The David Linton Award 1991     

Colin R. Thorne 《地球表面变化过程与地形》1992,17(5):433-434

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Balanced Sediment Fluxes in Southern California’s Mediterranean-Climate Zone Salt Marshes   总被引：1，自引：0，他引：1  

Jordan A. Rosencranz  Neil K. Ganju  Richard F. Ambrose  Sandra M. Brosnahan  Patrick J. Dickhudt  Glenn R. Guntenspergen  Glen M. MacDonald  John Y. Takekawa  Karen M. Thorne 《Estuaries and Coasts》2016,39(4):1035-1049

Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Niño storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km² salt marsh (Seal Beach) and a less modified 1-km² marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits.  相似文献   

Assessment of adult salmon in near-surface waters of Cook Inlet, Alaska     

Tarbox  K. E.; Thorne  R. E. 《ICES Journal of Marine Science》1996,53(2):397-401

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A Comparison of Near-Bed Acoustic Backscatter and Laser Diffraction Measurements of Suspended Sediments   总被引：2，自引：0，他引：2  

Thorne  P. Agrawal  Y. Cacchione  D. 《Oceanic Engineering, IEEE Journal of》2007,32(1):225-235

As part of the U.S. Office of Naval Research (ONR, Arlington, VA) mine burial program, an experiment was conducted off the pier at Santa Cruz, CA, to measure the near-bed suspended sediment reference concentration under waves and currents. Two tripods were deployed to carry out the measurements; one consisting mainly of acoustical instrumentation and the other solely of optical instruments. The tripods were located within 15 m of one another on a sandy bed and measurements of the suspended sediment were made using acoustics and optics. Although the experiment was not primarily designed to conduct an intercomparison of acoustical and optical measurements, it was considered interesting to take advantage of the situation and to examine if these two techniques gave comparable results. In particular, measurements of particle size and concentration, obtained using a triple frequency acoustic backscatter system (ABS) have been compared with the commercially available laser miniature scattering and transmissometry instrument (MSCAT). It was found that the mean grain size estimated by the two methods was consistent; however, in contrast, the concentration time series showed differences, both in magnitude and form.  相似文献   

Maintenance of the middle-latitude nocturnal D-layer by energetic electron precipitation     

Walther N. Spjeldvik  Richard M. Thorne 《Pure and Applied Geophysics》1976,114(4):497-508

Summary Energetic electrons are continually removed from the radiation belts by resonant pitch-angle scattering with ELF turbulence. A realistic simulation of the concomitant precipitation loss of such electrons to the atmosphere shows it to be a significant source for the nocturnal ionospheric D-region. During geomagnetically quiet (non-storm) periods, precipitating electrons are expected to provide the dominant nocturnal ionization source at medium invariant latitudes corresponding to field lines just inside the plasmapause. When the level of scattering turbulence is high the quiet time precipitation can dominate for an extended range of latitudes ( 55° to 65°). Observed fluctuations in the level of scattering turbulence should produce modulations in the concentration of nocturnal middle latitude D-region electrons which may be detected using radio probing techniques.  相似文献   

Stability of composite river banks     

Colin R. Thorne  N. Keith Tovey 《地球表面变化过程与地形》1981,6(5):469-484

The stability of a river bank depends on the balance of forces, motive and resistive, associated with the most critical mechanism of failure. Many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size, geometry and structure of the bank, the engineering properties of the bank material, the hydraulics of flow in the adjacent channel and climatic conditions. Rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt/clay. Bank erosion occurs by fluvial entrainment of material from the lower, cohesionless bank at a much higher rate than material from the upper, cohesive bank. This leads to undermining that produces cantilevers of cohesive material. Upper bank retreat takes place predominantly by the failure of these cantilevers. Three mechanisms of failure have been identified: shear, beam and tensile failure. The stability of a cantilever may be analysed using static equilibrium and beam theory, and dimensionless charts for cantilever stability constructed. Application of the charts requires only a few simple measurements of cantilever geometry and soil properties. In this analysis the effects of cracks and fissures in the soil must be taken into account. These cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface. Following mechanical failure, blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue. Hence, the rate of bank retreat is fluvially controlled, even though the mechanism of failure of the upper bank is not directly fluvial in nature. This cycle of bank erosion: undermining, cantilever failure and fluvial scour of the toe, operates over several flood events and has important implications for river engineering, channel changes, and the movement of sediment through fluvial systems.  相似文献   

Earthquake doublets in the Solomon Islands     

Thorne Lay  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1980,21(4):283-304

Large, shallow, thrust earthquakes in the Solomon Islands region tend to occur in closely related pairs. Two recent sequences are July 14, 1971 (M_S = 7.9) and July 26, 1971 M(_S = 7.9) and 14^h37^m, July 20, 1975 (M_S = 7.9) and 19^h54^m, July 20, 1975 (M_S = 7.7). The mechanism of these seismic doublets has important bearing on the triggering mechanism of earthquakes in subduction zones. Detailed analysis of the seismic body waves and surface waves were performed on the 1971, 1974, and 1975 doublets, providing a better understanding of: (1) the mechanics of seismic triggering, (2) the state of stress on the fault plane, and (3) the nature of subduction between the Pacific and Indian plates. The results indicate that although the geometry of the subduction zone in the Solomon Islands is complicated by the presence of several sub-plates, the slip direction of the Indian plate with respect to the Pacific plate is relatively uniform over the entire region. The large seismic moments of the 1971 sequence (1.2 · 10²⁸ and 1.8 · 10²⁸ dyne cm) indicate that these events directly represent the underthrusting of the Indian and Solomon plates beneath the Pacific plate. The body waves from these doublets, recorded on the WWSSN long-period seismograms, are remarkably impulsive and simple compared with those from events of comparable seismic moment in other subduction zones. In addition, the source dimensions of the body waves are 30–70 km in length, substantially smaller than the overall rupture surfaces radiating the surface waves which are 100–300 km in length. These facts suggest the existence of relatively large, isolated high-stress zones on the fault plane. This type of stress distribution is distinct from other regions which have more heterogeneous stress distribution on the fault plane, and this is proposed as the principal characteristic of this region responsible for the occurrence of the doublets and for the apparent efficiency of triggering in the Solomon trench. Prior to the 1971 sequence, similar sequences have occurred in the same area in 1919–1920 and 1945–1946. From the amount of slip (1.3 m) determined for the 1971 sequence and the apparent recurrence interval of 25 years, a seismic slip rate of 5 cm yr^?1 is determined. This value is a significant portion of the convergence rate between the Indian and Pacific plates indicating that the plate motion here is taken up largely by seismic slip.  相似文献   

Applicability of Slug Interference Tests for Hydraulic Characterization of Unconfined Aquifers: (2) Field Test Examples   总被引：3，自引：0，他引：3  

F. A. Spane  Jr.    P. D. Thorne  L. C. Swanson 《Ground water》1996,34(5):925-933

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Effects of drilling fluid invasion on hydraulic characterization of low-permeability basalt horizons: A field evaluation     

F. A. Spane Jr.  P. D. Thorne 《Environmental Geology》1985,7(4):227-236

Low-permeability basalts at the Hanford Site, in south-central Washington State, are currently being investigated for suitability as repository horizons for the terminal storage of commercial, high-level radioactive wastes As part of on-going Basalt Waste isolation Project (BWIP) studies, a field evaluation was conducted to assess the effect that drilling fluid invasion may have on the hydraulic characterization of low-permeability basalts The test formation selected for the field evaluation was a 24 7-m section of basalt flow interior that had been previously core-drilled utilizing only fresh water. The test design of the field evaluation included an initial phase (phase I) of hydrologic testing followed by the injection of bentonite-base drilling fluid into the test section, removal of the drilling fluid from the borehole, and a final phase (phase II) of hydrologic testing Hydrologic tests conducted during each phase included overpressure pulse tests (pressurized slug tests) and a multiple-step, constant head injection test Results of the field evaluation indicate that no discernible impact on hydraulic property estimates or test response could be attributed to drilling fluid invasion.  相似文献   

Diffuse auroral precipitation in the jovian upper atmosphere and magnetospheric electron flux variability     

Bidushi Bhattacharya  Richard M. Thorne  Krishan K. Khurana 《Icarus》2005,178(2):406-416

The deposition of energetic electrons in Jupiter's upper atmosphere provides a means, via auroral observations, of monitoring electron and plasma wave activity within the magnetosphere. Not only does particle precipitation indicate a potential change in atmospheric chemistry, it allows for the study of episodic, pronounced flux enhancements in the energetic electron population. A study has been made of the effects of such electron injections into the jovian magnetosphere and of their ability to provide the source population for variations in diffuse auroral emissions. To identify the source region of precipitating auroral electrons, we have investigated the pitch-angle distributions of high-resolution Galileo Energetic Particle Detector (EPD) data that indicate strong flux levels near the loss cone. The equatorial source region of precipitating electrons has been determined from the locations of Galileo's in situ measurements by tracing magnetic field lines using the KK97 model. The primary source region for Jupiter's diffuse aurora appears to lie in the magnetic equator at 15-40 RJ, with the predominant contribution to precipitation flux (tens of ergs cm⁻² s⁻¹ sr⁻¹) stemming from <30 RJ. Variability of flux for energetic electrons in this region is also important to the irradiation of surfaces and atmospheres for the Galilean moons: Europa, Ganymede, and Callisto. The average diffuse auroral precipitation flux has been shown to vary by as much as a factor of six at a given radial location. This variability appears to be associated with electron injection events that have been identified in high-resolution Galileo EPD data. These electron flux enhancements are also associated with increased whistler-mode wave activity and magnetic field perturbations, as detected by the Galileo Plasma Wave Subsystem (PWS) and Magnetometer (MAG), respectively. Resonant interactions with the whistler-mode waves cause electron pitch-angle scattering and lead to pitch-angle isotropization and precipitation.  相似文献