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81.
Seismic Moment Tensor Resolution on a Local Scale: Simulated Rockburst and Mine-induced Seismic Events in the Kopanang Gold Mine, South Africa 总被引:2,自引:0,他引:2
Seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock
mass. The effect of wave propagation is usually not well known as only simplified models of geological structures are available.
Therefore, the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge
of the rock mass along the propagation path, which in turn cause a distortion in the calculated moment tensor (MT). The distortion
of the MT on a local scale was observed by inverting records of a simulated rockburst conducted at the Kopanang gold mine
in South Africa. A dominant isotropic component of the explosive characteristics was found from the inversion. The deviatoric
components retrieved from the blast are spurious. A test of their stability indicated that they are not significant, assuming
an uncertainty above 5% for velocities and 10% for attenuation within the homogeneous model available for the mine. Thus,
the retrieval of the MT from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible.
However, the homogeneous model of the rock mass can only be applied to close stations, within a few kilometers of the source.
The seismic records from distant stations were too complex to be modelled by a homogeneous rock mass. Records of six mine-induced
seismic events recorded at the Kopanang gold mine were also inverted. A vertical linear dipole along the pressure (P) axis
was found for three of the events, suggesting a pillar burst. The mechanism of two events contains an isotropic implosion
together with a nearly vertical dip-slip, and seems to indicate a combination of a cavity collapse with a down dip-slip along
a nearly vertical fault. One event corresponds to a dipole along the tensional (T) axis. However, it is vertical, thus its
association with tensile faulting of the hangingwall is uncertain. 相似文献
82.
S. Gambino 《Studia Geophysica et Geodaetica》2006,50(4):663-674
During 1991–93 at Mount Etna, long-period (LP) events occurring in swarms characterized the evolution of the eruption. The
presence of multiplets i.e. groups of events with similar waveform signatures, has been recognized within this activity.
Traditional techniques for locating LP events do not allow obtaining reliable hypocenters, which have only succeeded in placing
earthquakes in a roughly 1 km2 area slightly east of the Mt. Etna Northeast Crater.
Hypocenters have been relocated in two steps: the absolute location has been improved using Thurber’s code and a complex 3D
velocity model; a highly precise relative location has been applied on multiplets to define the source geometry.
3D locations and high precision analysis suggest that during the 1991–93 eruption the resonator producing LP events was a
part of the uppermost Northeast Crater conduit, measuring 210 meters in height and 45–50 meters in diameter. 相似文献
83.
84.
Mistreatment of the economic impacts of extreme events in the Stern Review Report on the Economics of Climate Change 总被引:1,自引:0,他引:1
The Stern Review on the Economics of Climate Change has focused debate on the costs and benefits of alternative courses of action on climate change. This refocusing has helped to move debate away from science of the climate system and on to issues of policy. However, a careful examination of the Stern Review's treatment of the economics of extreme events in developed countries, such as floods and tropical cyclones, shows that the report is selective in its presentation of relevant impact studies and repeats a common error in impacts studies by confusing sensitivity analyses with projections of future impacts. The Stern Review's treatment of extreme events is misleading because it overestimates the future costs of extreme weather events in developed countries by an order of magnitude. Because the Stern Report extends these findings globally, the overestimate propagates through the report's estimate of future global losses. When extreme events are viewed more comprehensively the resulting perspective can be used to expand the scope of choice available to decision makers seeking to grapple with future disasters in the context of climate change. In particular, a more comprehensive analysis underscores the importance of adaptation in any comprehensive portfolio of responses to climate change. 相似文献
85.
21世纪初极端天气气候事件研究进展 总被引:22,自引:0,他引:22
由于极端天气气候事件的严重影响,越来越多的研究开始关注其变化情况。从观测分析到模拟研究,几乎都发现极端气温、降水事件发生了显著变化,而且在全球变暖的大背景下,未来有些极端事件可能会发生频数更高或强度更强。当然,研究结论也存在一定程度的不确定性,从模式模拟来看,目前模拟结果仍存在不确定性,不同模式的结果间常常存在较大的差异;而从观测分析来看,研究主要局限于20世纪后半叶,如果对更长时间作分析,结论或许会有所不同。文章从最基本的极端天气气候事件的定义出发,结合观测事实和模拟研究两个主要方面来介绍近几年来极端事件研究取得的主要进展,最后简单地总结了这些进展,并提出了进一步研究的思路。
相似文献
86.
Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past. 相似文献
87.
本文对东南极拉斯曼丘陵出露的石榴斜长角闪岩中的角闪石进行了40Ar-39Ar年龄测定,分别得到角闪石视年龄1586Ma、1011~1080Ma、761Ma和529~582Ma,角闪石坪年龄1036Ma和554Ma,角闪石Ar-Ar等时线年龄1010Ma,这些同位素年龄证据,首次完整地记录了该区所经历的几乎所有构造变质热事件,为近几年国内外地质学家关于该区构造变质热事件争论的焦点问题,即晚元古代的1000Ma格林维尔事件(Grenvilian)与早古生代的500Ma泛非事件(Pan-African)孰轻孰重以及前者是否存在,提供了答案。角闪石的40Ar-39Ar年龄测定结果表明,拉斯曼丘陵地区经历了复杂的多期变质演化历史,其原岩可能形成于早-中元古代,占主导地位的应该是晚元古代的1000Ma格林维尔事件,而500Ma泛非事件则是晚期较强烈的变质热事件。 相似文献
88.
Gui-Qing Zhang 《地震学报(英文版)》1998,11(4):495-500
The relations between sunspot numbers and earthquakes (M≧6), solar 10.7 cm radio flux and earthquakes, solar proton events and earthquakes have been analyzed in this paper. It has
been found that: (1) Earthquakes occur frequently around the minimum years of solar activity. Generally, the earthquake activities
are relatively less during the peak value years of solar activity, some say, around the period when magnetic polarity in the
solar polar regions is reversed. (2) the earthquake frequency in the minimum period of solar activity is closely related to
the maximum annual means of sunspot numbers, the maximum annual means of solar 10.7 cm radio flux and solar proton events
of a whole solar cycle, and the relation between earthquake and solar proton events is closer than others. (3) As judged by
above interrelationship, the period from 1995 to 1997 will be the years while earthquake activities are frequent. In the paper,
the simple physical discussion has been carried out.
These results supported the exploration and studies of some researchers to a certain extent.
This work is supported by Foundation of the Chinese Academy of Sciences (major item). 相似文献
89.
The importance of energetic particle precipitation on the chemical composition of the middle atmosphere 总被引:1,自引:0,他引:1
Richard Mansergh Thorne 《Pure and Applied Geophysics》1980,118(1):128-151
An assessment is made of the relative contribution of certain classes of energetic particle precipitation to the chemical composition of the middle atmosphere with emphasis placed on the production of odd nitrogen and odd hydrogen species and their subsequent role in the catalytic removal of ozone. Galactic cosmic radiation is an important source of odd nitrogen in the lower stratosphere but since the peak energy deposition occurs below the region where catalytic removal of O3 is most effective, it is questionable whether this mechanism is important in the overall terrestrial ozone budget. The precipitation of energetic solar protons can periodically produce dramatic enhancement in upper stratospheric NO. The long residence time of NO in this region of the atmosphere, where catalytic interaction with O3 is also most effective, mandates that this mechanism be included in future modelling of the global distribution of O3. Throughout the mesosphere the precipitation of energetic electrons from the outer radiation belt (60°70°) can sporadically act as a major local source of odd hydrogen and odd nitrogen leading to observable O3 depletion. Future satellite studies should be directed at simultaneously measuring the precipitation flux and the concomitant atmosphere modification, and these results should be employed to develop more sophisticated models of this important coupling. 相似文献
90.
We have used two different sampling techniques to study the geochemical response of a small lowland rural catchment to episodic storm runoff. The first method involves traditional daily spot sampling and has been used to develop a standard end‐member mixing analysis (EMMA) of the relative contributions of ground water flow and surface runoff to the total stream flow. The second method utilizes a continuous sampling device, powered by an osmotic pump, to produce an integrated 24‐h sample of the stream flow. When combined with the EMMA results from the spot samples, analyses of the integrated samples reveal the presence of a third component that makes a significant contribution to the dissolved NO3, Ca and K export from the catchment during the rising limb of the hydrographic profile of a storm event following a prolonged dry period. The storm occurred in the middle of the night, so that the response of the stream chemistry was not captured by the daily samples. We hypothesize that this third component is derived from the flushing of stored soil water that contains the geochemical signature of decaying vegetation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献