Aftershock Statistics of the 1999 Chi–Chi, Taiwan Earthquake and the Concept of Omori Times     

Ya-Ting Lee  Donald L. Turcotte  John B. Rundle  Chien-Chih Chen 《Pure and Applied Geophysics》2013,170(1-2):221-228

In this paper we consider the statistics of the aftershock sequence of the m = 7.65 20 September 1999 Chi–Chi, Taiwan earthquake. We first consider the frequency-magnitude statistics. We find good agreement with Gutenberg–Richter scaling but find that the aftershock level is anomalously high. This level is quantified using the difference in magnitude between the main shock and the largest inferred aftershock $ {{\Updelta}}m^{ *}. $ Typically, $ {{\Updelta}}m^{ *} $ is in the range 0.8–1.5, but for the Chi–Chi earthquake the value is $ {{\Updelta}}m^{ *} $  = 0.03. We suggest that this may be due to an aseismic slow-earthquake component of rupture. We next consider the decay rate of aftershock activity following the earthquake. The rates are well approximated by the modified Omori’s law. We show that the distribution of interoccurrence times between aftershocks follow a nonhomogeneous Poisson process. We introduce the concept of Omori times to study the merging of the aftershock activity with the background seismicity. The Omori time is defined to be the mean interoccurrence time over a fixed number of aftershocks.  相似文献   

Earth observations during space shuttle mission STS‐34: 18–23 October 1989     

Michael R. Helfert  Kamlesh P. Lulla  Victor S. Whitehead  M. Justin Wilkinson  Donald E. Williams  Michael J.. McCulley 《国际地球制图》2013,28(3):65-79

Abstract

Although high‐resolution microwave synthetic aperture radar (SAR) sensors possess all‐weather capability for mapping soil moisture from spaceborne platforms, continuous temporal and spatial monitoring of this important hydrological parameter has been relatively limited. However, the recent launch of operational SAR sensors aboard various satellites have made possible synoptic soil moisture monitoring a reality. Such systems operate over a wide range of frequencies, look angles, and polarization combinations, and thus show synergistic advantages when combined for estimating soil moisture patterns. Two soil moisture inversion algorithms have been developed using as inputs radar backscattering data at L, S, and C bands in the microwave frequency range. These models have been tested using radar image simulation with speckle added. It is observed that the neural network algorithm yields superior results in mapping actual soil moisture patterns over the linear statistical inversion technique, although both models show comparable errors in soil moisture estimation. We infer that using statistical estimation errors alone for comparison purposes may lead to erroneous conclusions regarding the advantages of one soil moisture inversion algorithm over another.  相似文献   

A “classification based method” for color‐composite image generation on an eight‐bit graphics workstation     

Liping Di  Donald C. Rundquist 《国际地球制图》2013,28(2):23-29

Given the level of contemporary technological accomplishment in computing, it is now possible to undertake image‐processing tasks on a variety of “smaller” systems. While a typical hardware configuration includes 24 bits of refresh memory for color. 8 bits each for red, green, and blue, it is feasible to construct color‐composite images comprised of three spectral bands of remotely sensed data using workstations configured with only a single eight‐bit graphics plane for color. Such systems are commonly available in colleges and universities, since they are less expensive than fully configured color workstations.  相似文献   

Blue Earth River quality monitoring using ARCHER hyperspectral data and field measurements     

Fei Yuan  Bryce Hoppie  Donald Friend  Namyong Lee 《国际地球制图》2013,28(8):683-706

In past decades, remote sensing studies on water quality mapping mainly focused on lakes using medium resolution imagery. Little research utilizes hyperspectral images to assess river water quality. This study aims to assess the capability of using Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance (ARCHER) for river water quality mapping and to characterize spatial patterns of turbidity and chlorophyll in the Blue Earth River (BER) system of Minnesota. The BER was characterized by both hyperspectral imagery (HSI) and laboratory analysis of synchronously collected water quality data. The optimal bands for water quality mapping were determined using a method based on hyperspectral profiles and derivative analysis. Finally, based on the regression analysis and modelling, we mapped continuous surface water turbidity. The results revealed that the ratio of HSI band 17 to band 9 effectively determined turbidity and chlorophyll concentrations. The study also found that turbidity and chlorophyll in the river generally increases downstream.  相似文献   

A comparison between above-water surface and subsurface spectral reflectances collected over inland waters     

Asif M. Bhatti  Donald Rundquist  John Schalles  Luis Ramirez  Seigo Nasu 《国际地球制图》2013,28(2):133-141

The objective of the research was to undertake a quantitative comparison of spectral-reflectance measurements made slightly above the surface of water bodies with the measurements made slightly below the surface. The study is focused on three rivers; two in Georgia, USA and one in Japan. As expected, the differences in reflectance are not constant and vary with the wavelength. The contribution of surface-reflection effects to the surface reflectance measured slightly above the water is both pronounced and highly variable, but although they do alter the magnitude of the upwelling signal, they do not change the general shape of the spectral profiles. The correction of surface-reflection effects by assuming a proportionality factor (ρ) is not considered to be efficient for inland fresh water bodies. For in situ spectroscopy, the recommended approach is to measure upwelling radiance slightly below the water's surface as a means of minimizing extraneous noise. Researchers should be aware of the potential for diminishing the validity of findings because of measurement errors.  相似文献   

Reference hydrologic networks II. Using reference hydrologic networks to assess climate-driven changes in streamflow     

Donald H. Burn  Jamie Hannaford  Glenn A. Hodgkins  Paul H. Whitfield  Robin Thorne  Terry Marsh 《水文科学杂志》2013,58(8):1580-1593

Abstract

Reference hydrologic networks (RHNs) can play an important role in monitoring for changes in the hydrological regime related to climate variation and change. Currently, the literature concerning hydrological response to climate variations is complex and confounded by the combinations of many methods of analysis, wide variations in hydrology, and the inclusion of data series that include changes in land use, storage regulation and water use in addition to those of climate. Three case studies that illustrate a variety of approaches to the analysis of data from RHNs are presented and used, together with a summary of studies from the literature, to develop approaches for the investigation of changes in the hydrological regime at a continental or global scale, particularly for international comparison. We present recommendations for an analysis framework and the next steps to advance such an initiative. There is a particular focus on the desirability of establishing standardized procedures and methodologies for both the creation of new national RHNs and the systematic analysis of data derived from a collection of RHNs.

Editor Z.W. Kundzewicz; Associate editor K. Hamed

Citation Burn, D. H., et al., 2012 Whitfield, P.H. 2012. Reference hydrologic networks, I. The status of national reference hydrologic networks for detecting trends and future directions. Hydrological Sciences Journal, 57(8) this issue[Taylor & Francis Online] , [Google Scholar]. Reference hydrologic networks II. Using reference hydrologic networks to assess climate-driven changes in streamflow. Hydrological Sciences Journal, 57 (8), 1580–1593.  相似文献   

The effect of anisotropic heat transport in the earth's core on the geodynamo     

John T. Donald & Paul H. Roberts 《地球物理与天体物理流体动力学》2013,107(5):367-384

Intermediate dynamos are axisymmetric, spherical models that evade Cowling's theorem by invoking an α-effect to create the meridional magnetic field from the zonal. Usually the energy source maintaining the motions is a specified thermal wind, but here the dynamo is driven by the buoyancy created by a uniform distribution of heat sources. It has been argued by Braginsky and Meytlis (this journal, vol. 55, 1990) that, in a rapidly rotating, strongly magnetic system such as the Earth's core, heat is transported principally by a small-scale turbulence that is highly anisotropic. They conclude that the diffusion of heat parallel to the rotation axis is then significantly greater than it is in directions away from that axis. A preliminary study of the consequences of this idea is reported here. Solutions are derived numerically using both isotropic and non-isotropic thermal diffusivity tensors, and the results are compared. It is shown that even a small degree of anisotropy can materially alter the character of the dynamo.  相似文献   

Knowledge,influence, and firm-level change: A geographic analysis of board membership associated with Canada’s growing and declining businesses     

Murray D. Rice  Sean Tierney  Sean O’Hagan  Donald Lyons  Milford B. Green 《Geoforum》2012,43(5):959-968

Clarification of the factors that drive business expansion and contraction is among the most important topics that can be addressed by research in economic geography and related disciplines. This study analyzes the development of Canadian business by examining the connection between firm-level growth and decline and elite knowledge and influence connections that Canadian businesses use to link themselves to other corporations and cities nationally and globally. The research focuses on the inter-firm and inter-city linkages embodied in the boards of directors of Canada’s leading corporations. Corporate directorships have an important geographic dimension, as firms invite people from a variety of places and backgrounds to serve on their boards. This study finds that board member selection practices among Canadian firms can be linked directly to business growth and decline. Benchmarking board composition against firm expansion and decline in terms of inflation-adjusted annual revenue change over the 1991–2006 period, this study shows that growing Canadian firms are associated with directors from a much broader range of national and international cities than firms that experienced decline over the same period. Firm growth in Canada thus appears to be related to boards encompassing diverse members from national and international locations, while firm decline appears to be associated with boards including more local and regional members. The conclusion interprets the implications of board member diversity and suggests that broadly-based boards can play a role in encouraging firm growth through access to elite knowledge and influence networks.  相似文献   

An Investigation on Erodibility and Geotechnical Characteristics of Fine Grained Fluvial Soils from Lower Michigan     

Matthew A. McClerren  Hiroshan Hettiarachchi  Donald D. Carpenter 《Geotechnical and Geological Engineering》2012,30(4):881-892

Scour and erosion potential of a soil are closely related to each other. Similarities or differences between them have not been defined fully and the terms are often used interchangeably or in association with one another. Erodibility is a property of soil that describes erosion potential. Therefore, a proper understanding of erodibility should help predict scour more accurately. In the past, researchers have looked into erosion of soils with the ultimate objective of understanding the erodibility with respect to the standard geotechnical properties. Most research has shown the difficulties associated with correlating erodibility to any one or more soil properties. The research described in this paper is mainly focused on the relationship between erodibility and dry unit weight of soil with varying fractions of fines. Soils tested using laboratory Jet Erosion Test (JET) indicated that the logarithm of erodibility makes a linear inverse relationship with the dry unit weight. In situ JETs confirmed the range of erodibilities established by the laboratory JETs. The best correlations between erodibility and dry unit weight appeared within a single category of soil as classified by the Unified Soil Classification System. In addition, it was also determined that the logarithm of erodibility is inversely related to the angle of internal friction of the fluvial soils tested during this investigation.  相似文献   

A Dye Tracer Approach for Quantifying Fluid and Solute Flux Across the Sediment–Water Interface     

Ryan N. Cascarano  Donald M. Reeves  Mark A. Henry 《Ground water》2021,59(3):428-437

We propose a dye tracer method to characterize fluid and solute fluxes across the sediment-water interface. Zones of groundwater discharge within the streambed are first identified, and small volume slugs of 0.5 to 1 mL fluorescein dye are released at known subsurface depths. Fluorescein dye allows for visual identification of interface breakthrough locations and times, and dye concentrations at the point of discharge are recorded over time by a fluorometer to generate high resolution breakthrough curves. Groundwater velocities and dispersivities at the demonstration site are estimated by numerically fitting dye breakthroughs to the classical advection-dispersion equation, although the methodology is not limited to a specific transport model. Breakthroughs across the stream-sediment interface at the demonstration site are nonlinear with tracer release depth, and velocity estimates from breakthrough analysis are significantly more reliable than visual dye (time to first dye expression) and Darcy methods which tend to overestimate and underestimate groundwater velocity, respectively. The use of permanent injection points within the streambed and demonstrated reproducibility of dye breakthroughs allow for study of fluid and solute fluxes under seasonally varying hydrologic conditions. The proposed approach also provides a framework for field study of nonconservative, reactive solutes and allows for the determination of characteristic residence times at various depths in the streambed to better understand chemical and nutrient transformations.  相似文献