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3.
本文对近年来我国西部地区发生的某些强震及中强震（M S>5.0）的波速比异常作了一些初步探讨.文中给出并讨论了这些地震的波速比异常的一些共同特征,即随时间变化的曲线形态、异常特征量（异常持续时间与异常幅度）和异常的统计分布特征.此外还讨论了波速比异常的特性与地震序列类型、震源深度及震源机制的关系,探索了波速比异常与波速异常间的关系.最后还指出了地震活动性与波速比异常的某种对应关系,并作了简要的讨论. 相似文献
5.
针对泥质砂岩黏土附加导电还没有综合定量评价指标的现状,从Archie公式和Waxman-Smits方程计算的含水饱和度的相对误差出发定义了黏土附加导电强度指数 η,并考察了地层水电导率 Cw、阳离子交换容量 Qv、含水饱和度 Sw、饱和度指数 n对 η的影响,给出了黏土附加导电强度判别方法和图版,通过低阻油气层的工程应用实例探讨了 η在饱和度方程选取中的应用.结果表明, η随 Cw、 Sw、 n值的增大而以近似乘幂规律减小,随 Qv的增大而近似线性增大; Cw与 Qv对 η的影响最大, n与 Sw次之;无法由单一因素判断黏土附加导电性强弱,必须综合考虑 Qv、 Cw、 Sw、 n的影响;对于低阻油气层,可利用该指数按照"三步法"及判别图版定量判断低阻成因并为饱和度模型的选取提供技术依据. 相似文献
6.
Magnetic domain patterns have been observed on particles of natural pyrrhotite and titanomagnetite undergoing hysteresis. These observations indicate that hysteresis properties are governed by two distinct mechanisms: (1) wall-pinning and (2) nucleation of reverse domains. Particles which are dominated by wall-pinning spontaneously nucleate reverse domains in saturation remanence ( Jrs). The coercivity of such grains is determined by the presence of potential wells encountered by the wall in its traverse across the grain. However, many pseudosingle-domain particles (PSD) between 5 and 30 μm in diameter do not nucleate reverse domains in Jrs, but remain as saturated single-domains. These particles require a reverse field Hn to nucleate domain walls. When Hn is sufficiently large, the nucleating field controls magnetization reversal by driving the wall across the particle in a single Barkhausen jump, and the muscopic coercivity is nucleation-dominated. The proportion P (w=0) of particles of a given size d which fail to nucleate walls in Jrs is found to be given by A exp(−Bd1/2), where A and B are experimentally determined constants. The nucleation field Hn in pyrrhotite is observed to increase with decreasing grain size, exceeding 500 Oe in 5 μm particles. The difficulty with which reverse domains are nucleated subsequent to saturation may thus provide a mechanism for achieving the high values of Jrs/Js and coercive force observed in fine, pseudosingle-domain particles. 相似文献
7.
根据 G-R公式和非线性动力学观点, 在分析不同类型地震序列震级分布细结构基础上, 提出用震级变异系数δ m、 b值和震级熵H(m)、 马尔柯夫链理论值h和信息量维数D 1等统计量, 来综合描述和界定不同类型、 性质的地震序列; 同时对截止震级问题、 b值、 平均震级m、 h和D 1等统计物理含义进行了探讨。 认为δ m、 b值和H(m)及其与理论指数分布的震级熵H(∞)的差值 ΔH(m)相结合将有助于区分前震序列、 前兆性震群和各种不同类型(主-余震型、 震群型、 孤立型)地震序列, 并且可以对这些类型进行早期判断。 相似文献
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Clinopyroxene-silicate liquid partition coefficients for U and Th have been determined by particle track radiography from 1 atm crystallization experiments at controlled fO2. Two natural basaltic and one synthetic composition were studied at fO2 values from the NiNiO oxygen buffer to 1 log unit more oxidizing than FeFeO ( IW+ 1). Over the range of fO2 values and compositions studied, DUcpx/liq = 0.0034–0.015, DThcpx/liq = 0.008–0.036, and DThDU= 3.4–1.1. With decreasing fO2, DThDU can decrease by up to a factor of 3 for a given composition, primarily from an increase in DUcpx/liq, which we interpret as resulting from an increase in the proportion of tetravalent U in the system with decreasing fO2. This demonstrates that crystal-liquid UTh fractionation is fO2 dependent and that U in terrestrial magmas is not entirely tetravalent. DThcpx/liq appears to decrease in the two basalts at the lowest fO2, possibly as a result of changes in composition with fO2. Our data show the sense of UTh fractionation by clinopyroxene-liquid partitioning is consistent with previous experimental determinations, in thatDThcpxDUcpx> 1 in all cases. This indicates that, during partial melting, the liquid will have aTh/U ratio less than the clinopyroxene in the source. The observed238U230Th disequilibrium in MORB requires that the partial melt should have aTh/U ratio greater than the bulk source, and, therefore, cannot result from clinopyroxene-liquid partitioning. Further, the magnitudes of the measured partition coefficients are too small to generate significant UTh fractionation in either direction. Assuming that clinopyroxene contains the bulk of the U and Th in MORB source, our results indicate that238U230Th disequilibrium in MORB may not be caused by partial melting at all. 相似文献
9.
地震灾害可接受风险水平反映了社会对地震灾害的风险认知。本文基于1991年～2020年中国大陆地区 MS≥5.0地震灾害数据,分析地震灾害的时空分布特征,并在此基础上应用 F－N曲线法构建不同震级的地震灾害生命损失概率分布函数,进而绘制出灾害可接受风险曲线,以此确定出地震灾害生命可接受风险标准。研究结果表明:中国大陆地区 MS≥5.0地震活动、灾害次数、成灾率和致人员死亡的成灾率分别在2008年、2003年、2011年和1996年表现出高值,在空间上 MS≥5.0地震和地震灾害集中分布在西部地区。 MS5.0～ MS5.9、 MS6.0～ MS6.9和 MS≥5.0地震灾害致1人死亡概率分别超过6.19×10 －6/a、1.37×10 －5/a和1.62×10 －5/a为不可接受风险, MS≥7.0地震灾害致4人死亡的累计概率超过1.96×10 －5/a为不可接受风险,而 MS5.0～ MS5.9、 MS6.0～ MS6.9、 MS≥7.0和 MS≥5.0地震灾害导致死亡人数分别超过8人、44人、2417人和2468人的年死亡概率为任意值均是不可接受的。该研究结果可以为我国地震灾害风险评估与管理、灾害保险费率的厘定以及灾害教育的开展提供一定的理论和实践依据。 相似文献
11.
Abstract Rocks from Karaginsky accretionary prism (Karaginsky Island, Bering Sea) yield both prefolding (close to original) and postfolding magnetic vectors. The prefolding vectors suggest that the Maastrichtian–Paleocene volcanic–terrigenous sequences of Karaginsky Island formed at approximately 40°N to 50°N ( n = 45, D G = 325, I G = 57, K G = 6, α 95G = 8, F G = 15.06, D S = 332, I S = 63, K S = 20, α 95S = 4.5, F S = 0.3297, F cr = 2.64) and were not originally part of either Eurasia ( F = 19, Δ F = 6.5) or North America ( F = 17, Δ F = 4.4). The geologic blocks rotated insignificantly counterclockwise about the horizontal plane, suggesting that the structure of Karaginsky Island arose without major strike-slip motions. Analysis of secondary magnetizations (for example, n = 28, D G = 311, I G = − 50, K G = 9, α 95G = 8.7, F G = 2.44; D S = 293, I S = − 41, K S = 5, α 95S = 11, F S = 12.04, F cr = 2.65) reveals that the development of this framework involved at least two stages of deformation. During the second stage the sequences must have been tilted to west-northwest and northwest directions at 45–65°. This agrees with the northwest vergence of the structure of Karaginsky Island. 相似文献
12.
使用删除余震后的地震目录, 综合运用多种方法进行 Mc值的定量计算和对比分析, 对河套地震带的台网监测能力的时空变化进行分析判定。 结果表明, 1970年以来, 河套地震带的台网监测能力整体呈现逐步增强趋势。 在Bootstrap次数为200的条件下, MAXC方法确定的研究区整体 Mc值为 ML2.7±0.07, δ Mc的分布基本控制在 ML0.1～0.4之间, EMR方法给出的 Mc时序变化范围是 ML1.6～2.8; 多方法联合测定的 Mc值变化范围为 ML1.8～3.3, R/S检验给出的结果是 ML3.4。 对比发现, 余震删除对最小完整性震级的计算有一定影响, R/S检验求取的最小完整性震级在余震删除前后相差 ML0.9; 整体来看, Mc值随时间演化逐渐减小, 较小时空范围内的 Mc值仍有显著的非均匀性变化现象, 不同时段内台网布局的空间调整以及地震事件的时空非均匀性活动可能是主要原因。 相似文献
13.
Soil-solution samplers and shallow ground water monitoring wells were utilized to monitor nitrate movement to ground water following H 2O 2 application to a clogged soil absorption system. Nitrate-nitrogen concentrations in soil water and shallow ground water ranged from 29 to 67 mg/L and 9 to 22 mg/L, respectively, prior to H 2O 2 treatment. Mean nitrate-nitrogen concentrations in soil water and ground water increased and ranged from 67 to 115 mg/L and 23 to 37 mg/L, respectively, one week after H 2O 2 application. Elevated concentrations of nitrate-nitrogen above background persisted for several weeks following H 2O 2 treatment. The H 2O 2 treatment was unsuccessful in restoring the infiltrative capacity of a well-structured soil. Application of H 2O 2 to the soil absorption system poses a threat of nitrate contamination of ground water and its usefulness should be fully evaluated before rehabilitation is attempted. 相似文献
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对于地震灾害与风险评估,人们更关注的是地震辐射能量 ES和能量震级 Me的大小,能量震级 Me反映震源动态特征,适合描述地震的潜在破坏性。本文介绍地震波能量 ES和地震矩 M0的物理意义及能量震级 Me的定义和测定方法,并测定得到2017年8月8日四川九寨沟 MS 7.0地震的能量震级 Me为6.3。 相似文献
17.
采用新疆地区1990年以来的浅源地震目录,利用扩散链法去除余震,在小震空间集中度C值的研究基础上,进一步发展了C值变化量,即ΔC值的时空扫描计算方法,针对2000年以来天山地震带11次6级以上地震前ΔC值的演化过程,进行回顾性研究。结果表明,2012年新源—和静交界M_(S)6.6地震、2017年精河M_(S)6.6地震和2020年伽师M_(S)6.4地震之前,均出现较为明显的区域ΔC值异常,且3次地震前ΔC值异常演化时间均小于6个月,属于震中附近区域震前中短期异常变化。 相似文献
18.
3He/4He ratios have been measured for olivine and clinopyroxene phenocrysts in 7–15 m.y. old basaltic lavas from the island of St. Helena. Magmatic helium was effectively resolved from post-eruptive radiogenic helium by employing various extraction techniques, including in vacuo crushing, and stepwise heating or fusion of the powders following crushing. The inherited 3He/4He ratio at St. Helena is 4.3–5.9 R A. Helium isotope disequilibrium is present within the phenocrysts, with lower 3He/4He upon heating and fusion of the powders following crushing, due to radiogenic ingrowth or to -particle implantation from the surrounding (U + Th)-rich lavas. A single crushing analysis for clinopyroxene in a basalt from Tubuaii gave3He/4He= 7.1 RA.3He/4He ratios at St. Helena and Tubuaii (HIMU hotspots characterized by radiogenic Pb isotope signatures) are similar to3He/4He ratios previously measured at Tristan da Cunha and Gough Island (EM hotspots characterized by low206Pb/204Pb). Overall, the HeSrPb isotope systematics at these islands are consistent with a mantle origin as contiguous, heterogeneous materials, such as recycled crust and/or lithosphere.3He/4He ratios at HIMU hotspots are similar to mantle xenoliths which display nearly the entire range of Pb isotope compositions found at ocean islands, and are only slightly less than values found in mid-ocean ridge basalts (7–9 RA). This suggests that the recycled materials were injected into the mantle within the last 109 yrs. 相似文献
19.
选取2010-2016年重庆地震台网记录的 MS>3.0地震,对P波进行波谱分析,得到P波零频极限值、地震矩及拐角周期,拟合得到拐角周期与重庆地震台网 MS的关系、P波零频极限值与重庆地震台网 MS的关系,利用P波地震矩计算矩震级 MWP,分析 MWP与 MS的差异。结果显示,当 MS ≤ 4.0时, MWP > MS;当 MS > 4.0时, MWP < MS,对得到的震级计算关系式检验发现,P波矩震级及通过零频极限计算得到的震级与重庆地震台网 MS较为接近,而通过拐角周期计算得到的震级与 MS相差较大。 相似文献
20.
基于Sato单次散射模型,利用轮台地震台单台记录,计算并分析2016年1月14日新疆轮台 MS5.3地震及余震序列尾波 Qc值震后变化,拟合得出 Qc值随频率的变化关系为 Qc ( f) =（18.0±3.19） f1.184±0.072。结果表明, Qc值在序列初期起伏较大,随着强震后能量的释放, Qc值趋于平缓;低频段的 Qc值在较大余震发生前有显著变化;不同中心频率点的 Qc值变化形态不一致。对 Qc值变化特征的研究,可为地震预报提供参考依据。 相似文献
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