各向异性ATI介质剪切位错点源P波远场辐射   总被引：2，自引：0，他引：2  

蔡晓刚 《CT理论与应用研究》2011,20(4):433-452

假设震源区为ATI介质,传播介质为全空间各向同性介质情况下,给出了剪切位错源P波远场辐射解析表达式,讨论了震源区各向异性对远场P波振幅和震源球的影响。结果表明,震源区裂隙密度,裂隙方位等参数的动态变化导致P波远场辐射花样也随之动态变化,同时也会造成非双力偶百分含量的动态变化。研究认为,在井中对中小地震的非双力偶机制进行...  相似文献   

Brunhes chron excursion/polarity episode recorded during the late pleistocene, Albuquerque Volcanoes, New Mexico, USA     

J. W. Geissman  L. Brown  B. D. Turrin  L. D. Mcfadden  S. S. Harlan 《Geophysical Journal International》1990,102(1):73-88

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Fabric symmetry of low anisotropic rocks inferred from ultrasonic sounding: Implications for the geomechanical models     

Richard P&#x;ikryl  Tom&#x; Lokají ek  Zdenk Pros  Karel Klíma 《Tectonophysics》2007,431(1-4):83

The geomechanical models were established based on the absence or presence of certain rock fabric elements — texture (crystallographic preferred orientation), microstructure (shape preferred orientation) and microcracks (flat voids). The proposed models include both (i) the ideal material showing random texture and structure but no microcracks, i.e. the material which is hardly to be found in nature, and (ii) the materials possessing various combinations of fabric elements that show different spatial arrangements. The mutual relationship between those parameters and seismic and geomechanical properties are discussed.Selected models were experimentally verified during laboratory experiments. These consist of measurement of P-wave velocities in 132 independent directions under several confining pressures in the range 0.1–400 MPa. From measured data 3D P-wave patterns can be constructed and the influence of microcracks and of texture and structure on the rock seismic anisotropy can be determined. The seismic anisotropy established at different levels of confining pressure can be used for the interpretation of rock fabric symmetry of rocks showing low anisotropy in macroscale and for the selection of directions in which the geomechanical test can be performed. The measured P-wave velocities were then mathematically processed by using a fitting function which reflects contribution of P-wave velocity in the mineral skeleton of an ideal sample without microcracks extrapolated to the atmospheric pressure level from high confining pressure interval (ca. 200–400 MPa) (v₀), linear compressibility of the samples (k_v), and confining pressure during which most of the cracks are closed (P₀). These parameters improve the understanding of the response of various rock fabric elements on increasing confinement and corresponding changes in elasticity.The observed seismic and geomechanical anisotropies reflect intensity of the fabric of rock-forming minerals and microcracks. The magnitude of seismic anisotropy measured at atmospheric pressure corresponds to the anisotropy of static elastic modulus and is governed by the spatial arrangement of microcracks. The magnitude of strength anisotropy (uniaxial compressive strength) correlates more likely to the seismic anisotropy determined at high confining pressure and is connected to the preferred orientations (either CPO or SPO or both) of rock-forming minerals.  相似文献   

江苏省测震台网井下地震计方位角检测     

宫杰  张朋  张扬  张敏  王佳  居海华 《震灾防御技术》2022,17(1):181-187

为获取江苏省测震台网井下地震计精确方位角,架设地面参考地震计,将其精确指北,并与井下地震计检测结果进行对比,利用相关分析法计算22个深井台站精度较高的方位角。研究结果表明,受多因素制约,井下地震计检测结果普遍偏差较大,部分台站水平向分量几乎反向,如提井,需重新进行方位角检测;地面与井下地震计同频带有利于提高相关性,从而获取高精度检测结果;利用不同频带地震计进行井下地震计方位角检测时,对较宽频带地震计进行仿真处理尤为重要;溧阳2台站新建井下地震计检测结果表明相关分析法可应用于井下地震计方位角检测;尽可能选择台基噪声功率谱密度曲线具有明显波峰频段作为滤波频段,有利于提高地面与井下地震计观测数据相关性,提高方位角检测精度。  相似文献   

Paleomagnetic evidence for the emplacement mechanism of an enigmatic boulder accumulation on a coastal cliff top in New South Wales: implications for the Australian Megatsunami Hypothesis     

D. N. Thomas  P. W. Schmidt 《Australian Journal of Earth Sciences》2018,65(4):503-515

Paleomagnetic sampling and measurement of a boulder accumulation on Little Beecroft Head on the Illawarra coastline of New South Wales was undertaken to evaluate potential emplacement mechanisms. This deposit is of central importance in the Australian Megatsunami Hypothesis (AMH) debate, but to date, there has been no unequivocal determination of its provenance. The most likely emplacement mechanisms are by slow collapse during denudation of overlying strata, storm wave overwash or a combination of these. Characteristic Remanent Magnetisation (ChRM) directions were obtained from 15 individual boulders and the in situ bedrock platform on which they currently rest. The in situ Permian bedrock has a normal polarity mean ChRM direction of D/I = 1.6°/–66.7° (α₉₅ = 5.2°; k = 33.9) that is statistically indistinguishable from the Present Earth Field direction at the site. The magnetisation is most likely due to Cenozoic/recent weathering, which is common in surficial rocks throughout the Sydney Basin. ChRM directions for the boulders are stable but scattered, although not random, and the mean boulder direction is indistinguishable in geographic (i.e. current in situ) coordinates, at the 5% significance level, from the mean direction of the in situ bedrock. Further statistical tests confirm that the scatter in the mean directions of the boulders and the in situ bedrock is different, at the 5% significance level, with the boulder mean being more scattered. At an individual boulder level, some blocks have mean ChRM directions that are statistically indistinguishable from the mean in situ rock ChRM direction, whereas others are distinguishable at the 5% significance level.

These results indicate that the boulders were magnetised prior to emplacement but were not moved far from their original positions during emplacement. The emplacement age is constrained to the last ca 780 000 years. These observations strongly support the hypothesis that the Little Beecroft Head boulder deposit was emplaced by a non-catastrophic mechanism, namely slow collapse during denudation of pre-existing cliff material or overtopping from severe storms, which occur regularly on the east coast of New South Wales. Even if a catastrophic wave were responsible, the results constrain the age of that event to be older than 780 000 years. Therefore, the results presented here are not supportive of the AMH as it currently stands. Further paleomagnetic work, on similar deposits along the Illawarra coastline and from elsewhere in Australia, is needed to evaluate the interpretations presented here.  相似文献   

有限导电内核的驱动方式对发电机模型的影响     

丁嘉威  王正涛  詹文臻  刘美琴 《地球物理学报》2021,64(4):1320-1327

本文以两种绝缘内核的发电机为基准,设置内核电导率与外核相同,选择了以固定速度超速旋转和在外核驱动下发生旋转的两种内核旋转模式,比较分析不同模型间的能量差异、磁场强度、磁雷诺数、磁极翻转频率和四个类地发电机参数.结果表明:对于弱偶极子发电机模型,有限导电内核的引入会对其偶极子强度的相对变化量造成较大影响,最高达103.00%;由外核驱动旋转的有限导电内核模型对于本文其他目标研究量所带来的影响比较小,均小于5%;而固定旋转速度的有限导电内核的模型对磁极翻转频率、赤道对称性和纬向性均存在较明显影响,最大变化量达124.62%.综合本文所选用的发电机模型的特征和数值分析结果,可以发现虽然由外核驱动旋转的有限导电内核模型其转速不可控且存在较大波动,但各物理量变化量与实际内核与外核的能量比更为接近,因此可以推断其驱动机制较自驱动模式更为合理可靠.  相似文献   

利用时移层析成像方法揭示与2014年云南鲁甸M_S6.5地震有关的P波速度变化     

曹颖  黄江培  钱佳威  付虹 《地球物理学报》2021,64(5):1569-1584

基于双差层析成像的时移层析成像方法能够获得不同时间段之间的地下介质的速度变化,且不同的数据分布和质量对结果影响较小.在本研究中我们使用云南地震区域台网所记录到的P波绝对到时及相对到时数据,利用时移层析成像方法得到了2014年鲁甸M S6.5地震发生前后震源区高精度的P波速度变化的时空分布.结果表明:2014年鲁甸地震发生后,震源区同震期P波速度下降,但没有下降至最大,而是在震后1—4个月内下降至最大,接着P波速度开始上升,震源区开始愈合,愈合过程从浅层逐渐发展至深层,逐渐恢复至震前水平.同时发现在空间上P波速度变化与余震分布变化相一致,鲁甸地震同震应力变化与速度变化之间也有较好的一致性,所以认为地震引起的应力变化是造成鲁甸地震速度变化的一个重要原因,余震的动态和静态应力造成了震源区介质物理属性的改变从而影响了P波速度的变化.  相似文献   

小江断裂带周边地区三维P波速度结构及其构造意义   总被引：18，自引：6，他引：12       下载免费PDF全文

吴建平  杨婷  王未来  明跃红  张天中 《地球物理学报》2013,56(7):2257-2267

作为青藏高原的东南边界,小江断裂带在高原物质的侧向逃逸中发挥着重要的作用.本文利用流动地震台阵及固定台站的走时观测资料,对小江断裂带及周边区域的壳幔三维P波速度结构进行了研究.结果表明,在中上地壳,小江断裂带内部主要为低速异常,其东侧主要为高速异常.在中下地壳,小江断裂带中部为低速异常,北部和南部主要为高速异常,其中北部的高速异常可延伸到地表附近,南部的高速异常可一直延伸到上地幔.我们推测,小江断裂带中部的低速异常与深部热作用有关;北部的高速异常可能是晚古生代地幔柱活动导致大量基性和超基性幔源物质侵入地壳引起的,它的存在对青藏高原物质向南逃逸起到了一定的阻挡作用,可能是导致川滇活动块体北部次级块体快速抬升的重要因素;南部顶界面向北倾斜的高速异常体对川滇活动块体向南滑移起到了进一步的阻挡作用,导致其上覆的中上地壳低速异常区发生较强的变形和强烈的地震活动,同时在上地幔深度范围起到了稳定的作用,使其南部区域的介质受青藏高原物质向南挤出的影响明显减小.  相似文献   

青藏高原东北缘宽频带地震台阵远震记录波形及背景噪声分析   总被引：1，自引：0，他引：1  

刘旭宙  沈旭章  李秋生  张元生  秦满忠  叶卓 《地球学报》2014,35(6):759-768

本文利用远震极性分析和概率密度函数统计法对国家深部探测专项Sino Probe"青藏高原东北缘宽频带地震台阵"40个台站的远震记录波形和背景噪声进行了评估和影响因素分析。结果表明:(1)该台阵对远震有较好的记录和识别能力,且单台定位结果较好;(2)被检测台站背景噪声达到或接近同类地区固定台站的噪声水平标准,观测数据品质较高;(3)根据实际观测资料计算的各台站概率密度函数PDF分析结果建议,在青藏高原东北缘黄土层较厚地区开展宽频带流动观测,应首选基岩台基以保证三分量观测效果,在不得已选择非基岩台基情况下,应深埋地震计以达到最大程度降噪。  相似文献   

Geophysical evidence on segmentation of the Tancheng-Lujiang fault and its implications on the lithosphere evolution in East China     

《Journal of Asian Earth Sciences》2013

The north–south trending Tancheng-Lujiang (Tanlu) fault belt extends from northeast China to the Dabie–Sulu orogenic belt, for a length of more than 3000 km. This fault belt probably has close links with the lithosphere evolution, seismic activity and mineral resource concentration in East China. Surface geological mapping and studies on sedimentation and basin formation have indicated segmentation at the southern, middle and northern domains of the fault. Here we employ geophysical constraints to evaluate these fault segments. Unlike previous geophysical studies focused on laterally varying crust/mantle seismic velocity structure across the fault, in this study we have integrated a variety of geophysical data sets, such as crustal P-wave velocity, earthquake occurrence and released seismic energy, seismogenic layer thickness, surface heat flow and geothermal field, to understand the deep structure and strength of the lithosphere along the Tanlu segmented fault belt. The results demonstrate remarkable crustal-scale north-to-south segmentation this major fault. The geophysical evidence and some geochemical constraints suggest that the Tanlu fault belt probably served as a channel for melt and fluid percolation, and exerted a significant control on the lithosphere evolution in East China.  相似文献