Buried Quaternary valleys in western Denmark—occurrence and inferred implications for groundwater resources and vulnerability

Numerous geophysical investigations in the western part of onshore Denmark constitute the basis for a delineation of buried Quaternary valleys. The geophysical methods comprise primarily Transient ElectroMagnetic (TEM) and reflection seismic surveys, and the geophysical data have been combined with lithological data from boreholes. Buried valleys appear both as single valleys and in dense networks. The internal structure of the valleys is typically complex due to repeated erosional and depositional events. Buried valleys are common geological structures in the region and they influence the distribution of Tertiary and Quaternary sediments greatly. A large number of buried valleys in the region contain important aquifers, whose natural protection varies depending on thickness and character of overlying clay layers. Many of these aquifers are deep-seated and well protected, but because of the prevailing heterogeneity of the valley infill and the erosional incisions created by different valley generations, preferential flow paths for downward transport of contaminated water from shallow aquifers may occur.     

Imaging buried Quaternary valleys using the transient electromagnetic method

Buried Quaternary valleys in Denmark are complex structures filled with various deposits consisting primarily of glacio-lacustrine clay, till and meltwater sand, and gravel. The valleys are important geophysical targets, because they often contain significant volumes of groundwater used for public water supply. About 700 km of buried valley structures have been imaged in the western part of Denmark by the transient electromagnetic (TEM) method. The ability to map the valleys depends primarily on valley geometry, infill architecture and the resistivity of the fill sediments as well as the substratum. One-dimensional (1-D) inversion models of the TEM soundings have been used to construct contour maps of 20 m average resistivities and depth to a good conductor, which provide images for geological interpretation. Images of buried valley morphology, fill properties, infill architecture, such as cut-and-fill structures, valley distribution and valley generations, are characterized for case studies from Hornsyld, Holstebro and the Vonsild/Agtrup areas of Denmark.     

用共偏移距反射法拓展地质剖面的解释深度

针对核电工程选址中的能动断层地质调查工作需要,提出了利用共偏移距浅层地震反射时间剖面来拓展地质剖面解释深度的技术方法,通过物性和岩性的综合解释来提高对能动断层鉴别及其产状确定的可靠性.探测试验结果表明该方法是有效可行的.地质剖面上描述的断裂破碎带在共偏移距时间剖面上反应明显,二者可以相互印证,优势互补.该技术方法可用于类似工程地质调查和第四系覆盖较薄地区的隐伏断层探测.     

青岛沧口断裂的地质构造特征与第四纪活动性研究

本文根据青岛市活断层探测与地震危险性评价项目初查阶段第四纪地层分析、遥感影像解译、地球化学探测、地质地貌调查与探槽开挖、浅层地震勘探与钻孔探测、地质年代测定等获得的丰富的第一手资料,对青岛沧口断裂的地质构造特征和第四纪活动性进行了详细分析与综合研究,结果表明:沧口断裂经历多期构造变动,是本区的重要断裂之一,它由多支断层组成,控制了中生代的火山活动、盆地沉积和岩浆侵入以及晚第四纪的盆地沉积、山体隆升和水系发育;第四纪以来,沧口断裂的主要活动发生于中更新世晚期至晚更新世早期,表现出中高角度向南东倾的逆冲活动特点,错断了上更新统底面1—6m,而最新活动时代为晚更新世中期,以走滑活动为主,垂直错距0.2—1.1m。     

高分辨率浅层人工地震勘探探测隐伏断裂实例

利用高分辨率浅层地震勘探反射波法探测了福建某火电厂场址内的隐伏断裂。结果表明断裂显示清楚,为一走向NE40~55°,上断点埋深为11 m和31 m,断距2~4 m的正断层,为工程避让提供较可靠的依据。     

凤凰山地区蒲江-新津-德阳隐伏断裂反射波法地震勘探与断裂活动性研究

利用反射波法地震勘探确定了在凤凰山地区蒲江-新津-德阳隐伏断裂通过的具体位置以及断裂的规模和性质,证明了该断裂在向东俯冲的过程中错切了晚更新统沉积物,具有明显的第四纪活动性,对凤凰山台地的形成起到了一定的控制作用。地面地质调查及历史地震研究也证明蒲江-新津-德阳隐伏断裂具有晚更新世活动性,且断裂南段的活动性明显强于北段,表明该断裂的北段是成都平原内部的一条弱地震活动带。同时,文中还对在城市近郊人烟繁杂地带反射波法地震勘探中野外观测系统的布置及地震参数的选取进行了探索,小道间距、小偏移距、多接收道、短排列、多次覆盖、高频检波器接收的工作方法和野外地震参数的合理选取对实现主要干扰波和反射波信号的有效分离,提高地震勘探分辨率起到了至关重要的作用     

Geophysical investigation of buried Pleistocene subglacial valleys in Northern Germany

Buried Pleistocene subglacial valleys are extensively used as groundwater reservoirs by waterworks in northern Germany, although little is known about the locations and size of these valleys and the internal structure of the sediment fill. This lack of knowledge about important groundwater reservoirs is a challenge for geophysics.This paper summarizes the geophysical investigation of two buried Pleistocene subglacial valleys in northern Germany—the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne—including seismic, gravity, and airborne electromagnetic (AEM) surveys. Seismic sections show the detailed structure of the paleovalleys. The reliability of interpretation is enhanced by vertical seismic profiles in wells. The maximum depths of the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne were found to be 360 and about 400 m, respectively. Gravity survey revealed Bouguer anomalies above the sediment fill of both buried valleys. The Ellerbeker Rinne produces a negative residual anomaly of −0.5 mGal, whereas the sediments of the Bremerhaven–Cuxhavener Rinne produce a positive anomaly. The latter one is superimposed by negative gravity anomalies due to near-surface structures. The Bremerhaven–Cuxhavener Rinne can be mapped by airborne electromagnetics at locations without saltwater intrusion, which would affect the measurements. The electrical conductivity of the clay layer at the top of the valley fill differs significantly from that of the surrounding sand. The combined use of these three geophysical methods, which measure different physical parameters, leads to a better understanding of the subsurface geology and the hydrogeology of the Pleistocene subglacial valleys.     

SEISMIC FACIES ANALYSIS CONCEPTS *

Seismic facies analysis makes use of different seismic parameters in order to get other than structural information. A review is given of possibilities and usefulness of seismic facies analysis in oil exploration. A seismic facies unit can be defined as a sedimentary unit which is different from adjacent units in its seismic characteristics. Parameters that should be taken into consideration in the seismic facies analysis are as follows: reflection amplitude, dominant reflection frequency, reflection polarity, interval velocity, reflection continuity, reflection configuration, abundance of reflections, geometry of seismic facies unit, and relationship with other units. Interpretation of seismic facies data may be either direct or indirect. The purpose of the direct interpretation is to find out geological causes responsible for the seismic signature of a seismic facies unit. So, the direct interpretation may be aimed at predicting lithology, fluid content, porosity, relative age, overpressured shales, type of stratification, geometry of the geological body corresponding to the seismic facies unit and its geological setting. The indirect interpretation is intended to reach some conclusions on depositional processes and environments, sediment transport direction, and some aspects of geological evolution (transgression, regression, subsidence, uplift, erosion). The results of the seismic facies analysis may be shown on seismic facies cross-sections and seismic facies maps. Depending on the available seismic data and geological conditions in the area under consideration, the seismic facies maps may be of different types such as general seismic facies maps showing distribution of different seismic facies units, sand-shale ratio maps, direction of cross-bedding and paleo-transport maps etc. Several kinds of seismic facies units and their geological interpretation are discussed as examples of seismic facies analysis.     

COMBINED REFRACTION SEISMIC AND GRAVIMETRIC INVESTIGATIONS IN A PALEOGEOGRAPHICAL AND GEOLOGICAL RESEARCH PROGRAM*

Refraction seismic and gravity investigations were executed to solve geological and hydrographical problems in recent strata: These loose sediments necessitated a special arrangement for the energy source in the seismic measurements, By the use of a falling weight the refracted wave could be registered from a depth of more than 30 m. Quaternary fluviatile sands are characterized by lower velocities than the Tertiary sediments. Even a marked velocity difference between different Tertiary formations could be observed. Sand-filled valleys in Tertiary clays give relatively important variations in the gravity field caused by the small differences of densities. Thus buried channels in a clay subsoil can be found by accurate gravity measurements.     

南沙海域海底浅层第四系地震地层结构与地质意义

科技进步使得地震采集数据量及其精度实现质的飞跃,南沙海域的地震调查,采用国际先进水平的等离子震源,获得地震剖面精度优于3 m局部甚至可在1 m之内,为科学研究、工程、浅层资源、地质灾害预警等研究奠定基础.在南沙第四系识别出了七个地震反射界面,确定500 ms至海底沉积区间内地震层序与三期海平面升降并与冰期、间冰期对应,典型地震剖面展示第四纪至少有三套完整的具有三角洲顶积层、前积层、底积层的地震相证据,与全球的第四纪海平面的变化一致.精细的浅层地震结构表明：南沙的地质现象丰富,浅层断层非常发育,下切河谷、泥石流、滑坡等地质遗迹的形成的地震相清晰,是地质活动频繁的地区.     

北京断陷黄庄—高丽营断层伪随机可控震源地震剖面

位于北京断陷西北边界的黄庄—高丽营断层是区域新构造运动中的一条重要的隐伏断层,本研究利用伪随机可控震源及其高精度反射地震方法,调查了该断层在北京奥林匹克公园段的特征.研究工作首先从理论上分析了可控震源解码原理和抗噪声能力,然后利用三分量波动方程正演指导了黄庄—高丽营断层的野外地震观测,在城市强噪声环境下采集了高精度的地震数据,经过数据处理在该地区第一次得到地震偏移深度剖面.获得的地震偏移深度剖面清晰地显示了黄庄—高丽营断层的位置,地质解释结果为进一步明确剖面上断层两侧新生代地层的厚度提供了依据.     

唐山地震深浅构造关系研究

地表观察和浅层高分辨率地震探测表明 ,唐山断裂与地震地表主破裂带的位置、产状均一致 ,且具有高角度西倾的逆冲走滑性质 ,发生过右旋水平错动和向东逆冲的垂直活动 ,而次破裂带与褶皱构造活动引起的其他断裂直接相关。根据瞬变磁场和深地震探测结果分析 ,唐山地区存在莫霍面斜坡和地壳“背斜”、中地壳水平滑脱和扩展断裂、上地壳高角度逆冲走滑断裂和背向斜构造 ,它们组成 1幅多层次、多级序的复式逆断裂 -扩展背斜构造图像 ,控制了唐山地震的孕育和发生     

The Activity of Liaocheng-Lankao Buried Fault During the Quaternary——An Important Buried Active Fault in the Eastern China Plain

On the basis of locating by the geochemical prospecting,shallow seismic sounding,drilling,geological profiling,and neogeochronological dating,we first found out the dislocation amount along the Liaocheng-Lankao buried fault since the Quaternary and the age of its latest activity phase and determined that the upper break point by the fault dislocation reaches 20m below the surface,The latest activity phase was in the early Holocene and the Fault is a shallow-buried active fault.An average dislocation rate along the fault is 0.12mm/a since the Quaternary.Thus,it is a buried active fault with intermediate to strong movement strength in the eastern china.     

苏鲁超高压变质带北部地球物理调查(1)─—深反射地震

苏鲁超高压变质带是世界上研究陆一陆碰撞俯冲和壳幔作用的最佳地质场所之一．为了解超高压变质带岩石的形成、折返和相应的动力学过程,必须了解该区的地壳和浅地幔构造．本文介绍了该区北部的地质情况和进行深反射地震调查取得的成果,包括（１）在五莲─青岛断裂南侧超高压变质岩片向北倾斜,呈现叠复组构,反映岩片的折返;（２）根据地震资料推测在１４６Ｍａ前后胶南地块的隆升一伸展构造内幕;（３）超高压变质岩片厚约１２ｋｍ,由于含有大量相辉岩透镜体,地震波速高达６．８─７．３ｋｍ／ｓ;（４）莫霍面附近有许多楔形反射体,反映陆一陆碰撞;（５）石门地区７ｋｍ深处存在高波速的强反射体,可作为在该区进行大陆科学钻探的候选场址．     

浅层地震勘探资料揭示汤东断裂特征

汤东断裂是汤阴地堑的东界断裂,也是太行山山前一条重要的隐伏活动断裂。为了查明汤东断裂的产状、性质及其浅部构造特征,跨断裂开展了高分辨率浅层地震剖面探测,获得了高信噪比的浅层地震反射波叠加剖面。本文根据浅层地震剖面结果并结合研究区地质资料和已有深地震探测成果,对汤东断裂的浅部构造特征进行了分析和讨论。结果表明:汤东断裂为1条走向NNE、倾向NWW的铲型正断层,其浅部表现为由2—3条断层组成的Y字形构造,并错断了埋深约30—50m第四纪地层,断裂向下延伸至上地壳底部,属晚第四纪以来的隐伏活动断裂。汤东断裂两侧新生代沉积差异明显,断裂上升盘内黄隆起一侧,新生代沉积层较薄,其底界埋深约480m,下降盘汤阴地堑一侧,沉积了巨厚的新生代地层。研究结果为确定汤东断裂位置、评价断裂的活动性提供了基础资料。     

影响松潘地区深反射地震数据品质的几种因素

深反射地震剖面技术是揭示岩石圈精细结构的有效手段,获得高质量的原始资料是揭示岩石圈精细结构探讨地球动力学过程的前提和基础.松潘地块地表条件和地下地质构造复杂,资料信噪比低.本文针对松潘地区地表地质条件、激发接收条件及环境等因素,通过实例数据对比分析影响该工区原始单炮记录品质的主要原因,为反射地震勘探数据采集工作提供几点参考和建议.     

利用地震反射法探测安宁河断裂带北段

通过在四川石棉城区内利用地震反射法探测其隐伏断裂的实例,阐述了在地形变化大、人口密集、环境干扰强的条件下浅层地震勘探方法的实施.本次勘探针对场地条件使用了小能量激发和小偏移距、小道间距、短排列接收、高覆盖次数的观测系统,获得的高信噪比时间剖面清晰地揭示了石棉城区内覆盖层的厚度和隐伏断裂的展布情况.探测结果表明:石棉城区内普遍存在一个明显且连续的反射界面,结合区域地质资料推测该界面是埋深约为15-60 m深浅不等的早更新世底界与上新世晚期顶界的第四系分界面. 4条地震反射时间剖面均揭示了安宁河断裂带北段所属的石棉断裂东支在石棉城区内为全新世隐伏活动断裂.      

北京平原西北部地壳浅部结构和隐伏活动断裂——由地震反射剖面揭示

已有地质和地球物理研究结果表明,北京平原区存在有多条第四纪隐伏活动断裂和隐伏盆地.为了研究该区的地壳浅部结构、断裂的空间展布、断裂活动性以及深浅构造关系,2006年,在北京平原的西北部地区完成了1条60次覆盖的中深层地震反射剖面和跨断裂的浅层地震反射剖面.结果表明,沿剖面结晶基底埋深约为3～6 km在结晶基底以上,地震反射剖面揭示了一套连续性较好的强反射震相,应是新生代、中生代和古生代的沉积岩系;在结晶基底之下,为一系列横向连续性较差、能量较弱的短小反射事件,可能代表了变质程度较高的结晶变质岩系或不成层的其他岩体.中深层和浅层地震剖面揭示的断裂具有上下一致的对应关系和明显的第四纪活动,对本区地堑-地垒状盆岭构造和新生代地层厚度具有重要的控制作用.本项研究不仅可进一步提高对北京地区新构造活动的认识,而且研究中所采用的方法技术对其他地区的深浅构造探测研究也有借鉴意义     

若尔盖盆地-西秦岭造山带结合部位深反射资料的静校正和去噪技术

深地震反射剖面技术是探测岩石圈精细结构的有效手段.通常情况下工区地质情况复杂,尤其在盆山结合部位,地表地形起伏大,地下构造复杂,其深地震反射资料具有低信噪比、干扰强、构造复杂等特点,给后续处理和解释造成很大困难,因此获得真实的叠加剖面是地质解释的前提和基础.复杂地区低信噪比深地震反射资料处理的关键是做好静校正和去噪工作.本文以若尔盖盆地－西秦岭造山带接合部位深地震反射资料作为例,通过方法试验和参数测试,找到适合该工区的静校正方法和去噪技术,得到较好的处理结果,为揭示若尔盖盆地－西秦岭造山带结合部位的细结构提供了可靠的依据.     

薄覆盖层地区隐伏断层及其上断点探测的地震方法技术——以废黄河断层为例

通过在同一条测线上应用三种不同地震勘探手段(共偏移距地震反射法、横波反射法与高分辨率折射法)联合反演的方法,获得了测线控制地段内废黄河断层的确切位置、上断点埋深以及速度分布图像.探测结果表明:在薄覆盖层地区的断裂调查中,上述三种技术手段的联合反演要比单独使用其中任何一种手段更加可靠,并能从不同角度查明断层的位置、性质及其特征,为钻孔联合剖面位置的布设和钻孔深度的设计提供地震学依据.经高精度钻孔联合地质剖面证实,三种地震勘探方法反演得到的主要地层界面和构造特征都与钻孔联合地质剖面吻合较好.试验表明了上述三种地震勘探方法在基岩面埋深较浅地区联合反演的可行性以及地震勘探与钻孔联合地质剖面相结合的工作方法的有效性.