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Elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources. Changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source. Contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source. Both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities. Numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions, which disregard topography, elastic heterogeneities and density subsurface structures. With this in mind, we reviewed the expected gravity changes accompanying the 1993–1997 inflation phase on Mt Etna by setting up a fully 3-D finite element model in which we used the real topography, to include the geometry, and seismic tomography, to infer the crustal heterogeneities. The inflation phase was clearly detected by different geodetic techniques (EDM, GPS, SAR and levelling data) that showed a uniform expansion of the overall volcano edifice. When the gravity data are integrated with ground deformation data and a coupled FEM modelling was solved, a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations. 相似文献
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Volcanic ash can cause physical damage to an aircraft to the point of mechanical and electrical malfunction. In the event of an ash plume, aircraft would likely be diverted or grounded, leading to economic losses. This article presents two indices to compare the economic vulnerability of flight paths to volcanic ash plumes. The first index includes three factors for a flight path: wind direction, distance to the volcano, and flight‐path attributes (i.e., number of flights per day, number of potential passengers, and average ticket cost). The second index compares the threat posed by different volcanoes to an airline flight‐path network. A case study is presented for two airlines in the northwest United States to a Mt. Adams eruption. The results show that although the first airline has more flight paths in the region, the second airline is slightly more vulnerable due to the spatial relationships of its flight paths to the volcano and their attributes. 相似文献
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In addition to surface geologic and geophysical investigations, Panchromatic SPOT and Landsat Thematic Mapper (TM) data were merged using an IHS approach to produce a satellite composite image to use as a basis for structural geologic analysis of the oil- and gas-bearing regions of Azerbaijan, including the South Caspian and Kura Basins. With the development of new exploration technology, various nonseismic reconnaissance methods, such as remote sensing, gravity, and magnetics for oil exploration have been substantiated and improved. The Azerbaijan and surrounding mountain ranges are favorable for studying natural hydrocarbon seepages. Most of the seepage occurs in faulted and mud volcano areas onshore of the Caspian Sea in Azerbaijan. Determining the geometry of the fault system from analysis of remote-sensing data allows prediction of (1) vertical oil migration from source rocks into tectonic traps in overlying formations and (2) quantitative volume of oil reservoirs. 相似文献
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世界火山分布具有规律性。火山旅游资源具有广泛性和高品味性。火山旅游资源的开发利用需要具有科学的态度和综合性的手段。世界许多国家开发利用火山旅游资源的经济值得我们借鉴。 相似文献
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The paper presents the results of a ground penetrating radar (GPR) application for the detection of ground ice. We combined a reflection traveltime curves analysis with a frequency spectrogram analysis. We found special anomalies at specific traces in the traveltime curves and ground boundaries analysis, and obtained a ground model for subsurface structure which allows the ground ice layer to be identified and delineated. 相似文献
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Mammoth Mountain is a seismically active volcano 200 000 to 50 000 years old, situated on the southwestern rim of Long Valley caldera, California. Since 1989 it has shown evidence of unrest in the form of earthquake swarms (Hill et al. 1990), volcanic 'long-period' earthquakes (Pitt & Hill 1994), increased output of magmatic 3 He (Sorey et al. 1993) and the emission of about 500 tonnes day −1 of CO2 (Farrar et al. 1995; Hill 1996; M. Sorey, personal communication, 1997), which has killed trees and poses a threat to human safety. Local-earthquake tomography shows that in mid-1989 areas of subsequent tree-kill were underlain by extensive regions where the ratio of the compressional and shear elastic-wave speeds VP /VS was about 9 per cent lower than in the surrounding rocks. Theory (Mavko & Mukerji 1995), experiment (Ito, DeVilbiss & Nur 1979), and experience at other geothermal/volcanic areas (Julian et al. 1996) and at petroleum reservoirs (Harris et al. 1996) indicate that VP /VS is sensitive to pore-fluid compressibility, through its effect on VP . The observed VP /VS anomaly is probably caused directly by CO2 , and seismic VP /VS tomography is thus a promising tool for monitoring gas concentration and movement in volcanoes, which may in turn be related to volcanic activity. 相似文献
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《自然地理学》2013,34(3):192-215
This work investigates the initial colonization on recent lahar deposits of the northeast slope of Popocatepetl volcano, Mexico, where 29 circular sample plots (1.57 m2) were established to determine the development stages of colonization in four types of habitats: 1997 lahar, 2001 lahar, margins, and terraces at the channel's bottom. Cluster analysis and the Sørensen Index were used to determine the floristic affinity of these lahars. Richness, frequency, percentage of species contribution, plant cover, density, and stem height were analyzed to determine the composition and structure of plant communities. The distribution of these variables reveals that the communities often have a simple internal structure; however, a relationship has already been established between changes in resilience and the age of the four lahars. Thus, floristic composition develops rapidly (1 sp. in terraces, 11 spp. in the margins, 29 spp. in the 2001 lahar, and 34 spp. in the 1997 lahar). Except for the 1997 lahar, however, structural characteristics are poorly developed in other incipient stages. As colonization advances, the affinity among the various components and sectors of the laharic deposits decreases, thus promoting the gradual incorporation of species found on the adjacent gorge slopes. The Principal Components Analysis used to identify other explanatory factors shows that of 15 variables studied, those associated with the morpho-sedimentology, the hydrovolcanic dynamics and stability of deposits (microtopography, thickness of the deposit, clast shapes, length of the deposit, depth of the gorge, and slope processes) explain a large percentage of variance. Only a few species (Lupinus campestris, Alchemilla procumbens and Penstemon gentianoides), are well adapted to poor soils and the effects of intense erosion caused by the flows. 相似文献
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In order to monitor the Stromboli submarine slope after the 30 December 2002 landslide and tsunami, repeated marine surveys were carried out offshore of Sciara del Fuoco. The morphological changes and depositional processes that brought to the gradual filling of the slide scar have been studied in detail. Thirteen surveys in a period of little more than 4 years provided a unique opportunity to reconstruct the morpho-sedimentary evolution of the submarine slope and its recovery after the mass-wasting event. The scar has been progressively filled with lava and volcanoclastic debris; in the first month and a half, the filling rate was very high due to the entrance of lava flows into the sea and to the morphological readjustment of the slope; in the following months/years the rate dramatically decreased when the eruptive vents moved upwards and the eruption finally stopped. After 4 years (February 2007) more than 40% of the scar was already filled. In early 2007, a new eruption occurred and a lava delta was constructed in the 2002 scar, influencing the natural readjustment of the slope; therefore, our reconstruction only encompasses the period between the 2002 and 2007 eruptions.The swath bathymetry reconstruction of geometry and volume of scar filling during the period 2002–2007 evidenced a punctuated and fast shift of depocenters and debris emplacement through avalanching processes. This process quickly obliterated the features produced by the 2002 tsunamigenic landslide so that a major question about the preservation potential of mass-wasting features on active volcanic flanks emerges. 相似文献
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Michael Commer Stefan L. Helwig reas Hördt Carsten Scholl Bülent Tezkan 《Geophysical Journal International》2006,167(3):1172-1187
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Array analysis using circular-wave-front geometry:an application to locate the nearby seismo-volcanic source 总被引：4，自引：0，他引：4
Javier Almendros Jesús M. Ibáñez Gerardo Alguacil & Edoardo Del Pezzo 《Geophysical Journal International》1999,136(1):159-170
The zero-lag cross-correlation technique, used for array analysis in the hypothesis of plane waves, has been modified to allow the wave front to be circular. Synthetic tests have been performed to check the capability of the method, which returns the input test data when the source–array distances are not greater than two or three times the array aperture. For this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source. For more distant sources the method becomes equivalent to that based on the planar-wave approximation, which gives an estimate of the backazimuth to the source and the apparent velocity. The method has been applied to seismic data recorded at the active volcano located at Deception Island, Antarctica. 35 volcanic long-period events occurring in a small swarm were selected. Results show that the epicentres are close to the array (between 0.4 and 2 km) and aligned in a SW direction, in agreement with one of the main directions of the fracture system of Deception volcano. 相似文献
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大同火山活动的阶段性历史是一个尚未被揭示清楚的地学问题。野外实地考察及室内磁化率、化学成分、粒度和古地磁的测定结果显示：古湖滨处水平层理发育的火山碎屑层存在4个不同倾角的倾斜;古湖近岸处的湖相沉积层中含有4层火山碎屑层;古湖深处的湖相沉积层中出现4个磁化率显著正异常的层位,且这些层位粒度都较粗;古湖岸上的黄土沉积中出现3个磁化率为峰值、Rb/Sr比值为谷值的层位;古湖深处湖相沉积剖面中存在B/M和Jaramillo磁极性界限。据此进一步分析后认为：① 湖相沉积剖面中的磁化率显著正异常层位、黄土沉积中的高磁化率—低Rb/Sr比值层位可能是混入了大量火山灰物质;它们是区域火山活跃期的记录。② 系列沉积剖面特征指示区域火山活动曾经历4个活跃期,每个活跃期期间有多次密集的火山喷发。③ 4个活跃期的年代大约为早于0.90 Ma BP（第一活跃期）、~0.47 Ma BP（第二活跃期）、~0.31 Ma BP（第三活跃期）和~0.09 Ma BP（第四活跃期）;黄土沉积中还记录了区域北部有一个发生于~0.19 Ma BP的活跃期。此外,区域湖相沉积中所记录的4个火山活跃期都出现在湖退时期,平静期出现在湖侵时期。 相似文献