High-frequency radiation from crack (stress drop) models of earthquake faulting   总被引：1，自引：0，他引：1  

Raul Madariaga 《Geophysical Journal International》1977,51(3):625-651

We present a theory for the radiation of high-frequency waves by earthquake faults. We model the fault as a planar region in which the stress drops to the kinematic friction during slip. This model is entirely equivalent to a shear crack. For two-dimensional fault models we show that the high frequencies originate from the stress and slip velocity concentrations in the vicinity of the fault's edges. These stress concentrations radiate when the crack expands with accelerated motion. The most efficient generation of high-frequency waves occurs when the rupture velocity changes abruptly. In this case, the displacement spectrum has an ω^-2 behaviour at high frequencies. The excitation is proportional to the intensity of the stress concentration near the crack tips and to the change in the focusing factor due to rupture velocity. We extend these two-dimensional results to more general three-dimensional fault models in the case when the rupture velocity changes simultaneously on the rupture front. Results are similar to those described for two-dimensional faults. We apply the theory to the case of a circular fault that grows at constant velocity and stops suddenly. The present theory is in excellent agreement with a numerical solution of the same problem.
Our results provide upper bounds to the high-frequency radiation from more realistic models in which rupture velocity does not change suddenly. The ω^-2 is the minimum possible decay at high frequencies for any crack model of the source.  相似文献   

Identifying Environmental and Human Factors Associated With Tick Bites using Volunteered Reports and Frequent Pattern Mining   总被引：1，自引：0，他引：1       下载免费PDF全文

Irene Garcia‐Martí  Raul Zurita‐Milla  Arno Swart  Kees C. van den Wijngaard  Arnold J.H. van Vliet  Sita Bennema  Margriet Harms 《Transactions in GIS》2017,21(2):277-299

Tick populations and tick‐borne diseases like Lyme borreliosis have been steadily increasing since the mid‐1990s. Realizing the threat that ticks pose to public health, two Dutch citizen science projects have collected tick bite reports since 2006. This unique volunteered geographical dataset, which currently has nearly 35,000 reports, was used to identify environmental and other circumstantial factors associated with tick bites. For this, we first enriched the tick bite reports with temperature, precipitation, vegetation and volunteered data associated with the location of the tick bite. Using this enriched dataset, we then derived a series of features to characterize the environmental and volunteer‐related conditions in which each tick bite occurred. Next, we discretized these features using the Jenks Natural Breaks algorithm and, after that, we mined frequent environmental patterns associated with tick bites using the AprioriClose algorithm. Finally, we checked that these patterns are specifically associated with the tick bites by comparing them with the frequent patterns mined from pseudo‐random locations. The frequent patterns were visualized using heat maps and ring maps and two representative patterns associated with tick bites were projected into geographic space to study their spatio‐temporal distribution. Our results show that factors linked to human activity are more relevant to model tick bites than seasonal accumulations of temperature, vegetation or precipitation. In particular, the number of warm and dry days per season are present in a significant number of patterns and the majority of tick bites are produced within a distance of half a kilometer of a forest, recreational or built‐up area. The study of patterns in the time‐series revealed that there are several persistent patterns consistently occurring each year and the validation process showed that the volunteer tick bites collection is capturing environmental conditions associated with tick bites, suggesting that these reports have a high scientific value. These results support the creation of a Dutch tick bite risk map that, in turn, will open the door to the design of public health interventions to reduce the incidence of Lyme disease.  相似文献   

Context and differentiation: Comparative analysis of two community-based fishers’ organizations     

Raul P. Lejano  Alma Ocampo-Salvador   《Marine Policy》2006,30(6):726-736

There has evolved, as of late, a strong interest in decentralized modes of governance over fisheries and other marine resources, particularly that of community-based resource management (CBRM). However, analysis of this institutional model is hindered by simplistic, typological depictions of CBRM. We use organizational theory to argue how, within the broad category of CBRM, there exists a rich variation of institutional forms. We illustrate the analysis by showing how two ostensibly similar fishers’ organizations in Batangas, Philippines, differ in important ways and, furthermore, how these differences respond to particular challenges and opportunities found in their respective contexts. We also discuss implications of this research for program evaluation.  相似文献   

Long-term tidal level distribution using a wave-by-wave approach     

Sonia Castanedo  Fernando J. Mendez  Raul Medina  Ana J. Abascal 《Advances in water resources》2007

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Rubidium-strontium geochronology of granitic rocks from the Morro Vermelho area (Tiger Bay — Angola)     

Dr. Joaquim Raul Torquato  Dr. H. L. Allsopp 《International Journal of Earth Sciences》1973,62(1):172-179

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Using probabilistic analysis to improve greenhouse gas baseline forecasts in developing country contexts: the case of Chile     

Raul O’ Ryan  Carlos Benavides  Juan Pablo San Martín  Javier Mallea 《Climate Policy》2019,19(3):299-314

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Estimating Preferential Flow in Karstic Aquifers Using Statistical Mixed Models     

Angel A. Anaya  Ingrid Padilla  Raul Macchiavelli  Dorothy J. Vesper  John D. Meeker  Akram N. Alshawabkeh 《Ground water》2014,52(4):584-596

Karst aquifers are highly productive groundwater systems often associated with conduit flow. These systems can be highly vulnerable to contamination, resulting in a high potential for contaminant exposure to humans and ecosystems. This work develops statistical models to spatially characterize flow and transport patterns in karstified limestone and determines the effect of aquifer flow rates on these patterns. A laboratory‐scale Geo‐HydroBed model is used to simulate flow and transport processes in a karstic limestone unit. The model consists of stainless steel tanks containing a karstified limestone block collected from a karst aquifer formation in northern Puerto Rico. Experimental work involves making a series of flow and tracer injections, while monitoring hydraulic and tracer response spatially and temporally. Statistical mixed models (SMMs) are applied to hydraulic data to determine likely pathways of preferential flow in the limestone units. The models indicate a highly heterogeneous system with dominant, flow‐dependent preferential flow regions. Results indicate that regions of preferential flow tend to expand at higher groundwater flow rates, suggesting a greater volume of the system being flushed by flowing water at higher rates. Spatial and temporal distribution of tracer concentrations indicates the presence of conduit‐like and diffuse flow transport in the system, supporting the notion of both combined transport mechanisms in the limestone unit. The temporal response of tracer concentrations at different locations in the model coincide with, and confirms the preferential flow distribution generated with the SMMs used in the study.  相似文献   

Validation of recent geopotential models in Tierra Del Fuego     

Maria Eugenia Gomez  Raul Perdomo  Daniel Del Cogliano 《Acta Geophysica》2017,65(5):931-943

This work presents a validation study of global geopotential models (GGM) in the region of Fagnano Lake, located in the southern Andes. This is an excellent area for this type of validation because it is surrounded by the Andes Mountains, and there is no terrestrial gravity or GNSS/levelling data. However, there are mean lake level (MLL) observations, and its surface is assumed to be almost equipotential. Furthermore, in this article, we propose improved geoid solutions through the Residual Terrain Modelling (RTM) approach. Using a global geopotential model, the results achieved allow us to conclude that it is possible to use this technique to extend an existing geoid model to those regions that lack any information (neither gravimetric nor GNSS/levelling observations). As GGMs have evolved, our results have improved progressively. While the validation of EGM2008 with MLL data shows a standard deviation of 35 cm, GOCO05C shows a deviation of 13 cm, similar to the results obtained on land.  相似文献   

Lithium isotope variations in Tonga–Kermadec arc–Lau back‐arc lavas and Deep Sea Drilling Project (DSDP) Site 204 sediments     

Raul Brens  Xiao‐Ming Liu  Simon Turner  Tracy Rushmer 《Island Arc》2019,28(1)

Lithium isotopes have been identified as a promising tracer of subducted materials in arc lavas due to the observable variations in related reservoirs such as subducting sediments and altered oceanic crust. The Tonga–Kermadec arc–Lau back‐arc provides an end‐member of subduction zones with the coldest thermal structure on Earth. Reported here are Li isotope data for 14 lavas from the arc front and 7 back‐arc lavas as well as 12 pelagic and volcaniclastic sediments along a profile through the sedimentary sequence at DSDP Site 204. The arc and back‐arc lavas range from basalts to dacites in composition with SiO₂ = 48.3–65.3 wt% over which Li concentrations increase from 2 ppm to 16 ppm. Li/Y ratios range from 0.08 to 0.77 and from 0.24 to 0.65 in the arc and back‐arc lavas, respectively. The majority of the lavas have δ⁷Li that ranges from 2.5 ‰ to 5.0 ‰ with an average of (3.6 ±0.7) ‰, similar to that reported from other arcs and there is no distinction between the arc front and back‐arc lavas. The pelagic sediments have variable Li concentrations (33–133 ppm) and δ⁷Li that ranges from 1.2 ‰ to 10.2 ‰ while the volcaniclastic sediments have an even greater range of Li concentrations (3.6–165 ppm) and generally higher δ⁷Li values (8–14 ‰). However, δ⁷Li in the lavas does not correlate with commonly used trace element ratio or isotope signatures indicative of slab‐derived fluids or the sediments. This is probably because the range of δ⁷Li in the lavas and sediments overlap. Calculated sediment mass‐balance models require significantly more sediment than previous estimates based on Th–Nd–Be isotopes. This may indicate that a sizeable proportion of the total Li budget in the lavas is provided by Li‐enriched fluids from the subducting sediments and/or altered oceanic crust.  相似文献   

Mock galaxy redshift catalogues from simulations: implications for Pan-STARRS1     

Yan-Chuan Cai  Raul E. Angulo  Carlton M. Baugh  Shaun Cole  Carlos S. Frenk  Adrian Jenkins 《Monthly notices of the Royal Astronomical Society》2009,395(3):1185-1203

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