摘要:

Supervised and unsupervised classification procedures are developed and applied to synthetic aperture radar (SAR) polarimetric images in order to identify their various Earth terrain components. For supervised classification processing, the Bayes technique is used to classify fully polarimetric and normalized polarimetric SAR data. Simpler polarimetric discriminates, such as the absolute and normalized magnitude response of the individual receiver channel returns, in addition to the phase difference between the receiver channels, are also considered. Another processing algorithm, based on comparing general properties of the Stokes parameters of the scattered wave to that of simple scattering models, is also discussed. This algorithm, which is an unsupervised technique, classifies terrain elements based on the relationship between the orientation angle and handedness of the transmitting and receiving polarization states. These classification procedures have been applied to San Francisco Bay and Traverse City SAR images, supplied by the Jet Propulsion Laboratory. It is shown that supervised classification yields the best overall performance when accurate classifier training data are used, whereas unsupervised classification is applicable when training data are not available.

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07049

年代:1989

数据来源: WILEY

摘要:

For satellite orbit determination, the most accurate observable available today is microwave radio phase, which can be differenced between observing stations and between satellites to cancel both transmitter‐ and receiver‐related errors. For maximum accuracy, the integer cycle ambiguities of the doubly differenced observations must be resolved. To perform this ambiguity resolution, we propose a bootstrapping strategy. This strategy requires the tracking stations to have a wide ranging progression of spacings. By conventional “integrated Doppler” processing of the observations from the most widely spaced stations, the orbits are determined well enough to permit resolution of the ambiguities for the most closely spaced stations. The resolution of these ambiguities reduces the uncertainty of the orbit determination enough to enable ambiguity resolution for more widely spaced stations, which further reduces the orbital uncertainty. In a test of this strategy with six tracking stations, both the formal and the true errors of determining Global Positioning System satellite orbits were reduced by a fact

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07058

年代:1989

数据来源: WILEY

摘要:

As groundwater passes through porous rocks, exchange of oxygen between the fluid and the solid matrix causes a change in the oxygen isotope concentrations in both water and rock. If the rate at which the exchange takes place can be estimated (as a function of the isotope concentrations and temperature), then the time taken for a rock/water system to come to equilibrium with respect to isotope concentration might be calculated. In this paper, conservation laws are used to derive equations for the isotope transport in a porous medium; these are combined with fluid flow equations and a simple equation describing the rate of oxygen isotope exchange between the water and the rock. The resulting set of equations is solved analytically for the zero‐dimensional (lumped‐parameter) model, and numerically, using typical parameters, for the one‐dimensional

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07065

年代:1989

数据来源: WILEY

摘要:

COCORP deep reflection data on the Colorado Plateau reveal complex reflections to about 16 s two‐way travel time (50+ km), beyond which there is an abrupt decrease of reflectivity. This boundary is interpreted to represent the Moho, an inference consistent with the existing but limited refraction data sets when they are reconciled with the recent independent determination of an 8.10–8.15 km/s Pn velocity beneath the Colorado Plateau. This ∼50 km depth to Moho and 8.10–8.15 km/s Pn velocity for the Colorado Plateau closely resembles that of the High Plains just east of the Rocky Mountains. The absence of continuous strong reflections at the Moho suggests that the Moho beneath the Colorado Plateau is a transition, not a velocity step function on the scale of the reflection experiment. The reflection boundary may represent the base of complex and discontinuous reflectors of the crust and crust/mantle transition, below which the mantle may be largely peridotite with a velocity of 8.1 km/s. These results strongly reinforce the suggestion that the Moho on deep reflection data in relatively stable continental regions is represented by an abrupt decrease in reflectivity, below which the mantle is relatively seismically tran

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07071

年代:1989

数据来源: WILEY

摘要:

The massive International Seismological Centre data set of the past 20 years and the two‐station method are used to determinePnvelocities in the mantle lid beneath the Colorado plateau. In this method the event is located at distances wherePnis the first arrival (2°–16°) and the path is in or very near the azimuth of the two‐station pair and crosses the plateau. This technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source, since only the difference in travel times at the two stations is used. However, this technique has a few underlying assumptions and possible sources of errors (such as the quality of thePndata base and station delays caused by varying crustal structure) that require an extremely careful application of the method. A detailed study of the source of errors and a methodology of selection of the data are presented. Application of this method to the Colorado plateau using all possible two‐station pairs from 53 stations located within or along the margin of the plateau yields an average highPnvelocity of 8.12±0.09 km/s. This value is considerably larger than the average value of 7.83 km/s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8.1 km/s for the relatively stable midcontinent region. Our newPnvelocity for the Colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between averagePnvelocities beneath the Colorado plateau and the Basin and Range Province while their tectonic and magmatic Cenozoic history is dramatically different. Previous models for the structure and evolution of the plateau have used the lowPnvelocity as an important constraint on density and thermal state of the lithosphere. Hence such models should be reexamined on the basis of this new uppermost mantlePnvelocity determination. There are two main models that have been proposed to explain the 2‐km uplift of the Colorado plateau. One is based on a combination of thermal thinning of the lithosphere and crustal thickening, and the other involves a combination of the delamination of the subducted, subhorizontal Farallon oceanic plate from the overriding North American plate and crustal thickening. We show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the Cenozoic evolution of western N

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07083

年代:1989

数据来源: WILEY

摘要:

Constraints on the current stress regime of the actively extending northern Basin and Range province are provided by deformation data (focal mechanisms and fault slip studies), hydraulic fracturing in situ stress measurements, borehole elongation (“breakouts”) analyses, and alignment of young volcanic vents. The integrated data indicate significant variations both in principal stress orientations and magnitudes. An approximately E‐W least principal stress direction appears to characterize both the eastern and western margins of the Basin and Range province, whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented NW to N60°W. The contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins. Active deformation along the southeastern and western province margins is characterized by a combination of strike‐slip and normal faulting. Focal mechanisms along northeastern province margin (Wasatch front) and in central Nevada indicate a combination of normal and oblique‐normal faulting. Temporal, regional, and depth‐dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles. However, some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated. Evidence for significant temporal variation (or multiple cycles of variation) in relative stress magnitude comes from the Sierran front‐Basin and Range boundary region where recent earthquakes are predominantly strike slip, whereas the profound relative vertical relief across the Sierra frontal fault zone in the last 9–10 m.y. implies a normal faulting stress regime. Using the best data on stress orientation, relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements. Analysis of well‐constrained slip vectors in the Owens Valley, California, area indicate that large temporal variations in the magnitude of the approximately N‐S oriented maximum horizontal stress are required to explain dominantly dip‐slip and strike‐slip offsets on subparallel faults. Similar faulting relations are observed throughout much of the boundary zone between the Basin and Range‐Sierra Nevada (including the Walker Lane belt). Along the eastern province margin in the Wasatch front area in Utah, available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of<4–5 km. Earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth. Furthermore, superimposed sets of young fault striae along a segment of the Wasatch fault also indicate temporal variations of relative stress magnitudes. Sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion, thermally induced flow, and the influence of the San Andreas plate boundary. Although difficult to date accurately, the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle (1000–5000 years) and multiple ear

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07105

年代:1989

数据来源: WILEY

摘要:

We describe an experiment to measure variations in the state of stress within a horizontally bedded Devonian shale/sandstone/limestone sequence in western New York. A total of 75 stress measurements were made in three wells a kilometer or so apart using a wireline‐supported hydraulic‐fracturing system. The stress profiles indicate that a major drop in horizontal stress level occurs in the generally massive shales. This drop occurs principally across the lowermost member of a group of sand beds and corresponds to an offset inShandSHof 3.5 and 9 MPa, respectively. Above the sands, “thrust” regime conditions prevail, although the amount by whichShexceedsSvis undetermined since instantaneous shut‐in pressures (ISIPs) were clipped at the level ofSvdue to fracture rotation. Below the sands, the regime is strike slip with both horizontal stresses showing lateral uniformity despite substantial variations in topography. The magnitude ofShin the sand beds themselves and a lower limestone remains at least as great asSvdespite the decline in shale stress. Hence stress contrasts between these beds and neighboring shales become pronounced with depth. The contrast inShandSHbetween the lowermost sand and the immediately underlying shale is at least 6 and 14.5 MPa, respectively.SHlevels in the lower strike‐slip regime are about 1.75 times greater thanShand are less than the value required to initiate slippage on favourably oriented frictional interfaces. For the upper thrust regime and the sand and limestone beds, however, the inferred lower bound onSHis close to the slippage threshold for a Coulomb friction coefficient of 0.6. The orientation ofSHis ENE with a standard deviation of 20°. Fracture traces were usually splayed, occasionally spanning 30° of well bore. No systematic correlation between mean orientation and lithology is evident. Significantly different orientations were obtained for adjacent tests in which almost identical ISlPs were observed, suggesting that the fractures quickly reorient themselves to propagate normal to the least principal stress direction. Similarly, vertical traces were observed in those tests where ISIPs apparently reflectSv, suggesting that rotation to horizon

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07129

年代:1989

数据来源: WILEY

摘要:

Detailed stress measurements in three boreholes penetrating horizontally bedded Devonian silt‐stones, sandstones, and limestones above a prominent salt decollement in the Appalachian Plateau of western New York have revealed variations in horizontal stress magnitudes which correlate with lithologic and stratigraphic units in all wells. High differential stress levels (up to 20 MPa) were found in shales of very high clay content, contrary to the proposition that such materials have negligible long‐term strength. Elastic modulus data show that stiffer beds generally host higher stress levels and suggest that sand/shale stress contrasts result in large part from elastic shortening of the section in response to regional ENE compression. No correlation between stress and Poisson's ratio was found. However, a major systematic drop in stress level within the generally massive shales, which occurs across a group of sand beds near the base of the Rhinestreet formation, appears to be of different origin. The stress offset corresponds to the top of a section which we conclude, on the basis of local and regional total strain data derived from chlorite fabric measurements, once hosted abnormally high pore pressures. The total strain data also suggest the entire section above the salt has been uniformly shortened during Alleghanian compression. To explain the stress discontinuity, two kinematic patterns for Alleghanian deformation of the Devonian section are proposed, both involving abnormal pore pressure development in the sub‐Rhinestreet section in response to limited drainage of fluid. Drainage of this paleo‐overpressure is the best available explanation of the stress offset, although an additional remnant stress component must also be present to satisfy the stress data pr

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07155

年代:1989

数据来源: WILEY

摘要:

Boreholes drilled into rock, which is subjected to stresses that amount to a significant fraction of the strength of the rock, may cause the rock to fail adjacent to the borehole surface. Often this results in the elongation of the cross section of the borehole in the direction of the minimum principal (compressive) stress orthogonal to the borehole axis. Such breakouts are valuable indicators of the direction of the minimum compressive stress orthogonal to the axis of the borehole. Their shapes may provide information about the magnitudes of both the maximum and minimum stresses relative to the strength of the rock. Borehole breakouts also may be impediments to drilling and to in situ measurement techniques, such as hydraulic fracturing. Observations and analyses of borehole breakouts raise three important questions. First, how does the shape of the borehole breakout evolve? Second, why are breakout shapes stable despite the very high compressive stress concentrations that they produce? Third, how is the shape of the breakout related to the magnitudes of the stresses in the rock? In this paper, extensile splitting of rock in unconfined, plane strain compression is assumed to be the process of rock failure adjacent to the circumference of the borehole, by which a breakout forms. To simulate the evolution of a borehole breakout, this process is combined with a numerical boundary element analysis of the stresses around a borehole as its cross section evolves from the originally circular shape to that of a stable breakout. The tangential stresses around a stable breakout cross section are found to be everywhere less than the unconfined, plane strain tensile or compressive strength of the rock. The stresses outside the stable breakout are found to be everywhere less than the limiting values of shear strength given by a Mohr‐Coulomb criterion. In the regions of great stress concentrations at the ends of a breakout cross section, which have a pointed shape, the state of stress approaches that of equal biaxial compression in plane strain, as it does ahead of a mathematical crack or notch. The fact that the stresses around a breakout are less than the relevant strength establishes both the stability of the final breakout cross section and the appropriateness of an elastic analysis of the stresses. According to this model, the cross‐sectional shapes of stable breakouts are not related uniquely to the state of stress and the strength of the rock. For example, stable breakouts created instantly in rock already subjected to stress are much larger than stable breakouts created in the same rock with a preexisting borehole by subsequently increasing the stresses to the same values. The results of drilling into an actual rock probably lie between these extremes. Modest changes in borehole cross section as a result of breakout do not alter significantly the minimum tangential (tensile) stress around a borehole with internal pressure from that given by the Kirsch solution for a circular hole subjected to the same stresses. Therefore hydraulic fracturing interpretations based on the Kirsch solution give the correct values for the far‐field str

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07171

年代:1989

数据来源: WILEY

摘要:

Recent observations of particle motion in vertical seismic profile surveys suggest the existence of borehole waves for which the formation horizontal particle motion is polarized in a specific azimuthal direction, possibly the direction of a local principal axis of stress. From an analysis of the static displacement of a pressurized vertical cylindrical borehole in a transversely isotropic formation with a horizontal axis of symmetry, we conclude that horizontal particle motion should not be azimuthally polarized for “tube waves” (lowest mode symmetric borehole wave) even in an ideal azimuthally anisotropic medium. Azimuthally polarized particle motion does exist for the “bending mode” of the borehole (lowest antisymmetric mode) even in isotropic formations; the polarization direction being determined by the source direction. Finite element calculations for a vertical borehole in a transversely isotropic formation with a horizontal axis of symmetry show that two bending modes with different velocities exist. The horizontal particle motion of one is polarized along the symmetry axis and the other is polarized orthogonal to that axis. At low frequencies the velocity of each approaches the velocity of a vertically propagating formation body shear wave with the same polarization direction. The recent experimental observations include one borehole arrival with a propagation velocity and a ratio of horizontal to vertical formation particle motion consistent with the hypothesis that it is a bending mode in an azimuthally anisotropic medium. The polarization direction and excitation of such a mode do not seem unreasonable. Other polarized arrivals cannot be easily ex

ISSN:0148-0227    

DOI:10.1029/JB094iB06p07183

年代:1989

数据来源: WILEY