Characterization of dipping fractures in a transverselyisotropic background

Although it is believed that natural fracture sets predominantly have near‐vertical orientation, oblique stresses and some other mechanisms may tilt fractures away from the vertical. Here, we examine an effective medium produced by a single system of obliquely dipping rotationally invariant fractures embedded in a transversely isotropic with a vertical symmetry axis (VTI) background rock. This model is monoclinic with a vertical symmetry plane that coincides with the dip plane of the fractures. Multicomponent seismic data acquired over such a medium possess several distinct features that make it possible to estimate the fracture orientation. For example, the vertically propagating fast shear wave (and the fast converted PS‐wave) is typically polarized in the direction of the fracture strike. The normal‐moveout (NMO) ellipses of horizontal reflection events are co‐orientated with the dip and strike directions of the fractures, which provides an independent estimate of the fracture azimuth. However, the polarization vector of the slow shear wave at vertical incidence does not lie in the horizontal plane – an unusual phenomenon that can be used to evaluate fracture dip. Also, for oblique fractures the shear‐wave splitting coefficient at vertical incidence becomes dependent on fracture infill (saturation). A complete medium‐characterization procedure includes estimating the fracture compliances and orientation (dip and azimuth), as well as the Thomsen parameters of the VTI background. We demonstrate that both the fracture and background parameters can be obtained from multicomponent wide‐azimuth data using the vertical velocities and NMO ellipses of PP‐waves and two split SS‐waves (or the traveltimes of PS‐waves) reflected from horizontal interfaces. Numerical tests corroborate the accuracy and stability of the inversion algorithm based on the exact expressions for the vertical and NMO velocities.     

Effect of morphology and discharge on hyporheic exchange flows in two small streams in the Cascade Mountains of Oregon,USA

Stream‐tracer injections were used to examine the effect of channel morphology and changing stream discharge on hyporheic exchange flows. Direct observations were made from well networks to follow tracer movement through the hyporheic zone. The reach‐integrated influence of hyporheic exchange was evaluated using the transient storage model (TSM) OTIS‐P. Transient storage modelling results were compared with direct observations to evaluate the reliability of the TSM. Results from the tracer injection in the bedrock reach supported the assumption that most transient storage in headwater mountain streams results from hyporheic exchange. Direct observations from the well networks in colluvial reaches showed that subsurface flow paths tended to parallel the valley axis. Cross‐valley gradients were weak except near steps, where vertical and cross‐valley hydraulic gradients indicated a strong potential for stream water to downwell into the hyporheic zone. The TSM parameters showed that both size and residence time of transient storage were greater in reaches with a few large log‐jam‐formed steps than in reaches with more frequent, but smaller steps. Direct observations showed that residence times in the unconstrained stream were longer than in the constrained stream and that little change occurred in the location and extent of the hyporheic zone between low‐ and high‐baseflow discharges in any of the colluvial reaches. The transient storage modelling results did not agree with these observations, suggesting that the TSM was insensitive to long residence‐time exchange flows and was very sensitive to changes in discharge. Disagreements between direct observations and the transient storage modelling results highlight fundamental problems with the TSM that confound comparisons between the transient storage modelling results for tracer injections conducted under differing flow conditions. Overall, the results showed that hyporheic exchange was little affected by stream discharge (at least over the range of baseflow discharges examined in this study). The results did show that channel morphology controlled development of the hyporheic zone in these steep mountain stream channels. Copyright © 2005 John Wiley & Sons, Ltd.     

Consistency of stress state,locations and source mechanisms of events induced by hydraulic fracturing: downhole monitoring

We present results of processed microseismic events induced by hydraulic fracturing and detected using dual downhole monitoring arrays. The results provide valuable insight into hydraulic fracturing. For our study, we detected and located microseismic events and determined their magnitudes, source mechanisms and inverted stress field orientation. Event locations formed a distinct linear trend above the stimulated intervals. Source mechanisms were only computed for high‐quality events detected on a sufficient number of receivers. All the detected source mechanisms were dip‐slip mechanisms with steep and nearly horizontal nodal planes. The source mechanisms represented shear events and the non‐double‐couple components were very small. Such small, non‐double‐couple components are consistent with a noise level in the data and velocity model uncertainties. Strikes of inverted mechanisms corresponding to the nearly vertical fault plane are (within the error of measurements) identical with the strike of the location trend. Ambient principal stress directions were inverted from the source mechanisms. The least principal stress, σ₃, was determined perpendicular to the strike of the trend of the locations, indicating that the hydraulic fracture propagated in the direction of maximum horizontal stress. Our analysis indicated that the source mechanisms observed using downhole instruments are consistent with the source mechanisms observed in microseismic monitoring arrays in other locations. Furthermore, the orientation of the inverted principal components of the ambient stress field is in agreement with the orientation of the known regional stress, implying that microseismic events induced by hydraulic fracturing are controlled by the regional stress field.     

Sensitivity of time-lapse seismic to reservoir stress path

The change in reservoir pore pressure due to the production of hydrocarbons leads to anisotropic changes in the stress field acting on the reservoir. Reservoir stress path is defined as the ratio of the change in effective horizontal stress to the change in effective vertical stress from the initial reservoir conditions, and strongly influences the depletion‐induced compaction behaviour of the reservoir. Seismic velocities in sandstones vary with stress due to the presence of stress‐sensitive regions within the rock, such as grain boundaries, microcracks, fractures, etc. Since the response of any microcracks and grain boundaries to a change in stress depends on their orientation relative to the principal stress axes, elastic‐wave velocities are sensitive to reservoir stress path. The vertical P‐ and S‐wave velocities, the small‐offset P‐ and SV‐wave normal‐moveout (NMO) velocities, and the P‐wave amplitude‐versus‐offset (AVO) are sensitive to different combinations of vertical and horizontal stress. The relationships between these quantities and the change in stress can be calibrated using a repeat seismic, sonic log, checkshot or vertical seismic profile (VSP) at the location of a well at which the change in reservoir pressure has been measured. Alternatively, the variation of velocity with azimuth and distance from the borehole, obtained by dipole radial profiling, can be used. Having calibrated these relationships, the theory allows the reservoir stress path to be monitored using time‐lapse seismic by combining changes in the vertical P‐wave impedance, changes in the P‐wave NMO and AVO behaviour, and changes in the S‐wave impedance.     

Wave‐driven inertial oscillations

Abstract

In a nonrotating system, the shear Reynolds stresses exerted by surface or internal gravity waves vanish on account of the exact quadrature between the horizontal and vertical orbital velocities. It is shown that a rotation of the system induces small in‐phase perturbations, resulting in a mean Reynolds stress which can generate low frequency currents. If both the wave field and the ocean are homogeneous with respect to the horizontal coordinates, the low‐frequency response is an undamped inertial oscillation. If either the wave field or the ocean are weakly inhomogeneous, the oscillation disperses in the vertical and horizontal directions due to phase‐mixing of modes with closely neighboring frequencies. Other effects which produce small frequency shifts also contribute to phase‐mixing, for example the horizontal component of the Coriolis vector and nonlinear interactions with geo‐strophic currents. The analysis is based on operator representations which avoid normal mode decomposition and yield simple integro‐differential operators for each phase‐mixing process. Numerical results are presented for a continuously stratified model typical for a shallow sea (Baltic). The orders of magnitude and qualitative features are in reasonable agreement with observations.     

Weak‐anisotropy approximation for P‐wave reflection coefficient at the boundary between two tilted transversely isotropic media

Existing and commonly used in industry nowadays, closed‐form approximations for a P‐wave reflection coefficient in transversely isotropic media are restricted to cases of a vertical and a horizontal transverse isotropy. However, field observations confirm the widespread presence of rock beds and fracture sets tilted with respect to a reflection boundary. These situations can be described by means of the transverse isotropy with an arbitrary orientation of the symmetry axis, known as tilted transversely isotropic media. In order to study the influence of the anisotropy parameters and the orientation of the symmetry axis on P‐wave reflection amplitudes, a linearised 3D P‐wave reflection coefficient at a planar weak‐contrast interface separating two weakly anisotropic tilted tranversely isotropic half‐spaces is derived. The approximation is a function of the incidence phase angle, the anisotropy parameters, and symmetry axes tilt and azimuth angles in both media above and below the interface. The expression takes the form of the well‐known amplitude‐versus‐offset “Shuey‐type” equation and confirms that the influence of the tilt and the azimuth of the symmetry axis on the P‐wave reflection coefficient even for a weakly anisotropic medium is strong and cannot be neglected. There are no assumptions made on the symmetry‐axis orientation angles in both half‐spaces above and below the interface. The proposed approximation can be used for inversion for the model parameters, including the orientation of the symmetry axes. Obtained amplitude‐versus‐offset attributes converge to well‐known approximations for vertical and horizontal transverse isotropic media derived by Rüger in corresponding limits. Comparison with numerical solution demonstrates good accuracy.     

Qualitative and quantitative applications of LiDAR imagery in fluvial geomorphology

The potential for geomorphological mapping and quantitative calculations of light detection and ranging (LiDAR) data within fluvial geomorphology was studied for two river catchments within Belgium (Dijle and Amblève), which differ in physical settings and floodplain morphology. Two commercial, of‐the‐shelf LiDAR datasets with different specifications (horizontal resolution and vertical accuracy) were available for parts of the floodplains of both catchments. Real‐time kinematic (RTK) Global Positioning System (GPS) data were used as ground truth for error calculations. Qualitative analysis of LiDAR data allowed the identification of former channel patterns, levees, colluvial hillslope and fan deposits. These results were confirmed by field data, topographic surveys and historical maps. The pixel resolution proved to be an important factor in the identification of small landforms: only features with a width equal to or larger than LiDAR resolution can be detected. This poses limits on the usability of regionally available LiDAR data, which often have a horizontal resolution of several metres. The LiDAR data were also used in a quantitative analysis of channel dynamics. In the study area, the width of the Dijle River channel increased 3 m on average between 1969 and 2003. A sediment budget of channel processes for the period 1969–2003 indicated a total river bank erosion of 16·1 10³ m³ and a total within channel deposition of 7·1 10³ m³, resulting in a net river erosion of 9·0 10³ m³ or c. 0·4 Mg year^?1 per metre river length. Sequential LiDAR data can in theory be used to calculate vertical sedimentation rates, as long as there is control on the error of the reference levels used. Copyright © 2008 John Wiley and Sons, Ltd.     

THE RESPONSE OF SAG POND SEDIMENT TO THE PALEOEARTHQUAKE EVENT ON THE XIADIAN FAULT ZONE

The wedge-shaped deposit formed in front of fault scarp is called colluvial wedge. Repeated faulting by faults may produce multiple colluvial wedges, each of which represents a paleoseismic event. When there are two or more colluvial wedges, the new colluvial wedge is in sedimentary contact with the fault, while the old ones are in fault contact with the fault. The shape of colluvial wedge is usually in the form of horizontal triangle, and the sedimentary facies is usually of binary structure. The overall grain size decreases gradually from bottom to top. Soil layer generally develops on the top, and different types of soil are developed under different climate or soil environments. Another deposit in front of fault scarp is the sag pond graben. The graben in front of sag pond is generally a set of sedimentary assemblages of colluvial facies, alluvial diluvial facies and swamp facies. The area close to the fault, especially the main fault, is of colluvial facies, while the area away from the fault is of alluvial and pluvial facies and marshy facies. In an accumulative cycle, the size of the deposit decreases from bottom to top, and soil layers develop on the top or surface. Multiple pile-ups may be a marker for identifying multiple faulting events. The pile-up strata such as colluvial wedge and fault sag pond can be used as identification markers for paleoseismic events. Colluvial wedge and sag pond, as the identification markers for paleoearthquake, have been well applied to practical research. However, there is still lack of detailed research on the lithological structure and genetic evolution in the interior of colluvial wedge and sag pond sediment, meanwhile, there is still a deficiency in the analysis of the completeness and the regional characteristics of paleoearthquake by using colluvial wedge and sag pond sediment. This paper discusses the method of identifying paleoearthquake by using sag pond sediments and colluvial wedge. We discuss the lithologic combination and sedimentary evolution of sag pond and choose the surface rupture zone of the 1679 M8.0 earthquake on the Xiadian Fault as the research area. In this paper, the distribution range and filling sequence of sag pond are analyzed, using borehole exploration. Four paleoearthquake events are identified since 25ka to 12ka, based on the sag pond sediments and colluvial wedge. The in situ recurrence interval of these seismic events is 480a, 510a, 7 630a and 2 830a, respectively. The lithologic combination and sedimentary evolution law of the sag pond sediments caused by an ancient earthquake are discussed. The sag pond distribution range and filling sequence are determined by the surface elevation survey and drilling exploration. The exploratory trench exposes the sag pond filling strata sequence and lithologic combination. Based on this, we analyze the three sedimentation stages of sag pond sediments formed by a paleoearthquake event near the earthquake fault. It is believed that the filling sequence is composed from bottom to top of the colluvial wedge, the erosion surface or unconformity surface, the fine detrital sediments(containing biological debris)and paleosols. For the fault-sag ponds formed by active faults, the paleoearthquakes occurred near the unconformity or erosion surface of the sediments of the fault-plug ponds. An ancient earthquake event includes the combination of organic deposits such as sediments, clastic deposits, bioclasts, burrow, plant roots and other organic deposits on the vertical scour surface or unconformity. The time interval between two paleoseismic events is defined by two adjacent unconformities(or scour surfaces). According to the vertical facies association and chronological test results of the sediments in the Pangezhuang trough of the Xiatan Fault, four paleo-seismic events are identified since the late Pleistocene period of 25~12ka BP, with recurrence intervals of 480a, 510a, 7 630a and 2 830a, respectively.     

Effective stresses and shear failure pressure from in situ Biot's coefficient,Hejre Field,North Sea

We propose a combination of Biot's equations for effective stress and the expression for shear failure in a rock to obtain an expression for minimum pore pressure in a stable vertical well bore. We show that a Biot's coefficient calculated from logging data in the Hejre Field, North Sea, is significantly different from 1. The log‐derived Biot's coefficient is above 0.8 in the Shetland Chalk Group and in the Tyne Group, and 0.6–0.8 in the Heno Sandstone Formation. We show that the effective vertical and horizontal stresses obtained using the log‐derived Biot's coefficient result in a drilling window for a vertical well larger than if approximating Biot's coefficient by 1. The estimation of the Biot's coefficient is straightforward in formations with a stiff frame, whereas in formations such as shales, caution has to be taken. We discuss the consequence of assumptions made on the mineral composition of shales as unphysical results could be obtained when choosing inappropriate mineral moduli.     

HOLOCENE ACTIVE CHARACTERISTICS OF THE NORTHERN SEGMENT OF THE MINJIANG FAULT IN THE EASTERN MARGIN OF THE TIBETAN PLATEAU

As a part of the north-south seismic zone in China, a lot of M6.0-7.2 earthquakes have occurred in the margin faults of the Minshan block in history. This work attempted to characterize the geometry and activity of the north section of the Minjiang fault in this region based on high-resolution satellite images, geologic and geomorphic investigations, micro-geomorphic surveys, and trench excavation. The results show left-lateral-slip and Holocene activity of this structure. Along it, the offset landform has a continuous linearity on Ⅱ terraces near the Chuanpan village. The vertical height of the fault scarp measures 3.1 meters, which is almost the same as the accumulative horizontal displacement of the gully. The accumulative horizontal shortening due to faulting is 3.0 meters. Calculation using the model of displacement-dependent characteristic earthquakes shows both the vertical and horizontal co-seismic displacements and the horizontal shortening amount are about 1.0 meter. While strata dating suggests that the vertical and horizontal slip rates are all about 0.7-0.9mm/a, and the horizontal shortening rate is approximately 1.0-1.1mm/a. The excavated trench, perpendicular to the fault trace, reveals low-angle thrust dipping in 260åt 29°. From the relationship of the fault, colluvial wedge and stratigraphy ages, three palaeoseismic events are identified from youngest to oldest at 0-295a BP, 1 405-1 565a BP, and 2 750-2 875a BP, respectively, with recurrence intervals 1 110-1 565 years and elapsed time about 0-295 years。According to the relationship between magnitude and active parameters, it is considered that the northern segment of the Minjiang fault is capable of generating M7 or greater earthquakes. Now it is in the process of stress accumulation, having a certain seismic risk.     

An Easy Method for Interpretation of Gravity Anomalies Due to Vertical Finite Lines

A new method is introduced to determine the top and bottom depth of a vertical line using gravity anomalies. For this, gravity at a distance x from the origin and horizontal derivative at that point are utilized. A numerical value is obtained dividing the gravity at point x by horizontal derivative. Then a new equation is obtained dividing the theoretical gravity equation by the derivative equation. In that equation, assigning various values to the depth and length of vertical line, several new numerical values are obtained. Among these values, a curve is obtained for the one that is closest to the first value from attending the depth and length values. The intersection point of these curves obtained by repeating this procedure several times for different points x yield the real depth and length values of the line. The method is tested on two synthetics and field examples. Successful results are obtained in both applications.     

方形多铅芯橡胶支座力学性能研究

本文通过对方形多铅芯橡胶支座竖向压缩性能试验,水平剪切性能试验以及其等效刚度、屈服强度、屈服后刚度、等效阻尼比等水平特征参数与水平剪切应变和竖向压应力的关系,特别是对其在不同方向上压缩剪切变形状态下的性能试验,分析了这种隔震支座各种水平特征参数在不同方向上变化的相关规律。得出在这种类型橡胶隔震支座在双向水平荷载同时作用下,竖向性能和水平性能较为稳定,是较为理想的桥梁结构的减隔震装置。     

Geophone orientation and coupling in three-component sea-floor data: a case study

We analyse the geophone orientation and coupling in a data set from the North Sea. Based on the polarization of the water-break on the sea-floor, we have derived processing algorithms for determining the receiver orientation for gimballed and non-gimballed geophone systems. For a gimballed system, the problem reduces to a simple horizontal rotation. However, for a non-gimballed system, where all three geophone axes may vary due to varying acquisition conditions such as dipping sea-floor, twisting of recording cable, etc., the three orientation angles cannot be found directly from the recorded displacement vectors. Using the data redundancy within a common-receiver gather, a robust two-stage method is derived for the non-gimballed system in which all three orientations can initially be unknown. Testing on the North Sea data set acquired with a gimballed system shows that the three-component geophones in the data set are orientated satisfactorily within an error of 5°. However, there are some undesirable cross-couplings between the vertical and horizontal geophones, which results in leakage of shear-wave energy from the horizontal components to the vertical components.     

Clarification of regional and local in situ stresses using the compact conical-ended borehole overcoring technique and numerical analysis

Abstract Stress measurement is performed to estimate the states of in situ rock stress at the Torigata open‐pit limestone mine in Japan using the compact conical‐ended borehole overcoring (CCBO) technique. A set of back and forward analyses are then carried out to evaluate the states of regional and local in situ rock stresses and the mine‐induced rock slope stability using a 3‐D finite element model. The maximum horizontal local in situ rock stress measured by the CCBO technique acts in the northeast–southwest direction. The horizontal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal local in situ rock stress measured by the CCBO technique. However, the horizontal regional tectonic stress is more compressive than the horizontal local in situ rock stress. This is because the horizontal regional stress due to gravity is not considered in the back‐analyzed horizontal regional tectonic stress, but it is included in the local in situ rock stress measured by the CCBO technique. The local stress obtained by the forward analysis, especially its horizontal components, is in good agreement with the horizontal local in situ rock stress measured by the CCBO technique, and the magnitude of the vertical normal stress increases more rapidly than those of the horizontal normal stresses with depth. As a result, the ratio of the horizontal normal stress to the vertical normal stress is largest at the nearest excavation level and decreases with depth. This means that the stress field within the mine‐induced rock slope is affected by the horizontal components of the local in situ rock stress.     

Evaluation of horizontal stiffness of fibre‐reinforced elastomeric isolators

Unbonded fibre‐reinforced elastomeric isolator (U‐FREI) is relatively new seismic base isolator in which fibre layers are used as reinforcement to replace steel shims as are normally used in conventional isolators. Further, the top and bottom end steel connector plates of conventional isolators are also removed. In general, the horizontal response of U‐FREI is nonlinear because of reduction in contact area due to rollover deformation and reduction in shear modulus of isolator under large deformation. Thus, evaluation of horizontal stiffness of U‐FREI is a challenging problem. Most previous studies were focused on the investigation of horizontal response of scaled models of U‐FREIs with low shape factors. A few analytical approaches were suggested for predicting the horizontal response of U‐FREI; but their results were not in good agreement with experimental observations. In the present study, the horizontal responses of prototype U‐FREIs are evaluated under a constant vertical pressure and cyclic loading using both experiments and finite element analysis. Prototype U‐FREIs with different shear moduli and with different shape factors are considered. Finite element simulations of corresponding bonded FREIs are also performed under the same loadings as in U‐FREIs. A rational analytical approach including the influence of rollover deformation and simultaneous reduction in shear modulus is proposed as a basic analytical tool for predicting the horizontal stiffness of FREIs (both bonded and unbonded). It is in reasonably good agreement with the results obtained from experiments and numerical analysis. Copyright © 2017 John Wiley & Sons, Ltd.     

Transport measurement with a horizontal and a vertical pipe microphone in a mountain stream: taking account of particle saltation

The pipe microphone has been shown to be an effective means for monitoring bedload transport in mountain streams. It is commonly installed perpendicular to the flow direction on a stable river bed, such as that of a check dam. Acoustic pulses caused by bedload collisions with the pipe are detected by a microphone. However, bedload particles saltating over the pipe remain undetected. To overcome this disadvantage, we installed a horizontal as well as a vertical pipe microphone in the Ashi‐arai‐dani supercritical channel located in the Hodaka mountain range, Japan. The vertical pipe was installed on the wall of the channel and the horizontal pipe was installed on the channel bed. The acoustic response of the horizontal pipe is expected to be larger than that of the vertical pipe, because the bedload concentration decreases with increasing height above the bed. However, at high amplifications, the peak pulse value from the vertical pipe is higher than that from the horizontal pipe. We explain this observation as follows: under high bedload discharge conditions, the pulses of the horizontal pipe are saturated but those of the vertical pipe are not. We proposed a ratio (R_hv) between the pulses detected by these sensors, and applied this ratio for calibrating the contemporaneous pulses detected by a microphone located immediately upstream of a bedload slot sampler. Indeed the R_hv‐corrected pulses correlated well with the bedload discharge calculated from the sampler, supporting our explanation. We conclude that bedload monitoring using concomitant vertical and horizontal pipe microphones can be used to calibrate centrally located pipe microphones when the bedload concentration is approximately homogeneous laterally across the width of the channel cross‐section, and thereby represent bedload discharges more accurately than with only a single pipe microphone. Copyright © 2017 John Wiley & Sons, Ltd.     

A method for evaluating horizontal well pumping tests

Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.     

Erosion rates in the southern oregon coast range: Evidence for an equilibrium between hillslope erosion and sediment yield

The relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm³cm^?1yr^?1 and average bedrock lowering rates of about 0.07 mm yr^?1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr^?1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin-wide denudation rates of between 0.05 and 0.08mm yr^?1, suggesting an approximate steady-state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km², suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape.     

Computational simulation of slab vibration and horizontal‐vertical coupling in a full‐scale test bed subjected to 3D shaking at E‐Defense

This paper focuses on slab vibration and a horizontal‐vertical coupling effect observed in a full‐scale 5‐story moment frame test bed building in 2 configurations: isolated with a hybrid combination of lead‐rubber bearings and cross‐linear (rolling) bearings, and fixed at the base. Median peak slab vibrations were amplified—relative to the peak vertical shake table accelerations—by factors ranging from 2 at the second floor to 7 at the roof, and horizontal floor accelerations were significantly amplified during 3D (combined horizontal and vertical) motions compared with 2D (horizontal only) motions of comparable input intensity. The experimentally observed slab accelerations and the horizontal‐vertical coupling effect were simulated through a 3D model of the specimen using standard software and modeling assumptions. The floor system was modeled with frame elements for beams/girders and shell elements for floor slabs; the insertion point method with end joint offsets was used to represent the floor system composite behavior, and floor mass was finely distributed through element discretization. The coupling behavior was partially attributed to the asymmetry of the building that was intensified by asymmetrically configured supplemental mass at the roof. Horizontal‐vertical coupled modes were identified through modal analysis and verified with evaluation of floor spectral peaks.