable sector to their arable land such practices had a considerable impact on soil development and characteristics the use of inductively coupled plasma mass spectrometry icp ms in this study has allowed the geoarchaeological significance of a broad range of elements to be investigated on soils collected from a former settlement site on the trotternish peninsula isle of skye the on site geochemical data are expressed as enrichment factors relative to the mean concentration of the control samples of the elements investigated in this study ba la ce pr k cs th and rb were found to be indicative of human settlement at greaulin whilst the spatial enrichment patterns for ca and sr suggest additions of shell sand to the arable land over the central region of the site vanadium co zn pb ni ga sc mg cu and u all showed minimal or no on site enrichment the generally lower on site levels of percentage loss on ignition relative to the control soils are interpreted as reflecting the former use of the fields for cultivation interpretation of the p results in the light of documentary evidence suggest that some of the 19th century croft farmsteads may have reoccupied sites formerly inhabited during pre clachan times hence the clachan at greaulin may not have been as long standing a settlement feature as traditionally envisaged

effects of near source seafloor topography on long period teleseismic p waveforms in the study of the shallow earthquakes in the subduction zones reverberations inside the water layer near the source are known to affect very significantly the far field body waveforms the usual correction is to take a horizontally layered model as the near source structure but it is not realistic for the trench geometry therefore finite difference simulation combined with far field ray theory is employed in order to examine the effects of the realistic non flat seafloor topography as a realistic trench model the japan trench is selected the response of the structure near the source is calculated by two dimensional finite difference simulation then teleseismic p waveforms are calculated by using reciprocal theorem our results suggest that 1 around the trench bottom effects of non planar structure are remarkable and the realistic seafloor cannot be approximated by any model of planar structure however 2 effects of the continental slope are well approximated by a model of planar dipping seafloor of appropriate dip therefore the near source structure must include the realistic seafloor topography or the waveform analyses may lead to spurious subevents in a later stage of rupture process and mislocation of events our results also show that present knowledge about the seafloor topography is enough to incorporate the complicated geometry

teleseismic synthetics obtained from 3 d calculations in 2 d media summary at subduction zones the laterally heterogeneous medium such as the steeply dipping sea bottom and thick sedimentary layers causes large effects on the teleseismic body waveforms from the shallow events occurred in this region we develop a new method to incorporate these effects from near source structure in calculating the teleseismic body waveforms to incorporate the structural effects we simulate 3 d elastic wave propagation in a two dimensionally heterogeneous structure although the simulated wavefield is 3 d our method does not require huge computer storage this is because we assume a 2 d structure to reduce the dimension of the equations of motion by spatial fourier transform because of the strong laterally heterogeneous features such as steeply dipping sea bottom and thick sedimentary layers and because of the 2 d geometry of the oceanic trench our method is particularly applicable to the shallow subduction zone earthquakes in our formulation we assume a 2 d model structure in which the physical properties are constants in the direction parallel to the trench axis then we apply the spatial fourier transform to the equations of motion in that direction the resultant wavenumber domain equations can be solved as independent sets of 2 d equations on a computer with a moderate sized storage we solve these wavenumber domain equations by the staggered grid finite difference method finally the inverse fourier transform provides the 3 d displacement field the reciprocal principle is used to obtain the teleseismic displacement first the response of the near source structure to an input plane p wave is calculated by the 3 d method introduced here then based on the reciprocal principle convolution of the response strain at the source position with the moment tensor is calculated to get far field p wave displacement as an example of the application of the present method we calculated the waveforms from a shallow thrust event that occurred at the kurile trench 1964 october 16 ms 6 5 the synthetics calculated by the new method reproduce the large amplitude later arrivals in the observed seismograms furthermore a reasonable source position is obtained from the waveform analysis

historical seismicity and implications for diffuse plate convergence in the northeast indian ocean large historical earthquakes provide constraints on the geographical extent and kinematics of the slow diffuse plate boundary extending from the central indian ridge to the sumatra trench the fault parameters of pre 1963 earthquakes are derived using a grid search for the best fit between observed and synthetic body waveforms surface wave spectral amplitudes and polarity and polarization constraints and location uncertainties are determined using a bootstrap resampling method the march 9 1928 ninetyeast ridge m 7 7 event shows left lateral strike slip faulting along a plane approximately coincident with the orientation of the ninetyeast ridge two small events which occurred at the location of the 1928 event in 1980 show focal mechanisms nearly identical to that determined for the 1928 earthquake and apparently reactivated the same fault the 1928 waveforms can also be fit by a thrust faulting solution with ene striking fault planes but a variety of evidence including the recent strike slip earthquakes at the same location suggest the strike slip solution these earthquakes are located along the western scarp of the ridge and do not represent reactivation of the ninetyeast fracture zone to the east of the edifice which was a major plate boundary in the early cenozoic the january 23 1949 m 6 75 and march 22 1955 m 7 0 wharton basin earthquakes although only 350 km apart show different strike slip and thrust faulting mechanisms all earthquakes show a regionally consistent pattern of horizontal compressional stress which changes from nw se in the wharton basin to n s in the central indian basin the compressional axes are oriented perpendicular to linear gravity anomalies associated with lithospheric flexure indicating little change in stress orientation since the onset of folding seismic deformation along the diffuse boundary consists of sinistral strike slip faulting associated with n s features such as the ninetyeast ridge and the 86 e fracture zone and thrust or reverse faulting in regions between fracture zones assuming transform motion the approximate slip rate along the northern ninetyeast ridge calculated from the summed moments of earthquakes is 2 8 mm yr this value is an order of magnitude less than previous estimates and suggests that at most only a small fraction of the current relative plate motion 7 mm yr occurs along the ridge the geographic distribution of seismicity suggests that the wharton basin east of the ninetyeast ridge is nearly as seismically active as the central indian basin to the west this result along with observed long wavelength gravity anomalies in the wharton basin indicates that the india australia plate boundary intersects the sumatra trench along a diffusely deforming region several thousand kilometers long rather than along a discrete transform zone

effects of near source bathymetry on teleseismic p waveforms teleseismic p waveforms from submarine earthquakes show water reverberations that are often poorly modeled by synthetic seismograms this study suggests that considerable misfit results from the non horizontal nature of the seafloor in the epicentral region and examines this effect for a planar dipping water crust interface geometric ray theory synthetics calculated for a double couple source show that p waveforms are extremely sensitive to seafloor orientation because of the large impedance contrast across the boundary seafloor dips as small as 0 5 significantly modify the ray paths affecting the take off angle at the source reflection and transmission coefficients at the interface geometric spreading and travel time to test the applicability of such modeling p waveforms from the march 29 1976 cocos ridge intraplate earthquake were studied the waveforms many of which show prominent water multiples poorly modeled with flat lying bathymetry were inverted for the best fitting planar ocean bottom orientation using a grid search technique synthetics computed for the best fitting seafloor orientation match the data much better than synthetics for a flat lying structure and reproduce the observed azimuthal dependence of water multiple amplitudes the derived ocean bottom dip angle and direction are in agreement with bathymetric charts suggesting p waveforms provide constraints on the seafloor orientation in the epicentral region green s functions incorporating the effects of bathymetry should provide better resolution of the source parameters of submarine earthquakes

bathymetric effects on body waveforms from shallow subduction zone earthquakes and application to seismic processes in the kurile trench resolution of earthquake source characteristics is limited by structural complexities in the source region this study explores the effects of dipping near source bathymetry and structure on long period teleseismic body waveforms from shallow subduction zone earthquakes ray theory synthetics calculated for shallow double couple sources and velocity structures incorporating planar dipping interfaces suggest that p waveforms are most sensitive to water depth and sea bottom orientation for sources beneath a substantial water layer the seafloor dip of the inner trench slope can give rise to prominent later arrivals and waveform complexity not found on synthetics calculated for horizontal bathymetry sediment thickness and the dip of the sediment crust and crust mantle interfaces generally have lesser effects the high amplitude arrivals result largely from changes in the source takeoff angles of the reverberations these arrivals present difficulties for source depth and time function determination from p waveforms and may cause spurious complexity in the derived pattern of earthquake moment release sh waveforms show little effect of sea bottom orientation or local structure for shallowly dipping thrust faulting events suggesting that sh waveform analysis can stabilize source parameter studies with respect to unknown or incompletely parameterized bathymetry and structure effects of nonhorizontal structure are observed in the p waveforms from shallow kurile trench events ms 5 8 7 2 which show prominent later arrivals not observed on sh waveforms synthetics calculated for a dipping water crust interface provide a better fit to these arrivals than those calculated for a horizontal interface suggesting that the p waveforms show systematic effects of seafloor dip the synthetics are highly sensitive to the assumed orientation of the seafloor the data are fit best for seafloor orientations consistent with the dip of the inner trench slope the distorting effect of the water layer gives rise to systematic differences in p wave complexity between shallow events near the seismic front which occur beneath a thick water layer and show numerous later arrivals and deeper arcward events which occur beneath a thin water layer and show simple waveforms large reverberations in the p waveforms of the october 20 1963 and june 10 1975 kurile tsunami earthquakes have previously been used as evidence for a long source duration and a change in focal mechanism during rupture however sh waveforms suggest simple source time functions with durations of 25 and 43 s inversion of p and sh waveforms and amplitudes yields shallowly dipping thrust mechanisms with no conclusive evidence for a previously proposed steepening of the fault dip during rupture the large p wave reverberations cannot be fit using a point source and a horizontal seafloor detailed modeling of the 1963 event as an upward propagating rupture extending through low velocity sediments to the ocean bottom combined with the effects of the dipping seafloor allow the reverberation amplitudes to be matched the anomalous tsunami excitation appears to be related to the location of the sources at shallow depths within low velocity sediments

waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes abstract yoshida s 1992 waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 45 59 we inverted teleseismic p waveforms to infer rupture processes of subduction zone earthquakes using green s functions computed for realistic seafloor topography because reverberations in the water layer near the source affect the teleseismic waveforms we modeled the seafloor by a series of several plane surfaces with appropriate dip and performed three dimensional ray tracing to compute green s functions from the gdsn seismograms spatial and temporal slip distributions were estimated for the 1986 andreanof islands earthquake m s 7 7 and the 1985 chile earthquake m s 7 8 to suppress unstable parts of the least squares solution we introduced some stabilizing constraints the 1986 andreanof islands earthquake was analyzed using two kinds of source models the first one has a prescribed rupture velocity and the second one allows any point to slip at any time the solutions by the two models gave similar patterns of slip distribution a relatively small subevent initially occurred and then a dominant subevent with a moment of about five times larger occurred with a center about 80 km west of the hypocenter for the 1985 chile earthquake a small initial subevent was also found and a major rupture with a ten times larger moment extended approximately from 20 to 70 km south of the hypocenter for both the earthquakes it was found that most of the one day aftershocks occurred in areas where a small moment was released during the main shock

factors determining magnetic enhancement of burnt clay from archaeological sites abstract the magnetic susceptibility of a collection of 212 archaeological samples of burnt clay of different origin burnt soil ovens and bricks taken from 60 archaeological sites from bulgaria were studied in order to determine factors which may have affected their magnetic enhancement the highest magentic susceptibility values were obtained for bricks and the lowest for burnt soils suggesting that the firing temperature and the duration of burning are important conditions for determining magnetic enhancement specific spatial pattern of the low field magnetic susceptibility was also observed characterized by separation of sites situated in northern and southern parts of the country divided by the west east trending mountain chain stara planina maximum susceptibility values are obtained for burnt soils in southern bulgaria and minima in northern bulgaria in contrast burnt clay plasters and bricks show the opposite picture it is supposed that the observed pattern is due to differences in the outcropped geological formations and variable climate conditions between the two regions which determine different iron supply during burning of initial clay material results from the thermomagnetic analyses show that the dominant ferrimagnetic mineral in all burnt clay materials studied is magnetite titanomagnetite with low ti content and different grain sizes high values of frequency dependent magnetic susceptibility indicate the presence of significant amount of fine grained d

site identification and correlation using geoarchaeological methods at the cabeco do porto marinho cpm locality rio maior portugal abstract several geoarchaeological techniques have been employed in evaluating an open air site within a uniform sand matrix near rio maior portugal electrical resistivity data acquired at the upper palaeolithic site complex of cabeco do porto marinho cpm delineated an important new occupational locus this result was confirmed first by auger testing which recovered subsurface artefacts and then by direct excavation in addition 107 samples were recovered at the site for magnetic susceptibility measurements comparisons between magnetic susceptibility profiles from two loci including the new area at cpm show distinctive patterns which allow direct correlation between the occupation areas these methods provide quick and inexpensive means for investigators to evaluate new sites or to correlate between and within sites without resorting to other more time consuming and expensive techniques

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

the gulf stream influence on wintertime north atlantic jet variability in this paper we investigate the influence of the gulf stream sst front on the north atlantic eddy driven jet and its variability by analysing the ncep cfsr dataset and a pair of agcm simulations forced with realistic and smoothed gulf stream sst boundary conditions the gulf stream sst front acts to generate stronger meridional eddy heat flux in the lower troposphere and an eddy driven jet over the eastern north atlantic that is located further polewards compared to the simulation with smoothed sst the strong gulf stream sst gradient is found to be crucial in more accurately capturing the trimodal distribution of the eddy driven jet latitude with the more poleward climatological jet being the result of the jet occupying the northern jet position more frequently in the simulation forced with observed ssts the more frequent occurence of the northern jet location is associated with periods of high eddy heat flux over the gulf stream region composite analysis of high eddy heat flux events reveals that the significantly higher heat flux is followed by larger and more persistient poleward jet excursions in the simulations with realistic ssts compared to the simulation with smoothed ssts with upper tropospheric eddy momentum fluxes acting to maintain the more poleward eddy driven jet periods of high eddy heat flux over the gulf stream region are also shown to be associated with increased blocking frequency over europe which are clearly distinct from periods with a northern jet position

chemical characterisation of anthro technosols from bronze to middle age in bologna italy abstract the aim of this research was the understanding of a peculiarly expanded soil sequence in bologna i e roman bononia etruscan felsina one of the most important archaeological poles for etruscan colonisation and settlement in northern italy the uppermost part of the chronological sequence dating from the bronze age up to medieval and modern times was analysed for the first time from geochemical and pedological viewpoints the integration of archaeological stratigraphical and pedological data supported by soil chemical analysis a fundamental key for reconstructing a correct evolutionary sequence made it possible to recognise seventeen buried soil units ancient technosols anthrosols and cambisols characterised by different kinds and degrees of intensity of anthropogenic influence in some cases the results show a relatively severe element concentration cu sn mainly characterising the iron age etruscan and villanovan stratigraphic units representing an ancient industrial pollution linked to local dispersal of melting activity dump products generated in near site surrounding areas therefore a comparison was possible between natural blank and anthropogenically polluted geochemical values for some local soils

a southern indian middle palaeolithic occupation surface sealed by the 74 ka toba eruption further evidence from jwalapuram locality 22 this paper reports further evidence from an archaeological occupation surface in southern india that was buried by tephra from the toba volcanic super eruption ca 74 000 years ago the open air site designated jwalapuram locality 22 and located in the kurnool district of andhra pradesh preserves more than 1600 stone artefacts assigned to the indian middle palaeolithic sedimentological isotopic and lithic data along with optically stimulated luminescence ages confirm the site as occupied closely prior to the eruption the hominin taxon responsible for creating the site is not known but the stone tool evidence is most consistent with contemporaneous homo sapiens technologies in africa and to the east of south asia the findings have relevance for understanding indian middle palaeolithic technology and for identifying the behavioural and environmental adaptations of the hominin group s that occupied india when toba erupted

magnetic and geochemical variations as indicators of palaeoclimate and archaeological site evolution examples from 41tr68 fort worth texas abstract the river bend site 41tr68 is located on the west fork of the trinity river near fort worth texas in the upper trinity river floodplain a magnetometer survey was performed at this site to identify hearths and utilizing these data backhoe trenches were placed adjacent to significant magnetic anomalies test excavations were then conducted several physical properties measurements including magnetic susceptibility an indicator of magnetic mineral concentration calcium carbonate percentages and percent spectral reflectance in the red colour range were performed on samples from stratigraphic sections adjacent to two excavation units at the site the data are interpreted in terms of cultural and palaeoclimatic controls during sediment accumulation distinctive peaks in all parameters were exhibited by samples associated with hearths and shell concentrations broad magnetic susceptibility highs indicative of high magnetic mineral concentrations are closely associated with hearths and result from the production of new magnetic minerals by chemical redox reactions during heating variations in red spectral reflectance percentages indicative of hematite mineral concentration appear to be the result of pedogenesis at the site and therefore are controlled primarily by climate susceptibility highs are correlated with reduced hematite concentrations apparently resulting from the chemical reduction of hematite during heating calcium carbonate percentage peaks are indicative of shell debris concentrations from mollusks which were an abundant food source at those times superimposed on these peaks are broad variations in calcium carbonate percentages which reflect palaeosol development at the riverbend site and suggest the presence of several indistinct palaeosols while overall variations appear to be the result of palaeoclimate we interpret the local variations associated with hearths to result from several factors first the presence of abundant carbonate and sulphur at the site has resulted in the formation of authigenic iron carbonate and iron sulphide minerals from dissimulatory iron reduction by bacteria during pedogenesis second at low temperatures these iron carbonates and sulphides oxidize to highly magnetic mineral phases including magnetite and maghemite thus increasing the observed magnetic susceptibility in samples acquired from the site and third at moderate temperatures produced in sediments surrounding and beneath hearths the abundant hematite at the site is reduced to maghemite thus further increasing the magnetic susceptibility in the samples collected

magnetic susceptibility applied as an age depth climate relative dating technique using sediments from scladina cave a late pleistocene cave site in belgium abstract here we demonstrate that magnetic susceptibility ms data from scladina cave belgium provide a time depth climate relationship that is correlated to the marine oxygen isotopic record and thus yields a high resolution relative dating method for sediments recovered from many archaeological sites this methodology will help resolve one of the major problems facing archaeologists namely the difficulty of acquiring absolute dates with reasonable precision for the period from 40 000 to 400 000 years or so the problem is that dating techniques applicable to most materials within this age range are subject to significant errors relative dating techniques such as magnetic secular variation or stable isotope methods offer the potential to improve this precision but both methods suffer from problems that make broad application to many sites impossible however for most archaeological cave sites ms measurements of cave sediments offers the potential for intra site correlation and paleoclimate estimation this is possible in protected cave environments because the ms of cave sediments results from climate processes active outside caves which cause variations in magnetic properties of the sediments that ultimately accumulate inside caves once deposited these materials are often preserved and their stratigraphy provides a time depth climate signal that can be identified therefore ms data can be used as an independent methodology alongside conventional methods such as sedimentology and palynology for relative age dates and correlation within and between sites by tracing evidence of paleoclimatic change this correlation has been used to infer an age of 90 000 7000 years for neanderthal skeletal remains recovered from scladina cave an important middle paleolithic archaeological site in belgium

source mechanisms of earthquakes near mid ocean ridges from body waveform inversion implications for the early evolution of oceanic lithosphere to investigate the early tectonic evolution of oceanic lithosphere we present a synthesis of the characteristics of near ridge earthquakes i e earthquakes which occur off the axis of major mid ocean spreading centers but in lithosphere less than 35 m y old near ridge seismicity for the past two decades has been rather evenly distributed along the major ridge systems with the exception of the central indian ocean and the eastern part of the cocos plate which have experienced a high rate of earthquake activity during that time for 32 near ridge earthquakes we determined the double couple orientation seismic moment centroid depth and source time function using a formal inversion technique based on matching synthetic and observed p and sh waveforms all types of faulting styles are observed seismogenic deformation in young oceanic lithosphere is concentrated in the first 15 m y and occurs almost entirely in the uppermost mantle from just below the moho to depths at which the temperature estimated from standard thermal models exceeds 800 c thrust faulting is not observed at depths greater than 10 km below the seafloor the deepest near ridge earthquakes are generally characterized by normal faulting focal mechanisms with the t axis oblique or perpendicular to the local spreading direction most of these earthquakes occur in the central indian ocean the transition from mechanisms characteristic of ridge axes to those characteristic of the near ridge environment occurs within the first few million years for lithosphere less than 35 m y old horizontal compressive stress associated with the cooling and subsidence of the lithosphere ridge push does not appear to be the dominant source of stress released in earthquakes this result may be used to place a lower bound of several hundred bars on the typical stress difference in young oceanic lithosphere this bound together with the observed depth of faulting implies that the strain rate associated with seismic deformation is locally at least 10 15 s 1 we propose that thermoelastic stresses associated with plate cooling play an important role in near ridge earthquakes this source of stress can account for the mechanisms and depths of many near ridge earthquakes and for the concentration of activity in very young lithosphere the comparative aseismicity of the oceanic crust may reflect the concentration of thermoelastic stress below the moho due to different material properties for the crust and upper mantle or the early release of thermoelastic stresses through hydrothermal circulation and cracking throughout the crust at or near the ridge axis the higher level of near ridge seismicity in the indian ocean may be the result of modification or enhancement of the more typical near ridge stress state by such local processes as the continental collision between india and asia or active secondary convection beneath the young lithosphere of the indian plate

a methodological approach for identifying archaeological evidence of fire resulting from human activities abstract the identification of unequivocal evidence of humanly controlled fire is extremely problematic in archaeological contexts where obvious remains such as charcoal and ash have not been preserved until recently the difficulty of identification had been magnified by the lack of an established methodological approach which addressed the problem a methodological approach which can be used to identify and discriminate between archaeological evidence of fire resulting from natural processes and archaeological evidence of fire resulting from human activities is now available the approach utilizes several parameters of investigation including 1 macroscopic examinations of fire feature surfaces and profiles 2 analyses of magnetometer data 3 magnetic susceptibility studies 4 analyses of alternating field demagnetization characteristics 5 studies of isothermal remanent magnetization irm acquisition 6 analyses of coercivity of remanence characteristics and 7 palaeointensity studies the methodological approach is illustrated by comparing the results from analyses of features and samples from grass fire experiment sites isolated tree stump fire experiment sites multiple burn campfire experiment sites modern forest fire sites known archaeological hearths from modoc rock shelter illinois and known archaeological clay ovens from tell ashkelon israel for each available parameter of investigation comparisons revealed that multiple burn campfire sites exhibited basin shaped three dimensional configurations of oxidized sediments and diagnostic magnetic anomalies while multiple burn campfire samples displayed dramatic increases in magnetic susceptibility highly stable to very highly stable responses to alternating field demagnetization dramatic differences in irm acquisition and coercivity of remanence responses and diagnostic palaeointensity results when compared with the responses of adjacent unfired control samples archaeological hearth features and samples and samples from archaeological clay oven features exhibited results which were broadly consistent with the results from multiple burn campfire sites and samples the results displayed by grass fire isolated tree stump fire and forest fire sites and samples were generally found to be mutually exclusive from the results exhibited by multiple burn campfire and archaeological hearth and oven sites and samples for all parameters of investigation the results demonstrate that the methodological approach can be used to unequivocally identify archaeological evidence of humanly controlled fire resulting from multiple burn campfires fire hearths ovens and similar kinds of humanly produced fires

azimuthal distortion of the seismic focal sphere application to earthquakes in subduction abstract new broadband seismographs enable us to analyse in more detail mantle waves perturbed by the complexity of the medium around the source we propose to apply ray tracing for complex media around the source and more efficient ray tracing for a spherically symmetric earth through the mantle up to the stations we show on synthetic examples that the complexity around the source may indeed modify considerably the seismograms we analyse theoretical teleseismic waveforms and relate modulation of the amplitude to the medium s structure around the source for the example of the romanian earthquake of 30 may 1990 we analyse three seismograms which were not modelled correctly with a spherically symmetric earth model by adding some near surface interfaces we were able to improve the fit between observed and computed seismograms the deduced hypothetical model which may not be the only possible model is in agreement with proposed published models in the area

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea

rupture characteristics of the 1982 tonga and 1986 kermadec earthquakes source time functions are obtained for the december 19 1982 tonga and october 20 1986 kermadec earthquakes from deconvolution of p waves using a model including a significant dip of the ocean bottom in such a geometry the amplitudes of subsequent water multiples are large and irregular as a result we can model these two events as consisting of a single pulse of short duration 23 s in the case of the 1982 event and 19 s for the 1986 one despite complex teleseismic waveshapes this is in contrast to inversions using flat layered models which required very complex source time functions which were mutually inconsistent at different stations the anomalously large tsunami generated by the 1982 event is modeled as the result of propagation of the rupture into the sedimentary wedge at the trench rather than due to a long lived complex source time function the latter being also incompatible with the total lack of excitation of the earth s normal modes in the low frequency limit for the 1986 event we derive a source duration 19 s very short in relation to its moment 8 1027 dyn cm this earthquake a high stress drop rupture featuring a unique combination of strike slip and thrust motion on a plane dipping oceanwards of the trench is interpreted as expressing internal deformation of the subducting pacific slab at a depth of 40 km under the compressional stresses resulting from the collision

long period precursors to pp from deep focus earthquakes the moho underside reflection pmp summary moho underside reflection pmp is a weak precursor to the surface reflection pp it is best observed in long period records from deep focus earthquakes provided that the p coda has sufficiently low amplitudes pmp reflection in continental or shelf regions produces a clear arrival whereas pmp reflection at the oceanic moho produces a smooth transition from pmp to pp these properties are illustrated by wwssn seismogram examples for events below the sea of japan the sea of okhotsk argentina and tonga fiji synthetic seismograms are calculated with a simple reflectivity method and comparison with observed seismograms corresponding to continental pmp reflection gives estimates of crustal thickness and moho p velocity change they are averages over reflection zones with a diameter of about 300 km application to the crust of north korea indicates an increase of crustal thickness from about 27 to 32 km over about 300 km from n to s accompanied by a decrease in the velocity change at the moho from about 1 3 to 0 9 km s