Electromagnetic mapping of electrical conductivity beneath the Columbia basalts1     

H. Frank Morrison  Yoram Shoham  G. Michael Hoversten  Carlos Torres-Verdín 《Geophysical Prospecting》1996,44(6):963-986

Sedimentary rocks beneath the Columbia River Basalt Group are recognized as having potential for oil and gas production, but the overlying layered basalts effectively mask seismic reflections from the underlying sediments. Four electromagnetic (EM) methods have been applied on profiles crossing Boylston Ridge, a typical east–west trending anticline of the Yakima Fold Belt, in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments. The EM surveys detected strong variations in resistivity within the basalts, and in particular the continuous magnetotelluric array profiling (EMAP) revealed resistivity lows beneath the surface anticlines. These low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile. The controlled-source EM surveys (in-loop transient, long-offset transient, and variable-offset frequency-domain) were designed in anticipation of relatively uniform high resistivity basalts, and were found to have been seriously distorted by the intrabasalt conductors discovered in the field. In particular, the resistivity sections derived from 1D inversions were found to be inconsistent and misleading. The EMAP survey provided the most information about the subsurface resistivity distribution, and was certainly the most cost-effective. However, both controlled-source and EMAP surveys call for accurate 2D or 3D inversion to accommodate the geological objectives of this project.  相似文献   

Infrasonic Signal Detection and Source Location at the Prototype International Data Centre   总被引：1，自引：0，他引：1  

D. J. Brown  C. N. Katz  R. Le Bras  M. P. Flanagan  J. Wang  A. K. Gault 《Pure and Applied Geophysics》2002,159(5):1081-1125

—?This paper describes an automatic and interactive data processing system designed to locate impulsive atmospheric sources with a yield of at least one kiloton by detecting and characterizing the airborne infrasound radiated by the source. The infrasonic processing subsystem forms part of a larger system currently under development at the Prototype International Data Center (PIDC) in Arlington, Virginia where seismic, hydroacoustic, radionuclide and infrasonic methods are used to detect and locate impulsive sources in any terrestrial environment. Infrasonic signal detection is achieved via a coincidence detector which requires both the normalized cross correlation and the short-term-average/long-term-average ratio of a beam in the direction of maximum correlation to exceed predetermined threshold values simultaneously before a detection is declared. The infrasound propagation model currently used to infer travel-time information assumes the horizontal sound speed across the ground to be 320.0?m/s. This crude model is currently being replaced by a model which predicts travel-time information through a ray-tracing algorithm for acoustic waves in an atmosphere with seasonal representations for temperature and wind. A novel feature of the source location process is the fusion of all available arrival information, whether it be seismic, hydroacoustic or infrasonic to locate a single source where it is reasonable to hypothesize a common source. In its final configuration the infrasonic subsystem will routinely process data from the global 60-station International Monitoring System (IMS) infrasonic network currently under development.  相似文献   

Extreme events in a changing climate: Variability is more important than averages   总被引：34，自引：2，他引：34  

Richard W. Katz  Barbara G. Brown 《Climatic change》1992,21(3):289-302

Extreme events act as a catalyst for concern about whether the climate is changing. Statistical theory for extremes is used to demonstrate that the frequency of such events is relatively more dependent on any changes in the variability (more generally, the scale parameter) than in the mean (more generally, the location parameter) of climate. Moreover, this sensitivity is relatively greater the more extreme the event. These results provide additional support for the conclusions that experiments using climate models need to be designed to detect changes in climate variability, and that policy analysis should not rely on scenarios of future climate involving only changes in means.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Aqueous Geochemistry of the Sand-and-Gravel Aquifer, Northwest Florida     

Brian G. Katz  Anne F. Choquette 《Ground water》1991,29(1):47-55

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Plate margin transition from oceanic arc-trench to continental system: The Kermadec-New Zealand example     

H.R. Katz 《Tectonophysics》1982,87(1-4)

The East Coast Fold Belt (ECFB) of the North Island, New Zealand, is the continuation of the Tonga-Kermadec arc-trench system. Structurally its tectonic front to the east defines the Indian-Pacific plate boundary. This, however, is not continuous with the Kermadec Trench. Large-scale fragmentation of the ECFB into segments of greatly varying width, strike and structure may be caused by a strongly segmented subducting plate, individual segments of which strike in different directions and have different dips and rates of subduction. Towards the southwest, regional change of strike with respect to plate motion has resulted in the formation of a broad shear zone marked by a strongly subsiding trough filled with rapidly deposited, largely undeformed sediments in front of the ECFB. This foredeep (Hikurangi Trough), which thus occupies the gap between ECFB (Indian plate) and the continental Chatham Rise (Pacific plate) is gradually being involved in the overall deformation, due to continuing motion of the Pacific plate to the southwest, in a slightly oblique sense along the shear zone. As a result, the Hikurangi Trough is shifting with time to the east-northeast. From a tectonic, structural and morphological point of view, it is unrelated to the Kermadec Trench which terminates in the region of East Cape.The structure of the ECFB is characterized mainly by extension normal to the plate boundary, with regional tilting and down-faulting of the continental margin. Effects of compression are observed only locally, and are often due to diapiric uplifts caused by widespread, undercompacted shale. Such diapirs form elongate structural highs which in many cases have supplied sediments into adjacent basins on their landward side. Overall the continental slope and margin are underlain by land-derived sediments which exhibit in-place deformation. Locally they extend as undeformed sediment aprons beyond the tectonicfront. There is no compelling evidence of a subduction complex of imbricate thrust slices. It is concluded that the tectonic evolution is not controlled by accretion but rather by subsidence and tectonic erosion along the continental margin. The conditions are complicated, however, because of the discrete change from an oceanic arc-trench subduction system to an intercontinental shear zone.  相似文献   

Mechanical Performance of Snow under Loading | Masaharu Fukue. Tokai University Press,Tokyo, 1979, xvi + 136 pp., 6000 Yen     

D.L. Katz 《Engineering Geology》1982,19(1):75-76

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Effects of ultrasonic cleaning on the amino acid geochemistry of foraminifera tests     

Barry J. Katz  Eugene H. Man 《Geochimica et cosmochimica acta》1979,43(9):1567-1570

Although investigations into amino acid geochemistry of foraminifera have included the use of ultrasonic cleaners as part of their cleaning procedure, there apparently has been no attempt to determine what effects this procedure may have on the observed chemical changes. This paper presents the results of a time study showing the effects of cleaning on ten protein amino acids and the non-protein alloisoleucine. The data suggest that there are three loosely defined groups which all ultimately undergo an exponential decrease in concentration, but which vary within the initial 45 min of treatment: Group I, stable; Group II, constantly decreasing; Group III, showing slight increases. The observed effects suggest that studies based on amino acid enantiomeric ratios probably are the least affected by procedural errors introduced by ultrasonification.  相似文献   

Urbanization in Israel: Efrat,E. London: Croom Helm, 1984, 225 pp. £14.95 hardback     

Yoram Bar-Gal 《Applied geography (Sevenoaks, England)》1985,5(2):173-174

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Interpretation of spring recession curves   总被引：4，自引：0，他引：4  

Amit H  Lyakhovsk V  Katz A  Starinsky A  Burg A 《Ground water》2002,40(5):543-551

Recession curves contain information on storage properties and different types of media such as porous, fractured, cracked lithologies and karst. Recession curve analysis provides a function that quantitatively describes the temporal discharge decay and expresses the drained volume between specific time limits (Hall 1968). This analysis also allows estimating the hydrological significance of the discharge function parameters and the hydrological properties of the aquifer. In this study, we analyze data from perennial springs in the Judean Mountains and from others in the Galilee Mountains, northern Israel. All the springs drain perched carbonate aquifers. Eight of the studied springs discharge from a karst dolomite sequence, whereas one flows out from a fractured, slumped block of chalk. We show that all the recession curves can be well fitted by a function that consists of two exponential terms with exponential coefficients alpha1 and alpha2. These coefficients are approximately constant for each spring, reflecting the hydraulic conductivity of different media through which the ground water flows to the spring. The highest coefficient represents the fast flow, probably through cracks, or quickflow, whereas the lower one reflects the slow flow through the porous medium, or baseflow. The comparison of recession curves from different springs and different years leads to the conclusion that the main factors that affect the recession curve exponential coefficients are the aquifer lithology and the geometry of the water conduits therein. In normal years of rainy winter and dry summer, alpha1 is constant in time. However, when the dry period is longer than usual because of a dry winter, alpha1 slightly decreases with time.  相似文献   

Use of Weighted Least-Squares Method in Evaluation of the Relationship Between Dispersivity and Field Scale   总被引：11，自引：1，他引：11  

Moujin Xu  Yoram Eckstein 《Ground water》1995,33(6):905-908

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