Array analyses of volcanic earthquakes and tremor recorded at Las Cañadas caldera (Tenerife Island, Spain) during the 2004 seismic activation of Teide volcano   总被引：1，自引：0，他引：1  

Javier Almendros  Jesús M. Ibez  Enrique Carmona  Daria Zandomeneghi 《Journal of Volcanology and Geothermal Research》2007,160(3-4):285-299

We analyze data from three seismic antennas deployed in Las Cañadas caldera (Tenerife) during May–July 2004. The period selected for the analysis (May 12–31, 2004) constitutes one of the most active seismic episodes reported in the area, except for the precursory seismicity accompanying historical eruptions. Most seismic signals recorded by the antennas were volcano-tectonic (VT) earthquakes. They usually exhibited low magnitudes, although some of them were large enough to be felt at nearby villages. A few long-period (LP) events, generally associated with the presence of volcanic fluids in the medium, were also detected. Furthermore, we detected the appearance of a continuous tremor that started on May 18 and lasted for several weeks, at least until the end of the recording period. It is the first time that volcanic tremor has been reported at Teide volcano. This tremor was a small-amplitude, narrow-band signal with central frequency in the range 1–6 Hz. It was detected at the three antennas located in Las Cañadas caldera. We applied the zero-lag cross-correlation (ZLCC) method to estimate the propagation parameters (back-azimuth and apparent slowness) of the recorded signals. For VT earthquakes, we also determined the S–P times and source locations. Our results indicate that at the beginning of the analyzed period most earthquakes clustered in a deep volume below the northwest flank of Teide volcano. The similarity of the propagation parameters obtained for LP events and these early VT earthquakes suggests that LP events might also originate within the source volume of the VT cluster. During the last two weeks of May, VT earthquakes were generally shallower, and spread all over Las Cañadas caldera. Finally, the analysis of the tremor wavefield points to the presence of multiple, low-energy sources acting simultaneously. We propose a model to explain the pattern of seismicity observed at Teide volcano. The process started in early April with a deep magma injection under the northwest flank of Teide volcano, related to a basaltic magma chamber inferred by geological and geophysical studies. The stress changes associated with the injection produced the deep VT cluster. In turn, the occurrence of earthquakes permitted an enhanced supply of fresh magmatic gases toward the surface. This gas flow induced the generation of LP events. The gases permeated the volcanic edifice, producing lubrication of pre-existing fractures and thus favoring the occurrence of VT earthquakes. On May 18, the flow front reached the shallow aquifer located under Las Cañadas caldera. The induced instability constituted the driving mechanism of the observed tremor.  相似文献   

A disaster risk management performance index   总被引：2，自引：4，他引：2  

Martha Liliana Carreño  Omar Darío Cardona  Alex H. Barbat 《Natural Hazards》2007,41(1):1-20

The Risk Management Index, RMI, proposed in this paper, brings together a group of indicators that measure risk management performance and effectiveness. These indicators reflect the organizational, development, capacity and institutional actions taken to reduce vulnerability and losses in a given area, to prepare for crisis and to recover efficiently from disasters. This index is designed to assess risk management performance. It provides a quantitative measure of management based on predefined qualitative targets or benchmarks that risk management efforts should aim to achieve. The design of the RMI involved establishing a scale of achievement levels or determining the distance between current conditions and an objective threshold or conditions in a reference country, sub-national region, or city. The proposed RMI is constructed by quantifying four public policies, each of which is described by six indicators. The mentioned policies include the identification of risk, risk reduction, disaster management, and governance and financial protection. Risk identification comprises the individual perception, social representation and objective assessment; risk reduction involves the prevention and mitigation; disaster management comprises response and recovery; and, governance and financial protection policy is related to institutionalization and risk transfer. Results at the urban, national and sub-national levels, which illustrate the application of the RMI in those scales, are finally given.  相似文献   

Changed thinning regimes may increase carbon stock under climate change: A case study from a Finnish boreal forest     

Jordi Garcia-Gonzalo  Heli Peltola  Elemer Briceño-elizondo  Seppo Kellomäki 《Climatic change》2007,81(3-4):431-454

A physiological growth and yield model was applied for assessing the effects of forest management and climate change on the carbon (C) stocks in a forest management unit located in Finland. The aim was to outline an appropriate management strategy with regard to C stock in the ecosystem (C in trees and C in soil) and C in harvested timber. Simulations covered 100 years using three climate scenarios (current climate, ECHAM4 and HadCM2), five thinning regimes (based on current forest management recommendations for Finland) and one unthinned. Simulations were undertaken with ground true stand inventory data (1451 hectares) representing Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula) stands. Regardless of the climate scenario, it was found that shifting from current practices to thinning regimes that allowed higher stocking of trees resulted in an increase of up to 11% in C in the forest ecosystem. It also increased the C in the timber yield by up to 14%. Compared to current climatic conditions, the mean increase over the thinning regimes in the total C stock in the forest ecosystem due to the climate change was a maximum of 1%; but the mean increase in total C in timber yield over thinning regimes was a maximum of 12%.  相似文献   

Cloud cover analysis associated to cut-off low-pressure systems over Europe using Meteosat Imagery     

G. Delgado  A. Redaño  J. Lorente  R. Nieto  L. Gimeno  P. Ribera  D. Barriopedro  R. García-Herrera  A. Serrano 《Meteorology and Atmospheric Physics》2007,96(1-2):141-157

Summary This paper reports a cloud cover analysis of cut-off low pressure systems (COL) using a pattern recognition method applied to IR and VIS bispectral histograms. 35 COL occurrences were studied over five years (1994–1998). Five cloud types were identified in COLs, of which high clouds (HCC) and deep convective clouds (DCC) were found to be the most relevant to characterize COL systems, though not the most numerous. Cloud cover in a COL is highly dependent on its stage of development, but a higher percentage of cloud cover is always present in the frontal zone, attributable due to higher amounts of high and deep convective clouds. These general characteristics are most marked during the first stage (when the amplitude of the geopotencial wave increases) and second stage (characterized by the development of a cold upper level low), closed cyclonic circulation minimizing differences between rearward and frontal zones during the third stage. The probability of heavy rains during this stage decreases considerably. The centres of mass of high and deep convective clouds move towards the COL-axis centre during COL evolution.  相似文献   

A dynamical equivalent to the equilateral libration points of the earth-moon system     

Carles Díez  Àngel Jorba  Carles Simó 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):13-29

Consider the Earth-Moon-particle system as a Restricted Three Body Problem. There are two equilateral libration points. In the actual world system, those points are no longer relative equilibrium points mainly due to the effect of the Sun and to the noncircular motion of the Moon around the Earth. In this paper we present the problem as a perturbation of the RTBP and we look for the dynamical equivalent of L _4,5. It turns out to be a quasiperiodic orbit. It is obtained for a simplified model but the procedure to obtain it is general and can be carried out with an additional computational effort.  相似文献   

Beyond maximum entropy: Fractal pixon-based image reconstruction     

R. C. Puetter  R. K. Piña 《Experimental Astronomy》1994,3(1-4):293-296

We have developed a new Bayesian image reconstruction method that has been shown to be superior to the best implementations of other methods, including Goodnessof-Fit (e.g. Least-Squares and Lucy-Richardson) and Maximum Entropy (ME). Our new method is based on the concept of the pixon, the fundamental, indivisible unit of picture information. Use of the pixon concept provides an improved image model, resulting in an image prior which is superior to that of standard ME.  相似文献   

Single multipurpose reservoir design: a modified optimal control problem by chance-constrained programming     

Miguel A. Mariño  Slobodan P. Simonovic 《Advances in water resources》1981,4(1):43-48

This paper presents a chance-constrained programming model for optimal control of a multipurpose reservoir and its modification to a model for single reservoir design. An algorithm is developed for solving complex stochastic problems of multipurpose reservoir planning and design. The complexity of the problem is resolved by a two-step algorithm: (1) transformation of chance constraints on the state and control variables is performed at the first step; and (2) the choice of optimum control or optimal reservoir storage is carried out in the second step. The method of iterative convolution is chosen for the first step, while linear programming is selected for the second step. The algorithm allows the use of random inflows and random demands together with other deterministic demands. The reservoir design problem is presented as a modified optimal control problem. The procedure is illustrated with an example of a hypothetical reservoir design problem with three different types of downstream releases (hydropower production, municipal water supply, and irrigation).  相似文献   

Early Paleozoic orogeny in southern South America     

F.G. Aceñolaza  H. Miller 《Precambrian Research》1982,17(2):133-146

In northwest Argentina, weakly metamorphic clastic and calcareous sedimentary rocks of latest Precambrian to Lower Cambrian age (Puncoviscana Formation and related units) contain an abundant ichnofauna of both chronostratigraphic and paleoenvironmental value. In the western and central Sierras Pampeanas, metasedimentary and metavolcanic rocks are considered to form part of the same geotectonic unit. This “Pampean orogenic cycle” includes geosynclinal sedimentation of latest Precambrian to Lower Cambrian age, as well as magmatism, metamorphism and deformation of Middle to Upper Cambrian age, documented by an angular unconformity below the Upper Cambrian to Devonian rocks of the “Famatinian orogenic cycle”. In some of the metamorphic rocks of the Pampean Cycle a pre-Ordovician folding is also distinguished from a later tectonic overprinting. Hence, the concept of a Pampean cycle differs from other concepts of late Precambrian orogenic cycles of South America which are only defined by radiometric ages. The Pampean orogenesis may be compared with the Ross orogenesis of the Transantarctic Mts., the Tyennan orogenesis of Australia and some of the deformation phases of the Damara orogen in Namibia.  相似文献   

Spatial statistics for urban analysis: A review of techniques with examples   总被引：8，自引：0，他引：8  

Antonio Páez  Darren M. Scott 《GeoJournal》2004,61(1):53-67

Traditionally, urban analysis has been quick to adopt and benefit from developments in technology (e.g., microcomputer, GIS) and techniques (e.g., statistics, mathematical programming). This has not been the case, however, with newer methods of spatial analysis — in particular, spatial statistics. Only recently has this situation started to change. This paper documents the confluence of spatial statistics and urban analysis by first reviewing developments in spatial statistics, and then presenting examples of recent applications in urban analysis. The developments reviewed fall under the rubric of global and local forms of spatial analysis, and cover three major technical issues: spatial association, spatial heterogeneity and the modifiable areal unit problem. The examples highlight the relevance and usefulness of the techniques reviewed for urban transportation and land-use applications. The paper concludes with conjectures concerning future developments at the intersection of spatial statistics and urban analysis.  相似文献   

A warning model based on temporal changes of coda Q for volcanic activity at Nevado Del Ruiz Volcano, Colombia     

John M. Londoño  Yasuaki Sudo 《Bulletin of Volcanology》2002,64(5):303-315

The coda Q has been calculated for Nevado del Ruiz Volcano, Colombia (NRV) from 1985 to 1999 by using a single scattering model. During this period, the inverse of Q (Q^-1 proportional to attenuation) exhibited a long-term decrease with time, as well as shorter-term variations related to the volcanic activity. Q^-1 increased prior to volcanic crises and decreased afterward. Based on these observations, a seismic warning criterion has been developed. The parameters (frequency band, size of moving average window, and threshold levels) necessary to evidence clear and significant short-term changes in Q^-1 have been investigated and appropriated values are proposed. We suggest a phenomenological model with three stages for the short-term temporal changes in Q^-1 at NRV. Firstly, Q^-1 increases before a volcanic crises because of accumulation of gas and/or liquid, which decreases the aspect ratio of fluid pockets and increases the fractional volume of fluid in the rocks and the pore aspect ratio. Secondly, Q^-1 starts to decrease during the crises by the discharging of fluids such as gas, water, etc. from the volcano. Finally, Q^-1 becomes more stable after the crisis at a lower value because of the degassing and/or increasing of rigidity of the medium because of the long-term crystallization and cooling processes. Q^-1 seems to be a promising monitoring tool at NRV. It is possible that the observed temporal changes of Q^-1, combined with other parameters, may help to predict with greater accuracy a volcanic crisis at NRV.  相似文献