Preliminary study of the straticulate structure of crust-mantle beneath east Guangdong and south Fujian Provinces of China

Using the 12 deep focus teleseismic P waveforms recorded by 6 short-period seismographs in east Guangdong and Fujian region of China as the observed data, synthetic P waveforms comparable to the observed ones are obtained by gradually adjusting the crust-mantle model and calculating the corresponding synthetic seismograms. The results suggest that the crust-mantle structure in this region is a vertically straticulate media structure consisting of 3 pairs of thin layers with a high- and low-velocity alternation. The crustal thickness tends to increase gradually from south to north, being 31.5 km in the south and 32.4 km in the north. Finally, the suggested model is tested using the explosive data of Yunfu, Guangdong Province. The theoretical travel-time of P waves agrees fairly well with the observed travel-time. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 172–179, 1992.     

On the crust structure near focus and the far-field body wave synthetic seismograms

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.     

A study on 3-D velocity structure of crust and upper mantle in Sichuan-Yunan region, China

Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others show the characteristic of tectonic boundary, indicating that the faults likely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the India and the Asia plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below. Foundation item: National Scientific and Technological Development Program (95-973-02-02), the Climb Program (95-S-05-01) of National Scientific and Technological Ministry of China, and the State Natural Sciences Foundation of China (49874021). Contribution No. 02FE2004, Institute of Geophysics, China Seismological Bureau.     

华北地区地壳上地幔S波三维速度结构

利用华北地区大型流动地震台阵的记录资料,采用近震和远震联合成像方法,得到了水平分辨率0.5°×0.5°、深至600km的S波速度结构.研究结果表明,上地壳S波速度结构与地表地质构造基本一致,燕山—太行山山脉均呈现高速异常,延庆—怀来盆地、大同盆地表现为低速异常,华北盆地内部的拗陷和隆起分别呈现低速和高速.唐山地区中地壳、山西裂陷盆地中下地壳存在明显的低速异常,可能分别与流体和热物质作用有关,有利于形成孕育强震的地质构造环境.90km的速度结构图像依然与地表的构造特征有较大的相关性,可能说明深部结构对地表构造有一定的控制作用.燕山隆起区岩石圈的厚度可达120～150km左右,华北盆地的岩石圈厚度可能在80km左右,太行山地区的岩石圈厚度介于两者之间.山西裂陷盆地上地幔低速层较厚,反映了该区不稳定的构造环境造成了地幔热物质的上涌.华北盆地下方220～320km出现的高速异常体,可能揭示了华北盆地上地幔仍然存在拆沉后残留的难熔、高密度的古老岩石圈地幔.研究区东部地幔转换带呈低速异常,推测可能与太平洋板块俯冲至该区下方地幔转换带前缘120°E左右的俯冲板块相变脱水有关.     

A study on 3-D velocity structure of crust and upper mantle in Sichuan -Yunnan region, China

Many evidences indicate that the collision of two plates deformed strongly the crust of the SYR, and the deformation has been continued up to the present. In addition, the SYR is in the south segment of the South-North Seismic Zone of China, which is one of the regions in the Chinese mainland, where the seismic activity is very high, and the strong earthquakes frequently occurred. Since the 1970s, a series of large earthquakes with magnitude M>7.0 occurred in SYR, such as the 1970 Tongha…     

基于频率-慢度域叠前地震记录的合成与并行方法研究

正演模拟是叠前弹性波反演的基础.采用慢度法计算层状介质的叠前地震记录,分别对频率和慢度进行积分变换得到时-空域的地震道集,并对在慢度积分过程中产生的计算噪音提出了解决方案.为得到高精度合成地震记录,需将地层细分,但地层层数很多时,计算量较大;而对地层粗分虽然会大大加快运算速度,但合成记录会丢失很多信息,文中给出了地层的划分原则.该方法能够计算出包括转换波和多次反射在内的全地震响应.但在提高合成记录精度的同时,也导致计算量增大、计算效率降低,因此,本文对基于慢度法全波场模拟进行了并行算法设计,采用计算域分割、工作池并行技术,建立了慢度法全波场正演模拟的并行算法,使得弹性波正演问题求解更加高效,为充分利用叠前地震资料进行叠前反演提供了研究基础.     

3-D velocity structure beneath the crust and upper mantle of Aegean Sea region

The region of the Aegean Sea and the surrounding areas in the Eastern Mediterranean lies on the boundary zone between the Eurasian and the African plates. It is a zone of widespread extensive deformation and, therefore, reveals a high level of seismicity.Three-dimensional velocity structure, beneath the crust and upper mantle of the region between 33.0°N–43.0°N and 18.0°E–30.6°E, is determined.The data used are arrival times ofP-waves from 166 earthquakes, recorded at 62 seismological stations. In total, 3973 residual data are inverted.The resultant structure reveals a remarkable contrast of velocity. In the top crustal layer, low velocities are dominant in Western Turkey and on the Greek mainland, while a high velocity zone is dominant in the Ionian Sea and in the southern Aegean Sea.In the upper mantle, high velocity zones dominate along the Hellenic arc, corresponding to the subducting African plate and in the northern part of the region, corresponding to the subducting African plate and in the northern part of the region, corresponding to the margin of Eurasian plate.A low velocity zone is dominant in the Aegean Sea region, where large-scale extension and volcanic activity are predominant, associated with the subduction of the African plate.     

华北地区上地幔及过渡带电性结构研究

采用远参考道和Robust技术,处理了华北地区14个地磁台站资料,得到了相干度超过0.8的地磁测深响应函数.并将其转换为大地电磁测深的响应函数,获取了105~107 s周期范围内的视电阻率和相位.应用ρ+理论对数据进行了一致性检验和反演,结果表明417 km,850 km深度附近可能存在电性间断面.同时采用基于一维最光滑模型的Occam反演方法得到了300~1000 km范围的地幔电性结构,并与前人在其他地区的研究结果进行了对比.发现华北地区地幔过渡带的电导率在大兴安岭—太行山重力梯度带东西两侧表现不同,重力梯度带附近及西侧台站下方过渡带深度的电导率和北美的Tucson地区相当,而华北地区东部的电导率在地幔过渡带范围高出西侧约2~5倍,这很可能和太平洋板块的俯冲有关.     

Upper mantle P wave velocity structure of the northern part of China and Mongolia

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Velocity structure of the crust and upper mantle in Xingtai earthquake region and its adjacent area

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华北地区地壳上地幔三维P波速度结构

利用华北地震科学台阵和首都圈地震台网记录的4511次近震和625次远震的P 波到时数据,采用纬度和经度方向分别为0.5deg;times;0.5deg;的网格划分,反演得到了华北北部地区（111deg;E——120deg;E,37deg;N——42deg;N）深至400km 的地壳上地幔三维P 波速度结构.层析成像结果表明,研究区的速度存在明显的横向不均匀性,随着深度增加横向不均匀性总体呈现减弱趋势.燕山隆起带在60——120km 深度内存在明显的高速异常,这与较大的岩石圈厚度有关;山西裂陷盆地、华北平原下方60km 深度存在明显低速异常,与软流圈的出现有关.燕山隆起带岩石圈厚度在120km 以上,明显比太行山隆起的岩石圈厚度大,与稳定大陆地区的岩石圈厚度一致.太行山山前断裂已切穿莫霍面,贯入岩石圈.研究区上地幔顶部大范围的低速异常反映了软流圈上隆的特点.在华北平原及燕山隆起下方200——300km 存在高速异常可能与太古代大陆板块岩石圈的残留体有关.     

华北克拉通东北部及邻区地壳和地幔转换带厚度研究

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.     

华北地区地壳上地幔速度各向异性研究

本文介绍面波反演得到的华北地区地壳上地幔速度各向异性分布图像,并与S波分裂的结果作初步的定性比较.不同周期瑞利波群速度的方位各向异性图像呈现显著的横向变化,与华北地区地壳上地幔的构造分块和垂直分层结构有比较密切的联系.在鄂尔多斯和阿拉善等稳定地块中,岩石圈地幔到160 km深度都保持比较一致的显著各向异性;而在发生过岩石圈减薄的华北克拉通东部,大约80~150 km深度范围内基本没有探测到方位各向异性,可能说明岩石圈减薄过程抹去了原有的各向异性印迹而且没有显著的水平构造运动造成新的方位各向异性.地球介质的各向异性具有明显的分层特征,面波的反演结果是如此,而S波分裂测量所表现的离散性,也可能是由各向异性的分层差异和倾斜的各向异性对称轴等因素引起.采用多层的各向异性模型,在多数情况下可以定性地解释面波反演和S波分裂结果之间的差异.进一步的工作要求增大面波的探测深度和改善分辨能力,获取更多的S波分裂测量资料,从而建立定量或半定量的三维各向异性模型.     

中国东北地区地壳、上地幔速度结构及其对矿产能源形成的控制作用

中国东北地区处于古亚洲洋和滨太平洋构造域叠合部位, 地质构造极其复杂. 利用东北及华北地区部分台网所接收的近震及远震走时资料获得东北地区地壳与上地幔三维P波速度结构, 成像分辨率在80 km左右. 成像结果表明东北地区地壳与上地幔具有较强的横向不均匀性. P波速度异常走向大体呈北东向, 与该区地表构造走向一致. 5 km深度的速度异常与地表起伏形态有很好的对应关系: 阴山、燕山与大兴安岭造山带表现为高速异常; 渤海湾盆地, 松辽盆地表现为低速异常, 渤海湾低速异常一直延伸至 >200 km深度. 东北地区呈现两个明显的低速异常条带, 分别是沿着长白山一线与松辽盆地地区, 其中长白山低速异常延伸至400 km深度附近. 地幔转换带 (410~660 km)表现为显著高速异常体, 这与西向俯冲的高速太平洋板块在地幔转换带中的滞留相对应. 较高分辨率的三维速度成像结果表明东北地区构造演化 (如岩浆活动、岩石圈演化、深震与火山活动等) 与东北亚地区大地幔楔内软流圈上涌与西太平洋板块在地幔转换带中的滞留密切相关. 东北地区的岩浆活动在矿产与油气资源的形成过程中起着提供物源和深层控制作用.     

Three dimensional shear wave velocity structure of crust and upper mantle in South China Sea and its adjacent regions by surface waveform inversion

IntroductionHistorically, surface waves provided much of our understanding of the lateral heterogeneity in the crust and the upper mantle, especially in oceans or desert areas. Traditional method utilizes the great circle theorem for surface waves. It assumed that surface wave propagates along the great circle connecting epicenter with station. Firstly, traditional surface wave analysis was carried out by using multi-frequency-filter dispersion analysis to acquire the group or phase velocity d…     

青藏高原东缘地壳上地幔电性结构研究进展

经过数十年的努力,中国学者针对青藏高原东缘地壳上地幔探测,累积完成超过20000 km的大地电磁测深剖面,取得了一系列重要科学数据和认识,为青藏高原东缘构造格局、地壳上地幔电性结构、地震机制和动力学研究奠定了基础.根据青藏高原东缘的主要构造和断裂分布特征,本文重点对龙门山构造带、川滇构造带和三江构造带三个构造带分区进行研究,主要依据大地电磁探测工作成果和壳幔电性结构特征,系统地对青藏高原东缘地壳上地幔电性结构、与扬子西缘接触关系、汶川地震和芦山地震的电性孕震环境及弱物质流通道等几个方面进行了梳理和分析.一是青藏高原东缘地壳表层岩块和物质沿壳内高导层向龙门山造山带仰冲推覆,表现为逆冲推覆特征的薄皮构造;二是高原东部地壳中下部及上地幔顶部向龙门山造山带和上扬子地块西缘岩石圈深部俯冲,呈现刚性的上扬子地块西缘高阻楔形体向西插入柔性青藏块体的楔形构造;三是将汶川地震和芦山地震的震源投影到大地电磁剖面上,发现震源位于剖面下方的高阻块体与低阻体之间靠近高阻体的一侧,龙门山构造带岩石圈表现出高阻、高密度和高速的"三高"特征,这种非均匀电性结构可能构成地震孕育发生条件;四是川滇和三江地区的多条大地电磁剖面探测结果表明,在青藏高原东缘中下地壳存在下地壳流和局部管道流,大地电磁结果对其空间分布形态、位置及大小进行了较好的刻画.根据研究区壳幔电性结构特征的构造解析和综合实例分析,总结了青藏高原东缘六类壳幔电性结构模型,提出了下一步重点研究领域和目标.总之,青藏高原东缘壳幔电性结构的研究对揭示研究区岩石圈结构和构造格局提供了重要依据,对油气及矿产资源远景评价提供了背景资料,对"Y"型多地震区的构造关系和发震机理研究具有重要指导意义.     

中国西部及其邻域地壳上地幔横波速度结构

本文首次采用Rayleigh面波双台法研究中国西部及其邻域的三维横波速度结构.共处理了超过3000条双台资料,经仔细挑选共获得110条高质量的双台Rayleigh波相速度频散资料.采用Tarantola的概率方法反演得到研究区域内15～120 s的Rayleigh相速度分布图像.采用Tarantola非线性问题的最小二乘反演方法反演得到研究区域内2°×2°的三维横波速度结构.利用不同周期的Rayleigh面波相速度大致对λ/3波长附近深度的横波速度最为敏感这一物理特性,在反演过程中引入一种层速度自适应调整的技巧,可以较好地加快收敛和提高反演的稳定性.反演得到的横波速度结构的主要结论为：（1）青藏高原的西部地区下地壳和上地幔顶部横波速度很高,软流层不发育;而青藏高原东缘地区的下地壳和上地幔顶部速度明显偏低,很可能是青藏高原地壳低速物质沿青藏高原东部边缘地区向南运动、形成经川滇地区连接缅甸北部低速区的低速物质运移通道;在青藏高原东北部边缘地区,下地壳的速度明显低于中地壳的速度;（2）青藏高原南部的拉萨地块具有较高速度的上地幔顶盖层,从南向北拉萨地块的软流层埋深约从130 km减至100 km,软流层厚度约从40 km增至80 km;北部羌塘地块的下地壳速度偏低,上地幔顶盖层缺失,速度很低,软流层的厚度较大;（3）塔里木盆地和准噶尔盆地都表现出较高的上地幔横波速度结构,软流层不明显,准噶尔盆地下地壳的厚度和速度都比塔里木盆地的高;（4）蒙古高原西部的下地壳上地幔顶部速度明显低于蒙古高原东部地区的,且在蒙古高原中西部地区存在巨厚的低速软流层.该软流层越往蒙古高原东部厚度越小,上覆顶盖层的速度和厚度越大.对上述反演结果作了地质解释.     

中国大陆东南缘地震接收函数与地壳和上地幔结构

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.     

Surface wave tomography of the crust and upper mantle of Chinese mainland and its neighboring region

Introduction The three-dimensional S wave velocity of Chinese mainland and its neighboring region in-verted by surface wave dispersion data plays an important role in studying the lateral variation of lithosphere and geodynamic process, and understanding the forming and evolution of Chinese mainland and the relationship between shallow and deep structures. The three-dimensional veloc-ity structures of China and its major tectonic blocks were respectively studied by SONG, et al (1993), ZHOU…     

Crust and upper mantle structure in east China and sea areas

Introduction Rayleigh wave is a kind of seismic wave propagating along the surface of the Earth, its propagation speed depends chiefly on the S-wave velocity structure of the Earth. Rayleigh wave energy of different periods concentrated in different depth ranges. The layered structure of the Earth causes the phenomenon of dispersion of surface waves, that is, surface waves of different periods are propagated with different speeds. By measuring the dispersion curves of surface waves the S-wav…