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1.
Receiver functions in northeast China - implications for slab penetration into the lower mantle in northwest Pacific subduction zone 总被引：6，自引：0，他引：6
Seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest Pacific subduction zone beneath Japan and northeast China have suggested contrary subduction scenarios. There was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660-km discontinuity over several hundred kilometers. We calculate receiver functions from a recent seismic broadband station network located in northeast China and find topographic variations of the upper mantle discontinuities. A deeper-than-normal 660-km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography. The 660-km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab. These observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle. 相似文献
2.
利用牡丹江(MDJ)和海拉尔(HIA)台1988-2000年的宽频带三分量数字地震记录,通过地幔间断面产生的P-SV转换波,研究台站下方地幔间断面的分布以及日本海俯冲带对660km间断面的影响.为了提高所得结果的可靠性,采用了线性-偏振滤波方法和修正的N次根倾斜叠加方法来提取P-SV转换波.前一方法通过实验选取适当的光滑平均和提出立体角的约束;对后一方法进行了震源深度校正和间断面倾斜的修正.结果表明,在MDJ和HIA台下方,除在660,410,220和520km深度附近均存有间断面外,在140,350,570,740和1080km深度附近也存在间断面,显示了地幔中径向分层的复杂性;另外,MDJ台下方660-840km之间的间断面结果比HIA台下方的复杂,似有分层结构,可能反映了俯冲带的影响. 相似文献
3.
利用国家测震台网固定台站和“中国地震科学台阵探测”项目在南北地震带北段布设的宽频带流动台阵记录到的极远震事件,通过SS前驱波震相研究,获得了阿留申—阿拉斯加俯冲带东段及邻区下方410 km和660 km间断面的埋深和起伏形态特征.为增强对SS前驱波震相的识别,我们采用了时差校正和共反射点叠加分析.叠加结果显示,毗邻阿留申俯冲带的白令海、阿拉斯加半岛、以及阿拉斯加中南部和东部地区下方,410 km和660 km间断面的埋深基本呈正相关关系,因而具有正常的过渡带厚度.这表明在阿留申—阿拉斯加俯冲带东段,北太平洋板块还没有俯冲到地幔过渡带深度范围内.其次,在阿拉斯加西部地区下方,660 km间断面出现明显下沉,而上覆的410 km间断面埋深接近于全球平均值,从而导致过渡带明显加厚.据此,我们推测在阿拉斯加西部地区下方地幔过渡带底部可能存在库拉残留板块. 相似文献
4.
K. M. Fischer M. J. Fouch D. A. Wiens M. S. Boettcher 《Pure and Applied Geophysics》1998,151(2-4):463-475
—We have obtained constraints on the strength and orientation of anisotropy in the mantle beneath the Tonga, southern Kuril, Japan, and Izu-Bonin subduction zones using shear-wave splitting in S phases from local earthquakes and in teleseismic core phases such as SKS. The observed splitting in all four subduction zones is consistent with a model in which the lower transition zone (520–660 km) and lower mantle are isotropic, and in which significant anisotropy occurs in the back-arc upper mantle. The upper transition zone (410–520 km) beneath the southern Kurils appears to contain weak anisotropy. The observed fast directions indicate that the geometry of back-arc strain in the upper mantle varies systematically across the western Pacific rim. Beneath Izu-Bonin and Tonga, fast directions are aligned with the azimuth of subducting Pacific plate motion and are parallel or sub-parallel to overriding plate extension. However, fast directions beneath the Japan Sea, western Honshu, and Sakhalin Island are highly oblique to subducting plate motion and parallel to present or past overriding plate shearing. Models of back-arc mantle flow that are driven by viscous coupling to local plate motions can reproduce the splitting observed in Tonga and Izu-Bonin, but further three-dimensional flow modeling is required to ascertain whether viscous plate coupling can explain the splitting observed in the southern Kurils and Japan. The fast directions in the southern Kurils and Japan may require strain in the back-arc mantle that is driven by regional or global patterns of mantle flow. 相似文献
5.
Introduction The detail structure of the Earths interior is a major field of geophysics and the existences and properties of mantle discontinuities are its important content. Based on the seismic tomographic results (Fukao, et al, 1992, Van der Hilst, et al, 1991) and the distribution of earthquake hypocenters in the Circum-Pacific region and other regions, the effects of subducting slab at different regions on the 660 km discontinuity are different: some subducting slabs penetrate through; … 相似文献
6.
总结了近年来西北太平洋俯冲前端东北地区地壳的精细结构和上地幔间断面410和660km的研究成果.认为：该区莫霍面深约为30～39km.410km的间断面有30km的深度异常,这种异常是否在过渡带正常或含水相变展布厚度的内,还是于该区俯冲带的后退有关,还需做进一步的研究论证.在中国东北地区,日本海俯冲带向西倾斜,在660km的间断面上近似水平停滞汇集被大多数层析成像、接收函数、波形拟和以及深震研究所认同.然而,俯冲带具体的形式、大小范围,向下渗透到多深以及在局部地区表现的横向不连续性的看法并不一致.由此带来的动力学模式什么力来支撑着停滞的板片,在板片最终下沉到下地幔以前,有多少俯冲的板片能停滞在间断面之上,这些问题都还需要更合理的解释. 相似文献
7.
The crust and upper mantle structure beneath southeastern China 总被引：1，自引：0，他引：1
Yinshuang Ai Qi-fu Chen Fei Zeng Xing Hong Wenyan Ye 《Earth and Planetary Science Letters》2007,260(3-4):549-563
We analyzed teleseismic waveforms recorded by 44 stations in the Fujian and Taiwan provinces of China and obtained 5344 high quality receiver functions. The crustal thickness (H) and average crustal VP/VS ratio (k) beneath every station were estimated using the H–k stacking method. Crustal thicknesses near the Fujian Province range from 28.3 to 32.8 km with an average of 31.1 km, and the corresponding VP/VS ratios vary from 1.70 to 1.84 with a mean of 1.76. From inland to offshore of the Fujian Province, the crustal thicknesses decrease and Poisson's ratios increase. These may indicate decreasing SiO2 and increasing calc-alkaline contents in the crust. The discontinuity structures such as the Moho, subducting slab, the 410- and 660-km discontinuities (hereafter we call them the 410 and the 660) are also studied using common converted point (CCP) stacking of receiver functions. Along two NW–SE lines of central and northern Taiwan, the CCP stacking results show a western dipping structure at depths above 50 km, suggesting that the Philippine Sea plate is probably subducting beneath the Eurasian continent plate near the central and northern Taiwan. The CCP stacking results show sharp and flat 410- and 660-km discontinuities, and the transition zone thickness (TZT) is the same as that of ambient mantle beneath Fujian and Taiwan Strait, but thickens in the east of Taiwan. These results suggest that (1) the subducting Eurasian continent plate is confined to the depths above 410 km beneath Fujian and Taiwan Strait; and (2) the South China Sea slab may reach the transition zone beneath the east of Taiwan. 相似文献
8.
本文基于中国数字地震台网记录的发生于日本北海道地区的一次中源地震的三重震相资料研究了日本海俯冲区地幔转换带的速度结构．结果表明,该区域P波速度结构与S波速度结构的一致性整体上较强．冷的西太平洋俯冲板块导致410 km间断面出现了10 km的抬升,660 km间断面出现了25 km的下沉;410 km和660 km间断面之上均存在与俯冲板块相关的高速层;660 km间断面下方存在厚度为65 km的低速异常．纵横波波速比vP/vS值在210—400 km深度范围内偏低,约为1.827,体现出海洋板块低泊松比的特征;在560—685 km深度范围内,该值偏高,约为1.831,可能预示地幔转换带底部含有一定量的水． 相似文献
9.
大洋板块俯冲到地幔转换带,进而可形成不同的形态:板块可以停滞在660km不连续面,抑或穿过地幔转换带进入下地幔.这些不同的俯冲模式可进一步影响到海沟的运动.为更好地理解上地幔中俯冲板片的变形行为以及俯冲过程与海沟运动之间的关系,本文通过建立一系列高精度二维热-力学自由俯冲的数值模型,揭示了俯冲板块在上地幔中的变形方式及其与地幔转换带之间的相互作用过程.模拟结果显示,在俯冲板块与地幔转换带的相互作用过程中,其动力学过程可以分为以海沟后撤主导、海沟前进主导以及稳定型海沟等三种主要动力学类型.对于年龄较老,厚度较大的俯冲板块容易形成海沟后撤型俯冲,俯冲板块停滞在660km不连续面.相反,年龄较小,塑性强度较小的板块容易形成海沟前进型俯冲,俯冲板块穿越660km不连续面. 相似文献
10.
利用布设在长白山地区的19个PASSCAL宽频带流动地震台站近一年的远震记录和布设在镜泊湖火山区14个宽频带轻便数字地震仪三个月的远震记录,共得到高质量的423个接收函数,通过对这些接收函数的共转换点叠加得到研究区的间断面的分布及形态.研究结果表明,研究区存在410、520km和660km间断面.410km和660km间断面较为连续且具有正相关性质,410km间断面在长白山天池火山下局部上隆,660km间断面具有复杂的多界面性质.410km和660km之间的过渡带厚约250km,接近全球平均水平.珲春深震区下660km界面下陷,其上还有多组震相,这些震相在珲春深震区东西两侧不连续,推测西太平洋板块至少已经俯冲到欧亚大陆下的上地幔过渡带中.410km间断面在长白山火山区下局部上隆,660km间断面具有的复杂结构和珲春深源地震的发生均与俯冲板块在过渡带中的活动有关. 俯冲板块在受到660km间断面的强大阻力后,在660km间断面之上变为近水平扩张.推测在欧亚大陆下西太平洋板块的最前端可能已经不是一个完整的整体,或许是由几个有一定联系的板块残片组成. 相似文献
11.
本文利用宽频流动台阵记录的远震波形资料和接收函数波动方程叠后偏移方法,获得了华北克拉通东北部边界及其邻近地区的地壳和地幔转换带的间断面结构图像.结果显示研究区域的地壳厚度存在显著的横向变化:以南北重力梯度带为界,西北部的兴蒙造山带地壳较厚(~40 km),东南部的燕山带、松辽盆地和辽东台隆地壳明显较薄(30~35 km).这有可能反映,研究区南北重力梯度带两侧地壳在中-新生代区域构造伸展过程中经历了不同程度的改造和减薄.地幔转换带成像结果显示,研究区410 km和660 km间断面结构存在横向差异.经度121°E-122°E之间,上地幔底部出现双重间断面,深度分别为660 km和690 km.经度122.5°E以东(北黄海地区),410 km间断面有5~20 km幅度的下沉,660 km间断面有5~15 km幅度的抬升;该地区地幔转换带厚度相对全球平均偏薄10~20 km,指示着该地区较热的上地幔底部温度环境.我们认为太平洋俯冲板块可能停滞在研究区119°E-122°E经度范围的地幔转换带中,但未延伸至118°E以西;而俯冲板块在124°E以东可能局部穿透了上地幔底部而进入下地幔,同时引起小尺度的地幔对流,导致北黄海地区下地幔物质的上涌. 相似文献
12.
自20世纪90年代首次探测到410-km间断面上覆低速层以来,全球多个俯冲带和大陆克拉通地区都陆续发现了该低速层结构.对其特性及形成机理的探讨是深部地幔结构、物性和动力学研究的热点问题.本文聚焦于西北太平洋俯冲地区410-km间断面上覆低速层的探测及特性研究上.通过对发生于日本北海道地区两个中等深度地震区域波形资料的分析,利用三重震相波形拟合方法获得了我国东北及日本海西北部下方410-km间断面附近的P波速度结构.速度模型明确显示,410-km间断面上方存在厚~47±14 km,异常值~2%的低速层,横向展布近700 km.结合区域地震层析成像、矿物高温高压物理实验及动力学模拟结果,我们否定了"从下至上"的上涌热物质导致410-km间断面上覆低速层的模型;认为较老且快速俯冲的太平洋板块在地幔过渡带顶部脱水导致硅酸盐矿物的部分熔融,由于熔体密度较大能够稳定存在于410-km间断面之上,从而产生了观测到的横向展布较广的410-km间断面上覆低速层结构. 相似文献
13.
Over the past decades, there have been hot debates in the geodynamic community regarding to the deep evolution mechanisms of Cenozoic volcanism in the Central Asian Orogenic Belt(CAOB). Of all the constraints available, high resolution structure of upper mantle discontinuities, especially the discontinuities at depths of 410 km(D410) and 660 km(D660), is of the most important, which may provide reliable clues on the magma channel as well as its evolution. In this work, we adopt the common conversion point stacking technique with teleseismic radial P-wave receiver functions to examine the D410 and D660 discontinuities. The primary results exhibit that the major characteristics of the mantle transition zone(MTZ) obtained by different velocity models are largely consistent. Obviously elevated D410 and slightly depressed D660 are observed beneath the Hannuoba Volcano, suggesting possible delamination of the local lithosphere deposited at the D410. This process may induce upwelling of the asthenospheric materials filling the space left by the delaminated lithosphere, and subsequently trigger volcanic eruptions. Strong depressions are observed at both D410 and D660 depths beneath west of the Dariganga Volcano, and the depression of D660 is more pronounced. It leads to the apparently thickened MTZ, indicating the presence of cold material at the D660. This cold material is speculated as a stagnant slab from the subducted Pacific Plate or the remains of a detached island arc system from the collision and formation of the CAOB. Slightly thinner MTZ is found beneath the Hentey Mountains and the Middle Gobi Volcano. Apparently, this thinner MTZ is not significant enough to support the existence of high thermal anomalies,which may rule out the possibility of large-scale hot material upwelling from either the local MTZ or even the lower mantle. 相似文献
14.
围绕中国东北地区下方俯冲的西太平洋板块是停滞在地幔过渡带内水平向西伸展, 还是穿透660 km间断面直接进入下地幔, 始终是一个具有争议的问题. 本文基于P--SV转换波对速度间断面的敏感性, 利用中国数字地震台网在东北地区布设的136个固定地震台站记录到的远震波形数据, 通过提取台站下方的接收函数并采用共转换点(CCP)叠加技术, 得到了该区域660 km间断面的起伏变化图像. 结果显示, 东北地区下方660 km间断面下沉幅度超过20 km的区域主要集中在44°N以南、 东西跨度约400 km的范围内. 660 km间断面的下沉表明西北太平洋板块俯冲到了中国东北地区下方, 在较小区域范围内观测到的较大深度异常可能暗示着俯冲板片穿透660 km间断面直接进入了下地幔. 相似文献
15.
从2008-2011年,分别在中国大陆东南缘沿海和内陆两条NE向剖面上进行了宽频地震观测,利用记录到的远震波形资料提取得到1446个远震P波接收函数,用H-κ叠加扫描和CCP偏移叠加方法研究了中国大陆东南缘地壳及上地幔过渡带的结构及其变化特征.结合固定台网25个台站的H-κ结果,获得中国大陆东南缘(福建地区)地壳厚度从内陆到沿海逐渐减薄的图像:地壳从闽西北山区的33 km减薄到厦门沿海一带的29 km以下,平均地壳厚度为31.3 km,具有陆地向洋壳过渡的特征;地壳泊松比从内陆到沿海显示出分带特征,闽中西部内陆地区小于0.26,沿海地带高于0.26,且在断裂带的交汇区域表现为相对异常高值.地壳上地幔顶部(0~200 km)的CCP偏移叠加成像结果显示闽江断裂等NW向断裂深切Moho界面,在断裂两侧Moho面急剧抬升或下沉,产状改变,这些特征向内陆地区逐渐变得不明显.闽江等NW向断裂对研究区地壳厚度、地震等有明显控制作用.上地幔尺度(300~700 km)的CCP偏移叠加成像,未见410 km和660 km速度间断面突变和起伏异常,其绝对深度略大于IASP91模型的,上地幔转换带厚度正常(250±5 km),表明中国大陆东南缘上地幔转换带未受欧亚与菲律宾板块碰撞的明显影响,推断中国大陆东南缘及台湾海峡下方不存在俯冲板块,或俯冲前缘未扰动到410 km的深度. 相似文献
16.
410 km间断面是地幔转换带的顶界面,对其速度结构和起伏形态开展地震学探测有助于认识地球内部物质组成和相关的地球动力学过程.本文选取了由中国数字地震台网记录到的位于琉球俯冲区的一个中源地震P波宽频带波形资料,利用三重震相波形拟合研究了中国东海地区410 km间断面附近的精细速度结构.结果表明：中国东海地区下方410 km间断面整体表现为一尖锐的速度界面且有8~15 km的小幅抬升;该间断面之上存在52~62 km厚的低速层,其P波速度降低0.5%~1.6%;440 km深度以下存在1.0%~3.0%的P波高速异常.结合前人在该地区的层析成像结果,我们推测该高速异常体与西太平洋俯冲板片在中国东海地区地幔转换带内的滞留有关;板片内水相E分解使得转换带内水含量增加,这引发了410 km间断面的抬升;410 km间断面之上的低速层应与含水矿物脱水导致的地幔橄榄岩部分熔融有关. 相似文献
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日本俯冲带与IBM俯冲带位于太平洋板块、菲律宾海板块和欧亚板块三者的交汇地带,是典型的"俯冲工厂"地区,具有重要的研究意义.本文利用震源分布资料与卫星重力数据对日本俯冲带与IBM俯冲带进行了研究.通过空间重力异常反映了俯冲带地区的区域构造形态,在此基础上基于艾利模式计算了均衡异常以反映地壳均衡特征.利用震源分布资料,分别从垂直俯冲带走向与沿俯冲带走向划定了横截剖面(cross-sections)进行了地震提取,讨论了俯冲带地区的Wadati-Benioff带形态特征,并借助于俯冲带地震等深线图直观描述了俯冲带的俯冲形态.在日本俯冲带与伊豆—小笠原俯冲带各选取了一条典型剖面进行了重力2.5D反演,研究了俯冲带地区的壳幔结构特征.研究结果表明,九州—帕劳海脊与IBM岛弧在均衡异常上存在差异,前者已逐渐趋向于地壳均衡.IBM的Wadati-Benioff带存在明显的南北差异,反映出伊豆—小笠原俯冲板片停留在了660km转换带中,而马里亚纳俯冲板片很可能垂直穿过了这一转换带,造成这种南北差异的原因与板块相对运动、岩石圈黏性和年龄差异以及俯冲板片的重力效应等因素有关.在IBM的中部和南部存在板片撕裂现象.日本俯冲带的俯冲洋壳密度随俯冲深度变化较小,洋幔存在一定程度的蛇纹岩化,地幔楔蛇纹岩化作用不典型,海沟处有一范围较小的含水畸变带;伊豆—小笠原俯冲带俯冲洋壳密度随深度增大而明显增大,洋幔蛇纹岩化程度较日本俯冲带低,地幔楔蛇纹岩化作用强烈,板块交汇处存在明显的蛇纹岩底辟.日本俯冲带与IBM俯冲带一线自北向南板片俯冲变陡,两侧板块耦合度降低,与俯冲带两侧的板块运动速率差异有关. 相似文献
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Jacek Stankiewicz S bastien Chevrot Rob D. van der Hilst Maarten J. de Wit 《Physics of the Earth and Planetary Interiors》2002,130(3-4):235-251
The technique of receiver function analysis is applied to the study of crustal and upper mantle structures beneath the Kaapvaal craton in southern Africa and its surroundings. Seismic data were recorded by the seismic array of 82 sites deployed from April 1997 to April 1999 across southern Africa, as well as a dense array of 32 sites near Kimberley, in operation from December 1998 to June 1999. Arrival times for phases converted at the Moho are used to determine crustal thickness. The Moho depth in the south–western section of the craton was found to vary between 37 and 40 km, except for one station that recorded a depth of 43 km (SA23). Farther north along the western block of the craton (into Botswana) the depth increases up to 43 km. The depth increases even further in the north–eastern section of the craton, where results vary from 40 to 52 km. Just north of the Kaapvaal craton, in the neighbouring Zimbabwe craton, the crustal thickness drops significantly. The results obtained there varied from 36 to 40 km. For the Kimberley area, using the dense array, the Moho depth was found to be 37.3 km. Arrivals of the Ps and Ppps phases were used to determine the Poisson’s ratio in the region. This was found to be 0.26±0.01. Arrivals of phases from the 410 and 660 km mantle discontinuities are used to interpret the relative positions of these discontinuities, as well as for comparison of mantle temperatures and seismic velocities in the region with global averages. In the Kimberley area the 410 and 660 km discontinuities were found at their expected depth, implying that mantle temperatures in the region are close to the global average. The seismic velocities above the ‘410’ were found up to 5% faster than the averages from the global iasp91 model, which is fast even by Precambrian standards. In other sections of the Kaapvaal craton, the velocities are also faster than global averages, but not as fast as beneath Kimberley. In these sections, the ‘410’ is also slightly elevated, while the ‘660’ is depressed, which implies a slightly lower mantle temperature relative to the global average. Beneath the Kaapvaal craton we find evidence suggesting the presence of a zone with a reduced wavespeed gradient at an upper bound of approximately 300 km, which may mark the lower chemical boundary of the craton. 相似文献
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利用海南、广东及广西区域台网和国家台网共88个宽频带地震台站记录的2007年8月至2010年3月75个远震事件波形资料,采用接收函数共面元叠加的方法,得到了海南及其邻区上地幔410 km和660 km间断面结构和转换带厚度.结果表明,研究区410 km间断面形态较复杂,局部下沉到447 km,而660 km间断面相对简单,其深度分布在670 km左右.海南岛东北部存在一个直径约200 km的转换带异常薄的区域,其厚度较全球平均值薄25±5 km,相当于转换带中存在约180℃的高温异常,转换带厚度局部偏薄暗示海南地幔柱可能起源于下地幔. 相似文献