利用接收函数方法研究西秦岭构造带及其邻区地壳结构

根据西秦岭构造带及其周边地区117个宽频带地震台站的高质量波形数据, 利用远震P波接收函数的H-k叠加方法, 求得地壳厚度和平均波速比. 通过分析地壳厚度、 波速比及其关系和接收函数CCP叠加剖面, 研究了该区域的地壳结构特征. 结果表明, 研究区域内地壳结构差异大, 呈过渡带特征. 地壳厚度总体上呈北北西向分布, 自西南向东北逐渐减小. 羌塘块体地壳厚度为72 km, 渭河盆地附近为39 km. 西秦岭构造带的地壳厚度为42—56 km, 南北向莫霍界面平坦. 研究区域P波与S波波速比平均为1.74, 其中西秦岭构造带平均为1.72. 较低的波速比主要分布在西秦岭构造带、 祁连山块体、 松潘—甘孜地块北部以及香山—天景山断裂区域, 这可能是由于含长英质酸性岩组分的上地壳叠置增厚而导致的. 该区域缺少超高波速比, 表明这一区域发生岩浆底侵或上地壳熔融的可能性很小. 综合分析表明, 西秦岭构造带及邻区的地壳结构主要是由于青藏高原隆升并在向东北向扩张中受到周边块体的阻挡而引起的地壳构造变形所致. 西秦岭构造带的莫霍界面变化和波速比分布与该构造带经历碰撞地壳增厚后的伸展走滑运动有关.     

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.     

利用接收函数方法确定青藏高原东北缘近地表S波速度

利用襄樊台2015—2018年记录的震中距30°—90°,震级5.5级以上（含5.5级）的高信噪比远震波形事件,通过时间域反褶积方法提取台站接收函数,并用H-k扫描叠加方法得到台站下方地壳厚度和波速比。结果表明,襄樊台下方地壳厚度为35 km,略高于大陆地壳平均厚度33 km,处于西部山区厚地壳与中东部薄地壳的过渡地带。泊松比偏低,存在因区域内地壳应力积累发生微小地震的可能性。     

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.     

The crustal structure of Norway from inversion of teleseismic receiver functions

Teleseismic body waves from seismic broadband and short periodstations were used to investigate the crustal structure of Norwaythrough inversion of the receiver functions. The Moho depths ofthe Baltic Shield are quite well known from previous studiesincluding seismic experiments and spectral ratio technique.However, the results on the details of the crustal structure areinconsistent. This study provided more detailed crustalstructure information at 16 locations than previously known andgenerally confirmed Moho depth results obtained in earlier studies. Significant differences are seen at a few sites. The Moho for the various sites was found at depths between28 and 44 km. In summary, the crustal thicknessincreases from the West Coast of Norway, away from thecontinental margin, towards the centre of the Baltic Shield andfrom Southwest to the Northeast. This corresponds to theincreasing age of the crust. The P velocities in the crust atmost sites show a gradual increase from about 6.0 to 7.1 km/s, withoutclear layering.     

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。     

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.     

用接收函数方法研究云南及其邻区地壳上地幔结构

利用云南和中国地震台网30个台站记录的远震资料,采用接收函数扫描法和线性反演方法对云南及其邻区的壳幔速度结构进行了研究,获得了研究区内地壳厚度、Vp/Vs以及壳幔速度的分布特征.利用接收函数扫描（H-k）法和线性反演方法获取的台站下方地壳厚度结果表明,研究区地壳厚度变化剧烈.速度结构研究结果表明,红河断裂以西的腾冲-保山地块和思茅地块,以及南华板块北部地区的台站（如攀枝花、丽江、东川、永胜等）下方地壳均存在下地壳低速层,且具有高的地壳平均Vp/Vs值.这些不仅暗示研究区的下地壳低速异常可能为高温甚至高温导致的部分熔融所致,同时,也意味着该区下地壳的物质易于发生塑性流动,为地壳的变形和增厚创造了条件.红河断裂带作为云南地区的一个主要边界断裂,其西侧地区地壳厚度变化较东侧剧烈,另一方面,红河断裂西侧的平均地壳Vp/Vs值较其东侧要高.综合前人关于研究区岩石圈速度结构、地热流值、重力场和上地幔各向异性等地球物理场的研究结果.我们推断,现今的思茅块体和保山-腾冲块体在大地构造上应归属于冈瓦纳板块.     

远震P波接收函数揭示的张家口(怀来)-中蒙边境(巴音温多尔)剖面地壳厚度与泊松比

本文使用时间域迭代反褶积算法,从张家口(怀来)-巴音温多尔一线布设的41个宽频地震台站、1年期间记录的连续三分量数据中提取到高质量的P波接收函数1844个.用H-κ扫描方法获得了测线下方Moho深度与波速比值(VP/VS)进而计算出泊松比,用共转换点(CCP)叠加方法获得了沿测线Moho面起伏图像.结果显示:(1)测线下方Moho深度平均40 km,仅各块体边界处出现Moho深度小尺度急剧变化.整体上,Moho面产状相对于索伦缝合带大致对称,在缝合带南侧的温都尔庙带和白乃庙带下方呈南倾趋势,在缝合带北侧的宝力道带、贺根山杂岩带下方呈北倾趋势.(2)华北克拉通北缘泊松比总体较高,兴蒙造山带整体较低;各次级块体内部泊松比分布相对稳定,块体分界带附近往往存在泊松比值的升降扰动.(3)整条测线地壳厚度和泊松比之间存在弱的负相关关系,表明存在构造作用的影响.(4)整条测线泊松比呈现以索伦缝合带南缘为对称轴的非线性分布.本文所获得的地壳上地幔结构以及泊松比分布特征,支持古亚洲(索伦)洋(南北)双向俯冲,最终沿林西断裂闭合的动力学模式.     

基于GPS数据分析渭河盆地现今地壳形变特征

基于2001—2015年流动及连续GPS观测资料,借助多面函数拟合法建立渭河盆地水平速度场模型,并计算球面坐标下的应变特征参数。结合陕西地区地质构造背景,分析渭河盆地水平速度场及应变场分布特征。结果表明:(1)渭河盆地西部GPS速度场受青藏块体及鄂尔多斯块体共同作用明显,西部GPS速度场大于中东部,且GPS速度场有顺时针旋转的运动特征。(2)渭河盆地西部主应力场变化复杂,中部的西安地区主应变差异变化明显,与2009年11月5日高陵M_S4.4地震对应;渭河盆地西部出现最大剪应变及面应变高值区及差异变化高梯度带,在西安附近出现最大剪应变及面应变差异变化梯度带,高陵地震震中位于零值线附近。(3)2001—2010年的主应变、最大剪应变、面应变变化比2011—2015年显著,表明高陵地震发生后,应力场进行了释放调整,近期渭河盆地地震紧迫性相对较低。     

用接收函数方法研究上海地震台阵下地壳结构

利用上海地震台阵16个台站记录的远震资料,采用接收函数线性反演方法,对台阵下的地壳速度结构进行研究,获得了研究区域内地壳厚度和地壳速度的分布特征。研究结果表明,研究区域Moho面深度约为33±2 km,Moho面深度基本不变,地幔顶部S波速度约4.4 km/s,地壳内没有发现明显的低速层。     

青藏高原东北缘地壳S波速度结构与泊松比及其意义

利用甘肃地震台网16个台站记录的远震资料,采用最大熵谱反褶积方法,得到了各个台站的接收函数. 采用接收函数扫描法和线性反演方法对研究区的壳幔结构进行了研究,这两种接收函数方法得出的结果具有很好的一致性. 青藏高原东北缘地壳厚度变化剧烈,祁连块体为50～55 km、柴达木块体和河西走廊为45 km左右（合作台除外）,由北向南,Moho界面呈中央下凹的准对称状. 研究区地壳VP/VS介于1.66～1.85（σ=0.215～0.294,均值0.254）,其均值接近或略低于全球平均值;S波速度结构可见壳幔过渡带具有明显的突跳,结合其他地球物理学证据,推断该区可能不存在岩浆底侵作用和地壳部分熔融现象. 该区地壳VP/VS值与地壳厚度呈反相关关系,推断该区地壳的主要组成成分以中酸性岩石为主,其45～55 km厚的地壳可能主要是通过上地壳的叠置形成的.     

利用远震接收函数探测四川盆地及周边地区的地壳结构

青藏高原东南缘的龙门山断裂两侧具有陡峭的地形特征,在约50~100 km的水平距离内,地形高程从2000 m增加到4000 m,该区强烈的壳幔变形特征及地球动力学模式一直是研究的热点问题.本文从四川地区49个固定台站记录的远震资料提取了P波接收函数,获得了四川盆地及周边的地壳厚度和泊松比,并以此构建反演的初始模型.在线性反演的基础上,引入了分别拟合低频和高频接收函数的两步反演技术,用以反演台站下方的地壳S波速度结构.数字试验表明,该方法可以有效抑制接收函数反演的不唯一性,为了得到最优解,最后用Bootstrap重采样技术估计解的不确定性.结果表明,四川盆地的地壳厚度在40~46 km,松潘-甘孜块体北部的地壳厚度为46~52 km,而南部增厚到50~60 km.从四川盆地向西跨过龙门山断裂,地壳厚度增加了10~15 km.在四川盆地及周边地区,地壳泊松比在0.26~0.32之间,呈块体分布特征,高泊松比（0.28~0.32）主要沿龙门山断裂以及安宁河-小江断裂分布.地壳S波速度结构表明,来自青藏高原中部的中下地壳低速层可能受到了坚硬的四川盆地阻挡,改变原来的运动方向并沿龙门山断裂展布,由于低速层的囤积导致该区地形陡峭和下地壳增厚.

     

利用宽频带地震数据资料研究辽宁地区的地壳结构

通过收集辽宁省地震局数字地震台网34个地震台站记录的2008—2009年的60个震中距为30°~90°之间,震级6,信噪比较高的远震记录数据,采用频率域反褶积方法计算获得各台站的远震P波接收函数,并用H-Kappa叠加方法对获得的接收函数进行叠加处理获得各台站下方的地壳厚度以及泊松比。通过研究表明,辽宁地区的地壳泊松比在0.24~0.29之间,地壳厚度介于30~36km之间。     

利用远震P波接收函数研究中国福建地区地壳厚度和泊松比

地壳厚度和泊松比是反映地壳结构和内部物质组成的重要参数,能够为区域构造和动力学研究提供重要依据.本文基于福建地区分布相对均匀的88个测震台2014—2017年的远震波形数据提取P波接收函数,采用H-κ叠加获得台站下方的地壳厚度和泊松比,并与该地区已有的研究结果进行对比、分析及整合,最终获得了研究区117个观测台站下方的地壳厚度和泊松比,揭示了中国福建地区地壳结构和泊松比变化特征.结果显示：（1）研究区内地壳厚度整体较薄,在27.4~34.3 km之间,平均值为31.4 km.地壳厚度从西北往东南减薄,具有明显条带和块状特征,与地壳主要深大断裂的分布有一定相关性.本文以更为密集的台站结果进一步验证了研究区具有由陆壳向洋壳逐渐减薄的过渡特征,并揭示了地壳新的局部起伏.这也意味着福建地区从内陆到沿海并非线性减薄,存在小尺度横向非均匀性.（2）研究区内泊松比平均值为0.25,范围为0.20~0.30,北部整体偏高,南部整体较低,泊松比分布特征与该区地壳物质组成和矿物含量密切相关.沿海地区泊松比明显高于内陆地区,推测与沿海地区较高的热流值和幔源物质底侵过程有关.（3）地壳厚度与泊松比成负相关,推测在地壳伸展背景下,古太平洋板块俯冲华南大陆,幔源物质进入地壳,在造成莫霍面抬升的同时提高了泊松比.

     

运用H-k扫描和人工读取震相到时两种方法对比研究云南地区地壳结构

利用云南及其邻区59个宽频地震台站记录到的30°~100°远震资料,采用P波接收函数方法对云南地区的地壳厚度和地壳平均泊松比分布进行分析。研究结果显示:用H-k扫描和人工读取震相到时两种方法得到的云南地区地壳厚度和泊松比分布情况较为吻合。研究区域内Moho面埋深南浅北深,横向变化达30~40 km。在川滇菱形块体东南缘,地壳厚度等值线呈东南向舌状突出。泊松比呈块体分布特征,断裂两侧差异显著。高泊松比的分布主要集中在滇缅泰块体内和研究区域北部以及小江断裂附近,这与该区处于印度板块与欧亚板块碰撞俯冲前缘的特殊地理位置有关。     

渭河盆地及邻区现今地壳形变及构造特征研究

基于2009—2014年渭河盆地及邻区GPS资料,利用Shen提出的连续形变场与应变场计算方法,获得渭河盆地及邻区的水平形变场及应变率场,结合构造地质、地震目录等资料对渭河盆地及邻区的现今地壳形变及构造特征进行研究,并得到如下结论:(1)鄂尔多斯地块南缘西段和东段GPS形变场变化差异明显,六盘山—陇县—宝鸡断裂带形变场...     

Crustal structure of northeastern margin of the Tibetan Plateau by receiver function inversion

Using seismic data of about one year recorded by 18 broadband stations of ASCENT project,we obtained 2547 receiver functions in the northeastern Tibetan Plateau.The Moho depths under 14 stations were calculated by applying the H-κ domain search algorithm.The Moho depths under the stations with lower signal-noise ratio(SNR) were estimated by the time delay of the PS conversion.Results show that the Moho depth varies in a range of ~40–60 km.The Moho near the Haiyuan fault is vague,and its depth is larger than those on its two sides.In the Qinling-Qilian Block,the Moho becomes shallower gradually from west to east.To the east of 105°E,the average depth of the Moho is 45 km,whereas the west is 50 km or even deeper.Combining our results with surface wave research,we suggest a boundary between the Qinling and the Qilian Mountains at around 105°E.S wave velocities beneath 15 stations have been obtained through a linear inversion by using Crust2.0 as an initial model,and the crustal thickness that was derived by H-κ domain search algorithm was also taken into account.The results are very similar to the results of previous active source studies.The resulting figure indicates that low velocity layers developed in the middle and lower crust beneath the transition zone of the Tibet Block and western Qinling,which may be related to regional faults and deep earth dynamics.The velocity of the middle and lower crust increases from the Songpan Block to the northeastern margin of Tibetan Plateau.Based on the velocity of the crust,the distribution of the low velocity zone and the composition of the curst(Poisson's ratio),we infer that the crust thickening results from the crust shortening along the direction of compression.     

Crustal structure beneath Aso Caldera,Southwest Japan,as derived from receiver function analysis

Aso Volcano experienced a huge pyroclastic eruption 90 thousand years ago, and formed a large caldera (18 km × 25 km). In order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically, we investigated seismic velocity discontinuities and velocity structure beneath Aso Caldera using receiver functions and a genetic algorithm inversion. We confirm the existence of the Moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath Aso Caldera, from imaging of receiver functions observed only at stations outside the caldera. As a result of a more detailed examination with GA inversion, a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera. S-wave velocity of the layer is estimated to be 2.0–2.4 km/s. We estimate that the low velocity layer contains at most 15% melt or 30% aqueous fluid. The layer exists near the Conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle-eastern part of the caldera. Fluid contained in the layer might be related with huge pyroclastic eruptions of Aso Volcano.     

Constraining the crustal structure under the central and western Tian Shan based on teleseismic receiver functions and gravity anomalies

The Tian Shan is a vast range that spans several countries in Asia. Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics. In this study, we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region. A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P- to S-wave velocities (v_P/v_S) for 91 broadband seismic stations in the central and western Tian Shan. Our results revealed significant lateral variations in crustal thickness and v_P/v_S. A ~45-km-thick crust and an intermediate-high v_P/v_S (~1.74–1.84) were found in the Kazakh Shield and Tarim Basin, which we interpreted to indicate a mafic crystalline basement and lower crust. The central Tian Shan varied greatly in crustal thickness (40–64 km) and v_P/v_S ratio (1.65–2.00), which may be due to crustal shortening, mafic underplating, and crustal melting. In contrast, we observed a relatively thin crust (42–50 km) with an intermediate v_P/v_S ratio (~1.78) in the western Tian Shan. The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.