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1.
Probabilistic characterizations of possible future eruptive scenarios at Vesuvius volcano are elaborated and organized within a risk-based framework. In the EXPLORIS project, a wide variety of topics relating to this basic problem have been pursued: updates of historical data, reinterpretation of previous geological field data and the collection of new fieldwork results, the development of novel numerical modelling codes and of risk assessment techniques have all been completed. To achieve coherence, many diverse strands of evidence had to be unified within a formalised structure, and linked together by expert knowledge. For this purpose, a Vesuvius ‘Event Tree’ (ET) was created to summarise in a numerical-graphical form, at different levels of detail, all the relative likelihoods relating to the genesis and style of eruption, development and nature of volcanic hazards, and the probabilities of occurrence of different volcanic risks in the next eruption crisis. The Event Tree formulation provides a logical pathway connecting generic probabilistic hazard assessment to quantitative risk evaluation. In order to achieve a complete parameterization for this all-inclusive approach, exhaustive hazard and risk models were needed, quantified with comprehensive uncertainty distributions for all factors involved, rather than simple ‘best-estimate’ or nominal values. Thus, a structured expert elicitation procedure was implemented to complement more traditional data analysis and interpretative approaches. The structure of the Vesuvius Event Tree is presented, and some of the data analysis findings and elicitation outcomes that have provided initial indicative probability distributions to be associated with each of its branches are summarized. The Event Tree extends from initiating volcanic eruption events and hazards right through to human impact and infrastructure consequences, with the complete tree and its parameterisation forming a quantitative synoptic framework for comprehensive hazard evaluation and mapping of risk impacts. The organization of the Event Tree allows easy updating, as and when new information becomes available.  相似文献   

2.
We propose a long-term volcanic hazards event tree for Teide-Pico Viejo stratovolcanoes, two complex alkaline composite volcanoes that have erupted 1.8–3 km3 of mafic and felsic magmas from different vent sites during the last 35 ka. This is the maximum period that can be investigated from surface geology and also represents an upper time limit for the appearance of the first phonolites on that volcano. The whole process of the event tree construction was divided into three stages. The first stage included the determination of the spatial probability of vent opening for basaltic and phonolitic eruptions, based on the available geological and geophysical data. The second, involved the analysis of the different eruption types that have characterised the volcanic activity from Teide during this period. The third stage focussed on the generation of the event tree from the information obtained in the two previous steps and from the application of a probabilistic analysis on the occurrence of each possible eruption type. As for other volcanoes, the structure of the Teide-Pico Viejo Event Tree was subdivided into several steps of eruptive progression from general to more specific events. The precursory phase was assumed as an unrest episode of any geologic origin (magmatic, hydrothermal or tectonic), which could be responsible for a clear increase of volcanic activity revealed by geophysical and geochemical monitoring. According to the present characteristics of Teide-Pico Viejo and their past history, we started by considering whether the unrest episode would lead to a sector collapse or not. If the sector collapse does not occur but an eruption is expected, this could be either from the central vents or from any of the volcanoes' flanks. In any of these cases, there are several possibilities according to what has been observed in the period considered in our study. In the case that a sector collapse occurs and is followed by an eruption we considered it as a flank eruption. We conducted an experts elicitation judgement to assign probabilities to the different possibilities indicated in the event tree. We assumed long term estimations based on existing geological and historical data for the last 35 Ka, which gave us a minimum estimate as the geological record for such a long period is incomplete. However, to estimate probabilities for a short term forecast, for example during an unrest episode, we would need to include in the event tree additional information from the monitoring networks, as any possible precursors that may be identified could tell us in which direction the system will evolve. Therefore, we propose to develop future versions of the event tree to include also the precursors that might be expected on each path during the initial stages of a new eruptive event.  相似文献   

3.
Disasters from explosive volcanic eruptions are infrequent and experience in emergency planning and mitigation for such events remains limited. The need for urgently developing more robust methods for risk assessment and decision making in volcanic crises has become increasingly apparent as world populations continue to expand in areas of active explosive volcanism. Nowhere is this more challenging than at Vesuvius, Italy, with hundreds of thousands of people living on the flanks of one of the most dangerous volcanoes in the world. We describe how a new paradigm, evidence-based volcanology, has been applied in EXPLORIS to contribute to crisis planning and management for when the volcano enters its next state of unrest, as well as in long-term land-use planning. The analytical approach we adopted enumerates and quantifies all the processes and effects of the eruptive hazards of the volcano known to influence risk, a scientific challenge that combines field data on the vulnerability of the built environment and humans in past volcanic disasters with theoretical research on the state of the volcano, and including evidence from the field on previous eruptions as well as numerical simulation modelling of eruptive processes. Formal probabilistic reasoning under uncertainty and a decision analysis approach have provided the basis for the development of an event tree for a future range of eruption types with probability paths and hypothetical casualty outcomes for risk assessment. The most likely future eruption scenarios for emergency planning were derived from the event tree and elaborated upon from the geological and historical record. Modelling the impacts in these scenarios and quantifying the consequences for the circumvesuvian area provide realistic assessments for disaster planning and for showing the potential risk–benefit of mitigation measures, the main one being timely evacuation, but include for consideration protecting buildings against dilute, low dynamic pressure surges, and temporary roof supports in the most vulnerable buildings, as well as hardening infrastructure and lifelines. This innovative work suggests that risk-based methods could have an important role in crisis management at cities on volcanoes and small volcanic islands.  相似文献   

4.
This paper presents an automatic system for the elaboration of volcanic hazard maps and scenarios. The methodology used for the generation of both maps is based on the use of numerical simulation of eruptive processes. The system has been developed in a Geographical Information System (GIS) framework, where models for the numerical simulation of different volcanic hazards have been integrated. The user can select in a toolbar one hazard and then decide whether to generate a scenario map (usually with a unique vent) or a hazard map (generally with a broader source area). Once the input parameters are selected, the system automatically generates the corresponding map. The system also incorporates a module to determine the spatial probability of vent opening, as this could be an important parameter for the computation of hazard maps. The tool has been designed in such a way that the inclusion of new numerical models and functionalities is rather easy. Each numerical model is programmed and implemented as an independent program that is launched from the system and, when it finishes the computation, returns the control to the GIS, where the results are shown. This structure allows that further analyses (specifically, risk analyses, that use as an input a hazard or a scenario map), could be also automated inside the system. Additional information, including tutorial and downloadable files can be found in www.gvb-csic.es.  相似文献   

5.
A new perspective in identifying the precursory patterns of eruptions   总被引：2，自引：2，他引：0  
The complexity of the processes responsible for volcanic eruptions makes a theoretical approach to forecasting the evolution of volcanic unrest rather difficult. A feasible strategy for this purpose appears to be the identification of possible repetitive schemes (patterns) in the pre-eruptive unrest of volcanoes. Nevertheless, the limited availability and the heterogeneity of pre-eruptive data, and the objective difficulty in quantitatively recognizing complex pre-eruptive patterns, make this task very difficult. In this work we address this issue by using a pattern recognition approach applied to the seismicity recorded during 217 volcanic episodes of unrest around the world. In particular, we use two non-parametric algorithms that have proven to give satisfactory results in dealing with a small amount of data, even if not normally distributed and/or characterized by discrete or categorical values. The results show evidence of a longer period of instability in the unrest preceding an eruption, compared to isolated unrest. This might indicate, even if not necessarily, a difference in the energy of processes responsible for the two types of unrest. However, if the unrest is followed by an eruption, it seems that the seismic energy released during the unrest (parameterized by the duration of the swarm and the maximum magnitude recorded) is not indicative of the magnitude of the impending eruption. We also found that, in general, unrest followed by the largest explosive eruptions have a longer repose time than those related to moderate eruptions. This evidence supports the fact that the occurrence of a large eruption needs a sufficient amount of time after the last event in order to re-charge the feeding system and to achieve a closed-conduit regime so that a sufficiently large amount of gas can be accumulated.Editorial responsibility: T. Druitt  相似文献   

6.
A new method to calculate volcanic susceptibility, i.e. the spatial probability of vent opening, is presented. Determination of volcanic susceptibility should constitute the first step in the elaboration of volcanic hazard maps of active volcanic fields. Our method considers different criteria as possible indicators for the location of future vents, based on the assumption that these locations should correspond to the surface expressions of the most likely pathways for magma ascent. Thus, two groups of criteria have been considered depending on the time scale (short or long term) of our approach. The first one accounts for long-term hazard assessment and corresponds to structural criteria that provide direct information on the internal structure of the volcanic field, including its past and present stress field, location of structural lineations (fractures and dikes), and location of past eruptions. The second group of criteria concerns to the computation of susceptibility for short term analyses (from days to a few months) during unrest episodes, and includes those structural and dynamical aspects that can be inferred from volcano monitoring. Thus, a specific layer of information is obtained for each of the criteria used. The specific weight of each criterion on the overall analysis depends on its relative significance to indicate pathways for magma ascent, on the quality of data and on their degree of confidence. The combination of the different data layers allows to create a map of the spatial probability of future eruptions based on objective criteria, thus constituting the first step to obtain the corresponding volcanic hazards map. The method has been used to calculate long-term volcanic susceptibility on Tenerife (Canary Islands), and the results obtained are also presented.  相似文献   

7.
BET_VH: a probabilistic tool for long-term volcanic hazard assessment   总被引：2，自引：0，他引：2  
In this paper, we illustrate a Bayesian Event Tree to estimate Volcanic Hazard (BET_VH). The procedure enables us to calculate the probability of any kind of long-term hazardous event for which we are interested, accounting for the intrinsic stochastic nature of volcanic eruptions and our limited knowledge regarding related processes. For the input, the code incorporates results from numerical models simulating the impact of hazardous volcanic phenomena on an area and data from the eruptive history. For the output, the code provides a wide and exhaustive set of spatiotemporal probabilities of different events; these probabilities are estimated by means of a Bayesian approach that allows all uncertainties to be properly accounted for. The code is able to deal with many eruptive settings simultaneously, weighting each with its own probability of occurrence. In a companion paper, we give a detailed example of application of this tool to the Campi Flegrei caldera, in order to estimate the hazard from tephra fall.  相似文献   

8.
Accurately observing and interpreting volcanic unrest phenomena contributes towards better forecasting of volcanic eruptions, thus potentially saving lives. Volcanic unrest is recorded by volcano observatories and may include seismic, geodetic, degassing and/or geothermal phenomena. The multivariate datasets are often complex and can contain a large amount of data in a variety of formats. Low levels of unrest are frequently recorded, causing the distinction between background activity and unrest to be blurred, despite the widespread usage of these terms in unrest literature (including probabilistic eruption-forecasting models) and in Volcanic Alert Level (VAL) systems. Frequencies and intensities of unrest episodes are not easily comparable over time or between volcanoes. Complex unrest information is difficult to communicate simply to civil defence personnel and other non-scientists. The Volcanic Unrest Index (VUI) is presented here to address these issues. The purpose of the VUI is to provide a semi-quantitative rating of unrest intensity relative to each volcano’s past level of unrest and to that of analogous volcanoes. The VUI is calculated using a worksheet of observed phenomena. Ranges for each phenomenon within the worksheet can be customised for individual volcanoes, as demonstrated in the companion paper for Taupo Volcanic Centre, New Zealand (Potter et al. 2015). The VUI can be determined retrospectively for historical episodes of unrest based on qualitative observations, as well as for recent episodes with state-of-the-art monitoring. This enables a long time series of unrest occurrence and intensity to be constructed and easily communicated to end users. The VUI can also assist with VAL decision-making. We present and discuss two approaches to the concept of unrest.  相似文献   

9.
The Auckland Volcanic Field (AVF) is a young basaltic field that lies beneath the urban area of Auckland, New Zealand’s largest city. Over the past 250,000 years the AVF has produced at least 49 basaltic centers; the last eruption was only 600 years ago. In recognition of the high risk associated with a possible future eruption in Auckland, the New Zealand government ran Exercise Ruaumoko in March 2008, a test of New Zealand’s nation-wide preparedness for responding to a major disaster resulting from a volcanic eruption in Auckland City. The exercise scenario was developed in secret, and covered the period of precursory activity up until the eruption. During Exercise Ruaumoko we adapted a recently developed statistical code for eruption forecasting, namely BET_EF (Bayesian Event Tree for Eruption Forecasting), to independently track the unrest evolution and to forecast the most likely onset time, location and style of the initial phase of the simulated eruption. The code was set up before the start of the exercise by entering reliable information on the past history of the AVF as well as the monitoring signals expected in the event of magmatic unrest and an impending eruption. The average probabilities calculated by BET_EF during Exercise Ruaumoko corresponded well to the probabilities subjectively (and independently) estimated by the advising scientists (differences of few percentage units), and provided a sound forecast of the timing (before the event, the eruption probability reached 90%) and location of the eruption. This application of BET_EF to a volcanic field that has experienced no historical activity and for which otherwise limited prior information is available shows its versatility and potential usefulness as a tool to aid decision-making for a wide range of volcano types. Our near real-time application of BET_EF during Exercise Ruaumoko highlighted its potential to clarify and possibly optimize decision-making procedures in a future AVF eruption crisis, and as a rational starting point for discussions in a scientific advisory group. It also stimulated valuable scientific discussion around how a future AVF eruption might progress, and highlighted areas of future volcanological research that would reduce epistemic uncertainties through the development of better input models.  相似文献   

10.
The Campi Flegrei caldera is a restless structure affected by general subsidence and ongoing resurgence of its central part. The persistent activity of the system and the explosive character of the volcanism lead to a very high volcanic hazard that, combined with intense urbanization, corresponds to a very high volcanic risk. One of the largest sources of uncertainty in volcanic hazard/risk assessment for Campi Flegrei is the spatial location of the future volcanic activity. This paper presents and discusses a long-term probability hazard map for vent opening in case of renewal of volcanism at the Campi Flegrei caldera, which shows the spatial conditional probability for the next vent opening, given that an eruption occurs. The map has been constructed by building a Bayesian inference scheme merging prior information and past data. The method allows both aleatory and epistemic uncertainties to be evaluated. The probability map of vent opening shows that two areas of relatively high probability are present within the active portion of the caldera, with a probability approximately doubled with respect to the rest of the caldera. The map has an immediate use in evaluating the areas of the caldera prone to the highest volcanic hazard. Furthermore, it represents an important ingredient in addressing the more general problem of quantitative volcanic hazards assessment at the Campi Flegrei caldera.  相似文献   

11.
Long-term multi-hazard assessment for El Misti volcano (Peru)   总被引：1，自引：1，他引：0  
We propose a long-term probabilistic multi-hazard assessment for El Misti Volcano, a composite cone located <20 km from Arequipa. The second largest Peruvian city is a rapidly expanding economic centre and is classified by UNESCO as World Heritage. We apply the Bayesian Event Tree code for Volcanic Hazard (BET_VH) to produce probabilistic hazard maps for the predominant volcanic phenomena that may affect c.900,000 people living around the volcano. The methodology accounts for the natural variability displayed by volcanoes in their eruptive behaviour, such as different types/sizes of eruptions and possible vent locations. For this purpose, we treat probabilistically several model runs for some of the main hazardous phenomena (lahars, pyroclastic density currents (PDCs), tephra fall and ballistic ejecta) and data from past eruptions at El Misti (tephra fall, PDCs and lahars) and at other volcanoes (PDCs). The hazard maps, although neglecting possible interactions among phenomena or cascade effects, have been produced with a homogeneous method and refer to a common time window of 1 year. The probability maps reveal that only the north and east suburbs of Arequipa are exposed to all volcanic threats except for ballistic ejecta, which are limited to the uninhabited but touristic summit cone. The probability for pyroclastic density currents reaching recently expanding urban areas and the city along ravines is around 0.05 %/year, similar to the probability obtained for roof-critical tephra loading during the rainy season. Lahars represent by far the most probable threat (around 10 %/year) because at least four radial drainage channels can convey them approximately 20 km away from the volcano across the entire city area in heavy rain episodes, even without eruption. The Río Chili Valley represents the major concern to city safety owing to the probable cascading effect of combined threats: PDCs and rockslides, dammed lake break-outs and subsequent lahars or floods. Although this study does not intend to replace the current El Misti hazard map, the quantitative results of this probabilistic multi-hazard assessment can be incorporated into a multi-risk analysis, to support decision makers in any future improvement of the current hazard evaluation, such as further land-use planning and possible emergency management.  相似文献   

12.
By using BET_VH, we propose a quantitative probabilistic hazard assessment for base surge impact in Auckland, New Zealand. Base surges resulting from phreatomagmatic eruptions are among the most dangerous phenomena likely to be associated with the initial phase of a future eruption in the Auckland Volcanic Field. The assessment is done both in the long-term and in a specific short-term case study, i.e. the simulated pre-eruptive unrest episode during Exercise Ruaumoko, a national civil defence exercise. The most important factors to account for are the uncertainties in the vent location (expected for a volcanic field) and in the run-out distance of base surges. Here, we propose a statistical model of base surge run-out distance based on deposits from past eruptions in Auckland and in analogous volcanoes. We then combine our hazard assessment with an analysis of the costs and benefits of evacuating people (on a 1 × 1-km cell grid). In addition to stressing the practical importance of a cost-benefit analysis in creating a bridge between volcanologists and decision makers, our study highlights some important points. First, in the Exercise Ruaumoko application, the evacuation call seems to be required as soon as the unrest phase is clear; additionally, the evacuation area is much larger than what is recommended in the current contingency plan. Secondly, the evacuation area changes in size with time, due to a reduction in the uncertainty in the vent location and increase in the probability of eruption. It is the tradeoff between these two factors that dictates which cells must be evacuated, and when, thus determining the ultimate size and shape of the area to be evacuated.  相似文献   

13.
One of the largest explosive eruptions in the past several thousand years occurred at Tianchi volcano, also known as Changbaishan, on the China–North Korea border. This historically active polygenetic central volcano consists of three parts: a lower basaltic shield, an upper trachytic composite cone, and young comendite ash flows. The Millennium Eruption occurred between 938 and 946?ad, and was preceded by two smaller and chemically different rhyolitic pumice deposits. There has been at least one additional, small eruption in the last three centuries. From 2002 to 2005, seismicity, deformation, and the helium and hydrogen gas contents of spring waters all increased markedly, causing regional concern. We attribute this event to magma recharge or volatile exhalation or both at depth, followed by two episodes of addition of magmatic fluids into the overlying aquifer without a phreatic eruption. The estimated present magma accumulation rate is too low by itself to account for the 2002–2005 unrest. The most serious volcanic hazards are ash eruption and flows, and lahars. The available geological information and volcano monitoring data provide a baseline for comprehensive assessment of future episodes of unrest and possible eruptive activity.  相似文献   

14.
Starting from the 1980's of last century, China has launched the national plan of constructing nuclear power plants along the coastline region in eastern China. Currently, in some of these candidate sites, nuclear facilities have been installed and are in operation, but some other nuclear power plants are still under construction or in site evaluation. In 2012 the Atomic Energy Commission issued the specific guide for volcanic hazards in site evaluation for nuclear installations(IAEA Safety Standards Series No. SSG-21), which was prepared under the IAEA's program for safety standards. It supplements and provides recommendations for meeting the requirements for nuclear installations established in the safety requirements publication on site evaluation for nuclear installations in relation to volcanic hazards. To satisfy the safety standards for volcanic hazard, we follow the IAEA SSG-21 guidelines and develop a simple and practical diffusion program in order to evaluate the potential volcanic hazard caused by tephra fallout from the explosive eruptions. In this practice, we carried out a case study of the active volcanoes in north Hainan Province so as to conduct the probabilistic analysis of the potential volcanic hazard in the surrounding region. The Quaternary volcanism in north Hainan Island, so-called Qiongbei volcanic field is characterized by multi periodic activity, in which the most recent eruption is dated at about 4 000a BP. According to IAEA SSG-21, a capable volcano is one for which both 1)a future eruption or related volcanic event is credible; and 2)such an event has the potential to produce phenomena that may affect a site. Therefore, the Qiongbei volcanic field is capable of producing hazardous phenomena that may reach the potential nuclear power plants around. The input parameters for the simulation of tephra fallout from the future eruption of the Qiongbei volcanic field, such as the size, density and shape of the tephra, the bulk volume and column height, the diffusion parameter P(z), wind direction and intensity, were obtained by field investigation and laboratory analysis. We carried out more than 10000 tephra fallout simulations using a statistical dataset of wind profiles which are obtained from China Meteorological Data Sharing Service System(CMDSSS). Tephra fallout hazard probability maps were constructed for tephra thickness threshold of 1cm. Our results show that the tephra produced by the future large-scale explosive eruption from the Qiongbei volcanic field can affect the area in a range about 250km away from the eruption center. In summary, the current key technical parameters related to volcanic activity and potential hazards in IAEA/SSG-21 guidelines, such as 10Ma volcanic life cycle and 1×10-7 volcanic disaster screening probability threshold, etc. are based on the volcanic activity characteristics in the volcanic island arc system. In consideration of the relatively low level of volcanic activity compared with volcanic island arc system due to the different tectonic background of volcanism in mainland China, the time scale of volcanic disaster assessment in IAEA SSG-21 guideline is relatively high for volcanoes in mainland China. We suggest that the study of "conceptual model" of volcanic activity should be strengthened in future work to prove that there is no credible potential for future eruptions, so that these volcanoes should be screened out at early stage instead of further evaluation by probabilistic model.  相似文献   

15.
Long-range dispersal of volcanic ash can disrupt civil aviation over large areas, as occurred during the 2010 eruption of Eyjafjallaj?kull volcano in Iceland. Here we assess the hazard for civil aviation posed by volcanic ash from a potential violent Strombolian eruption of Somma-Vesuvius, the most likely scenario if eruptive activity resumed at this volcano. A Somma-Vesuvius eruption is of concern for two main reasons: (1) there is a high probability (38?%) that the eruption will be violent Strombolian, as this activity has been common in the most recent period of activity (between AD 1631 and 1944); and (2) violent Strombolian eruptions typically last longer than higher-magnitude events (from 3 to 7?days for the climactic phases) and, consequently, are likely to cause prolonged air traffic disruption (even at large distances if a substantial amount of fine ash is produced such as is typical during Vesuvius eruptions). We compute probabilistic hazard maps for airborne ash concentration at relevant flight levels using the FALL3D ash dispersal model and a statistically representative set of meteorological conditions. Probabilistic hazard maps are computed for two different ash concentration thresholds, 2 and 0.2?mg/m3, which correspond, respectively, to the no-fly and enhanced procedure conditions defined in Europe during the Eyjafjallaj?kull eruption. The seasonal influence of ash dispersal is also analysed by computing seasonal maps. We define the persistence of ash in the atmosphere as the time that a concentration threshold is exceeded divided by the total duration of the eruption (here the eruption phase producing a sustained eruption column). The maps of averaged persistence give additional information on the expected duration of the conditions leading to flight disruption at a given location. We assess the impact that a violent Strombolian eruption would have on the main airports and aerial corridors of the Central Mediterranean area, and this assessment can help those who devise procedures to minimise the impact of these long-lasting low-intensity volcanic events on civil aviation.  相似文献   

16.
During volcanic explosions, volcanic ballistic projectiles (VBP) are frequently ejected. These projectiles represent a threat to people, infrastructure, vegetation, and aircraft due to their high temperatures and impact velocities. In order to protect people adequately, it is necessary to delimit the projectiles’ maximum range within well-defined explosion scenarios likely to occur in a particular volcano. In this study, a general methodology to delimit the hazard zones for VBP during volcanic eruptions is applied to Popocatépetl volcano. Three explosion scenarios with different intensities have been defined based on the past activity of the volcano and parameterized by considering the maximum kinetic energy associated with VBP ejected during previous eruptions. A ballistic model is used to reconstruct the “launching” kinetic energy of VBP observed in the field. In the case of Vulcanian eruptions, the most common type of activity at Popocatépetl, the ballistic model was used in concert with an eruptive model to correlate ballistic range with initial pressure and gas content, parameters that can be estimated by monitoring techniques. The results are validated with field data and video observations of different Vulcanian eruptions at Popocatépetl. For each scenario, the ballistic model is used to calculate the maximum range of VBP under optimum “launching” conditions: ballistic diameter, ejection angle, topography, and wind velocity. Our results are presented in the form of a VBP hazard map with topographic profiles that depict the likely maximum ranges of VBP under explosion scenarios defined specifically for Popocatépetl volcano. The hazard zones shown on the map allow the responsible authorities to plan the definition and mitigation of restricted areas during volcanic crises.  相似文献   

17.
Volcanic ash fallout subsequent to a possible renewal of the Vesuvius activity represents a serious threat to the highly urbanized area around the volcano. In order to assess the relative hazard we consider three different possible scenarios such as those following Plinian, Sub-Plinian, and violent Strombolian eruptions. Reference eruptions for each scenario are similar to the 79 AD (Pompeii), the 1631 AD (or 472 AD) and the 1944 AD Vesuvius events, respectively. Fallout deposits for the first two scenarios are modeled using HAZMAP, a model based on a semi-analytical solution of the 2D advection–diffusion–sedimentation equation. In contrast, fallout following a violent Strombolian event is modeled by means of FALL3D, a numerical model based on the solution of the full 3D advection–diffusion–sedimentation equation which is valid also within the atmospheric boundary layer. Inputs for models are total erupted mass, eruption column height, bulk grain-size, bulk component distribution, and a statistical set of wind profiles obtained by the NCEP/NCAR re-analysis. We computed ground load probability maps for different ash loadings. In the case of a Sub-Plinian scenario, the most representative tephra loading maps in 16 cardinal directions were also calculated. The probability maps obtained for the different scenarios are aimed to give support to the risk mitigation strategies.  相似文献   

18.
The two-island Republic of Trinidad and Tobago in the eastern Caribbean has enjoyed increased physical and industrial development in recent years; however, these islands have been subjected to damaging earthquakes during their history and an up-to-date risk assessment is needed. We examine two approaches to quantifying this problem: (a) the risk estimated probabilistically using recent instrumental data and (b) the hazard inferred from regional tectonic movements. The probabilistic approach indicates that peak ground accelerations with a probability of exceedance of 10 per cent in 50 years could range from 0–23g in Tobago to 0–36g in North-West Trinidad. Tectonic considerations suggest that a maximum-moment earthquake occurring directly under either land mass could generate accelerations as high as 0–6g; the probability of occurrence of such an event is estimated to be about 2 per cent in 50 years for Trinidad and about a tenth this risk for Tobago. This level of hazard would be significant for critical facilities such as LNG plants.  相似文献   

19.
Dykes are the principal channels through which magma reaches the surface in volcanic eruptions. For this reason dykes observed in the field are commonly assumed to be feeders to lava flows. The actual proportion of dykes reaching the surface is, however, poorly known. In order to develop models for the purpose of estimating volcanic hazard, this proportion must be known. This follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes, but also the probability of the injected dykes being arrested. This paper presents field data on several thousand dykes from Iceland and Tenerife (Canary Islands) indicating that many, and probably most, dykes become arrested at various crustal levels and never reach the surface to feed eruptions. Using the results of analytical and numerical models, it is shown that, for common loading conditions, the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest. This means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested. The implication is that during periods of unrest in volcanoes, the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber.  相似文献   

20.
地震、形变、火山气体地球化学等观测结果表明2002~2005年长白山天池火山经历了1次扰动事件。长白山站地震台（CBS台）记录到了扰动事件前后连续稳定的宽频带地震观测资料。前人的观测研究结果认为长白山天池火山扰动期间的火山地震类型主要为构造型火山地震，伴随少量的谐频型地震。本文通过匹配滤波技术，对1999~2007年扰动事件前后CBS台单台三分量地震观测数据进行模板扫描，获得3763个清晰的火山地震事件，其中谐频（HS）事件125个，构造（VT）事件3618个，并发现长周期（LP）事件20个。进而将火山扰动期间火山地震事件分为3种类型：构造型事件、长周期事件和谐频型事件，并提出2002~2005年长白山天池火山扰动机制模型：深源地震-火山能量传递模型，即汪清深源地震能量释放和传递，引发长白山火山区岩石圈应力状态波动。地幔岩浆房受应力干扰后，岩浆通道打开，少量岩浆侵入地壳岩浆房。岩浆混合脱气导致地壳岩浆房升压，引起顶部岩石微破裂，产生构造型火山地震，气体和流体填充这些裂隙，从而产生LP和HS型火山地震事件。  相似文献   

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