Anisotropic elastic full‐waveform inversion of walkaway vertical seismic profiling data from the Arabian Gulf          下载免费PDF全文

John C Owusu  Marwan Charara  Scott Leaney  Allan Campbell  Shujaat Ali  Igor Borodin  Les Nutt  Henry Menkiti 《Geophysical Prospecting》2016,64(1):38-53

Borehole seismic addresses the need for high‐resolution images and elastic parameters of the subsurface. Full‐waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium. Full‐waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data—multi‐component measurements; anisotropic effects; compressional and shear waves; and transmitted, converted, and reflected waves and multiples. Full‐waveform inversion, therefore, has the potential to provide a more accurate result compared with conventional processing methods. We present a feasibility study with results of the application of high‐frequency (up to 60 Hz) anisotropic elastic full‐waveform inversion to a walkaway vertical seismic profile data from the Arabian Gulf. Full‐waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium.  相似文献   

Surface inflow into the South China Sea through the Luzon Strait in winter     

������  ����Ң  ������  �Ƿ���  Ԭҵ�� 《中国海洋湖沼学报》2012,30(1):163-168

We studied the driving force of the Kuroshio intrusion into the South China Sea (SCS) during the winter monsoon, using satellite-tracked drifters entering the Luzon Strait (LS) through the Balintany and Babuyan Channels from the Philippine Sea. Most drifters passing through the Babuyan Channel in winter entered the interior SCS without a significant change in velocity. However, half of the drifters passing through the Balintany Channel entered the SCS at ~30 cm/s, which was faster than when they entered the LS. The other half continued moving northwestward into the Kuroshio and returned to the North Pacific. Quantitative analyses, using surface climatological wind and sea surface height anomaly (SSHa) data explained both the difference in velocity of drifters between the two channels and their acceleration through the Balintany Channel. The results suggest that the positive meridional gradient of sea surface height in the Luzon Strait, caused by the pileup of seawater driven by the Northeast monsoon, as well as Ekman flow, contribute to the Kuroshio intrusion into the SCS through the Babuyan and Balintany Channels. The former may be the main driving force.  相似文献   

Turbidite deposition and the development of canyons through time on an intermittently glaciated continental margin: The Bonanza Canyon system,offshore eastern Canada     

Gang Li  David J.W. Piper  D. Calvin Campbell  David Mosher 《Marine and Petroleum Geology》2012,29(1):90-103

Bonanza Canyon is a complex canyon system on the slope from the intermittently glaciated Grand Bank on the south side of Orphan Basin. A 3D seismic reflection volume, 2D high-resolution seismic reflection profiles and ten piston cores were acquired to study the evolution of this canyon system in relation to glacial processes on the continental shelf and the effects of different types of turbidity currents on the development of deep water channels. Mapped reflector surfaces from the 3D seismic volume show that the Bonanza Canyons developed in a depression created by a large submarine slide of middle Pleistocene age, coincident with the onset of glacigenic debris flows entering western Orphan Basin. Two 3–5 km wide, flat-floored channels were cut into the resulting mass-transport deposit and resemble catastrophic glacial meltwater channels elsewhere on the margin. Both channels subsequently aggraded. The eastern channel A became narrower but maintained a sandy channel floor. The western channel, B, heads at a spur on the continental slope and appears to have been rather passively draped by muds and minor sands that have built 1500-m wave length sediment waves.Muddy turbidites recorded by piston cores in the channel and on the inter-channel ridges are restricted to marine isotope stage (MIS) 2 and were deposited from thick, sheet-like, and sluggish turbidity current derived from western Orphan Basin that resulted in aggradation of the channels and inter-channel ridges. Sandy turbidites in channels and on inner levees were deposited throughout MIS 2–3 and were restricted to the channels, locally causing erosion. Some coincide with Heinrich events. Channels with well-developed distributaries on the upper slope more readily trap the sediments on Grand Bank to form sandy turbidity currents. Channel B dominated by muddy turbidity currents has wide and relatively smooth floor whereas channel A dominated by sandy turbidity currents has a sharp geometry.  相似文献   

Glaciation of a mixed-phase boundary layer cloud at a coastal arctic site as depicted in continuous lidar measurements     

James R. Campbell  Masataka Shiobara 《Polar Science》2008,2(2):121-127

The dynamic seeding and glaciation of a mixed-phase cloud by ice crystals injected from above at Ny Ålesund, Svalbard, Norway is described using continuous lidar measurements and thermodynamic data. Glaciation of this cloud was caused by ice crystal growth and sedimentation due to the preferential differences in saturation vapor pressure over ice versus liquid water and riming. The lidar data suggest that precipitation reached the ground for nearly 4 h as a result. The symbiosis between ice and liquid water hydrometeor presence in the polar troposphere is unique. Thermal perturbations and airmass fluctuations influence microphysical cloud characteristics and radiative balance, which makes the otherwise pristine region sensitive to lower-latitude anthropogenic and biogenic influences and a focal point for observing indirect effects and their influence on climate change. The development of lidar technologies capable of continuous and autonomous measurements is yielding important datasets to study unique atmospheric phenomena.  相似文献   

Toward an integrated view of inner magnetosphere and radiation belts     

Yihua Zheng  Yongliang Zhang  Janet U. Kozyra  Jay Albert  Jacob Bortnik  Dennis L. Gallagher  Ramona L. Kessel 《Journal of Atmospheric and Solar》2009,71(16):1613

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The geometry of decoupled line driven winds     

John M. Porter  Janet E. Drew 《Astrophysics and Space Science》1995,224(1-2):541-542

Bjorkman & Cassinelli (1993) have proposed a mechanism that is expected to produce strong equatorial focusing of the radiation-driven winds from rapidly-rotating B stars. Here the possibility of the decoupling of the stellar radiation field and the outflow is considered. We find that greater equator to pole density ratios may be generated than the standard model, bringing it more into line with results implied by observations.  相似文献   

Secondary mineral formation associated with respiration of nontronite,NAu-1 by iron reducing bacteria     

S?Erin?O'Reilly  Janet?Watkins  Yoko?FurukawaEmail author 《Geochemical transactions》2005,6(4):67

Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial Fe(III) respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred regardless of the extent of microbial Fe(III) reduction in all of our experimental systems, including those that contained heat-killed bacteria and those in which O₂, rather than Fe(III), was the primary terminal electron acceptor. The solid alteration products observed under transmission electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free amorphous aluminosilicate with increased Al/Si ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount of Fe partitioned to the aqueous phase was primarily in the form of dissolved Fe(III) species even in the systems in which Fe(III) was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial respiration of Fe(III) in our laboratory systems proceeded through the following: (1) alteration of NAu-1 and concurrent release of Fe(III) from the octahedral sheets of NAu-1; and (2) subsequent microbial respiration of Fe(III).  相似文献   

Corroded Pollen and Spores as Indicators of Changing Lake Sediment Sources and Catchment Disturbance     

Janet M.?WilmshurstEmail author  Matt S.?McGlone 《Journal of Paleolimnology》2005,34(4):503-517

Pollen and spores with resistant exines are preferentially preserved in soils, and during periods of soil erosion they can become incorporated into lake sediments. As a result, the contemporary vegetation may be poorly represented by the palynomorphs in the lake sediments because of the reworked component of inwashed pollen and spores. We record the proportion of palynomorphs with corroded exines in sediment cores from four lakes in the eastern North Island of New Zealand to document changing sources of palynomorphs over the last 2000 years. During this period, the catchments experienced major vegetation disturbances, both natural (from volcanism and fire) and anthropogenic including deforestation ca. 600 years ago, and the European conversion of fern-scrubland to pasture in the 19th century. Corroded palynomorphs are more abundant in inwashed sediments than authigenic sediments. Catchment soil disturbance was minor during the forested period, and characterised by small, inwashed, sediment pulses after storms, and a relatively low percentage of corroded palynomorphs. Although initial Maori forest clearance by fire led to a temporary increase in erosion in one lake catchment, rapid replacement of forest by a dense bracken fern cover helped to minimise soil erosion and reworking of palynomorphs in this period. European pastoralists replaced the bracken fern with shallow-rooted pasture grasses about 150 years ago. In erosion prone lake catchments, this led to a rapid increase of inwashed eroded soils and littoral sediments, and their component of resistant palynomorphs, reaching the lake sediments. As a result, the palynological records from these catchments during the European period are distorted by reworking. By contrast, over the same period, the palynological record from a lake with no inflowing streams and stable catchment soils more faithfully represented the contemporary vegetation cover. Exine corrosion has been used to help identify periods of reworking in the lake sediments and to allow for a correction of distortion caused by reworking.  相似文献   

Distributed velocity method of solving the convective-dispersion equation: 1. Introduction,mathematical theory,and numerical implementation     

James E. Campbell  Dennis E. Longsine  Mark Reeves 《Advances in water resources》1981,4(3):102-108

This is the first part of a two-part paper presenting a new method for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers, the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives, and the ability to treat leach- or solubility-limited sources. To the extent it has been tested to date, the distributed velocity method (DVM) appears to satisfy these demands. This part contains an overall introduction and presents the mathematical theory, numerical implementation, and example results.  相似文献   

Swath bathymetry with GLORIA     

Le Bas  T.P. Somers  M.L. Campbell  J.M. Beale  R. 《Oceanic Engineering, IEEE Journal of》1996,21(4):545-553

For many years, GLORIA has been producing sonar images of the deep ocean floor. In the mid-1980's, the SeaMARC II system came to prominence producing depth values as well as sonar images. The basic method compares the phases of the signals returning from the seafloor to two rows of transducers. The phase differences are converted into angles of arrival and together with the arrival times converted into range and depth values. This capability has now been added to the GLORIA system. The fact that GLORIA uses a 2s FM pulse means the backscattered reverberation can come from a strip of seafloor up to 1.5 km wide. To accommodate this, overlapping complex FFT's are used to produce a time-frequency matrix for the returning signals. In this matrix, a constant range feature appears as a diagonal. Phases are then calculated using a least-mean-squares estimate along diagonals. The main source of error and bias is due to surface reflection, and this is taken into account. The GLORIA swath bathymetry system was tested on two cruises and it was possible to produce depth contours with a good level of confidence. The total swath width was over eight water depths and would have been greater with a more favorable velocity profile. Comparison with other bathymetry data (such as multibeam systems) showed excellent correlation, having a standard deviation of only 4% of total water depth  相似文献