Location of Triassic Tectonic Suture Between Collided Sino-Korean and Yangtze Cratons in Dabie-Sulu Region, China

INTRODUCTIONTheageofultrahigh-pressuremetamorphism(UHPM)andhigh-pressuremetamorphism(HPM)hasbeendeterminedat24OMato2loMabyseveralchronologicalmethods(Lietal.,1998;Maruyamaetal.,l998iAmesetal.,l9961Hack-erandWang,l995;Johnetal,,1994).Theseagedatare-f1ecttheTriassicobliquecollisionbetweentheSino-KoreanandYangtzecratons.ThermobarometricestimatesoftheUH-PMandHPMintheDabie-SuluregionshowthatthecoldcontinentalcrustmaterialoftheYangtzecratonwasunder-thrust,alongthesuture,northwardtoma…     

放射性测量在岩浆岩区大比例尺填图中的应用

应用放射性地球物理手段,取得地质研究所需的地球化学数据,用以划分岩浆岩谱系单位,建立等级体制,解决岩浆岩不同序列或同一序列中众多侵入体的区分和归属,在岩浆岩区大比尺填图时划分填单位,找到了一种新的简便可行的技术方法。     

南黄海地震区的地震活动性研究

北纬３１°—３５°、东经１１９°—１２５°范围内的南黄海地震区,中强地震活动频繁,这主要是由一组北北东向和北西—北西西向共轭走滑活动断层及张性铲形活动断层引起的,该区内的中强震活动具有准周期性,震中呈东移趋势,区内地震在原地或同一构造部位重复发生的概率比较高,且空间分布是不均匀的,其中,海域地震强度明显高于陆域地震,在第Ⅲ、Ⅳ地震活跃期内,中强震主要发生在北纬３３°±１°、东经１２１°±１°所在的南黄海海域的南部盆地,本区第Ⅳ活跃期内中强地震的活动水平与近期内中小地震的活动水平相当,同时,海域地震还具有成丛性及５７ 年、６ 年的节律,地震震中具有南北迁移的特征     

地震体波成像中的几个问题

本文在论述地震体波成像中速度模型间断面的引入,体波多震相的利用等优越性的同时,利用研究区之处,能改善或分辨地球内部更深处的远震资料,得到研究区平均相对走时残差的分布。结果表明：１．采用相对走时残差消除了模型区域外的地球模型的影响,从而使 远震理论走时计算中,球状分层各向同性参考地球模型的选取是不重要的;２．平均相对走时残差的分布与研究区内构造分区相关;３．研究区中地球形状的椭率对反演结果影响很小。     

青海都兰地电场地震异常统计特征研究

在地震孕育发生过程中,不同频率地电场观测出现异常现象已有相关报道,但地电场不同频率成分与地震震级(能量)的相关性统计特征仍不清晰。文章基于小波变换对都兰台地电场观测资料进行分析处理,使用滑动相关性方法对地电场不同频率成分与台站周围400km范围内地震事件进行分析研究,并以青海玛多M_S7.4地震前后大地电场优势方位角计算结果进行回溯性检验。结果表明：(1)都兰地电场不同频率成分不仅在地震孕育发生过程中会出现异常现象,而且出现异常的频率与地震事件震级(能量)存在一定关联性：高频成分(3.4h和8h)与■及■两个地震序列的地震事件均有关联性,其中与■在震前约25(±5)天、10天和5天相关性异常显著,与■在震前约55天、35天、15天和5天相关性异常显著,而低频成分(24h)则仅与■地震序列中的地震事件在约55、35、20及5天左右出现较强的相关性;(2)玛多M_S7.4地震前,都兰地电场低频成分(24h)的大地电场优势方位角在地震前约55(±5)、20(±5)天左右出现明显异常现象,其出现的时间与相关性统计特征具有较高的一致性,原因可能是孕震断层与...     

中国东北地区高分辨率地壳结构:远震接收函数

利用分布在东北地区的国家地震局台网、NECESSArray台网、吉林大学在长白山及其周边地区布设的26个临时台站总计259个台站接收到的16,070条高质量的P波接收函数,采用H-k和CCP(Common Conversion Point,共转换点)叠加成像方法,获得该区高分辨率的地壳结构.观测结果显示,东北地区莫霍界面深度和地表高程总体呈镜像关系;西部大兴安岭—太行山重力梯级带附近存在莫霍界面深度陡变带;中部的松辽盆地地区受晚中生代的地壳拉伸作用影响,地壳厚度较薄,北部的小兴安岭地区和南部的华北北缘造山带可能同样受拉伸运动影响,具有较小的地壳厚度;松辽盆地莫霍界面深度由西向东逐渐减小,推测这与太平洋板块俯冲作用有关;东部地区莫霍界面结构比较复杂,依兰—伊通断裂与敦化—密山断裂之间出现复杂震相,可能与该区存在地幔物质的底侵作用有关;长白山火山地区地壳厚度较大,对应较高的波速比,推测在该区地壳内存在岩浆囊.     

Spatial behaviour of Rayleigh waves in layered half‐spaces under active surface sources

In the free state, Rayleigh waves are assumed to travel in the form of planar wavefronts. Under such an assumption, the propagation behaviour of the modes of Rayleigh waves in layered half‐spaces is only frequency dependent. The frequency behaviour, which is often termed as dispersion, is determined by the shear wave velocity profile of layered soils within the depth related to wavelength (or frequency). According to this characteristic, the shear wave velocity profile can be back‐analysed from the dispersion. The technique is widely used in the surface wave testing. However, the wavefronts of Rayleigh waves activated by the surface sources are non‐planar. The geometric discrepancy could result in Rayleigh waves manifesting distance‐dependent behaviour, which is referred to as spatial behaviour in this paper. Conventional analysis ignoring this spatial behaviour could introduce unexpected errors. In order to take the effects of sources on the propagation behaviour into account, a new mathematical model is established for Rayleigh waves in layered elastic media under vertical disc‐like surface sources using the thin‐layer method. The spatial behaviour of the activated modes and the apparent phase velocity, which is the propagation velocity of Rayleigh waves superposed by the multiple modes, are then analysed. Aspects of the spatial behaviour investigated in this paper include the equilibrium path, the particle orbit, and the geometric attenuation of the activated Rayleigh waves. The results presented in this paper can provide some guidelines for developing new inverse mathematical models and algorithms.     

Application of Ultra-shallow Seismic Survey to the Wanggezhuang Fault in Qingdao

At present, there is less theoretical research and practical experience in the aspect of ultra-shallow seismic exploration to the target layers at depths of only tens of meters both at home and abroad. Seismic exploration plays an important role in the location of faults and active structures, but the depth dozens of meters below the ground surface is the blind area of any kind of deep and shallow seismic exploration. Starting from the point of view of detecting urban active faults, and using related theories and methods of geology, geophysics and mathematics, the paper discusses the preconditions for acquiring efficient ultra-shallow seismic survey results in complicated geological backgrounds in Qingdao. Taking the Qingdao area as an example in this paper, we study the depth condition of Quaternary deposits, and apply 4-8 stacking folds to satisfy the requirement to get the exploration results with high-resolution and high-SNR. Preliminary results reveal that selecting a proper surveillance layout is one of the keys to acquire authentic exploration results in ultra-shallow P-wave reflection exploration. Our results also show that ultra-shallow seismic reflection method in detecting faults in the Qingdao area has good application prospects.     

电阻率成像及浅层地震勘探在控盆构造探测中的应用——以万全断裂为例

万全断裂是洋河盆地北缘断裂带组成断裂之一,控制沿线构造活动及地貌发育。断裂走向NE,倾向SE,在沟口处隐伏于第四纪覆盖层,采用电阻率成像和浅层地震联合勘探方法,获得该断裂隐伏段落综合物探异常,结合地质地貌调查,判定隐伏段落展布的具体位置、产状、活动特征及地下结构特征等。研究结果表明,万全断裂隐伏段落走向NE,倾向SE,倾角约75°,上断点埋深约20 m,20—240 m深度可见断裂破碎带（宽约10—20 m）物探异常特征及断裂两侧地层结构差异。该联合探测模式可有效探测复杂地质构造条件下的隐伏活动断裂,具有较强实用性,值得推广。     

Seismic imaging of the middle and upper crust by double-difference tomography: the Haicheng earthquake (Ms 7.3) in Liaoning Province

The Haicheng earthquake (Ms 7.3) occurred in Liaoning Province (39°N–43°N, 120°E–126°E ), China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate prediction, although the area affected by the earthquake was 9200 km² and covered cities with a population density of 1000 p/km². In this study, the doubledifference (DD) tomography method was used to obtain high-resolution three-dimensional (3D) P- and S-wave velocity (Vp and Vs) structures and Vp/Vs as well as the earthquake locations. Tomography results suggest that velocity structure at shallow depth coincides well with topography and sediment thickness. The earthquake locations form a northwest-striking zone associated with the Jinzhou(JZ) Fault and a northeast-striking zone associated with the Haichenghe-Dayanghe (HD) Fault, and suggest that the JZ Fault consists of three faults and the Ms 7.3 Haicheng earthquake originated at the intersection of the JZ and the Faults. Lowvelocity zones (LVZs) with low Vp/Vs are observed at 15–20 km depth beneath the Haicheng (HC) region. We interpret the LVZs in the middle crust as regions of fluids, suggesting rock dehydration at high temperatures. The LVZs and low Vp/Vs in the upper crust are attributed to groundwater-filled cracks and pores. We believe that large crustal earthquakes in this area are caused by the combination of faulting and fluid movement in the middle crust.