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1.
Ground total magnetic field data of Albania were used to produce estimates of the Curie point isotherm. The strategy followed
was to estimate the depth to the bottom of the deepest magnetic sources. Firstly, the average depth to the top of the deepest
crustal block, zt, was computed by linear fitting to the second lowest-frequency segment of the azimuthally averaged power spectrum of the
total magnetic field data. Then, the depth to the centroid of the deepest crustal block, z0, was computed by linear fitting to the lowest-frequency segment of the azimuthally averaged power spectrum of a distribution
of magnetic dipoles. Finally, the depth to the bottom, the inferred Curie point depth, zb, was calculated from zb=2z0−zt. Curie depth estimates for Albania vary from about 17 to 25.5 km (below sea level). These results are consistent with the
depths inferred by extrapolating geothermal gradient and heat-flow values, suggesting that the Curie point depth analysis
is useful to estimate the regional thermal structure. It also suggests that the approach was valid and that ground total magnetic
field data can be used for this purpose. 相似文献
2.
The magnetic map of Slovakia used in the paper was compiled as part of a project titled Atlas of Geophysical maps and profiles in 2001. The residual magnetic data were analyzed to produce Curie point estimates. To remove distortion of magnetic anomalies
caused by the Earth’s magnetic field, reduction to pole transformation was applied to the magnetic anomalies using the magnetization
angle of the induced magnetization. Anomalies reduced to the pole tend to be better correlated with tectonic structures. We
applied a 3-km upward continuation to the residually compiled magnetic anomalies in order to remove effects of topography.
The depth of magnetic dipoles was calculated by an azimuthally averaged power spectrum method for the entire area. Such estimates
can be indicative of temperatures in the crust, since magnetic minerals lose their spontaneous magnetization according to
Curie temperature of the dominant magnetic minerals in the rocks. The computed Curie point depths in the Slovakia region vary
between 15.2 km and 20.9 km. Heat flow higher than 100 mWm−2 occurs at the central volcanics and eastern part of Slovakia, where the Curie point depths values are shallow. The correlation
between Curie point depths, heat flow and crust depth was investigated for two E-W cross sections. Heat flow and Curie point
depth values are correlated with each other however, these values could not be correlated with crust depth. The Curie point
isotherm, which separates magnetic and non-magnetic parts of the crust, is represented in two cross sections. 相似文献
3.
In this paper we discuss two types of crust models with abnormal density, velocity of wave and certain geometrical structures.
The far-field synthetic seismograms of P and SH wave are calculated by the far-field vertical displacement formulas of P and
SH waves with the double couple point source and the formulas of reflection coefficient, radiation pattern and travelling
time difference derived from the models suggested in the paper. It is shown by the results that the effect of special crust
structures near focus on the far-field seismograms can be ignored if the densities and wave velocity of the special structure
are less than average those of the crust (model I). However the effect should be noticed if the densities and wave velosities
of the structure are large than average those of the crust (modelI). The effect of the special crust structure on the far-field seismograms has not been studied further before. Seismic records
of the Haicheng earthquake and the crust structure in Haicheng region are studied by the calculation method in the paper.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 1993. 相似文献
4.
利用航磁资料和三维磁性层反演理论,对菏泽震区的航磁资料进行了数据处理,计算出震区枧磁化强度分布图、基底磁性界面埋深图和居里等温面埋深图。结果显示东濮凹陷基底磁性界面深达12km,下部居里等温面上隆,凹陷内被弱磁性物质填充。地震发生在凹陷附近视磁化强度、基底磁性界面、居里等温面的变异带上。 相似文献
5.
Crustal thermal regime inferred from magnetic anomaly data and its relationship to seismogenic layer thickness: The Japanese islands case study 总被引：2，自引：0，他引：2
The seismogenic layer thickness correlates with surface heat flow beneath the Japanese islands. However, this correlation is shown at restricted area, where seismic activity is high. In order to overcome this spatial limitation, we used another approach to estimate the regional thermal structure in the crust beneath the Japanese islands with more uniform coverage. The bottom depths of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. We applied this method to estimate the crustal thermal structure in square windows of 2.125° × 2.125°. The obtained depths ranging from 11 to 30 km with average value of 18 km, correlate with the seismogenic layer thickness. It suggests that the Curie point depth is a useful indicator of the crustal thermal structure in these regions. 相似文献
6.
Using observational data of geomagnetic total intensity from 13 stations in the Beijing-Tianjin region, 3 stations in the
western Yunnan region of China, and 6 stations in California of U. S. A., the daily variations and their spectra of geomagnetic
total intensity were analyzed and compared. The results show that the morphology, the range and spectrum of daily variations
in geomagnetic total intensity are basically the same within the local extent of 100–200 km and are different in the large
extent of 500 km. The latitude factor of the daily variation range of geomagnetic total intensity is about 1–2 nT/degree within
the latitude extent of 25°–40°.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 83–89, 1992.
This work is supported by the State Seismological Bureau and the Chinese Joint Seismological Science Foundation, and U.S.
Geological Survey. 相似文献
7.
Using the P-and S-wave arrivals from the 150 earthquakes distributed in Tibetan Plateau and its neighboring areas, recorded
by Tibetan seismic network, Sichuan seismic network, WWSSN and the mobile network situated in Tibetan Plateau, we have obtained
the average P-and S-wave velocity models of the crust and upper mantle for this region:
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 573–579, 1992. 相似文献
| (1) | The crust of 70 km average thickness can be divided into two main layers: 16 km thick upper crust with P-wave velocity 5.55 km/s and S-wave velocity 3.25 km/s; and 54 km thick lower crust with P-wave velocity 6.52 km/s and S-wave velocity 3.76 km/s. |
| (2) | The p-wave velocity at the upper most mantle is 7.97 km/s, and the S-wave 4.55 km/s. The low velocity layer in the upper mantle occurs approximately at 140 km deep with a thickness of about 55–62 km. The prominent velocity gradient beneath the LVZ is comparable to the gradient above it. |
8.
Using the techniques of seismic tomography three-dimensional velocity images at crust and upper mantle in Yunnan province
and its adjacent region have been successfully reconstructed. The results of image are: (1) The image of the velocity in the
upper crust is closely related to the well-known geological structure of the surface, the Kangdian earth axis is a distinct
high velocity area, and a high velocity rock stratum, which appoaching the surface of the earth, has been formed. (2) There
is a low-velocity layer between 26°–31°N and 100°–104°E in deep crust, the depth of Moho discontinuity in Sichuan bass in
is less than 50 km. (3) The results of seismological tomography not only reveal the lateral heterogeneity in the researched
region, but also find approximately the strike of Honghe fault from the image at bottom of crust, and the velocity in both
side of the fault are different obviously. (4) There is a low-velocity column within 25 km to 110 km in Tengchong region,
which may be occured by upward moving of the basalt in the mantle. (5) In studied area, the thickness of the crust in west
part is thicker than in southeast part. (6) From the image at bottom of the crust we can find that earthquakes with magnitude
greater than 5 occurred in big velocity gradient zones, especially in transition zone between high and low velocity. There
are a few earthquake in the low-velocity area. (7) We can see from Figure 6 that there still clearly exists lateral heterogeneity
at 450 depth.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 61–67, 1993. 相似文献
9.
Xiwen Wang 《地震学报(英文版)》1992,5(1):133-143
In this paper, the application of Backus—Gilbert’s inversion method to the potential field anomalies for evaluating gravity
and magnetic inversion solutions is discussed. Errors in data and singularity of kernels in the equations result in difficulties
in solving equations. The application of regularization method similar to spectral expansion method makes calculation fast
and easily. To make solution stable, constraints are used, which make the spread of solutions become narrow, standard deviation
become small and iterative computations of inversion become fast. Finally, the author analyses specifically two profiles of
Yunchen basin and calculated the Moho interface and the Curie isotherm of these two profiles.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 212–221, 1991. 相似文献
10.
我们曾提出过一种可能导致地磁和地壳电导率异常的来源：地壳中的二级磁相变,即居里（尼尔）深度附近磁化率的显著提高.这一现象能很好地解释一些来源不明的地磁异常.本文总结了在中地壳深度处、薄且高磁导率异常体的一维和多维大地电磁特征.高磁导率层引起的异常与高电导率层导致的异常相比,大小上可相比拟,但符号相反.无论在什么情况下,经典的大地电磁解释容易导致一个不真实的极厚高阻层,并且在地磁异常附近有与之对应的空间波长,二级磁相变也被认为是这一现象的可能解释.尽管在地壳中是否存在二级磁相变还有一定争议,但最近的一些固体物理实验结果进一步表明它可能是地壳各种地球物理异常的来源之一. 相似文献
11.
Jörg Ebbing Laurent Gernigon Christophe Pascal Odleiv Olesen Per Terje Osmundsen 《Geophysical Prospecting》2009,57(4):665-681
We discuss the correlation between the depth extent of magnetic sources, the Curie temperature depth and crustal structures on the mid-Norwegian margin. Spectral methods can be used to estimate the depth extent of magnetic sources, even if the bottom is located in the lower crust, however, only with limited resolution. The bottom of the magnetic surfaces is often regarded to represent the depth to the Curie isotherm. However, comparison with a 3D model based on the interpretation of potential field and seismic reflection data and thermal modelling shows that the depth extent of the magnetic sources is merely controlled by the overall geometry of the crystalline crust and not the temperature distribution. The observed changes in the magnetic field between the inner and outer part of the mid-Norwegian margin appears not to reflect, as previously assumed, the depth to the Curie temperature but the geometry of the basement and lower crust. Our 3D model of the mid-Norwegian margin reveals a basement configuration that involves a basement with different petrophysical properties, which can be connected with lithological basement units of onshore Norway. 相似文献
12.
本文利用CHAMP卫星磁测资料建立的新一代高阶地磁场模型POMME-4.2S,计算中国及邻区400 km高度的卫星磁异常及其垂直梯度,给出7个磁场分量的分布图,比较了截断水平对磁异常分布的影响,初步分析了磁异常与岩石圈构造的关系.主要结果表明,在四川盆地、塔里木盆地和松辽盆地等主要磁异常区,ΔZ异常中心的南北两边出现ΔX的异常中心,东西两边出现ΔY的异常中心.在球谐模型为90阶时,磁异常分布的基本形态已经确定,更高的模型阶数对磁异常只有微小调整.在磁异常较强的地区,磁异常及其垂直梯度同步变化.卫星磁异常与地形变化、断裂带分布、莫霍面深度和岩石圈厚度没有直接的对应关系,而与居里等温面深度、磁性层厚度有明显的相关性.居里等温面深、磁性层较厚的地区显示正磁异常,居里等温面浅、磁性层较薄的地区显示负磁异常. 相似文献
13.
本文采用Hilbert-Huang变换分别对磁暴干扰下的“天宫二号”空间实验室大气质谱信号和乌鲁木齐地磁基准台FHDZ-M15所产出地磁数据进行特征分析.实验首先采用小波分析方法分析两种信号的能量谱,结果可得:“天宫二号”空间实验室大气质谱信号和M15地磁信号在磁暴时段能量较为集中,且幅值较大.该实验表明两种信号的能量分布成正相关性.基于Hilbert-Huang变换的时频聚集性及处理非平稳信号的能力,实验进一步采用Hilbert-Huang变换对磁暴干扰下的两种信号进行时频特性分析.通过对两种信号的Hilbert-Huang谱分析可得:“天宫二号”空间实验室大气质谱信号和M15地磁信号在磁暴干扰下的频率均主要集中在0.2 Hz之内.同时,Hilbert-Huang谱实验清晰反映出了两种信号能量随时间和频率的分布情况. 相似文献
14.
本文用1980—2000年M≥1.5的2 032个天然地震事件的38 052个〖AKP-〗、〖AKS-〗、Pm、Sm、Pn和Sn震相到时及人工地震测深给出的Moho面形态资料,利用地震层析技术反演了32°~40°N, 100°~108°E区域内地壳地震波速度结构.从层析成像图象中可以得到,本区的地壳可分成4个层位.第1层（埋深约在0~3 km）为沉积层, 速度梯度约为0.2 s-1;第2层（埋深约在3~17 km）为上地壳, 其顶部速度梯度约为0.1 s-1, 下部速度横向变化较大且存在低速块体;第3层（埋深约在17~36 km）为中地壳, 速度梯度约为0.03 s-1;第4层（埋深约在36 km—Moho）为下地壳, 是一个契形层,总的趋势是西厚东薄,青藏高原较厚逐渐向鄂尔多斯地块和扬子准地台方向变薄,各处的地震波速度梯度不尽相同. 相似文献
15.
A three-component geomagnetic survey was carried out during the period from 2002 to 2004 in China including Jiujiang-Ruichang region. Comparing the ＂2005.0 surface spline model of China geomagnetic field＂ created on the basis of the survey data with the ＂1970.0 surface spline model of China geomagnetic field＂, we can see an obvious abnormity in the geomagnetic horizontal component within a range of about 100 km around the epicenter of the Ms=5.7 Jiujiang-Ruichang earthquake occurred on November 26, 2005. After the earthquake, we carded out a repeated geomagnetic survey at 21 stations in the Jiujiang-Ruichang region and created a corresponding ＂2005.0 partially revised surface spline model of China geomagnetic field＂. By comparing the above three models, analyzing the geomagnetic horizontal component at the profile in the Jiujiang-Ruichang region and quantitatively studying the geomagnetic data of every stations around the Ms=5.7 earthquake, we have obtained the geomagnetic abnormity associated with this earthquake. Then the geomagnetic abnormity and its relation with seismic activity are discussed in this paper. 相似文献
16.
Zhong-Yang Lin Hong-Xiang Hu Wen-Bin Zhang Hui-Fen Zhang Zheng-Qin He Zhen-Ming Lin Tao-Xing Qiu 《地震学报(英文版)》1993,6(4):867-881
The preliminary interpretation of Project western Yunnan 86–87 is presented here. It shows that there obviously exists lateral
velocity heterogeneity from south to north in western Yunnan. The depth of Moho increases from 38 km in the southern end of
the profile to 58 km in its northern end. The mean crustal velocity is low in the south, and high in the north, about 6.17–6.45
km/s. The consolidated crust is a 3-layer structure respectively, the upper, middle and lower layer. P
1
0
is a weak interface the upper crust, P
2
0
and P
3
0
are the interfaces of middle-upper crust and middle-lower crust respectively. Another weak interface P
3
0′
can be locally traced in the interior of the lower crust. Interface Pg is 0–6 km deep, interface P
1
0
9.2–16.5 km deep, and interfaces P
2
0
and P
3
0
respectively 17.0–26.5 km, 25.0–38.0 km deep. The velocity of the upper crust gradually increases from the south to the north,
and reaches its maxmium between Nangaozhai and Zhiti, where the velocity of basement plane reaches 6.25–6.35 km/s, then it
becomes small northward. The velocity of the middle crust varies little, the middle crust is a low velocity layer with the
velocity of 6.30 km/s from Jinhe-Erhai fault to the north. The lower crust is a strong gradient layer. There exists respectively
a low velocity layer in the upper mantle between Jinggu and Jingyunqiao, and between Wuliangshan and Lancangjiang fault, the
velocity of Pn is only 7.70–7.80 km/s, it is also low to the north of Honghe fault, about 7.80 km/s. Interface P6/0 can be traced on the top of the upper mantle, its depth is 65 km in the southern end of the profile, and 85 km in the northern
end.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 427–440, 1993. 相似文献
17.
Xinling Qin L. B. Pedersen Yulin Zhao Ping Zhang Fuye Qian Wei Qian Zhengnan Li Jingxian Du 《地震学报(英文版)》1992,5(2):355-365
It is shown by the result of digital magnetotelluric soundings in the Tangshan seismic area and its surrounding regions that
the crust under the surface conductive sediments is divided into two layers,i. e., the resistive upper crust and the conductive
lower crust. The upper crust wherein the Tangshan main shock and most of the aftershocks occurred is a convex lens-like body
which is cut by faults at the east, south and west sides. The focus of the mainshock was located at the position of maximum
thickness of the resistive upper crust while the spatial variation of Curie point isothermal surface and the deepest limit
of the depths of aftershocks coincide with the downward depression of the bottom of the resistive upper crust. Thus, the Tangshan
main shock and most of its aftershocks were related closely to the resistive upper crust from the view points of either vertical
layering or lateral variations. And there were only a very few aftershocks in the conductive lower crust. The mechanical property
of the rocks transforms from being brittle in the upper crust into ductile in the lower crust mainly due to the combination
of different factors, e.g., increase of confining pressure, change in minerals, rise in temperature as well as stabilization
of slips by high pore—pressure. A small amount of water and a rise in temperature may lead to a decrease of the electric resistivity
within the rock while a change in the static pressure and mineral content within the rock causes very little change in the
electric resistivity. Thus it is deduced that a resistive upper crust and a more conductive lower crust from the view points
of either vertical or lateral variations are related to the brittle and ductile properties respectively. Hence it is possible
that there is a relationship between the electric structure of the crust and zones of potential seismic hazard.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 354–363, 1991.
The project is supported by the Chinese Joint Seismological Science Foundation, and the Swedish International Development
Authority. 相似文献
18.
本文根据重力、航磁、地壳视厚度、地震活动性及震源深度等资料,对鲜水河断裂带形成的深部状况及其与地震发生的关系进行了初步分析和讨论。结果表明: 1.该断裂带在上地幔顶部的壳幔界面上並未得到清晰和直观的反映,因此推测它可能未切穿岩石圈,而属一条壳内区域大断裂。2.该断裂是在前海西期构造隆起背景上发育起来的。3.从地壳剖面上看,古生代变质岩系底板以下到磁性居里等温面之间的带状空间,是该断裂带的孕震和发震的层位。4.磁性居里等温面的隆起或高点部位,因岩浆或高温流体的侵入,往往是孕震断层的根部,根部增温,上部锁住,故有利于应力的集中,最易产生错动,而成为强震孕育、发生的重要场所。 相似文献
19.
20.
中国东北地区位于西伯利亚和华北地块之间,中、新生代本区受西太平洋板块俯冲的影响,由于多期构造作用,导致地质构造形态极为复杂.本文通过分析航磁异常场,认识研究区的构造特征,并利用航磁异常数据的功率谱法反演居里等温面.航磁异常场和居里面分布特征均揭示研究区地质构造发展具有继承性;通过居里面起伏变化特征,并结合满-绥地学断面、及与大地热流分布的关系,讨论研究区地壳的热结构状态特点,结果显示居里面起伏趋势与软流圈起伏具明显的相关性;结合地震活动和地震层析成像研究,探讨了太平洋板块俯冲受阻引起岩浆和火山活动,进而导致居里面上隆的影响机制. 相似文献