Regional Attenuation of Short-Period P and S Waves in the United States     

Zoltan A. Der  Robert P. Massé  John P. Gurski 《Geophysical Journal International》1975,40(1):85-106

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Modal decomposition method for stationary response of non-classically damped systems     

Takeru Igusa  Armen Der Kiureghian  Jerome L. Sackman 《地震工程与结构动力学》1984,12(1):121-136

The stationary response of multi-degree-of-freedom non-classically damped linear systems subjected to stationary input excitation is studied. A modal decomposition procedure based on the complex eigenvectors and eigenvalues of the system is used to derive general expressions for the spectral moments of response. These expressions are in terms of cross-modal spectral moments and explicitly account for the correlation between modal responses; thus, they are applicable to structures characterized with significant non-classical damping as well as structures with closely spaced frequencies. Closed form solutions are presented for the important case of response to white-noise input. Various quantities of response of general engineering interest can be obtained in terms of these spectral moments. These include mean zero-crossing rate and mean, variance and distribution of peak response over a specified duration. Examples point out several instances where non-classical damping effects become significant and illustrate the marked improvement of the results of this study over conventional analysis based on classical damping approximations.  相似文献   

Minimum continental velocities with respect to the pole since the Archean     

Laura Ullrich  Rob Van Der Voo 《Tectonophysics》1981,74(1-2)

Paleomagnetic apparent polar wander paths provide a method for estimating minimum plate velocities which can be extended much further into the geologic past than can be estimated based on sea-floor magnetic anomalies. Minimum velocities can be determined from the rate of change of latitude as derived relative to a fixed pole. Such latitudinal velocities have been determined for the center of mass of the North American, Baltic, Siberian and African shields since the Archean. The results indicate that plate velocities in the past have at times easily exceeded those for present-day continents, and that they often were equivalent to present-day oceanic velocities, although there are peaks and troughs through time. North American velocities are significantly greater prior to one billion years ago than those of Siberia or Baltica.  相似文献   

Mechanisms of fine extinction band development in vein quartz: new insights from correlative light and electron microscopy     

Tine?Derez  Tom?Van Der?Donck  Oliver?Plümper  Philippe?Muchez  Gill?Pennock  Martyn?R.?Drury  Manuel?SintubinEmail author 《Contributions to Mineralogy and Petrology》2017,172(7):56

Fine extinction bands (FEBs) (also known as deformation lamellae) visible with polarized light microscopy in quartz consist of a range of nanostructures, inferring different formation processes. Previous transmission electron microscopy studies have shown that most FEB nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands. Here we show that three types of FEB nanostructure occur in naturally deformed vein quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium). Prismatic oriented FEBs are defined by bands of dislocation walls. Dauphiné twin boundaries present along the FEB boundaries probably formed after FEB formation. In an example of two sub-rhombohedral oriented FEBs, developed as two sets in one grain, the finer FEB set consists of elongated subgrains, similar to FEBs described in previous transmission electron microscopy studies. The second wider FEB set consists of bands with different dislocation density and fluid-inclusion content. The wider FEB set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain. The nanometre-scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains. Larger fluid inclusions aligned along FEBs are explained by fluid-inclusion redistribution along dislocation cores. The prismatic FEB nanostructure and the relation between FEBs and growth bands have not been recognized before, although related structures have been reported in experimentally deformed quartz.  相似文献   

Tolerance factors in human-wildlife conflicts in protected areas: the case of Cross River National Park,Cross River State Nigeria     

Digun-Aweto  Oghenetejiri  Van Der Merwe  Peet  Saayman  Melville 《GeoJournal》2022,87(1):349-361

GeoJournal - Anthropogenic activities cause habitat loss for wildlife, thus increasing human-wildlife conflicts globally. This study focused on highlighting factors that need to be explored when...  相似文献