Influence of rainfall-induced wetting on the stability of slopes in weathered soils

Shallow failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration. This paper reports trends of rainfall-induced wetting band depth in two types of weathered soils that are commonly found in Korea. Both theoretical and numerical analyses for wetting band depth are presented based on the soil–water characteristic curve obtained using filter paper as well as tensiometer tests. It is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils. Theoretical analysis based on modified Green and Ampt model tends to underestimate the wetting band depth for typical Korean weathered soils. It was also deduced that for Korean weathered soils, the factor of safety drops rapidly once the wetting band depth of 1.2 m reached.     

Pharmaceuticals and Other Organic Waste Water Contaminants Within a Leachate Plume Downgradient of a Municipal Landfill

Ground water samples collected from the Norman Landfill research site in central Oklahoma were analyzed as part of the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program's national reconnaissance of pharmaceuticals and other organic waste water contaminants (OWCs) in ground water. Five sites, four of which are located downgradient of the landfill, were sampled in 2000 and analyzed for 76 OWCs using four research methods developed by the USGS. OWCs were detected in water samples from all of the sites sampled, with 22 of the 76 OWCs being detected at least once. Cholesterol (a plant and animal steroid), was detected at all five sites and was the only compound detected in a well upgradient of the landfill. N,N-diethyltoluamide (DEBT used in insect repellent) and tri(2-chloroethyl) phosphate (fire-retardant) were detected in water samples from all four sites located within the landfill-derived leachate plume. The sites closest to the landfill had more detections and greater concentrations of each of the detected compounds than sites located farther away. Detection of multiple OWCs occurred in the four sites located within the leachate plume, with a minimum of four and a maximum of 17 OWCs detected. Because the landfill was established in the 1920s and closed in 1985, many compounds detected in the leachate plume were likely disposed of decades ago. These results indicate the potential for long-term persistence and transport of some OWCs in ground water.     

Coronal magnetic-field model with non-spherical source surface

Previous global models of coronal magnetic fields have used a geometrical construction based on a spherical source surface because of requirements for computational speed. As a result they have had difficulty accounting for (a) the tendency of full magnetohydrodynamic (MHD) models to predict non-radial plasma flow out to r 10r and (b) the appreciable magnitude, 3, of B _r , (the radial component of B) consistently observed at r 1 AU. We present a new modelling technique based on a non-spherical source surface, which is taken to be an isogauss of the underlying potential field generated by currents in or below the photosphere. This modification of the source surface significantly improves the agreement between the geometrical construction and the MHD solution while retaining most of the computational ease provided by a spherical source surface. A detailed comparison between the present source-surface model and the MHD solution is made for the internal dipole case. The resulting B field agrees well in magnitude and direction with the coronal B field derived from the full MHD equations. It shows evidence of the slightly equatorward meridional plasma flow that is characteristic of the MHD solution. Moreover, the B field obtained by using our non-spherical source surface agrees well with that observed by spacecraft in the vicinity of the Earth's orbit. Applied to a solar dipole field with a moment of 1 G-r ³ , the present model predicts that B _r at r 1 AU lies in the range of 1–2 and is remarkably insensitive to heliomagnetic latitude. Our method should be applicable also to more general (i.e., more realistic) configurations of the solar magnetic field. Isogauss surfaces for two representative solar rotations, as calculated from expansions of observed photospheric magnetic-field data, are found to show large and significant deviations from sphericity.     

Taxonomy of asteroids

A taxonomic system was introduced by C. R. Chapman, D. Morrison, and B. Zellner [Icarus25, 104–130 (1975)], in which minor planets are classified according to a few readily observable optical properties, independent of specific mineralogical interpretations. That taxonomy is here augmented to five classes, now precisely defined in terms of seven parameters obtained from polarimetry, spectrophotometry, radiometry, and UBV photometry of 523 objects. We classify 190 asteroids as type C, 141 as type S, 13 as type M, 3 as type E, and 3 as type R; 55 objects are shown to fall outside these five classes and are designated U (unclassifiable). For the remaining 118, the data exclude two or more types but are insufficient for unambiguous classification. Reliable diameters, from radiometry or polarimetry or else from albedos adopted as typical of the types, are listed for 396 objects. We also compare our taxonomy with other ones and discuss how classification efforts are related to the interpretation of asteroid mineralogies.     

A test of the plausibility of eclipsing binary asteroids

We present an analytic method for producing the lightcurve of a system of spherical bodies in circular orbit about their common center of mass and then use it to model a lightcurve of 171 Ophelia. We find that a model in which the components have a diameter ratio of 1:2.96, have equal albedos, and circle one another in a synchronous orbit (period = 13.146 hr) inclined by 15° to our line of sight provides a reasonable fit to the observed lightcurve. An expression is given for the density in terms of the model parameters. If this lightcurve of Ophelia is produced by mutual eclipses of spherical components the mean density of the system can not exceed 1.7 g cm^?3. In view of these results we conclude that it is possible for Ophelia to be a binary.     

The gravitational field of a disk

This note gives the gravitational potential of the disk {(x, y, z):x ² +y ² p ² , z=0} and the gravitational field at the point (x, y, z). Formulas for a ring can be obtained as the difference of our results for two different values ofp. Results are obtained in terms of elliptic integrals and we indicate how these functions can be computed efficiently. Formulas necessary for the computation of partial derivatives are also given.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract NAS7-100, sponsored by the National Aeronautics and Space Administration.     

ROOF BOUNDARY EXTRACTION USING MULTIPLE IMAGES

Urban area building extraction is one of the most challenging problems in photogrammetry. Well-extracted buildings are needed for a variety of applications, such as cartography, building GIS databases for cities, and urban planning. This paper presents a new technique to extract 3D building wire-frames using a robust multi-image line-matching algorithm. Although one pair of images is adequate to find the 3D position of two visibly corresponding image features, it is not sufficient to solve the general building extraction problem due to obscured parts in the building. Four images are used in this research to extract the building wire-frames. First the images are segmented into regions. Regions are then classified into roof regions and non-roof regions based on their size, shape, and intensity values. The roof region boundary pixels are located and used to find the region perimeters. Region correspondence is solved in a pair-wise mode over all images using the epipolar constraint, region size, region shape, and region intensity values. Image lines within the corresponding regions are matched over all images simultaneously by first creating a plane for each region line. Planes are then intersected simultaneously and geometric consistency is used to determine acceptance or rejection. Results with high overlap and sidelap aerial images are presented and evaluated. The results show the completeness and accuracy that this method can provide for extracting complex urban buildings. The average coordinate accuracy is about 0·8 m using 1:4000 scale aerial photographs scanned at 30 μ m. Six buildings were examined; the line detection rate is 98%.     

Heterogeneous structure of western Nankai seismogenic zone deduced by multichannel reflection data and wide-angle seismic data

The 1946 Nankai earthquake (Ms=8.2) at the forearc region of the western Nankai Trough showed slow slip deformation off Cape Muroto, which did not propagate until the western end of the Nankai seismogenic zone. New seismic investigations show a low-velocity layer (LVL) on the subducting oceanic crust in the coseismic area. Two prestack depth-migrated sections show reflectivity events in the clay-rich boundary layer on the oceanic crust. Narrowly spaced imbricated slices develop in the nonrupture area. The reflective boundary layer indicates probably that underplating develops in the nonrupture area rather than the coseismic area. It is suggested that the friction is larger in the nonrupture area than the coseismic area because of the lack of LVL on the oceanic crust, the well developed underplating and the narrowly spaced imbricated thrusts in the nonrupture area. The topographic high of the oceanic crust with about 50 km width and maximum 3 km height is also revealed and is related to bending and thickening of the oceanic crust, the well developed underplating and the narn spaced imbricated thrusts in the nonrupture area. These structural characters may be the reason why the slow slip deformation did not propagate until the western end of the Nankai seismogenic zone and toward the trough side.     

Shallow SH-wave seismic investigation of the Mt. Angel Fault, Northwest Oregon, USA

The Mt. Angel Fault is likely one of the most active faults near the Portland metropolitan area, and was probably associated with the 1993 Scotts Mills earthquake. SH-wave seismic techniques used to image the Mt. Angel Fault suggest that the fault offsets late Pleistocene gravel (22 to 34 ka) at several locations. Within the study area, displacement of the late Pleistocene gravel along the strike of the Mt. Angel Fault increases from no obvious displacement on the northwest to approximately 18 m on the southeast. This trend of increasing offset along the strike of the fault is paralleled by topographic and geomorphic trends. A reconnaissance geologic investigation at an anomalous bend in the Pudding River near the projected trace of the Mt. Angel Fault revealed potential tectonic deformation in sediments younger than the late Pleistocene gravel imaged by SH-wave data. The results of this study have contributed to the paleoseismic record of the Mt. Angel Fault, laid the groundwork for future geologic investigations along the Pudding River, and determined potential sites for future paleoseismic trenching investigations.