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71.
72.
本文分析了有海底扩张无海沟后退、有海沟后退无海底扩张以及海底扩张与海沟后退共存等3种情况下,俯冲板片运动与海沟迁移的关系.用幂律流体有限元方法计算海沟后退对地幔对流的影响.地幔有效粘度除依赖应力偏张量的第二不变量以外,尚与温度、压力(含流体静压力和流动压力)有关.计算表明,对流环、高流动负压区以及低粘区的个数和位置,均受控于海沟是否后退以及海底是否扩张;温度场与海沟后退无明显关系.流动压力对形成洋中脊和弧后火山、驱动地幔对流以及维持板片的倾斜角度都具有重要意义. 相似文献
73.
运用滑块模型建立了一个地震活动的计算机模拟系统。对地震活动计算机模型进行反复试验,认识到断层失稳过程中摩擦强度分布的重要性。把在断层滑动中摩擦阻力分布比较均匀的段称为匀阻段。对大地震而言,断层摩擦阻力的大或小都不是决定因素,而具有较长的匀阻段才是发生大震的首要条件 相似文献
74.
通过实验,对饱和粘性土的渗透规律进行研究,得到几点新认识。利用此认识建立了饱和粘性土越流补给量的计算公式,并在实际应用中得到验证。 相似文献
75.
肖天贵 《南京气象学院学报》1995,18(3):444-449
时间标度计算表明,西北太平洋热带气旋路径是一个无标度性的系统,其关联方差谱遵从频率的-2 ̄-3次方幂律,不同背景下的路径系统均如此。由此得到的不同季节、不同地域的热带气旋路径可预报时间尺度基本上为3 ̄4d,但异常热带气旋路径的可预报时间尺度则为1 ̄2d。 相似文献
76.
The paper studies the effect of magnitude errors on heterogeneous catalogs, by applying the apparent magnitude theory (seeTinti andMulargia, 1985a), which proves to be the most natural and rigorous approach to the problem. Heterogeneities in seismic catalogs are due to a number of various sources and affect both instrumental as well as noninstrumental earthquake compilations.The most frequent basis of heterogeneity is certainly that the recent instrumental records are to be combined with the historic and prehistoric event listings to secure a time coverage, considerably longer than the recurrence time of the major earthquakes. Therefore the case which attracts the greatest attention in the present analysis is that of a catalog consisting of a subset of higher quality data, generallyS
1, spanning the interval T
1 (the instrumental catalog), and of a second subset of more uncertain magnitude determination, generallyS
2, covering a vastly longer interval T
2 (the historic and/or the geologic catalog). The magnitude threshold of the subcatalogS
1 is supposedly smaller than that ofS
2, which, as we will see, is one of the major causes of discrepancy between the apparent magnitude and the true magnitude distributions. We will further suppose that true magnitude occurrences conform to theGutenberg-Richter (GR) law, because the assumption simplified the analysis without reducing the relevancy of our findings.The main results are: 1) the apparent occurrence rate exceeds the true occurrence rate from a certain magnitude onward, saym
GR; 2) the apparent occurrence rate shows two distinct GR regimes separated by an intermediate transition region. The offset between the two regimes is the essential outcome ofS
1 being heterogeneous with respect toS
2. The most important consequences of this study are that: 1) it provides a basis to infer the parameters of the true magnitude distribution, by correcting the bias deriving from heterogeneous magnitude errors; 2) it demonstrates that the double GR decay, that several authors have taken as the incontestable proof of the failure of the GR law and of the experimental evidence of the characteristic earthquake theory, is instead perfectly consistent with a GR-type seismicity. 相似文献
77.
Herak Marijan Herak Davorka Markušić Snježana Ivančić Ines 《Studia Geophysica et Geodaetica》2001,45(3):251-266
The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M
L
4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock. 相似文献
78.
79.
We consider the advantages of a formalism based on concept of the asymmetric continuum and we present some equivalence theorems
relating it to the asymmetric elasticity and to micropolar and micromorphic theories as founded by Nowacki, Cosserats and
Eringen.
We consider the basic processes in an asymmetric continuum which could be reduced to the point basic motions/deformations.
The co-action of spin and shear motions is assumed to play the main role in fracturing process, while the constitutive relation
between the antisymmetric stresses and rotations replaces the friction constitutive law. 相似文献
80.
我国春玉米水分供需状况分析 总被引:4,自引:1,他引:4
论述了作物需水量的概念及其计算方法,利用最新的气候和作物资料,计算了我国春玉米的作物需水量,分析其时空分布特征,并利用水发订正系来评价春玉米需水量的满足程度。计算分析结果表明,气候条件对我国在玉米生产是有利的,但在播种期、出苗期及拔节期(4-6月份),存在明显的水亏缺现象,这一时期应采取相应的栽培技术及节水灌溉、人工增雨等措施来缓解旱情。 相似文献