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1.
本文通过地震层析成像研究获得了华北克拉通及其东邻地区（30°N-50°N,95°E -145°E）1°×1°的P波速度扰动图像.结果显示,在西太平洋俯冲带地区,上地幔中西倾的板片状高速异常体与其上方的低速异常区构成俯冲带与上覆地幔楔的典型速度结构式样.俯冲板片高速体在约300~400 km深度范围内被低速物质充填,暗示俯冲板片可能发生了断离.在华北克拉通地区的上地幔中发现三个东倾排列的高速异常带.在此基础上,本文构建了华北克拉通及其东邻西太平洋活动大陆边缘地区的上地幔速度结构模式图,并据此探讨克拉通岩石圈减薄与西太平洋活动大陆边缘的深部动力学联系.本文认为,太平洋板片的俯冲（断离）,触发热地幔物质上涌并在上覆地幔楔中形成对流,使克拉通岩石圈受到改造（底侵与弱化）.随着俯冲板片后撤,地幔楔中的对流场以及对岩石圈改造的影响范围均随之东移,最终导致华北克拉通岩石圈自下而上、从西向东分三个阶段依次拆沉减薄.这一模式能很好地解释现今克拉通岩石圈自西向东呈台阶状减薄的深部现象. 相似文献
2.
菲律宾群岛受到欧亚板块、菲律宾海板块和印度-澳大利亚板块的碰撞作用,地质环境复杂,构造因素多样.尽管近几年来已经有了少数关于该区域层析成像的研究,但这些研究的区域主要集中在马尼拉海沟、吕宋岛及中菲律宾地区,而关于群岛周围其他海沟和南菲律宾地区的讨论相对较少.到目前为止,还没有同时获得过关于菲律宾群岛深部纵、横波速度结构的研究,本次研究通过反演155779条P波震相和59642条S波震相,同时获得了菲律宾群岛从地表至150 km深度的纵、横波速度结构.地震层析成像结果表明该地区的壳幔速度结构具有较强的不均一性,地壳内部存在着广泛的低速异常,而表征俯冲板块的高速异常则沿着群岛周边的海沟展布.南海块体在马尼拉海沟中段的俯冲角度和俯冲活动性比南段小;菲律宾海板块在东吕宋海槽南段微弱的俯冲作用很有可能同本哈姆海台的碰撞有关.菲律宾群岛大部分MW>6.0的强震沿着各个板块的边界发生,体现出菲律宾海板块同欧亚板块之间的强耦合作用,群岛西侧的南海块体在马尼拉海沟16°N-20°N之间呈现出的弱耦合状态可能跟北吕宋地区的拉张应力环境有关,南海块体在16°N以南的地区同上覆块体之间的耦合作用较强;群岛东侧的菲律宾海板块在14°N以北的地区没有强震发生,它与菲律宾群岛之间的耦合程度从北向南逐渐增强,在12°N以南的地区要强于12°N以北的地区;此外苏禄海盆和菲律宾构造带之间也存在着强耦合关系. 相似文献
3.
将宽频带OBS用于海底天然地震长期观测,在国内尚处于实验阶段.2015年在马尼拉俯冲带北段开展了为期6个月的宽频带海底天然地震观测试验.根据回收的1台海底地震仪(OBS04)与国际地震台网的718台陆地地震台站,共记录到7562个P波走时和5002个S波走时数据,利用Hyposat地震定位方法,对马尼拉俯冲带北部(119°E—123°E,19°N—22°N)在2015年8月至2016年2月期间的264个地震进行了重定位.地震重定位的结果及定位误差分析表明,在海域布设的OBS04台站让地震观测的空间分布更为合理,提高了地震定位精度;重定位后的震中分布更为集中,与地质构造吻合良好;浅部的地震活动较为活跃,分布密集,与浅部断层发育有关;重定位后的4条震源深度投影剖面,从不同角度较好地约束了俯冲板片上边界的板片形态,板片倾角在浅部0～30km区间约为10°～22°,随着深度的增加,俯冲板片逐渐变陡,在深度120～180km处倾角约为41°～58°.该项研究为马尼拉俯冲带北段的板片形态提供了重要约束,而且为今后长期天然地震观测提供了重要而宝贵的经验与借鉴. 相似文献
4.
马尼拉俯冲带是南海的东部边界,记录了南海形成演化的关键信息,同时也是地震和海啸多发区域.本文利用过马尼拉俯冲带北段的高分辨率多道地震剖面,分析了研究区内海盆和海沟的沉积特征,精细刻画了区内增生楔前缘的构造变形、结构以及岩浆活动特征.研究区内增生楔下陆坡部分由盲冲断层、构造楔和叠瓦逆冲断层构成,逆冲断层归并于一条位于下中新统的滑脱面上,滑脱面向海方向的展布明显受到增生楔之下埋藏海山和基底隆起的影响;上陆坡的反射特征则因变形强烈和岩浆作用而难以识别;岩浆活动开始于晚中新世末期并持续至第四纪.马尼拉俯冲带北段增生楔的形成时间早于16.5 Ma,并通过前展式逆冲向南海方向扩展;马尼拉俯冲带的初始形成时间可能在晚渐新世,而此时南海海盆扩张仍在持续.南海东北缘19°N-21°N区域为南海北部陆坡向海盆的延伸,高度减薄的陆壳的俯冲造成马尼拉海沟北段几何形态明显地向东凹进. 相似文献
5.
从Global CMT目录搜集了1976年1月至2016年6月之间的震源深度大于70km的255个震源机制解,用阻尼应力反演方法,分70～160km和170～310km两个深度,计算了帕米尔—兴都库什地区的构造应力场;同时以10km为间隔计算了兴都库什地区深度介于70～310km之间的应力形因子.得到以下初步结论:兴都库什板片向下俯冲和帕米尔地区断裂带的横向拉张,可能是导致应力场不同的原因.兴都库什俯冲带与帕米尔俯冲带碰撞,导致交汇地区(37°N—37.5°N)的应力场参数突变.兴都库什俯冲板片受到深部温度、压力等因素,出现薄弱面进而形成拆离板片.其脱离了主俯冲板片的束缚后,重力的上下拉张作用导致空区附近张轴倾伏角接近90°,拆离板片俯冲至上地幔不连续面,导致板片部分熔融进而应力形因子随着深度变小.而拆离板片受到地幔挤压其内部发生破碎,其压应力轴由西部的NS到东部NW-SE方向偏转及纵向张应力轴倾伏角变小. 相似文献
6.
使用纵波震相及同台同源纵波和横波震相的走时资料及层析成像反演方法，分别给出了菲律宾海板块(PHP)和南海地区的纵波速度Vpf及同台同源的纵波和横波速度Vp和Vs结构. 结果表明，（1） PHP与欧亚板块(EUAP)的俯冲接触关系随地段而异，在琉球海沟，PHP向EUAP之下俯冲深达400 km；在台湾岛，EUAP先近陡直地俯冲到深度400 km，然后折向PHP之下达到660 km左右；在马尼拉海沟北段，俯冲板片几乎垂直达到660 km附近；在菲律宾海沟，PHP向EUAP之下的俯冲深度超过660 km．（2）南海地区之下是一个深达300～400 km的宽阔低速区，并且大致在莺琼海盆与700 km深处另一低速区曲折相通；在该宽阔低速区内部，有两个小而明显的低速区分别在海口火山和珠江口盆地下方．（3）对Vp和Vs及据其算出的容声速度Vb作分析发现，Vs和Vb的平均扰动量对深度的变化在一些深度范围内是反向的；年龄较大的太平洋板块俯冲体的Vs相对扰动量的平均值大于Vb的，而在较年轻的PHP俯冲体中则正好相反． 相似文献
7.
本文利用地震资料并结合地质资料,讨论了印度板块与欧亚板块在中国周边的相互作用及其对中国应力场的影响,指出两板块在喜马拉雅山前断裂地区碰撞,碰撞边界向西延续到35°N,74°E附近,其主要挤压方向为NNE,并形成SE方向的物质流动.帕米尔地区有强烈的构造运动,并存在俯冲带形态的构造.在26.5°N,97°E附近,板块边界的走向发生突变,并形成东倾的缅甸山弧俯冲带,但印度板块挤压造成的主压应力方向为NNE向.在安达曼—尼科巴—苏门答腊—爪哇岛弧,印度板块俯冲于欧亚板块之下,在中国南海一带形成NNW向或近Ns向的主压应力. 相似文献
8.
北京时间2019年4月24日04∶15,西藏自治区林芝市墨脱县发生了MS6.3地震,该地震位于印度板块与欧亚板块俯冲碰撞的东北犄角地区,构造背景十分复杂.本研究基于我们在东喜马拉雅构造结地区架设的宽频带地震台站记录的近震波形数据,结合中国和国际地震台网的波形和到时资料,对该地震的震源位置、震源机制解和破裂过程进行了重新确定.结果显示,此次墨脱6.3级地震发生在（94.56±0.01°E,28.41±0.01°N）,震源深度为地表以下13.3±1.6（或海平面以下11.5±1.6）km.震源机制解走向/倾角/滑移角分别为202°/17°/20°,震源破裂较大的位置主要集中在初始破裂点NNE侧约5 km附近.结合其他地球物理和地质学资料,我们推测该地震位于主喜马拉雅逆冲断裂发生近90°突然偏转的大拐弯地区,桑构造结相对于其西侧南迦巴瓦构造结的西向俯冲和北向推挤是该地震发生的主要构造背景. 相似文献
9.
岩石圈有效弹性厚度是表征岩石圈力学性质的参数,其反映了岩石圈挠曲变形的特征.本文在传统二维挠曲模型的基础上,提出了适用于俯冲及碰撞带的三维薄板挠曲模型.并发展了基于粒子群算法的俯冲带三维有效弹性厚度反演方法.该方法适用于挠曲参数存在横向差异的俯冲-碰撞带.最后利用该方法反演了马尼拉海沟处岩石圈的有效弹性厚度,结果显示:南海中央海盆岩石圈的有效弹性厚度随着距洋中脊距离的增加而增大;马尼拉海沟轴部弯矩在洋中脊两侧呈分段性变化,这表明南海俯冲板片在深部撕裂可能对浅部的挠曲形态产生影响. 相似文献
10.
《世界地震译丛》2020,(5)
地震层析成像方法为俯冲板片的形态、形变与流变(间接)提供了独特的约束条件。本文利用远震双差P波成像技术对伊豆—小笠原板片的复杂结构进行了非常清晰的成像,结果显示位于26.5°N～28°N之间的地幔过渡带(MTZ)中存在一个板片撕裂。撕裂以北,板片在MTZ发生折叠,在褶皱枢纽的正上方,剪切带内初期的黏性耗散形成了P波衰减区。撕裂以南,在MTZ底部板片发生翻转且平铺于MTZ的底部。2015年小笠原地震(M_W约为7.9)的震源深度约为680km,该地震发生在翻转板片的最北端。伊豆—小笠原板片的局部撕裂、剪切和屈曲表明,其经过上地幔和地幔过渡带后仍然保持了较高的黏滞性。 相似文献
11.
Sean C. Solomon 《Physics of the Earth and Planetary Interiors》1975,11(2):97-108
The top of the olivine-spinel phase change in subducted oceanic lithosphere can be located by the travel times of seismic waves which have propagated through the slab. P-wave travel-time residuals from deep earthquakes in the Tonga island are observed at Australian seismic stations are grouped according to the depth of the earthquake. The change in mean residual with a change in earthquake depth is related to the velocity contrast between slab and normal mantle at that depth. The curve mean residual versus earthquake depth displays a region of markedly increased slope between earthquake depths of about 250 and 350 km. The most probable explanation of this observation is an elevation by 100 km of the olivine-spinel phase change within the relatively cooler slab. No evidence was found for vertical displacements within the slab of any deeper phase changes.A temperature contrast between slab and normal mantle of about 1,000°C at 250 km depth is implied. This finding confirms current thermal models for subducted lithosphere but is inconsistent with the global intraplate stress field unless only a few percent of the negative buoyancy force at subduction zones is transmitted to the surface plates. 相似文献
12.
Using P-wave travel time data from local seismicity, the crustal structure ofthe central and southern part of Colombia was determined. A very stableand narrow range of possible velocity models for the region was obtainedusing travel time inversion. This range of models was tested with earthquakelocations to select the best velocity model. The 1D velocity modelproposed has five layers over a halfspace, with interfaces at depths of 4,25, 32, 40 and 100 km and P-wave velocities of 4.8, 6.6, 7.0, 8.0, 8.1and 8.2 km/sec, respectively. According to this model the Moho lies at32 km depth on average. For P-waves, the station corrections range from–0.62 to 0.44 sec and for S-wave they range from –1.17 to 0.62 sec.These low variations in station residuals indicate small lateral velocitychanges and therefore the velocity model found should be well suited forearthquake locations and future starting model for 3D tomography studies.Using this new velocity model, the local earthquakes were relocated. Theshallow seismicity, < 30 km, clearly shows the borders betweentectonic plates and also the main fault systems in the region. The deepseismicity, > 80 km, shows two subduction zones in the country: theCauca subduction zone with a strike of N120°E, dip of 35°and thickness of 35 km, and the Bucaramanga subduction zone which has,for the northern part, a strike of N103°E, dip of 27° andthickness undetermined and, for the southern part, a strike ofN115°E, dip of 40° and thickness of 20 km. Based ondifferences of thickness of brittle crust in the subducted slab and spatialdistribution of the seismicity, the Cauca and Bucaramanga subduction zonesseem to represent independent processes. The Cauca subduction seems tobe connected to the process of the Nazca plate being subducted under theNorth Andes Block. In the Bucaramanga subduction zone, the transitionbetween southern and northern parts and changes in geometry of the slabseem to be gradual and there is no evidence of a tear in the slab, howeverthe local seismicity does not allow us to determine which plate or plates arebeing subducted. The Bucaramanga nest appears to be included into thesubducted slab. 相似文献
13.
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
14.
为深入理解华北克拉通破坏机理,本研究通过鄂尔多斯盆地北缘南北向宽频带线性高密度流动地震台观测记录的远震波形数据,获得了1985条高质量到时资料,进而利用FMTT(Fast Marching Teleseismic Tomography)快速行进层析成像方法获得了华北克拉通西部鄂尔多斯盆地北缘深至300km范围的P波速度模型.结果显示,鄂尔多斯盆地下方呈现出深至150~200km的高波速异常,说明华北克拉通其西部岩石圈保存完好尚未遭到明显破坏.河套地堑下方存在向鄂尔多斯盆地下方延伸的明显低波速异常,其深度可达300km深度,而阴山造山带下方上地幔存在深至100km左右的弱高波速异常,说明鄂尔多斯盆地周边地区的岩石圈均遭到一定程度破坏并减薄,可能与新生代时期太平洋板块的俯冲引起深部热物质上涌等作用密切相关.这些研究结果说明,华北克拉通在构造演化过程中不同块体经历了不同的破坏演化历史,这对于认识克拉通破坏减薄机制具有重要意义. 相似文献
15.
Detailed regional body wave tomographic inversion of the Western Pacific region has been performed using P and S travel times from common sources and receivers, with a joint inversion in terms of bulk-sound and shear wave-speed variations in the mantle. This technique allows the separation of the influence of bulk and shear moduli, and hence a more direct comparison with mineral physics information. The study region is parameterized with cells of side 0.5° to 2° and 19 layers to a depth of 1500 km, while the rest of the mantle was parameterized with 5×5° cells with 16 layers between the surface and the core–mantle boundary. A simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image. A nested iterative inversion scheme is employed with local linearization and three-dimensional ray tracing through the successive model updates. The results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the Kurile–Kamchatka trench, while flattening of slabs above this depth is observed in the Japan and Izu–Bonin subduction zones on both the bulk-sound and shear wave-speed images. The penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the Bonin trench, Mariana, Philippine, and Java subduction zones. Fast shear wave-speed perturbations associated with the subducted slabs, down to the 410 km transition zone, are larger than the comparable bulk-sound perturbations for all these subduction zones except the Philippines. The bulk-sound signature for the subducted slab is more pronounced than for shear in the Philippines, Talaud, New Guinea, Solomon, and Tonga subduction zones, where penetration of the slab into the middle mantle is observed. Variation in the amplitude ratio between bulk-sound and shear wave-speed anomalies correlates well with the subduction parameters of the descending slab. Slabs younger than 90 Ma at the trench show bulk-sound dominance in the upper mantle, while older slabs have a stronger shear wave-speed signature. Spreading of the fast shear wave-speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration, but has no comparable expression in the bulk-sound images. This high-velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs. 相似文献
16.
南北地震带南段位于青藏高原东南缘,是青藏高原与扬子克拉通的过渡地带.本文收集了该区域内90个固定台站和356个流动台站的远震波形数据,采用波形互相关方法拾取了88691个P波走时残差数据,应用FMTT(Fast Marching Teleseismic Tomography)层析成像方法获取了南北地震带南段深部的三维P波速度结构.结果显示了研究区深部的结构具有显著的不均匀性:腾冲火山地区深部400km以浅的深度内分布着明显的低速异常;四川盆地西南部下方300km内具有较强的高速异常;在上地幔顶部,沿川滇菱形块体周边的大型断裂带及川滇菱形块体南端分布着显著的低速异常,这些低速异常为青藏高原物质向东南方向挤出提供了必要的通道;保山地块下方存在一东倾的高速异常带,该高速异常带为印度板块岩石圈向东俯冲的体现. 相似文献
17.
The time evolution of negative buoyancy of a subducting slab is modelled from the beginning of subduction under various kinematic conditions (dip angle and subduction velocity). The calculations take into account the thermal and density effects of the variations of the thermophysical parameters with temperature and pressure, and of phase transitions. The magnitude of the negative buoyancy increases during subduction of oceanic lithosphere, up to values in the (2–4) × 1013 N m−1 range when the tip of the slab reaches a depth of 600–700 km. If continental material arrives at the trench and is subducted, the downward buoyancy decreases by an amount proportional to the volume of the subducted continental crust. Assuming that subduction stops when the buoyancy becomes zero, and that delamination of the continental crust or slab breakoff do not occur, the maximum downdip length of the subductable continental crust is estimated as a function of the dip angle, subduction velocity and geometry of the margin. In most cases, subduction of continental material down to depths of 100–250 km is possible, and continental subduction can continue for times up to 10–15 Ma if the velocity is low. These estimates are not significantly affected by the hypothetical occurrence of a metastable olivine wedge within the slab, and could be lower bounds if the lower continental crust is mafic and transforms to eclogite. 相似文献