首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   9篇
  免费   0篇
专业分类
地球物理   8篇
地质学   1篇
出版年
  2014年   1篇
  2012年   1篇
  2009年   1篇
  2007年   1篇
  2006年   1篇
  2002年   1篇
  1999年   1篇
  1981年   1篇
  1978年   1篇
排序方式： 共有9条查询结果，搜索用时 93 毫秒
1
1.
A system is proposed for the monitoring of changes in the underground structure of an active volcano over time by applying a transient electromagnetic method. The monitoring system is named ACTIVE, which stands for Array of Controlled Transient-electromagnetics for Imaging Volcano Edifice. The system consists of a transmitter dipole used to generate a controlled transient electromagnetic (EM) field and an array of receivers used to measure the vertical component of the transient magnetic field at various distances, with automatic operation of both units. In order to verify the performance of the proposed system, numerical and field experiments were carried out by application of the system to the Izu-Oshima volcano, where a remarkable change in the apparent DC resistivity over time had been detected in association with the eruption in 1986.  相似文献   
2.
The resistivity structure of Unzen Volcano has been revealed by extensive magnetotelluric surveys since the first eruption on November 17, 1990. This structure comprises a highly resistive surface layer, a low-resistive second layer at several hundred meters depth, interpreted as a water-saturated layer, a resistive third layer, and a low-resistive fourth layer at 10 km depth, possibly related to the deep magmatic activity. The structure has influenced the volcanic activity of Unzen. This activity was characterized by a series of dramatic changes in eruption type: a minor phreatic eruption on November 17, 1990; phreatic eruptions after February 12, 1991, preceded by several weeks of volcanic tremor; phreatomagmatic eruptions after April 9, and dome effusion beginning May 19, 1991. This paper presents a hypothesis in which the top of the magma column rose about 20 m/day, reached the base of the water-saturated layer at the end of January, 1991, and approached the upper boundary of this layer on April 9. Thus, the temporal change of eruption type and associated phenomena are systematically explained by an interaction between magma and groundwater contained in the saturated layer.  相似文献   
3.
Magnetic and electric field variations associated with the 2000 eruption of Miyake-jima volcano are summarized. For about 1 week prior to the July 8 phreatic explosion, significant changes in the total intensity were observed at a few stations, which indicated uprising of a demagnetized area from a depth of 2 km towards the summit: this non-magnetic source can be regarded as a vacant space itself. Electric and magnetic field variations were observed simultaneously associated with the tilt-step event, which was the abrupt (∼50 s) inflation at a few km depth within the volcano followed by gradual recovery (∼several hours). The electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source, while the magnetic field to the piezomagnetic effect due to increased pressure. Large magnetic variations amounting to a few tens of nT were observed at several stations since July 8, and they turned almost flat after the August 18 largest eruption. Magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth. A large increase in the self-potential by 130 mV was also observed near the summit caldera associated with the August 18 eruption, which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption.  相似文献   
4.
The first crater of Nakadake, peak of Aso volcano, Japan, contains a hot water lake that shows interesting variations in water level and temperature. These variations were discovered by precise, continuous observations of the lake independent of precipitation. We developed a numerical model of a hot crater lake and compared with observational data for the period from July 2006 to January 2009. The numerical model revealed seasonal changes in mass flux (75–132 kg/s) and enthalpy (1,840–3,030 kJ/kg) for the fluid supplied to the lake. The relation between the enthalpy and mass flux indicates that the bottom input fluid is a mixture of high- and low-temperature fluids. Assuming a mixture of high-temperature steam at 800°C and liquid water at 100°C, we evaluated the liquid and steam fluxes. The liquid water flux shows a seasonal increase lagging behind the rainy season by 2 months, suggesting that the liquid water is predominantly groundwater. The fluctuation pattern in the flux of the high-temperature steam shows a relation with the amplitude of volcanic tremor, suggesting that heating of the hydrothermal system drives the tremor. Consequently, precise observations of a hot crater lake represent a potential method of monitoring volcanic hydrothermal systems in the shallow parts of the volcanoes.  相似文献   
5.
A drastic change in lake water color from blue-green to brown was observed in the summit crater lake of Mt. Shinmoe-dake, Kirishima Volcano about 8 months after its 2008 eruption. The color change lasted for about 2 months (April–June 2009). The discoloration was attributed to a brownish color suspension that had formed in the lake water. X-ray fluorescence and Fourier transform infrared analyses of a sample of the suspension identified schwertmannite (Fe8O8(OH)6(SO4)). A cultivation test of iron-oxidizing bacteria for the sampled lake water with lakebed sediment revealed that the crater lake hosts iron-oxidizing bacteria, which likely participated in schwertmannite formation. We suggest that pyrite (FeS2) provided an energy source for the iron-oxidizing bacteria since the mineral was identified in hydrothermally altered tephra ejected by the August 2008 eruption. From consideration of these and other factors, the brownish discoloration of the summit crater lake of Mt. Shinmoe-dake was inferred to have resulted from a combined volcanic–microbial process.  相似文献   
6.
A new infra-red radiometer for volcanological purposes consists of a commercially available infra-red optical unit (IR camera), mounted on a balloon-tracking theodolite in place of the telescope. The device has a motor-driven horizontal scan at two speeds, and the output signal is fed to a portable recorder. Thus, it is possible to obtain the horizontal temperature profile of an objective area. With successive scanning with different vertical angles of the camera, the spatial temperature distribution can be obtained.The IR ground scanner was successfully utilized at two volcanoes — Kusatsu-shirane and Mihara-yama, O-shima. Repeated IR surveys were made after minor eruptive events. Variations of the surface temperature with time were detected for both volcanoes. The IR scanner is also suitable for monitoring the time and temperature of eruptions from active vents.  相似文献   
7.
We separated and analyzed several organic and inorganic phases of the carbonaceous chondrite matrix to determine whether they contained any inherent asymmetry. Our intent was to determine any possible foci of asymmetry besides the one determined for meteoritic amino acids. As a probe, we employed a very sensitive asymmetric autocatalytic reaction. We were able to determine that asymmetry still resides in powders after extraction with water and solvents as well as in the insoluble organic material (IOM) obtained after demineralization. Asymmetry is not found any longer in the IOM after hydrothermal treatment and in meteorite powders from which all organics had been removed by O2 plasma at low temperature. The data are interpreted to indicate a diverse molecular asymmetry residing in yet unknown meteorite organics; these organics might have had an inductive effect on organic molecular evolution upon exogenous delivery to the early Earth.  相似文献   
8.
The rates at which thermal energy is released by non-eruptive mechanisms associated with active volcanoes in Japan have been estimated from surface temperature distributions or from shapes of the fumarolic plume rise. Values of 5.3 x 107 W and 1.2 x 108 W have been calculated for non-eruptive release rates in 100-km segments of the Northeast and the Southwest Japan Arc, respectively. It appears that non-eruptive heat discharge is of the same order as that caused by eruptions.  相似文献   
9.
In the present research, an attempt is made to derive the generalized expressions for the transient electromagnetic response of a large loop source over the surface of a homogeneous earth model for arbitrary receiver positions inside or outside the source loop. Expressions are derived for the impulse as well as step excitations of the source loop. As a cross check for validity of expressions, the step response expression is obtained from the impulse response expression and vice versa. Computations are performed for the TEM response over a homogeneous earth model for source-receiver offset (r = 0) pertinent to the central loop configuration and the results are compared with the published results for the central loop TEM responses. The results are in well coincidence with each other and thus provide the check for the authenticity of the expressions. To exemplify the nature of TEM response at various source receiver offsets, results are presented for the TEM response at source receiver offsets r = 0, r = a/2, r = a and r = 2a, 6a, 12a pertaining to the central loop, in-loop, on-loop and offset loop configurations, respectively. The results depict their characteristic variations. At receiver positions inside the loop source, both the impulse as well as step responses are of same sign, whereas at the receiver positions outside the loop source, both the curves exhibit a change of sign that shifts towards the later times with increase in the offset distances. The change of sign in impulse response occurs at a relatively later time than that in the step response. This is the initial presentation of TEM response expressions for the large loop source over a homogeneous earth model for arbitrary receiver position inside and/ or outside the loop source except for the case of receiver at the center of the loop and at the coincident loop point. This research would be of immense use in the development and use of the large loop TEM method in its various configurations and thus would enhance the applicability and cost effectiveness of the large loop source TEM method.  相似文献   
1
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号