rank ordering statistics of extreme events application to the distribution of large earthquakes rank ordering statistics provide a perspective on the rare largest elements of a population whereas the statistics of cumulative distributions are dominated by the more numerous small events the exponent of a power law distribution can be determined with good accuracy by rank ordering statistics from the observation of only a few tens of the largest events using analytical results and synthetic tests we quantify the systematic and the random errors we also study the case of a distribution defined by two branches each having a power law distribution one defined for the largest events and the other for smaller events with application to the worldwide harvard and southern california earthquake catalogs in the case of the harvard moment catalog we make more precise earlier claims of the existence of a transition of the earthquake magnitude distribution between small and large earthquakes the b values are b2 2 3 0 3 for large shallow earthquakes and b1 1 00 0 02 for smaller shallow earthquakes however the crossover magnitude between the two distributions is ill defined the data available at present do not provide a strong constraint on the crossover which has a 50 probability of being between magnitudes 7 1 and 7 6 for shallow earthquakes this interval may be too conservatively estimated thus any influence of a universal geometry of rupture on the distribution of earthquakes worldwide is ill defined at best we caution that there is no direct evidence to confirm the hypothesis that the large moment branch is indeed a power law in fact a gamma distribution fits the entire suite of earthquake moments from the smallest to the largest satisfactorily there is no evidence that the earthquakes of the southern california catalog have a distribution with two branches or that a rolloff in the distribution is needed for this catalog b 1 00 0 02 up to the largest magnitude observed mw 7 5 hence we conclude that the thickness of the seismogenic layer has no observable influence whatsoever on the frequency distribution in this region

an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

mean flow and variability in the kuroshio extension from geosat altimetry data using altimeter data from the geosat exact repeat mission erm we investigated the mean flow and temporal and spatial variations of the kuroshio extension in the region of 140 180 e and 30 40 n mean surface height profiles were estimated along individual tracks by assuming the velocity profile of the kuroshio extension to be gaussian shaped and by successively fitting this synthetic current s height profile to the residual height data using the mean profiles from ascending and descending tracks we derived the mean surface height field by an inverse method and obtained the absolute surface height fields for the first 2 5 years of the geosat erm both the mean and the instantaneous height fields thus derived compared well with the available hydrographic data and the sst patterns from the noaa satellites the mean surface height difference across the kuroshio extension attains its maximum around 146 e between the two quasi stationary meanders and its decrease thereafter is mainly due to large scale recirculations on the southern side of the kuroshio extension the ratio of the eddy kinetic energy over the mean kinetic energy has a nearly constant value of 1 5 2 0 along the kuroshio extension path propagation of mesoscale fluctuations in the height fields is generally westward except for the upstream region of the kuroshio extension effects of deep mean flow and baroclinic shear are found to be important in explaining the observed propagation speeds in the upstream region of 141 e and 154 e annual variations in the surface height difference across the kuroshio extension h have a september maximum with an average amplitude of 0 2m for large scale interannual fluctuations anomalies in h are found to be significantly correlated with those of the current axis positions a larger surface height difference corresponds to a more northerly position of the kuroshio extension the interannual changes in h are possibly related to the 86 87 enso event in the low latitude pacific ocean

the enigma of the arthur s pass new zealand earthquake 1 reconciling a variety of data for an unusual earthquake sequence the 1994 arthur s pass earthquake mw6 7 is the largest in a recent sequence of earthquakes in the central south island new zealand no surface rupture was observed the aftershock distribution was complex and routine methods of obtaining the faulting orientation of this earthquake proved contradictory we use a range of data and techniques to obtain our preferred solution which has a centroid depth of 5 km m0 1 3 1019 n m and a strike dip and rake of 221 47 112 respectively discrepancies between this solution and the harvard centroid moment tensor together with the global positioning system gps observations and unusual aftershock distribution suggest that the rupture may not have occurred on a planar fault a second strike slip subevent on a more northerly striking plane is suggested by these data but neither the body wave modeling nor regional broadband recordings show any complexity or late subevents we relocate the aftershocks using both one dimensional and three dimensional velocity inversions the depth range of the aftershocks 1 10 km agrees well with the preferred mainshock centroid depth the aftershocks near the hypocenter suggest a structure dipping toward the nw which we interpret to be the mainshock fault plane this structure and the harper fault 15 km to the south appear to have acted as boundaries to the extensive aftershock zone trending nnw sse most of the ml 5 aftershocks including the two largest ml6 1 and ml5 7 clustered near the harper fault and have strike slip mechanisms consistent with motion on this fault and its conjugates forward modeling of the gps data suggests that a reverse slip mainshock combined with strike slip aftershock faulting in the south is able to match the observed displacements the occurrence of this earthquake sequence implies that the level of seismic hazard in the central south island is greater than previous estimates

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

effects of pre existing discontinuities on the residual strength of rock mass insight from a discrete element method simulation abstract when rock failure is unavoidable the designer of engineering structures must know and account for the residual strength of the rock mass this is particularly relevant in underground coal mine openings pre existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre existing discontinuities on the residual strength for this purpose the present study demonstrates a numerical analysis using a discrete element method simulation the numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses independent of confining conditions as confining pressures increase both peak and residual strengths increase with residual strength increasing at a faster rate the finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars a comprehensive interpretation of the finding was conducted using a cohesion weakening friction strengthening cwfs model the effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses

investigation of microearthquake activity following an intraplate teleseismic swarm on the west flank of the southern east pacific rise between february 1991 and may 1992 33 intraplate earthquakes having body wave magnitudes between 4 3 and 6 0 were located on the west flank of the southern east pacific rise by the international seismological center seven months after the last teleseismic event we deployed four ocean bottom seismometers at the site of the teleseismic swarm one hundred and ninety two microearthquakes were located using p and s travel times of events recorded by three or more instruments during the 16 day deployment most of the microearthquakes were in a band about 30 km long and 6 km wide between and parallel to seamount chains in addition several events were distributed along a line perpendicular to the main seismicity band and parallel to the ridge axis the focal depths of the microearthquakes range from 1 to 15 km and most are between 5 and 12 km similar to the depth range of the teleseismic events hung and forsyth 1996 the composite p wave polarities indicate that the microearthquakes had a variety of focal mechanisms we developed a new grid search inversion technique that utilizes the p wave polarities and the empirically corrected ratios of p and s wave amplitudes to find the focal mechanisms of individual events within the acceptable travel time and amplitude misfits focal solutions are fairly stable normal faulting is found in the ridge parallel seismicity line the thrust and strike slip faulting in the main seismicity band is distinctly different from the exclusively normal faulting mechanisms of the teleseismic events there is no apparent depth dependence of fault types none of the existing models of the sources of stress ridge push thermoelastic stresses loading by local topographic features caldera collapse and north south extension of the pacific plate provides a satisfactory explanation for both the teleseismic swarm and microearthquakes we propose a new tectonic scenario in this scenario the lithosphere is prestressed by the cooling of the plate magma rising from the deeper mantle induces normal faulting ahead of the dike tips in the lower lithosphere which is already under extensional thermal stress producing the larger teleseismically detected events once the dikes propagate into the lithosphere the region surrounding the dikes behind the tips is compressed by the overpressure of magma depending on the geometry of the dikes the local orientations of the minimum principal stress and the local weaknesses in the lithosphere thrust or strike slip faulting the microearthquakes may occur

centroid moment tensor solutions for january march 1992 abstract centroid moment tensor solutions are presented for 160 earthquakes that occurred during the first quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

relative sea levels of japan from tide gauge records we attempted to separate tectonic ocean ographic and eustatic components of change in relative sea levels derived from the many tide gauge records of japan acquired during the past 50 yr a modified eigenanalysis permitted use of station data of unequal lengths regression analysis and eigenanalysis revealed systematic spatial differences in relative sea level rise of 25 mm yr although the difference is too great to be solely eustatic in origin data are insufficient to permit accurate separation of tectonic and eustatic effects on relative sea levels the low frequency patterns periods longer than 50 yr may have been derived from subduction of the pacific and philippine plates beneath japan higher frequencies 12 6 and 2 yr periods are correlated with oceanographic factors such as shifts in the position of the kuroshio and the el nino southern oscillation the contours of relative change in sea levels provide convincing evidence that neither a single nor several japanese tide gauges can be selected to authentically demote present or past eustatic sea level rise

microscale modeling of fluid flow geomechanics seismicity relationship between permeability and seismic source response in deformed rock joints studying rock joint deformation including both slippage and opening mechanisms provides an opportunity to investigate the connection between the permeability and seismic source mechanisms a microscale fluid flow geomechanics seismicity model was built to evaluate the transport response and failure mechanism of microcracks developed along a joint in berea sandstone samples during deformation the modeling method considers comprehensive grain cement interactions fluid flow behavior is obtained through a realistic network model of the pore space in the compacted assembly the geometric description of the complex pore structure is characterized to predict permeability of the rock sample as a function of rock deformation by using a dynamic pore network model as a result of microcracks development forces and displacements in grains involved in bond breakage are measured to determine seismic moment tensor shear and nonshear displacements are applied to the joint samples to investigate their effects on permeability evolution and failure mechanism of microcracks during joint deformation in addition the effect of joint roughness is analyzed by performing numerical compression tests we also investigate how confining pressure affects volumetric deformation leading to opening or closure of developed microcracks and permeability changes of samples with joints

location of the africa australia india triple junction and motion between the australian and indian plates results from an aeromagnetic investigation of the central indian and carlsberg ridges accepted 1994 june 7 received 1994 may 23 in original form 1993 may 24 summary prior studies have proposed and examined the hypothesis that india and australia are separate rigid plates separated by a wide near equatorial e w striking plate boundary attempts to place narrow limits on the location of the africa australiaindia triple junction have been hindered however by the lack of useful magnetic profiles crossing the eastern carlsberg ridge and northern central indian ridge herein we present near ridge portions of new profiles from an aeromagnetic survey of the carlsberg ridge east of 66 e and of the central indian ridge north of 19 s these new data are used to estimate 35 new spreading rates averaged from the middle of chron 2a 3 03 ma to the present all other plate motion data along the central indian and carlsberg ridges are also analysed to investigate the present kinematics of the indian ocean especially the motion and boundary between the indian and australian plates unlike prior efforts we objectively estimate uncertainties in the strikes of transform faults along the carlsberg and central indian ridges

centroid moment tensor solutions for october december 1992 abstract centroid moment tensor solutions are presented for 205 earthquakes that occurred during the fourth quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

inter annual and decadal sea level variations in the north western pacific marginal seas abstract long term sea level changes in the okhotsk japan east east china and yellow seas have been explored based on mean monthly values of sea level from tide gauge and altimetry measurements the analysis of low frequency sea level variability reveals clearly differentiated areas the okhotsk sea and the northern sector of the japan east sea display lower sea level variances and no sea level rise the southern japan east sea presents larger sea level variability associated with the circulation regime of the warm current entering through the tsushima strait and inter annual sea level variations that are driven by steric and atmospheric changes the largest sea level variances are found in the yellow sea due to the effect of atmospheric forcing over the continental shelf inter annual variability is spatially varying within the yellow sea and the east china sea and is mainly related to the steric sea level changes regional mean sea level indices have been synthesized for each area using the longest tide gauge records and have revealed correlations between the southern japan east and yellow seas with pdo and np climatic indices linear trends at coastal sites in the japan east east china and yellow seas show a rather heterogeneous pattern with values between 1 5 and 5 5 mm yr for the period 1960 2000 during the period 1993 2008 linear trends derived from coastal tide gauges and from altimetry observations are coherent and reveal a southwards increasing pattern with maximum averaged values reached at the yellow sea 4 9 1 9 mm yr followed by the japan east sea 3 8 0 9 mm yr decadal rates of sea level change show distinct behaviour among basins as well as with the global average the southern japan east sea the east china sea and the yellow sea display decadal variability which is out of phase with respect to the global values

centroid moment tensor solutions for july september 1992 abstract centroid moment tensor solutions are presented for 224 earthquakes that occurred during the third quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

oil and gas developments in far east in 1983 in 1983 the far east region was again one of the more active regions of the world for exploration exploratory drilling increased 19 line kilometers of seismic increased and development drilling was up 40 despite the active exploration pace in 1983 no major oil or gas discoveries were made in the region indonesia india japan and pakistan recorded multiple discoveries but reserves in individual finds appear to be modest as usual indonesia was the most active country for which detailed data is available india followed with the next most active exploration program its effort appears to be gaining momentum and showing significant positive results the remainder of the region with the exception of onshore thailand proceeded slowly at the same pace as previous years and generally speaking with the same results possible bright spots in this picture are japan and pakistan where encouraging oil discoveries were found during the year oil production in the far east region increased 7 in 1983 the majority of the 300 000 bopd increase came from india 81 000 bopd malaysia 79 860 and people s republic of china 100 000 gas production increased a healthy 8 mainly due to start up of the bintulu lng facility in malaysia and inclusion of additional processing trains at indonesia s lng facilities several new companies began to explore in the far east during 1983 although acreage acquisition appears to have declined during the year continued enthusiasm for exploration projects was evidenced by increases in exploratory drilling and seismic throughout the region

relative sea level changes from tide gauge records of eastern asia mainland records from 22 tide gauge stations along the mainland coast of eastern asia document low frequency vertical movements of the land perhaps biased by unevaluated changes of sea level the land is rising relative to sea level as much as 5 mm yr 1 in the areas of massifs and ancient foldbelts and subsiding as much as 9 mm yr 1 in areas of cenozoic basins and foldbelts although the tide gauge records are sparse inferences from them are supported by the stratigraphy and structure of the region and by raised and submerged sea level terraces thus relative changes of sea level are heavily influenced here by tectonic and isostatic as well as eustatic factors just as in japan scandinavia and north america where tide gauge records are much more abundant higher frequency 2 25 yr periods sea level fluctuations show broad peaks between 2 and 4 yrs and near 10 yrs some of these fluctuations correlate with behavior of the kuroshio current which along with freshwater inflow dominates the hydrography of the eastern asian continental shelves observations of water mass fluctuations are too sparse to identify direct causes of all high frequency variability

subinertial to interannual transport variations in the korea strait and their possible mechanisms 1 the voltage derived transport in the korea strait from march 1998 to april 2002 reveals various temporal variations such as subinertial monthly seasonal and interannual variations the driving mechanisms of these temporal variations in the flows through the straits and the mean sea level of the east sea sea of japan are investigated using a simple analytical barotropic model the east sea is simplified as a flat bottomed semienclosed basin and it is forced by the atmospheric pressure the along strait wind stress and the sea level differences along the straits despite its simplicity this model explains most variations and helps us understand dominant driving forces on each timescale at the subinertial periods of 2 10 days the atmospheric pressure dominantly drives the flows into or out of the east sea due to a helmholtz resonance whose period is about 3 days and the mean sea level cannot respond isostatically the effects of the atmospheric pressure on the transport variations become weak at long periods because there is enough time for the east sea to be drained or filled through the strait flows as its mean sea level responds isostatically on the other hand the changes in the adjusted sea levels outside the straits of the east sea cause the pressure gradient forces along the straits and induce most of variations in the strait flows and the mean sea level at the monthly to interannual periods

discrete element modelling of deformation and damage of a roadway driven along an unstable goaf a case study abstract roadways driven alongside a previously extracted longwall panel goaf are a common situation in underground coal mining the unstable goaf can have a significant detrimental impact on the stability of the roadway this paper presents a combined srm udec trigon numerical approach to investigate the failure mechanism of a roadway driven alongside an unstable goaf the synthetic rock mass srm method is used to derive the rock mass properties and the newly developed udec trigon approach is used for simulating brittle fracture and consequent roadway damage the results indicate that the roadway suffers asymmetric damage characterized by a major rib convexity a severe floor heave and a relatively stable roof with limited fracturing this failure mechanism is consistent with field observations a quantitative evaluation of the damage around the roadway indicates that shear failure plays a major role in the roadway damage our study suggests that the proposed combination of srm and the udec trigon is well suited to the evaluation of failure mechanisms around underground coal mine excavations

recirculation and seasonal change of the kuroshio from altimetry observations surface height fluctuations across an eastward flowing boundary current such as the gulf stream and the kuroshio can be caused by changes both in the upstream inflow and in the neighboring recirculation gyres clarifying these causes is important in understanding the time dependent nature of the boundary currents and their relationship to the surface wind and buoyancy forcing using satellite altimetry data to identify these causes however requires mean surface height field information which is not readily available from the altimetry observation owing to lack of accurate geoid data the present study presents a method to estimate the mean surface height profile across a boundary current system including recirculation gyres by combining altimetrically measured residual height data and historical hydrographic data applying this method to the kuroshio revealed that the absolute surface height profiles thus estimated agree well with the results from quarterly in situ hydrographic observations by separating the signals of the surface height fluctuations into those of the eastward flowing jet and the recirculation gyres we found that the seasonal cycle in the surface transport of the kuroshio which has a maximum in july and august is primarily due to the seasonal change in the intensity of the recirculation gyre south of the kuroshio

geologic evolution of petroliferous basins on continental shelf of china the coastline of southeastern china is about 18 000 km 11 200 mi in length and its aggregate continental shelf area within 200 m 660 ft water depth is well over 1 million km2 390 000 mi2 recent geophysical exploration and petroleum drilling records aid in understanding the geologic evolution of these petroliferous basins two types of tectonic basins are present on the continental shelf areas 1 bohai gulf south yellow sea and beibu gulf are intraplate polyphase rift depression basins and 2 east china sea mouth of the pearl river and the yingge sea are epicontinental rift depressions basins both types are believed to be of extensional origin the severe convergence of the indian plate with the eurasia plate produced east northeast s reading of the south china sea basin which resulted in two triple junctions on its northern margins the pacific plate was subducted by downthrust beneath the eurasia continental crust the extension mechanism could be the rising of an upper mantle plume to produce two weak north northeast trending fracture zones a series of intraplate and epicontinental rift depression basins was formed the depositional models and sea level variations of these basins have been interpreted from drilling records and seismic profiles they can be explained by the tectonoeustatic changes in sea level and cenozoic climatic changes in china

recent large earthquakes near cape mendocino and in the gorda plate broadband source time functions fault orientations and rupture complexities the northward migration of the mendocino triple junction is associated with complex faulting within the gorda plate and in the convergent zone between the gorda and north american plates this region has experienced substantial recent large earthquake activity and quantification of these faulting processes is essential for understanding the evolution of the triple junction using an empirical green function deconvolution method for teleseismic and regional surface waves and body waves we obtain relative source time functions for the april 25 1992 cape mendocino thrust earthquake m w 7 2 its two large strike slip aftershocks on april 26 1992 m w 6 5 6 6 and two large strike slip events in the gorda plate that occurred july 13 1991 m w 6 8 and august 17 1991 m w 7 1 the removal of propagation effects using empirical green functions provides unusually detailed source rupture information and indicates that all the ruptures are less than 16 s in duration analyzing the directivity effects observed in the source time functions we resolve rupture directions and corresponding fault orientations for the four largest events and place some constraints on the smaller aftershock significant differences in the rupture duration and stress drop are observed between the cape mendocino mainshock and its two largest aftershocks the mainshock which ruptured westward on a shallow dipping plane either on or paralleling the interplate contact between the gorda and north american plates had a smooth 9 s long rupture with a 0 9 4 6 mpa static stress drop the two largest aftershocks occurred within the uppermost mantle of the gorda plate and have more complex ruptures with total durations of 14 15 s and static stress drops of less than 0 3 mpa perhaps reflecting a difference between mantle and crustal earthquakes in this region the aftershocks appear to have ruptured conjugate strike slip faults accounting for differences in their damage patterns the august 17 1991 gorda plate event ruptured a southwest striking fault while the july 13 1991 event ruptured a southeast striking fault with both events relieving north south compression within the deforming gorda plate the existence of multiple active faults in the region constitutes a significant earthquake hazard associated with the complex stress environment of the migrating triple junction

fracture network engineering for hydraulic fracturing fracture network engineering fne involves the design analysis modeling and monitoring of infield activities aimed at enhancing or minimizing rock mass disturbance fne relies specifically on advanced techniques to model fractured rock masses and correlate microseismic ms field observations with simulated microseismicity generated from these models hydrofracture stimulation is an example where fne is playing a role with hydraulic treatments now being widely used to optimize production volumes and extraction rates in petroleum reservoirs enhanced geothermal systems and preconditioning operations in caving mines ms monitoring is now becoming a standard tool for evaluating the geometry and evolution of the fracture network induced during a given treatment principally by source locating ms hypocenters and visualizing these with respect to the treatment volume and infrastructure the integrated use of synthetic rock mass srm modeling of the hydrofracturing with enhanced microseismic analysis ema

centroid moment tensor solutions for october december 1996 abstract centroid moment tensor solutions are presented for 237 earthquakes that occurred during the fourth quarter of 1996 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 in emert h harjes h p eds acoustical imaging plenum 19 pp 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 bull seism soc am 86 144 158 is used to predict the decay of the waveforms

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

centroid moment tensor solutions for october december 1991 centroid moment tensor solutions are presented for 160 earthquakes that occurred during the fourth quarter of 1991 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8

distinct element modeling of hydraulically fractured lac du bonnet granite 1 the aim of this study is to better understand the mechanics of fracture development and propagation during hydraulic fracturing this paper presents some development and applications of discrete particle modeling of this problem a discontinuum modeling approach idealizes the material as separate particles bonded together at their contact points and utilizes the breakage of individual structural units or bonds to represent damage the numerical models are correlated with existing hydrofracture laboratory experiments which are presented in other publications a simulation of a laboratory scale hydrofracture experiment and the acoustic emission ae data from the experiment is used to validate the synthetic aes produced in the hydrofracture model this technique has been used to examine the mechanics of fracture initiation and time and spatial distributions of ae the modeling results demonstrate that the mechanism of hydraulically induced fracture in the lac du bonnet ldb granite core sample is predominantly tensile failure and that the shear cracks recorded in the hydrofracture experiment were due to slip on preexisting fractures numerical modeling of hydrofracture on homogeneous and heterogeneous synthetic samples seems to capture much of the behavior observed in the laboratory hydrofracture experiments

aftershock sequence parameters in new zealand abstract regional generic models describing the temporal and magnitude distribution of aftershocks are routinely used in california to assess aftershock hazard this note applies the reasenberg and jones 1989 formulation of aftershock parameters to 17 new zealand earthquake sequences of m 5 5 from 1987 through 1995 the median values of the aftershock parameters are similar to those obtained for california

the annual cycle of the western boundary current in the gulf of mexico it has been known for decades that the mean circulation in the western gulf of mexico is a large anticyclone this flow is driven both by wind stress curl and detached rings from the loop current this paper is an attempt to examine their relative importance by focusing on the annual cycle of the observed flow a new compilation of ship drift data shows that the flow along the western boundary is strongest in july and weakest in october it appears physically plausible that the annual variation of this western boundary current is driven by the annual variation in wind curl augmented by ekman pumping over the western gulf because the maximum in wind curl is so close to the western boundary the phase delay between the annual cycles of curl and current is only approximately 1 month the magnitudes of the curl and resulting current seem physically plausible the response is baroclinic and penetrates to 1000 m the bottom of the main thermocline the change in velocity at the sea surface is consistent with the cross stream pressure gradient as determined by the changes in sea level at the coast and dynamic height changes offshore the annual cycle is relatively large at the annual minimum the flow is only approximately 25 of the maximum the data suggest that this flow could be driven by wind curl but the uncertainty is high consequently the contribution of loop current rings turns out to be relatively small the reason for this is that when rings reach the western wall the steep bottom topography intersects the sloping fluid contours of the rings the rings decay slowly by normal deepwater processes until they reach the edge of the continental shelf and then they decay more rapidly by loss of fluid once the rings have reached the western boundary the decay time scale is found to be only 70 days

fluctuations of sea level in the western north pacific and inferred flow of the kuroshio abstract monthly sea level elevations at naze and aburatsu sites on either side of the tokara strait through which the kuroshio flows were analyzed for the period 1963 74 the sea level elevations were adjusted to uniform atmospheric pressure using a barometric factor of 1 cm mb 1 the adjusted elevations are presented as 1 long term mean seasonal values and 2 deviations from the long term means differences in the elevations between the two sites were then used as indices of the transport of the kuroshio the seasonal amplitude of the elevation differences across the kuroshio naze minus aburatsu is 13 of the mean surface geopotential anomaly difference of 0 6 dyn m 0 1000 db the phase of this difference signal indicates maximum northward flow in summer zonally integrated wind stress curl at this latitude in the pacific interior however is most anticyclonic during winter instead the seasonal fluctuations of the kuroshio are more nearly in phase with the fluctuations in the latitudinal grad

some relationship between van seismic electric signals ses and earthquake parameters abstract a possible correlation between ses seismic electric signals of the van method characteristics and earthquake parameters is investigated for the period january 1 1983 december 31 1994 for western greece during this period there were total of 55 earthquakes of mb 5 0 in the region of the so called selectivity maps of the ioannina ioa and pirgos pir van stations cmt solutions are available for 29 of these earthquakes eighteen were preceded by ses at ioa and eleven at pir none of them was preceded by simultaneous ses at both stations the main results are as follows 1 the direction of the ses vector at ioa is correlated with the focal position of predicted earthquakes although nearby earthquakes often have ses with dissimilar vector directions 2 the ses of all nine thrust events of the 29 earthquakes were observed at ioa but their vector direction was not unique 3 eleven earthquakes in the zone west of kefallinia to peloponese preceded by ses at pir were of the strike slip type with varying degrees of normal component the vector direction of ses at pir for these earthquakes was predominantly westward 4 the source mechanism changed from largely strike slip type to thrust type in the above zone at the end of 1987 and this coincided with a shift in the sensitive site from pir to ioa indicating a possible correlation between the source mechanism and selectivity characteristics of van stations

motion of the philippine sea plate consistent with the nuvel 1a model summary we determine euler vectors for 12 plates including the philippine sea plate ph relative to the fixed pacific plate pa by inverting the earthquake slip vectors along the boundaries of the philippine sea plate gps observed velocities and 1122 data from the nuvel 1 and the nuvel 1a global plate motion model respectively this analysis thus also yields euler vectors for the philippine sea plate relative to adjacent plates our results are consistent with observed data and can satisfy the geological and geophysical constraints along the caroline cr ph and pa cr boundaries the results also give insight into internal deformation of the philippine sea plate the area enclosed by the ryukyu trench nankai trough izu bonin trench and gps stations s102 s063 and okino torishima moves uniformly as a rigid plate but the areas near the philippine trench mariana trough and yap palau trench have obvious deformation

changing coastal levels of south america and the caribbean region from tide gauge records abstract tide gauge records from southern mexico the caribbean islands and central and south america that span the interval 1940 1970 reveal long term changes of relative sea level according to regression analysis and eigenanalysis the results indicate such large variations in both direction and rate of secular movement as to rule out changes in volume of ocean water as being more than a subordinate factor the only satisfactory explanation is that the land level beneath the tide gauges is rising in some places and sinking in others complex spatial patterns of relative seal level change in southern mexico and the caribbean mirror the tectonic regime of these regions exhibiting both submergence and emergence of the land central american tide gauge records similarly show considerable complexity responding to relative movement along plate boundaries the pacific coast of south america appears to correlate with the depth of the benioff zone subduction of aseismic ridges produces local highs in the benioff zone flanked by troughs at either side near the benioff highs relative land level is rising between these ridges relative land level is falling sea level trends in southern and atlantic coasts of south america are closely linked with continental crustal rifting and subsidence data do not allow unambiguous separation of changes in ocean level from changes in land level and no simple eustatic ocean level change can be estimated accurately from these data

new seismic gap hypothesis five years after we use earthquake data from 1989 1994 to test a forecast by nishenko based on the seismic gap theory we refer to this forecast as the new seismic gap hypothesis because it is the first global forecast based on the seismic gap hypothesis that considers the recurrence time and characteristic earthquake magnitude specific to each plate boundary segment nishenko s forecasts gave probabilities that each of about 100 zones would be filled by characteristic earthquakes during periods of 5 10 and 20 years beginning on the first day of 1989 only the first of these can be tested now we used three tests based on 1 the total number of zones filled by characteristic earthquakes 2 the likelihood that the observed list of filled zones would result from a process with the probabilities specified in nishenko s hypothesis and 3 the likelihood ratio to that of a poissonian null hypothesis the null hypothesis uses a smoothed version of seismicity since 1977 and assumes a gutenberg richter magnitude distribution we used both the harvard centroid moment tensor and the national oceanic and atmospheric administration preliminary determination of epicenters catalogs in our test we also used several different magnitude cutoffs in our tests because nishenko s forecast did not specify a clear relationship between the characteristic earthquake magnitude and the threshold magnitude for a successful prediction using a strict interpretation that only earthquakes equal to or larger than the characteristic magnitude should be counted both catalogs show only two qualifying earthquakes in the entire area covered by the forecast the predicted number is 9 2 and the discrepancy is too large to result from chance at the 99 confidence level the new seismic gap hypothesis predicts too many characteristic earthquakes for three reasons first forecasts were made for some zones specifically because they had two or more earthquakes in the previous centuries biasing the estimated earthquake rate second open intervals before the first event and after the last event are excluded in calculation of recurrence rate third the forecast assumes that all slip in each zone is released in characteristic earthquakes of the same size while in fact considerable slip is released by both smaller and larger earthquakes the observed size distribution of earthquakes is inconsistent with the characteristic hypothesis instead of a deficit of earthquakes above the characteristic limit earthquake numbers are distributed according to the standard gutenberg richter relation by lowering the magnitude threshold for qualifying earthquakes it is possible to reduce the discrepancy between the observed and predicted number of earthquakes to an acceptable level however for every magnitude threshold we tried the new seismic gap model failed the test on the number of filled zones or the likelihood ratio test or both at least at the 95 confidence level

long term probabilistic forecasting of earthquakes we estimate long term worldwide earthquake probabilities by extrapolating catalogs of seismic moment solutions we base the forecast on correlations of seismic moment tensor solutions the forecast is expressed as a map showing predicted rate densities for earthquake occurrence and for focal mechanism orientation focal mechanisms are used first to smooth seismicity maps to obtain expected hazard maps and then to forecast mechanisms for future earthquakes several types of smoothing kernels are used in space domain we use the 1 distance kernel for the distribution of seismicity around any epicenter the kernel is parameterized using two adjustable parameters maximum distance and directivity distribution of seismicity around an epicenter with regard to the focal mechanism of an earthquake for temporal prediction we use the poisson hypothesis of earthquake temporal behavior we test these forecasts we use the first half of a catalog to smooth seismicity level and the second half of the catalog is used to validate and optimize the prediction to illustrate the technique we use available data in the harvard catalog of seismic moment solutions to evaluate seismicity maps for several seismic regions the method can be used with similar catalogs the technique is completely formal and does not require human operator intervention hence the prediction results can be objectively tested moreover the maps can be used as the poisson null hypothesis for testing by the likelihood method against any other prediction model which shares the same sample space the same zones time window and acceptance criteria

sediment accumulation in a modern epicontinental shelf setting the yellow sea sediment accumulation in the yellow sea epicontinental shelf environment is investigated on 100 yr and 1000 yr time scales using 210pb and 14c geochronologies the distribution of modern 210pb accumulation rates in the yellow sea reveals that the loci of modern huanghe sediment accumulation are the topset 1 2 mm yr foreset 4 9 mm yr and proximal bottomset deposits 2 4 mm yr of the shandong subaqueous delta which extends south from the shandong peninsula 210pb rates in the distal bottomset deposits of the subaqueous delta in the central and southern yellow sea are generally low 0 3 0 9 mm yr a sediment budget demonstrates that between 9 15 of the annual huanghe discharge is accumulating in the yellow sea about two thirds of this sediment is accumulating in the topset foreset and proximal bottomset deposits of the shandong subaqueous delta with the remaining third accumulating as widespread distal bottomset deposits 14c age dates of subaqueous delta sediments indicate that the thick 40m clinoform structure formed predominantly between 6200 and 4060 yrs b p at rates approaching 20 mm yr observations in the yellow sea as well as on the amazon and ganges brahmaputra shelves demonstrate that subaqueous deltaic stratigraphy is the general rule where major rivers enter energetic shelves whether epicontinental or pericontinental the development of extensive bottomset deposits may be restricted to epicontinental shelf environments and may be diagnostic of sedimentation in this type of setting

centroid moment tensor solutions for april june 1992 abstract centroid moment tensor solutions are presented for 245 earthquakes that occurred during the second quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward the solution for an earthquake under mindanao philippines on 9 may represents the 10 000th event in the cmt catalogue

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

shallow subduction tectonics and fault interaction the weber new zealand earthquake sequence of 1990 1992 a series of four large earthquakes with epicenters very close to one another occurred in 1990 1992 in the weber region of the southeast coast of the north island new zealand the region is one of oblique plate convergence and subduction the plate interface being at about 20 km depth the first event february 19 1990 ml 6 1 mw 6 2 occurred within the upper part of the subducting pacific plate on a steeply northwest dipping normal fault as defined by relocated aftershocks the mechanism of this event reflects downdip tension within the subducting plate due to slab pull forces as is common in new zealand the second event may 13 1990 ml 6 2 mw 6 4 occurred on an imbricate fault in the overlying australian plate dipping shallowly northwest with components of both thrusting and dextral strike slip motion the slip vector is similar to the direction of plate convergence showing no arc normal rotation as observed for subduction thrust events in other areas of oblique convergence it is unlikely that the spatial and temporal closeness of these events is coincidence a similar pair occurred to the south in 1942 but the coupling mechanism is not clear perhaps being related to aseismic slip downdip on the subduction interface two subsequent events both of ml 5 5 occurred on august 15 1990 and march 2 1992 and extended the aftershock zone of the deeper first main shock to the northeast matching the extent of the shallower second main shock mechanisms of aftershocks of the two larger events are quite variable but as a whole are similar to the relevant mainshock the time history of the aftershocks of the first deeper event shows a period of quiescence beginning 35 days before the second shallow event the mean magnitude of those events that did occur was high this observation cannot be explained by station biases weather or changes in analysis methods and may be due to stress changes induced by precursory aseismic slip which would discourage aftershock occurrence

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

seismic characterization of a highly stressed rock mass using tomographic imaging and induced seismicity a seismic tomography study was carried out at falconbridge s lockerby mine sudbury canada in april 1989 the objective was to determine the integrity of a rock mass at 1 km depth and to investigate the correlation between induced seismicity and p wave velocity structure the tomographic image showed two distinct and significant p wave velocity anomalies a low velocity zone at the source region of a mn 2 3 mining induced tremor recorded in 1985 and a high velocity zone at the source region of a mn 2 6 mining induced tremor recorded in 1988 analysis of mining induced microseismicity showed that the high velocity zone was the focus for seismic activity prior to and after the 1988 tremor in contrast to the low velocity zone which remained aseismic for the same period the seismic anomalies were diamond drilled following the tomographic imaging to verify the physical characteristics of the zones the seismically active high velocity zone showed severe core disking indicative of a highly stressed strong rock while the low velocity zone was characterized by extensive fracturing and failed rock the results showed that the 1985 tremor and rock burst sequence resulted in a major failure of the rock mass in the source region of the event and stress was redistributed and concentrated in the source region of the 1988 tremor the 1988 event and rock burst sequence did not result in failure of the source region which therefore remains a seismically active high velocity zone with a potential for significant seismic energy release and further rock bursting the study has highlighted a correlation between p wave velocity structure and induced seismicity which can be used to characterize highly stressed rock masses in underground mines

recent temporal change in the stress state and modern stress field along the north anatolian fault zone turkey summary the north anatolian fault naf is a dextral strike slip fault which runs about 1400 km from east to west from the karliova triple junction to the aegean domain it was active during the plio quaternary as a consequence of the collision between the eurasian and arabian plates the naf intracontinental deformation zone contributes with the sinistral east anatolian fault to the westward extrusion of anatolia as a consequence of the northward drift of arabia the central naf zone forms a northward convex bend where the eastern naf n110 e trending segment extending from karliova is connected to the western naf n75 e trending segment running to aegea analysing the slip occurring in major earthquakes around the naf we show that the present day stress pattern along the naf agrees with stress magnitude and strike variations from east to west the stress regime along the naf is nnw trending hmax 1 transpression in eastern naf this progressively changes westwards to nw trending 1 transtension in central anatolia this lateral variation means a relative decrease of the hmax magnitude which evolves progressively to an extensional regime 1 vertical around the westernmost naf characterized by a nne trending hmin 3 the drastic change in the tendency of the regional stress state in the north anatolian block from compressional to extensional is effective within the central naf bend the stress regime determined by inversion of slip vectors measured on fault planes of various scales confirms the present day transtensional regime in the central part of the naf bend however the fault kinematic analysis of quaternary stress states within the central naf indicates that this stress state was not continuous throughout the quaternary indeed chronologies of fault slip vectors provide evidence for two distinct quaternary regional strike slip stress states within this zone both states have consistent ne and nw trending 3 and 1 axes respectively but have significantly different r values the change in the strike slip stress regime probably occurred in the middle pleistocene the older mean stress state is characterized by a n142 8 e trending 1 a n52 13 e trending 3 and a mean arithmetic rm value of 0 75 which indicates that the regional stress regime is transpressional the younger strike slip regime is characterized by a n142 14 e 1 axis a n52 10 e 3 axis and a mean rm of 0 24 which indicates the transtensional character for this regime the low r values of the stress deviators related to the recent stress state reflect normal component slips these temporal and spatial stress changes along the naf result from the coeval influence of forces due to the aegean subduction in the west and to the northward drift of arabia in the east over these boundary forces shear is superimposed along the naf which accommodates the anatolia extrusion however the timing of the temporal stress change permits the suggestion that the quaternary stress regime variation in north anatolia is mainly due to the influence of the aegean domain

numerical investigation of the scale effect and anisotropy in the strength and deformability of coal abstract the decrease in strength and stiffness of coal with increase in specimen size has long been recognized as scale effect in this study a synthetic rock mass srm approach has been used to investigate this scale effect and the anisotropy of coal a discrete fracture network dfn for the coal was created and then embedded into bonded particle models to form a range of varying size of srm coal specimens unconfined compression tests on the srm specimens showed that the srm approach is capable of quantitatively reproducing the dependency of the strength and stiffness on the size of the coal specimens the strength and stiffness anisotropy of coal can also be reproduced the numerical results are shown to be in good agreement with published laboratory and field test results