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Nearly 150 measurements of the total magnetic field intensity were made in Kuwait in early 1988. Observation points are located primarily along major highways over lines varying in length from few to several tens of kilometers. Measurements were made with a proton magnetometer. Station spacing varied from nearly 1 to 5 km. Diurnal correction to the data was made possible by frequent excursions to the base station.
Preliminary analysis of the data indicates that the field intensity undulates in SW-NE direction nearly perpendicular to the regional tectonic trend. The amplitude of these variations range approximately from 30 to 90 γ over wavelengths varying nearly from 38 to 70 km. We have made a combined inversion of the data with the unpublished Bouguer gravity map of the country along a N-S profile in the central region and find that the data are reasonably well matched with predictions of a simple two-dimensional block model. The model consists of a layer overlying a half-space. The variables of the model are the thickness and density of the surface layer and the susceptibility of the basement rock. The observed variation of the magnetic field and Bouguer anomalies for the selected profile may be accounted for either by the simultaneous northward density reduction of about 0.06 g/cm3 in the surface layer and approximately 15% increase of the basement susceptibility, or else by nearly 800 m variation of the sedimentary thickness. 相似文献
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Mansour Niazi 《Pure and Applied Geophysics》1984,122(6):966-981
Around 700 reported precursors of about 350 earthquakes, including the negative observations, have been compiled in 11 categories with 31 subdivisions. The data base is subjected to an initial sorting and screening by imposing three restrictions on the ranges of main shock magnitude (M≥4.0), precursory time (t≤20 years), and the epicentral distance of observation points (X m≤4.100.3M ). Of the 31 subcategories of precursory phenomena, 18 with 9 data points or more are independently studied by regressing their precursory times against magnitude. The preliminary results tend to classify the precursors into three groups:
- The precursors which show weak or no correlation between time and the magnitude of the eventual main shock. Examples of this group are foreshocks and precursory tilt.
- The precursors which show clear scaling with magnitude. These include seismic velocity ratio (V p/Vs), travel time delay, duration of seismic quiescence, and, to some degree, the variation ofb-value, and anomalous seismicity.
- The precursors which display clustering of precursory times around a mean value, which differs for different precursors from a few hours to a few years. Examples include the conductivity rate, geoelectric current and potential, strain, water well level, geochemical anomalies, change of focal mechanism, and the enhancement of seismicity reported only for larger earthquakes. Some of the precursors in this category, such as leveling changes and the occurrence of microseismicity, show bimodal patterns of precursory times and may partially be coseismic.
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A method is proposed for assessing the modifying effects of precursory observations on long-term probabilities of strong earthquakes (M6). Estimated short-and intermediate-term probabilities so estimated rely on the mean precursory time and its uncertainty as a function of the mainshock magnitude and epicentral position. Short-and intermediate-term modification of long-term probabilities within a 120,000 km2 circular area covering most of Southern California are estimated for one or more observations of strain, resistivity, and ground water anomalies centered near Palmdale in the central Transverse Ranges. The principal assumptions employed are log normal distribution of globally reported waiting periods and assumed predictive reliability of precursory phenomena. As expected, the significance of short-and intermediate-term modifications scale with the reliability of precursory observations, and are particularly enhanced within window lengths of a precursory characteristic time. 相似文献
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Vulnerability assessment of the impact of sea-level rise and flooding on the Moroccan coast: The case of the Mediterranean eastern zone 总被引：1，自引：0，他引：1
The eastern part of the Mediterranean coast of Morocco is physically and socio-economically vulnerable to accelerated sea-level rise, due to its low topography and its high ecological and touristic value. Assessment of the potential land loss by inundation has been based on empirical approaches using a minimum inundation level of 2 m and a maximum inundation level of 7 m, where scenarios for future sea-level rise range from 200 to 860 mm, with a ‘best estimate’ of 490 mm. The socio-economic impacts have been based on two possible alternative futures: (1) a ‘worst-case’ scenario, obtained by combining the ‘economic development first’ scenario with the maximum inundation level; and (2) a ‘best-case’ scenario, by combining the ‘sustainability first’ scenario with the minimum inundation level. Inundation analysis, based on Geographical Information Systems and a modelling approach to erosion, has identified both locations and the socioeconomic sectors that are most at risk to accelerated sea-level rise. 相似文献
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Soil erosion and sediment yield modeling using RS and GIS techniques: a case study, Iran 总被引：1，自引：1，他引：0
Water erosion is a serious and continuous environmental problem in many parts of the world. The need to quantify the amount of erosion, sediment delivery, and sediment yield in a spatially distributed form has become essential at the watershed scale and in the implementation of conservation efforts. In this study, an effort to predict potential annual soil loss and sediment yield is conducted by using the Revised Universal Soil Loss Equation (RUSLE) model with adaptation in a geographic information system (GIS). The rainfall erosivity, soil erosivity, slope length, steepness, plant cover, and management practice and conservation support practice factors are among the basic factors that are obtained from monthly and annual rainfall data, soil map of the region, 50-m digital elevation model, remote sensing (RS) techniques (with use of Normalized Difference Vegetation Index), and GIS, respectively. The Ilam dam watershed which is located southeast part of Ilam province in western Iran is considered as study area. The study indicates that the slope length and steepness of the RUSLE model are the most effective factors controlling soil erosion in the region. The mean annual soil loss and sediment yield are also predicted. Moreover, the results indicated that 45.25%, 12.18%, 12.44%, 10.79%, and 19.34% of the study area are under minimal, low, moderate, high, and extreme actual erosion risks, respectively. Since 30.13% of the region is under high and extreme erosion risk, adoption of suitable conservation measures seems to be inevitable. So, the RUSLE model integrated with RS and GIS techniques has a great potential for producing accurate and inexpensive erosion and sediment yield risk maps in Iran. 相似文献
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Cone Penetration Test Based Direct Methods for Evaluating Static Axial Capacity of Single Piles 总被引：1，自引：0，他引：1
The direct cone penetration test (CPT) based pile design methods use the measured penetrometer readings by scaling relationships or algorithms in a single-step process to enable the assessment of pile capacity components of shaft and base resistance (f p and q b, respectively) for evaluation of full-size pilings. This paper presents a state-of-the-art review of published works that focus on direct CPT evaluation of static axial pile capacity. The review is presented in a chronological order to explicate the evolution over the past six decades of an in situ test based solution for this soil-structure interaction problem. The objective of this study is an attempt to assemble maximum published methods proposed as a result of past investigations in one resource to afford researchers and practitioners with convenient access to the respective design equations and charts. In addition to an all-inclusive summary table and the design charts, a compilation of significant findings and discussions thereof are presented. Furthermore, potential future research directions are indicated, with special emphasis on the optimal use of the modern multi-channel hybrid geophysical-geotechnical seismic CPT to evaluate the complete axial pile load–displacement response. 相似文献
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