an attempt to detect reflected waves from the lower boundary of a descending slab abstract we attempted to detect reflected waves from deep focus earthquakes at the lower boundary of a descending slab for this purpose we calculated theoretical waveforms in the realistic heterogeneous velocity and q structures beneath the japanese islands and compared them with seismic waveforms observed in the kanto tokai districts of central japan assuming that earthquakes occur within the deeper portion of the slab we investigated the effects of variation in focal mechanisms focal depths velocity contrasts near the lower plate boundary and the q structures on theoretical seismograms on the earth s surface the results show that the amplitudes of the p to p and s to s reflected waves gradually increase toward the subduction zone and take maximum values near the trench axis however travel time difference between the direct wave and the following reflected wave decreases there making it difficult to detect the reflected wave based on these theoretical calculations we investigated digital three component seismograms observed in the kanto tokai districts by the national research institute for earth science and disaster prevention science and technology agency nied the seismograms observed were obtained from deep focus earthquakes from 1990 through 1996 with magnitude of 5 0 and greater after carefully checking seismograms from 15 deep focus events we could not detect the reflected waves from the lower plate boundary systematically at expected arrival times from the theoretical calculation this indicates that the reflected waves are either masked by coda waves followed by the direct p and s waves or below the noise level that is detectable by seismometers there is also a possibility that the seismic velocity contrast between the slab and the underlying upper mantle may not be so sharp however the possibility to detect the s to s reflected waves increases if we check observed waveforms in the horizontal range between 200 to 300 km landward from trench axis for a moderate size deep focus earthquake with down dip compression which occurs near the upper plate boundary at depths of 300 to 400 km

continuous high velocity aseismic zone beneath the izu bonin arc since 1904 eleven unusually deep earthquakes have been reported near the southern end of the izu bonin arc about 24 n 142 e these isolated events are separated from ordinary deep earthquakes in the wadati benioff w b zone of the izu bonin i b arc by a distance of about 300 km parallel to the trench axis they also are located 200 km closer to the trench than the natural extension of the shallower earthquakes above them using 3 d ray tracing a detailed analysis is performed of the difference in travel time residuals between the anomalous events and the deep events within the w b zone to the north this analysis yields higher reliability and resolution than can be obtained from ordinary tomographic imaging we find that these unusual events occurred in a high velocity zone which is connected to the northern w b zone of the i b arc the aseismic high velocity zone has a p velocity at least 3 faster than the surrounding mantle both our result and previous evidence for a horizontally lying slab west of the w b zone at 27 n e g okino et al 1989 are consistent with the existence of a prominent contortion of the subducted slab in the i b region

seismic velocity structure of the subducting pacific plate in the izu bonin region although numerous studies have been made on the contrast between subducting slabs and surrounding mantle little is known about the internal structure of the oceanic lithosphere after it descends into the mantle at subduction zones the velocity structure within the slab can be expected to be heterogeneous based on thermal and petrological considerations in this study observed travel time residual data from a spatially dense seismic network above deep earthquakes in the izu bonin region are compared with three dimensional ray tracing calculations the data are inconsistent with a homogeneous slab model and consistent with a heterogeneous slab model with regional velocity variations the residual data can be explained by a model that has a velocity gradient within the slab in the subducting pacific plate the velocity near the center of the slab is faster than that near the upper boundary and gradually decreases toward the bottom of the plate a model with a velocity decrease of 3 as predicted by a thermal profile explains the observed data

surface subsurface water interactions in an alluviated mountain stream channel data from an instream tracer experiment performed in north fork dry run shenandoah national park virginia illustrate that the transport of water and conservative solute in the stream is greatly influenced by interaction with water present in both the relatively shallow gravel bed and in the relatively deeper alluvial infill material the shape of concentration time curves from the field tracer experiment exhibit storage of tracer in the subsurface short term storage imposed by exchange with the gravel bed and long term storage by exchange with the deeper alluvial infill time series models fit the observed concentration data very well estimates of mixing volumes generated by the time series analysis indicate that a large volume of the gravel bed participates in rapid mixing with the surface stream at one point along the study reach a second order time series model is supported by the data suggesting two independent parallel flow paths observations of tracer in wells more than 10 m from the stream and the very extended recession of the tracer in the stream where it flows over a bedrock ledge support the contention that the deeper alluvium plays an important role in transient storage of solute in north fork dry run the work implies that physically based models to predict transport and storage in alluviated mountain catchments may have to account for interactions between the stream and large portions of its floodplain

fine structure of deep wadati benioff zone in the izu bonin region estimated from s to p converted phase abstract mechanism of deep earthquakes is one of the most important and still unsolved problems in the field of solid geophysics determining precise location of the deep earthquakes can provide us with clues to approach this problem in this study we address the problem by estimating the separation distances between hypocenters of the deep earthquakes and slab asthenosphere interface we use later arrivals immediately after initial p arrivals from the deep earthquake events in the izu bonin region we interpret these later arrivals as an sp phase which is converted s to p at the upper slab interface our results prove that the hypocenters underlie the subducting upper slab interface using time delays between p and sp phases we find that the interface is located 20 km above the earthquake hypocenters moreover our results also indicate that the almost all deep earthquake hypocenters are distributed within a thin zone about 7 km wide rather than being scattered throughout the slab this observation fits a hypothesis that deep earthquakes are caused by transformational faulting of metastable olivine model

seismic detection of the untransformed basaltic oceanic crust subducting into the mantle summary subcrustal earthquakes occur in a slab like zone beneath sw japan in association with the subduction of the philippine sea plate they generate a distinct pair of p and s later phases with anomalously low apparent velocities of about 7 and 4 km s 1 which cannot be explained by a laterally homogeneous velocity structure these later phases are observed for particular source receiver geometries the sources at depths shallower than 50 60 km and the receivers beneath which the subcrustal seismic zone comes in contact with the bottom of the continental crust we examined the nature of these later phases using two methods one is to determine two types of apparent velocities an event common apparent velocity and a station common apparent velocity which may be different from one another for a laterally inhomogeneous velocity structure the other is to trace seismic rays numerically for a laterally heterogeneous velocity model an extensive analysis using these two methods leads to a conclusion that the slab like seismic zone constitutes a low velocity channel in the uppermost mantle with p and s velocities comparable to those of the lower continental crust beneath sw japan the waves trapped within the low velocity channel escape from it through its contact with the continental moho and are observed as a distinct pair of later phases the head waves guided by the bottom boundary of the low velocity channel are observed as weak arrivals of initial phases the thickness 10 km and the velocities vp 7 km s 1 vs 4 km s 1 of the subcrustal seismic zone indicates that it is made up of the untransformed basaltic oceanic crust subducted with the underlying lithospheric mantle and that the transformation of basalt to eclogite does not take place in the subducting slab at least down to depths of 50 60 km we present laterally heterogeneous structural models of the crust and the uppermost mantle along two profiles in sw japan the models are characterized by an apparent thickening of the lower continental crust in particular regions due to a direct contact of the subducting oceanic crust to the continental moho such features are qualitatively consistent with the results of explosion seismology and with the bouguer anomaly pattern in the relevant regions the oceanic lithosphere with the untransformed light oceanic crust at its top might still be buoyant after subduction a factor which must be taken into account in considering the driving mechanisms of plate tectonics the slab geometry and the earthquake related tectonic process

simultaneous determination of the three dimensional crustal structure and hypocenters beneath the kanto tokai district japan abstract a new method is proposed for determining the two dimensional depth distributions to the conrad and the moho together with station corrections and source parameters from first arrival time data in the present study the velocity structure is modelled by a hyperbolic function tanh and the configuration of each interface is expressed in a series of chebyshev functions with coefficients which are unknown parameters a non linear inversion method by tarantola and valette is applied for inversion an approximate ray tracing method with sufficient accuracy for a complex region is adopted for computation of seismic ray paths and travel times the method is applied to p wave first arrival time data from local earthquakes and explosions gathered in the seismological network by the national research center for disaster prevention to reveal the crustal structure beneath the kanto tokai district japan the results obtained in this study are very interesting and show the usefulness of the present method for the study of the crustal structure the distribution of station corrections is reasonable where there is information on the shallow structure low velocity zones appear around tokyo bay and the cape of omae and high velocity zones appear in the mountainous regions the depth to the conrad is about 12 16 km and its lateral change is gentle while the lateral change in the depth to the moho is comparatively large and there is a narrow region where the depth to the moho exceeds 40 km except for this region the central mountainous region the agreement of the crustal structure obtained in the present study with those by the previous refraction studies is fairly good in comparing our results to fractional velocity perturbation in layer 1 0 32 km derived with aki and lee s method by ishida and hasemi our work provides good information on the features causing the crustal velocity anomalies which have been unable to be constrained in ishida and hasemi s work

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

longshot experiments to study velocity anisotropy in the oceanic lithosphere of the northwestern pacific abstract several long range explosion seismology experiments have been conducted in the northwestern pacific basin where one of the oldest oceanic lithospheres is postulated to exist the experiments were conducted from 1974 to 1980 highly sensitive ocean bottom seismographs which had been developed for longshot experiments were used the lengths of the profiles ranged from 1000 to 1800 km and the directions were chosen to provide wide azimuthal coverage one of the aims of this series of experiments was to test the existence of velocity anisotropy on a large regional scale the results show that the oceanic lithosphere has anisotropy wherein the velocity changes by 4 7 the anisotropy extends from a depth of at least 40 to 140 km beneath the sea bottom however the magnitude of the anisotropy may vary with depth the azimuth of the maximum velocity is 150 160 clockwise from north and coincides with the fossil direction of spreading of the pacific plate whereas it differs from the present direction of plate motion by 30 the azimuth does not seem to depend on depth in the direction of maximum velocity the lithosphere is basically two layered 8 0 8 2 and 8 6 km s 1 the depth of the interface is 50 60 km beneath the sea floor

seismological constraints on the gabbro eclogite transition in subducted oceanic crust abstract dispersion of seismic waves travelling along the strike of the subducted pacific plate beneath tonga kermadec shows evidence for a high velocity layer of crustal thickness extending to a depth of at least 450 km the opposite dispersion with low frequencies arriving first is observed in japan and has been taken together with inferences from converted phases as evidence of a thin low velocity layer both layers have in previous studies been interpreted as subducted oceanic crust which has been transformed to eclogite but in tonga kermadec the eclogite must have high seismic velocity and beneath japan it must have a low seismic velocity an apparent contradiction therefore exists here we find theoretical estimates of the seismic velocities of eclogite and normal mantle using the data and equations of duffy and anderson and a variety of mineral assemblages and bulk compositions we find a range of both low and high seismic velocities the high end of the range depending mainly on the contents of jadeite pyrope and grossular it is therefore possible in principle to explain both the high velocity layer beneath tonga kermadec and the low velocity layer beneath japan as being consistent with an eclogitic crust provided they have significantly different compositions however we can find no clear reason for such a difference between that part of the pacific plate currently subducting beneath japan and that beneath tonga kermadec

alluvial characteristics groundwater surface water exchange and hydrological retention in headwater streams conservative solute injections were conducted in three first order montane streams of different geological composition to assess the influence of parent lithology and alluvial characteristics on the hydrological retention of nutrients three study sites were established 1 aspen creek in a sandstone siltstone catchment with a fine grained alluvium of low hydraulic conductivity 1 3 10 4 cm s 2 rio calaveras which flows through volcanic tuff with alluvium of intermediate grain size and hydraulic conductivity 1 2 10 3 cm s and 3 gallina creek located in a granite gneiss catchment of coarse poorly sorted alluvium with high hydraulic conductivity 4 1 10 3 cm s all sites were instrumented with networks of shallow groundwater wells to monitor interstitial solute transport the rate and extent of groundwater surface water exchange determined by the solute response in wells increased with increasing hydraulic conductivity the direction of surface water groundwater interaction within a stream was related to local variation in vertical and horizontal hydraulic gradients experimental tracer responses in the surface stream were simulated with a one dimensional solute transport model with inflow and storage components otis model derived measures of hydrological retention showed a corresponding increase with increasing hydraulic conductivity to assess the temporal variability of hydrological retention solute injection experiments were conducted in gallina creek under four seasonal flow regimes during which surface discharge ranged from baseflow 0 75 l s in october to high 75 l s during spring snowmelt model derived hydrological retention decreased with increasing discharge the results of our intersite comparison suggest that hydrological retention is strongly influenced by the geologic setting and alluvial characteristics of the stream catchment temporal variation in hydrological retention at gallina creek is related to seasonal changes in discharge highlighting the need for temporal resolution in studies of the dynamics of surface water groundwater interactions in stream ecosystems 1997 by john wiley sons ltd

dispersion of regional body waves at 100 150 km depth beneath alaska in situ constraints on metamorphism of subducted crust phase delays at high frequencies are observed in body waves that travel in the alaska slab along its strike at 100 150 km depth the delays between 2 6 hz energy and the direct 0 5 1 hz arrival are 0 5 1 5 s for p waves and 1 5 4 s for s waves such dispersion suggests a waveguide structure that parallels the slab perhaps near its top a channel that is 2 6 km thick and 2 5 5 slower than surrounding mantle can explain the observations the thickness of the layer is comparable to that of subducted oceanic crust or somewhat thinner the layer may be crust that is slow at these depths the required velocity anomaly is too small to be due to a continuous layer of metastable gabbro yet too large to represent an eclogite layer it may indicate a mixture of the two or persistence of hydrated mineral assemblages to depth

upper mantle velocity structure estimated from ps converted wave beneath the north eastern japan arc summary the upper boundary of the descending oceanic plate is located by using ps waves converted from p to s at the boundary in the tohoku district the north eastern part of honshu japan the observed ps p time data are well explained by a two layered oceanic plate model composed of a thin low velocity upper layer whose thickness is less than 10 km and a thick high velocity lower layer the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle the estimated location of the upper boundary is just above the upper seismic plane of the double planed deep seismic zone this result indicates that events in the upper seismic plane at least in the depth range from 60 to 150 km occur within the thin low velocity layer on the surface of the oceanic plate

convective transport within stable river sediments local pressure variations of the order of 100 1000 n m2 can be observed between the upstream and downstream faces of the typically triangular shaped dunelike sediment structures that form at the sediment water interface of rivers laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment numerical modeling of the in bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions the laboratory experiments and numerical simulation of the in bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert nonsorbed contaminants in stable sediments in bed peclet numbers were of the order of 100 1000 indicating the negligible influence of diffusion under the conditions examined

rupture velocity estimation of large deep focus earthquakes surrounding japan 1 rupture velocity is an important source parameter which is often difficult to determine especially for deep focus earthquakes where there is usually limited near source information to help overcome this problem we developed a new method to estimate rupture velocities of deep focus earthquakes with better resolution we first carry out teleseismic p waveform inversions to determine slip distributions for a range of rupture velocities on the two nodal planes then forward modeling of regional data is performed using the slip distributions determined in the teleseismic inversions to estimate the rupture velocity using this method we attempted to determine the rupture velocities of large deep focus earthquakes surrounding japan which are well recorded on teleseismic and regional networks empirical green functions are used for both the teleseismic and regional analyses although it is difficult to determine the rupture velocity from only the teleseismic data the analyses including regional data show clear difference which can resolve the rupture velocity and fault geometry for three deep earthquakes we obtained rupture velocities of about 1 2 km s which correspond to 20 40 of the shear wave velocity and are much slower than typical values for shallow earthquakes

p wave velocity structure inside the subducting pacific plate beneath the japan region abstract little is known of the internal structure of the subducting pacific plate previous studies suggest the existence of an intermediate boundary within the subducting slab the low density of seismological stations in oceanic regions has prevented high resolution studies recently seismological stations in japan have accumulated digitally recorded seismograms beneath the kanto region central japan the pacific plate is subducting with a high inclination compared with that of the tohoku region northern japan the ray paths from deep earthquakes to seismological stations are expected to penetrate more inner parts of the subducting plate this region is suitable to resolve the velocity structure within the plate in this study travel time residuals and seismograms of the deep focus earthquakes that occurred beneath the kinki region southern japan are used to constrain various parameters related to the velocity structure model within the slab the seismograms of deep focus earthquakes at the geographically restricted stations located in the kanto region central japan show a remarkable high frequency later arrival of the p wave the later arrival was studied and recognized as the reflected wave at the intermediate boundary inside the plate the velocity structure within the plate is also studied our best fit model has a velocity of jeffreys bullen j b model plus 1 5 in the upper layer and j b plus 2 5 in the lower layer

characterization of transport in an acidic and metal rich mountain stream based on a lithium tracer injection and simulations of transient storage physical parameters characterizing solute transport in the snake river an acidic and metal rich mountain stream near montezuma colorado were variable along a 5 2 km study reach stream cross sectional area and volumetric inflow each varied by a factor of 3 because of transient storage the residence time of injected tracers in the snake river was longer than would be calculated by consideration of convective travel time alone distributed inflows along the stream were a significant source of in stream chemical variations these transport characteristics of the snake river were established on the basis of the assumption of lithium as an ideally conservative tracer and use of simulations of advection dispersion and transient storage evaluations of the validity of this combined tracer and simulation approach lend confidence to the estimation of the physical transport parameters but further development is warranted for methods of onsite transport experimentation in hydrologically complex chemically reactive environments

effect of instream wood on vertical water flux in low energy sand bed flume experiments 1 in streams interaction of current with bed forms and solid objects can produce vertical water flux across the streambed instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams in the present experimental study in large circulating flumes simulating sand bed streams with low constant slope we compared systems with and without natural quantities of wood the introduction of wood resulted in the production of irregular bed forms as a result flow resistance tripled and vertical water flux across the streambed increased by a factor of 1 8 to 2 5 the mixing depth was spatially variable and seemed unrelated to the local bed form after the addition of wood surface water mixed deeper into the sediments and the total sediment pore water volume involved in mixing increased by factors of 1 2 to 1 5 the practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams

a seismological constraint on the depth of basalt eclogite transition in a subducting oceanic crust the oceanic crust primarily has a basaltic composition1 2 which must transform into eclogite on subduction of the oceanic crust beneath continents3 4 there has been a considerable debate about the role of the basalt eclogite transformation in driving lithospheric plate motion5 and in the thermal regieme of subducting plates6 how important this transformation is in tectonics critically depends on the depth of transformation which is affected by factors such as temperature7 8 bulk rock chemical composition2 water content9 and perhaps stress environment becuase it would be practically impossible to evaluate all these factors correctly we attempt here to constrain the transformation depth by a more direct seismological method

the effects of metastable olivine α wedge in subducted slabs on theoretical seismic waveforms of deep earthquakes 1 assuming three kinds of materials 100 olivine mg0 89fe0 11 2sio4 pyrolite and piclogite as composition of the upper mantle we constructed pressure temperature dependent seismic velocity structure models in the upper mantle beneath a subduction zone for this purpose we employed values of physical properties of composite minerals newly determined by using a genetic algorithm ga and obtained the thermal structure beneath the subduction zone as a numerical solution of a two dimensional 2 d thermal fluid coupled problem furthermore we investigated the effects of a metastable olivine wedge in subducted slabs on theoretical seismic waveforms of deep earthquakes which propagate through the velocity structure by solving the p sv problem numerically the effects of center frequency of the excited waves at hypocenters focal mechanism location of hypocenter upper mantle compositions values of physical properties a dip angle of subducting slabs anelastic attenuation subducting velocity and depth of deep earthquakes on seismic waveforms were investigated in detail theoretical seismograms at the earth s surface indicate that coda waves with small amplitudes of duration time of 20 30 s appear following direct p and s waves for models with the metastable olivine wedge inside the slabs the coda waves can be explained by the excitation by reflections and conversions at a large seismic velocity discontinuity between the metastable olivine wedge and the surrounding slab for models with center frequency of 0 25 hz purer olivine composition a faster subducting velocity and focal depth of 500 km waves with larger amplitudes were excited at the discontinuity the results of this study may give important clues to detect the existence of the metastable olivine wedge from seismological observations

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

subduction zone guided waves and the heterogeneity structure of the subducted plate intensity anomalies in northern japan 1 the subducting pacific plate acts an efficient waveguide for high frequency signals and often produces anomalously large intensity on the eastern seaboard of northern japan during deep earthquakes the waveform records in the region of high intensity show a low frequency f 2 hz later arrivals with a long coda this behavior is not explained by a simple subduction zone model comprising a high velocity plate with low attenuation from the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the pacific subduction zone we demonstrate that the high frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0 5 km in thickness the standard deviation of wave speed fluctuations from the averaged background model is about 2 this new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness but low frequency waves with long wavelengths can easy tunnel through such lamina structure the result is frequency selective propagation characteristics with a faster low frequency phase followed by large and high frequency signals with very long coda a low wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high frequency coda three dimensional simulations using the earth simulator supercomputer for modeling of high frequency seismic wave propagation in the pacific subduction zone including plate heterogeneity clearly demonstrate the scattering waveguide effects for high frequency seismic waves traveling in the plate the region of large intensity for the heterogeneous model migrates away from the hypocenter into northern japan with an elongated zone along the pacific coast almost comparable to the observations from deep events in the pacific plate

determining in channel dead zone transient storage by comparing solute transport in a bedrock channel alluvial channel sequence oregon 1 current stream tracer techniques do not allow separation of in channel dead zone e g eddies and out of channel hyporheic transient storage yet this separation is important to understanding stream biogeochemical processes we characterize in channel transient storage with a rhodamine wt solute tracer experiment in a 304 m cascade pool type bedrock reach with no hyporheic zone we compare the solute breakthrough curve btc from this reach to that of an adjacent 367 m alluvial reach with significant hyporheic exchange in the bedrock reach transient storage has an exponential residence time distribution with a mean residence time of 3 0 hours and a ratio of transient storage to stream volume of 0 14 demonstrating that at moderate discharge bedrock in channel storage zones provide a small volume of transient storage with substantial residence time in the alluvial reach though pools are similar in size to those in the bedrock reach transient storage has a power law residence time distribution with a mean residence time of 100 hours estimated at nearly 1200 hours and a ratio of storage to stream volume of 105 because the in channel hydraulics of bedrock reaches are simpler than alluvial step pool reaches the bedrock results are probably a lower end member with respect to volume and residence time though they demonstrate that in channel storage may be appreciable in some reaches these results suggest that in stream dead zone transient storage may be accurately simulated by exponential rtds but that hyporheic exchange is better simulated with a power law rtd as a consequence of more complicated flow path and exchange dynamics