synchronism of holocene east asian monsoon variations and north atlantic drift ice tracers eighteen radiocarbon dated eolian and paleosol profiles within a 1500 km long belt along the arid to semi arid transition zone of north central china record variations in the extent and strength of the east asian summer monsoon during the holocene dated paleosols and peat layers represent intervals when the zone was dominated by a mild moist summer monsoon climate that favored pedogenesis and peat accumulation brief intervals of enhanced eolian activity that resulted in the deposition of loess and eolian sand were times when strengthened winter monsoon conditions produced a colder drier climate the monsoon variations correlate closely with variations in north atlantic drift ice tracers that represent episodic advection of drift ice and cold polar surface water southward and eastward into warmer subpolar water the correspondence of these records over the full span of holocene time implies a close relationship between north atlantic climate and the monsoon climate of central china

a seismic structure study in the kaoping area southwestern taiwan the difference between s wave and s to p wave conversion s p phase arrival times is enhanced with rectilinear motion detector filtering to describe alluvial sediment thickness in the kaohsiung pingtung kaoping plains area a more complete understanding of the underground structures of the kaoping area is provided in this paper and explains why the surrounding regions in taiwan experience more earthquakes than the kaoping area data are based on seismic activity recorded by the portable array for numerical data acquisition panda for the period from 1995 to 1997 the difference between s wave and s p phase arrival times shows that the sedimentary layer is thicker along the west and southwest coasts p wave travel time residuals high frequency attenuation parameters kappa and quality factor q p q s and coda waves confirm this result we also determined the orientation of the chaochou fault using the first motion of p wave arrivals to the east of the chaochou fault stress trends southeast northwest while to the west it trends northeast southwest the change in stress trends east and west of chaochou fault suggests the presence of a highly fluid accretionary wedge in the kaoping area the chaochou fault forms a seismically active tectonic boundary with the uplift of the hanging wall leading to westward tilting of the basement of the kaoping plains we demonstrate that these features are the reason there are relatively few earthquakes in the kaoping area the presence of a highly fluid accretionary wedge is indicated by a thick alluvial layer in the west and southwest kaoping coasts the peikung high acts as the indenter that may allow seismic energy to escape and reduce the number of earthquakes in the region online material figures illustrating calculations of kappa q c p and s wave spectra q p and q s from ground motion data

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

how tides and river flows determine estuarine bathymetries abstract for strongly tidal funnel shaped estuaries we examine how tides and river flows determine size and shape we also consider how long it takes for bathymetric adjustment both to determine whether present day bathymetry reflects prevailing forcing and how rapidly changes might occur under future forcing scenarios starting with the assumption of a synchronous estuary i e where the sea surface slope resulting from the axial gradient in phase of tidal elevation significantly exceeds the gradient in tidal amplitude an expression is derived for the slope of the sea bed thence by integration we derive expressions for the axial depth profile and estuarine length l as a function of and d the prescribed depth at the mouth calculated values of l are broadly consistent with observations the synchronous estuary approach enables a number of dynamical parameters to be directly calculated and conveniently illustrated as functions of and d namely current amplitude u ratio of friction to inertia terms estuarine length stratification saline intrusion length flushing time mean suspended sediment concentration and sediment in fill times four separate derivations for the length of saline intrusion li all indicate a dependency on d 2 f u u o uo is the residual river flow velocity and f is the bed friction coefficient likely bathymetries for mixed estuaries can be delineated by mapping against and d the conditions li l however the length of saline intrusion in a funnel shaped estuary is also sensitive to axial location observations suggest that this location corresponds to a minimum in landward intrusion of salt by combining the derived expressions for l and li with this latter criterion an expression is derived relating di the depth at the centre of the intrusion to the corresponding value of uo this expression indicates uo is always close to 1 cm s 1 as commonly observed converting from uo to river flow q provides a morphological expression linking estuarine depth to q with a small dependence on side slope gradients these dynamical solutions are coupled with further generalised theory related to depth and time mean suspended sediment concentrations as functions of and d then by assuming the transport of fine marine sediments approximates that of a dissolved tracer the rate of estuarine supply can be determined by combining these derived mean concentrations with estimates of flushing time ft based on li by further assuming that all such sediments are deposited minimum times for these deposition rates to in fill estuaries are determined these times range from a decade for the shortest shallowest estuaries to upwards of millennia in longer deeper estuaries with smaller tidal ranges

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

new evidence for segmentation of the alaska subduction zone the purpose of this article is to provide additional evidence for segmentation of the subducted plate in alaska and to introduce a catalog of the relocated earthquakes for future studies we used the joint hypocenter determination method to relocate 14 099 subduction zone earthquakes that occurred from july 1988 to july 1998 and were located between 58 n and 65 n latitude the earthquake data were taken from the alaska earthquake information center catalog the selected earthquakes were divided into 16 blocks on the basis of their hypocentral locations and each block was relocated separately average epicenter shift was 3 8 km and average upward and downward depth shifts were 4 1 and 4 4 km respectively roughly the same number of earthquakes shifted upward 47 and downward 53 the overall change with respect to the initial locations is that the seismicity became more compact revealing details about the fine structure of the wadati benioff zone in particular we were able to identify more precisely the boundary between the kenai and mckinley blocks of the subducting plate in addition there is evidence for plate segmentation within the mckinley block manuscript received 15 november 2000

loess sedimentation in tibet provenance processes and link with quaternary glaciations abstract well preserved loess deposits are found on the foothills of mountains along the middle reaches of the yarlung zangbo river in southern tibet optically stimulated luminescence osl dating is used to determine loess ages by applying the single aliquot regeneration technique geochemical mineralogical and granulometric measurements were carried out to allow a comparison between loess from tibet and the chinese loess plateau our results demonstrate that i the loess deposits have a basal age of 13 11 ka suggesting they accumulated after the last deglaciation ii loess in southern tibet has a glacial origin resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near surface winds and iii the present loess in the interior of tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt the lack of full glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial such processes would have been repeated during each glacial interglacial cycle of the quaternary

age constraints on the late quaternary evolution of qinghai lake tibetan plateau dating and geomorphology of shoreline features in the qinghai lake basin of northwestern china suggest that contrary to previous interpretations the lake likely did not reach levels 66 140 m above modern within the past 90 000 yr maximum highstands of 20 66 m above modern probably date to marine isotope stage mis 5 mis 3 highstands are undated and uncertain but may have been at or below post glacial highs the lake probably reached 3202 3206 m 8 12 m during the early holocene but stayed below 3202 m after 8 4 ka this shoreline history implies significantly different hydrologic balances in the qinghai lake basin before 90 ka and after 45 ka possibly the result of a more expansive asian monsoon in mis 5

pedogenic response to millennial summer monsoon enhancements on the tibetan plateau abstract the asian summer monsoons experienced both rapid episodic enhancement and long term evolution with the uplift of tibet the response of pedogenesis to those events on the tibetan plateau at mean elevations of 4000 5000 m is of great interest and significance in deciphering the history of asian and tibetan summer monsoons and in understanding soil development deterioration and management the over 22 m loess paleosol sequence at hezuo on the eastern tibetan plateau extending back through the last interglaciation and the thickest late pleistocene sequence identified thus far on the plateau provides a unique opportunity to tackle the above topics detailed chronology and soil development determined by field pedofeatures and soil proxies have revealed a millennial fluctuation of the asian and tibetan summer monsoons resembling the late pleistocene north atlantic climatic record the end of each heinrich event is closely followed by formation of a stronger paleosol and then some much weaker thin soil horizons weathered loess or loess the episodes of stronger soil development or paleosol events correspond without exception to strongest summer monsoon enhancement at the beginning or in the early part of each bond cycle recorded in the north atlantic the strongest pedogenesis and summer monsoon enhancement is observed to occur during 43 36 ka bp which is not observed in climatic records outside tibet probably indicating a coherent enhancement of asian and tibetan summer monsoons in the last mega interstadial mis3 increase of organic matter excluding decomposition and change of soil types from last interglacial calcic cambisols to holocene chernozems suggests an increase of relative humidity implying partially an increase of elevation due to late pleistocene rapid uplift of the tibetan plateau

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

application of the tidal random walk model to calculate water dispersion coefficients in the ems estuary abstract longitudinal and lateral dispersion coefficients are computed for the ems estuary using a modified version of the tidal random walk model developed by zimmerman this model relates the mixing properties of the flow to the velocity and length scales of the tidal current and the residual eddies it is found that values of the longitudinal dispersion coefficient are 200 1200 m 2 s 1 depending on the position in the estuary and lateral dispersion coefficients are a factor of c 50 smaller these results are three to four times larger than earlier reported values which were determined from field observations this difference is attributed to the fact that in the tidal random walk model the dependence of the dispersion mechanism on the detailed kinematics of the flow is neglected since a statistical distribution of residual eddies is assumed however the model predicts the spatial distribution of the dispersion coefficients in the estuary quite well particular attention is paid to the presence of three peaks in the dependence of these coefficients on the distance to the river mouth using the concepts underlying the tidal random walk model these peaks are related to the presence of tidally induced residual circulations around sand banks it is also concluded that the effect of shear dispersion on the horizontal mixing processes in the ems estuary can be neglected

subduction zone calibration and teleseismic relocation of thrust zone events in the central aleutian islands abstract teleseismically determined epicenters for thrust zone earthquakes in the central aleutian islands are systematically mislocated by about 40 km to the north relative to local network solutions we attribute the mislocation to travel time anomalies produced by the higher p wave velocity in the subducting slab these travel time anomalies can be estimated by seismic ray tracing through a thermally modeled velocity structure for the slab observed teleseismic station residuals and slab travel time anomalies computed from local network hypocenters plotted as a function of event distance to the center of curvature of the island arc show good agreement this distance versus residual relationship can be used to validate the local network hypocenters and to constrain the length of subducting lithosphere computed slab source corrections when incorporated in a standard location program reduce teleseismic mislocations to 20 km the addition of empirical station corrections reduces the mislocation to about 10 to 15 km depth and origin time estimates can be further improved through use of better station corrections a local station within 2 and depth phases

locations of mid oceanic earthquakes constrained by seafloor bathymetry 1 earthquakes associated with the creation of new oceanic crust are difficult to locate precisely because they normally occur far away from seismic stations we assume that epicenters of these events can be constrained by seafloor topography and use the harvard centroid moment tensor cmt focal mechanism of an interplate earthquake to relate the event to either a transform fault a parallel in a coordinate system defined by the pole of rotation between two plates or a mid oceanic ridge a meridian using arrival times from the international seismological center isc bulletin we have relocated about 1500 globally distributed events for the time period 1976 1998 the isc locations can be as much as 70 km away from appropriate topographic features our new locations support that large interplate earthquakes occur on or very close to the primary bathymetric features for earthquakes with unknown mechanism or magnitude below the cmt threshold or predate the cmt catalog we use a simultaneous joint hypocenter determination procedure with respect to the already relocated master events jhdme we invert for earthquakes first for the romanche fracture zone rfz and then for a region extending from 30 n to 30 s seismicity agrees well with the main active ridge or transform however a small number of events might be related to the secondary bathymetry features the improved locations for mid oceanic earthquakes based on bathymetry could help improve our understanding of the oceanic crustal and deep earth structure seismic slip and budget constraint along plate boundaries and dynamics of plate tectonics

longitudinal mixing in the upper reaches of the bay of fundy a time dependent one dimensional advection diffusion equation is used to predict the salinity distribution in the vertically well mixed upper regions of the bay of fundy it is shown that the longitudinal diffusion coefficient must increase in a seaward direction from the head of the bay to give a good agreement between the model and observations and a simple parameterization of the coefficient is sought in terms of the product of appropriate length and velocity scales a coefficient equal to b1u0l0 where b1 is a constant u0 the amplitude of the tidal current and l0 the tidal excursion is tried but does not give this increase and produces a poor description of the salinity distribution however a diffusion coefficient of the form cu h where c is a constant u the r m s friction velocity from the tidal current averaged over the m2 tide h is the water depth and the overbar denotes a cross sectional average does give the required increasing value and allows a good agreement between the model and observations for c 200 this form of parameterization is the same as that for shear dispersion except that the coefficient c is in order of magnitude too large it is suggested instead that the diffusion process results from the interaction of tidal residual eddies with the oscillatory tidal flow a mechanism described by zimmerman 1976 and capable of producing large diffusion coefficients preliminary estimates show that the construction of a tidal power barrage across minas basin would considerably reduce the salinity in the headpond of the barrage but have little effect seaward a sinusoidally varying freshwater input to the estuary is shown to have a significant effect on the salinity distribution only for periods of oscillation exceeding a month while variations in the longitudinal diffusion coefficient due to an apogee perigee tidal cycle have little effect on the salinity distribution

an integrated 3d velocity inversion joint hypocentral determination relocation analysis of events in the northridge area abstract a subset of 3371 events recorded in the northridge area by the southern california seismic network during january to april 1994 was relocated with the joint hypocentral determination jhd technique this analysis showed two unexpected results a the jhd locations are shifted about 3 9 km on average in a northwest direction with respect to the locations determined using a single event location sel program and b the station corrections vary between 0 55 and 1 26 sec a rather large range in addition the jhd locations are less scattered than the sel locations for each station the weighted average of the arrival time residuals obtained when the events are located with the sel program which does not apply distance or error weighting are generally smaller than the corresponding jhd corrections the locations determined with sel and using the weighted average residuals as station corrections do not differ much from the sel locations but on average the rms residuals become as small as those corresponding to the jhd locations as the magnitude of the station corrections indicates the presence of large lateral velocity variations a 3d velocity model for the area was determined using the arrival times of 1012 events recorded by at least 17 stations the initial velocity model was that used routinely by the southern california earthquake center the first two layers 5 5 and 10 5 km thick were subdivided into 100 blocks each 12 12 km these layers show a pronounced low velocity anomaly 24 and 16 respectively immediately to the northwest of the epicentral area this low velocity zone coincides with the west ventura basin another pronounced low velocity zone to the southeast of the epicentral area reflects the presence of the los angeles basin the locations obtained with the 3d velocity model are consistently to the southeast of the jhd locations 2 4 km on average to establish the effect of these pronounced lateral velocity variations on the sel and jhd locations synthetic travel times were analyzed the synthetic times were generated for event locations determined by jhd shifted by various amounts and the 3d velocity model and were subsequently treated as the actual data the most important result of this analysis is that the jhd locations are affected by a quasi systematic shift in a northwest direction up to about 2 7 km on average depending on the initial shift but that the relative locations are well preserved therefore both the velocity inversion of the actual data and the analysis of the synthetic data indicate that the jhd locations determined for the actual data are quasi systematically mislocated to account for this mislocation an overall shift of 2 5 km to the southeast was applied to all the jhd locations one of the most important implications of the shifted locations is the possibility that the northeasterly dipping santa susana fault to the northwest of the epicentral area was seismically active during the aftershock sequence this feature is more diffuse in other published locations

using automated high precision repicking to improve delineation of microseismic structures at the soultz geothermal reservoir an automatic adaptive correlation based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re analyze waveforms manually or semi automatically we apply this technique to induced seismicity at the soultz sous forets geothermal site france the method is first applied to a small previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking visual cross correlation based techniques relative centroid adjusted hypocenters show a decrease in median mislocation from 31 to 7 m for preliminary and automatically adjusted picks respectively compared to the manual results narrow intersecting joint features not observed in the preliminary hypocenter cloud but revealed through manual repicking are also recovered using the automatic method we then address a larger catalogue of 7000 microearthquakes after relocating the events using automatic repicks the percentage of events clustering within 5 m of their nearest neighbor increases form 5 to 26 of the catalogue hypocenter relocations delineate narrow linear features previously obscured within the seismic cloud interpreted as faults or fractures which may correspond to fluid propagation paths or to changes in stress as a result of elevated pore pressures rms travel time residuals for the larger data set are reduced by only 0 2 however phase pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations which will affect location residuals these pick biases are apparent on the adjusted stacked waveforms and correcting them will be important prior to future velocity model refinements

a simple algorithm for local earthquake location using 3d vp and vs models test examples in the central united states and in central eastern taiwan traditional local earthquake location using a horizontally layered homogeneous velocity model is limited in its resolution and reliability due to the existence of frequently overlooked 3d complexity of the real earth during traditional 3d seismic tomography simultaneous earthquake relocation using the resultant 3d velocity model has produced reliable earthquake locations however only a small subset of events are typically used and thus relocated in the inversion the rest of the events in a catalog must then be relocated using the 3d models the repeated calculation of travel times across 3d v p and v s models is also not efficient and not practical for a routine network earthquake location when the very time consuming exact 3d raytracing is used because high resolution earthquake data are now available from many modern seismic networks representative high resolution 3d v p and v s models for a region can be better determined by taking advantage of recently available high speed computer technology and large disk space we implemented a simple algorithm to efficiently locate every local earthquake using the best available regional 3d v p and v s models once the v p and v s information for all cubic cells in a 3d grid model are determined p and s travel times from each grid point to all seismic stations can be calculated and stored on disk files for later usage during the iteration process for earthquake location travel times from a trial hypocenter to all recording stations can be determined simply by a linear interpolation from those of the adjacent eight grid points available in the previously stored disk files without the need for raytracing the iterations continue until the hypocenter adjustments at the end of the last iteration are below the given criteria and the travel time residual or the difference between the observed and the calculated travel times is a minimum therefore any local earthquake can be efficiently and reliably located using the available 3d velocity models this simple location program has been applied to relocate earthquakes in the new madrid seismic zone nmsz of the central united states and in the central eastern taiwan region preliminary results in both regions reveal that earthquake hypocenters can be efficiently relocated in spite of the very significant lateral structural variations tests with data from taiwan further demonstrate that the resolution of seismic tomography and the relocated seismicity is sensitive to relative distribution of seismic network stations and background seismicity thus this single event location program can be applied to relocate all earthquakes in a seismic network catalog and more importantly to allow routine earthquake location for any seismic network using the available 3d velocity models

the denver earthquakes of 1967 1968 abstract a detailed study of the earthquakes associated with the rocky mountain arsenal disposal well is presented long period surface wave studies are used together with p wave first motions to show that the 10 april 9 august and 27 november 1967 earthquakes occurred at depths of 3 to 5 km and were characterized by normal faulting along a northwest striking fault plane a joint hypocenter relocation of 103 microearthquakes of a data set of 279 recorded between 1967 and 1968 shows a hypocenter pattern striking n50 w with most of the events located about 5 km northwest of the disposal well at depths between 3 to 8 km a fault plane dipping southwest is tenuously suggested by those earthquakes with depths less than 5 km modeling of near field seismoscope observations lend support to the focal mechanisms derived

statistical analysis and clustering features of the phlegraean fields earthquake sequence may 1983 may 1984 abstract the seismic activity at the phlegraean fields volcanic area southern italy during the period may 1983 may 1984 5 301 selected events has been analyzed from a statistical point of view the analysis of the time series associated to the microearthquakes shows a high degree of interdependence among the events the main feature being the occurrence of dense swarms the generalized poisson process provides a good fit for the sequence the clustering of the events has not substantially changed during the analyzed period while the mean rate of occurrence of the swarms has generally increased the distribution of the magnitudes within the swarms shows pronounced maxima of energy around the center of the subsequences in agreement with theoretical models of fractures in highly heterogeneous media

progressive multiple event location pmel abstract this paper introduces a new method of using earthquake arrival times to simultaneously determine earthquake hypocenters and station corrections progressive multiple event location pmel forms a solution in three major steps 1 hypocenters are located by conventional single event methods using current station correction estimates 2 an annulled data set pavlis and booker 1980 is formed and accumulated using householder transformations and 3 station correction perturbations are calculated from a pseudoinverse solution of the annulled data set in practice pmel converges rapidly we analyze the non uniqueness of pmel estimates in terms of resolution and covariance matrices one of the most important features of pmel is the computer algorithm that we describe which requires only a modest amount of computer memory that is independent of the number of earthquakes to be processed consequently this algorithm can process a virtually unlimited number of earthquakes we apply pmel to a set of 8049 arrival times from 652 earthquakes and 4 explosions recorded by a network in the coso range inyo county california pmel converges after four adjustments to the station corrections the final rms misfit of 0 05 sec is remarkably good and the station correction estimates correlate strongly with surface geology

analysis of analog and digital records of the 1982 arkansas earthquake swarm abstract the arkansas swarm is the largest earthquake swarm ever recorded in the central or eastern united states three component digital and single component analog recordings for 88 earthquakes occurring during a 12 day period provide a quality data set of manageable proportions for study of the swarm9s seismic properties these 88 earthquakes occurred within a small volume of about 45 km 3 at depths from 4 to 7 km composite focal mechanisms indicate predominantly strike slip motion with the p axis oriented ne sw seismic wave velocity studies indicate that significant temporal and spatial variations of seismic wave velocities are present the v p v s ratio ranges from as low as 1 59 to as high as 1 78 with the majority of values falling between 1 67 to 1 70 an anomalous region immediately north of the center of swarm activity is found where both the p and s wave velocities and v p v s ratio increase dramatically starting about 1 day before the 5 july m d 3 8 event two strong secondary arrivals between the direct p and s arrivals can be clearly identified especially at stations nnw of the activity these secondary arrivals must be converted p waves from s waves incident on two deep discontinuities the above observations are compatible with a small highly heterogeneous swarm source volume within which the ambient stress regime can vary rapidly in both time and space some identified clustering and v p v s changes are clearly precursory to the major events of the sequence but no simple repeating pattern is evident in this restricted data sample

reconstruction of the 2 4 million km2 late pleistocene ice sheet on the tibetan plateau and its impact on the global climate during 20 expeditions new data were obtained on the maximum extent of glaciation in tibet and the surrounding mountains evidence was found of moraines at altitudes as low as 460 m on the southern flank of the himalayas and 2300 m on the northern slope of the tibetan plateau in the qilian shan on the northern slopes of the karakorum aghil and kuen lun moraines occurred as far down as 1900 m in southern tibet radiographic analyses of erratics document former ice thicknesses of at least 1200 m glacial polishing and knobs in the himalayas and karakorum are proof of glaciers as thick as 1200 2000 m on the basis of this evidence a 1100 1600 m lower equilibrium ela line was reconstructed for the ice age which would mean 2 2 4 million km2 of ice covering almost all of tibet since the equilibrium ela line was far below the average altitude of tibet on mount everest and k2 radiation was measured up to 6650 m yielding values of 1200 1300 w m2 because of the subtropical latitude and the high altitude solar radiation in tibet is 3 4 times greater than the energy intercepted between 60 and 70 n or s with an area of 2 2 4 million km2 and an albedo of 90 the tibetan ice sheet caused the same heat loss on the earth as a 6 9 6 million km2 sized ice sheet at 60 70 n because of its proximity to the present day equilibrium ela line tibet must have undergone large scale glaciation earlier than other areas being subject to intensive radiation the tibetan ice must have performed an amplifying function during the onset of the ice age

late quaternary aeolian sedimentation in central and south eastern tibet abstract the geomorphology and the cover sediments in the central and south eastern part of the tibetan plateau provide information about climatic change luminescence dating of aeolian and colluvial silts on top of different moraine sequences provides the first indications for the timing of these sediments during the late quaternary and holocene although there is a widespread cover of aeolian mantles in tibet only a few papers have focussed on them up to now samples from silt layers on top of pleistocene moraines or solifluction debris from central and southern tibet at elevations above 4000 m asl provide early holocene ages in most sections the aeolian silt on top of the bomi moraine in southeastern tibet situated at an elevation of about 3000 m asl provides an age of 25 ka according to geomorphological investigations the bomi moraine dates from the last ice age which can be confirmed by the luminescence data moreover one sample from a silt layer in between gravel layers xainxa is also pleistocene in age according to its sedimentary and geomorphological situation in the tibetan plateau pleistocene loess mainly occurs below 4000 m asl the holocene material a more sandy silt lying above 4000 m asl however aeolian material capping the moraines provides only minimum ages for the terminal moraines the time interval between glacier retreat and the accumulation of aeolian sediments may be several thousand years the most important fact is the trapping of dust in general lakes and a denser vegetation cover are or were the main traps for the typical loess found in the mountain areas of the tibetan plateau

a high resolution local network study of the nazca plate wadati benioff zone under western argentina this paper presents a precise determination of the fine structure of a wadati benioff zone based on analysis of analog and digital seismic data recorded by a local network in the san juan province of western argentina the network is located above one of the subhorizontal segments of the subducted nazca plate without the complicating effects of a dipping slab on the locations of earthquakes the nearly flat geometry of the subducted plate provides an excellent opportunity to determine the thickness and structure of the wadati benioff zone we found that the depth of the wadati benioff zone beneath the network is 107 5 km for a set of digitally recorded events the distance between the shallowest and the deepest event gives a thickness of 20km with 90 of the data concentrated in a zone 12 km thick the spatial distribution of hypocenters shows no evidence of complex internal structure such as a double wadati benioff zone the local network data also suggest that in the region near 32 s where the dip of the wadati benioff zone changes from flat to steep the nazca plate flexes rather than tears at depths less than at least 125 km the intermediate depth seismicity is separated from an active zone of crustal seismicity by an aseismic region between depths of about 40 and 95 km the upper surface of the subducted plate inferred to be at about 90 km provides an upper limit to the thickness of the south american plate in this region an apparent westward dip of the wadati benioff zone as determined by the local network data can be accounted for by a 6 westward dip of the moho beneath the san juan region a result that is in agreement with regional gravity and topographic data

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

the 1982 enola arkansas swarm and scaling of ground motion in the eastern united states abstract the north central arkansas swarm which began in january of 1982 and was still active as of december 1983 has produced over 30 000 events three of these events had duration magnitudes greater than 4 0 fifty three locatable events in the magnitude range 3 8 and below were recorded during the 2 1 2 weeks our 10 digital seismographs were in place the hypocentral locations are confined to a tight cluster with a radius of approximately 1 km depths range between 4 and 7 km focal mechanisms determined for 10 of the events show a combination of strike slip and normal faulting source parameters seismic moment source radius and stress drop were calculated for 48 of the events the seismic moments range from 10 18 to 10 21 dyne cm while the stress drops range from 0 2 to 60 bars acceleration spectra are band limited at the high end at 30 hz the stress drops increase with seismic moment up to 10 20 dyne cm but appear to be constant at greater moment values the arkansas source parameters are similar to other body wave source parameters determined from near source investigations of earthquakes in eastern and central north america e g new brunswick and south carolina and in california e g mammoth lakes oroville and anza but differ substantially from lg wave source parameters estimated for earthquakes in the eastern and central united states

how flat is tibet high resolution digital topography three arc second grid for most of tibet provides new information to characterize the relief of the highest and largest plateau on earth the arid to semiarid central and northern part of the plateau interior has low relief average slopes of over 250 m windows and a mean elevation of 5023 m above sea level at moderate wavelengths of m relief is or less for most of tibet as opposed to the much higher relief of up to 6 km on the plateau edges where glacial and fluvial dissection is greater because of higher levels of precipitation the only faults manifesting significant topographic relief are the relatively small scale generally north trending graben systems primarily in southern tibet and several large scale fault systems near the edges of tibet the flatness of tibet implies that 1 there has been little deformation especially shortening of the uppermost crust north of the graben systems during the late cenozoic and 2 shallow crustal isostatic compensation has been acting to level the surface of the plateau

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

assessment of regional distance location calibration using a multiple event location algorithm abstract we test the use of a multiple event seismic location method to improve epicenter accuracy estimates regional arrival time observations of 74 nevada test site explosions with known locations comprise the test data set we investigate epicenter accuracy as a function of the number of events in the multiple event system that are constrained at the known hypocenter calibration the effect of distance between calibration and unconstrained events and the use of velocity models with varying travel time prediction accuracy further we test the utility of using a posteriori travel time residuals to assess location and travel time prediction accuracy we find that constraining one event at the known hypocenter reduces epicenter error for all other events by 58 on average compared to locations produced without constraining events the incremental improvement in epicenter accuracy rapidly diminishes as more hypocenters are constrained and incremental location improvement is minimal when the number of constrained hypocenters exceeds 10 events closest to a constrained event exhibit small location bias distinct epicenter bias occurs when the distance between the calibration event and the relocated event is greater than a few tens of kilometers last we confirm that metrics based on a posteriori travel time residuals are poor indicators of both epicenter accuracy and velocity model based travel time prediction accuracy

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

luminescence dated aeolian deposits of late quaternary age in the southern tibetan plateau and their implications for landscape history abstract aeolian deposits are widely distributed in the interior of the tibetan plateau and their chronology is poorly known it is not yet clear whether they accumulated only after the last deglaciation or over a longer time we applied quartz osl dating to aeolian samples from the lhasa area with osl ages ranging from 2 9 0 2 to at least 118 11 ka the probability density frequency pdf distribution of 24 ages reveals age clusters at about 3 8 16 21 33 and 79 83 ka indicating enhanced sediment accumulation then the results show that aeolian deposition occurred throughout most of the last 100 ka this implies that 1 an ice sheet covering the whole tibetan plateau during the last glacial maximum lgm could not have existed and 2 erosion during the last deglaciation was not as strong as previously proposed such that not all pre holocene loess was removed the age distribution shown in the pdf indicates that aeolian accumulation is episodic sand formation events revealed by age clusters at 3 8 and 16 21 ka imply roughly synchronous environmental responses to corresponding global scale arid events

seismic velocity changes of p and s waves associated with the 2011 tohoku oki earthquake mw 9 0 as inferred from analyses of repeating earthquakes

wind and tide induced resuspension of sediment and microphytobenthos from tidal flats in the ems estuary the resuspension of microphytobenthos mainly benthic diatoms and mud 55 pm fraction from tidal flats was studied in the ems estuary netherlands germany of which 50 is covered by intertidal areas mud and microphytobenthos are resuspended simultaneously from the tidal flats in the estuary the concentrations of these parameters in the main channels of the estuary are strongly affected by erosion due to wind induced waves and by settlement during calm weather conditions the resuspension of mud can be described as a linear function of the effective windspeed which is defined as the windspeed averaged over three high water 6 h bracketing high water periods preceding sampling the resuspended fraction of microphytobenthos from the top 0 5 cm layer of sediment can also be described as a linear function of the effective windspeed our data indicate that for this estuary the proper quantification of resuspension of mud and microphytobenthos requires consideration of relatively large areas

tidal flow and residual flow in the ems estuary tidal water flow and residual tidal flow between and within channels was ascertained for 20 cross sections in the ems estuary the netherlands the tidal prism of the estuary is approximately 1 10 9 m 3 in the middle reaches the residual ebb and flood transports over the cross sections varied between 1 and 18 of the tidal water transport increasing to 43 near the river proper and near the tidal watersheds the overall mean is c 11 tidally averaged residual current velocities in the cross sections varied from less than 0 01 to 0 33 m s 1 with an overall mean of 0 06 m s 1 the distribution of the tidally averaged residual currents along and over the cross sections studied corresponds very well with the results of a horizontally two dimensional water transport simulation model the data from this study show that the distribution of large scale between channels and small scale within channels residual currents is reflected in the local cross sectional bathymetry it is hypothesized that deviations from a good correspondence between the location of residuals and bathymetry indicate a hydraulically unstable situation which implies a changing local morphology

holocene environmental changes in the central inner mongolia based on single aliquot quartz optical dating and multi proxy study of dune sands abstract alternating units of dune sands and paleosols in the central inner mongolia imply multiple episodes of dune building and stabilization in response to the waxing and waning of the east asian monsoon such eolian deposits were dated by using the single aliquot quartz optical dating method combined with the multi proxy study on the deposits the past environmental changes during the holocene have been reconstructed our results indicate that widespread eolian sand mobilization occurred in the studied region during the beginning of the early holocene from 11 5 ka to 9 ka the climate became warm and humid during the period between 9 ka and 5 6 ka holocene optimum after 5 6 ka the region again became arid as inferred from dune building however the environmental changes during the late holocene have been affected by both climate and human impacts and the presence of desert environment in such semiarid region is not only the result of climatic drought of the late holocene but also related to poor land use practices

geometry and brittle deformation of the subducting nazca plate central chile and argentina summary we use data from the chile argentina geophysical experiment charge broad band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the south american subduction zone between 30 s and 36 s this region contains a zone of flat slab subduction where the subducting nazca plate flattens at a depth of 100 km and extends 300 km eastward before continuing its descent into the mantle we use a grid search multiple event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the wadati benioff zone these contours reflect slab geometries from previous studies of intermediate depth seismicity in this region with some small but important deviations our hypocentres indicate that the shallowest portion of the flat slab is a

quaternary glaciation of tibet the geological evidence the question of the number and extent of pleistocene glaciations on the qinghai xizang tibet plateau remains contentious there has been considerable research activity in tibet by chinese scientists since the late 1950s and their principal findings including data on glacial and periglacial geomorphology sedimentology tectonics stratigraphy and lake history have been used to reconstruct ice margins and palaeosnowlines three and in places four distinct glaciations have been recognised the most extensive occurring in the later middle pleistocene valley and piedmont glacial systems with some mountain ice caps and a small ice sheet on the upper reaches of the huang he have been recognised but there is no evidence of a single tibetan ice sheet as the plateau and the himalaya karakoram underwent accelerating uplift through the quaternary there occurred progressive desiccation in the interior as the influx of indian ocean moisture was constrained equilibrium line elevations in the last glacial maximum were 4000 m in the south east and northeast plateau margins rising to 5500 m in the northwest interior the heat island provided by the plateau the progressive reduction in precipitation most marked during the glacials and the strong southeast to northwest precipitation gradients produced a glacier distribution pattern dominated by the trans tibetan mountain ranges tectonics and periglacial including aeolian processes have played an equal role with glaciation in generating the plateau s quaternary sedimentary succession

simultaneous inversion for hypocenters and lateral velocity variations an iterative solution with a layered model an iterative inversion technique has been developed that uses the direct p and s wave arrival times from local earthquakes to compute simultaneously a three dimensional velocity structure and relocated hypocenters crustal structure is modeled by subdividing flat layers into rectangular blocks an interpolation function is used to smoothly vary velocities between blocks allowing ray trace calculations of travel times in a three dimensional medium tests using synthetic data from known models show that solutions are reasonably independent of block size and spatial distribution but are sensitive to the choice of layer thicknesses application of the technique to observed earthquake data from north central utah shows the following 1 lateral velocity variations in the crust as large as 7 occur over 30 km distances 2 earthquake epicenters computed with the three dimensional velocity structure were shifted an average of 3 0 km from locations determined assuming homogeneous flat layered models and 3 the laterally varying velocity structure correlates with anomalous variations in the local gravity and aeromagnetic fields suggesting that the new velocity information can be valuable in acquiring a better understanding of crustal structure

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

the deep seismicity of the tyrrhenian sea the deep seismicity of the tyrrhenian sea is analysed using data from a new instrumental catalogue of the seismicity of the italian area we use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab the structure of the benioff zone although simpler than previously indicated reveals anomalous traits both in the seismicity distribution and in the stress geometry confirming that standard subduction models cannot be applied in the tyrrhenian region the velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the apenninic chain approximately to the latitude of the irpinia region in central italy 42 n

joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections abstract the application of a new implementation of the joint determination of hypocenters origin times and station correction terms jhd technique to data from the arkansas swarm usa the campi flegrei italy and the nazca plate argentina throws new light onto the problem of earthquake location in all these cases good quality p and s wave arrival times were available the main results are as follows 1 large lateral velocity variations llvv are generally associated with relatively large station corrections these corrections in turn are usually much larger than the average of the station residuals determined when the same set of events is located using a single event location sel method 2 the locations determined by the jhd and sel methods may be substantially different 3 since the effect of llvv on jhd locations is not well established simple 3 d velocity models are constructed so that the jhd technique applied to synthetic data generated using these models produce station corrections similar to those observed 4 the analysis of the synthetic data also shows that the locations determined by the jhd method are much closer to the true locations than the locations determined with the sel method the use of the weighted average of the sel station residuals as station corrections does not give better located events although there is a large decrease in the r m s residual computed for each event therefore the use of r m s residuals to estimate the quality of event locations is not always warranted in view of these results it is possible to conclude that the jhd station corrections can be used to detect lateral velocity variations and to produce locations substantially less affected by these variations than the locations determined by the sel method furthermore under appropriate conditions the jhd station corrections can also be used in a forward modeling scheme to get a semiquantitative velocity model such a model may be the only information that can be obtained from a data set when the station and event distributions are not adequate for 3 d velocity inversion

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

the role of constraints on joint hypocentre determination in seismotectonic studies in this paper we show how the performance of the joint hypocentre determination jhd method can be improved leading to reduced instability in cases close to singularity the method has been extended by imposing a number of constraints introduced by other authors and adding a new one we tested the stability of the method and the relative advantages of the various constraints by simulating a geometrical space distribution of hypocentres recorded by a regional seismic network we then applied this method to deep earthquakes that occurred in the southern tyrrhenian sea subduction zone and to the seismicity of the northern apennines which is moderately deeper than the typical shallow seismicity of the apennines the results obtained from the analysis of synthetic data and actual earthquakes confirm that the jhd method produces less scatter in the hypocentral determinations with respect to the standard locations the main conclusion of our study is that we can significantly reduce the systematic mislocations that result from applying jhd to very clustered seismicity if we introduce the appropriate set of constraints

seismicity active faults stress patterns and rupture processes in the hualien region taiwan investigated using the 1990 hualien earthquake sequence abstract the hualien mainshock aftershock sequence from december 1990 to january 1991 was used to investigate seismicity active faults stress patterns and complex rupture processes in the hualien region of eastern taiwan a combined data set compiled from observations by the regional seismic network taiwan telemetered seismograph network ttsn and a dense aftershock monitoring array hualien temporary seismic network htsn provided high quality seismic data using these data earthquake source parameters could be well constrained by the joint hypocenter determination jhd and double difference relocation methods these two relocation methods presented similar results and produced improved estimations of earthquake location station corrections determined by jhd showed significant lateral velocity variations across the yuehmei fault the relocated seismicity indicated that a previously known active fault the chimei fault extends to offshore earthquake relocations also revealed a northwest dipping seismicity probably related to the chimei fault in addition three sets of focal mechanism solutions are presented and their discrepancies are attributed to the complex rupture process at first earthquakes were initiated by thrust motions later the rupture pattern changed to strike slip motions variations in slip may reflect the fault geometry or rupture boundary conditions in the region the observed stress patterns are considered to relate not only to the regional collision and mountain building processes but also to active faults in local structures

on the problem of quaternary glaciations and the extent and patterns of pleistocene ice cover in the qinghai xizang tibet plateau abstract data accumulated during investigations since the 1960s indicate that up to four pleistocene glaciations can be recognized in the qinghai xizang tibet plateau and the adjacent himalaya mountains in order of decreasing age these are the xixabangma nyanyaxungla guxiang and baiyu glacial episodes the history of pleistocene glacial evolution in various areas throughout the plateau differs and the pattern is very complex throughout the early pleistocene the elevation of the qinghai xizang plateau was approximately 2000 m above sea level during the xixabangma glacial episode recorded at higher elevations the climate and topographical conditions on the plateau were largely unfavourable for the development of glaciers present investigations have revealed that the oldest till is only found at isolated localities on the plateau glaciofluvial or alluvial deposits such as the gongba conglomerate dating from 2 4 to 0 73 ma bp and the fluvial lacustrine deposits of the qiantang group dating from 2 4 to 1 7 ma bp are present rather than glacial till therefore the postulate of a large early pleistocene ice sheet proposed previously has been disproves during the most recent glaciation uplift of the plateau and the himalayas continued the majority of the qinghai xizang plateau reached 4000 m a s l and the great himalaya were approximately 6000 m a s l the mountains formed a barrier against the incursion of the indian monsoon so that precipitation decreased sharply on the northern flank of the himalayas and the climate to the north became cold and dry all of the glaciers on the qinghai xizang plateau underwent extensive retreat thus during the pleistocene no unified glacial cover existed over the qinghai xizang plateau similarly the source area of the hwang he yellow river did not support a local ice sheet

variations of p wave travel time residuals before and after the 1999 chi chi taiwan earthquake p wave velocity variations may provide precursory information before large earthquakes we present results from a simple study on variations of p wave travel time residuals before and after the 1999 chi chi taiwan earthquake the short period seismic network deployed in taiwan by the central weather bureau cwb is routinely used for earthquake location the accuracy of earthquake location is often judged by the travel time residual of seismic waves because the velocity model used by the cwb was one dimensional the travel time residuals will show lateral inhomogeneity of the velocity structures and unmodeled vertical structures also the travel time residuals may change with time if the velocity structure changes temporally we used the data of the central weather bureau seismic network cwbsn from 1991 to 2002 to obtain the difference between observed and calculated p wave travel times which is defined as the p wave travel time residual the purpose of this study is to find the mean value of the p wave travel time residuals at each station and its possible temporal changes at stations near the chelungpu fault our results show that the mean p wave travel time residuals at stations 40 km east of the chelungpu fault changed very little before and after the chi chi earthquake but the mean p wave travel time residuals at the stations immediately west of the chelungpu fault clearly changed before and after the chi chi earthquake the anomalous zone is bounded by stations nsy twq1 tcu wnt wgk chn5 yus wdt and whf these temporal changes of p wave travel time residuals can be attributed to changes in the velocity structure which in turn might be caused by crustal deformation east of the chelungpu fault beginning about 6 years before the chi chi earthquake in other words before the chi chi earthquake there was a long term 6 year precursor of p wave velocity decrease possibly due to dilatancy or development of cracks the variations of p wave travel time residuals with time at the anomalous stations are also confirmed by statistical tests that show clear significance this method can be used to monitor and identify variations of p wave travel time residuals which may be precursors to a large earthquake

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

tidal and subtidal hydrodynamics and energetics in a constricted estuary abstract the dynamics of coastal plain estuaries are mainly associated with variable tidal forcing and local winds in combination with bathymetric complexity and coastline irregularity specific features such as constricted areas can potentially affect and energize the hydrodynamics of these types of systems particularly tidal range and tidal currents can be significantly amplified where the incoming tidal wave becomes constricted in this work the impact of a narrow constriction on a mesotidal estuary was analysed at tidal and subtidal time scales tidal hydrodynamics energy fluxes and energy dissipation were determined for the entire cadiz bay southwestern spain using the delft3d numerical model field observations were used to analyse tidal propagation and energy dissipation along the bay constriction and to calibrate and test the numerical model the results indicate that the presence of the constriction transformed and distorted the tide and increased the tidal range and flow velocities along the channel with implications on energy dissipation the tidal currents were oriented along channel at the central part of the constriction although abrupt bathymetric changes at the channel inner boundary provoked a sudden rotation of the flow although the energy fluxes were higher for spring tides and were strongly influenced by winds the energy dissipation was controlled by bed shear stresses and vertical dispersion the significance of this energy dissipation was that it destabilized the water column which resulted in a weakly stratified system with implications on water quality at a subtidal scale the residual water volume exchange was the result of the combined effects of the neap spring tides wind and waves whereas tides were dominant at the tidal scale

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

lateral velocity variations in the andean foreland in argentina determined with the jhd method abstract lateral velocity variations in the andean foreland near san juan province argentina were detected by analyzing the station corrections computed as part of the joint location of local earthquake data the events recorded by a portable network panda have intermediate and shallow depths about 100 km and less than 40 km respectively the jhd technique was applied to intermediate depth events and to two subsets of shallow events that concentrate on two distinct geologic units precordillera and pampean ranges the computed station corrections have a strong dependence on the data processed analysis of the different patterns of corrections shows that the corrections are consistent with the presence of large scale lateral velocity variations bounded by major fault systems based on these corrections a qualitative velocity model is proposed that has relatively high velocities between the eastern precordillera and a westerly dipping plane on the eastern edge of pie de palo one of the mountain blocks of the pampean ranges velocities are lower immediately east of this plane and between the central and eastern precordillera this model has important tectonic implications because it suggests that there is a major boundary between the central and eastern precordillera and that the pampean basement whose extent is unknown underlies the eastern precordillera the existence of large velocity variations across the precordillera is consistent with a westward shift of almost 10 km of the relocated intermediate depth events and with the removal of an apparent westward dip opposite to the direction of subduction observed in the wadati benioff zone as determined from single event location the analysis of the intermediate depth events also exemplifies the deleterious effect on the jhd results introduced by the cancellation of small singular values in the computation of the station corrections

new evidence of azimuthal variations at campi flegrei attenuation and predominant frequency in this paper we have determined apparent q from body wave dispersion and a spectral ratio method for the campi flegrei area a contour map of azimuthal variations of apparent q ranging from q 4 to q 40 reveals that the lower q higher attenuation corresponds to an area that includes the solfatara crater with active fumaroles near the site of maximum uplift produced during the bradyseismic crisis of 1984 and just over the site evidencing the presence of a magmatic body a strong azimuthal variation of the predominant frequency of the first pulse of the p wave has been found and is interpreted in terms of a vertical travel time in a surficial resonant layer 1 km thick over a halfspace the attenuation maps the interpretation of the resonant frequencies and the additional information provided by the p wave velocity suggest the presence of a circular structure in the area not only does the distribution of the thickness of the resonant layer obtained through the estimation of the contribution of different harmonics show the circular structure but it also agrees with the presence of a thin layer of lighter sediments determined by means of a microgravimetric study and with the total magnetic map previously obtained for this area the results of the azimuthal variation provide new evidence of the structure that can be used to improve the knowledge of the area

velocity structure and seismicity of southeastern tennessee the seismic zone in southeastern tennessee is at the confluence of major crustal features which have been interpreted largely from potential data and their relation to seismicity could help us understand why major earthquakes sometimes occur in the eastern united states in this paper we solve for the previously unknown velocity structure of the upper crust by an inversion of travel time residuals from relocated earthquakes the gravity anomalies are included by using a linear relation between average anomalous density and average anomalous velocity the velocity model demonstrates that the seismicity is concentrated in areas of average to below average velocity and does not appear to be associated with one of the previously identified major crustal features the high velocity zones mark areas that are generally lacking in seismicity the association of earthquake hypocenters with regions of low velocity crustal rocks is consistent with other intraplate seismic zones and this association supports the conjecture that intraplate earthquakes occur in crust that may have been weakened the velocity anomalies at midcrustal depths do not support the new york alabama ny al lineament as a linear feature extending through southeastern tennessee and parallel to contours in gravity anomalies as originally proposed a continuation of the ny al lineament to the southwest requires either a 15 degree southwestward change in direction or a displacement to be consistent with the velocity anomalies the seismically active areas in southeastern tennessee do not appear to be constrained by the major crustal features but instead the seismicity is characterized by the distribution of hypocenters and their association with low velocity regions at midcrustal depths

analysis of the microseismicity induced by fluid injections at the egs site of soultz sous forets alsace france implications for the characterization of the geothermal reservoir properties in june july 2000 a hydraulic stimulation experiment took place at the geothermal egs site of soultz sous forets alsace france in order to enhance the permeability of the fractured granitic massif at 5 km depth as it is well known that fluid injections tend to induce microseismic events a downhole and a surface seismological network have been installed to monitor the seismic activity during the stimulation test 23400 m3 of fluid have been injected in the rock volume through the open hole section 4400 m 5000 m of the well gpk2 at increasing rates of 30 l s 1 40 l s 1 and then 50 l s 1 more than 7200 microseismic events in the magnitude range 0 9 to 2 6 have been precisely located through a simultaneous inversion of the seismic velocity structure and location parameters the analysis of the behavior of the seismicity relative to the hydraulic parameters gives important information about the geothermal reservoir it appears that the evolution of the seismicity strongly depends on the variations of the injection rate an increase or a decrease leads to changes of the velocity structure the number and magnitude of microseismic events this involves different hydro mechanical processes between the fluid flow and the fracture planes which will control the final shape of the microseismic cloud moreover the study of the variations of the b value with time suggests that the stimulation experiment produces a large proportion of small earthquakes but records of events of magnitude higher than 2 indicate that fluid injection could reactivate structures whose dimensions allow the generation of such earthquakes

stratigraphy and palaeoenvironmental implications of pleistocene and holocene aeolian sediments in the lhasa area southern tibet china abstract along the middle and lower reaches of the kyichu river and its tributaries lhasa area southern tibet a multidisciplinary study was carried out in order to investigate the areal distribution sedimentological properties ages and palaeoenvironmental implications of aeolian deposits including intercalated palaeosols this research was initiated to investigate to what extent southern tibet is influenced by past human activity as even recent evaluations perceive the present treeless desertic environment as natural fifteen profiles were recorded at an altitude of 3540 4580 m a s l with subsequent sedimentological geochronological osl ams 14 c and palaeobotanical charcoal analyses sediment properties of both loesses and aeolian sands reveal an origin from aeolian sorting of nearby fluvial deposits the calculated ages are the oldest obtained thus far on aeolian sediments from southern and interior tibet revealing natural aeolian sedimentation before and around the last glacial maximum c 20 ka however a distinct portion of late holocene sandy aeolian sediments also occurs both the evidence for the aeolian dynamics widespread pleistocene loess and aeolian sand deposition local late holocene aeolian sand deposition modern reactivation of widespread pleistocene aeolian sands and the palaeobotanical findings late holocene vegetation change from a tree bearing to a widely treeless landscape provide evidence that the lhasa area was strongly influenced by human activity since at least the late neolithic c 4200 cal yrs bp thus the present day desertic environment might not primarily be a result of the semiarid climate or the high altitude conditions but rather of activities of the humans and their collateral effects however once established this semi natural ecosystem persisted controlled by strong grazing firewood extraction erosion and harsh edaphic conditions preventing the recovery of trees

locating the boundary between the pleistocene and the holocene in chinese loess using luminescence a detailed chronology has been obtained for a loess section at yuanbao situated at the northwestern edge of the chinese loess plateau the ages were obtained by the measurement of the optically stimulated luminescence osl from coarse silt sized quartz grains these ages showed that deposition at this site was continuous from 17 ka to the present but that there was a decrease in the sedimentation rate from 0 60 to 0 10 m ka at 13 489 1 15 ka and this is proposed as the location of the pleistocene holocene p h boundary a change in osl sensitivity occurs at this depth the depth and sharpness of this boundary is compared with the change obtained in low field magnetic susceptibility ms measurements on 65 samples from the section the ms changes gradually over 1 9 m and thus does not provide an easily discernible boundary the new osl based sedimentation rates are used to calculate the mass accumulation rates for the holocene and the end of the pleistocene

a coupled environmental system formed at about 2 5 ma in east asia abstract the somewhat abrupt commencement of loess deposition on a large scale in north central china is palaeomagnetically measured at about 2 5 ma the formation of the dynamical conditions responsible for windblown loess processes implies a reorganization of the atmospheric circulation over eastern asia it is speculated that at that time the accelerated uplift of the tibetan plateau had reached a threshold height giving rise to the intensification and northward shift of the siberian high and deepening of the cyclone in the lee of the tibetan plateau the uplift of tibet and the resulting reorganization of atmospheric circulation at about 2 5 ma would initiate a coupled environmental system tibetan plateau inland desert loess plateau in eastern asia that could be a key system in understanding the onset of glaciation in northern hemisphere and climatic change in the quaternary the climatic shift from near continuous warm condition before 2 5 ma to frequent and chaotic fluctuations after is speculated to be triggered to a significant extent by the uplift of the tibetan plateau an orography cold surge albedo temperature feedback mechanism is developed in explaining the harsher climate over east asia during glacial time and is thought to be one of the major contributors in promoting glacial development on the globe

unprecedented last glacial mass accumulation rates determined by luminescence dating of loess from western nebraska abstract a high resolution chronology for peoria last glacial period loess from three sites in nebraska midcontinental north america is determined by applying optically stimulated luminescence osl dating to 35 50 m quartz at bignell hill nebraska an osl age of 25 000 yr near the contact of peoria loess with the underlying gilman canyon formation shows that dust accumulation occurred early during the last glacial maximum lgm whereas at devil s den and eustis nebraska basal osl ages are significantly younger 18 000 and 21 000 yr respectively at all three localities dust accumulation ended at some time after 14 000 yr ago mass accumulation rates mars for western nebraska calculated using the osl ages are extremely high from 18 000 to 14 000 yr much higher than those calculated for any other pre holocene location worldwide these unprecedented mars coincide with the timing of a mismatch between paleoenvironmental evidence from central north america and the paleoclimate simulations from atmospheric global circulation models agcms we infer that the high atmospheric dust loading implied by these mars may have played an important role through radiative forcing in maintaining a colder than present climate over central north america for several thousand years after summer insolation exceeded present day values

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

sequence of strong intraplate earthquakes in the kodiak island region alaska in 1999 2001 a sequence of strong earthquakes was registered in 1999 2001 in the kodiak island region of the alaska aleutian subduction zone two mw 7 earthquakes occurred in december 1999 and january 2001 and an mw 6 5 event occurred in july 2000 these events and their aftershocks recorded by the regional seismograph network were relocated using a joint hypocenter determination jhd method regional broadband data were used to obtain seismic moment tensors for the main shocks and their largest aftershocks relocation and moment tensor inversion results indicate that these events originated inside the subducting pacific plate the focal mechanisms indicate down dip tension with the fault planes being nearly vertical and parallel to the strike direction of the subducting plate the 1999 and 2000 events were located down dip of the locked portion of the megathrust while the 2001 event was located directly beneath it

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

optical dating of dune sands in the northeastern deserts of china abstract optical dating has been used to obtain the ages of fossil stabilized sand dunes from four sections in the northeastern deserts of china our results indicate that the optically stimulated luminescence ages of the four sections correlate well even though the samples were collected from different deserts about 600 km apart our results also indicate that active dune formation in this region lasted from the last glacial maximum to about 10 ka and that the warm climate of the holocene was interrupted by a cold dry dune formation episode about 3 5 1 7 ka the holocene optimum in this region is between 10 and 3 6 ka and a later warm humid dune stabilization phase lasted from at least 1 6 to 1 0 ka the youngest age on the uppermost sand unit yielded an age of only 40 yr supporting the previous argument that the existence of modern active eolian sands in the regions with a mean annual precipitation of up to 450 mm is not mainly due to drought but to extensive land cultivation over historic time from the luminescence properties of the quartz grains it is hypothesized that the sands in most of the sections are probably derived from more than one source with a minor source of quartz having a different thermal history before deposition

comment on laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data by m zamora g sartoris and w chelini

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

refinement of thrust faulting models for the central new madrid seismic zone abstract we present the results of the joint relocation of events recorded during 1989 1992 by the panda network in the central new madrid seismic zone the near surface material in the study area is a gently dipping layer of poorly consolidated sediments with low p wave velocity and high v p v s estimated values 1 8 km s 1 and 3 the sediments are underlain by high velocity paleozoic rocks under the network the difference in sediment thickness is only 0 6 km but because of the low velocities the location of the events using layered models is affected by errors application of the joint hypocentral determination jhd technique to a subset of 580 events shows that the single event locations may be in error by as much as 1 km in depth depending on where the events are located analysis of synthetic data generated for a realistic 3 d velocity model supports the jhd results the analysis of synthetic data also suggests that a v p v s 2 3 is more appropriate for the post paleozoic mississippi embayment sediments based on the jhd locations we present a new interpretation of the seismicity with two en echelon sw dipping thrust faults connected by a west dipping thrust fault these faults appear associated with the reelfoot scarp and its northern extension the kentucky bend scarp

palaeoclimatic evidence from sand seas abstract sand seas can be an important source of information on the quaternary history of many deserts because sand seas appear to react sensitivity to climatic changes the quality of palaeoenvironmental information obtained from them is frequently much better than that from adjacent rocky desert areas patterns of dune alignments may be used to reconstruct the wind directions that formed currently inactive or fixed dunes and thus can provide information on palaeocirculation patterns the climatic conditions under which these dunes formed can be examined using palaeoclimatic models to explore the combinations of wind velocity rainfall and evaporation rates required to reactivate them choice of appropriate values for these parameters may be hampered by the problems of dating episodes of dune activity in many sand seas the best palaeoclimatic information comes from studies of interdune lacustrine or playa deposits which may reflect increased local rainfall or higher groundwater discharge or greater penetration of the sand sea by rivers with headwaters outside the desert caution should be taken in the interpretation of such deposits for juxtaposition of aquatic and aeolian environments can occur even in modern hyperarid and seas the record of climatic changes preserved in the deposits of modern sand seas suggests that periods of dune formation may have been interrupted by long periods of stability which may also have included deposition of interdune lacustrine deposits for example within the past 40 000 years active dune formation in many sand seas appears to have been restricted to the interval between about 20 000 and 12 000 yr b p and to the late holocene approximately 1 4 to 1 3 rd of the time

the sequence of quaternary glaciation in the bayan har mountains four periods of quaternary glaciation in the pleistocene have been found in the area of the bayan har mountains they represent respectively the two stages of the last glacial age the penultimate ice age and an earlier ice age during the late stage of the last glacial age glaciers developed only near the mountain ridges of the bayan har in the earlier stage glaciers expanded down to the piedmont of the bayan har mountains and were as much as 40 km long in the penultimate ice age an extensive ice cover developed depositing an areally widespread till sheet erratics were transported 60 km from bayan har peak to qingshuihe town to the south and to yematan land to the north granitic erratics are also distributed over elevated geomorphological positions such as chalaping ridge the area of ice cover encompassed up to 50 000 km2 furthermore evidence including glacial landforms and sediments shows that a larger glaciation existed in this area in an earlier time possibly during the third most recent ante penultimate glaciation the scale of this glaciated area is greater than those of the more recent events in the qinghai xizang plateau extending over 80 000 km2 this glaciation covered the source area of the yellow river from xingsuhai in the west to duogerangtan in the east including the areas of gyaring and ngoring lakes based on the extent and locations of the glaciations the bayan har stage and galalahai stage of the last glacial age the yematan ice age and the huanghe glacial age can be recognized

separated earthquake location we present a practical method of locating earthquakes in laterally varying media the procedure has two distinct phases an estimation phase and an application phase in the estimation phase all existing arrival time residuals relative to some reference one dimensional velocity model for a region are used to estimate a set of path anomalies station corrections that vary as a function of source position this is done by sorting earthquakes into groups localized in space and applying a novel multiple event location algorithm this algorithm uses a pair of complementary projection operators to combine a priori information about the lateral structure that is indeterminate from the available data with the information that can be determined uniquely from the available data having estimated path anomalies as a function of source location we can generate a table of path anomalies that can be accessed and interpolated for future earthquake location this is the application phase of the method we have tested the method on synthetic data designed to study how well earthquakes can be located in the vicinity of the rupture zone of the 1984 morgan hill california earthquake we found precise absolute locations could be obtained provided the a priori information was specified appropriately distortion of relative locations occurred near large lateral velocity gradients and for groups of events spread over large areas because of the inadequacy of fitting a single set of path anomalies to the whole group

application of the jhd technique to the loma prieta california mainshock aftershock sequence and implications for earthquake location relocation of the loma prieta mainshock aftershock sequence using the jhd technique places the events an average of 1 km to the southwest of the locations determined by other authors the new locations show a concentration of seismic activity in the wedge between the san andreas and sargent faults furthermore there seems to be little seismic activity to the east of the sargent fault these features of the seismicity are not observed in other published locations determined using similar data sets a depth cross section perpendicular to the sargent fault near its intersection with the san andreas fault shows two clusters of events along a line segment between 3 and 10 km that dips to the ne and that intersects the main sw dipping plane these clusters may correspond to secondary faults postulated by other authors the jhd station corrections vary between 0 6 and 0 6 sec and indicate the presence of large velocity variations across and along the san andreas fault these corrections are very close to the weighted average of the station residuals obtained when the events are located singly the locations obtained with a single event location program and using the average residuals as station corrections give locations almost coincident with the jhd locations this high similarity of locations is very unusual and is interpreted as the result of quasi random lateral velocity variations in the loma prieta area to estimate the effect of these variations on the location of events synthetic travel times were computed for a realistic although preliminary three dimensional 3d velocity model these synthetic data were then treated as the actual data the corresponding results show that the jhd technique is able to locate events with an average error of 0 5 km in epicenter depths on the other hand are consistently deeper by about 1 km in addition the station corrections are close to the observed corrections additional tests with synthetic data also show that the observed station corrections suggest velocity variations of up to 40 in the top 3 km of the crust although these variations may seem extremely large they are within the range of variation found by other authors and most importantly are required by the observations

late quaternary landscape evolution in the kunlun mountains and qaidam basin northern tibet a framework for examining the links between glaciation lake level changes and alluvial fan formation abstract the qaidam basin in northern tibet is one of the largest hyper arid intermontane basins on earth alluvial fans pediment surfaces shorelines and a thick succession of sediments within the basin coupled with moraines and associated landforms in the adjacent high mountain catchments of the kunlun mountains record a complex history of late quaternary paleoenvironmental change and landscape evolution the region provides an ideal natural laboratory to examine the interaction between tectonics and climate within a continent continent collision zone and to quantify rates of landscape evolution as controlled by climate and the associated glacial and hydrological changes in hyper arid and adjacent high altitude environments geomorphic mapping analysis of landforms and sediments and terrestrial cosmogenic radionuclide surface exposure and optically stimulated luminescence dating serve to define the timing of formation of late quaternary landforms along the southern and northwestern margins of the qaidam basin and in the burhan budai shan of the kunlun mountains adjacent to the basin on the south these dates provide a framework that suggests links between climatic amelioration deglaciation lake desiccation and alluvial fan evolution at least three glacial advances are defined in the burham budai shan of the kunlun mountains on the northern side of this range these occurred in the penultimate glacial cycle or early in the last glacial cycle during the last glacial maximum lgm lateglacial and during the holocene on the south side of the range advances occurred during the penultimate glacial cycle mis 3 and possibly the lgm lateglacial or holocene several distinct phases of alluvial fan sedimentation are likewise defined alluvial fans formed on the southern side of the kunlun mountains prior to 200 ka ice contact alluvial fans formed during the penultimate glacial and during mis 3 extensive incised alluvial fans that form the main valley fills north of the burham budai and extend into the qaidam basin are dated to 30 ka these ages suggest that there was a period of alluvial fan aggradation and valley filling that persisted until desiccation of the large lakes in the qaidam basin post 30 ka led to base level lowering and active incision of streams into the valley fills the continued lateglacial and holocene desiccation likely led to further degradation of the valley fills ice wedge casts in the qaidam basin date to 15 ka indicating significant lateglacial climatic amelioration while holocene loess deposits north of the burham bdudai suggest that aridity has increased in the region since the early holocene from these observations we infer that the major landscape changes within high glaciated mountains and their adjacent hyper arid intermontane basins such as the kunlun mountains and qaidam basin occur rapidly over millennial timescales during periods of climatic instability

degradation of linear dunes in northwest ngamiland botswana and the implications for luminescence dating of periods of aridity the long morphodynamic history of the linear dune system of northwest ngamiland comprises both construction and degradation processes here we describe features resulting from the latter crest lowering during wet periods is associated with lateral transfer of sand into the straats weathering and leaching have mobilised iron to the base of the dune profiles and have corroded the quartz grains satellite image interpretation indicates that dune sand has been diluted by bioturbation which transferred damaran saprolite from below the dunes to the surface flooding and waterlogging have modified and in places completely destroyed the original crisply linear morphology small linear collapse features across the linear dunes are associated with open fractures or faults where water infiltration is facilitated the implications for luminescence dating of dune sands to identify periods of aridity are discussed the dunes cannot simply be regarded as providing a stacked record of such periods they are very old and much of the record is missing as a result of crest lowering the chronostratigraphy includes degradational components which must be distinguished from those of construction bioturbation cannot be disregarded as a complication which overprints the luminescence signals

earthquake distribution in southern tibet and its tectonic implications 1 a temporary 37 station seismic array was operated in southern tibet from june 2004 to august 2005 close to xigaze along a traverse from tangra yum co rift in the west to yadong gulu rift in the east this lateral array of the international hi climb project recorded a total of 885 local earthquakes during the 14 month deployment hypocenter locations of these events were obtained using hypoinverse2000 and about half of them were relocated by the joint hypocenter determination method lateral variations in crustal seismic p and s wave velocities beneath the array were obtained simultaneously as part of the station corrections during the relocation procedure while earthquakes were scattered in the region more than 250 earthquakes were clustered within a small area at about 50 km north of the indus yalu suture and west of the pumqu xianza rift crustal and uppermost mantle earthquakes are concentrated beneath the himalayan crest projection of all earthquakes to a north south profile shows that the subducting indian plate passes the indus yalu suture below the lhasa terrane while earthquakes are concentrated in the upper crust and upper mantle beneath the himalayas seismicity is mostly restricted to the upper crust to the north which is consistent with a ductile middle lower crust beneath southern tibet about 20 deep crustal and uppermost mantle events at depths of 50 70 km were observed to be associated with the subducting indian lithosphere our relocation results of these local earthquakes in southern tibet support the popular jelly sandwich model for the rheology of continental lithosphere in which the strong seismogenic layers of upper curst and uppermost mantle are separated by a weak lower crust