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The April 16, 1991, eruption of Volcán de Colima represents a classical example of partial dome collapse with the generation of progressively longer-runout, Merapi-type pyroclastic flows that traveled up to 4 km along the El Cordoban gullies (East, Central and West). The flows filled the gullies with block-and-ash flow deposits up to 10 m thick, of which, after 7 years of erosion, only remnants remained in the El Cordoban West and East gullies. The El Cordoban Central gully, however, provided a well-preserved and incised longitudinal section of the 1991 deposits. The deposits were emplaced as proximal and distal facies, separated by a change in slope angle from >30° to <20°. The proximal facies consists of massive, clast-supported flow units (up to 1 m thick) with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading. The distal facies consists of a massive, matrix-supported deposit up to 8 m thick, which contains dispersed andesite blocks in a fine ash matrix. In the distal facies, a train of blocks marks flow-unit upper boundaries and, although sorting is poor, some grading is present. Thin, finely stratified, or dune-bedded layers of fine ash material are locally present above or below units of both facies. Sedimentologic parameters show that the size or fraction of large pyroclasts (larger than –1 ) decreases from proximal to distal facies, as the percentage of matrix (0 to 4 ) increases, especially immediately beyond the break in slope. We propose that the propagation of the Colima pyroclastic flows is critically dependent on local slope angle, the presence of erodible slope debris, and the decrease in grain size with distance from the vent. The progressive fining is probably caused by some combination of erosion, clast breakup and deposition of larger pyroclasts, and is itself influenced by the slope angle. In the proximal region, the flows moved as granular avalanches, in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud. The maximum runout distance of the avalanches was controlled by the angle of repose of the material, and the volume and grain size of source and eroded material. Because the slope angle is close to the repose angle for this debris, granular avalanches were not able to propagate far beyond the change in slope. If, however, an avalanche had enough mass in finer grain size fractions, at least part of the flow continued beyond the break in slope and across the volcano apron, propagating in a turbulent state and depositing surge layers, or in an otherwise settling-modified state and depositing block-and-ash flow layers.Editorial responsibility: T Druitt 相似文献
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D. Rouwet Y. Taran S. Inguaggiato N. Varley J.A. Santiago Santiago 《Journal of Volcanology and Geothermal Research》2008
El Chichón volcano (Chiapas, Mexico) erupted violently in March–April 1982, breaching through the former volcano–hydrothermal system. Since then, the 1982 crater has hosted a shallow (1–3.3 m, acidic (pH ∼ 2.2) and warm (∼ 30 °C) crater lake with a strongly varying chemistry (Cl/SO4 = 0–79 molar ratio). The changes in crater lake chemistry and volume are not systematically related to the seasonal variation of rainfall, but rather to the activity of near-neutral geyser-like springs in the crater (Soap Pool). These Soap Pool springs are the only sources of Cl for the lake. Their geyser-like behaviour with a long-term (months to years) periodicity is due to a specific geometry of the shallow boiling aquifer beneath the lake, which is the remnant of the 1983 Cl-rich (24,000 mg/l) crater lake water. The Soap Pool springs decreased in Cl content over time. The zero-time extrapolation (1982, year of the eruption) approaches the Cl content in the initial crater lake, meanwhile the extrapolation towards the future indicates a zero-Cl content by 2009 ± 1. This particular situation offers the opportunity to calculate mass balance and Cl budget to quantify the lake–spring system in the El Chichón crater. These calculations show that the water balance without the input of SP springs is negative, implying that the lake should disappear during the dry season. The isotopic composition of lake waters (δD and δ18O) coincide with this crater lake-SP dynamics, reflecting evaporation processes and mixing with SP geyser and meteoric water. Future dome growth, not observed yet in the post-1982 El Chichón crater, may be anticipated by changes in lake chemistry and dynamics. 相似文献
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It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit M
max, which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of M
max from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of
four popular M
max estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in
practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for
combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the M
max estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of M
max. 相似文献
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Studia Geophysica et Geodaetica - 相似文献
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V. V. Shcherbakova G. V. Zhidkov V. P. Shcherbakov 《Izvestiya Physics of the Solid Earth》2008,44(10):816-821
A large volume of data on the paleointensity H an obtained by A.S. Bol’shakov and G.M. Solodovnikov is ignored in modern reconstructions because the authors did not indicate whether they used the check-point procedure for the detection of chemical alterations in rocks associated with determination of H an. The paper presents new values of H an determined by the Thellier-Coe method with the use of the checkpoint procedure from samples of the Armenian collection of Cretaceous rocks used in published studies of Bol’shakov and Solodovnikov. The new results are close to the published ones and point to a small value of the geomagnetic field in the Cretaceous, thereby corroborating Bol’shakov-Solodovnikov’s hypothesis on a low paleofield in the Mesozoic. Our study of samples of the collection studied confirms the reliability of Bol’shakov-Solodovnikov’s determinations of H an. 相似文献
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Based on cross-dating tree rings from the Tianmu Mountain, Zhejiang Province, the tree rings α-cellulose σ13C time series was measured. By spectrum analysis, the variation of tree-ring σ13C sequence shows a quasi periodicity of 4.4 years, which is coincident with the standard cycle of El Niño. After removing the long-term decrease trend of the σ13C variation related to atmospheric CO2 concentration, the response of the σ13C to climate elements was analyzed using meteorology data from a nearby weather station. The results suggest that there is a distinct relativity between high-frequency variation of tree ring σ13C series and seasonal climate parameters, e.g. temperature and precipitation, with a significant time-lag effect. In addition, the high frequency also reflects the strength change of the East Asian Monsoon. The multiple regression method was employed to reconstruct the historical climate, and to analyze the climate change and trend in the last 160 years in the northern Zhejiang Province. 相似文献
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V. F. Belyi 《Journal of Volcanology and Seismology》2010,4(3):149-163
A detailed petrographic study of the impactites found in the El’gygytgyn depression suggested a division of those into the
dacite-rhyolite (dominant) and the andesite-basalt (about 1% of the total impactite volume) groups. The protolith for the
dacite-rhyolite group was the Cretaceous ignimbrite rock association of the Okhotsk-Chukchi volcanic belt (OChVB), from which
the depth of their origin is estimated as 1–1.5 km. The impactites of the andesite-basalt group, which are generally older,
formed from protoliths of apparently metamorphic and magmatic complexes in the OChVB basement occurring at depths of 6.5–8.5
km. The hypothesis that the depths of origin for these groups are different is supported by certain features of clinopyroxene
composition. Geochemical relationships are found to exist between deep and shallow impactites, as shown in the distribution
of Ni, Cr, and Co. The succession of development for the shallow impactite generation forms the following series: impact ignimbrite
→ pumice → cinder → massive glass. The glasses have the most homogeneous overall chemical composition, but these too are characterized
by a high inhomogeneity in the composition of the vitric phases, indicating a rapid and discrete impactite generation that
impeded melt homogenization. The glasses are the final product of impactite generation; they show a dramatic drop in fluid
content and the associated reducing components. 相似文献
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The seismogenic fault and the dynamic mechanism of the Ning’er, Yunnan Province MS6.4 earthquake of June 3, 2007 are studied on the basis of the observation data of the surface fissures, sand blow and water eruption, landslide and collapse associated with the earthquake, incorporating with the data of geologic structures, focal mechanism solutions and aftershock distribution for the earthquake area. The observation of the surface fissures reveals that the Banhai segment of the NW-trending Ning’er fault is dominated by right-lateral strike-slip, while the NNE-trending fault is dominated by left-lateral strike-slip. The seismo-geologic hazards are concentrated mainly within a 330°-extending zone of 13.5 km in length and 4 km in width. The major axis of the isoseismal is also oriented in 330° direction, and the major axis of the seismic intensity VIII area is 13.5 km long. The focal mechanism solutions indicate that the NW-trending nodal plane of the Ning’er MS6.4 earthquake is dominated by right-lateral slip, while the NE-trending nodal plane is dominated by left-lateral slip. The preferred distribution orientation of the aftershocks of MS≥2 is 330°, and the focal depths are within the range of 3～12 km, predominantly within 3～10 km. The distribution of the aftershocks is consistent with the distribution zone of the seismo-geologic hazards. All the above-mentioned data indicate that the Banhai segment of the Ning’er fault is the seismogenic fault of this earthquake. Moreover, the driving force of the Ning’er earthquake is discussed in the light of the active block theory. It is believed that the northward pushing of the Indian plate has caused the eastward slipping of the Qinghai-Tibetan Plateau, which has been transformed into the southeastern-southernward squeezing of the southwest Yunnan region. As a result, the NW-trending faults in the vicinity of the Ning’er area are dominated by right-lateral strike-slip, while the NE-trending faults are dominated by left-lateral strike-slip. This tectonic framework might be the main cause of the frequent occurrence of MS6.0～6.9 earthquakes in the area. 相似文献
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D. S. Kotova M. V. Klimenko V. V. Klimenko V. E. Zakharov 《Geomagnetism and Aeronomy》2017,57(3):288-300
A study of HF wave propagation in the three-dimensional inhomogeneous ionosphere has been carried out in an approximation of geometrical optics. The three-dimensional medium of radio wave propagation is considered to be inhomogeneous, absorbing, and anisotropic due to the influence of the geomagnetic field. The parameters of the medium are described by the results of calculations on the basis of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP). The propagation of radio waves in the equatorial, middle-, and high-latitude ionosphere was studied. Comparisons of the ray trajectories, integral attenuation, deviations of the projection of radio wave trajectories onto the Earth’s surface from the great-circle arc, and the behavior of the angle between the wave phase and wave energy directions, as well as the angle between the direction of propagation and the external magnetic field obtained for quiet and disturbed conditions, have been performed. We consider a geomagnetic storm that occurred in 2011, with the main storm phase occurring on September 26, and the day after geomagnetic disturbances, September 29, as disturbed conditions in the ionosphere. 相似文献
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Five ground-tilt stations were established on the flanks of the Soufriere of St. Vincent; two in 1977, two in 1980, and one in 1983. Four of these stations have survived; two consist of lines oriented radially to the volcano, and the other two consist of cross-shaped arrays. Collectively, this network showed that the volcano inflated gradually before the eruption of 1979 and then deflated rapidly during the eruption and for about a year after it had ended. The volcano then reinflated during much of 1981 and inflated only slightly, if at all, during the 7-year period 1982–1989. The measured amount of ground tilt from 1977 to 1989 was relatively small; the maximum recorded change of radial tilt at a station 6.5 km from the summit of the volcano totaled about 20 rad. Local seismicity correlates well with measured ground deformation: numerous earthquakes accompanied the 1979–1981 deflation/inflation cycle; relatively few earthquakes occurred during the 1982–1989 period of little or no ground deformation. In the hope that the experience we have gained might be of use to others who are considering a program of ground-tilt monitoring on volcanoes elsewhere in the humid tropics, we describe many practical aspects of our program that have evolved over the years. For example: (1) stainless steel bench marks cemented into solid bedrock appear to be stable for at least 12 years, (2) bench marks can be located in concrete-filled drums where bedrock is absent, (3) bench marks should be concealed to protect them from vandalism, (4) care must be exercised where sight lines graze the ground (<0.5 m), and (5) automatic levels are preferable because of their efficiency of operation, especially with inexperienced personnel. 相似文献
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《中国地震研究》2016,(1)
The Qianguo M_S5. 8 earthquake swarm of 2013 occurred in Qianguo,Jilin Province,China. There are five earthquakes with M_S≥5. 0 in the Qianguo earthquake swarm,with magnitudes of M_S5. 5,M_S5. 0,M_S5. 3,M_S5. 8 and M_S5. 0. In this study,the far-field seismic radiated energy characteristics of the earthquakes are compared based on the source spectrum and the ground motion spectrum of the earthquake swarm. The ground motion spectrum of the five earthquakes at Changchun seismic station( CN2),which is the national standard station,is first investigated with the recorded ground motions,and then the far-field seismic radiated energy is calculated and combined with the relationships of the source spectrum to describe the variable characteristics of the Qianguo earthquake swarm. Research results indicate that the second earthquake( No. 2) with M_S5. 0 is the key event of the earthquake swarm,which occurred on October 31,the same day following the first M_S5. 5 earthquake( No.1). In fact,the magnitude of event No. 2 decreased compared to event No.1,which did not agree with its large far-field seismic radiated energy. It needs to be pointed out that event No. 2 was the turning point event of the Qianguo earthquake swarm,as being a significant transition before the largest M_S5. 8 earthquake. 相似文献
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Izvestiya, Physics of the Solid Earth - 相似文献
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The problem of systematic overestimation (20–50%) of the retrieved ozone concentrations in the altitude range of 60–80 km in the TIMED–SABER satellite experiment in the daytime has been solved. The reason for overestimation is the neglect of the electronic vibrational kinetics of photolysis products of ozone and molecular oxygen O2(b1Σg +, ν) and O2(a1Δg, ν). The IR emission band of O2(a1Δg, ν = 0) at 1.27 μm can be correctly used in remote sensing in order to obtain the ozone altitude profile in the altitude range of 50–88 km only with the use of a complete model of electronic vibrational kinetics of O2 and O3 photolysis products (YM2011) in the Earth’s mesosphere and lower thermosphere. Alternative ozone tracers have been considered, and an optimum tracer in the altitude range of 50–100 km such as O2(b1Σg +, ν = 1) molecule emissions has been proposed. 相似文献
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Qian Xiaodong 《中国地震研究》2007,21(1):43-54
Based on the data recorded by the regional digital seismic network of Yunnan and using new methods, the short-term variations of the ambient stress field of Yunnan and its adjacent areas are monitored in real time. With the in-depth analyses of the spatial-temporal evolution of the ambient stress field prior to the 2004, Shuangbai M_S5.0 earthquake, concrete procedures for predicting the three elements of the earthquake are presented. 相似文献
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Izvestiya, Physics of the Solid Earth - Abstract—In my comment on the paper by A.A. Lyubushin, G.N. Kopylova, and Yu.K. Serafimova, I focus on the problem of legitimacy of seismological data... 相似文献