multivariate statistical analysis for the assessment of groundwater quality under different hydrogeological regimes multivariate statistical analysis has been widely used for hydrogeochemical characterization of groundwater quality in this study hydrochemical data from three hydrological basins were used and two methods factor and cluster analyses were applied the first area is the coastal area of eastern thermaikos gulf where groundwater is influenced by seawater intrusion and geothermal fluids the other two areas are the inland basins of gallikos and perdikas in which agricultural and industrial activities constitute the main anthropogenic pollution sources of groundwater initially the aforementioned methods were applied for each area separately and resulted in a different number of significant factors and clusters while the natural and anthropogenic influences were spatially determined in each area additionally factor and cluster analyses were applied coupling data from all areas therefore five clusters and three major factors were determined distinguishing the hydrochemical processes and impacts from anthropogenic activities in more detail it is worth mentioning that the application of cluster analysis in the coupled groundwater samples of all studied areas resulted beneficially in the most hydrochemically complex area salinization dominates in the coastal area while in gallikos and perdikas basins high concentrations of no3 occur mainly due to agricultural activities and small livestock units the numerous hydrochemical samples are identified as the main issue for the higher discretization and reliability of the second approach nevertheless this study is associated with a number of limitations of multivariable statistical analysis regarding extreme concentrations of cl and na this issue stimulates further research in overcoming and understanding these drawbacks

simulated ground motions for hypothesized mw 8 subduction earthquakes in washington and oregon the amplitude and duration of strong ground motions from hypothesized mw 8 subduction zone thrust earthquakes in the puget sound portland region were estimated using a semi empirical method the simulation procedure assumes the rupture surface may be represented by a grid of fault elements finite difference wave simulation in a detailed 2 d velocity structure identifies direct s and the moho postcritical reflection as the primary components of the s wave field at horizontal distances of 0 to 150 km green s functions containing these two arrivals are computed with generalized ray theory in an equivalent 1 d structure for each source element receiver propagation path scattering and attenuation structure are empirically modeled by the use of corrected accelerograms from mw 7 michoacan mexico and valparaiso chile aftershocks for the fault element source functions different site conditions are empirically included in the simulation procedure by using empirical source functions recorded on rock and soil sites spatial variations in slip on the fault asperities are introduced by weighting the fault elements the technique has been validated for large subduction zone earthquakes by modeling acceleration time histories and response spectra from the 1985 michoacan mw 8 0 and valparaiso mw 8 0 main shocks somerville et al 1991 fault models for the puget sound and portland regions and seismic velocity structure models have been adapted from published regional studies uncertainty in the location of the asperities on the fault surface results in a large degree of uncertainty in the simulated ground motions at a given site if distance is defined as the distance to the closest asperity then the variability in the ground motions is reduced indicating that this uncertainty can be lessened by constraining the depth of the asperity the ground motion estimates are relatively insensitive to the difference in fault dip between the puget sound and portland fault models the attenuation of peak acceleration with distance r from the fault asperity for a mw 8 subduction earthquake is given by in pga 1 5 3 33 in r 128 0 79 s where s is a site term equal to 0 for rock and 1 for soil when distance r is the distance to the fault plane the attenuation relation is in pga 2 8 1 26 in r 0 79 s formal estimates of uncertainty in the calculated ground motions have been obtained by estimating both parametric uncertainty from the range of source models of hypothesized cascadia subduction earthquakes and modeling and random uncertainty from the misfit between recorded and simulated ground motions of the 1985 michoacan and valparaiso earthquakes for periods less than 1 sec the estimated response spectral velocities on soil sites in the seattle olympia region are about twice those recorded during the 1949 olympia and 1965 seattle wadati benioff zone earthquakes and the durations of strong motion on rock sites are significantly longer 45 to 60 sec versus 10 to 15 sec

statistical and hydrochemical methods to compare basalt and basement rock hosted groundwaters atherton tablelands north eastern australia multivariate analysis of physico chemical and chemical data has enabled differentiation among groundwaters sourced from different lithological formations in the atherton tablelands region of north eastern australia the main water resource is stored in basalt although basement rocks such as granite and metamorphics also contain variable amounts of water groundwater in the basalt is mostly mg ca na hco3 type with electrical conductivities less than 300 s cm and ph values from 6 5 to 8 5 some of the other groundwater is quite similar making the identification of hydrochemical facies difficult groundwater samples were grouped based on the results of a principal component factor analysis of the major dissolved constituents h4sio4 na ca2 mg2 and hco3 as well as ph and electrical conductivity based on this differentiation it was possible to identify the likely host rocks of groundwaters from unidentified lithological units define the basalt thickness and provide a better understanding of the groundwater resource principal component factor analysis has also been useful in identifying the likely hydrochemical processes controlling the composition of these groundwaters including the production of weak acids in the soil layers silicate mineral weathering ion exchange reactions evapotranspiration and the leaching of ions from organic matter supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00254 002 0667 z

local time and space scales of organized tropical deep convection the time and space scales of tropical deep convection are estimated via analysis of 3 hourly global cloud imagery gci data for 3 yr at 35 70 km resolution the emphasis is on estimating local time and space scales rather than traditional zonal wavenumber frequency spectra this is accomplished through estimation of local spatial lag autocorrelations the conditional probability of convection at neighboring points and the expected duration of convective events the spatial autocorrelation scale is found to be approximately 130 km and the mean duration of convective events approximately 5 5 h in the convectively active areas of the tropics there is a tendency for the spatial autocorrelation scales to be shorter over the continents than oceans 95 155 versus 110 170 km the expected duration of convective events likewise tends to be shorter 4 6 versus 5 7 h in the far western pacific these differences are sharp enough to legitimize the notion of the indonesian archipelago as an extended maritime continent with a distinctive shape consistent with many other studies the diurnal variation of the convection is also found to be strikingly different over the continents and oceans the diurnal amplitude over land is comparable to the long term mean raising the possibility of significant aliasing across timescales the simple analysis of this paper should be useful in evaluating and perhaps even improving the representation of convective processes in general circulation models

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

modeling the jiyang depression northern china using a wave field extrapolation finite difference method and waveform inversion we study the 2d seismic velocity structure of the south edge of the jiyang depression in the bohai bay basin northern china using recordings from 28 broadband seismic stations and a method combining an shear horizontal sh forward synthetic calculation and waveform inversion the forward synthetic cal culations are performed by a finite difference fd method with its computational domain localized in the basin area and input motions at the base of the model ex trapolated from the displacement recorded at a nearby hard rock station in waveform inversion the shapes of the strata are varied to search for a best fitting model based on the fit of relative timing amplitude and phase of the synthetics to the seismic data numerical experiments using synthetic data and test models demonstrate the validity resolution and sensitivity of our technique with this technique we obtain two cross sections of the south edge of the jiyang depression the bohai bay basin northern china the waveform inversions using the seismic data from four teleseis mic events show consistent results for both cross sections those inversion results are also in agreement with a geological cross section available in the region our models estimate that the south edge of the jiyang depression is juxtaposed against the luxi uplift and its structures our inversion results also reveal a blind fault in the region and features suggesting major extensions in paleogene

large potential energy of gravity waves over a smooth surface with little convection simulation and observation 1 a numerical experiment is conducted using an atmospheric general circulation model agcm to investigate the presence of the large potential energy over a region of low topography and little convective activity focusing on the tropical atlantic region 10 e to 20 w 0 to 20 s it is found that gravity waves with a time period of 24 hours are excited near the equator 5 15 n in a region of large moist heating extending vertically up to 10 13 km the gravity waves propagate upward from this region with a bias toward the south and are manifested as large energy fluxes in the cross equatorial region enhanced energy fluxes are therefore simulated at 20 30 km altitude over a region with no significant source of gravity waves and are confirmed using global positioning satellite meteorology gps met experiment data

composite life cycle of maritime tropical mesoscale convective systems in scatterometer and microwave satellite observations this study examines scatterometer observed surface wind divergence and vorticity along with precipitable water pw across the life cycle of tropical maritime mesoscale convective systems mcss as resolved in 0 5 data simple composites were constructed around first appearances of cold 210 k cloud tops in infrared ir data at 3 hourly resolution many thousands of such events from the tropical indopacific in 2000 were used composites of subpopulations were also constructed by subdividing the dataset according to ir event size and duration as well as by prevailing values of pw and vorticity at a 5 scale the composite mcs life cycle here spans about a day and covers a few hundred kilometers with a remarkable sameness across subpopulations surface wind convergence and pw buildup lead cold cloud appearance by many hours afterward there are many hours of divergence indicative of downdrafts contrary to motivating hypotheses the strength of this divergence relative to convergence is scarcely different in humid and dry subpopulation composites normalized time series of composite vorticity show an evolution that seems consistent with vortex stretching by this convergence divergence cycle with peak vorticity near the end of the period of convergence 3 h prior to cold cloud appearance in rotating conditions the common 1 day mcs life cycle is superposed on large scale mean vorticity and convergence approximately in proportion which appear to be well scale separated covering the whole of the 48 h and 5 10 averages and are as strong as or stronger than the mcs signature

an ecology oriented exploitation mode of groundwater resources in the northern tianshan mountains china abstract in recent years ecological degradation caused by irrational groundwater exploitation has been of growing concern in arid and semiarid regions to address the groundwater ecological issues this paper proposes a groundwater resource exploitation mode to evaluate the tradeoff between groundwater development and ecological environment in the northern tianshan mountains northwest china s xinjiang uygur autonomous region field surveys and remote sensing studies were conducted to analyze the relation between the distribution of hydrological conditions and the occurrence of ecological types the results show that there is a good correlation between groundwater depth and the supergene ecological type numerical simulations and ecological assessment models were applied to develop an ecology oriented exploitation mode of groundwater resources the mode allows the groundwater levels in different zones to be regulated by optimizing groundwater exploitation modes the prediction results show that the supergene ecological quality will be better in 2020 and even more groundwater can be exploited in this mode this study provides guidance for regional groundwater management especially in regions with an obvious water scarcity

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

application of multivariate statistical methods and inverse geochemical modeling for characterization of groundwater a case study ain azel plain algeria abstract multivariate statistical methods and inverse geochemical modeling were jointly used to define the variation and the genetic origin of chemical parameters of groundwater in the ain azel plain algeria interpretation of analytical data shows that the abundance of the major ions is as follows ca mg na k and hco 3 cl so 4 q mode hierarchical cluster analysis hca was employed for partitioning the water samples into hydrochemical facies also known as water groups or water types three major water groups resulted from the hca analysis the samples from the area were classified as recharge area waters group 1 ca mg hco 3 water transition zone waters group 2 ca mg cl hco 3 water and discharge area waters group 3 mg ca hco 3 cl water inverse geochemical models of the statistical groups were developed using phreeqc to elucidate the chemical reactions controlling water chemistry the inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area in a broad sense the reactions responsible for the hydrochemical evolution in the area fall into three categories 1 dissolution of evaporite minerals 2 precipitation of carbonate minerals and 3 weathering reactions of silicate minerals

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

factors determining the extratropical response to equatorial diabatic heating anomalies abstract the steady linear response of a spherical baroclinic atmosphere to an equatorial diabatic heat source having a simple horizontal and vertical structure is examined this source is imposed upon representative zonally symmetric as well as zonally varying flows during the boreal winter two climatologies are considered one is a 6 year average of global observations analyzed at the european centre for medium range weather forecasts ecmwf the other is a 30 year average taken from a general circulation model gcm run at the geophysical fluid dynamics laboratory in princeton the extratropical response is found to be very sensitive to the basic state around which the governing primitive equations are linearized and in the case of the ecmwf climatology to the longitudinal position of the source with respect to the climatological waves there is also some sensitivity to the vertical level of maximum heating although again this is more evident in the case of the ecmwf basic state these results ar

hydrochemical characterization of groundwater mixing in sedimentary and metamorphic reservoirs with combined use of piper s principle and factor analysis abstract a procedure to interpret hydrochemical data based on a combined use of factor analysis correspondence analysis and piper s classification principle is outlined and applied to the study of a multi reservoir hydrothermal system allevard located in the french western alps values of physico chemical parameters determined on 95 water samples related to a single point allevard spring and gathered from previous studies extending over several decades were submitted to this procedure the approach proved successful in differentiating groundwater masses of different hydrogeological origin which mix and discharge at the outlet of the system the statistical analysis supported by structural and isotopic information allowed formulation of a flow and mixing model in agreement with geological evidence and comprising near surface subsurface and deep subsystems

global distribution of atmospheric waves in the equatorial upper troposphere and lower stratosphere agcm simulation of sources and propagation 1 the global distribution sources and propagation of atmospheric waves in the equatorial upper troposphere and lower stratosphere were investigated using an atmospheric general circulation model with t106l60 resolution 120 km horizontal and 550 m vertical resolution the quasibiennial oscillation qbo with a period of 1 5 2 years was simulated well without gravity wave drag parameterization the zonal wave number versus the frequency spectra of simulated precipitation represent realistic signals of convectively coupled equatorial trapped waves eqws the temperature spectra in the stratosphere also indicate dominant signals of eqws eqws with equivalent depths in the range of 8 90 m from the n 1 mode to n 2 mode were extracted separately each eqw in the stratosphere generally corresponded well with the source of each convectively coupled eqw activity in the troposphere the propagations of kelvin waves and n 0 eastward westward propagating eqws are strongly influenced by the walker circulation and the phase of the qbo potential energy associated with eqws is generally larger in the westerly than in the easterly shear phase of the qbo eqws with vertical wavelengths 7 km contribute up to 30 of total potential energy 7 km over the equator at an altitude of 20 30 km gravity waves generated by cumulus convection with periods 24 h are clearly visible over areas of africa the amazon and around indonesia and result in localized pe distributions in areas short distances from the source region comparisons of the model results and recent satellite observations are discussed

a study on the response of a soft basin for incident s p and rayleigh waves with special reference to the long duration observed in mexico city abstract the responses of two types of soft basins for incident sh sv p and rayleigh waves in a 2 d elastic half space are investigated with special reference to the long duration of strong motions observed in mexico city during the michoacan mexico earthquake of 1985 first the difficulty for simple 1 d models to reproduce the later part of the accelerogram observed in mexico city is shown then the effect of a 2 d deep basin structure of a relatively large scale 10 km wide and 1 km deep and a moderate impedance ratio 2 5 is studied the results show that surface waves generated at the edges of the basin are clearly propagating inside the basin back and forth however the increase in duration by these surface waves is 20 sec at most introducing another much softer layer inside the basin we found that the calculated durations and envelop shapes become very similar to the observed ones because of the slowness of surface wave propagation these theoretical studies suggest that the exceptionally long duration observed in mexico city might be caused by a strong constructive interaction of soft surface layers with a deep basin structure beneath the city

latitudinal variations of the convective source and propagation condition of inertio gravity waves in the tropics latitudinal variations of the convective source and vertical propagation condition of inertio gravity waves igws in the tropical region 30 s 30 n are examined using high resolution global cloud imagery gci and 6 hourly ncep ncar reanalysis data respectively for 1 yr march 1985 february 1986 the convective source is estimated by calculating the deep convective heating dch rate using the brightness temperature of the gci data the latitudinal variation of dch is found to be significant throughout the year the ratio of the maximum to minimum values of dch in the annual mean is 3 2 and it is much larger in the june august jja and december february djf means spectral analyses show that dch has a dominant period of 1 day a zonal wavelength of about 1600 km and a gaussian type phase speed spectrum with a peak at the zero phase speed the vertical propagation condition of igws is determined in the zonal wavenumber and frequency domain by two factors i latitude which determines the coriolis parameter and ii the basic state wind structure in the target height range of wave propagation it was found that the basic state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hpa and accordingly a large portion of the source spectrum is filtered out this is prominent not only in the latitudes higher than 15 where strong negative shear exists but also near the equator where strong positive shear associated with the westerly phase of the quasi biennial oscillation qbo filters out large portions of the lowfrequency components of the convective source there is no simple relationship between the ground based frequency and latitude lower latitudes are not always favorable for low frequency igws to be observed in the stratosphere the basic state wind in the tropics which has seasonal annual and interannual variations plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere

basin structure estimation by waveform modeling forward and inverse methods we introduce a technique for using broadband seismograms recorded from earthquakes at local and regional distances to refine basin structure for the region outside the basin we assume a one dimensional 1d crustal model and analytical techniques grt to propagate the energy from sources to the basin edge where the motions are then interfaced with a 2d finite difference algorithm wen and helmberger 1996 we parameterize the basin section by isovelocity layers with linear dipping segments between control points the control point depths are allowed to vary to improve the modeling of waveform data of stations inside the basin the comparison between data and synthetics is qualified by a fitness function defined by two factors the timing shift required for best alignment and the correlation coefficient the procedure was applied to a strong motion waveform profile across the extended los angeles basin produced by the 1992 landers california earthquake to refine the velocity structure using sensitivity testing and forward modeling only the correlation coefficient and amplitude were used because absolute timing was unknown the procedure was extended to a direct waveform inversion by employing a conjugate gradient approach which uses numerical derivatives numerical tests using the new inversion process with synthetic data demonstrate that it is possible to recover a detailed basin structure if a sufficient amount of high quality data exists

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

diurnal patterns of rainfall in northwestern south america part i observations and context one of the rainiest areas on earth the panama bight and pacific western littoral of colombia is the focal point for a regional modeling study utilizing the fifth generation pennsylvania state university ncar mesoscale model mm5 with nested grids in this first of three parts the observed climatology of the region is presented the seasonal march of rainfall has a northwest southeast axis with western colombia near the center receiving rain throughout the year this study focuses on the august september season the diurnal cycle of rainfall over land exhibits an afternoon maximum over most of south and central america typically composed of relatively small convective cloud systems over some large valleys in the andes and over lake maracaibo a nocturnal maximum of rainfall is observed a strong night morning maximum of rainfall prevails over the coastal ocean propagating offshore and westward with time this offshore convection often takes the form of mesoscale convective systems with sizes comparable to the region s coastal concavities and other geographical features the 10 day period of these model studies 28 august 7 september 1998 is shown to be a period of unusually active weather but with a time mean rainfall pattern similar to longer term climatology it is concluded that the rain producing processes during this time period are likely to be typical of those that shape the seasonal climatology

factors which determine the hydrogeochemical behaviour of karstic springs a case study from the betic cordilleras spain the cabra alcaide karstic massif situated in the south of spain constitutes an important part of the so called natural park of the subbetic sierras this aquifer system is drained by various springs which supply a population of some 100 000 inhabitants the feed areas of these springs show very different characteristics with respect to their geological structure size of the drainage area thickness of the vadose zone elevation and degree of karstification in addition the carbonate rocks lie over a clayey substratum which contains large masses of intercalated evaporites due to these conditions the hydrochemical composition of the springs is relatively variable in this study a hydrogeochemical characterization of the aquifer in both space and time is undertaken and the factors that determine it are discussed to achieve this 19 monthly samples were taken from the 6 most significant springs of the hydrogeological system the commencement of sampling coincided with the transition from a period of several years of severe drought and a very wet two year period which amplified considerably the hydrochemical and hydrodynamic response of the springs to the recharge identification of hydrogeochemical processes was performed by studying hydrographs the temporal evolution of physico chemical parameters ionic ratios mainly mg ca and by means of simple and multivariate statistical analyses the saturation status was established using the wateqf program and the mass transfer was quantified using phreeqc with the exception of the epikarstic subsystem i e the zarza spring the majority of the results indicate that the aquifer exhibits a diffuse flow model in which piston flow phenomena are seen closely linked to the most intense precipitation along the direction of flow hydrochemical trends are seen as the water type changes from ca hco3 to ca mg hco3 at the same time enrichment in some ions derived from the dissolution of evaporitic minerals of the impermeable substratum and dedolomitization processes occur in this way almost 90 of the water samples were oversaturated in calcite the majority of cases being a consequence of the dissolution of the gypsum of the substratum only in the epikarstic springs can it be considered that the oversaturation in calcite is due to loss of co2 from the emerging groundwater it is concluded that hydrodynamic aspects together with hydrogeochemical characteristics need to be taken into account to correctly explain the hydrochemical evolution of the karstic springs moreover the use of both approaches permits a more accurate establishment of the degree of aquifer karstification which in turn needs to be known in order to assess its vulnerability to contamination and to protect recharge zones

seismic characteristics of earthquakes along the offshore extension of the western transverse ranges california the short and long period body waves of five moderate m l 5 to 6 earthquakes that took place in the nearshore region of southcentral california between 1969 and 1981 are modeled to obtain the source parameters both regional pnl waveforms and teleseismic p waveforms are used in this analysis four of the events are thrust earthquakes with strikes that rotate southwestward as the epicenters move southward the fifth is a strike slip event occurring on a fault subparallel to the san andreas fault the focal mechanisms for all five events are consistent with known faults in the source localities and suggest that the regional stress field is compressional in a north south direction at least three events have complex source time histories suggesting that complex sources are common even for events of this size the most exotic event started with a low stress drop subevent ruptured bilaterally and concluded with strong asperity ruptures at each end since pnl waveforms for thrust events are particularly sensitive to crustal thickness regionalized crustal models were developed the crustal thickness appears to increase southward but may be a function of the distance of the event from shore rather than of latitude basin and range paths yield the thinnest crustal models while paths crossing the colorado plateau and rockies yield the thickest we also examined amplitude variations with station and path in general the amplitudes seem to be controlled by the station site rather than the path

complex faulting deduced from broadband modeling of the 28 february 1990 upland earthquake ml 5 2 the 1990 upland earthquake was one of the first sizable local events to be recorded broadband at pasadena where the green s functions appropriate for the path are known from a previous study the synthetics developed in modeling the 1988 upland sequence were available for use in rapid assessment of the activity first motion studies from the caltech usgs array data gave two solutions for the 1990 main shock based on the choice of regional velocity models although these focal mechanisms differ by less than 5 in strike and 20 rake it proved possible to further constrain the solution using these derived green s functions and a three component waveform inversion scheme we obtain from long period waves a fault plane solution of 216 77 5 0 m 0 2 5 10 24 dyne cm depth 6 km and a source duration of 1 2 sec for which the orientation and source depth are in good agreement with the first motion results of hauksson and jones 1991 comparisons of the broadband displacement records with the high pass wood anderson simulations suggests the 1990 earthquake was a complicated event with a strong asperity at depth double point source models indicate that about 30 per cent of the moment was released from a 9 km deep asperity following the initial source by 0 0 to 0 5 sec our best fitting distributed fault model indicates that the timing of our point source results is feasible assuming a reasonable rupture velocity the rupture initiated at a depth of about 6 km and propagated downward on a 3 5 by 3 5 km length by width fault both the inversion of long period waves and the distributed fault modeling indicate that the main shock did not rupture the entire depth extent of the fault defined by the aftershock zone a relatively small asperity about 1 0 km 2 with a greater than 1 kbar stress drop controls the short period wood anderson waveforms this asperity appears to be located in a region where seismicity shows a bend in the fault plane

source parameters of the sierra madre earthquake from regional and local body waves we inverted the three component long period data recorded by the terrascope array for the june 28 1991 sierra madre california event to determine the seismic moment and source orientation of the mainshock ml 5 8 remarkably four of the six stations were located 159 2 0 7 km from the epicenter variations in absolute traveltime were smaller than 2 and 3 for pn and sn whereas the surface waves displayed greater variation similarities in the waveforms and the small variance in traveltime suggest that a common green s function can be used to invert the data we used the whole waveforms excluding the fundamental surface waves at the more distant stations to invert for source parameters the results of the inversion indicated that this event was predominately a thrust type earthquake where the strike rake and dip were determined to be 235 74 and 50 respectively the seismic moment was determined to be 2 5 1024 dyne cm the source duration was found to be about 1 0 seconds by direct measurement of the s wave recorded at the pasadena station located 21 km from the epicenter considering circular rupture we obtain a stress drop of 460 bars

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

investigation of the rupture process of the 28 june 1992 landers earthquake utilizing terrascope abstract displacement seismograms recorded by terrascope for the 28 june 1992 landers earthquake m w 7 3 are deterministically modeled using a forward point source summation technique although the data set is sparse it was possible to robustly determine important rupture parameters such as gross slip distribution rupture velocity rise time and total source duration the relatively simple approach lends itself to rapid application following large earthquakes provided that a catalog of green9s functions appropriate for the region is available the fault used in the modeling of the landers mainshock has a length of 70 km along strike and a width of 15 km along dip a model was found in which the distribution and amplitude of slip at the surface matches the observed surface slip and provides a very good level of fit to the seismic data seismically the landers earthquake is characterized as two subevents the peak slip of the first subevent is 10 km north of the epicenter and the second is 40 km northwest along strike from the epicenter the seismic moment is distributed as 2 10 26 dyne cm to the first and 6 10 26 to the second subevent respectively it was assumed in our modeling that the distribution of seismic moment along strike was the same at all depths this assumption implies that slip at depth is 69 of that at the surface as a result of differences in the material properties in the velocity model the sensitivities of the source model to rupture velocity and dislocation rise time were examined a rupture velocity of 2 9 km sec 80 of the shear wave velocity and a rise time of 1 to 3 sec were found to satisfy the data the rise time is only a fraction of the total source process time of 24 sec and implies that slip on the fault occurred within a narrow band 3 to 10 km at any instant during the rupture

propagational corrections for basin structure landers earthquake transfer functions appropriate for correcting for propagational distortion caused by basin structures 2d given a hard rock 1d response are developed the transfer functions are generated theoretically using a hybrid method where the finite difference technique is employed only in the basin this allows for efficient computation and the ability to separate path contributions due to body waves and surface waves the procedure is used to explain some strong motions observed in the los angeles basin relative to the hard rock site pasadena during the 1992 landers earthquake

an analysis of west african dynamics using a linearized gcm abstract this study utilizes a linear primitive equation spherical model to study the development and propagation of easterly wave disturbances over west africa perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time the perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the sahel and two dry years the model simulations show consistent contrasts in wave activity between the wet and dry years the waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere the waves tend to extend throughout the troposphere to the level of the tropical easterly jet tej in the wet years but not in the dry years the upper tropospheric shear which is stronger in wet years appears to be a key factor in wave development this shear is dependent on the intensity of the tej suggesting that the t

modeling the seismic response of basin edge structure by a sequential waveform method a sequential waveform method is developed to simulate the seismic response of basin edge structure excited by a plane incident p wave the full procedure involves a a previous parameterization of the investigated model using the seismic wave velocities and depths of the sedimentary stratifications b an input motion determined from the records at stations installed on hard rock c forward computation of the p sv elastic wave field by means of a two dimensional finite difference fd method d the optimization of the model vector using simulated annealing technique and comparing the simulated seismic response of the tested structure with the observed wave field e the correction of the initial model by trial and error by testing the differences between synthetics and observed data and f the final solution obtained by iteration using the conjugate gradient algorithm the search of an optimal basin edge model has been parallel processed by varying the shapes and velocities of strata on the basis of the fitting of relative timing amplitude and phase between the output and the observed data the input motion and sensitivity have been checked and the validity of the method has been demonstrated by numeric analysis using the teleseismic records generated by 7 earthquakes recorded at 26 broadband seismic stations we have studied the seismic velocity structure of the southern edge of the jiyang depression located in the bohai bay basin northern china two cross sections show an agreement between the velocity results and the geological sections available in the region in addition we obtain evidence of three hidden faults under the sections and features that suggest major extensions at the paleogene

behavior of deep convective clouds in the tropical pacific deduced from isccp radiances abstract we analyze the properties of deep convection over the equatorial pacific and its relationship to sea surface temperature sst and surface wind divergence using isccp radiance data for july 1983 and january 1984 deep convective clouds dcc are diagnosed with both a combined visible infrared threshold method and an infrared only threshold method the visible channel is important in diagnosing deep convection in different regions with different surface and atmospheric properties because of the existence of large scale variations of dcc top altitudes the itcz and spcz exhibit changes in these two months that are characteristic of both the el nino and seasonal cycles deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing longwave radiation diurnal variations of dcc cover and associated mesoscale cirrus anvil cloud cac cover are out of phase with deep convection peaking in the early morning throughout the equatorial pacific the diurna

the diurnal cycle of tropical convection the diurnal cycle of tropical convection is investigated with global cloud imagery constructed from 11 m radiance measurements taken aboard six satellites four harmonics of the diurnal cycle are resolved in the cloud imagery with about 50 km horizontal resolution to isolate deep convective activity from other processes which cause diurnal fluctuations in longwave radiance an index of deep convective activity is constructed by thresholding to brightness temperatures less than 230 k significant diurnal amplitude of deep convection is found only over tropical landmasses over the tropical oceans the diurnal cycle is weak and is barely discernible from the background red spectrum of convective variance nonetheless oceanic convection exhibits a systematic diurnal fluctuation with maximum intensity in the early morning nocturnal subsidence along the cloud free equator is postulated to play a role in forcing diurnal variation in the intertropical convergence zones other mechanisms are also implied to contribute as a similar early morning maximum in deep convection is seen even where no adjoining cloud free regions occur the diurnal cycle of deep convection is found to be organized on planetary scales predominantly in nonmigrating modes i e modes with phase speeds not equal to that of the sun the nonmigrating modes are postulated to be produced by the nonuniform distribution of convective centers the nonmigrating zonally symmetric component is found to be especially large while the role of this mode in forcing diurnal variations of the tropospheric circulation e g the hadley cell is questionable its role in modulating the ionospheric electric potential is well established discrepancies with the traditional notion that cloud to ground lightning is the dominant mechanism by which the earth is negatively charged are discussed in particular the probable role of nonlightning producing clouds e g the stratiform portion of convective complexes in diurnally modulating the negative charge on earth is discussed

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

source mechanism and rupture directivity of the 18 may 2009 mw 4 6 inglewood california earthquake on 18 may 2009 an m w 4 6 earthquake occurred beneath inglewood california and was widely felt though source mechanism and its location suggest that the newport inglewood fault nif may be involved in generating the earthquake rupture directivity must be modeled to establish the connection between the fault and the earthquake we first invert for the event s source mechanism and depth with the cut and paste method in the long period band 5 s because of the low velocity shallow sediments in the los angeles la basin we use two velocity models in the inversion for stations inside and outside the la basin however little difference is observed in the resolved source mechanism m w 4 6 strike 246 145 dip 50 77 rake 17 138 and depth 7 to 9 km compared to an inversion using the standard southern calfornia model with the resolved source parameters we calibrate the amplitude anomaly of the short period 0 5 2 hz p waves with amplitude adjustment factors aaf these aafs are used as corrections when retrieving source mechanisms of the smaller aftershocks using short period p waves alone most of the aftershocks show similar source mechanisms as that of the mainshock providing ideal empirical green s functions egfs for studying its rupture process we use a forward modeling approach to retrieve rupture directivity of the mainshock consistent with movement on the nif with rupture toward the southeast although we focus on p waves for analyzing rupture directivity the resolved unilateral pattern is also confirmed with the azimuthal variation of the duration of sh waves observed in the basin the high rupture velocity near the shear velocity and relatively low stress drop are consistent with the hypothesis of rupture on a mature fault

a case study on geochemical anomaly identification through principal components analysis supplementary projection abstract based on a case study in which a single geochemical anomaly was located in the vicinity of an abandoned mine in central portugal a recursive methodology for anomaly background separation was developed this methodology relies on the supplementary projection of each of the samples taken from a subset of anomaly candidates onto the axes provided by principal components analysis of the background subset the concept of anomaly intensity defined by the average of the distances from the original to the supplementary projections is the basis for final anomaly identification

impact of broadband seismology on the understanding of strong motions most analyses of strong motion attenuation assume simple whole space type geometrical spreading namely 1 r or its modified form e kr r however broadband data presently becoming available suggests a more complex behavior with substantial crustal effects events such as the sierra madre event m 5 8 triggered the strong motion channels at all of the terrascope stations allowing for 0 01 sec sampling of the wavefield we find that most of the well defined crustal bodywave arrivals defined and modeled in the 1 to 0 1 hz bandpass also contain high frequency energy by comparing the triggered channels with the continuous channels we see that several of the more distant stations triggered on the depth phase sp m p these phases as well as the depth phase ss m s are obvious in velocity and quite apparent in accelerations our best models for southern california contain a relatively thick low velocity layer at the surface roughly 5 km thick with shear velocities below 3 km sec this layer or zone because it appears to vary considerably controls the wavefield at nearly all frequencies out to about 60 km and yields attenuation decay faster than 1 r at large ranges the lower crustal triplications dominate and the attenuation curve flattens adding random scatters to these layered models adds additional complexity but does not alter the basic flat layer predictions

maintenance of the intertropical convergence zones and the large scale tropical circulation on a water covered earth abstract how the surface boundary heating sea surface temperature and cumulus adjustment process affect the location structure energetics and dynamics of the intertropical convergence zones itczs is investigated a series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature sst an aqua planet all experiments are run using equinoctal insolation with no longitudinal variation in sst two different convective parameterization schemes kuo and moist convective adjustment and several different zonally symmetric sst distributions are used in these experiments the location of the itcz is found to be sensitive to the convective parameterization scheme and the sst distribution the model with the moist convective adjustment scheme produces an itcz over the tropical sst maximum even under conditions where the sst gradient is weak by contrast the model with the kuo convective parameterization is not as sensit

delineation of shallow seismic source zones using k means cluster analysis with application to the aegean region the selection of specific uniform seismic source zones for use in probabilistic seismic hazard analysis is often controversial recognizing that a consistent approach to source model development is not always possible as the information available relating to geology and seismotectonics can vary from region to region the k means algorithm for hierarchical cluster analysis can be used to partition regions based on observed seismicity the aegean incorporating greece albania former yugoslav republic of macedonia f y r o m southern bulgaria and western turkey with its varied seismotectonics and generally high seismicity is used as an important area of seismicity in which to develop and demonstrate the application of k means two types of algorithm are considered the first is a point source k means that can be used to partition a catalogue of earthquake hypocentres the second is a novel line source development of the algorithm appropriate in seismology as these are analogues for the traces of active faults which is then applied to a catalogue of known fault ruptures in the aegean the common problems of the k means methodology are also addressed ensemble analyses are used to identify better choices of initial estimates for the cluster centres a cluster quality index is used to identify the optimum number of clusters and its robustness assessed when considering different subsets of the observed earthquake catalogue an alternative approach is also implemented monte carlo seismic hazard analysis is used to compare models with different numbers of clusters with the observed seismicity of the 20th century considerable variation is found in the optimum number of clusters identified either by the quality index or by stochastic seismic hazard analysis ultimately the k means partitions of seismicity are developed into source models and their representation of aegean seismotectonics assessed the result is that models containing between 20 and 30 clusters emerge as the most appropriate in capturing the spatial variation in hypocentral distribution and fault type in the aegean

middle atmosphere simulated with high vertical and horizontal resolution versions of a gcm improvements in the cold pole bias and generation of a qbo like oscillation in the tropics abstract the large scale circulation in the geophysical fluid dynamics laboratory skyhi troposphere stratosphere mesosphere finite difference general circulation model is examined as a function of vertical and horizontal resolution the experiments examined include one with horizontal grid spacing of 35 km and another with 100 km horizontal grid spacing but very high vertical resolution 160 levels between the ground and about 85 km the simulation of the middle atmospheric zonal mean winds and temperatures in the extratropics is found to be very sensitive to horizontal resolution for example in the early southern hemisphere winter the south pole near 1 mb in the model is colder than observed but the bias is reduced with improved horizontal resolution from 70 c in a version with 300 km grid spacing to less than 10 c in the 35 km version the extratropical simulation is found to be only slightly affected by enhancements of the vertical resolution by contrast the tropical middle atmospheric s

convectively coupled kelvin and easterly waves in a regional climate simulation of the tropics this study evaluates the performance of a regional climate model in simulating two types of synoptic tropical weather disturbances convectively coupled kelvin and easterly waves interest in these two wave modes stems from their potential predictability out to several weeks in advance as well as a strong observed linkage between easterly waves and tropical cyclogenesis the model is a recent version of the weather research and forecast wrf system with 36 km horizontal grid spacing and convection parameterized using a scheme that accounts for key convective triggering and inhibition processes the domain spans the entire tropical belt between 45 s and 45 n with periodic boundary conditions in the east west direction and conditions at the meridional lower boundaries specified based on observations the simulation covers 6 years from 2000 to 2005 which is long enough to establish a statistical depiction of the waves through space time spectral filtering of rainfall data together with simple lagged linear regression results show that both the horizontal phase speeds and three dimensional structures of the waves are qualitatively well captured by the model in comparison to observations however significant biases in wave activity are seen with generally overactive easterly waves and underactive kelvin waves evidence is presented to suggest that these biases in wave activity which are also correlated with biases in time mean rainfall as well as biases in the model s tropical cyclone climatology stem in part from convection in the model coupling too strongly to rotational circulation anomalies nevertheless the model is seen to do a reasonable job at capturing the genesis of tropical cyclones from easterly waves with evidence for both wave accumulation and critical layer processes being importantly involved

strong motion and broadband teleseismic analysis of the 1991 sierra madre california earthquake short period and broadband teleseismic waveform data and three component strong motion records were analyzed to obtain the source parameters of the 1991 sierra madre earthquake close in strong motion velocity records analyzed from 5 s to 5 hz show two distinct pulses about 0 35 s apart requiring some rupture complexity the near field shear wave displacement pulse from this event has a relatively short duration about 1 s for the magnitude of the event requiring a particularly high average stress drop to further constrain the rupture process the data were used in a finite fault source inversion to determine the temporal and spatial distribution of slip we chose a fault plane orientation striking s 62 w and dipping 50 toward the northwest as required by the distribution of aftershocks the first motion mechanism and the teleseismic bodywave point source inversion in addition to the aftershock locations depth constraints are provided by teleseismic short period and broadband recordings which require a centroid depth of 10 11 km our inverse modeling results indicate that both the teleseismic and strong motion data sets can be fit with a compact rupture area about 12 km2 southwest and up dip from the hypocenter the average slip is approximately 50 cm and the maximum slip is 120 cm the seismic moment obtained from either of the separate data sets or both sets combined is about 2 8 0 3 1024 dyn cm and the potency is 0 01 km3 using the area of significant slip estimated from the finite fault inversion the resulting stress drop is on the order of 150 200 bars

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

seismic waveform modeling in the los angeles basin the proximity of several recent earthquakes to the los angeles sedimentary basin provides an opportunity to isolate the effects of the basin on wave propagation the 4 october 1987 aftershock m l 5 3 of the whittier narrows sequence and the 28 june 1991 sierra madre mainshock m l 5 8 are on a similar azimuth to stations overlying the deepest part of the basin a distinctive feature of records from basin stations recording the 4 october after shock is the large amplitude of multiple s ss etc the multiples have up to twice the amplitude of the direct s phase on the tangential component at such a short range less than 25 km a horizontal seismic velocity gradient is needed to turn rays rapidly enough for large amplitude multiples to form a forward modeling approach is employed using finite difference numerical techniques that produce double couple point source solutions a model based on a recent geologic cross section constructed for the east edge of the los angeles basin generates more phases than are seen in the seismic records simpler models based on dipping layers with low shear velocities in the top few layers fit the data better the seismic velocity depth and dip of the layers are varied to fit the timing between the direct p the direct s and the first s multiple the timing and amplitude of the direct and first multiple s pulses are well modeled though the phase of the first multiple does not match the data including a steeply dipping west edge in the basin model has little effect on the synthetic waveforms except at distances near that basin edge the amplitude of ss is greatest in the deepest part of the basin where it is two times larger than direct s the coda duration increases from 8 sec to more than 20 sec from the ne to the sw the sierra madre mainshock occurred about 25 km to the ne of the whittier narrows sequence the model for whittier narrows was extended to this distance with a shallow basin between whittier and the sierra madre hypocenter to simulate the san gabriel sedimentary basin phases generated by the edge of the deep basin continue to dominate the synthetic waveforms but this model generates a lengthy coda this study shows that specific phases with frequencies up to 1 hz that have traveled through deep sedimentary basins can be explained by two dimensional seismic velocity models

hydrochemical characteristics of aquifers near sutherland in the western karoo south africa the western karoo depends entirely on groundwater for domestic and agricultural use an understanding of the chemical evolution of the groundwater provides insight into the interaction of water with the environment and contributes to better resource management descriptive statistics correlation matrices and factor analysis together with stable isotope data were used to gain an understanding of the hydrochemical processes of the groundwaters in the fractured rocks around sutherland in the western karoo the main processes influencing the groundwater chemistry are salinisation mineral precipitation and dissolution cation exchange and human activity the stable isotope data indicate that the infiltration of evaporated water is partly responsible for the occurrence of saline subsurface waters the ionic oxygen and hydrogen stable isotope composition of the groundwaters suggests that the effects of localised topography are one of the overriding factors controlling the groundwater chemistry in higher lying areas ca hco3 2 type waters are prevalent while in topographical flat areas nacl type waters dominate in areas where water collects close to or at the surface saline soils are formed from these areas salts are leached to the subsurface during significant recharge periods these findings are important in that they contribute to the identification of suitable locations for developing groundwater resources that could yield a relatively better quality water q 2001 elsevier science b v all rights reserved

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

two dimensional reconstruction of the surface ground motions of an earthquake the september 21 1999 chi chi taiwan earthquake the observed time history and spatial dependence of the surface ground motions of the september 21 1999 chi chi taiwan earthquake over the entire island are presented for the first time this report presents an analysis of time dependent spatial ground motions at both near source and local distances using strong motion records the two dimensional ground motions of the chi chi earthquake were reconstructed from more than 400 free field strong motion records after being corrected for absolute times the reconstructed seismic wavefields can be considered as a new type of observed data named 3 d seismograms here results of this study offer some insight into the study of earthquake source and wave propagation based on 3 d numerical modelling and greatly compliment our ability to distinguish wave generations due to sources and or structures

a finite difference simulation of wave propagation in two dimensional random media a finite difference algorithm is used to generate synthetic seismograms for waves propagating through two dimensional random media the media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle the finite difference technique retains all multiply scattered and diffracted waves and also accounts for transmission losses the synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering for a medium with a white wavenumber spectrum of velocity fluctuations the coda is higher frequency than the initial pulse the apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength the spectra of the coda generally increase in frequency as the scatterers decrease in size examples demonstrate how scattering can produce spectra with broad peaks and sharp fall offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

three dimensional structures of tropical nonmigrating tides in a high vertical resolution general circulation model this paper investigates nonmigrating tides from the ground to the lower mesosphere using data from a high resolution general circulation model kanto gcm as well as observational data from the sounding of the atmosphere using broadband emission radiometry instrument on board the thermosphere ionosphere mesosphere energetics and dynamics satellite and from gps radio occultation measurements obtained with the cosmic formosat 3 mission we extract nonmigrating tides using a composite as a function of universal time in physical space without performing a zonal wave number decomposition the kanto gcm clearly demonstrates that tropical nonmigrating tides are regarded as gravity waves excited by diabatic heating enhanced over two major continents specifically africa and south america they propagate zonally in a direction away from their sources that is west and eastward propagating waves are dominant on the western and eastern sides of the continents respectively these characteristics are observed in two satellite data sets as well except that the amplitudes in the kanto gcm are larger than those in the observations seasonal variations of nonmigrating tides are also investigated it is suggested that filtering owing to the stratopause semiannual oscillation as well as diabatic heating in the troposphere is important for the seasonal variations of nonmigrating tides in the stratosphere and the lower mesosphere

the excitation of equatorial waves by deep convection in the ncar community climate model ccm3 the forcing of equatorial waves by convective heating in the national center for atmospheric research community climate model ccm3 is investigated and compared with the forcing deduced from observations of convective clouds the analysis is performed on two different simulations wherein convection is represented by the zhang mcfarlane and the hack parameterization schemes respectively spectra of equatorial waves excited by convective heating rossby kelvin and gravity waves are obtained by projecting the heating field onto hough modes the dynamical response to the heating is then calculated in terms of the vertical component of the eliassen palm flux fz focusing on waves that are able to propagate into the middle atmosphere the same analysis is repeated using observations of outgoing longwave radiation as a proxy for tropical convection comparison of ccm3 results with those derived from observations indicates that high frequency heating variability is underestimated in both ccm3 simulations despite the fact that time mean values of convective heating are well represented moreover the two convective parameterization schemes differ substantially from each other compared to observations fz is severely underestimated at most frequencies when ccm3 is run with the zhang mcfarlane scheme when the hack scheme is used fz at frequencies v 0 5 cycles per day is comparable to the observations but it is underestimated at higher frequencies misrepresentation of the variability of convective heating is likely to have important consequences for the dynamical simulation of the middle atmosphere and even the troposphere