artificial tracers for geothermal reservoir studies safe disposal of thermally spent geothermal brines that contain environmentally hazardous constituents is commonly obtained by reinjection the reinjection process also serves to maintain reservoir pressure enhance thermal recovery and eliminate possible compactional subsidence to avoid premature thermal breakthrough of reinjected fluids tracer tests are employed for detection and evaluation of preferential path networks in this paper some promising tracers that have not received much attention in geothermal reservoir studies are discussed and a comprehensive tabulation of field sites of artificial tracer utilization is presented chemical and transport processes responsible for tracer retention by the formation of reservoir solids as well as available tracer detection techniques are emphasized

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

a new self organizing mechanism for deep focus earthquakes the mechanism of deep focus earthquakes has been a puzzle since their discovery almost 70 years ago1 2 because brittle fracture and frictional sliding at depths in excess of 100 200 km would require unrealistic rock strengths3 4 rock strength does increase with pressure but a few hundred mpa equivalent to 10 20 km depth suffices to inhibit most fracture and elevated temperature activates ductile mechanisms that operate at stresses less than the fracture stength a range of mechanisms has been proposed for deep earthquakes including plastic instabilities5 7 shear induced melting8 11 and instabilities accompanying recrystallization12 13 or polymorphic phase transformation14 23 each of these proposed mechanisms has exhibited certain inherent weaknesses see kirby22 for review and discussion here we report experimental observations of high pressure faulting of metastable mg2geo4 olivine as it undergoes incipient transformation to a spinel 24 25 structure we present a model in which this faulting arises from the generation propagation and linking up of spinel filled anticracks26 when applied to the olivine spinel transformation in the earth s mantle the anticrack model27 satisfactorily accounts for the similarities and differences between shallow and deep earthquakes and removes the problems associated with frictional sliding

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

effect of climate change on sea water intrusion in coastal aquifers there is increasing debate these days on climate change and its possible consequences much of this debate has focused in the context of surface water systems in many arid areas of the world rainfall is scarce and so is surface runoff these areas rely heavily on groundwater the consequences of climate change on groundwater are long term and can be far reaching one of the more apparent consequences is the increased migration of salt water inland in coastal aquifers using two coastal aquifers one in egypt and the other in india this study investigates the effect of likely climate change on sea water intrusion three realistic scenarios mimicking climate change are considered under these scenarios the nile delta aquifer is found to be more vulnerable to climate change and sea level rise copyright 1999 john wiley sons ltd

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

borehole dilution tests in the vicinity of an extraction well abstract a mathematical solution is derived for a borehole dilution test conducted in the proximity of an extraction well under conditions where the theis assumptions are applicable the solution is similar to the steady state velocity case except for a factor that accounts for the transient response of the aquifer to pumping curves calculated from the derived solution show a delay in response that increases with the specific storage of the aquifer and with the radius from the extraction well the delay decreases with increasing values of hydraulic conductivity and aquifer thickness deviations of the response curves from the straight line steady state velocity case can be used to calculate the hydraulic diffusivity while the limiting slope at late time can be used to calculate groundwater flux when borehole dilution tests are conducted at several intervals over the thickness of the aquifer under steady state velocity conditions k z can in principle be calculated using several equations depending on the type of information available two existing methods to account for the distortion of the flow lines near the open test interval are related to well construction and development reasonable estimates of borehole factors can only be obtained for minimally developed wells

nonlinear interactions of waves and tides in a subterranean estuary previous studies have revealed hysteretic behavior in subterranean estuaries in response to intensified wave conditions caused by offshore storm events showing dependence of submarine groundwater discharge sgd and subsurface salt distribution on historic wave conditions although most shorelines worldwide are also exposed to tidal fluctuations it is unclear how tides moderate wave induced sgd and salinity distribution in subterranean estuaries this study presents numerical simulations that explore the combined influence of intensified wave conditions and tides on groundwater flow and salt transport in a subterranean estuary the results show that tides weaken the hysteretic wave effect on sgd suggesting that a tidally influenced subterranean estuary is less sensitive to intensified wave conditions with respect to the water fluxes across the aquifer sea interface however due to enhancement of salt freshwater mixing tides strengthen the hysteretic wave effect on the salt fluxes across the aquifer sea interface prolonging the recovery of salt distribution in the subterranean estuary to the prestorm state these findings reveal the nonlinear coupling nature of processes driven by oceanic oscillations at different time scales in subterranean estuaries

a generic classification for the morphological and spatial complexity of volcanic and other landforms landform studies require that morphological identification description and classification use an accurate and precise taxonomy this communication offers taxonomic criteria useful for landform classification as well as spatial statistical investigations of landform patterns the spatial statistical modeling of landform patterns poses new challenges concerning the systematic characterization of landforms for study within a gis geographical information system for example the sundry descriptions and non diagnostic descriptors for volcanoes are many and appear to have promoted the adoption of somewhat imprecise and confusing classes this communication presents a generic three tiered classification as a basic description of the complexity of the landform regardless of scale tectonic and petrologic setting climatic regime state of degradation or local definition importantly it offers a taxonomy that is useful to the geographical analysis of point pattern fields using spatial statistical techniques the scheme offered here was used to characterize mostly monogenetic volcanoes however the classification scheme may also be usable for other landscape features for instance such features may include landslide scars thermokarst dolines kettle and kame topography drumlins dome crescentic and star dunes pingos rootless cones lava domes and coulees and impact craters

influences on the variability of eruption sequences and style transitions in the auckland volcanic field new zealand abstract monogenetic basaltic volcanism is characterised by a complex array of eruptive behaviours reflecting spatial and temporal variability of the magmatic properties e g composition eruptive volume magma flux as well as environmental factors at the vent site e g availability of water country rock geology faulting these combine to produce changes in eruption style over brief periods minutes to days in many eruption episodes monogenetic eruptions in some volcanic fields often start with a phreatomagmatic vent opening phase that later transforms into dry magmatic explosive or effusive activity with a strong variation in the duration and importance of this first phase such an eruption sequence pattern occurred in 83 of the known eruption in the 0 25 my old auckland volcanic field avf new zealand in this investigation the eruptive volumes were compared with the sequences of eruption styles preserved in the pyroclastic record at each volcano of the avf as well as environmental influencing factors such as distribution and thickness of water saturated semi to unconsolidated sediments topographic position distances from known fault lines the avf showed that there is no correlation between ejecta ring volumes and environmental influencing factors that is valid for the entire avf in contrary using a set of comparisons of single volcanoes with well known and documented sequences resultant eruption sequences could be explained by predominant patterns of the environment in which these volcanoes were erupted based on the spatial variability of these environmental factors a first order susceptibility hazard map was constructed for the avf that forecasts areas of largest likelihood for phreatomagmatic eruptions by overlaying topographical and shallow geological information combining detailed phase by phase breakdowns of eruptive volumes and the event sequences of the avf along with the new susceptibility map more realistic eruption scenarios can be developed for different parts of the volcanic field this approach can be applied to tailoring field and sub field specific hazard forecasting at similar volcanic fields worldwide

insignificant isotropic component in the moment tensor of deep earthquakes the mechanism responsible for deep focus earthquakes which occur at depths of 300 700 km in subducting slabs has been a long standing problem in geophysics unlike shallow earthquakes deep earthquakes cannot be attributed to frictional instabilities across a fault plane because of high frictional resistance to sliding at depth a volumetric change associated with a phase transition expected to occur at depth1 3 is often invoked as the physical mechanism if so the resulting source mechanism should contain a major isotropic component although many researchers have attempted to observe such an isotropic component4 10 no one has yet convincingly proved or disproved its presence there exists a portion of the seismogram which is well suited to resolve the isotropic component of deep earthquakes but which has not been analysed by previous workers here i use this component in a systematic analysis of 19 large deep earthquakes and show that no significant isotropic component 10 of the seismic moment exists a sudden implosive phase change can thus be ruled out as the primary physical mechanism for deep earthquakes

late holocene lake levels of the dead sea this work presents a high resolution lake level record of the late holocene dead sea a hypersaline terminal lake whose drainage basin encompasses both mediterranean and hyperarid climatic zones the lake level curve reflects the regional hydrologic variations in the drainage basin which in turn represent the levant paleoclimates the curve is based on 46 radiocarbon ages of organic remains from well exposed sedimentary sequences along the dead sea shores these sequences record fluvial and lacustrine depositional environments the paleolakeshores are marked by shore ridges coarse sand units and aragonite crusts in the modern dead sea such features indicate the exact elevation of the shore the late holocene dead sea level fluctuated within the range of 390 to 415 m below sea level mbsl for most of the time the lake was below the topographic sill 402 mbsl separating the northern and southern basins of the dead sea and was confined to the deep northern basin nevertheless short term rises in the late holocene dead sea level caused the flooding of the shallow and flat southern basin highstands occurred in the second and first centuries b c and the fourth century a d during the roman and early byzan tine periods respectively in the eleventh and twelfth centuries a d during the crusader period and at the end of the nineteenth century a d the rises mark a significant change in the annual rainfall in the region which likely exceeded the instrumentally measured modern average the curve also indicates drastic drops that exposed the sedimentary sequences to erosion the oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries b c after a retreat from a higher lake stand the longest lowstand occurred after the byzantine period and continued at least until the ninth century a d this arid period coincided with the invasion of moslem arab tribes into the area during the seventh century a d the dramatic fall of the dead sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin but the magnitude is not considered exceptional for the late holocene although the past drops in the lake never exceeded the modern artificial drop rates they do represent extreme arid conditions that occurred frequently over the past several thousand years

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

seismicity shear failure and modes of deformation in deep subduction zones abstract planes of shear failure in deep seismic zones are identified as being parallel to focal mechanism nodal planes of deep focus earthquakes we relocate deep seismicity reported in the international seismological centre isc catalogue for earthquakes deeper than 400 km in the honshu bonin marianas java banda and south america subduction zones using the joint hypocentral determination method recent events with harvard centroid moment tensor cmt solutions and nearby seismicity are viewed from the direction of the cmt null axis comparing the two orthogonal nodal planes with the seismicity pattern planar features of seismicity parallel to cmt nodal planes are found in each deep seismic zone and are identified as planes of shear failure the sense of displacement on these planes is one of resistance to deeper penetration honshu and bonin show imbrication and horizontal displacement of the deepest part of the seismogenic slab while marianas and brazil show conjugate shear failure banda and argentina show patterns of vertical and horizontal shear planes for the western pacific slabs we find significant lateral displacements towards the south of the deepest part of the subduction flow tonga has been analyzed previously showing the same pattern as identified here in all benioff zones planes of shear failure are observed which act to shorten the slabs and displace matter horizontally normal to the slab moreover differential faulting acts to rotate the slab of subducted lithosphere to a more horizontal posture indicating that slabs experience resistance to penetration of the 670 km discontinuity

rupture of the large mw 7 8 deep earthquake of 1973 beneath the japan sea with implications for seismogenesis the earthquake of 29 september 1973 beneath the western edge of japan sea is the largest deep earthquake along the western pacific m w 7 8 focal depth 575 km the source region is near the tip of the japan wadati benioff zone where a continuous belt of seismicity clearly defines a unique shallow dipping 30 slab down to depths about 600 km this unique geometry of slab predicts a limited vertical extent available for earthquake rupture in direct conflict with previous reports of a large subvertical fault for the 1973 earthquake using a comprehensive data set of nearly 20 p and sh waveforms recorded at teleseismic distances we investigate rupture associated with this event in some detail by inversion of waveforms in particular we use wave trains with all relevant depth phases pp sp and ss that are crucial for resolving the vertical extent of rupture in addition to a northward component of rupture as in previous reports we find clear evidence for a significant component of eastward rupture propagation that cannot fit within a subvertical north south striking nodal plane meanwhile all regions of major slip are at essentially the same depth thus the true fault plane appears subhorizontal with the entire region of slip extending only about 15 6 km across the slab9s thickness the spatio temporal distribution of slip is well explained by a simple circular rupture front propagating at a speed of 3 4 km sec a comparison among the largest deep earthquakes shows that most rupture planes are more or less dimensionally equal with high aspect ratios ranging approximately from 0 5 to 1 while some events have fairly restricted source regions others seem to extend more than 30 km into the thickness of the slabs

moment tensor inversion from mednet data 1 large worldwide earthquakes of 1990 we develop a method for the rapid determination of the moment tensor of large worldwide earthquakes by inversion of long period data recorded by the mednet regional network and we apply it to the most significant events of 1990 march 3 fiji and 25 costa rica may 12 sakhalin 20 sudan and 30 romania june 20 iran july 16 luzon and december 30 new britain the comparison with cmts and moment tensors by usgs shows that an advanced regional seismic network is capable of providing reliable and rapid control of the seismic source for worldwide seismicity

relevance of solutions to the navier stokes equations for explaining groundwater flow in fractured karst aquifers 1 we examine the use of numeric flow solutions of the navier stokes n s equations to improve flow modeling in fractured karst aquifers the n s equations were discretized with both the meshed finite difference method fdm and the meshless smoothed particle hydrodynamics method the results using the fdm model were successfully compared with those taken from the literature the n s equations were solved numerically for two practical problems in karst aquifers a the horizontal displacement of the saltwater freshwater sharp interface in fissures due to groundwater overexploitation and b the pressure and velocity profiles in fissures in the vicinity of an injection well in the first problem the numeric n s solution suggests an exponential time advancement of the freshwater saltwater interface in fissures in the second problem the unsteady water velocity and pressure profiles were determined in fissures having variable apertures in the vicinity of an injection well the n s simulation results agreed well with the data collected during the test thereby removing any uncertainty in the estimation of the aquifer transmissivity

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

aftershocks of the march 9 1994 tonga earthquake the strongest known deep aftershock sequence the march 9 1994 mw 7 6 depth 564 km deep tonga earthquake produced an exceptionally strong aftershock sequence for a deep earthquake using eight temporary broadband stations deployed on the fiji tonga and niue islands we identify 144 aftershocks with mb ranging from 3 2 to 6 0 during the first 41 days following the mainshock the number and seismic moment of the march 9 aftershocks lie within the range of aftershock productivities of typical shallow earthquakes of similar moment the aftershocks show a power law decay with time following the mainshock with an exponent p value of 1 0 similar to shallow aftershock sequences fifty aftershocks can be accurately located using a hypocentroidal decomposition method these aftershocks align along a near vertical ene striking plane similar to one of the mainshock nodal planes sixteen of the 18 well located aftershocks during the first 2 5 hours are located to the nne of the mainshock epicenter consistent with nne rupture propagation derived from waveform analysis later aftershocks are located south of the epicenter suggesting aftershock expansion beyond the region of substantial moment release in the mainshock several of the aftershocks are located outside of the normal bounds of the seismically active slab consistent with evidence that the mainshock rupture terminated outside the active slab five possible foreshocks occurred along the preferred fault plane within the 22 days prior to the mainshock at least three triggered aftershocks occurred at distances of 50 to 110 km within the first six hours following the mainshock triggered aftershocks in adjacent slab material may be common for large deep earthquakes while there is some variation in the focal mechanisms of the aftershocks most resemble the mainshock focal mechanism all the mechanisms show compressional axes dipping to the west consistent with background seismicity in this region overall most of the aftershock characteristics of the 1994 tonga event are similar to those found for shallow earthquakes suggesting similarities between shallow and deep earthquakes in the mechanical processes that produce aftershocks

assessment of sharp interface approach for saltwater intrusion prediction in an unconfined coastal aquifer exposed to pumping water over exploitation becomes a common problem in coastal aquifers as it disarranges the dynamic equilibrium of saltwater and freshwater and causes saltwater intrusion swi mathematical simulations become a necessary tool nowadays to predict swi under future pumping scenarios this study aims to assess the validity of sharp interface approach for an unconfined coastal aquifer subjected to pumping by comparison with sand tank observation and dispersive approach results the comparison was in terms of 1 transient movement of saltwater toward the well screen and 2 prediction of well salinity in times the sharp interface approach produced acceptable results although it over predicted the toe position of saltwater wedge salinity of extracted water was less predicted by sharp interface modeling the sharp interface approach was then applied for a synthetic field scale unconfined aquifer in steady condition with different pumping rates and well placements to explore the sensitivity of the modeling the results were compared with salinity contours of dispersive modeling the sharp interface approach produced better result for higher pumping rates where the saltwater was reached to the well screen additionally the results of fully penetrating wells compare to partially penetrating one and also closer location of well to shoreline matched better with the dispersive modeling outputs in real cases where the saltwater may wend a long distance toward the well screen the sharp interface modeling weakly matched with the dispersive modeling specially in terms of well salinities that is attributed to wider mixing zone

the observation of inner core shear waves summary although the earth s inner core has long been thought to be solid there have not as yet been unequivocal observations of inner core shear waves here we present observations of the phases ppkjkp and skjkp for the flores sea event of 1996 june 17 the observations support the value of approximately 3 6 km s 1 for the inner core shear wave velocity and open up new possibilities for exploring the anisotropic structure and the attenuation properties of the inner core the analysis and validation of the observation is based on a new method that can be used in the search for and identification of inner core shear waves in this method normal mode synthetics for a solid inner core are compared with those for a fluid inner core it is only by such comparisons that it is possible to be certain that inner core shear waves rather than interferences of other phases are responsible for observed energy maxima in stacked seismic records

finite fault source study of the great 1994 deep bolivia earthquake we apply an empirical green s function method to recordings of teleseismic body waves from the june 9 1994 deep focus bolivia earthquake the far field source time functions reveal that rupture occurred on a sub horizontal fault plane the main rupture began some 25 km to the east of the hypocenter consists of three large subevents and covers a total area of about 60 40 km the static stress drop is quite large more than 150 mpa and the obtained rupture velocity is less than 2 km sec while the total dimensions of the earthquake are large compared to estimates of the width of a metastable olivine wedge at this depth the moment release is confined largely to a narrow band along an ew axis and may be compatible with phase transitions within a thickened slab core

a numerical solution for the movement of an interface in a layered coastal aquifer abstract this paper deals with seawater intrusion in a coastal aquifer where close to the coast the aquifer is divided into a number of subaquifers by impervious relatively thin layers as a result of changing the total fresh water discharge to the sea seawater intrusion occurs as a separate advancing wedge in each of the subaquifers assuming everywhere flow normal to the coast line and essentially horizontal in both the fresh water and the salt water zones the complete mathematical model is first stated in terms of depth to the interface in each subaquifer a numerical finite difference scheme is then presented for solving the model for the case of a two layered aquifer principles of a method for extending the model to a larger number of subaquifers is described

the june 9 bolivia and march 9 fiji deep earthquakes of 1994 i source processes we examined the source characteristics of the 1994 deep earthquakes of bolivia june 9 and fiji march 9 over a period range of 1 1000 s using moment tensor and body wave analyses moment tensor inversions from 100 1000 s reveal that these two earthquakes were essentially point sources at very long period with insignificant isotropic and non double couple components with scalar moments mo 2 56 1021 nm for the bolivia and mo 0 26 1021 nm for the fiji earthquakes body wave analysis for the bolivia event reveals a 45 s duration a nearly linear e ne 1 km s rupture on the subhorizontal focal mechanism plane giving a stress drop 114 mpa for the fiji earthquake we find a change in focal mechanism and a linear 3 km s rupture plunging shallowly to the north on the steep dipping nodal plane with a duration of at least 20 s and 14 mpa both ruptures propagated parallel their null 2 axis and suggests that their width is controlled by the thickness of the seismogenic volume in deep slabs

conceptualization of a fresh groundwater lens influenced by climate change a modeling study of an arid region island in the persian gulf iran summary understanding the fresh groundwater lens fgl behavior and potential threat of climatic induced seawater intrusion swi are significant for the future water resources management of many small islands in this paper the fgl of kish island an arid region case in the persian gulf iran is modeled using two dimensional 2d and three dimensional 3d simulations these simulations are based on the application of sutra a density dependent groundwater numerical model also the numerical model parameters are calibrated using pest an automated parameter estimation code firstly a detailed conceptualization of the fgl model is completed to understand the sensitivity of the fgl to some particular aspects of the model prior to analysis of climate change simulations for these investigations the fgl system is defined based on kish island system to accomplish the integrated comparison of features of a conceptual model that are representative of real world systems this is the first study which adopts such an approach the comparison of cross sectional simulations suggests that the two layer properties of the kish island aquifer have a significant influence on the fgl while the impacts of lateral boundary irregularities are negligible the impacts of sea level rise slr associated land surface inundation lsi and variations in recharge rate on the fgl salinization of kish island are investigated numerically variations of slr value 1 4 m and net recharge rate 17 24 mm year are considered to cover a possible range of climatic scenarios in this arid region island the 2d and 3d simulation results demonstrate that lsi caused by slr and recharge rate variation impacts are more important factors in the fgl in comparison to estimated slr impacts without lsi it is also shown that climate change impacts on the fgl are long term to reach a new fgl equilibrium in the case of kish island s aquifer system the comparative analysis of 2d and 3d results shows that three dimensionality is a significant factor especially in large scale 3d systems of small islands the results of this study are expected to have implications for the understanding and management of the fresh groundwater resources of kish island and are also expected to be relevant to the study of the impact of climate change on groundwater resources on islands worldwide

on the interpretation of subevents in teleseismic waveforms the 1994 bolivia deep earthquake revisited we evaluate the methodologies that aim at resolving the space time slip distribution during large earthquakes in one common approach the source process of an event is assumed to be composed of a series of subevents critical points in teleseismic body waves such as peaks and coherent arrivals are viewed as discrete points in the spatiotemporal history of an earthquake we show that these features can be interpreted as the instantaneous centroid locations of the moment release history we demonstrate this result with an analysis of the mw 8 2 bolivia 1994 deep event we reconstruct the slip distribution in two contrasting ways first broadband p waves are interpreted as being composed of subevents five peaks in the moment release rate are located relative to the onset of the rupture using the azimuthal variations of onset to peak times second we invert broadband p waves for the slip distribution on a subhorizontal fault we use a nonlinear tomographic imaging technique called simulated annealing and an l1 misfit norm rupture velocities appear to be 2 km s 1 and largest slip values are found to the east and north of the onset in a 40 by 50 km region the instantaneous centroids of the moment release history correspond closely to the locations found using the subevent analysis however especially near the middle and the end of the rupture the instantaneous centroid locations are in regions of little moment release we discuss how the subevent analysis and the instantaneous centroid approach lead to dissimilar interpretations of rupture processes especially for events with length to width ratios near unity another result of this study is that the rupture of the 1994 bolivia event appears to end 50 km to the northwest of the onset implying that the slip area is larger that previously thought comparing the slip distribution with the aftershock distribution suggests that more than one physical mechanism is necessary to account for the rupture process of this great deep event

lattice boltzmann methods applied to large scale three dimensional virtual cores constructed from digital optical borehole images of the karst carbonate biscayne aquifer in southeastern florida digital optical borehole images at approximately 2 mm vertical resolution and borehole caliper data were used to create three dimensional renderings of the distribution of 1 matrix porosity and 2 vuggy megaporosity for the karst carbonate biscayne aquifer in southeastern florida the renderings based on the borehole data were used as input into lattice boltzmann methods to obtain intrinsic permeability estimates for this extremely transmissive aquifer where traditional aquifer test methods may fail due to very small drawdowns and non darcian flow that can reduce apparent hydraulic conductivity variogram analysis of the borehole data suggests a nearly isotropic rock structure at lag lengths up to the nominal borehole diameter a strong correlation between the diameter of the borehole and the presence of vuggy megaporosity in the data set led to a bias in the variogram where the computed horizontal spatial autocorrelation is strong at lag distances greater than the nominal borehole size lattice boltzmann simulation of flow across a 0 4 0 4 17 m 2 72 m3 volume parallel walled column of rendered matrix and vuggy megaporosity indicates a high hydraulic conductivity of 53 m s 1 this value is similar to previous lattice boltzmann calculations of hydraulic conductivity in smaller limestone samples of the biscayne aquifer the development of simulation methods that reproduce dual porosity systems with higher resolution and fidelity and that consider flow through horizontally longer renderings could provide improved estimates of the hydraulic conductivity and help to address questions about the importance of scale

fate and transport of pathogens in a fractured aquifer in the salento area italy 1 this study investigates the fate and transport of pathogens introduced by artificial groundwater recharge at the nardo fractured aquifer in the salento area italy wastewater effluents from a municipal treatment plant with known pathogen concentrations were injected into a sinkhole and the migration of pathogens in the fractured aquifer was monitored at six sampling wells the fate of pathogens was quantified by a mathematical model describing colloid transport in a set of three dimensional parallel fractures with spatially variable aperture the number of parallel fractures and their average fracture aperture were determined from appropriate field pumping and tracer tests the aperture spatial distribution was described by an experimental semivariogram developed from available field data obtained from two tracer tests and 34 pumping tests the experimental results suggest that for the municipal wastewater injected into the nardo aquifer the required most conservative set back distance for drinking wells should be over 8000 m

determination of the isotropic component of the 1994 bolivia deep earthquake we determine the isotropic component of the moment tensor of the 1994 bolivia deep earthquake using various seismic waves including body waves surface waves and normal mode data in the period band between 20 s and 1000 s we carefully investigate whether the isotropic component can be obtained independently from the other components by checking the correlation matrices we show that it is possible to obtain a precise estimate of the isotropic component by using normal mode data in the period band between 550 and 1000 s we find that the bolivia earthquake did not have a significant isotropic component in this period band

reconstructing the evolution of an eroded miocene caldera volcano yamanlar volcano izmir turkey abstract the miocene yamanlar composite volcano is located in the central part of a shear zone in western turkey the volcano s deeply eroded interior provides excellent three dimensional exposure of a faulted caldera floor and caldera fill rocks as well as surrounding extracaldera ignimbrites we present a much revised stratigraphy and geological map of yamanlar in order to quantify the evolutionary stages of the volcano the yamanlar volcanic cone was composed of 800 m of basaltic andesite to andesite lavas and lava domes the volcano underwent at least one phase of caldera formation associated with an explosive eruption that deposited an ignimbrite sheet within and outside the caldera lithofacies architecture analysis is applied to the proximal and medial exposures of the early middle yamanlar formation which occurs outside of the caldera field evidence of the succession indicates a caldera forming eruption our results indicate that the formation of the yamanlar caldera resulted from one major catastrophic eruption that generated several sustained pyroclastic density currents pdcs subdivided by fall deposits with sharp contacts the ignimbrite sheet is composed of four flow units the presence of numerous coarse grained lithic rich horizons within the ignimbrite sheet is consistent with caldera subsidence post caldera volcanism is indicated by intrusions and lava domes erupted along the inferred caldera bounding faults some of which record 90 m of displacement widespread coarse grained breccias that overlie the ignimbrite sheet are interpreted as debris avalanche deposits resulting from gravitational failure of the flanks of the volcano or the caldera wall during or after caldera subsidence

the march 9 1994 m w 7 6 deep tonga earthquake rupture outside the seismically active slab we investigate the rupture process of the march 9 1994 m w 7 6 deep tonga earthquake and its relationship to the background seismicity of the subducted tonga slab variations in observed p and s wave pulse duration indicate that the rupture propagated to the nne and extended well beyond the background seismicity we inverted 47 p and sh waveforms including regional broadband waveforms from the southwest pacific seismic experiment using a method that solves for the focal mechanism change during the rupture and the distribution of moment release along the fault plane the results indicate that significant moment release occurred in previously aseismic regions outside the active seismic zone and that the rupture terminated 10 20 km beyond the bounds of the previous seismic activity a significant change in focal mechanism occurred when the rupture propagated into the previously aseismic region rupture along the near vertical nne striking nodal plane provides a somewhat better fit to the body waveforms than rupture along the near horizontal nodal plane this result combined with the planar alignment of aftershocks and the general nne directivity of the waveforms provides strong evidence that the rupture occurred on the near vertical plane thermal modeling of the tonga slab indicates that the rupture terminated in material about 200 c warmer than the temperature that normally limits the occurrence of smaller earthquakes additionally aftershocks seem to be suppressed in the outer regions of the rupture which contain about half of the moment release but only 1 of the 15 well located aftershocks we suggest that slabs may be composed of an inner cold core where seismic rupture initiates and small earthquakes occur and a thermal halo of warmer material which can sustain rupture and only a few aftershocks the mechanism by which rupture propagates through the warmer material need not be similar to the process governing rupture nucleation in the cold slab core nucleation may occur through a process limited to the cold core such as transformational faulting and propagation through the warmer material may occur through ductile faulting or plastic instabilities isolated deep earthquakes in other subduction zones such as the 1994 bolivia event may occur almost completely within the warmer zone accounting for the lack of background seismicity and the dearth of aftershocks

volcano morphology as an indicator of stress orientation in the java volcanic arc indonesia abstract stress fields in the earth s crust are important indicators leading to better understanding of geologic processes one way to acquire stress data is through morphometric analysis of volcanoes here we evaluate 141 quaternary age monogenetic and polygenetic volcanoes and volcanic fields in java indonesia using a 30 m srtm dem an 8 m demnas aerial photos published geological maps and landsat and google earth satellite imagery we analyze parameters that imply the geometry of the shallow magma plumbing system and ascent pathways crater ellipticity and elongation axis and the orientation of crater breaching bisectors the dominant trend of all of these parameters should indicate the direction of the maximum horizontal compressive stress hmax while the minimum horizontal stress hmin should be perpendicular to it the goal here is to estimate the principal stress axes at the time of dike emplacement to recognize any spatial variations in stress orientations and assess factors controlling the emplacement the resulting orientation of hmax in the western part of java is ne sw and the trend gradually rotates to nw se moving eastward abrupt changes in stress orientations and anomalies are also observed in the vicinity of prominent geologic structures highlighting the influence of preexisting structures on dike emplacement and eruption characteristics results of the morphometric analysis of volcanoes and volcanic fields conducted in this study help to estimate the past and present stress orientations in java and provide valuable understanding regarding the relationship between volcanic emplacement and crustal structures complementing other types of analysis

source retrieval for mantle earthquakes by iterative deconvolution of long period p waves abstract long period p waves of eighteen deep and intermediate depth earthquakes in a moment range 1 10 26 3 10 28 dyn cm are analysed by the method of kikuchi and fukao this issue to iteratively derive point dislocations on a plane the fault plane is defined as the plane of point dislocations that gives the best fit between the synthetic and observed waveforms for dip slip type earthquakes the fault plane is found to dip more steeply than the auxiliary plane in general point dislocations tend to cluster into one or a few subevents we characterize the largest subevent by its maximum moment rate m 0 m and its half duration from which the associated stress drop can be roughly estimated for earthquakes shallower than 400 km half duration is approximately constant 5 s so that stress drop increases from 1000 bar as m 0 m increases the value of for the great banda sea earthquake of 1963 h 100 km is exceptionally large 10 s for which 700 bar for earthquakes deeper than 400 km increases from 3 s to 9 s as m 0 m increases so that is approximately constant 700 bar stress drop so obtained approximates to an overall stress drop with a possible exception of the several largest earthquakes the distribution of point dislocations and the moment rate function indicate that rupture most often expands in a fan shaped fault area and that a large part of the rupture front ceases propagation in a coherent manner a sharp contrast in stress drop behavior across a depth of 400 km may be related to the olivine spinel transition within the downgoing slab of lithosphere

a multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems model development and application a quasi three dimensional finite difference model that simulates freshwater and saltwater flow separated by a sharp interface has been developed to study layered coastal aquifer systems the model allows for regional simulation of coastal groundwater conditions including the effects of saltwater dynamics on the freshwater system vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer leakage through confining layers is calculated by darcy s law accounting for density differences across the layer the locations of the interface tip and toe within grid blocks are tracked by linearly extrapolating the position of the interface the model has been verified using available analytical solutions and experimental results application of the model to the soquel aptos basin santa cruz county california illustrates the use of the quasi three dimensional sharp interface approach for the examination of freshwater saltwater dynamics in regional systems simulation suggests that the interface today is still responding to long term pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions

characteristics of active seawater intrusion abstract the inland migration of seawater in coastal aquifers known as seawater intrusion swi can be categorised as passive or active depending on whether the hydraulic gradient slopes downwards towards the sea or the land respectively despite active swi occurring in many locations it has received considerably less attention than passive swi in this study active swi caused by an inland freshwater head decline fhd is characterised using numerical modelling of various idealised unconfined coastal aquifer settings relationships between key features of active swi e g interface characteristics and swi response time scales and the parameters of the problem e g inland fhd freshwater seawater density contrast dispersivity hydraulic conductivity porosity and aquifer thickness are explored for the first time sensitivity analyses show that the swi response time scales under active swi situations are influenced by both the initial and final boundary head differences the interface is found to be steeper under stronger advection i e caused by the inland fhd higher dispersivity and hydraulic conductivity and lower aquifer thickness seawater density and porosity the interface movement is faster and the mixing zone is wider with larger hydraulic conductivity seawater freshwater density difference and aquifer thickness and with lower porosity dimensionless parameters peclet number and mixed convection ratio from previous steady state analyses offer only limited application to the controlling factors of passive swi and are not applicable to active swi the current study of active swi highlights important functional relationships that improve the general understanding of swi which has otherwise been founded primarily on steady state and passive swi

time response of the water table and saltwater transition zone to a base level drop 1 this paper investigates the effect of a drainage base level drop on the groundwater system in its vicinity using theoretical analysis simulations and field data we present a simple and novel method for analyzing the effect of a base level drop by defining two characteristic times that describe the response of the water table and the transition zone between the fresh and saline water the dead sea was chosen as a case study for this process because of the lake s rapid level drop rate during a continuous lake level drop the discharge attains a constant value and the hydraulic gradient remains constant we describe this new dynamic equilibrium and support it by theoretical analysis simulation and field data using theoretical analysis and sensitivity tests we demonstrate how different hydrological parameters control the response rate of the transition zone to the base level drop in some cases the response of the transition zone may be very rapid and in equilibrium with the water table or alternatively it can be much slower than the water table response as is the case in the study area

the effect of base level changes and geological structures on the location of the groundwater divide as exhibited in the hydrological system between the dead sea and the mediterranean sea summary the effects of base sea or lake level changes on the location and elevation of the groundwater divide were examined in the hydrological system between the mediterranean sea and the dead sea steady state simulations were conducted with a 1 d analytical model and transient conditions were simulated using feflow groundwater modeling software two hydrological scenarios were simulated a a transition to a new steady state following the expected drop of 150 m of the dead sea level and b the time of the precursor of the dead sea lisan lake some 20 000 years ago when the lake level was about 250 m above the present day dead sea level and the mediterranean sea level was 120 m below its present one the results of the simulations show that the dead sea level drop has led to a progressive decline in the groundwater level up to several kilometers inland from the shoreline the hydraulic gradient increases and thus the discharge to the lake also increases at the expense of the storage and also due to a small enlargement of the recharge zone by a 600 m shift of the divide broadly the subsurface hydrological system is compartmentalized into several sections separated by low permeability fold structures bounding the mountainous uplands most of the groundwater recharge occurs in the uplands given this geometry and the available water level measurements analytical and numerical modeling results show that only changes in the dead sea level and recharge rate result in dramatic changes for the scenarios examined limited by the low permeability folds the effects of the dead sea level on the groundwater level are most pronounced in the vicinity of the judea desert lowland the folds also greatly limit migration of the groundwater divide associated with changes in the dead sea level transient simulations show a peak increase of 30 in the dead sea groundwater flux in 75 years resulting from drainage of lowland aquifers after more than 500 years the groundwater flux is expected to return to values no more than 4 higher than at the beginning of the simulation this small net increase is consistent with the small shift in the groundwater divide

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

monitoring and simulation of salinity changes in response to tide and storm surges in a sandy coastal aquifer system tidal dynamics and especially storm surges can have an extensive impact on coastal fresh groundwater resources combined with the prospect of sea level rise and the reliance of many people on these resources this demonstrates the need to assess the vulnerability of coastal areas to these threats in this study we investigated the impact of tides and storm surges on coastal groundwater at a pilot location on the dutch coast viz the sand engine to monitor changes in groundwater salinity under a variety of conditions we performed automated measurements with electrical resistivity tomography for a period of 2 months between november 2014 and january 2015 the obtained resistivity images were converted to salinity images and these images served effectively as observations of the impact of tidal fluctuations salt water overwash during storm surges and the recovery of the freshwater lens after land surface inundations most of the observed changes in groundwater head and salinity could be reproduced with a two dimensional variable density groundwater flow and salt transport model this shows that groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh ground water resources given a thorough understanding of the local system comparisons of measurements and model simulations also showed that morphological changes and wave run up can have a strong impact on the extent of land surface inundations in low elevation dynamic coastal environments and can therefore substantially affect coastal fresh groundwater resources

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

body wave inversion of the 1970 and 1963 south american large deep focus earthquakes a comprehensive set of teleseismic waveforms from two south american deep focus earthquakes of the predigital era the 1970 colombia mw 8 1 and 1963 peru bolivia mw 7 7 events are inverted for source mechanism seismic moment rupture history and centroid depth the p and sh wave inversion of the colombia event confirms previous work indicating that rupture occurred on a plane that dips steeply west rupture direction paralleled the trend of the wadati benioff zone we decompose the source into subevents based on a source time function which shows two major moment release pulses separated by 20 s the first subevent is located near the initiation point at a depth of 630 km the main moment release was located 70 km to the southeast and 20 km shallower rupture subsequently propagated farther southeast the source time function has an initial subevent accounting for 30 of the moment release of the entire event whereas the long period centroid moment tensor cmt analysis russakoff et al 1997 has the initial subevent yielding 50 the high angle nodal plane rotated 15 clockwise during the rupture explaining the large compensated linear vector dipole clvd component inferred from cmt solutions individual subevents have large clvd and compressive isotropic components a full moment tensor inversion of the colombia and 1994 bolivia events suggests that the initial subevents might contain a large non double couple ndc component for the 1963 peru bolivia event using p waves rupture propagated nnw for a distance of 70 km parallel to the high angle nodal plane and the trend of the wadati benioff zone the focal mechanism changed dramatically after the second subevent causing a very large ndc component both events together with the 1994 bolivia earthquake have a precursor separated in space and time from the main rupture and show rupture velocities varying between 3 and 4 km s between subevents with 2 0 km s on average for the entire event low seismic efficiencies and rupture velocities support a highly dissipative temperature dependent rupture mechanism for large deep focus south american earthquakes compared with events in cold subducting slabs

sea level rise impact on fresh groundwater lenses in two layer small islands the fresh groundwater lenses fgls of small islands can be highly vulnerable to climate change impacts including sea level rise slr many real cases of atoll or sandy islands involve two layer hydrogeological conceptualizations in this paper the influential factors that affect fgls in two layer small islands subject to slr are investigated an analytical solution describing fgls in circular islands composed of two geological layers is developed for the simplified case of steady state and sharp interface conditions an application of the developed model is demonstrated to estimate the fgl thickness of some real world islands by comparison with existing fgl thickness data furthermore numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases sensitivity analyses are used to assess the importance of land surface inundation caused by slr relative to other parameters i e thickness of aquifer layers hydraulic conductivity recharge rate and land surface slope that influence the fgl dimensionless parameters are used to generalize the findings the results demonstrate that land surface inundation has a considerable impact on a fgl influenced by slr as expected although the fgl volume is more sensitive to recharge aquifer thickness and hydraulic conductivity than slr impacts considering typical parameter ranges the methodology presented in this study provides water resource managers with a rapid assessment tool for evaluating the likely impacts of slr and accompanying lsi on fgls

deep seismicity and modes of deformation in tonga subduction zone the geometry of deep 400 km earthquakes in the subducting western edge of the pacific plate when related to the local distribution of seismic activity reveals a complex pattern of planes of shear failure enabling the modes of deformation by which the descending plate shortens and thickens to be identified the deepest part of the slab is displaced laterally suggesting that it fails to penetrate the discontinuity at 670 km

a simplified equation of approximate interface profile in stratified coastal aquifers abstract in this study we provide a simplified equation with a new concise set of parameters defining the approximate interface profile in stratified coastal aquifers we derive the solution directly by applying the dupuit forchheimer approximation at the outset and mathematically prove its sameness for the uniform flow in a vertical plane with the interface profile computed using the comprehensive discharge potential theory by strack and ausk 2015 we present a surprising result that interface elevation in the case with a seepage and outflow face at the coastal boundary turns out to be same as in which water table and interface coincides with the coastline the interface profile is a function of the transmissivity field centroid elevation and the total transmissivity of the freshwater flow domain above the interface we found that the boundary potential at the coast in the discharge potential theory solution represents the first moment of the transmissivity we also analyzed the differences in the interface profiles in aquifers with different hydraulic conductivity contrasts for two sets of boundary conditions constant head and constant flux for a given flux boundary interface profiles in aquifer configurations with different conductivity contrasts converge in the upper part of the aquifer and diverge at the aquifer bottom leading to different toe positions conversely for a given head boundary interface profiles in aquifer configurations with different conductivity contrasts significantly differ in the upper part of the aquifer while converge at the aquifer bottom resulting in the same toe position we provide explicit solutions for the toe position and freshwater discharge in unconfined aquifers an extension to our previous work for confined aquifers insights from the newly identified parameters can also potentially help in reducing the uncertainty in the estimation of the real world swi extent and optimize the requirement of the extent of the hydraulic conductivity field characterization

assessment of the impact of sea level rise on seawater intrusion in sloping confined coastal aquifers abstract previous studies of the impact of sea level rise on seawater intrusion slr swi are mostly based on horizontal coastal aquifers despite that most coastal aquifers are sloping a recent study has shown that the effect of aquifer slope can not be neglected when assessing slr swi in unconfined coastal aquifers however the effect of slope in confined aquifers has not been evaluated in this study we apply existing analytical solutions to quantify the effect of the slope of both upper and lower confining layers on slr swi the results show that for flux controlled sloping confined coastal aquifer systems slr does not change the steady state interface location consistent with previous findings for horizontal aquifers therefore our analysis focuses on head controlled sloping confined coastal aquifer systems for which we find the assumption of horizontal confining units causes significant errors we demonstrate this by assessing the sensitivities of the seawater toe location and seawater volume to slr for various combinations of sloping confining layers the results indicate that the influence of the slope on slr swi is small in thin confined aquifers however the slope is an important factor in thick confined aquifers the influence of the slope in the lower confining layer on slr swi is much greater than that of the upper confining layer aquifers that thin towards the sea are most susceptible to slr swi whereas those that thin towards inland are least susceptible the assessment of slr swi in sloping confined coastal aquifers in the current study demonstrates application of a rapid first order assessment tool that can be applied to a wide range of other sloping coastal confined aquifer problems

sea level rise impacts on seawater intrusion in coastal aquifers review and integration summary sea level rise slr influences groundwater hydraulics and in particular seawater intrusion swi in many coastal aquifers the quantification of the combined and relative impacts of influential factors on swi has not previously been considered in coastal aquifers in the present study a systematic review of the available literature on this topic is first provided then the potential remaining challenges are scrutinized open questions on the effects of more realistic complexities such as gradual slr parameter uncertainties and the associated influences in decision making models are issues requiring further investigation we assess and quantify the seawater toe location under the impacts of slr in combination with recharge rate variations land surface inundation lsi due to slr aquifer bed slope variation and changing landward boundary conditions lwbcs this is the first study to include all of these factors in a single analysis framework both analytical and numerical models are used for these sensitivity assessments it is demonstrated that 1 lsi caused by slr has a significant incremental impact on the seawater toe location especially in the flatter coasts and the flux controlled fc lwbcs however this impact is less than the reported orders of magnitude differences which were estimated using only analytical solutions 2 lwbcs significantly influence the slr impacts under almost all conditions considered in this study 3 the main controlling factors of seawater toe location are the magnitudes of fresh groundwater discharge to sea and recharge rate regional freshwater flux entering from the landward boundary and the groundwater hydraulic gradient are the major contributors of fresh groundwater discharge to sea for both fc and head controlled hc systems respectively 4 a larger response of the aquifer and larger seawater toe location changes are demonstrable for a larger ratio of the aquifer thickness to the aquifer length particularly in the hc systems 5 the lowest sensitivity of seawater toe location is found for the density difference ratio of the seawater and freshwater and also for the aquifer bed slope 6 the early time observations show seawater fingers below the inundated lands due to slr which are diminished and ultimately extinguished and 7 a less than 2 reversal effect on the seawater toe location after overshoot mechanism is observed in the transient simulations which suggests that this mechanism is an insignificant and impractical factor compared to other more significant factors

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

gis and sda applications in geomorphology abstract this special issue of geomorphology consists mainly of selected papers from the s15 session gis and sda applications in geomorphology at the 6th international conference on geomorphology held in zaragoza spain in september 2005 for this session 53 abstracts from europe asia the americas africa and oceania were submitted and 18 oral communications and 35 posters were presented the session provided an opportunity to overview discuss and evaluate new advances of gis geographical information systems and sda spatial data analysis applications in the field of geomorphology eight of the manuscripts submitted for the publication call for this special issue survived the review process and two other invited contributions together form this special issue with 10 papers

on the interpretation of coastal aquifer water level trends and water balances a precautionary note the changes in seawater volumes caused by seawater intrusion are often neglected in coastal aquifer management studies the conditions under which this can result in significant water balance errors are not well understood interface movements also influence temporal trends in coastal aquifer water levels but there is little guidance on this effect in this study we use steady state sharp interface analytic modelling to generate idealised relationships between seawater volume freshwater volume and water levels the approach assumes quasi equilibrium conditions which are evaluated using a selection of transient dispersive simulations the results demonstrate that seawater volume changes can influence significantly coastal aquifer water level trends relative to the corresponding non coastal aquifer situation particularly within deep aquifers with high hydraulic conductivity and low net recharge it is also shown that seawater volume changes can be a significant component of coastal aquifer water balances e g relative to freshwater discharge to the sea especially within deep aquifers characterised by low hydraulic conductivity and low freshwater discharge transient simulations show that steady state conditions are a reasonable approximation for a range of transient seawater intrusion situations including two of the three cases considered in this analysis we conclude that changes in seawater volumes should be included routinely in coastal aquifer water balances also temporal trends in coastal aquifer water levels may not provide an adequate measure of freshwater storage trends it follows that the assessment of coastal aquifer condition should consider groundwater levels relative to the hydraulic head imposed by the ocean accounting for density effects

assessment of the impact of sea level rise on steady state seawater intrusion in a layered coastal aquifer abstract previous studies on the impact of sea level rise slr on seawater intrusion swi are mostly based on the assumption of a homogeneous coastal aquifer in this study we extend those studies by investigating slr induced swi in a layered coastal aquifer using the analytical method developed by strack and ausk 2015 we provide analytical solutions for steady state swi in confined and unconfined coastal aquifers where both constant head and constant flux inland boundary conditions are considered the analysis based on a three layer aquifer indicates that in general aquifer stratification affects either or both the initial location and response distance of the interface toe specifically for flux controlled unconfined coastal systems the toe response distance driven by slr is a linear function of the hydraulic conductivity of the top layer and independent of hydraulic conductivities of lower layers using an equivalent homogeneous hydraulic conductivity derived based on the initial interface toe location before slr would result in overestimation or underestimation of the toe response distance depending on the hydraulic conductivities and thicknesses of the layers for flux controlled confined layered coastal systems by contrast slr can not cause variation of the steady state interface toe location which is consistent with previous findings for homogeneous coastal aquifers the interface toe location in head controlled layered coastal systems is only a function of relative hydraulic conductivities between the layers moreover the effect of the layer thickness on the interface toe location and response distance in the head controlled system exhibits a more complicated pattern than in the flux controlled coastal system as changing the layer thickness changes both the overall aquifer transmissivity and inland freshwater flux the results obtained enhance the understanding of the impact of slr on swi which could provide a first order assessment tool for relevant practitioners

seawater intrusion in response to sea level rise in a coastal aquifer with a general head inland boundary seawater intrusion in response to sea level rise has been studied extensively in recent years by assuming largely a constant head or constant flux inland boundary condition however these two types of boundary conditions are not sufficient when the inland edge of the model domain is neither natural groundwater nor known hydraulic boundaries under these circumstances a general head inland boundary condition capable of characterizing the hydraulic response of model boundaries is needed previous studies adopting the general head inland boundary condition to assess coastal aquifer vulnerability to sea level rise are limited and all based on numerical modeling in this study we derive analytical solutions of the interface toe location in both confined and unconfined coastal systems with a general head inland boundary condition comparison among the performances of the three different types of inland boundary conditions in evaluating the sea level rise impact on aquifer salinization is carried out by assuming the same initial system condition it is found that the displacement of the interface toe predicted using a general head inland boundary is between those of using a constant head upper bound and constant flux lower bound inland boundary depending on the values of two general head boundary parameters i e hydraulic conductance and reference head more importantly analytical solutions developed could serve as a tool for calibrating the two boundary parameters defined in the general head boundary condition for site specific assessments

response of the mediterranean and dead sea coastal aquifers to sea level variations 1 the present study examines the response of groundwater systems to expected changes in the mediterranean sea rise of 1cm yr and dead sea levels decline of 1 m yr a fast response is observed in the dead sea coastal aquifer exhibited both in the drop of the water levels and in the location of the fresh saline water interface no such effect is yet observed in the mediterranean coastal aquifer as expected numerical simulations using the feflow software show that the effect of global sea level rise depends on the coastal topography next to the shoreline a slope of 2 5 is expected to yield a shift of the interface by 400 m after a rise of 1m 100 years whereas a vertical slope will yield no shift reduced recharge due to climate change or overexploitation of groundwater also enhances the inland shift of the interface

centroid moment tensor solutions for deep earthquakes predating the digital era discussion and inferences abstract we present a discussion of 139 new centroid moment tensor solutions for deep earthquakes covering the wwssn 1962 1976 and earlier years obtained by applying the standard harvard inversion algorithm to data sets of seismograms digitized from analog records our solutions fill several gaps in seismicity reflecting undersampling by the harvard catalogue while most focal mechanisms previously published for wwssn era earthquakes are in good agreement with our inverted solutions focal geometries for older events appear unreliable we confirm that the region of most intense moment release is around 650 km and that a minimum exists at 500 km however the local maximum around 450 km may be less marked than previously suggested the bonin marianas subduction zone exhibits a different pattern with an overall maximum of seismic activity at 420 km all other subduction zones demonstrate the potential for seismicity at least at the 1027 dyn cm level finally while non double couple components are found systematically in our enhanced data set they correlate neither with depth nor with earthquake size suggesting that their presence does not necessarily relate to the exiguity of the space available for rupture at the tip of subduction zones

national scale evaluation of groundwater chemistry in korea coastal aquifers evidences of seawater intrusion pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of korea therefore seawater intrusion monitoring stations were installed in eastern western and southern coastal areas and have been operated since 1998 in this study groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated groundwater was classified into fresh 3 000 s cm according to ec levels among groundwater samples n 233 56 7 and 37 were classified as the fresh brackish and saline respectively the major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater the enrichment of na and cl was especially noticeable due to seawater intrusion thus the brackish and saline groundwaters were classified as ca cl and na cl types while the fresh groundwater was classified as na hco3 and ca hco3 types the groundwater included in the na cl types indicated the effects of seawater mixing ca2 mg2 na k so4 2 and br showed good correlations with cl of over r 0 624 of these components the strong correlations of mg2 so4 2 and br with cl r 0 823 indicated a distinct mixing between fresh groundwater and seawater the ca cl and hco3 cl ratios of the groundwaters gradually decreased and approached those of seawater the mg cl na cl k cl so4 cl and br cl ratios of the groundwaters gradually decreased and were similar to or lower than those of seawater indicating that mg2 na k so4 2 and br as well as cl in the saline groundwater can be enriched by seawater mixing while ca2 and hco3 are mainly released by weathering processes the influence of seawater intrusion was evaluated using threshold values of cl and br which were estimated as 80 5 and 0 54 mg l respectively according to these criteria 41 50 of the groundwaters were affected by seawater mixing

occurrence of seawater intrusion overshoot a number of numerical modeling studies of transient sea level rise slr and seawater intrusion si in flux controlled aquifer systems have reported an overshoot phenomenon whereby the freshwater saltwater interface temporarily extends further inland than the eventual steady state position recently physical sand tank modeling has shown overshoot to be a physical process in this paper we have carried out numerical modeling of slr si to demonstrate that overshoot can occur at the field scale within unconfined aquifers this result is contrary to previous conclusions drawn from a restricted number of cases in addition we show that si overshoot is plausible under scenarios of gradual sea level rise that are consistent with conditions predicted by the intergovernmental panel for climate change overshoot was found to be largest in flux controlled unconfined aquifers characterized by low freshwater flux high specific yield and large inland extent these conditions result in longer timeframes for the aquifer to reach new steady state conditions following slr and the extended period prior to reequilibration of the groundwater flow field produces more extensive overshoot

modes of seawater intrusion during transgressions analytical methods and numerical experiments are used to study salinization of groundwater in response to sea level rise the system that is studied involves a saturated porous medium with an inclined upper surface the upper surface is progressively inundated during sea level rise to simulate transgression the landward migration of the shoreline four modes of seawater intrusion are distinguished 1 horizontal intrusion for slow transgression and a relatively high permeability substrate 2 vertical intrusion by seawater fingering for fast transgression and a sand silt substrate 3 vertical intrusion by diffusion for fast transgression and a low permeability clay substrate 4 vertical intrusion by combined diffusion and low salinity fingering for fast transgression and a clay layer at the seafloor overlying an aquifer these four modes are characterized by the development of very distinctive transition zones between the fresh and salt groundwater domains an analytical expression is derived for the critical transgression rate which separates horizontal mode 1 from dominantly vertical modes 2 4 intrusion for modes 3 and 4 salinization significantly lags behind sea level rise the results are consistent with observations of fossil fresh brackish groundwater beneath many continental shelves and shallow seas

frequency distribution and quantification of deep earthquakes the frequency distribution of deep earthquakes d 350 km is analyzed on a regional scale using magnitude data from 4660 events reported in the international seismological center bulletin 1964 1982 and 391 centroid moment tensor solutions 1977 1987 we use the moment magnitude mw to define b values comparable with studies of shallow seismicity scaling laws relating mw mb and mo are derived mw 1 6mb 3 2 mb log mo 4 3 2 4 which compare very favorably with published laws uncertainties and biases of the mb and mo data sets are considered the slope of the frequency distribution is evaluated over a restricted magnitude range the results are very robust and independent from the magnitude range used from the mb magnitude data we obtain regional b values in the range 0 4 b 1 22 with a worldwide average value b 0 87 these results are confirmed by the analysis of the seismic moment data the steepest frequency distribution is observed in the tonga islands region b 1 22 although 60 of the worldwide deep seismicity occurs here only few events since 1977 had seismic moment exceeding 1019 n m the high fractal dimension d 2 4 implies a volume partially filled with fault planes in agreement with the observations on the seismic morphology of the region at the other extreme south america is characterized by the largest recorded deep events and an almost complete absence of small ones b 0 4

mantle phase changes and deep earthquake faulting in subducting lithosphere inclined zones of earthquakes are the primary expression of lithosphere subduction a distinct deep population of subduction zone earthquakes occurs at depths of 350 to 690 kilometers at those depths ordinary brittle fracture and frictional sliding the faulting processes of shallow earthquakes are not expected a fresh understanding of these deep earthquakes comes from developments in several areas of experimental and theoretical geophysics including the discovery and characterization of transformational faulting a shear instability connected with localized phase transformations under nonhydrostatic stress these developments support the hypothesis that deep earthquakes represent transformational faulting in a wedge of olivine rich peridotite that is likely to persist metastably in coldest plate interiors to depths as great as 690 km predictions based on this deep structure of mantle phase changes are consistent with the global depth distribution of deep earthquakes the maximum depths of earthquakes in individual subductions zones and key source characteristics of deep events

field experiments in a fractured clay till 2 solute and colloid transport a field tracer experiment was conducted in a lateral flow field in the weathered and highly fractured upper 6 m of a 40 m thick clay rich till plain in southwestern ontario in the upper 3 m where fractures are closely spaced 5 m d simulations with a discrete fracture porous matrix flow and transport model which used the cubic law for flow in fractures showed that diffusion of the solutes but not the much larger colloids into the matrix pore water between fractures is sufficient to cause the observed difference in solute and colloid transport rates transport derived and hydraulic conductivity derived fracture aperture values were similar within a factor of 3 and falling mainly within a range of 5 40 m in the upper 3 m the solute tracers were evenly distributed between pore water in the fractures and the matrix and as a result solute transport can be closely approximated with an equivalent porous medium epm approach below this depth fractures are more widely spaced 0 13 to 1 m with concentration peaks tending to occur near visible fractures and solute transport cannot be adequately described with an epm approach

transience of seawater intrusion in response to sea level rise 1 understanding seawater intrusion swi induced by sea level rise slr is important for the future management of many coastal aquifers only simplified steady state sharp interface analyses of generalized slr swi exist in the literature and the important issue of associated time scales has been neglected we employ numerical modeling in order to explore the transience of dispersive slr swi in common unconfined coastal aquifer settings an instantaneous slr is adopted to compare with the instantaneous sea level drop sld case of a previous sld swi analysis temporal asymmetry between the swi responses to slr and sld is observed a slr swi simulation series indicates that toe representative response times time to reach 95 of new steady state range from decades to centuries for a 1 m slr significant discrepancies between the representative response times of various swi quantitative indicators e g toe position wedge center of mass are observed this demonstrates that the indication of steady state swi conditions depends upon the monitoring approach and thus holds implications for studies reporting that swi steady state has been attained we adopt 100 years as a typical planning time frame and compare 100 year and steady state slr swi as expected the simplified steady state sharp interface solution overpredicts the 100 year landward toe shift in most cases however some simulations exhibit temporary overshoot of the steady state interface position this is in contradiction to the presumption that steady state swi is the worst case steady state sharp interface estimates appear to be at best useful as initial approximations of slr swi given that they span 40 250 of 100 year dispersive interface results for the cases considered

observations of exotic inner core waves the seismic structure of earth s inner core is highly complex displaying strong anisotropy and further regional variations however few seismic waves are sensitive to the inner core and fundamental questions regarding the origin of the observed seismic features remain unanswered thus new techniques to observe different types of inner core waves are imperative to improve data coverage here we detail our method for detecting exotic inner core phases such as pkjkp and pkiikp using inner core compressional waves as proof of concept we use phase weighted stacking on long period data from a global distribution of stations and employ several synthetic methods including normal mode summation and specfem to identify and confirm the inner core phases we present evidence for two observations of exotic inner core compressional waves and apply the technique to a previously detected inner core shear wave a possible new inner core shear wave remains unconfirmed additionally we show how our method is important for rejecting potential observations and distinguishing between waves with similar traveltime and slowness the method is most successful for detecting exotic inner core compressional waves and will provide a new approach for studying the compressional wave structures in the upper inner core

a process for low temperature olivine spinel transition under quasi hydrostatic stress 1 the behavior of fayalite the fe2sio4 olivine end member fa100 has been monitored during high pressure and low temperature experiments using in situ x ray synchrotron radiation in order to investigate the effect of stress on the olivine phase spinel phase or ringwoodite transition the run products were investigated by optical and transmission electron microscopy tem a low temperature mechanism for the transformation is documented this shear induced mechanism is operative in hydrostatically compressed samples at temperature as low as 450 c and is driven by the shear stress generated by the volume change of the transformation itself projection to mantle compositions suggests that metastable subduction of olivine will not occur in the deep transition zone

the june 9 bolivia and march 9 fiji deep earthquakes of 1994 ii geodynamic implications the june 9 1994 bolivia earthquake mw 8 2 occurred in the pronounced bend in the morphology of the deep south american slab where several dynamic arguments can be put forward to explain the apparently anomalous mechanism and the horizontal fault plane the size of the event is huge but expected when the regional seismicity of the whole century is considered the march 9 1994 fiji earthquake fiji 7 5 suggests that a new mode of seismic deformation is active in the northernmost termination of the tonga fiji slab cutting across the dense cluster of seismicity of the last 30 years the size of the event is probably close to the largest to be expected over a century in this area having the steepest frequency moment distribution of all global deep seismicity

aquifer characteristics derived from the interaction between water levels of a terminal lake dead sea and an adjacent aquifer the water level of the dead sea a terminal hypersaline lake total dissolved solids approximately 340 g l has decreased at an average rate of 0 5 m yr since 1960 and by 0 8 m yr between 1981 and 1989 the dramatic long term water level variation of the dead sea and the seasonal short term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer a general methodology based on a simplified yet reliable one dimensional flow model together with continuous measurements of groundwater levels in observation wells enables analysis of aquifer structural and hydraulic properties furthermore this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels

t waves from the great 1994 bolivian deep earthquake in relation to channeling of s wave energy up the slab we report the observation of t phases recorded at a number of pacific island sites following the great bolivian deep earthquake of june 9 1994 by studying their arrival times at the various stations we unravel the process of conversion from seismic to acoustic energy at the south american coastline we find that the maxima of amplitude of the phase are incompatible with propagation along the great circle from source to receiver but rather require the generation of the acoustic wave at a common point at the arica bight for all stations in the south pacific and even farther south for stations in hawaii and the bonin islands the timing of these conversions corresponds to the arrival of regional s waves at the conversion points the high frequency nature of the t phase requires the channeling of the s wave from the seismic source to conversion point through low attenuation material which in turns adds supportive evidence for the mechanical continuity of the downgoing slab under that section of south america despite the observed gap in seismicity between 300 and 600 km

effects of tidal fluctuations on mixing and spreading in coastal aquifers homogeneous case while the hydraulics of tidally dominated groundwater systems have been studied extensively tidally induced solute spreading in the fresh saltwater transition zone of coastal aquifers remains largely unexplored here we systematically quantify tidal impacts on solute mixing and spreading in seawater intrusion problems for an idealized homogeneous system mixing is characterized by the spatial moments of the solute concentration distribution and quantified by an effective dispersion coefficient parametric analysis reveals that the key dimensionless parameter controlling the tidal mixing behavior is the tidal mixing number ntm which depends on the tidal amplitude the period and the hydraulic diffusivity we find that for ntm 600 tides lead to a significant impact on the shape and location of the interface the maximum effect on transverse and longitudinal dispersion occurs for large values of storativity a hydrogeologic parameter that has been previously understated in terms of its significance large storativity implies a nonuniform hydraulic response to the tidal forcing such that the resulting nonuniform time dependent velocity field enhances mixing as a result the interface spreads mainly at the bottom of the aquifer where the saline end of the mixing zone migrates seaward whereas the spatial extent of low salt concentrations migrates landward these insights critically underpin quantitative guidance on the inclusion and exclusion of tidal effects in the analysis of seawater intrusion

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

object representations at multiple scales from digital elevation models in the last decade landform classification and mapping has developed as one of the most active areas of geomorphometry however translation from continuous models of elevation and its derivatives slope aspect and curvatures to landform divisions landforms and landform elements is filtered by two important concepts scale and object ontology although acknowledged as being important these two issues have received surprisingly little attention this contribution provides an overview and prospects of object representation from dems as a function of scale relationships between object delineation and classification or regionalization are explored in the context of differences between general and specific geomorphometry a review of scales issues in geomorphometry ranging from scale effects to scale optimization techniques is followed by an analysis of pros and cons of using cells and objects in dem analysis prospects for coupling multi scale analysis and object delineation are then discussed within this context we propose discrete geomorphometry as a possible approach between general and specific geomorphometry discrete geomorphometry would apply to and describe land surface divisions defined solely by the criteria of homogeneity in respect to a given land surface parameter or a combination of several parameters homogeneity in its turn should always be relative to scale

the mechanism of the deep bolivia earthquake of june 9 1994 we analyzed the iris broad band seismograms for the june 9 1994 bolivia earthquake the largest deep focus earthquake ever recorded we inverted the record sections with a duration of 330 sec which include p pp and sp phases and obtained a dip slip mechanism dip rake strike 13 4 1 or 89 103 95 with a scalar moment of mo 2 9 10 21 nm mw 8 2 this mechanism is similar to that obtained from long period 175 to 250 sec rayleigh and love waves 83 100 90 mo 3 0 10 21 nm mw 8 3 the main rupture was preceded by about 10 sec by a cluster of smaller events with a total moment of 1 2 10 20 nm mw 7 3 the main rupture starts at about 20 km east or northeast of the initial break and propagates horizontally in the east to northeast direction the source duration is 40 sec and the rupture dimension is about 40km if a fault area of 40 40km is assumed the stress drop is 110 mpa an inversion of body waves p pp and sp with 6 basis moment tensors yielded a best fit solution with a 10 implosive component this result is of marginal significance and its confirmation would require more detailed information on the structures near the source region pp bounce points and stations the observed amplitude of the radial mode 0s 0 1226 sec is consistent with a double couple model with less than 2 isotropic component

the isolated 680 km deep 30 may 2015 m w 7 9 ogasawara bonin islands earthquake deep focus earthquakes located in very high pressure conditions 300 to 700 km below the earth s surface within sinking slabs of relatively cold oceanic lithosphere are mysterious phenomena the largest recorded deep focus earthquake m w 7 9 in the izu bonin slab struck on 30 may 2015 beneath the ogasawara bonin islands isolated from prior seismicity by over 100 km in depth and followed by only a few small aftershocks globally this is the deepest 680 km centroid depth event with m w 7 8 in the seismological record seismicity indicates along strike contortion of the izu bonin slab with horizontal flattening near a depth of 550 km in the izu region and rapid steepening to near vertical toward the south above the location of the 2015 event this event was exceptionally well recorded by seismic stations around the world allowing detailed constraints to be placed on the source process analyses of a large global data set of p sh and pp seismic phases using short period back projection subevent directivity and broadband finite fault inversion indicate that the mainshock ruptured a shallowly dipping fault plane with patchy slip that spread over a distance of 40 km with a multi stage expansion rate 5 km s down dip initially 3 km s up dip later during the 17 s total rupture duration the radiated energy was 3 3 10 16 j and the stress drop was 38 mpa the radiation efficiency is moderate 0 34 intermediate to that of the 1994 bolivia and 2013 sea of okhotsk m w 8 3 deep earthquakes indicating that source processes of very large deep earthquakes sample a wide range of behavior from dissipative more viscous failure to very brittle failure the isolated occurrence of the event much deeper than the apparently thermally bounded distribution of bonin slab seismicity above 600 km depth suggests that localized stress concentration associated with the pronounced deformation of the izu bonin slab and proximity to the 660 km phase transition likely played a dominant role in generating this major earthquake

water table salinization due to seawater intrusion seawater intrusion swi is a significant threat to freshwater resources in coastal aquifers around the world previous studies have focused on swi impacts involving salinization of the lower domain of coastal aquifers however under certain conditions swi may cause salinization of the entire saturated zone of the aquifer leading to watertable salinization wts in unconfined aquifers by replacing freshwater within the upper region of the saturated zone with seawater thereby posing a salinity threat to the overlying soil zone there is presently limited guidance on the extent to which wts may occur as a secondary impact of swi in this study physical experiments and numerical modelling were used to explore wts associated with swi in various non tidal unconfined coastal aquifer settings laboratory experiments and corresponding numerical simulations show that significant wts can occur under active swi i e the freshwater hydraulic gradient slopes towards the land because the cessation of freshwater discharge to the sea and the subsequent landward flow across the entire sea boundary eventually lead to watertable salinities approaching seawater concentration wts during active swi is larger under conditions of high hydraulic conductivity rapid swi high dispersivity and for deeper aquifers numerical modelling of four published field cases demonstrates that rates of wts of up to 60 m y are plausible under passive swi i e the hydraulic gradient slopes towards the sea minor wts may arise as a result of dispersive processes under certain conditions i e high dispersivity and hydraulic conductivity and low freshwater discharge our results show that wts is probably widespread in coastal aquifers experiencing considerable groundwater decline sustained over several years although further evidence is needed to identify wts under field settings this article is protected by copyright all rights reserved

an assessment of the importance of some parameters for seawater intrusion in aquifers and a comparison of dispersive and sharp interface modelling approaches abstract the problem considered is that of determining the location and shape of the steady interface in a coastal aquifer discharging fresh water to the sea for homogeneous isotropic aquifers the location of the interface is obtained by the boundary integral method for an abrupt interface model these results are compared with the distribution of salt in the dispersion zone where the two fluids meet as determined by a finite difference solution of the flow and convective dispersion equations considerations are restricted to a rectangular section of isotropic homogeneous aquifer and examples are limited to those showing the effects of different convection to dispersion ratios including anisotropic dispersion different fresh water flow gradients and different relative densities of seawater these examples give an indication of the relative accuracy of the abrupt interface model for different ratios of convection to dispersion and enable the influence of various parameters on the shape and extent of the dispersion zone to be studied

an implosive component to the source of the deep sea of okhotsk earthquake of 24 may 2013 evidence from radial modes and cmt inversion abstract we study the spectral amplitudes of the first two earth radial modes 0 s 0 and 1 s 0 excited by the sea of okhotsk earthquake of 24 may 2013 the largest deep event ever recorded in the search for an isotropic component to its source in contrast to the case of the 1994 bolivian earthquake we detect an implosive component m i 1 1 10 27 dyn cm equivalent to 3 of the full scalar moment but 14 of the lone deviatoric component exciting the earth s radial modes an independent moment tensor inversion using the standard globalcmt algorithm but after relaxing its zero trace constraint similarly yields an implosive isotropic component albeit with a larger amplitude while it fails to document one in the case of the 1994 bolivian deep earthquake an implosive component to the source is expected in the model of transformational faulting in which deep earthquake rupture nucleates and grows upon transformation of metastable olivine to ringwoodite in the cold subducting slab this interpretation is supported by quantitative estimates 0 9 4 m of the thickness of the transformed shear zone which scale favorably relative to earthquake fault length with the upper end of the range of laboratory results reported for ices germanates and silicates the resulting extent of the transformation in the metastable wedge is consistent with the local geometry of the deep slab as recently determined by rupture modeling and aftershock distribution our results are in contrast to those for the two runner up largest deep earthquakes the 1994 bolivian and 1970 colombian shocks for which a similar isotropic component could not be detected we attribute this difference to variability in the ratio of isotropic to deviatoric components which combined with the smaller size of the 1970 and 1994 events would make any putative implosive component fall below detection levels especially in the case of the 1970 colombian earthquake for which only analog narrow band records were available

the 1994 bolivia and tonga events fundamentally different types of deep earthquakes the 1994 bolivia and tonga events show large differences in source and aftershock properties the bolivia earthquake characterized by high stress drop slow rupture propagation and a weak aftershock sequence appears similar to other large deep earthquakes that are isolated from active seismic zones including the 1970 colombia earthquake in contrast the 1994 tonga event showed stress drop rupture propagation velocities and an aftershock sequence similar to that found for shallow earthquakes the aftershock sequence of the 1994 tonga event is many times stronger than has been observed for any other deep earthquake a survey of deep earthquake aftershocks suggests that aftershock occurrence is correlated with the overall subduction zone magnitude frequency relation b value the largest deep events occur in isolated regions lacking smaller earthquakes or in subduction zones characterized by anomalously low b values the 1994 tonga event is an exception and is the largest deep earthquake to occur within an active subduction zone showing a large b value perhaps explaining the strong aftershock sequence the bolivia and tonga events may represent end members of a population of deep earthquakes showing exceptional diversity in source properties or they may represent two fundamentally different types of deep earthquakes perhaps resulting from different physical mechanisms

a coupled field study of subsurface fracture flow and colloid transport field studies of subsurface transport of colloids which may act as carriers of contaminants are still rare this is particularly true for heterogeneous and fractured matrices to address this knowledge gap a 30 m long monitoring trench was constructed at the lower end of sloping farmland in central sichuan southwest china during the summer of 2013 high resolution dynamic and temporal fracture flow discharging from the interface between fractured mudrock and impermeable sandstone was obtained at intervals of 5 min for fast rising stages 30 60 min for slow falling stages or 15 min at all other times this discharge was analyzed to elucidate fracture flow and colloid transport in response to rainfall events colloid concentrations were observed to increase quickly once rainfall started 15 90 min and reached peak values of up to 188 mg l interestingly maximum colloid concentration occurred prior to the arrival of flow discharge peak i e maximum colloid concentration was observed before saturation of the soil layer rainfall intensity rather than its duration was noted to be the main factor controlling colloid response and transport dissolved organic carbon concentration and 6180 dynamics in combination with soil water potential were used to apportion water sources of fracture flow at different stages these approaches suggested the main source of the colloids discharged to be associated with the flushing of colloids from the soil mesopores and macropores beyond the scientific interest of colloid mobilization and transport at the field scale these results have important implications for a region of about 160 000 km 2 in southwest china that featured similar hydrogeologic settings as the experimental site in this agriculture dominated area application of pesticides and fertilizers to farmland is prevalent these results highlight the need to avoid such applications immediately before rainfall events in order to reduce rapid migration to groundwater via fracture flow in either dissolved form or in association with colloids c 2015 elsevier b v all rights reserved

motion of the seawater interface in a coastal aquifer by the method of successive steady states abstract the paper describes a method for determining the motion of the seawater interface in a phreatic coastal aquifer during a specified time period in response to changing hydrologic conditions provided a seaward flow of fresh water is maintained everywhere above the interface the method of successive steady states is used leading to an approximate analytical expression which gives the motion of the interface toe during the time period as a function of the initial conditions and the change in freshwater flow to the sea above the toe during the time period sensitivity of the results to values of parameters and to hydrologic conditions is investigated and the results are compared with those obtained by other methods of analysis the motivation for developing the approximate analytical expression for movement of the interface was to facilitate the introduction of seawater intrusion as a criterion in the multiobjective management model for coastal aquifers

centroid moment tensor inversion of low frequency seismic spectra using green s functions for aspherical earth models summary we present a new method for centroid moment tensor cmt inversion in which we employ the green s function computed for aspherical earth models using the direct solution method we apply this method to cmt inversion of low frequency seismic spectra for the 1994 bolivia and 1996 flores sea deep earthquakes the estimated centroid locations agree well with those obtained by multiple shock analyses using body wave data this shows that it is possible to obtain reliable cmt solutions by analyses of low frequency seismic spectra using accurate green s functions computed for present 3 d earth models

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