共查询到20条相似文献，搜索用时 15 毫秒
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External modulation of volcanic activity 总被引：1，自引：0，他引：1
Jürgen Neuberg 《Geophysical Journal International》2000,142(1):232-240
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Mark S. Bebbington 《Geophysical Journal International》2007,171(2):921-942
We examine the application of Hidden Markov Models (HMMs) to volcanic occurrences. The parameters in HMMs can be estimated from data by means of the Expectation–Maximization (EM) algorithm. Various formulations permit modelling the activity level of a volcano through onset counts, the intensity of a Markov Modulated Poisson Process (MMPP), or through the intervals between onsets. More elaborate models allow investigation of the relationship between durations and reposes. After fitting the model, the Viterbi algorithm can be used to identify the underlying (hidden) activity level of the volcano most consistent with the observations. The HMM readily provides forecasts of the next event, and is easily simulated. Data of flank eruptions 1600–2006 from Mount Etna are used to illustrate the methodology. We find that the volcano has longish periods of Poissonian behaviour, interspersed with less random periods, and that changes in regime may be more frequent than have previously been identified statistically. The flank eruptions of Mount Etna appear to have a complex time-predictable character, which is compatible with transitions between an open and closed conduit system. The relationship between reposes and durations appears to characterize the cyclic nature of the volcanoes activity. 相似文献
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Massimiliano Favalli Alessandro Fornaciai Maria Teresa Pareschi 《Geomorphology》2009,111(3-4):123-135
DEMs derived from LIDAR data are nowadays largely used for quantitative analyses and modelling in geology and geomorphology. High-quality DEMs are required for the accurate morphometric and volumetric measurement of land features. We propose a rigorous automatic algorithm for correcting systematic errors in LIDAR data in order to assess sub-metric variations in surface morphology over wide areas, such as those associated with landslide, slump, and volcanic deposits. Our procedure does not require a priori knowledge of the surface, such as the presence of known ground control points. Systematic errors are detected on the basis of distortions in the areas of overlap among different strips. Discrepancies between overlapping strips are assessed at a number of chosen computational tie points. At each tie point a local surface is constructed for each strip containing the point. Displacements between different strips are then calculated at each tie point, and minimization of these discrepancies allows the identification of major systematic errors. These errors are identified as a function of the variables that describe the data acquisition system. Significant errors mainly caused by a non-constant misestimation of the roll angle are highlighted and corrected. Comparison of DEMs constructed using first uncorrected and then corrected LIDAR data from different Mt. Etna surveys shows a meaningful improvement in quality: most of the systematic errors are removed and the accuracy of morphometric and volumetric measurements of volcanic features increases. These corrections are particularly important for the following studies of Mt. Etna: calculation of lava flow volume; calculation of erosion and deposition volume of pyroclastic cones; mapping of areas newly covered by volcanic ash; and morphological evolution of a portion of an active lava field over a short time span. 相似文献
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Formation and failure of volcanic debris dams in the Chakachatna River valley associated with eruptions of the Spurr volcanic complex, Alaska 总被引：1，自引：0，他引：1
Christopher F. Waythomas 《Geomorphology》2001,39(3-4)
The formation of lahars and a debris avalanche during Holocene eruptions of the Spurr volcanic complex in south-central Alaska have led to the development of volcanic debris dams in the Chakachatna River valley. Debris dams composed of lahar and debris-avalanche deposits formed at least five times in the last 8000–10,000 years and most recently during eruptions of Crater Peak vent in 1953 and 1992. Water impounded by a large debris avalanche of early Holocene (?) age may have destabilized an upstream glacier-dammed lake causing a catastrophic flood on the Chakachatna River. A large alluvial fan just downstream of the debris-avalanche deposit is strewn with boulders and blocks and is probably the deposit generated by this flood. Application of a physically based dam-break model yields estimates of peak discharge (Qp) attained during failure of the debris-avalanche dam in the range 104<Qp<106 m3 s−1 for plausible breach erosion rates of 10–100 m h−1. Smaller, short-lived, lahar dams that formed during historical eruptions in 1953, and 1992, impounded smaller lakes in the upper Chakachatna River valley and peak flows attained during failure of these volcanic debris dams were in the range 103<Qp<104 m3 s−1 for plausible breach erosion rates.Volcanic debris dams have formed at other volcanoes in the Cook Inlet region, Aleutian arc, and Wrangell Mountains but apparently did not fail rapidly or result in large or catastrophic outflows. Steep valley topography and frequent eruptions at volcanoes in this region make for significant hazards associated with the formation and failure of volcanic debris dams. 相似文献
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Katherine Donovan 《Area》2010,42(1):117-126
Social volcanology refers to the integration of social science research methods into the traditionally physical domain of volcanology. This emerging multi-methodological research area draws from many disciplines in order to examine hazard-mitigation strategies that are community focused. A key facet of social volcanology is the role of culture and this paper explores the influence of traditional cultural values in relation to the 2006 volcanic crisis at Mt Merapi (Java). This paper describes the complex amalgam of cultural and socio-economic factors that influence community reactions to volcanic hazards and demonstrates the need for interdisciplinary hazard research. 相似文献
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B. Di Lieto G. Saccorotti L. Zuccarello M. La Rocca R. Scarpa 《Geophysical Journal International》2007,169(2):699-705
Using data from two dense array of short period seismometers, we analyse the kinematic properties of volcanic tremor preceding and accompanying the 2004–2005 eruption of Etna Volcano, Italy. Results from slowness analyses indicate the action of at least two distinct sources. The first dominates the pre-eruptive period, and is likely associated with the main plumbing system feeding the Summit and southeast craters. Following the onset of the eruption, secondary directions of wave-arrival encompass the eruptive fissures, located on the lower eastern flank of the southeast crater. Nonetheless, significant energy radiation from this latter source was also occurring prior to the onset of the lava effusion, likely suggesting the presence of a resident magma batch, in agreement with independent petrologic and geochemical data. 相似文献
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The volcanic residuals of the Gawler Ranges together form an extensive massif that in its gross morphology differs markedly from most exposures of silicic volcanic rocks. The upland developed in two stages, the first involving differential fracture‐controlled subsurface weathering, the second the stripping of the regolith. As a result, an irregular weathering front was exposed, with domical projections prominent. These bornhardts are etch forms, and they are of considerable antiquity.
The differential weathering of the rock mass reflects the exploitation of various fracture systems by shallow groundwaters. Orthogonal fracture systems at various scales, sheet fractures and columnar joints control the morphology of the bornhardts in gross and in detail.
The exploitation of the structural base, which was established in the Middle Protero‐zoic, probably took place throughout the Late Proterozoic and the Palaeozoic, though only minor remnants of the Proterozoic land surface remain. The major landscape features developed during the Mesozoic. The weathering which initiated the bornhardts occurred in the Jurassic or earlier Mesozoic, and the landforms were exposed in Late Cretaceous to Early Tertiary times.
Though structural forms dominate the present landscape, some major and some minor landforms are best explained in terms of climatic changes of the later Cainozoic. The palaeodrainage system, established under humid conditions by the Early Tertiary, was alluviated during the Cainozoic arid phases, and salinas were formed. The sand dunes of the region also reflect this aridity. 相似文献
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Lake development in geologically active basins is a complex phenomenon as shown by the bed of the Pliocene Tlaxcala paleolake
disturbed by volcanic eruptions in central Mexico. A 5-m layered freshwater diatomite outcrop section shows volcanic ashes
throughout a bottom Stephanodiscus zone up to a more recent Aulacoseira zone. A 0.5-m transition region begins with an abrupt decrease in volcanic inputs and ends with a shift to Aulacoseira solida (Eulenstein) Krammer. Sediment analysis points to a shallow eutrophic lake in the bottom zone undergoing a transition to
higher water volume leading to a threshold depth for the species shift. The lake was apparently deeper and mesotrophic thereafter.
A common interpretation is to attribute such a volume change to a moisture increase. However, evidence of geological activity,
mainly volcanism and faulting, suggests that it could have also been rooted in geomorphological changes of the lake basin. 相似文献
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Michel Prévot 《Geophysical Journal International》1981,66(1):169-192
Summary. The magnetic viscosity of 334 Upper Tertiary and pre-Bruhnes Quaternary volcanic rocks from the Massif Central (France) and the Steens Mountain (Oregon), and of 40 basaltic cores from DSDP leg 37 has been investigated. Thellier's viscosity index follows a log normal distribution with mean values equal to 6 and 3.5 per cent for subaerial and submarine rocks respectively. For subaerial rocks, the average intensity of the viscous remanent magnetization (VRM) acquired in the Earth's field since the beginning of the Bruhnes polarity epoch ( t = 0.7 Myr) is estimated to be equal to one-quarter of the average intensity of the primary remanence. Alternating field demagnetization of VRMs acquired in low fields for acquisition times t ranging from 2 day to 32 month indicates the resistance to alternating fields is quite different from sample to sample and increases linearly with log t.
Néel's diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard VRM is carried by single-domain grains and soft VRM carried by multidomain particles. Single domain particles carrying hard VRM in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold, resulting from high temperature oxidation of titanomagnetite. Soft VRM is carried by low Curie point homogeneous titanomagnetite. Unlike his single domain theory, Néel's multidomain theory of magnetic viscosity does not account quantitatively for the resistance of VRM to alternating fields. 相似文献
Néel's diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard VRM is carried by single-domain grains and soft VRM carried by multidomain particles. Single domain particles carrying hard VRM in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold, resulting from high temperature oxidation of titanomagnetite. Soft VRM is carried by low Curie point homogeneous titanomagnetite. Unlike his single domain theory, Néel's multidomain theory of magnetic viscosity does not account quantitatively for the resistance of VRM to alternating fields. 相似文献
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Over the last 15 years there have been dramatic shifts in the consensus over how best to cope with natural hazards in economically developing regions such as South America. One very positive outcome of the United Nations sponsored International Decade for Natural Disaster Reduction (IDNDR 1990–2000) has been that there is now greater interchange between the work of earth scientists examining the processes and mechanics of hazard occurrence and impact, and social scientists exploring the causes of human vulnerability to hazard – and thereby disaster. This paper traces the development of this new understanding with reference to earthquakes and volcanic eruptions in Peru, one of the most hazardous countries in South America. Particular focus is placed on the excellent progress currently being made by scientists in better understanding the physical dimensions of natural hazard exposure, and the ground-breaking work by social scientists in promoting new approaches to understanding and mitigating human vulnerability to disaster. The paper concludes by emphasizing the need to build on this research to produce more inclusive, incultured and unified strategies of disaster mitigation at the local, national and international levels. 相似文献
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Applicability of time-to-failure analysis to accelerated strain before earthquakes and volcanic eruptions 总被引：6，自引：0，他引：6
Ian G. Main 《Geophysical Journal International》1999,139(3):F1-F6
We examine quantitatively the ranges of applicability of the equation Ω= A+B [1− t/t f ] m for predicting 'system-sized' failure times t f in the Earth. In applications Ω is a proxy measure for strain or crack length, and A , B and the index m are model parameters determined by curve fitting. We consider constitutive rules derived from (a) Charles' law for subcritical crack growth; (b) Voight's equation; and (c) a simple percolation model, and show in each case that this equation holds only when m < 0. When m > 0, the general solution takes the form Ω = A + B [1 + t / T ] m , where T is a positive time constant, and no failure time can be defined. Reported values for volcanic precursors based on rate data are found to be within the range of applicability of time-to-failure analysis ( m < 0). The same applies to seismic moment release before earthquakes, at the expense of poor retrospective predictability of the time of the a posteriori -defined main shock. In contrast, reported values based on increasing cumulative Benioff strain occur in the region where a system-sized failure time cannot be defined ( m > 0; commonly m ≈ 0.3). We conclude on physical grounds that cumulative seismic moment is preferred as the most direct measure of seismic strain. If cumulative Benioff strain is to be retained on empirical grounds, then it is important that these data either be re-examined with the independent constraint m < 0, or that for the case 0 < m + 1 < 1, a specific correction for the time-integration of cumulative data be applied, of the form ΣΩ = At + B '{1 − [1 − t/t f ] m+1 }. 相似文献
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HAN Mei 《地理学报(英文版)》2000,(4)
Neogene volcanic group (also called Linchang volcanic group) in Shandong is mainly distributed in the fault basins of Linqu and Changle area, the west block of the Middle belt of Tanlu fault belt. Its formation is related to the huge strike-slip activities of Tanlu fault belt and the shrinkage of Bohai Sea basin[1]. It is the famous protected area of Shanwang paleontologic fossil in the world, and also the famous mining area of sappire and diatomite in the country. It is of important impli… 相似文献