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991.
中国西天山矿产勘查十年成果 总被引:3,自引:2,他引:1
西天山(包括西南天山)是新疆重要的金和有色金属成矿远景区,“八五”、“九五”期间,新发现和评价了一批重要的矿产地,为新疆经济发展做出了重大贡献。从矿产普查勘探和找矿科研两个方面回顾近十年来西天山矿产工作中所取得的成果,并提出今后工作建议。 相似文献
992.
Horálek J. Šílený J. Fischer T. Slancová A. Boušková A. 《Studia Geophysica et Geodaetica》2000,44(4):491-521
In order to learn more about the nature of the dynamic processes taking place in the West Bohemia/Vogtland earthquake swarm region, we investigated the temporal and spatial variations of the source mechanisms of the January 1997 swarm beneath Nový Kostel (NKC). Visual analyses of WEBNET seismograms of over 800 events revealed that a specific feature of this swarm was the occurrence of eight classes of multiplet events. The result of single-source, absolute moment tensor inversion of the P and SH peak amplitudes of a subset of 70 events representing all multiplet classes indicated that eight statistically significant types of mechanisms occurred during the swarm. Two of them, types
A
and
B
in our denotation, comprised all M
L
1.3 events and predominated in the swarm. Type
A
were pure strike-slip mechanisms or strike-slip mechanisms containing a small normal component, with a nearly pure double-couple source. For class
B
events, oblique-thrust faulting and non-double-couple components significant at a fairly high confidence level were typical. Type
A
events predominated in the southern subcluster of the swarm, whereas most of type
B
events occurred in the subcluster northwards from NKC. This indicates that two major seismogenic planes were active during the swarm. The swarm essentially developed in four phases: in the first, type
A
events prevailed and the southern plane was active; during the second, characterised by the occurrence of both type
A
and
B
events (the former in the southern, the latter predominantly in the northern subcluster), the activity of the swarm culminated; in the third and fourth, the occurrence of type
B
events in the northern plane predominated, and only weak single events occurred southwards from NKC. Mechanisms of types
AB
,
C
,
D
,
E
,
F
and
G
, which were typical for M
L
1.2 events, occurred randomly throughout the swarm. Type
AB
events were identified in both the southern and northern clusters, type
C
,
E
,
F
and
G
mechanisms only southwards from NKC. Type
D
events exhibited a large scatter of hypocentres which fell in neither the southern nor the northern cluster. Focal mechanisms like those reported in this study and with analogous temporal and spatial variations were observed by other authors already fifteen years ago in the 1985/86 earthquake swarm and may, therefore, be typical for the region under study. 相似文献
993.
Focal mechanisms of 70 events of the January 1997 earthquake swarm were analysed using the Gephart and Forsyth method to determine the state of stress in the West Bohemia/Vogtland region and to reveal possible stress variations during the swarm activity. The method was applied to the whole set of 70 focal mechanisms and to several subsets distinguishing magnitudes of events and the spatial and temporal distribution of the swarm. The three representative stress models A (
1
,A: 0/45 (az/dip),
2
A: 134/35,
3
A: 243/25), B (
1
,B: 162/38,
2
B: 263/14,
3
B: 10/49), and C (
1
C: 135/30,
2
C: 1/50,
3
C: 239/23) which could characterise the state of stress in the region were found. Model C can be considered to be the most probable stress model because of its consistency with the European stress field. The results of the stress analysis applied to the individual subsets of focal mechanisms indicate that the state of stress was more uniform during the first phase of the swarm.
To distinguish between the fault plane and the auxiliary plane of fault plane solutions a statistical approach was used. The results showed that the fault planes striking NW-SE and dipping 45° to NE were activated during the swarm. 相似文献
994.
Comparison of Absolute and Relative Moment Tensor Solutions For The January 1997 West Bohemia Earthquake Swarm 总被引:2,自引:0,他引:2
Moment tensor solutions for 70 clustered events of the 1997 West Bohemia microearthquake swarm, as calculated by two different methods, are given. The first method is a single-event, absolute moment tensor inversion which inverts body-wave peak amplitudes using synthetic Green functions. The second method is a multiple-event, relative method for which Green functions are reduced to 2 geometrical angles of rays at the sources. Both methods yield similar moment tensors, which can be divided into at least two or three different classes of focal solutions, indicating that, during the swarm activity, different planes of weakness were active. The major source component of most events is a double couple. However, the deviations from the double-couple mechanisms seem to be systematic for some classes of solutions. Error analysis was based on transforming the estimate of the standard deviation of amplitudes extracting from the seismograms into confidence regions of the absolute moment tensor. They show that the non-DC components are significant at a fairly high confidence level. 相似文献
995.
Heterogeneous Saltation: Theory, Observation and Comparison 总被引:7,自引:0,他引:7
In the theory of saltation, under development since the 1940s, it is often assumed that saltation is homogeneous, i.e., saltating particles are uniform in size and follow identical trajectories. This assumption is a limitation to the development of saltation theory. In this paper, as in some other studies made since the 1980s, we are concerned with the saltation of multi-sized particles in turbulent flows, a process that we refer to as heterogeneous saltation. The theory deals with several questions, including the variation of particle size distribution with height, the entrainment rates of particles in different size ranges, and the associated profiles of saltation flux, particle momentum flux and particle concentration. It is hypothesised that saltation is dynamically similar and ‘universal’ similarity functions can be established. The similarity function for saltation flux is presented. Field observations are carried out at the southern fringe of the Takla Makan Desert in April 2002. Measurements of streamwise saltation flux of 32 particle size groups are made using a sand particle counter, together with measurements of wind speed and other atmospheric variables. These data are used to validate the saltation theory, by examining whether the observed saltation flux and particle size distribution can be reproduced. It is shown that the theory is promising in predicting these quantities. 相似文献
996.
997.
A peculiarity of the Vogtland/West Bohemia earthquake region is the appearance of earthquake swarms. The strongest swarms in this century occurred in 1908 and 1985/86. The swarm in 1985/86 is the first one, for which digital data (about 220 events, 400 waveforms, sampling rate 100 Hz) are available for stations Moxa (MOX) and Plauen (PLN). The waveforms of the swarms in the Vogtland show a high similarity. The similarity is quantified by cross-correlation applied to approximately 400 waveforms. The results are shown in the form of similarity matrices.
Four types of events have been detected using the results of the cross-correlation between the S-waveforms recorded at station PLN. Type IV occurs predominantly at the end of the swarm. The waveforms of type IV are clearly different from the waveforms of the other types. The differences between the waveforms of the first three types are less pronounced. Especially the first three types occur alternately. 相似文献
998.
The influence of a driving static shear stress on the liquefaction resistance of medium dense granular soils is investigated. A laboratory study of the behavior of five sands (percentage of silt varying between 2 and 42%, and D50 varying between 0.55 and 0.09 mm) was undertaken. These five sands were sampled from the foundations of two dams in Quebec (Canada). Sixty cyclic direct simple shear (DSS) tests were performed with and without a driving static shear stress. Relative densities Dr varied between 60 and 70%, and static shear stress ratios =τst/σ′vc varied between 0.2 and 0.6. The presence of static shear stress increased the cyclic strength of these soils. A relation between and K() factor giving the effect of preshearing on cyclic shear resistance is obtained. The mechanical competence is examined as a function of D50 and percentage of fines. The observed dilatancy yielded rather cyclic mobility than liquefaction. 相似文献
999.
1000.
R. Urgeles M. Canals J. Roberts the SNV Las Plamas
Shipboard Party 《Journal of Volcanology and Geothermal Research》2000,101(3-4)
In situ subseafloor pore pressure results from the western flank of the island of La Palma, Canary Islands, are presented. The data obtained with a Pop Up Pore Pressure Instrument (PUPPI) provide constraints on the fluid circulation and its causes in a very special context: The sediment piles near an intraplate oceanic island built on the continental rise of the Northwest African Margin. The ambient pore pressures estimated from 2 to 4 days long record are negative in almost all cases with values, at depths of a few meters below sea floor, usually on the order of −10 to −70 Pa. Excess pore pressures develop only in the distal most areas. The permeabilities and compressibilities obtained respectively from the decay of the insertion pressures and the amplitude of the tidally induced pore pressure variations range between 2.5×10−18 and 6.6×10−16 m2 and, 6.2×10−9 and 1.5×10−7 Pa−1. According to these permeabilities fluid flow is estimated to be mostly downward and usually on the range between 0 and −0.3 mm y−1. However, from the excess pore pressure profile a complex pattern of fluid circulation is inferred where horizontal fluid motion cannot be neglected. Horizontal flow is probably controlled by significant contrasts in the permeability of the different layers. The prevailing downward fluid flow is abnormal for a classical passive margin. We thus interpret these results as the superposition to the loss of fluids by sediment compaction (on the continental rise), of a large-scale flow system stimulated by thermal buoyancy (100 km wide) related to the volcanic activity on the island of La Palma. 相似文献