extreme waves in shallow and intermediate water depths this paper concerns the description of large transient waves in shallow and intermediate water depths it builds upon recent advances in the description of deep water waves and provides the first quantitative comparisons with a new kinematic model which has hitherto only been validated in deep water conditions a new series of experimental observations is presented in which the wave components within a random or irregular sea state are focused to produce a large transient wave group comparisons with both linear and second order solutions suggest that non linear wave wave interactions produce a steeper wave envelope in which the central wave crest is higher and narrower while the adjacent wave troughs are broader and less deep spectral analysis of the measured water surface elevation suggest that in addition to the development of significant long wave energy there is also a transfer of energy to the shorter high frequency harmonics this energy redistribution has a significant effect upon the underlying kinematics in particular the near bed velocities are shown to be in good agreement with the second order solution which includes the long wave or frequency difference terms first identified by longuet higgins and stewart furthermore the near surface kinematics are shown to be highly non linear indeed a linear wave theory based upon a correct representation of the freely propagating linear harmonics is generally found to under estimate the near surface horizontal velocity however if the linear calculations are based upon a measured wave spectrum the kinematic predictions suffer from high frequency contamination and require empirical correction in contrast the non linear numerical model presented by baldock and swan provides a good description of the measured kinematics over the entire water depth

transient landscapes at fault tips 1 fault growth produces patterns of displacement and slip rate that are highly variable in both space and time this transience is most pronounced near fault tips where along strike displacement gradients vary in time as the fault array lengthens we use a set of statistical and field observations to quantify the response of catchments and their associated fans in three large normal fault arrays to transient patterns of displacement and slip rate catchments near the fault tips show distinct scaling of channel slope with drainage area compared with catchments near the strike center this scaling becomes uniform beyond about 10 km from the fault tips and is therefore like footwall relief largely decoupled from the fault displacement profile the estimated catchment response times to a change in slip rate also vary between fault tips and strike center the response times for tip catchments are much longer than the inferred time since fault activity began indicating that they are unlikely to be in equilibrium with the current fault displacement field this disequilibrium combined with the decoupling of slope area scaling from displacement indicates that landscapes are most sensitive to fault activity near fault tips active faults characterized by along strike variation in slip rate thus provide excellent opportunities to explore the transient response of landscapes to tectonic forcing

geological modelling from field data and geological knowledge part ii modelling validation using gravity and magnetic data inversion the analysis of multiple data sets is required to select a realistic 3d geological model among an infinite number of possibilities an inverse method that aims at describing the 3d geometry of geological objects is presented the method takes into account the geology and the physical properties of rocks while respecting the topological properties of an a priori model the a priori model is built from the geological data set and its geometry is largely dependent upon assumptions about inaccessible geology at depth this method referred to as total litho inversion is a generalized 3d inversion that results in quantifying the lithology and the distribution of rock property in a probabilistic way its application is demonstrated through i a simple synthetic case and ii the relative distribution characterization of granites and diorites in an orogenic domain

3d stochastic inversion of gravity data using cokriging and cosimulation a new application has been developed based on geostatistical techniques of cokriging and conditional simulation for the 3d inversion of gravity data including geologic constraints the necessary gravity density and gravity density covariance matrices are estimated using the observed gravity data then the densities are cokriged or simulated using the gravity data as the secondary variable the model allows noise to be included in the observations the method is applied to two synthetic models a short dipping dike and a stochastic distribution of densities then some geologic information is added as constraints to the cokriging system the results show the ability of the method to integrate complex a priori information the survey data of the matagami mining camp are considered as a case study the inversion method based on cokriging is applied to the residual anomaly to map the geology through the estimation of the density distribution in this region the results of the inversion and simulation methods are in good agreement with the surface geology of the survey region

ellipsoid geoid gravity geodesy and geophysics geophysics uses gravity to learn about the density variations of the earth s interior whereas classical geodesy uses gravity to define the geoid this difference in purpose has led to some confusion among geophysicists and this tutorial attempts to clarify two points of the confusion first it is well known now that gravity anomalies after the free air correction are still located at their original positions however the free air reduction was thought historically to relocate gravity from its observation position to the geoid mean sea level such an understanding is a geodetic fiction invalid and unacceptable in geophysics second in gravity corrections and gravity anomalies the elevation has been used routinely the main reason is that before the emergence and widespread use of the global positioning system gps height above the geoid was the only height measurement we could make accurately i e by leveling the gps delivers a measurement of height above the ellipsoid in principle in

systematic variation of bedrock channel gradients in the central oregon coast range implications for rock uplift and shallow landsliding abstract in tectonically active regions bedrock channels play a critical role in dictating the pace of landscape evolution models of fluvial incision into bedrock provide a means of investigating relationships between gradients of bedrock channels and patterns of active deformation variations in lithology orographic precipitation sediment supply and erosional processes serve to complicate tectonic inferences derived from morphologic data yet most tectonically active landscapes are characterized by these complexities in contrast the central oregon coast range ocr which is situated above the cascadia subduction zone has experienced rock uplift for several million years did not experience pleistocene glaciation boasts a relatively uniform lithology and exhibits minor variations in precipitation although numerous process based geomorphic studies suggest that rates of erosion across the ocr are relatively constant it has not been demonstrated that bedrock channel gradients in the region exhibit spatially consistent values analysis of broadly distributed small drainage basins 5 20 km in the central ocr enables us to explore regional variability in bedrock channel gradients resulting from differential rock uplift or other sources consistent with previous studies that have documented local structural control of deformed fluvial terraces in the western portion of our study area our data reveal a roughly 20 km wide band of systematically elevated channel slopes roughly twice the background value roughly coincident with the strike of n s trending mapped folds although many factors could feasibly generate this pattern including variable rock strength precipitation gradients or temporal or spatial variations in forearc deformation the elevated bedrock channel slopes likely reflect differential rock uplift related to activity of local structures importantly our analysis suggests that rock uplift and erosion rates may vary systematically across the ocr although our calculations were focused on the fluvial dominated portion of study basins our results have implications for upstream areas including unchanneled valleys that often serve as source areas for long runout debris flows zero order basins or topographic hollows within the n s trending band of elevated channel slopes tend to be steeper than adjacent areas and may experience more frequent evacuation by shallow landsliding thus this region of the ocr may be highly sensitive to land use practices and high intensity rainstorms

structures in segment boundary zones of the lost river and lemhi faults east central idaho geologic mapping and structural analysis of the lost river and lemhi normal faults in east central idaho suggest that many rupture segment boundaries previously inferred from geomorphic data coincide with two classes of structural complexities 1 zones of distributed faults and steps or jogs in the range front faults and 2 intersections with preexisting eocene to oligocene cross faults at 10 15 km depth segment boundaries contain as many as 13 fault splays and are as much as 13 km long and 5 6 km wide in plan view in contrast simple fault traces characterize the range front faults in the interiors of segments thus segment boundaries of normal faults are broad zones of intersecting faults not discrete points the structural data further imply that segment boundaries contain large volumes of fractured and faulted rock and that zones of distributed normal faults have influenced rupture propagation and arrest along these two normal faults intersections of preexisting cross faults and range front faults may also have influenced the locations of rupture boundaries along the lost river and lemhi faults downdip projections of preexisting eocene to oligocene normal faults in the footwall of the lost river and lemhi faults may coincide with four or five segment boundary zones at about 15 km depth the depth at which large earthquakes nucleate in the basin and range province structural analyses also show that some cross faults which coincide with segment boundary zones at the surface are distant from these zones at depth conversely some potentially significant structures present at depth are far removed from the segment boundary zone at the surface thus a close spatial relationship between cross faults and segment boundary zones at the surface cannot prove or disprove a genetic relationship between these features because the near surface geometry of segment boundary zones may differ dramatically from the subsurface geometry of the zones where cross faults define segment boundaries the enhanced fracture toughness of preexisting fault planes and their damage zones may impede or arrest rupture on younger crosscutting faults

an experimental study on wave forces on a vertical cylinder due to spilling breaking and near breaking wave groups abstract this paper highlights the importance of spilling breaking waves in the design of offshore structures although wave loading on offshore structures due to non breaking waves has been extensively studied wave loading due to breaking waves is uncertain and not very well understood plunging breaking waves in deep water are very unusual whereas spilling breaking waves are very common in extreme seas nevertheless no significant research efforts have been made to study the effects of spilling breaking waves the present study addresses this comparing the wave loading from highly nonlinear non breaking waves and spilling breaking waves focused wave groups have been used to generate the non breaking and spilling breaking wave conditions in a wave tank the experiments have shown that spilling breaking waves generate significantly larger forces on the cylindrical model than highly non linear non breaking waves of equivalent size this is shown to be due to the direct excitation at high frequency as well as the resonant and impact excitation of higher natural frequency modes it is concluded that spilling breaking waves can generate very significant forces and should therefore be considered in the design of offshore structures

history and controls of subsidence in the late cretaceous tertiary great valley forearc basin california abstract analysis of the upper cretaceous tertiary fill of the great valley forearc basin of california reveals a complicated history of subsidence partitioned in time and space western oceanward parts of the basin record subsidence then uplift in apparent response to the angle and rate of descent of the underlying subducting plate specifically uplift in the forearc basin corresponds to the onset of the laramide orogeny and inferred low angles of subduction in contrast eastern arcward parts of the basin display subsidence histories suggestive of thermal contraction and compatible with continentward migration of sierran arc magmatism in the late cretaceous these results imply that subsidence histories of forearc basins are likely to be much more complicated and less predictable than those of rifted continental margins and foreland basins where single subsidence mechanisms predominate and time varying subduction is not an underlying controlling factor

an exact solution for the gravity curvature bullard b correction the complete bouguer reduction includes in addition to the simple bouguer slab correction bullard a both curvature bullard b and terrain bullard c corrections a new closed form formula for the curvature correction is derived for which the calculated values differ from those published by swick by more than 0 5 mgal for high elevations these corrections reduce those of an infinite slab bullard a to that of a spherical cap having a surface radius of 166 7 km the spherical cap produces a lesser effect than the infinite slab because of the truncation of that part of the slab above the earth and extending to infinity but it produces a greater effect than the slab because of subslab earth resulting from curvature the physical significance of the correction lies in the combination of these two differences which are each a function of elevation the bullard b surface radius 166 7 km outer radius of the hayford bowie system is reaffirmed by the exact formula to be appropriate for exploration su

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

the growth of fault bounded tilt blocks a series of uniformly tilted fault bounded blocks is a common feature in actively extending regions such as the basin and range province if the tilted blocks were produced by rigid domino style rotation one would predict large voids at either end of a series of these blocks using tilt data and a simple flexural calculation we suggest that much of the apparent rigid behavior could also be produced by internal block deformation in our model of normal fault growth isostatic elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults resulting in the appearance of a tilted rigid block we present tilt data sampled at varying distances from several block defining faults within the northeast basin and range province tilt measurements between a series of 30 km spaced block defining faults are found to be uniform while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km using a simple flexural calculation for internal block deformation we show that for this region the patterns of tilt are consistent with a flexural length scale of 8 12 km and deflections of 2 4 km these estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies

time scales of tectonic landscapes and their sediment routing systems abstract in regions undergoing active tectonics the coupling between the tectonic displacement field the overlying landscape and the redistribution of mass at the earth9s surface in the form of sediment routing systems is particularly marked and variable coupling between deformation and surface processes takes place at a range of scales from the whole orogen to individual extensional fault blocks or contractional anticlines at the large scale the attainment of a steady state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system with a time scale dependent on the vigour of the erosional system generally in the range 10 6 10 7 years the catchment fan systems associated with extensional fault blocks and basins of the western usa are valuable natural examples to study the coupling between tectonic deformation landscape and sediment routing systems even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation these response times originate from the development of uniform steady state relief during the accumulation of displacement on a normal fault c 10 6 years the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate c 10 6 years or the relaxation times of the integrated catchment fan system in response to changes in climatic and tectonic boundary conditions 10 5 10 6 years the presence of extensive bedrock or alluvial piedmonts increases response times significantly the sediment efflux of a mountain catchment is a boundary condition for far field fluvial transport but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre fluvial systems appear to act as buffers to incoming sediment supply signals with a diffusive time scale c 10 5 10 6 years dependent on the length of the system and the extent of its floodplains stream channels and proximal gravel fans the vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems landscapes are best differentiated as buffered or reactive depending on the ratio of the response time to the repeat time of the perturbation furthermore landscapes may be regarded as steady or transient depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions the response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture

linkage between turbulent kinetic energy waves and suspended sediment concentrations in the nearshore zone abstract knowledge about the tradeoffs among turbulent kinetic energy tke waves and suspended sediment concentrations sscs in the nearshore zone is relevant for understanding beach morphodynamics at different temporal and spatial scales a field measurement lasting for nearly three tidal cycles was conducted to holistically discern couplings between tke waves and sscs with further evaluation of the relative significance of tke and waves on sscs under various wave conditions over a meso macro tidal beach yintan to the north of beibu gulf china the results showed a dramatic increase in wave groupiness intensity from the shoaling wave condition to the breaking wave condition and a clear decrease further into the surf bore condition the near bed tkes under the surf bore condition were an order of magnitude larger than those under the breaking and shoaling wave conditions at the measurement position the averaged sscs in the near bed approximately 10 cm under the surf bore condition were 1 5 and 4 5 times larger than those under breaking and shoaling wave conditions respectively the variations in relative wave height were a decisive indicator for the differences in tke intensities among different wave conditions while the occurrence of peak tkes at the wave front within the intrawave cycle was associated with flow acceleration regardless of wave conditions mean sscs were well correlated with waves in terms of both incident wave scale and wave group scale which was limited to the shoaling wave condition and the occurrence of near bed intrawave peak sscs was always related to the offshore wave phase further tke contributed more effectively to sediment suspension at the wave group scale than at the incident wave scale especially under broken wave condition among the hydrodynamic factors tke played the most important role in the variations in sscs for all wave conditions flow acceleration served as the second most important factor under the broken wave condition while wave group single wave and advection were equivalent and less important factors for sscs

an experimental study of large waves in intermediate and shallow water depths part i wave height and crest height statistics abstract this paper describes a series of laboratory observations undertaken in a purpose built wave flume the objective of the study was to simulate a range of realistic ocean spectra evolving over a number of mild bed slopes m the chosen sea states allowing a systematic investigation of the role of local water depth spectral peak period significant wave height spectral bandwidth and bed slope the focus of the present paper lies in the statistical distribution of both the wave height h and the wave crest elevation c the laboratory data being used to provide both an understanding of the importance of the various parameters and an assessment of the commonly adopted design distributions the results of the study have shown that both the wave height and the crest height distributions are primarily dependent upon the effective water depth k p d where k p is the wave number corresponding to the spectral peak and d the water depth and the sea state steepness 1 2 h s k p where h s is the significant wave height conversely the distributions are independent of the mild bed slope for m 1 100 and the spectral bandwidth the latter result being very different to that which arises in deep water following detailed comparisons across a wide parameter range the wave height distributions in the deeper water depths k p d 1 0 are shown to be in reasonable agreement with the forristall 1978 and glukhovskii 1966 distributions the latter becoming more important as the proportion of breaking waves increases as the water depth reduces the mendez et al 2004 distribution as well as the battjes groenendijk 2000 composite weibull distribution cwd become increasingly applicable however comparisons between sea states of varying steepness but with all other parameters held constant suggest that the empirical parameters on which the latter solution is based may not be universally applicable finally in the shallowest water depths k p d 0 5 none of the existing distributions provide a good description of the measured data all leading to an over estimate of the largest wave heights

a mechanism to explain rift basin subsidence and stratigraphic patterns through fault array evolution rift basin stratigraphy commonly records an early stage of slow subsidence followed by an abrupt increase in subsidence rate the physical basis for this transition is not well understood although an increase in extension rate is commonly implied here a numerical fault growth model is used to investigate the influence of segment linkage on fault displacement rate patterns along an evolving normal fault array the linkage process we describe is controlled by a stress feedback mechanism which leads to enhanced growth of optimally positioned faults model results indicate that even with constant extension rates slow displacement rates prevail during an initial phase of distributed extension followed by an increase in displacement rates as strain becomes localized on linked fault arrays this is due to the dynamics of fault interactions rather than mechanical weakening comparison of model simulations with rift basin subsidence and stratigraphic patterns in the gulf of suez and north sea suggests that the occurrence and timing of rapid basin deepening can be explained by the mechanics of fault zone evolution without invoking a change in regional extension rates

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

on the average shape of the largest waves in finite water depths abstractthis paper investigates the average shape of the largest waves arising in finite water depths specifically the largest waves recorded in time histories of the water surface elevation at a

forward modeling of gravity data using geostatistically generated subsurface density variations abstractusing geostatistical models of density variations in the subsurface constrained by geologic data forward models of gravity anomalies can be generated by discretizing the subsurface and calculating the cumulative effect of each cell pixel the results of such stochastically generated forward gravity anomalies can be compared with the observed gravity anomalies to find density models that match the observed data these models have an advantage over forward gravity anomalies generated using polygonal bodies of homogeneous density because generating numerous realizations explores a larger region of the solution space the stochastic modeling can be thought of as dividing the forward model into two components that due to the shape of each geologic unit and that due to the heterogeneous distribution of density within each geologic unit the modeling demonstrates that the internally heterogeneous distribution of density within each geologic unit can contribute significantly to the resulting calculat

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

sedimentology of the debris flow dominated warm spring canyon alluvial fan death valley california facies analysis of widely distributed exposures of the 32 6 km2 and 8 1 km long warm spring canyon fan central death valley shows that it has been built principally by debris flow deposits these deposits were derived from a mature panamint range catchment mostly underlain by precambrian mudrock quartzite and dolomite stacked clast rich and matrix supported debris flow lobes of slightly bouldery muddy pebble cobble gravel in beds 20 150 cm thick dominate the fan from apex to toe accounting for 75 98 of most exposures interstratified with the debris flows are less abundant 2 25 of cuts thinner 5 30 cm and more discontinuous beds of clast supported and imbricated pebble cobble gravel deposited by overland flows and gully flows this facies formed by the surficial fine fraction water winnowing of the debris flows primarily during recessional flood stage of the debris flow events two other facies associations make up a small part of the fan the incised channel tract consists of a 250 m wide clast supported ribbon of irregularly to thickly bedded boulder pebble cobble gravel nested within debris flow deposits this channel fill is oriented generally perpendicular to the panamint range front it formed by extensive erosion and winnowing of debris flows deposited within the incised channel into which all water discharge from the catchment is funnelled the limited presence of this facies only straddling the present incised channel indicates that this channel overall has maintained a consistent position on the fan except for slight lateral shifts some caused by strike slip offset fault offset temporarily closed the upper incised channel causing recessional debris flow mud to be ponded behind the dam the other local facies assemblage consists of subrounded to rounded moderately sorted pebble gravel in low angle cross beds that slope both basinwards and fanwards this gravel was deposited in beachface backshore and shoreface barrier spit environments that developed where lake manly impinged on the warm spring fan during late pleistocene time these deposits straddle headcuts into and were derived from erosion of the debris flow deposits wave energy sorted finer sediment from the shore zone concentrated coarser sediment and rounded the coarse to very coarse pebble fraction by selective reworking

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

timing and patterns of debris flow deposition on shepherd and symmes creek fans owens valley california deduced from cosmogenic 10be debris flow fans on the western side of owens valley california show differences in their depths of fan head incision and thus preserve significantly different surface records of sedimentation over glacial interglacial cycles we mapped fan lobes on two fans symmes and shepherd creek based on the geometry of the deposits using field observations and high resolution airborne laser swath mapping alsm data and established an absolute fan lobe chronology by using cosmogenic radionuclide exposure dating of large debris flow boulders while both fans and their associated catchments were subject to similar tectonic and base level conditions the shepherd creek catchment was significantly glaciated while that of symmes creek experienced only minor glaciation differences in the depth of fan head incision have led to cosmogenic surface age chronologies that differ in the length of the preserved depositional records symmes creek fan preserves evidence of exclusively holocene deposition with cosmogenic 10be ages ranging from 8 to 3 ka in contrast the shepherd creek fan surface was formed by late pleistocene and holocene debris flow activity with major deposition between 86 74 33 15 and 11 3 ka these age constraints on the depositional timing in owens valley show that debris flow deposition in owens valley occurred during both glacial and interglacial periods but may have been enhanced during marine isotope stages 4 and 2 the striking differences in the surface record of debris flow deposition on adjacent fans have implications for the use of fan surfaces as paleoenvironmental recorders and for the preservation of debris flow deposits in the stratigraphic record

a healing reloading feedback control on the growth rate of seismogenic faults spatial and temporal variations in the growth rates of faults are explained in terms of a stress feedback mechanism operating in the seismogenic upper crust it is based on the idea that seismic rupture of a fault perturbs the surrounding stress field advancing the occurrence of future earthquakes on some faults that are optimally oriented while relaxing stress levels on others if post slip healing is geologically rapid then the earthquakes that are thus induced will contribute to reloading along the earlier rupture zone because of the symmetry of the optimal geometry a positive feedback is set up so that even in areas that are undergoing uniform tectonic straining some faults develop higher displacement rates and grow more rapidly while others experience reduced rates or become inactive using a thin plate elastic model for lithospheric scale faulting it is shown that this healing reloading feedback mechanism drives rapid localisation and the formation of major through going faults moving at plate boundary velocities enhanced displacement rates compared to an isolated fault develop shortly after the onset of deformation along those faults which are optimally positioned in the overall fault population thus the formation of a new plate boundary fault zone is predetermined and is a consequence of rather than the precursor of preferentially high displacement rates also fault segments located at points of rupture symmetry e g the central portion of a fault zone are reloaded more frequently and develop higher displacement rates and consequently have longer segment lengths and or larger displacement to length ratios episodic fault movement through time is a general feature of the model these predictions are consistent with available field observations over a wide range of scales thus elastic brittle failure and healing appear to be important rheological components of the lithosphere on long time scales 104 106 y as well as on the time scale of earthquake recurrence

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

constraints on north american plate velocity from the yellowstone hotspot deformation field oceanic hotspot tracks generally indicate that the mantle plumes that give rise to them are fixed in position relative to a lower mantle reference frame for timespans of 100 myr1 3 it has not been clear whether continental hotspots are equally stable for example there is evidence that the velocity of the yellowstone hotspot has been quite irregular with respect to the north ameri can plate over the past 16 myr4 7 but measurements of its velocity based on caldera locations have been too uncertain and irregular to be definitive here i describe a new method of obtaining the plume velocity which uses the broader lithospheric effects of the hotspot rather than the locations of individual calderas for the past 10 myr the results indicate a constant north american plate velocity of 2 2 cm yr 1 which agrees with independent estimates from global plate motion inversions8 9 this velocity is considerably lower than previous estimates obtained from caldera locations and clearly differs from the much higher but less well constrained velocities of the previous 6 myr refs 5 7