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1.
Synergy and fusion of optical and synthetic aperture radar satellite data for underwater topography estimation in coastal areas 总被引：1，自引：1，他引：0
Andrey Pleskachevsky Susanne Lehner Thomas Heege Claudius Mott 《Ocean Dynamics》2011,61(12):2099-2120
A method to obtain underwater topography for coastal areas using state-of-the-art remote sensing data and techniques worldwide
is presented. The data from the new Synthetic Aperture Radar (SAR) satellite TerraSAR-X with high resolution up to 1 m are
used to render the ocean waves. As bathymetry is reflected by long swell wave refraction governed by underwater structures
in shallow areas, it can be derived using the dispersion relation from observed swell properties. To complete the bathymetric
maps, optical satellite data of the QuickBird satellite are fused to map extreme shallow waters, e.g., in near-coast areas.
The algorithms for bathymetry estimation from optical and SAR data are combined and integrated in order to cover different
depth domains. Both techniques make use of different physical phenomena and mathematical treatment. The optical methods based
on sunlight reflection analysis provide depths in shallow water up to 20 m in preferably calm weather conditions. The depth
estimation from SAR is based on the observation of long waves and covers the areas between about 70- and 10-m water depths
depending on sea state and acquisition quality. The depths in the range of 20 m up to 10 m represent the domain where the
synergy of data from both sources arises. Thus, the results derived from SAR and optical sensors complement each other. In
this study, a bathymetry map near Rottnest Island, Australia, is derived. QuickBird satellite optical data and radar data
from TerraSAR-X have been used. The depths estimated are aligned on two different grids. The first one is a uniform rectangular
mesh with a horizontal resolution of 150 m, which corresponds to an average swell wavelength observed in the 10 × 10-km SAR
image acquired. The second mesh has a resolution of 150 m for depths up to 20 m (deeper domain covered by SAR-based technique)
and 2.4 m resolution for the shallow domain imaged by an optical sensor. This new technique provides a platform for mapping
of coastal bathymetry over a broad area on a scale that is relevant to marine planners, managers, and offshore industry. 相似文献
2.
Gegar Prasetya John Beavan Xiaoming Wang Martin Reyners William Power Kate Wilson Biljana Lukovic 《Pure and Applied Geophysics》2011,168(11):1973-1987
We undertake detailed near-field numerical modelling of the tsunami generated by the 15 July 2009 earthquake (Mw 7.8) in Fiordland,
New Zealand. High resolution bathymetry and topography data at Breaksea and Dusky Sounds, and Chalky and Preservation Inlets
are derived mostly from digitised New Zealand nautical charts, Shuttle Radar Topographic Mission (SRTM) 3 arc-second data,
and General Bathymetric Chart of the Ocean (GEBCO) 30 s data. A combination of continuous and campaign Global Positioning
System (GPS), satellite radar (ALOS/PALSAR InSAR images) and seismology data are used to constrain the seafloor deformation
for the initial tsunami condition. This source model, derived independently of DART observations, provides an excellent fit
to observed tsunami elevations recorded by DART buoy 55015. The model results in the near field show maximum tsunami elevations
in the range 0.5–2.0 m inside the sounds and inlets with maximum flow speeds of 3.0 m/s. Along the open coast, maximum tsunami
elevations reach 2.0 m. The high flow speeds through the inlets may change the inlet stratifications and water mass inside
the sounds. Media reports and field reconnaissance data show some tsunami evidence at Cormorant Cove, Duck and Goose Coves,
and Passage Point. 相似文献
3.
Rob A. Holman K. Todd Holland Dave M. Lalejini Steven D. Spansel 《Ocean Dynamics》2011,61(11):1927-1935
We investigate the issues and methods for estimating nearshore bathymetry based on wave celerity measurements obtained using
time series imagery from small unmanned aircraft systems (SUAS). In contrast to time series imagery from fixed cameras or
from larger aircraft, SUAS data are usually short, gappy in time, and unsteady in aim in high frequency ways that are not
reflected by the filtered navigation metadata. These issues were first investigated using fixed camera proxy data that have
been intentionally degraded to mimic these problems. It has been found that records as short as 50 s or less can yield good
bathymetry results. Gaps in records associated with inadvertent look-away during unsteady flight would normally prevent use
of the required standard Fast Fourier Transform methods. However, we found that a full Fourier Transform could be implemented
on the remaining valid record segments and was effective if at least 50% of total record length remained intact. Errors in
image geo-navigation were stabilized based on fixed ground fiducials within a required land portion of the image. The elements
of a future method that could remove this requirement were then outlined. Two test SUAS data runs were analyzed and compared
to survey ground truth data. A 54-s data run at Eglin Air Force Base on the Gulf of Mexico yielded a good bathymetry product
that compared well with survey data (standard deviation of 0.51 m in depths ranging from 0 to 4 m). A shorter (30.5 s) record
from Silver Strand Beach (near Coronado) on the US west coast provided a good approximation of the surveyed bathymetry but
was excessively deep offshore and had larger errors (1.19 m for true depths ranging from 0 to 6 m), consistent with the short
record length. Seventy-three percent of the bathymetry estimates lay within 1 m of the truth for most of the nearshore. 相似文献
4.
Jeong Woo Kim Ralph R. B. von Frese Bang Yong Lee Daniel R. Roman Seong-Jae Doh 《Pure and Applied Geophysics》2011,168(5):815-826
The gravity-geologic method (GGM) was implemented for 2′ by 2′ bathymetric determinations in a 1.6° longitude-by-1.0° latitude
region centered on the eastern end of the Shackleton Fracture Zone in the Drake Passage, Antarctica. The GGM used the Bouguer
slab approximation to process satellite altimetry-derived marine free-air gravity anomalies and 6,548 local shipborne bathymetric
sounding measurements from the Korea Ocean Research and Development Institute to update the surrounding off-track bathymetry.
The limitations of the Bouguer slab for modeling the gravity effects of variable density, rugged bathymetric relief at distances
up to several kilometers, were mitigated by establishing ‘tuning’ densities that stabilized the GGM predictions. Tests using
two-thirds of the shipborne bathymetric measurements to estimate the remaining third indicated that the tuning densities minimized
root-mean-square deviations to about 29 m. The optimum GGM bathymetry model honoring all the ship observations correlated
very well with widely available bathymetry models, despite local differences that ranged up to a few kilometers. The great
analytical simplicity of GGM facilitates accurately and efficiently updating bathymetry as new gravity and bathymetric sounding
data become available. Furthermore, the availability of marine free-air gravity anomaly data ensures that the GGM is more
effective than simply extrapolating or interpolating ship bathymetry coverage into unmapped regions. 相似文献
5.
A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount,Tyrrhenian Sea 
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下载免费PDF全文 Roxana Safipour Sebastian Hölz Marion Jegen Andrei Swidinsky 《Geophysical Prospecting》2018,66(7):1415-1432
We study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ～100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits. 相似文献
6.
根据重力地质法（GGM）,利用南中国海海域内63179个船测控制点水深将测高自由空间重力异常划分为长波参考场和短波残差场,并反演出了该海域112°E-119°E,12°N-20°N范围的1’×1’海底地形模型,该过程中使用的海水和海底洋壳密度差异常数1.32 g·cm-3通过实测水深估计得到.利用反演得到的GGM模型对剩余的10529个检核点船测水深插值计算后与实测水深进行比较,其较差结果的均值为-1.64 m,标准差为76.95 m,相对精度为4.06%.此外,根据船测点数量、分布和海底地形的不同,选择了三个海域进行统计,结果表明：在船测控制点分布均匀的海域,GGM模型精度优于ETOPO1模型,在控制点过于分散的海域其精度会有所下降,但好于船测水深的直接格网化结果.为进一步探究检核点的较差结果中出现较大数值的成因,本文对精度较差的点位进行了单独分析,选择了两条船测航迹剖面进行了研究,并分析了检核点的水深较差、相对精度与水深和重力异常的关系,结果表明：GGM模型精度受水深和重力异常的相关性影响较小,受海底地形复杂程度影响较大,地形坡度变化平缓海域的预测精度明显高于海山地区.最后,综合GGM模型和ETOPO1模型优势,利用所有船测水深作为控制,生成了综合的海底地形模型. 相似文献
7.
8.
The potential of long ship-induced waves to serve as a physical model for tsunami waves (called simply tsunami below) is examined.
Such waves (wavelengths more than 200 m at depths down to 10–20 m) are induced by high-speed ferries sailing at near-critical
speeds in semisheltered, relatively shallow areas. It is shown based on experience from Tallinn Bay, Baltic Sea, that for
many aspects these waves can model nearshore dynamics and runup of tsunami caused by landslides, including processes of wave
refraction, diffraction, and sea-bottom interaction in bays and harbors. Many governing nondimensional parameters (such as
the nonlinearity, dispersion, Reynolds and Ursell numbers, surf similarity parameter, breaking parameter, etc.) of the largest
ship waves and landslide tsunamis have the same order of magnitude. It is especially important that use of ship waves for
wave propagation and runup studies allows their spatial structure to be accounted for adequately. Near-critical ship waves
can therefore be used as a natural substitute for tsunami, for study under controlled and safe conditions. 相似文献
9.
The marine controlled source electromagnetic (CSEM) technique has been adopted by the hydrocarbon industry to characterize the resistivity of targets identified from seismic data prior to drilling. Over the years, marine controlled source electromagnetic has matured to the point that four‐dimensional or time lapse surveys and monitoring could be applied to hydrocarbon reservoirs in production, or to monitor the sequestration of carbon dioxide. Marine controlled source electromagnetic surveys have also been used to target shallow resistors such as gas hydrates. These novel uses of the technique require very well constrained transmitter and receiver geometry in order to make meaningful and accurate geologic interpretations of the data. Current navigation in marine controlled source electromagnetic surveys utilize a long base line, or a short base line, acoustic navigation system to locate the transmitter and seafloor receivers. If these systems fail, then rudimentary navigation is possible by assuming the transmitter follows in the ship's track. However, these navigational assumptions are insufficient to capture the detailed orientation and position of the transmitter required for both shallow targets and repeat surveys. In circumstances when acoustic navigation systems fail we propose the use of an inversion algorithm that solves for transmitter geometry. This algorithm utilizes the transmitter's electromagnetic dipole radiation pattern as recorded by stationary, close range (<1000 m), receivers in order to model the geometry of the transmitter. We test the code with a synthetic model and validate it with data from a well navigated controlled source electromagnetic survey over the Scarborough gas field in Australia. 相似文献
10.
There is a persistent need for high resolution photographic images of the sea floor and associated biota for marine habitat classification and fisheries stock assessment. This paper presents a novel low cost Lagrangian imaging platform that offers high quality images with reduced operational demands in comparison to existing methodologies such as diver surveys, drop cameras, ship towed systems and dedicated remote or autonomous underwater vehicles. The platform consists of a recently developed bottom following Lagrangian float fit with down looking stereo cameras and strobe lighting. The float can use active ballasting to perform constant altitude photographic drift surveys in coastal waters over varying bathymetry. Images from the float can be used to create large photomosaics, stereographic bathymetry estimates and image-derived current measurements. Test data are presented to demonstrate the operation of the Lagrangian float and summarize the data products. 相似文献
11.
High-resolution X-Band radar measurements of currents,bathymetry and sea state in highly inhomogeneous coastal areas 总被引：1，自引：1，他引：0
Katrin Hessner Konstanze Reichert Jose Carlos Nieto Borge Craig L. Stevens Murray J. Smith 《Ocean Dynamics》2014,64(7):989-998
In this paper, high-resolution wave, current and water depth fields derived by marine X-Band radar are presented for a coastal region of extreme tidal currents in the presence of inhomogeneous bathymetry at the south coast of New Zealand’s North Island. The current and water depth information for the presented location covers an area of approximately 13 km2 with a spatial resolution of 225 m and an update rate of 3 min. The sea state data provides a spatial representation of coastal effects like wave shoaling and refraction forced by bathymetry and current interaction. The near-surface current measurements about 3 km off the coast show expected tidal current pattern with maximum northwest/southeast current of 1.5–2 m/s alongshore. This is in agreement with currents from the RiCOM hydrodynamic model. The spatial resolution of the observed current field exhibits in addition small-scale current features caused by the influence of the local bathymetry. These data demonstrate the insight to be gained in complex, high-energy coastal situations through the use of high-resolution remote sensing techniques. 相似文献
12.
Investigation of topographic reductions and aliasing effects on gravity and the geoid over Greece based on various digital terrain models 总被引：2，自引：0，他引：2
The reduction of gravity-field related quantities (e.g., gravity anomalies, geoid heights) due to the topography plays a crucial
role in both geodetic and geophysical applications, since in the former it is an intermediate step towards geoid prediction
and in the latter it reveals lateral as well as radial density contrasts and infers the geology of the area under study. The
computations are usually carried out by employing a DTM and/or a DBM, which describe the topography and bathymetry, respectively.
Errors in these DTMs/DBMs will introduce errors in the computed topographic effects, while poor spatial resolution of the
topography and bathymetry models will result in aliasing effects to both gravity anomalies and geoid heights, both influencing
the accuracy of the estimated solutions. The scope of this work is twofold. First, a validation and accuracy assessment of
the SRTM 3″ (90 m) DTM over Greece is performed through comparisons with existing global models as well as with the Greek
450 m national DTMs. Whenever a misrepresentation of the topography is identified in the SRTM data, it is “corrected” using
the local 450 m DTM. This process resulted in an improved SRTM DTM called SRTMGr, which was then used to determine terrain
effects to gravity field quantities. From the fine-resolution SRTMGr DTMs, coarser models of 15″, 30″, 1′, 2′ and 5′ have
been determined in order to investigate aliasing effects on both gravity anomalies and geoid heights by computing terrain
effects at variable spatial resolutions. From the results acquired in two test areas, it was concluded that SRTMGr provides
similar results to the local DTM making the use of other older global DTMs obsolete. The study for terrain aliasing effects
proved that when high-resolution and accuracy gravity and geoid models are needed, then the highest possible resolution DTM
should be employed to compute the respective terrain effects. Based on the results acquired from two the test areas a corrected
SRTMGr DTM has been compiled for the entire Greek territory towards the development of a new gravimetric geoid model. Results
from that analysis are presented based on the well-known remove-compute-restore method, employing land and marine gravity
data, EGM08 as a reference geopotential model and the SRTMGr DTM for the computation of the RTM effects. 相似文献
13.
Sun glint is the specular reflection of light from the water surface, which often causes unusually bright pixel values that can dominate fluvial remote sensing imagery and obscure the water‐leaving radiance signal of interest for mapping bathymetry, bottom type, or water column optical characteristics. Although sun glint is ubiquitous in fluvial remote sensing imagery, river‐specific methods for removing sun glint are not yet available. We show that existing sun glint‐removal methods developed for multispectral images of marine shallow water environments over‐correct shallow portions of fluvial remote sensing imagery resulting in regions of unreliable data along channel margins. We build on existing marine glint‐removal methods to develop a river‐specific technique that removes sun glint from shallow areas of the channel without over‐correction by accounting for non‐negligible water‐leaving near‐infrared radiance. This new sun glint‐removal method can improve the accuracy of spectrally‐based depth retrieval in cases where sun glint dominates the at‐sensor radiance. For an example image of the gravel‐bed Snake River, Wyoming, USA, observed‐versus‐predicted R2 values for depth retrieval improved from 0.66 to 0.76 following sun glint removal. The methodology presented here is straightforward to implement and could be incorporated into image processing workflows for multispectral images that include a near‐infrared band. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
14.
The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important
in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate
shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the
waves trapped near the fluid–solid interface are called Scholte waves, and this is the subject of the study. In 1998, there
were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site.
The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources
has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate
frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion
source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear
wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We
find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and
20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths
levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling
data. As expected, the P- to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio
is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data. 相似文献
15.
《Journal of Applied Geophysics》2007,61(1):16-38
Unstable rocky slopes are major hazards to the growing number of people that live and travel though mountainous regions. To construct effective barriers to falling rock, it is necessary to know the positions, dimensions and shapes of structures along which failure may occur. To investigate an unstable mountain slope distinguished by numerous open fracture zones, we have taken advantage of three moderately deep (51.0–120.8 m) boreholes to acquire geophysical logs and record single-hole radar, vertical radar profiling (VRP) and crosshole radar data. We observed spallation zones, displacements and borehole radar velocity and amplitude anomalies at 16 of the 46 discontinuities identified in the borehole optical televiewer images. The results of the VRP and crosshole experiments were disappointing at our study site; the source of only one VRP reflection was determined and the crosshole velocity and amplitude tomograms were remarkably featureless. In contrast, much useful structural information was provided by the single-hole radar experiments. Radar reflections were recorded from many surface and borehole fracture zones, demonstrating that the strong electrical property contrasts of these features extended some distance into the adjacent rock mass. The single-hole radar data suggested possible connections between 6 surface and 4 borehole fractures and led to the discovery of 5 additional near-surface fracture zones. Of particular importance, they supplied key details on the subsurface geometries and minimum subsurface lengths of 8 of the 10 previously known surface fracture zones and all of the newly discovered ones. The vast majority of surface fracture zones extended at least 40–60 m into the subsurface, demonstrating that their depth and surface dimensions are comparable. 相似文献
16.
Recent Dasycladales (Chlorophyta) in Okinawa Jima in the Central Ryukyus,southwestern Japan: Paleontological implications 下载免费PDF全文
下载免费PDF全文 Recent dasycladalean algae (Dasycladales, Chlorophyta) are classified into two families, 11 genera, and 44 species, and inhabit the tropical to warm‐temperate waters of the world. Twelve species of dasycladalean algae occur in Okinawa Jima, Ryukyu Islands. In this paper, the present‐day dasycladalean species and their distributions in Okinawa Jima are reported and their paleontological implications are discussed. Dasycladalean algae grow mainly on coral rubble and rocks, often forming large meadows in calm shallow lagoons. However, Dasycladus vermicularis occurs in deeper waters, at depths of 15–89 m, around Okinawa Jima. Neomeris annulata is found at water depths of 0–30 m. These data throw doubt on the interpretation that the occurrence of dasycladalean algae is linked to warm shallow habitats. 相似文献
17.
Array measurements of microtremors were carried out at thirty sites in Damascus city, Syria to estimate S-wave velocity structures of shallow soil formations for site effect analysis. The microtremor data were recorded by 6 vertical-component seismometers distributed along the circumferences of two circles as well as a 3-component seismometer deployed in the center. The phase velocities were estimated at each site from the vertical components of recorded microtremor data by using the Spatial Autocorrelation method. Then, Genetic Simulated Annealing Algorithm technique was applied for inversion of the phase velocities to estimate 1-D S-wave velocity structures beneath the sites. The inverted Vs profiles are not uniform in Damascus city and the results show that a shallow soft layer (∼200 m/s) appears in the eastern part of the city as well as the central part along Barada River. This layer controls the amplification distribution in the city with a high amplification mainly observed at the locations having this layer. The inversion results also show that the depth to the engineering bedrock (∼750 m/s) is very shallow along the foothills of Mt. Qasyoun in the north-west. Then the depth increases towards the east and the south. The maximum depth to the engineering bedrock (∼80 m) was observed in the southern part of Damascus. To validate the results of the inversions, the spectral ratios between the horizontal and vertical components (H/V) of the recorded microtremor data at the central seismometer were compared with the computed ellipticities of the fundamental-mode Rayleigh-waves based on the respective Vs structure. The results show a good agreement in a period range of 0.05 s to 0.5 s. In this period range, the dominant peaks of the H/V ratios are due to the overall effect of the velocity contrasts between the shallow layers representing the subsurface S-wave velocity structure. Moreover, the average S-wave velocity for the top 10 m of soils (VS10) shows a better correlation with the averaged site amplification in a period range of 0.05 s to 0.5 s than VS30 which indicates that VS10 can be a better proxy for high-frequency site amplification in the case of Damascus city. 相似文献
18.
We investigate helicopter electromagnetic (HEM) inversion schemes applied to synthetic and measured HEM sea ice profiling data. Direct HEM data-to-ice-thickness inversion is compared to three different formal, least squares layered earth inversion algorithms.By making several approximations, it is possible to directly invert a single channel measurement (i.e., the in-phase or quadrature component of a single frequency measurement) to obtain an estimate of sea ice thickness. Measurements from multiple input channels, however, can be used in a layered earth inversion to simultaneously recover several model parameters such as sea ice thickness, sea ice conductivity and sub-ice bathymetry. Synthetic data sets for a particular two-frequency HEM system showed that simple least squares inversion algorithms produce reliable estimates of sea ice thickness in cases where the ice is thicker than 3 m. These methods could also recover acceptable estimates of sea ice thickness when a thin, conductive, partially melted sea ice layer was present, and could determine shallow, sub-ice bathymetry in brackish water. As expected, 1D transformations and inversions of synthetic data for a three-dimensional pressure ridge keel structure contained artifacts, notably broadening of the apparent width of the keel.Prior to inverting a field data set acquired over rather thin (~ 0.5 m) Antarctic sea ice, we found it necessary to recalibrate the phase angle of the measurements using a phasor diagram-based method. Direct transformation of a single channel from the recalibrated data set produced more accurate estimates of sea-ice thickness than formal inversion of multi-channel data. We suggest that the least squares inversion methods are inferior in this situation because of the particular characteristics of the two-frequency HEM system used in this evaluation; the extreme differences in sensitivity of high and low frequency data components, the overall low sensitivity to sea ice conductivity (especially for thin ice), and the partially low signal-to noise ratios of the measurements. The data sets used in this study will be made available to the public to allow alternate inversion approaches to be applied and evaluated. It is suggested that inclusion of parameter bounds and other forms of regularization could help to improve the inversion results. 相似文献
19.
Fiona M. Campbell A. Kaiser H. Horstmeyer A.G. Green F. Ghisetti A.R. Gorman M. Finnemore D.C. Nobes 《Journal of Applied Geophysics》2010,70(4):332-342
In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1–2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N–S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ～ 800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ～ 50° west-dipping primary fault plane. 相似文献
20.
《Journal of Applied Geophysics》2008,66(3-4):142-154
Very-high-resolution (VHR) seismic and magnetic investigations were carried out over a chemical munition dumpsite in the Bornholm Basin, south-western Baltic Sea. The main goal of the investigations was to image the shallow internal structure of the dumpsite and to map the lateral and vertical distribution of the dumped war material. The shallow geology was imaged in great detail on the seismic data. Seven seismic–stratigraphic units were identified, related to different stages in the Holocene and late-glacial history. A large number of diapir-like features were observed that most likely represent fluid expulsion phenomena. Four shipwrecks were identified in the dumpsite area. The wrecks have partly sunk into the soft upper sediments, their height above the sea floor reaching no more than 2 m. Seismic and magnetic data indicate the presence of a large number of buried objects. In most cases there is a good correlation between the seismic and magnetic data sets. The objects are generally buried no deeper than 1 to 2 m. Their size varies between 1.5 and 5 m, occasionally up to 10 m. Shallow pits in the sea bed are likely due to the impact of dumping. The data confirm the wide variety of dumped war material ranging from bombs and shells to encasements and containers. The distribution of the buried objects seems rather heterogeneous, with locally high object concentrations surrounded by areas of lower object density. The results of this case study demonstrate the benefit of complementary, concurrent geophysical investigations for munition dumpsite research. Finally this will yield a better assessment of the current status of the dumpsite and the possible ecological risks related to the dumped war material. 相似文献