山东地区各向异性、地壳厚度及泊松比分布特征

山东地区位于华北东部,包含沂沭断裂带、鲁西隆起等重要构造单元,地质构造演化非常复杂,但目前尚缺乏对山东地区整体的地壳结构、壳内形变、壳幔耦合等方面的研究.本文基于该地区52个地震台站两年的波形记录,采用接收函数Ps转换波分裂和H-κ叠加的方法得到了研究区地壳各向异性、平均地壳厚度以及泊松比特征,为该地区的构造演化提供了重要的地震学约束.结果 表明,研究区地壳结构存在较强的横向不均匀性.鲁西隆起南部地壳各向异性方向可能与断裂和地壳内部的构造拆离有关.泰山地区地壳厚度与泊松比呈现负相关,地壳各向异性不明显,表明泰山处在快速隆升阶段.胶东地区东部较小的地壳厚度和泊松比与地幔上涌和苏鲁造山带发育的超高压变质岩有关.沂沭断裂带南北段的地壳结构具有显著差异,南段地壳厚度与泊松比存在明显的横向变化,表明南段可能存在剧烈的地幔上涌.较厚的沉积层使得济阳凹陷内台站下方的泊松比偏小,而较薄的铁镁质下地壳层则可能是胶北隆起部分台站下方泊松比偏小的主要原因.     

利用H-Kappa方法反演宁夏地区的地壳厚度

利用宁夏区域数字地震台网记录到的远震提取接收函数,用H-Kappa叠加方法反演得到宁夏区域数字地震台网子台下方的地壳厚度和波速比。结果显示,宁夏地区地壳平均厚度约为46km,并且由西南向东北逐渐减薄,南北两端地壳厚度差异达15km,东西两端地壳厚度差异达8km。泊松比计算结果显示,宁夏北部和中南部的泊松比值较高,中北部泊松比值较低。     

用接收函数研究川滇地区国家地震台下地壳厚度及波速比

本文利用远震接收函数的方法,对川滇地区的昆明、腾冲、成都和攀枝花等4个国家地震台的台基下方不同方向的莫霍面深度及波速比进行了研究和分析。结果表明:昆明地震台台基下方的莫霍面深度基本在50km左右,波速比为1.62～1.69,地壳厚度和波速比不因方向不同而发生明显的变化;腾冲地震台台基下方的地壳厚度有着比较明显的方向性,东北方向厚为40.7km,东南方向为49.7km,两个方向的波速比相差也很大,差值达到0.2;成都地震台台基下方莫霍面的深度在40km左右,但是东北和西南方向要加深8km,两个方向波速比相差0.13;攀枝花地震台台基下方的地壳厚度比较稳定,厚度在60km左右,波速比变化也不明显。     

利用接收函数研究延边地震台下方地壳结构

收集整理2007年以来延边地震台记录的113个远震数字波形资料,采用远震接收函数反演延边地震台下方地壳结构,运用H-Kappa叠加方法,计算得到台站下方地壳厚度和泊松比.采用全球平均地壳模型作为初始模型,反演台站下方0-100 km的S波速结构.反演结果表明,延边地震台下方地壳厚度为30.8 km,波速比为1.84,泊松比较高,为0.29.在台站下方15-20 km及25-30 km处存在低速层.     

华北地区地壳厚度与泊松比研究

华北地区地壳结构和物理性质是研究华北克拉通破坏机制的重要依据.本文通过收集分布在华北克拉通区域的323个宽频带地震台记录到的2007年8月到2009年3月间发生在全球范围内6.5级到8.5级的共93个远震事件的波形资料,较完整地得到了华北及其周边区域台站下方的接收函数、地壳厚度和泊松比分布情况.研究发现:(1)华北克拉通地壳厚度大范围减薄不仅仅发生在东部,而是已经到达南北重力梯度带附近; (2)在鄂尔多斯的周边裂谷盆地,地壳也出现了减薄现象; 周边裂谷区的泊松比大于鄂尔多斯内部,局部区域的泊松比高达0.3左右; (3)从地壳厚度和地形的相关性来看,华北地区的地壳厚度与地表地形存在着明显负相关的关系,这与艾利均衡假说相一致,可能意味着华北地区的地壳正在经历着缓慢的破坏与均衡同时进行的过程; 而华北克拉通中西部和东北部则显示出明显的不均衡现象.     

云南腾冲火山区地壳及岩石圈厚度研究

使用云南腾冲火山监测台网9个宽频带地震台站的远震数据,采用P波和S波接收函数的方法研究了腾冲火山区的地壳厚度、泊松比值以及岩石圈和软流圈分界面(LAB)深度.研究结果表明: 1) 云南腾冲火山区的地壳厚度约在33.5~38.0 km之间; 2) 火山区的泊松比主要集中范围为0.26~0.32,其中6个台站均大于0.29,推测与地壳镁铁质成分的增加有关并且可能存有2个岩浆囊; 3) 火山区的岩石圈厚度在78.2~88.0 km,较周边地区明显隆起且横向差异较大.腾冲火山区岩石圈的明显穹隆,由软流圈上涌(地幔热物质上升)引起岩石圈的拉张与减薄所致.     

广东及其邻域的地壳厚度和泊松比分布

利用广东及其邻域福建、江西、湖南、广西、海南、台湾共82个宽频带数字地震台的远震资料,计算获得了所有台站下方的体波接收函数,并通过接收函数H-κ搜索叠加方法反演了这些台站下方的地壳厚度和平均泊松比.研究结果表明,广东及其周边地区的地壳厚度为26.8 ～ 33.6km,平均为29.5 km.由西北到东南逐渐变薄,表现出大陆地壳向大洋地壳的缓慢过渡过程.珠江三角洲、粤西、粤桂琼交界、广西南宁、广东南澳等地区地壳厚度较薄,为25.0～28.0km;海南的翁田、广东的湛江、上川岛等地壳厚度最薄,在26km左右;福建明溪、湖南永州周边地区地壳厚度较厚,为31.0～34.0km.研究区域内地壳泊松比为0.20～0.29,海南岛的东南部、粤东和闽西的沿海地区以及江西南部具有明显的高泊松比,这可能与这些地区具有广泛的温泉分布和高热流值的特性有关.地壳厚度和泊松比分布的分块特征明显,并与断层和历史地震的分布有关.     

广东及其邻域的地壳厚度和泊松比分布

利用广东及其邻域福建、江西、湖南、广西、海南、台湾共82个宽频带数字地震台的远震资料, 计算获得了所有台站下方的体波接收函数,并通过接收函数 搜索叠加方法反演了这些台站下方的地壳厚度和平均泊松比。研究结果表明,广东及周周边地区的地壳厚度介于26.8～33.6km之间,平均为29.5km。由西北到东南逐渐变薄,为大陆地壳向大洋地壳的缓慢过渡。珠江三角洲、粤西、粤桂琼交界、广西南宁、广东南澳地区地壳厚度较薄,为25.0－28.0km;海南的翁田、广东的湛江、上川岛地壳厚度最薄,在26km左右;福建明溪、湖南永州周边地区地壳厚度较厚、地壳厚度在31.0～34.0km间。研究区域内地壳泊松比为0．20～0．29,海南岛的东南部,粤东和闽西的沿海地区,以及江西南部具有明显的高泊松比,这可能与这些地区具有广泛的温泉分布和高热流值的特性有关。地壳厚度和泊松比的分布具有明显的分块特征,并与断层和历史地震的分布相关。     

甘肃省各数字测震台下方地壳速度结构研究

利用甘肃省数字台网的资料,应用远震接收函数方法对各个台站下方的地壳结构进行了分析研究.研究结果表明,Moho面的深度都在50 km左右,甘南的Moho面深度普遍大于河西;地壳可以分为两层,20 km为其分界面.上地壳普遍存在低速层,其成因不是岩石熔融所致,而是其它地球物理和地球化学因素所致.另外各台站下方地表盖层的速度也存在很大差异.     

华南沿海地区地壳厚度与泊松比研究

华南沿海地区地壳厚度和泊松比分布是了解该地区板块运动和地球内部物质结构的重要依据.本文利用广东台网和福建台网共75个固定地震台记录到的2001—2008年远震波形的接收函数,通过H-κ叠加法获得了74个台站下方平均地壳厚度和泊松比值的有效估计,结合该区断裂分布、地震活动和地形地貌特征,得出以下结论:(1)该区地壳厚度范围在26~32 km之间,由陆向洋、自北向南减薄.泊松比0.23~0.28,由陆向洋增加,地壳厚度与泊松比变化分别和地表地形呈正相关和负相关;(2)地壳厚度和泊松比呈块状和带状分布,对应该区的断裂活动,其过渡带变化地区与地震分布一致,震群区和地幔上隆区对应泊松比的急剧增加;(3)该区主要以中、酸性地壳物质为主,地壳厚度与泊松比在近海区的构造伸展作用和褶皱区的逆冲推覆作用影响下,分别呈正、负消长关系,揭示该区不同时代和不同区域构造演化模式的差异.     

The crust and upper mantle structure beneath southeastern China

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 V_P/V_S 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 V_P/V_S 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.     

利用远震接收函数反演乌江彭水电站地震台下方地壳厚度

乌江彭水电站目前是重庆市最大的水电站,电站总投资121亿元,总装机容量为175万kw.坝高116.5 m,水库正常蓄水水位293 m,总库容13.35亿m3,为河道型高坝水库.已有研究结果表明,彭水电站坝区是稳定的,但库区及外围地区仍存在5级左右的地震活动背景,在水库蓄水后有可能诱发中,强地震.本文利用彭水台网于200...     

Crustal structure beneath the central and western North China from receiver function analysis

The North China Craton (NCC) is one of the oldest cratons on earth. Several important tectonic transformations of Mesozoic-Cenozoic tectonic regime led to the destruction of the North China craton. The knowledge of crustal structure can provide important constraints for the formation and evolution of cratons. New maps of sediment thickness, crustal thickness (H) and v_P/v_S (κ) in the central and western NCC were obtained using sequential H-κ stacking. P-wave receiver functions are calculated using teleseismic waveform data recorded by 405 stations from ChinArray project. Benefiting from the densely distribution of temporary seismic stations, our results reveal details of the crustal structure in the study area. The thickness of sedimentary layer in North China ranges from 0–6.4 km, and the thickest sedimentary layer is in Ordos block and its surroundings (about 2.8–6 km); The thickness of sedimentary layer in the Mongolia fold belt and Yinshan orogenic belt is relatively thin (less than 1 km). The crustal thickness of the study area varies between 27–48 km, of which the crust of the North China Plain is about 30–33 km, the central NCC is about 33–40 km, and the Ordos block is 40–48 km thick. The average v_P/v_S ratios in the study area is mostly between 1.66 and 1.90, and that in the Yanshan-Taihang mountain fold belt is between 1.70 and 1.85, and that in the Ordos block is between 1.65 and 1.90, with an average value of 1.77, indicating the absence of a thick basaltic lower crust. The obvious negative correlation between crustal thickness and average v_P/v_S ratio within Ordos and Central Asia orogenic belt may be related to magmatic underplating during the crustal formation. There is no significant correlation between the crustal thickness and the v_P/v_S ratio in the Lüliang-Taihang mountain fold belt, which may be related to the multiple geological processes such as underplating and crustal extension and thinning in this area. The lack of correlation between crust thickness and topography in the central orogenic belt and the North China Basin indicates the topography of these areas are controlled not only by crustal isostatic adjustment but also by the lithospheric mantle processes.     

A notch structure on the Moho beneath the Eastern San Gabriel Mountains

Synthetic waveform modeling of the anomalous receiver functions for two stations in the eastern San Gabriel Mountains, California, suggests that a flat-topped notch structure exists on the Moho. North of the San Andreas Fault (SAF), the Moho depth is 36–38 km and is 33–35 km south of the San Gabriel Fault (SGF), but in-between under the Mt. Baldy block, it is only  29 km. The inferred notch structure is also supported by the Pms arrival times along the SCSN and the LARSE I profiles. The shallow Moho block correlates well with the surficial exposure of the lower plate Pelona Schist or where it resides at very shallow depth. The large Moho offsets across the two major faults can be either related to differential uplifting reflected by the difference in the denudation rate and the exposure of the lower plate Pelona Schist, or it can be the result of the juxtaposition of the distinctive terranes with initially different Moho depth due to the strike-slip movements along the two major faults.     

Crust and upper mantle structure beneath Bohai Sea inferred from receiver function study

We analyzed teleseismic waveforms recorded by 36 stations near Bohai Sea region and obtained 2 248 high quality receiver functions.The crustal thickness (H) and average crustal vP/vS ratio (κ) as well as the Poisson's ratios beneath 34 stations were estimated using the H-κ stacking method.The results indicate that crustal thicknesses near the Liaoning province range from 30.0 to 35.5 km,and the corresponding vP/vS ratios vary from 1.72 to 1.89 which corresponds to Poisson's ratio with a range from 0.243 to ...     

Crustal structure beneath Qiangtang and Lhasa terrane from receiver function

To determine the crustal structure in central Tibet, we used teleseismic waveform data recorded by 18 stations in the INDEPTH-Ⅲ seismic array across the central Tibet from the central Lhasa terrane to the central Qiangtang terrane. The S-wave velocity structures beneath stations are determined by inverting the stacked radial receiver function using the GA method. The first order features in the receiver function are modeled. Our results show that the Moho in Qiangtang is about 8 km shallower than that in Lhasa terrane along the INDEPTH-Ⅲ profile. It maybe suggests the northward subduction of the Lhasa mantle lid beneath the Qiangtang terrane is affected by the India-Asia collision. We conclude that there exist low velocity zone in the middle crust across the northern Lhasa and Qiangtang terrane, which can be related to the high temperature upper mantle beneath that.     

Preliminary analysis of teleseismic receiver functions of the Ningxia and its adjacent area

The teleseismic receiver functions of digital seismic network of Ningxia and its adjacent area are calculated with two different Gauss filter factors. The accuracy and stability of the receiver functions are discussed. The h-k stacking method is applied to estimate the crustal thickness and velocity ratio beneath seismic stations. The results indicate that there are sharp changes of crustal thickness and velocity ratio in the studied region. This region is located in the northeastern margin of Tibet, and also a junction of several first-grade blocks. The large contrast of crustal structure in this region is considered to be resulted from the interaction of these blocks. Our results are helpful to construct the completed model of the formation and evolution of the Tibet. Some local structures are also discussed combining with the geological faults.     

关于中国海陆莫霍面深度图编绘的思考

莫霍面是地壳和上地幔的分界面,是一个重要的密度界面.布格重力异常与莫霍面深度之间具有紧密的联系,利用重力异常反演莫霍面深度成是研究莫霍面深度和编制莫霍面深度图的主要手段之一.本文总结了前人编制莫霍图的方法和结果,并加以分析讨论.提出应用布格重力异常反演中国海陆莫霍面深度的方法与技术,并考虑到中国海、陆构造的一体性,进行海陆统一编图以展示莫霍面的海、陆演化与构造关系.