a correction factor to account for mixing in ghyben herzberg and critical pumping rate approximations of seawater intrusion in coastal aquifers 1 the classic ghyben herzberg estimate of the depth of the freshwater saltwater interface together with the dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems on the basis of these assumptions strack 1976 developed a single potential theory to calculate critical pumping rates in a coastal pumping scenario the sharp interface assumption and in particular this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers the sharp interface assumption neglects mixing and implicitly assumes that salt water remains static consequently this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply we investigate the error introduced by adopting the sharp interface approximation and we include the effects of dispersion on the formulation of strack 1976 to this end we perform numerical three dimensional variable density flow simulations we find that strack s equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor 1 t b 1 6 where t is transverse dispersivity and b is aquifer thickness we find that this factor can be used not only to estimate the critical pumping rate but also to correct the ghyben herzberg estimate of the interface depth its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions

flow dynamics and salt transport in a coastal aquifer driven by a stratified saltwater body lab experiment and numerical modeling this paper examines the transient development and the steady state configuration of groundwater within a coastal aquifer adjacent to a stratified saltwater body such systems consist of three different water types the regional fresh groundwater and low and high salinity brines forming the upper and lower water layers of the stratified water body respectively the dynamics location and the geometry of the interfaces and the density driven circulation flows that develop in the aquifer are examined using laboratory experiments and numerical modeling at the same scale the results show that the transient intrusion of the different water bodies into the aquifer takes place at different rates and that the locations of the interfaces between them change with time before reaching steady state under steady state conditions both the model and the experiments show the existence of three interfaces between the three water types the numerical model which is calibrated against the salinity distribution and groundwater discharge rate in the laboratory experiments allows the quantification of the flow rates and flow patterns within the aquifer these flow patterns which cannot be derived from laboratory experiments show the transient development of three circulation cells which are confined between the three interfaces these results confirm the hypothesis that has been previously suggested based solely on a steady state numerical modeling defined by a conceptual understanding parametric analysis shows that the creation of three circulation cells and three interfaces is limited to certain conditions and defines the ranges for the creation of this unique system

tidal influence on seawater intrusion in unconfined coastal aquifers studies of seawater intrusion in unconfined coastal aquifers typically neglect oceanic oscillations such as tides and assume a static seaward boundary condition defined by the mean sea level laboratory experiments and numerical simulations were conducted to investigate the influence of tidal oscillations on the behavior of the saltwater wedge for the conditions examined the experiments showed that an upper saline plume formed in the intertidal zone due to tide induced seawater circulation the presence of the upper saline plume shifted the fresh groundwater discharge zone seaward to the low tide mark and restricted the intrusion of the saltwater wedge the overall seawater intrusion extent as indicated by the wedge toe location was reduced significantly compared with the nontidal static case results from the numerical model matched these experimental observations and further demonstrated the similar type of tidal influence on the saltwater wedge in a field scale aquifer system the glover 1959 solution for predicting the saltwater wedge was modified to account for the tidal effect by including the tide induced circulation as a recharge to the aquifer the findings highlight the significant impact of the tide in modulating the groundwater behavior and salt freshwater dynamics not only within but also landward of the intertidal zone

hydrogeological characterization of seawater intrusion in tidally forced coastal fractured bedrock aquifer summary hydrogeological investigation was carried out to characterize seawater intrusion in a tidally forced coastal fractured bedrock aquifer in the west coast of korea peninsular which was also subject to heavy groundwater extraction times series analysis using the data of electrical conductivity ec groundwater level and tidal oscillation showed that intensive groundwater extraction from the wells near the shore caused a severe seawater intrusion the geophysical loggings and hydraulic tests indicated that the tidally forced coastal fractured aquifer in the study area was characterized by the shallow fresh groundwater transition zone and deep high saline water zone the extent of seawater intrusion highly depended on conductive fractures and their hydraulic connectivity in the deep saline water layer progressive seawater intrusion took place mainly by persistent intensive pumping and in part by tidal activity the conductive fractures acted as a pathway for saline water flow from the deep saline water zone to the transition zone when groundwater was extracted the extent of transition zone depended on the change of groundwater level by groundwater pumping or recharge this study indicated that a persistent intensive extraction of groundwater would intensify seawater intrusion in tidally forced coastal fractured aquifer and proper measures would be required to prevent it

configuration of subducting philippine sea plate beneath southwest japan revealed from receiver function analysis based on the multivariate autoregressive model 1 we construct a detailed image of velocity discontinuity beneath southwest japan by using receiver functions we first propose an improved receiver function estimation method based on the statistical multivariate autoregressive model then we apply the new method to the teleseismic waveform data recorded by the high density seismograph network in southwest japan the results show a clear velocity discontinuity at 30 km depth beneath the southern shikoku region this discontinuity corresponding to the boundary between the oceanic crust and the high velocity layer the oceanic moho of the philippine sea plate phs continues down to the north indicating that the aseismic phs extends to the central chugoku region the continental moho is also clearly imaged beneath the chugoku region the depth contour of the phs shows a rather complicated feature with ridges and valleys the most significant ridge is located around longitude 133 e west of which the contours are basically directed north south changing to west east to the east beneath the western part of this ridge hypocenters of microearthquakes are located above this velocity discontinuity while earthquakes mainly occur below the discontinuity within the oceanic mantle beneath the eastern part of the ridge

multiband x c l radar amplitude analysis for a mixed sand and gravel bed river in the eastern central andes abstract synthetic aperture radar sar amplitude measurements from spaceborne sensors are sensitive to surface roughness conditions near their radar wavelength these backscatter signals are often exploited to assess the roughness of plowed agricultural fields and water surfaces and less so to complex heterogeneous geological surfaces the bedload of mixed sand and gravel bed rivers can be considered a mixture of smooth compacted sand and rough gravel surfaces here we assess backscatter gradients over a large high mountain alluvial river in the eastern central andes with aerially exposed sand and gravel bedload using x band terrasar x tandem x c band sentinel 1 and l band alos 2 palsar 2 radar scenes in a first step we present theory and hypotheses regarding radar response to an alluvial channel bed we test our hypotheses by comparing backscatter responses over vegetation free endmember surfaces from inside and outside of the active channel bed area we then develop methods to extract smoothed backscatter gradients downstream along the channel using kernel density estimates in a final step the local variability of sand dominated patches is analyzed using fourier frequency analysis by fitting stretched exponential and power law regression models to the 2 d power spectrum of backscatter amplitude we find a large range in backscatter depending on the heterogeneity of contiguous smooth and rough patches of bedload material the sar amplitude signal responds primarily to the fraction of smooth sand bedload but is further modified by gravel elements the sensitivity to gravel is more apparent in longer wavelength l band radar whereas c and x band is sensitive only to sand variability because the spatial extent of smooth sand patches in our study area is typically

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

global land surface backscatter at ku band using merged jason1 envisat and jason2 data sets a unique method for investigating continental surfaces uses backscatter data measured by a radar altimeter at the nadir point of a satellite in contrast to other microwave sensors designed to work at oblique angles such as scatterometers and synthetic aperture radar to improve the altimetry resolution over land we generated 0 5 degrees x 0 5 degrees merged altimetry backscatter maps covering 66 degrees n to 66 degrees s over the global land surface every six days for the period from january 2002 to june 2009 by combining three altimeter data sets jason1 envisat jason2 in the ku band the four backscatter products of envisat ra2 from different retracking algorithms were evaluated prior to merging with the jason1 and jason2 data the global pattern and the seasonal variation of the merged altimetry backscatter were examined which show the merged results have better spatial sampling for the regional to global geophysical process due to the combination of three altimeters to understand how the altimetry backscatter is related to land surface parameters the advanced integral equation model for bare soil and water cloud model for vegetation are used to simulate the ku band backscatter response to soil and vegetation parameters at an incidence of 0 degrees furthermore we compared the time series of merged altimetry backscatter with the leaf area index lai determined by an optical sensor and the backscatter coefficients obtained from a scatterometer quikscat over seven selected vegetated areas over six years the results confirm the sensitivity of ocean altimetry to vegetation further studies relating altimetry backscatter to geophysical parameter are needed

site amplification factors in central and southern california determined from coda waves abstract site amplification factors at frequencies of 1 5 3 6 and 12 hz were determined for 158 stations of the southern california seismic network scsn from coda waves of 306 local earthquakes using a recursive stochastic inverse method our results for southern california are consistent with those of central california obtained by su et al 1992 in that the site amplification at a station is systematically related to the surface geology of the station site the site amplification is high for young quaternary sediments and decreases with increasing geologic age at all frequencies between 1 5 and 12 hz this decreasing rate is higher for younger rock sites gradually becomes lower with increasing geologic age and appears to be insignificant when the site reaches mesozoic age or older the relationship between site amplification and geologic age obtained for southern california agrees with that for central california amplification factors at 158 sites in southern california were combined with those at 132 sites in central california through a common reference site the result is a unique data base of site specific uniformly referenced amplification factors throughout central and southern california

laboratory scale investigation of saltwater intrusion dynamics 1 experiments were completed in a laboratory scale porous media tank to study the transport patterns of a saltwater wedge in a freshwater aquifer three types of experiments were performed to develop 1 steady state salt wedge data observed under different hydraulic gradient conditions 2 transient salt wedge data observed under intruding wedge conditions and 3 transient salt wedge data observed under receding wedge conditions furthermore flux measurements were made to quantify the flow characteristics of three distinct steady state experiments the saltwater intrusion model seawat was used to simulate these data sets the model results along with the experimental data are presented as benchmark problems for testing density coupled groundwater flow models a worthiness analysis was completed to test the sensitivity of these experimental problems to density coupling effects the results of our analysis show that the proposed benchmark is a more robust alternative to the traditional henry problem these new experimental data sets can be used to assess the performance of saltwater intrusion models under both steady state and transient conditions

multiangle backscattering observations of continental surfaces in ku band 13 ghz from satellites understanding the signals particularly in arid regions backscattering in ku band 13 ghz over continen tal surfaces is analyzed with the tropical rainfall measurement mission precipitation radar instruments incidence angles from 0 to 18 along with observations from the topex poseidon nadir looking altimeter and the quikscat scatterometer inci dence angles around 50 the signals from the three instruments are very consistent the backscattering tends to decrease with increasing vegetation density as expected making it possible to classify vegetation density with active microwaves over the northern african desert a very large spatial variability of the backscattering is observed with both surface and volume scatter ings contributing to the signals the use of multiangle observations does help characterizing the desert types but in some areas the ambiguity of the signals is still unexplained the french chinese joint mission chinese french oceanic satellite will carry two active microwave instruments with a large range of incidence angles from 0 to 50 we show that the combined use of ob servations at low and high incidence angles adds information particularly over desert surfaces

effects of kinetic mass transfer and transient flow conditions on widening mixing zones in coastal aquifers 1 the width of a mixing zone between freshwater and seawater is important primarily because it directly reflects the extent of mixing and the growth and decay of the mixing zone indicates changes of the flow regime and water exchange between freshwater and coastal seawater wide mixing zones have been found in many coastal aquifers all over the world however the mechanisms responsible for wide mixing zones are not well understood this work examines the hypothesis that kinetic mass transfer coupled with transient conditions which create the movement of the mixing zone may widen mixing zones in coastal aquifers the hypothesis is tested by conducting two dimensional numerical simulations based on a variable density groundwater model for a scaled tank model and a field scale model periodic water levels representing periodic tidal motion and freshwater table fluctuations are imposed at the seaward and landward boundary respectively which cause the movement of the mixing zone both the scaled tank model and the field model show that the combination of the moving mixing zone and kinetic mass transfer may significantly enhance the extent of mixing and create a wider mixing zone than the models without kinetic mass transfer in addition sensitivity analyses indicate that a larger capacity ratio immobile porosity mobile porosity of mass transfer leads to a wider mixing zone and the maximum width of the mixing zone may be reached for a given capacity ratio when the mean retention time scale in the immobile domain the reciprocal of mass transfer rate and the period of water level fluctuations are comparable

a multiple time window rupture model for the 1999 chi chi earthquake from a combined inversion of teleseismic surface wave strong motion and gps data 1 we present the results of a comprehensive analysis of the rupture process of the 1999 chi chi taiwan earthquake using a broad array of seismic as well as geodetic data spanning a very wide frequency band our results indicate that the rupture was quite smooth with the slip concentrated in a wide arcuate region north of the epicenter with very little slip to the east or south we found a moment of 3 3 1027 dyn cm which is consistent with the long period determinations for this earthquake the rupture velocity is approximately 2 25 km s and is quite uniform across the fault we have tested both a single fault plane model as well as a composite fault model with a second e w striking plane to the north of the rupture to improve the fit of the geodetic data overall the differences in slip distribution between the two models are negligible but the fit to the gps data is significantly better for the composite model which is thus our preferred solution this model is similar to other rupture models as far as the large scale features are concerned but differs for the smaller asperities that are present in other models but not as much in ours these are usually poorly constrained and with the use of the geodetic data we believe that there is little evidence for a significant amount of slip away from our main slip concentration

interrelation between fault zone structures and earthquake processes in order to develop capabilities for predicting earthquake processes on the basis of known fault zone structures and stress conditions we need to find relations between seismogenic structures and processes in the present paper we search for the scale dependence in various earthquake phenomena with the hope to find some structures in the earth that may control the earthquake processes among these phenomena we shall focus on 1 geologic structures which play some role in nucleation and stopping of earthquake fault rupture 2 depth ranges of the brittle seismogenic zone 3 asperities and barriers distributed over a fault plane 4 source controlled f max effect 5 nonfractal behavior of creep events and 6 temporal correlation between coda q 1 and seismicity of earthquakes with magnitude characteristic to a given area our review of various scale dependent phenomena leads us to propose a working hypothesis that the temporal change in coda q 1 may reflect the activity of creep fractures near the brittle ductile transition zone

experimental saltwater intrusion in coastal aquifers using automated image analysis applications to homogeneous aquifers summary this paper presents the applications of a novel methodology to quantify saltwater intrusion parameters in laboratory scale experiments the methodology uses an automated image analysis procedure minimising manual inputs and the subsequent systematic errors that can be introduced this allowed the quantification of the width of the mixing zone which is difficult to measure in experimental methods that are based on visual observations glass beads of different grain sizes were tested for both steady state and transient conditions the transient results showed good correlation between experimental and numerical intrusion rates the experimental intrusion rates revealed that the saltwater wedge reached a steady state condition sooner while receding than advancing the hydrodynamics of the experimental mixing zone exhibited similar traits a greater increase in the width of the mixing zone was observed in the receding saltwater wedge which indicates faster fluid velocities and higher dispersion the angle of intrusion analysis revealed the formation of a volume of diluted saltwater at the toe position when the saltwater wedge is prompted to recede in addition results of different physical repeats of the experiment produced an average coefficient of variation less than 0 18 of the measured toe length and width of the mixing zone

how significant is the slope of the sea side boundary for modelling seawater intrusion in coastal aquifers application of numerical models is a common method to assess groundwater resources the versatility of these models allows consideration of different levels of complexity but the accuracy of the outcomes hinges upon a proper description of the system behaviour in seawater intrusion assessment the implementation of the sea side boundary condition is of particular importance we evaluate the influence of the slope of the sea side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters freshwater inflow and longitudinal and transverse dispersivities model results reveal a multi dimensional dependence of the investigated variables with an increasing relevance of the sea side boundary slope for seawater intrusion decrease of up to 32 submarine groundwater discharge zone reduction of up to 55 and turnover times increase of up to 730 with increasing freshwater inflow or dispersivity values

a new physical barrier system for seawater intrusion control abstract the construction of subsurface physical barriers is one of various methods used to control seawater intrusion swi in coastal aquifers this study proposes the mixed physical barrier mpb as a new barrier system for seawater intrusion control which combines an impermeable cutoff wall and a semi permeable subsurface dam the effect of the traditionally used physical barriers on transient saltwater wedge dynamics was first explored for various hydraulic gradients and the workability of the mpb was thereafter thoroughly analysed a newly developed automated image analysis based on light concentration conversion was used in the experiments which were completed in a porous media tank the numerical code seawat was used to assess the consistency of the experimental data and examine the sensitivity of the performance of the barriers to various key parameters the results show that the mpb induced a visible lifting of the dense saline flux upward towards the outlet by the light freshwater this saltwater lifting mechanism observed for the first time induced significant reduction to the saline water intrusion length the use of the mpb yielded up to 62 and 42 more reduction of the saltwater intrusion length than the semi permeable dam and the cutoff wall respectively the performance achieved by the mpb with a wall depth of 40 of the aquifer thickness was greater than that of a single cutoff wall with a penetration depth of 90 of the aquifer thickness about 13 extra reduction this means that the mpb could produce better seawater intrusion reduction than the traditionally used barriers at even lower cost

a novel approach for characterizing the mixing zone of a saltwater wedge 1 the mixing zone between freshwater and seawater in a coastal aquifer is an important transition region that controls regional groundwater flow dynamics and reactive transport processes while experimental procedures have been developed to study the movement of salt wedges in aquifers so far no one has attempted to exclusively map the mixing zone associated with the wedge in a laboratory scale aquifer model we propose a colorimetric experimental method which employs the reaction between alkaline freshwater and acidic saltwater to map the mixing zone the experiment was completed in a two dimensional aquifer model to simulate a steady saltwater wedge we used the density dependent flow model sutra to simulate these experimental results and to estimate the mixing parameters i e dispersivity coefficients the results show that the proposed colorimetric technique is a useful experimental approach to visualize and quantify the level of mixing in a saltwater intrusion experiment

seismic energy for shallow earthquakes in southwest japan we estimated the radiated energy for 88 earthquakes with m w 4 0 that occurred in southwest japan by analyzing direct s waves recorded by the freesia broadband seismic network f net at local regional distances the attenuation factors for each source receiver group are estimated by the coda method using the recently established high sensitivity and high density seismic network hi net data the site amplification for each f net station is calculated by using the coda normalization method we find good agreement between the source spectra calculated by using these propagation effects and those determined by using an empirical green s function method for 4 m w 5 earthquakes the station variance of the energy estimates is a factor of 2 for earthquakes with m w 5 and it is a factor of 3 for the smaller ones the resultant energy estimations show that 1 the overall ratios between the radiated energy and seismic moment e s m 0 lie in a band of 5 10 7 to 5 10 5 for 88 earthquakes with m w 3 9 6 8 for the tottori 2000 earthquake and its 16 aftershocks with m 0 10 14 10 19 n m we found a very slight increase of e s m 0 with increasing seismic moment for the rest of earthquakes e s m 0 are almost constant for earthquakes occurring in the same source area the constants corresponding to each source area are slightly but systematically different indicating a location dependence of e s m 0 earthquakes that occur in volcanic areas show lower e s m 0 values relative to earthquakes occurring in nonvolcanic areas however the weak to non scaledependence is not certain because of the scantiness of large earthquakes in the data set 2 for earthquakes in the volcanic source areas there appears to be a trend of increasing e s m 0 with focal depth we believe this trend is a result of at least in part the decreasing attenuation with depth in volcanic areas for the nonvolcanic area earthquakes however e s m 0 tends to be a constant in a depth range of 12 50 km since the akinada earthquake 2001 m w 6 8 took place in the western part of subducting philippine sea slab and the two deeper earthquakes occurred in the upper mantle below the same subducting slab in its eastern part the constancy of e s m 0 may indicate that the apparent stress at the brittle patches in the ductile zone can be as high as in the brittle part of the crust 3 estimated e s m 0 are inversely related to the surface heat flow approximately such a relationship suggests that the geothermal structure may be the dominating tectonic factor that controls the level of apparent stress

seismic attenuation above 10 hz in southern california from coda waves recorded in the cajon pass borehole we estimate the attenuation around cajon pass southern california for frequencies above 10 hz and we find total q to exhibit only weak frequency dependence ranging from 800 at 10 hz to 1500 at 100 hz the intrinsic attenuation is approximately twice the level of the scattering attenuation measurements are made using earthquake seismograms recorded at 0 3 km depth using the multiple lapse time window method the results are not dependent on receiver depth and are consistent with previous estimates of q made from direct waves recorded at 2 5 km depth our q values are therefore thought to be representative of the seismogenic crust and the technique used is uncontaminated by the highly attenuating near surface at least above 10 hz we also calculate q from surface data between 1 and 10 hz and find a clear change in the frequency dependence of both intrinsic and scattering attenuation at 10 hz q exhibits strong frequency dependence below 10 hz 1 8 consistent with previous studies in active tectonic regions and only weak frequency dependence at higher frequencies 0 34 this change in behavior renders it unwise to extrapolate q measurements outside the frequency range from which they were derived for example in earthquake source studies possible factors responsible for the apparent change in frequency dependence of q are considered further work is required however to resolve the causes of this change

variable density flow in porous media steady state distributions of water potential and salt concentration in coastal aquifers are typically modelled by the henry problem which consists of a fully coupled system of flow and transport equations coupling arises from the dependence of water density on salt concentration the physical behaviour of the system is fully described by two dimensionless groups i the coupling parameter alpha which encapsulates the relative importance of buoyancy and viscous forces and ii the peclet number mbox textit pe which quantifies the relative importance of purely convective and dispersive transport mechanisms we provide a systematic analytical analysis of the henry problem for a full range of the peclet number for moderate mbox textit pe analytical solutions are obtained through perturbation expansions in alpha this allows us to elucidate the onset of density driven vertical flux components and the dependence of the local hydraulic head gradients on the coupling parameter the perturbation solution identifies the regions where salt concentration is most pronounced and relates their spatial extent to the development of a convection cell next we compare our solution to a solution of the pseudo coupled model wherein flow and transport are coupled only via the boundary conditions this enables us to isolate the effects caused by density dependent processes from those induced by external forcings boundary conditions for small mbox textit pe we develop a perturbation expansion around the exact solution corresponding to mbox textit pe 0 which sheds new light on the interpretation of processes observed in diffusion experiments with variable density flows in porous media the limiting case of infinite peclet numbers is solved exactly for the pseudo coupled model and compared to numerical simulations of the fully coupled problem for large mbox textit pe the proposed perturbation approach is applicable to a wide range of variable density flows in porous media including seawater intrusion into coastal aquifers and temperature or pressure driven density flows in deep aquifers

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

seawater groundwater mixing in and fluxes from coastal sediment overlying discrete fresh seepage zones a modeling study submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it we analyzed this phenomenon by a suite of variable density variably saturated groundwater flow simulations guided by field studies the field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones the discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone both fluxes and salinities varied with tides two dimensional simulations of the idealized beach ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets causing mixing brackish water discharges at the sediment water interface above where the plume mixes with the recirculating seawater sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased porewater flux across the sediment water interface sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone the subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines

heterogeneity induced mixing and reaction hot spots facilitate karst propagation in coastal aquifers the data provided in the included folders are results directly taken from simulations originating from comsol multiphysics all data are provided as text files each text file includes coordinate data and the raw values for the variable of interest presented in the manuscript and supporting information the files provided are separated into folders for homogeneous equivalent cases and heterogeneous cases for each of these folders the data is further subdivided by the variance of the hydraulic conductivity field finally the data is organiyed according to the output variable of interest

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

radar backscatter characteristics of a desert surface satellite radar altimeter measurements have shown spatial and temporal variations in the backscattered signal from desert surfaces in order to understand these variations we have carried out extensive in situ measurements for the validation of a compilation of existing backscatter models the model predictions are in excellent agreement with ground and satellite based measurements of the radar backscatter coefficient and show that the altimeter backscatter measurements are strongly affected by variations in soil moisture following rainfall and by the presence of dew on the surface regional but time invariant differences in backscatter are attributed to variations in surface topography

quantification of groundwater seawater interaction in a coastal sandy aquifer system a study from panama sri lanka the panama coastal aquifer system is an important water resource in the southeast coast of sri lanka that provides adequate supplies of water for agriculture and domestic uses one of the biggest threats to these fragile aquifers is the sea water intrusion in this study recharging mechanism and geochemical evaluation of groundwater in the coastal sandy aquifer of panama were evaluated using chemical and stable isotope techniques thirty groundwater samples were collected and analyzed for their major ion concentrations and stable isotope ratios of oxygen 18o 16o and hydrogen d h all studied samples showed a ranking of major anions in the order cl hco 3 so 4 2 n no3 while cations showed a decreasing order of abundance with na ca2 mg2 k dominant groundwater hydrogeochemical types were na cl and mixed ca mg cl results of saturation index calculations indicate that the investigated groundwater body was mostly saturated with respect to calcite dolomite and gypsum in addition stable isotope and geochemical data suggest that fresh groundwater in the aquifer is recharged mainly by local precipitation with slight modification from evaporation and saline water intrusions isotope data suggest that mixing of salt water with freshwater occurs in aquifers which are located towards the lagoon since the communities in the study area depend entirely on groundwater an understanding of the hydrogeochemical characteristics of the aquifer system is extremely important for the better water resource management in the region

spaceborne altimetry and scatterometry backscattering signatures at c and ku bands over west africa abstract this study presents a comprehensive comparison of radar signatures acquired over west africa between latitudes 0 25 n and longitudes 5 w 25 e at both c and ku bands using nadir looking altimeters 35 day orbital period envisat ra 2 over 2003 2010 and 10 day orbital period jason 2 over mid 2008 2011 and side looking scatterometers quikscat over 2003 2009 and ascat over mid 2008 2011 that covers the major bioclimatic zones soil and vegetation types encountered in this region the backscattering coefficient s time series measured by both radar instruments are generated over regional transects and local sites meridian transects from the wet tropics to the arid regions of the sahara desert demonstrate the spatial and temporal changes of the radar response over the west african bioclimatic gradient in terms of surface roughness land cover and soil wetness nadir looking altimetry appears more sensitive to variations of surface soil moisture than side looking scatterometry at both c and ku bands in contrast the impact of vegetation on the backscattered signals is found to be lower for nadir looking instruments compared to side looking ones

stress drops and radiated energies of aftershocks of the 1994 northridge california earthquake we study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern california earthquakes we use empirical green functions to obtain source time functions for 47 of the larger m 4 0 aftershocks of the 1994 northridge california earthquake m6 7 we estimate static and dynamic stress drops from the source time functions and compare them to well calibrated estimates of the radiated energy our measurements of radiated energy are relatively low compared to the static stress drops indicating that the static and dynamic stress drops are of similar magnitude this is confirmed by our direct estimates of the dynamic stress drops combining our results for the northridge aftershocks with data from other southern california earthquakes appears to show an increase in the ratio of radiated energy to moment with increasing moment there is no corresponding increase in the static stress drop this systematic change in earthquake scaling from smaller to larger m3 to m7 earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults

detailed fault structure of the 2000 western tottori japan earthquake sequence we investigate the faulting process of the aftershock region of the 2000 western tottori earthquake m w 6 6 by combining aftershock hypocenters and moment tensor solutions aftershock locations were precisely determined by the double difference method using p and s phase arrival data of the japan meteorological agency unified catalog by combining the relocated hypocenters and moment tensor solutions of aftershocks by broadband waveform inversion of freesia f net we successfully resolved very detailed fault structures activated by the mainshock the estimated fault model resolves 15 individual fault segments that are consistent with both aftershock distribution and focal mechanism solutions rupture in the mainshock was principally confined to the three fault elements in the southern half of the zone which is also where the earliest aftershocks concentrate with time the northern part of the zone becomes activated which is also reflected in the postseismic deformation field from the stress tensor analysis of aftershock focal mechanisms we found a rather uniform stress field in the aftershock region although fault strikes were scattered the maximum stress direction is n107 e which is consistent with the tectonic stress field in this region in the northern part of the fault where no slip occurred during the mainshock but postseismic slip was observed the maximum stress direction of n130 e was possible as an alternative solution of stress tensor inversion

experimental and numerical investigation of saltwater intrusion dynamics in flux controlled groundwater systems 1 sea level rise and reduction of groundwater fluxes due to changes in rainfall patterns are the two major climate change induced hydrological variables that can severely affect saltwater intrusion in coastal aquifers in this study we use a combination of laboratory experiments and numerical simulations to study the impacts of changes in one of these climate change induced hydrological variables groundwater flux on saltwater intrusion process we have completed experiments in a laboratory scale model to study the changes in two types of groundwater fluxes areal recharge flux and regional flux the experimental results were modeled using the numerical code seawat the transient data sets reported in this study are useful benchmarks for testing numerical models that employ flux type boundary conditions also based on the experimental observations we hypothesize that when the fluxes are perturbed it would require relatively less time for a salt wedge to recede from an aquifer when compared to the time required to advance into the aquifer this rather counterintuitive hypothesis implies that saltwater intrusion and receding processes are asymmetric and the timescales associated with these processes will be different we use a combination of laboratory and numerical experiments to test this hypothesis and use the resulting data set to explain the reason for the difference in intrusion rates