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1.
Summary The estimation of the theoretical magnitude for deep foci based on the vertica component of medium-period PKIKP waves, Earth model PREM and source spectra is presented. The given graphs are valid for period T ranging from 1·6 s to 10 s, source depth of 25 km to 600 km and distance range of 16 500 km to 19 800 km. A simplified method of representing calibration curves is used. 相似文献
2.
The International Seismological Centre (ISC) treats reports of the earliest observed core phase arrivals from earthquakes as PKIKP observations and provides residuals based on Jeffreys-Bullen PKIKP times. An analysis of some 30 000 such data from ISC bulletins for the year 1967 has shown that the data include, in addition to PKIKP, many observations of PKP1 and precursors to PKP. By the use of simple truncation and trimming techniques, travel-time curves (expressed as differences from JB), with standard errors, have been obtained for PKIKP in the ranges 110 to 139° and 152 to 173°, and for PKP1 in the range 144 to 154°. The PKIKP curve in these ranges agrees quite closely with the curve obtained by Cleary and Hales, and with one derived from model 1066B of Gilbert and Dziewonski, except that the Cleary-Hales curve is up to 0.7 s earlier at distances below 120°, and the 1066B curve is up to 1 s later beyond 152°. The PKP1 curve is in good agreement with that derived from 1066B.A plot of the number of observations in each 1° distance interval has been used to estimate the positions of the cusps B, C and D on the PKP curve as 144, 152.5 and 115°, again in reasonable agreement with 1066B. 相似文献
3.
通过对中国数字地震仪台网(CDSN)11个台1993—2012年间30个极远震记录的分析,识别出了PKP波入射到内外核界面(ICB)上的衍射波PKPdif波。PKPdif波在震中距120°左右时出现在PKIKP波之前,在震中距150°以后出现在PKIKP波之后,是一个长周期波。为了解释PKPdif波超前于PKIKP波的原因,设想在距地面约5 156.1～5 372.2 km的深度,即内外核界面下有可能存在一个PKIKP波的低速层(厚度约216.1 km)。该设想符合Jeffreys速度模型,给出的PKPdif波在震中距119.4°～176.1°间的走时表填补了目前使用的《IASPEI1991地震波走时表》的空白。讨论PKPdif波的运动学特征有助于对内外核界面物理性质的认识,有助于提高分析震相的水平和积累震相分析经验。 相似文献
4.
前临界内核边界反射震相PKiKP与核幔边界反射震相PcP构成组合,能有效压制浅部结构及震源因素的干扰,提供了对内核边界精细结构的直接约束. 本研究从华北克拉通西北部密集流动地震台阵一年观测资料中筛选出8个地震事件,得到共计 73对PcP-PKiKP组合,覆盖了从朝鲜半岛到我国东北及华中地区下方的内核边界. 本文系统分析了走时残差和振幅比数据,结果显示:(1)密集台阵资料有助于前临界PKiKP震相拾取,而浅源地震亦可提供高质量的PcP-PKiKP观测资料.(2)走时残差呈现了自西北向东南从正常到负异常的迅速变化(沿内核边界70 km范围内>0.5 s), 限制了研究区域内核界面不超过3 km的起伏. (3)相对振幅比变化表明了研究区内核边界密度差北西-南东向的系统增加, 揭示了内核结晶环境的小尺度扰动. 相似文献
5.
The hypothesis of scattering of PKP waves near the mantle-core boundary provides a comprehensive interpretation of the observed precursors to PKIKP, certain features of which have not been adequately accounted for by any alternative interpretation. These features include the variation with distance of the times and slownesses of precursor onsets, and the variations in amplitude, azimuth and slowness observed in precursor wavetrains.The observed times and slownesses of the earliest precursor onsets are in close agreement with the theoretical least time curve for singly scattered waves.Amplitudes and slownesses of scattered waves have been calculated for earth models which are spherically symmetrical except for random variations in density and elastic parameters in a layer 200 km thick at the base of the mantle. The calculations show that observed precursor amplitudes and slownesses can be accounted for by random variations of about one percent having a correlation distance of about 30 km in this layer. In particular, it is shown that scattering structures up to 900 km above the mantle-core boundary inferred by Doornbos and Vlaar (1973) are not required by their data. There is a suggestion that the main scattering may actually occur inside a layer much less than 200 km thick at the base of the mantle. 相似文献
6.
《中国科学:地球科学(英文版)》2021,(5)
Quantifying the density contrasts of the Earth's inner core boundary(ICB) is crucial to understand core-mantle coupling and the generation of the geodynamo. The PKiKP/PcP amplitude ratio is commonly used to obtain the density contrast at the ICB, but its applications are limited by scattered observed data. In this study, we selected the PKiKP and PcP phases reflected at the same region of inner-core and core-mantle boundaries beneath Northeast Asia from different earthquakes for the first time, and the observations suggested that the PKiKP/PcP amplitude ratio is widely scattered. We also compared the PKiKP and PcP amplitudes, which demonstrated that the scatter cannot be attributed only to ICB anomalies but might also arise from raypath differences and heterogeneities throughout the crust and mantle. By fitting the observed PKiKP/PcP amplitude ratio, we obtained a density contrast of approximately 0.65 g cm~(-3) and a compressional velocity contrast of approximately 0.87 km s~(-1) at the ICB beneath Northeast Asia. The larger contrast values indicate the possible occurrence of local crystallization occurring at the inner core surface. 相似文献
7.
兰州地震台阵监测能力研究 总被引：1，自引：1，他引：0
利用兰州地震台阵与兰州地震台数字化近两年的资料,对地震震相特征和震级进行对比分析,结果发现：地震记录震相特征基本相同,台阵有压低干扰背景和突出地震波信号的功能,说明台阵对记录较微弱地震有优势;在震中距小于1 000 km的范围内,兰州台阵的监测能力较明显高于兰州台,而震中距大于1 000 km时,兰州地震台阵与兰州地震台的监测能力相当. 相似文献
8.
J.C. Mondt 《Physics of the Earth and Planetary Interiors》1977,15(1):46-59
SH waves observed at epicentral distances greater than 90° contain considerable information on the lowest 200 km of the mantle, the D″ region. Seven event L.P. WWSSN station combinations at which SH was clearly observed have been analyzed. For each event the stations chosen were confined to a small azimuth range from the source. Assuming lateral homogeneity the differences between the received signals are only due to the different paths through the D″ region. Although the upper mantle and crust are certainly not laterally homogeneous, they are not known accurately enough to compensate for the differences beneath the stations. This, however, results in large standard errors of the decay parameters determined. After Fourier transformation the decay with distance for each frequency component (period range 64–68 s) was calculated assuming linearity with distance.The SH-wave potentials for the same frequencies were calculated using a point source and Langer's approximation for the calculation of the radial factor, for several models: PEM-C and related models with lower velocities in the D″ region. The decay with distance was also calculated assuming linearity.Direct comparison between the decay values of the calculated wave field and the observations was allowed at the level of approximation used. It was found that a velocity decrease with depth — i.e., a negative velocity gradient, in terms of the usual convention — of the order of 2.4% over a depth interval of a good 100 km explained the data satisfactorily. Lateral inhomogeneity was indicated by the observations but has to be corroborated by more data. 相似文献
9.
Frequency-time analysis was applied to records of Rayleigh surface waves due to teleseismic earthquakes (M ≥ 6.0) to obtain
dispersion curves of fundamental mode phase velocities for paths between 51 pairs of digital seismic stations in the Asian
IRIS networks; the range of periods was 10–200 s. For each of these pairs we derived 1D-shear-velocity sections that fit the
corresponding dispersion curves and image the integral earth structure down to depths of ∼650–700 km beneath each of the interstation
seismic paths, which traverse the area of study in different directions. These structures were used by Yanovskaya (2001) to
derive a 3D-shear-velocity model by 2D tomography, imaging the distribution of the larger horizontal inhomogeneities in the
Central Asia mantle for depths of 50 to 600 km, and to construct 2D-velocity sections for five lines passing through the major
tectonic features of Central Asia. 相似文献
10.
O'Leary González Leonardo Alvarez Mariangela Guidarelli Giuliano F. Panza 《Pure and Applied Geophysics》2007,164(10):1985-2007
An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of
the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group
velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the
Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic
maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification
techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each
one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region
are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper
mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle
structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located
over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and
upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. 相似文献
11.
新疆数字地震台网地方性震级量规函数的初步研究 总被引：2，自引：1，他引：1
基于2009～2014年新疆测震台网数字地震记录资料,运用震级残差统计方法,选择16269个2.0≤ML≤5.4地震事件,共计获得了179561个单台记录;利用最大地动位移衰减特性方法,选用3.6≤ML≤4.5的746个地震事件作为研究对象,对新疆数字台网地方性震级量规函数进行了研究。将得出的量规函数值进行对比后认为,现阶段使用的量规函数值在0～200km的震中距范围内偏小,导致此范围内台站测定的震级偏小;在200～800km的范围内,测算的震级值较稳定,偏差范围在±0.1的范围内;在400～800km震中距范围内,由最大地动位移衰减特性方法得出的量规函数偏小。由于目前各地震台站使用的地震计仪器响应不准确,造成量规函数偏小的原因有待用计量更加准确的台站仪器响应参数进行验证,以便得到更加精确的新疆台网地方性震级量规函数。 相似文献
12.
Wilhelm Weinrebe 《Pure and Applied Geophysics》1981,119(6):1107-1115
The deep seismic sounding project Blue Norma was carried out in the summer of 1977 in northern Scandinavia in order to investigate the deep structure of the Norwegian continental margin and the Caledonian mountain chain. During the measurements, by chance the core phase PKIKP of an earthquake at the New Hebrides was recorded with 30 seismic field stations along a profile through the central Caledonides. The results of the refraction seismic data, as obtained by a ray-tracing method, are presented and compared to the interpretation of the relative residuals of the PKIKP travel times. From both data sets a continentward down-dipping crust-mantle boundary is evaluated. From the interpretation of the refraction seismic measurements a crustal thickness of 32 km below the coastline and 42 km below the central mountain chain is obtained. The increase of the crustal thickness derived by the inversion of the travel-time residuals along this line amounts only to 6 km. This considerable discrepancy can only be explained by an eastward increasing seismic velocity in the mantle. 相似文献
13.
2013年4月20日的芦山7.0级地震是继2008年5月12日汶川8.0级特大地震之后,发生在龙门山断裂带上的又一次大震级逆冲型地震.与汶川地震相比,芦山地震的发震断层没有地表出露,断层的滑动角更大,其逆冲性质更强烈.本文挑选了芦山地震中断层距小于200km的45条强震动记录,基于地震动衰减关系进行统计分析,对比了上盘和下盘台站地震动参数相对于衰减关系的对数残差.结果表明：芦山地震的上下盘效应明显,近断层上盘地震动的高频成分要高于同断层距的下盘;上盘地震动衰减要明显快于下盘.地震动衰减关系用简单的一个距离参数很难描述近场断层尺寸效应的影响,也很难模拟地震动上下盘效应.因此,在近场强地面运动模拟中,应多考虑有限断层模型,以模拟断层的尺寸效应. 相似文献
14.
M. B. Barannik V. V. Kolobov V. N. Selivanov D. V. Kuklin A. A. Zhamaletdinov A. N. Shevtsov 《Seismic Instruments》2013,49(3):275-284
The structure and a possible practical application of the portable generator with extremely and super low frequency (ELF-SLF) range (0.1–200 Hz) and power of 2 kW are described. The generator is designed for deep sounding of the Earth’s crust for the purposes of mineral exploration and electromagnetic monitoring of source zones of earthquakes in seismically active regions. Computational and theoretical works, as well as numerical simulation for optimizing the generator’s parameters and element base, are carried out. The main constructive elements of the generator, namely, the power factor corrector, the driver control circuit for power transistors, the inverter of the high-frequency decoupling converter, the multichannel pulse power converter, the output inverter, and etc., are consistently described. The generator’s weight does not exceed 10 kg, and, therefore, the generator may be easily delivered to a testing site using any kind of transport, including planes. The generator is powered by the single-phase network with a voltage of 220 V. The full-scale testing of the generator is performed at the territory of the Yamalo-Nenets autonomous okrug via the connection to the high-voltage transmission line Urengoi-Pangody with a length of 114 km. The maximum current in the line is 12 A. The maximum distance of reliable signal recording is 110 km. 相似文献
15.
Gaubau等人于1978年提出的参考台技术,从理论上完全消除了计算张量阻抗时所具有的偏倚误差。但在实际测量中,参考台的距离多大才合适,尚无定论。本文所给的实例,采取了固定主测台、移动参考台的方法。结果表明,参考台距离从20 km变到40 km不会给测量结果带来明显的变化。 相似文献
16.
Eiji Ohtani 《Earth and Planetary Science Letters》1984,67(2):261-272
The densities of silicate liquids with basic, picritic, and ultrabasic compositions have been estimated from the melting curves of minerals at high pressures. Silicate liquids generated by partial melting of the upper mantle are denser than olivine and pyroxenes at pressures higher than 70 kbar, and garnet is the only phase which is denser than the liquid at pressures from 70 kbar to at least 170 kbar. In this pressure range, garnet and some fraction of liquid separate from ascending partially molten diapirs. It is therefore suggested that aluminium-depleted komatiite with a high Ca/OAl2O3 ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar (200–400 km in depth), where selective separation of pyropic garnet occurs effectively. On the other hand, aluminium-undepleted komatiite is probably derived from diapirs originating at shallower depths (< 200 km). Enrichment of pyropic garnet is expected at depths greater than 200 km by selective separation of garnet from ascending diapirs. The 200-km discontinuity in the seismic wave velocity profile may be explained by a relatively high concentration of pyropic garnet at depths greater than 200 km. 相似文献
17.
18.
Ram Datt 《Physics of the Earth and Planetary Interiors》1981,24(1):33-52
The fine structure of regional travel-time curves is investigated. About 200 events from the region north of Australia, recorded at the Warramunga array, are analysed to give the P-wave velocity structure for that region. The events were confined to a very narrow azimuth range. Results show that the 20° discontinuity is more complicated than a single velocity increase near 400 km depth, and that there are regions of rapid or discontinuous velocity increase at depths below 650 km. 相似文献
19.
本文利用已有的随机放电参数化方案,结合四次探空资料,进行了12.5 m的高分辨率二维雷暴云数值模拟实验,得到了各种雷暴云电荷结构下的地闪个例,并就地闪击地点与空间电荷、电位分布之间的相互关系进行了分析.结果表明:(1)由空间电荷唯一确定的电位分布决定了先导的传播最大趋势,而闪电传播的随机性所带来的地闪击地点的不确定范围被限制在3 km之内,利用动态聚类法迭代得出的三个击地点位置之间的差为1 km左右.(2)负地闪的初始点与击地点的位置差主要分布在0~6 km范围内,且93%的负地闪分布在0~4 km范围内,正地闪的分布相对较广,0~3 km范围内占48%,3~6 km范围内占34%,6~10 km范围内占18%.(3)正、负地闪主要产生于离地面最近的一对电荷堆之间,其起始高度越高,初始点与击地点位置差分布越广;另外,产生于三级性雷暴云电荷结构下的正地闪,其起始于上部的主正电荷堆与中部主负电荷堆之间,由于下行正先导会绕过底部的次正电荷堆,因此其击地点与初始点的距离基本在6 km以上. 相似文献
20.
基于河北测震台网现用速度模型,利用走时方程计算得到河北地区Pb震相的盲区范围大致为70km左右,作为初至震相的起始震中距范围为90~120km,作为后续震相的起始震中距范围为135~150km;收集近年京津冀地区2.0级以上地震88条,根据Pb震相理论波形特征,以及理论波形与实际波形到时比对,最终识别到158个有效Pb震相,拟合速度为6.69km/s,康拉德界面埋深21km,并得到河北地区Pb震相实际波形特征,弥补了河北台网Pb震相空白;利用Pb震相的射线分布,分析认为康拉德界面在河北北部山区发育程度较好,南部次之,中部渤海湾盆地地区连续性最差。 相似文献