共查询到19条相似文献，搜索用时 187 毫秒
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近年来，远震走时层析成像方法有了长足的发展，在地下结构反演的研究中获得了众多成果。针对射线在台站下方覆盖率较差而导致远震反演方法对地壳速度约束不足的问题，本文提出了一种新的地壳异常体改正方法——对同一台站的相对走时残差进行求和平均去均值，消除了地壳中复杂的速度异常体对上地幔速度结构反演的干扰，反演结果具有更优的相对走时残差分布，同时反演得到的速度模型具有更小的数据方差。 相似文献
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利用差异演化（Differential Evolution）非线性全局优化算法，设计了一种反演地壳速度模型和进行地震定位的方法，并给出了反演结果的具体分析.利用有限差分算法计算速度模型的走时场，可以节省大量的计算量，加快计算过程.反演得到的地壳速度模型和地震的震源参数可以直接用于地震层析成像研究，还可以利用地震层析成像得到的三维速度结构对地震重新定位，从而得到较为精确的震源参数.地壳速度模型的反演方法也可以用于三维速度结构的反演. 相似文献
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利用架设在沧州地区的20台流动地震台站于2006年12月至2010年7月间记录的271个远震事件,读取的2308个P波到时数据,采用地震层析成像方法反演得到沧州及其邻区(38.0°N～39.0°N,116.5°E～117.5°E)的地壳上地幔P波三维速度结构。层析成像结果表明,沧东断裂两侧的地壳介质的速度分布表现出明显的横向差异,浅层速度分布同地表地质结构分布相一致。沧东断裂西北侧沧县隆起的地壳速度较高,表明其基底抬升;断裂带东南边的黄骅拗陷速度较低,说明基底埋藏较深。本文的远震层析成像研究结果和前人使用重力、电磁和人工地震的探测结果都表明,沧东断裂带两侧的地质构造和地球物理性质有明显的变化,这种构造差异在整个地壳中都有体现。 相似文献
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为利用sPn与Pn波的走时差测定震源深度,进一步提高地震震源深度的测定精度,推导多层介质下sPn与Pn波的走时差与震源深度的关系,发现走时差与震中距无关,只与震源深度及区域地壳速度模型有关。震源在同一层中,走时差曲线的斜率不变,而当震源位于不同层中时,sPn-Pn走时差曲线的斜率不同,并呈分段直线的走时差曲线形态。地壳速度结构纵向越不均匀,多层和单层介质下利用sPn-Pn走时差计算的震源深度误差就越大,走时曲线的各分段直线斜率相差越大;探讨地壳中sPn与Pn波传播路径相同但波速不同的单层地壳速度模型,发现单层介质下波速越大,测定的震源深度越大;对于同一地区相同的地壳分层结构,测得的震源深度随着泊松比的增大而减小。基于前人给出的中国五个典型块体多层平均地壳模型,给出sPn-Pn走时差与震源深度计算公式速查表。 相似文献
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地震层析成像是研究地球内部结构的主要方法.文章利用首都圈区域内3231个地震挑选出来的29839条直达P波走时和29972条直达S波走时数据,首次使用拟波形层析成像方法对首都圈地区地壳的P波和S波速度,以及泊松比进行反演成像,获得了该区域三维高分辨率VP、VS以及泊松比结构.成像结果表明,首都圈地壳结构非均匀性强烈,地表地质构造特征与浅层的速度异常具有明显的一致性.中地壳康拉德面深度附近广泛存在的相对低速异常层可能是多期构造运动叠加的结果.该区域地震多发生于高低速及泊松比异常交界区域.唐山地震和历史上的三河-平谷地震震源下方都存在明显的相对低速异常,可能与流体的存在有关.深部速度结构异常的一致性可能暗示唐山地震和三河-平谷地震的深部发震构造具有一定的相似性.高分辨率精细速度结构的获得,为深入认识首都圈地区地壳结构的精细非均匀性和动力学机制提供了重要的科学依据. 相似文献
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H．J．Yoo R．B．Herrmann K．H．Cho K．Lee 《世界地震译丛》2007,(4):45-56
结合Cho等(2006b)的高频面波层析成像结果与朝鲜半岛80个点位上的远震P波接收函数,对朝鲜半岛南部的剪切波速度的三维变化进行了祥细的研究。这些接收函数是根据韩国气象局和韩国地球科学与矿产资源学院台网提供的高增益加速度、短周期和宽带数字数据集求出的。垂直剖面追踪了莫霍面深度的水平变化、近地表的低速度变化以及自地表速度到中地壳速度过渡带的厚度变化。根据获得的地壳结构提出了关于朝鲜半岛地壳演变的新观点。 相似文献
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Improving Regional Seismic Event Location in China 总被引：1，自引：0，他引：1
L.K. Steck A.A. Velasco A.H. CogbillL H.J. Patton 《Pure and Applied Geophysics》2001,158(1-2):211-240
—?In an effort to improve our ability to locate seismic events in China using only regional data, we have developed empirical propagation path corrections and applied such corrections using traditional location routines. Thus far, we have concentrated on corrections to observed P arrival times for crustal events using travel-time observations available from the USGS Earthquake Data Reports, the International Seismic Centre Bulletin, the preliminary International Data Center Reviewed Event Bulletin, and our own travel-time picks from regional data. Location ground truth for events used in this study ranges from 25?km for well-located teleseimic events, down to 2?km for nuclear explosions located using satellite imagery. We also use eight events for which depth is constrained using several waveform methods. We relocate events using the EvLoc algorithm from a region encompassing much of China (latitude 20°–55°N; longitude 65°–115°E). We observe that travel-time residuals exhibit a distance-dependent bias using IASPEI91 as our base model. To remedy this bias, we have developed a new 1-D model for China, which removes a significant portion of the distance bias. For individual stations having sufficient P-wave residual data, we produce a map of the regional travel-time residuals from all well-located teleseismic events. Residuals are used only if they are smaller than 10?s in absolute value and if the seismic event is located with accuracy better than 25?km. From the residual data, correction surfaces are constructed using modified Bayesian kriging. Modified Bayesian kriging offers us the advantage of providing well-behaved interpolants and their errors, but requires that we have adequate error estimates associated with the travel-time residuals from which they are constructed. For our P-wave residual error estimate, we use the sum of measurement and modeling errors, where measurement error is based on signal-to-noise ratios when available, and on the published catalog estimate otherwise. Our modeling error originates from the variance of travel-time residuals for our 1-D China model. We calculate propagation path correction surfaces for 74 stations in and around China, including six stations from the International Monitoring System. The statistical significance of each correction surface is evaluated using a cross-validation technique. We show relocation results for nuclear tests from the Balapan and Lop Nor test sites, and for earthquakes located using interferometric synthetic aperture radar. These examples show that the use of propagation path correction surfaces in regional relocations eliminates distance bias in the residual curves and significantly improves the accuracy and precision of seismic event locations. 相似文献
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Forough Keshvari Z. Hossein Shomali Mohammad Tatar Ayoub Kaviani 《Journal of Seismology》2011,15(2):329-339
Non-linear teleseismic S-phase tomography across the Zagros collision zone in southwestern Iran is used to determine a high-resolution
image of the upper-mantle structure. The inversion was done using 41 high-quality earthquakes recorded by 19 broad-band and
medium-band stations along a 620 km long profile across the collision zone. Smearing from strong crustal velocity anomalies
into the upper-mantle is suppressed by travel-time corrections calculated based on a 3-D crustal model for the study area.
Our results show that the relatively old and cold Arabian shield has a higher velocity (up to 6% faster, at depths between
70 and 300 km) than the younger lithosphere farther north in Central Iran. These two upper-mantle domains are separated by
a sharp near-vertical transition whose surface expression coinciding with the Main Zagros Thrust. 相似文献
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Introduction The Tengchong volcanic-geothermal area is located on the northeast edge of the collision zone between Indian and Eurasian plates, and belongs to Eurasian volcanic zone (the MediterraneanHimalayanSoutheast Asia volcanic zone). In Tengchong area, the Quaternary volcanic, geothermal and seismic activities are all intensive. These phenomena have been drawing the attention of many geoscientists in the world. Their studies are concerned with geology, geophysics, geochemistry, and cr… 相似文献
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中国大陆中西部乃至全球造山带普遍具有复杂地壳结构.随着矿产资源勘探和深部探测研究的深入,探测造山带及盆山耦合区下方地壳精细结构正逐渐成为当前面临的巨大挑战.人工源深地震测深方法正越来越清晰地揭示出不同构造域地壳速度结构的基本特征,然而传统的层状结构模型参数化方法难以准确描述复杂地质模型,通常情况下多忽略速度结构的精细间断面且采用层边界平滑处理,难以满足地壳精细结构成像的发展要求.针对上述困难,本文采用最近发展的块状结构建模方案构建三维复杂地壳模型,基于逐段迭代射线追踪正演走时计算方法,推导了走时对三角形界面深度以及网格速度的偏导数,开展了非线性共轭梯度走时反演方法研究.发展了利用直达波和反射波等多震相走时数据对界面深度和网格速度的多参数联合反演方法,并引人不同种类震相数据的权系数和不同类型参数偏导数归一化的方法.数值算例表明,基于块状结构的非线性共轭梯度走时反演方法适用于复杂地壳结构模型,在利用人工源走时数据反演复杂地壳精细结构领域具有良好的应用前景. 相似文献
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Zhifeng Ding Xiaofeng Zhou Yan Wu Guiyin Li Hong Zhang Institute of Geophysics China Earthquake Administration Beijing China 《地震学报(英文版)》2009,(4):403-408
The three-dimension crustal and upper mantle structures in the region around Beijing were studied by seismic tomography. We used the P wave arrival times from local and teleseismic events. These events were recorded by 250 stations of the North China Seismic Array and 108 stations of the Beijing Telemetry Seismic Network. 118 869 P wave arrivals from 10 285 local events and 12 189 P wave arrivals from 107 teleseismic events were used in the inversion. We obtained the 3-D P wave velocity structure of the cru... 相似文献
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本文选用首都圈数字地震台网2003年9月~2005年12月记录的300多个远震事件的波形资料,采用分频带多道互相关方法得到三个不同频段的P波相对走时数据共18499个,计算了每个频段的走时灵敏度核,应用有限频率层析成像反演得到首都圈地区的上地幔三维P波速度结构模型.利用检测板估计了反演结果的分辨率,并与射线层析成像方法的结果进行了比较,说明了反演结果的可靠性.研究结果表明,各构造单元具有明显不同的速度结构特征,其差异可到150 km深:燕山隆起区表现高速;太行山隆起区整体以低速为主并存在小范围高速块体;华北盆地、渤海湾下浅层上地幔中存在大范围的强低速异常,其顶面在50~70 km,可视为软流圈顶面的埋深,这一结果说明华北盆地、渤海湾下岩石圈明显减薄;张家口-蓬莱断裂带是上地幔浅部速度结构的变异带,也是岩石圈减薄的边界带,区内大部分强震都发生在该构造带上,由此看来该带上强震的发生不仅与地壳结构的不均匀性有关,还可能有较深的构造背景. 相似文献
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P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography 
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下载免费PDF全文 Bem Shadrach Terhemba Huajian Yao Song Luo Lei Gao Haijiang Zhang Junlun Li 《地震科学（英文版）》2022,35(6):427-447
Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D vS models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion. 相似文献
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利用青藏高原东北缘地区固定地震台网2010年4月至2015年3月期间记录的远震事件，采用多道波形互相关方法（Multi-Channel Cross-Correlation）拾取了10697个有效P波相对走时残差数据，进而采用FMTT （Fast Marching Teleseismic Tomography）方法获得了青藏高原东北缘上地幔400 km深度范围内的P波速度结构，结果显示：秦祁地块下面存在深达70 km的高速异常，阻断了青藏高原块体中下地壳低速层向东北方向的延伸；40~140 km深度范围内，四川西南部存在一个低速区，该低速区穿过龙门山断裂带进入到四川盆地内部；祁连山造山带东部低速异常区从地壳一直延伸到上地幔400 km处，表明这里可能存在一个上地幔到地壳间的热流通道；松潘-甘孜地块分布大面积的低速异常区，而鄂尔多斯地块西南缘相对速度较高，这与青藏高原为软块体、介质密度低和鄂尔多斯块体为硬块体、介质密度高相吻合. 相似文献