P-SV转换波真振幅DMO

基于运动学原理对转换波DMO脉冲响应近似公式进行修正,从修正后的公式出发推导出一种新的f-k域转换波真振幅DMO算法。脉冲响应曲线的对比表明对脉冲响应近似公式的修正明显减少了误差。理论模型试验结果表明算法具有较高的运动学精度及保幅性能,是一种可靠、理想的转换波DMO算法。     

浅谈地震映象法在工程勘探中的应用效果

着重介绍地震映象法在工程勘察中的优点, 叙述在水域、山区等复杂条件下如何提高它在工程勘察中的应用效果。     

A study of seismic reflection imaging using microearthquake sources

We present a method for processing three-component digital recordings of microearthquakes to obtain near-vertical reflection profiles in regions of shallow seismicity. The processing includes magnitude and focal depth normalization and event stacking, where stacking is by small localized groups, with ray theoretical time and distance corrections applied to compensate for varying focal depths. In areas with high seismicity, this procedure allows earthquakes to be treated as “controlled” sources to probe layered structures of the deep crust and upper mantle.The validity of our approach is examined using aftershocks of the Borah Peak, Idaho earthquake (M_s = 7.3). Several thousand events occurred in a NNW-trending zone about 10 km wide, 75 km long, and 15 km deep. A small (~ 10 ×10 km) array of nine University of Wisconsin three-component triggered short-period digital seismographs was installed in the region of aftershock activity. Over a 10-day period, about 1000 useable events were recorded, of which about 120 have been used for this study. Hypocenters have been computed using both P- and S-wave arrivals, the latter being essential for stable solutions of events outside the network.The Borah Peak data have been processed to obtain shear-wave reflection profiles for the central station (Station 8) of the digital station array. The stacked shear wave (transverse) record sections reveal coherent reflections from horizons at mid-crustal to Moho depths. The most prominent reflections are from crustal discontinuities in the depth range 18–28 km. Coherent reflections can be obtained only through stacking, which is necessary to improve the signal to noise ratio. The major sources of data scatter, as manifested by “smearing” of reflections on the stacked records, are crustal heterogeneity and errors in the determination of focal depth and origin time.     

基于分段波形互相关的井下随采地震数据成像

随采地震勘探是以采煤机为震源的被动地震探测技术,由于采煤机是不断移动的、且其激发的是一种连续信号,因此常规数据处理方法无法直接应用。提出分段波形互相关方法,通过将采煤机产生的数据分段,采用互相关方法提取有效信号的走时,然后利用速度层析成像方法对工作面内部和切眼前方进行速度成像。利用波动方程对含异常体的工作面模型进行随采地震数值模拟,反演得到的成像结果和速度模型基本吻合;实际随采地震数据测试中,利用该方法对采煤机震源数据反演得到采动过程中地震波传播速度的成像结果,实现了对工作面内应力异常变化区域的实时动态监测。研究结果表明：基于分段互相关成像方法能解决采煤机震源信号处理问题,满足随采地震勘探技术实时性和稳定性的要求。     

近地表隐伏断层地震波场响应特征与初至波成像应用研究

近地表隐伏断层直接影响工程安全施工。通过构建浅覆盖层下方陡立界面断层数值模型,分析近地表隐伏断层地震波场的传播与转换规律。通过工程实测数据验证了数值模拟波场响应特征的可靠性,并利用初至波走时层析成像技术对地下介质波速进行成像。研究结果表明：(1)初至波转换形成的断点绕射波具有1频率升高、速度突变的特点,可清晰指示测区内断裂带的存在,可作为现场数据采集时断层的直观反映;(2)工程实测中通过原始波形到时、频率信息可初步判断断层的存在,基于射线追踪的初至波层析成像结果与后期钻孔揭露情况基本吻合,说明初至波层析成像在浅层地震勘探中的实用性;(3)接收测线排列内布设震源的方式,两侧震源延拓距离短,无需额外为震源激发提供场地,在工程施工中具有经济、快速、高效的特点,可作为野外复杂地表条件地下浅层结构探测的有效观测系统使用。     

煤层下部地层地震成像研究

以内蒙地区某煤田三维地震资料为例,对煤层下部地震成像效果不佳的原因进行分析。在资料处理环节,对影响煤层下部成像效果的面波和多次波,根据空间和频率等特性进行压制和衰减;在地表激发条件差、震源能量衰减迅速、煤层对下部反射有强烈屏蔽作用的情况下,对弱信号进行针对性的补偿和保护。实际资料处理,得到了较满意的成像效果。     

Tomographic imaging of high seismic activities in underground island longwall face

Anomalous information identification is a key issue for seismic hazard prevention in underground mining. Velocity tomograms can image the stress redistribution around coal face and provide better understanding of strata failure mechanisms. In this paper, based on microseismic events recorded during mining operation, passive tomographic imagings have been presented to assess strong tremor hazard and locate high seismic activity zones around an island coal face under super-thick strata. The zones of high velocity or velocity gradient anomalies have been found to correlate well with the distribution of strong tremors, indicating that velocity tomography is feasible for seismic hazard assessment and risk region division in underground mining.     

反射地震成像技术在新疆喀拉通克铜镍矿区的应用

新疆喀拉通克铜镍矿自1989年建成投产,已生产27年,属中度危机矿山。为探测该矿山深部资源,需要提供地质构造和隐伏含矿岩体的信息,为此开展了地震数值模拟和高精度反射地震研究。地震正演模拟结果为该区金属矿地震数据采集观测系统设计和实际地震资料的解释提供了依据,地震勘探获得的反射地震剖面分辨率高,成像清晰,能够对测区深部地质结构和构造及隐伏岩体进行可靠解释。地震剖面的地质解释得到了钻探验证,证实了深部含矿岩体的存在。该地震探测结果为在矿山寻找深部隐伏矿指提供了线索。     

Broad depth range seismic imaging of the subducted Nazca Slab, North Chile

In this paper, we present a compilation of modern seismic and seismological methods applied to image the subduction process in North Chile, South America. We use data from active and passive seismic experiments that were acquired within the framework of the German Collaborative Research Center SFB267 ‘Deformation Processes in the Andes’. The investigation area is located between 20° and 25°S and extends from the trench down to 100 km depth. In the depth range between the sea bottom and 15 km, we process an offshore seismic reflection profile using a recently developed velocity-model-independent stacking procedure. We find that the upper part of the subducting oceanic lithosphere in this depth range is characterized by a horst-and-graben structure. This structure supports an approximately 3 km thick coupling zone between the plates. In the depth range between 15 and 45 km, we analyse the spatial distribution of aftershocks of the Antofagasta earthquake (1995). The aftershock hypocenters are concentrated in an approximately 3 km thick layer. Finally, in the depth range between 45 and 100 km, we apply Kirchhoff prestack depth migration to the onshore ANCORP profile. A double reflection zone is observed between 45 and 60 km depth, which may represent the upper and lower boundary of the subducted oceanic crust. Over the whole range down to more than 80–90 km depth, we obtain an image of the subducting slab. At that depth, the hypocenters of local earthquakes deviate significantly in the direction perpendicular to the slab face from the reflective parts of the slab. Consequently, our results yield a complete seismic image of the downgoing plate and the associated seismic coupling zone.     

低信噪比、复杂地质条件下地震成像因素分析

在低信噪比、复杂地质条件下,影响地震资料成像效果的因素包括:能量均衡、资料的信噪比、面元覆盖次数、速度模型。本文对各要素分析后并阐述了处理中相应的解决方法以及方法的适用条件、局限性。     

地震映像在工程探测中的野外工作方法试验及应用

用地震映像法探测地下目标体是近几年采用的方法。为获得理想的应用效果,选择合适的野外工作方法至关重要。这里通过几种主要的对地震映像探测的野外工作方法进行试验,并对记录到现场模型的地震映像时间剖面图进行对比分析,最后通过应用实例表明,针对地震映像探测选择合适的野外工作方法及参数,是精确探测地下目标体的重要因素。     

High-resolution reflection seismic imaging of the upper crust at Laxemar, southeastern Sweden

A major cost in exploring the upper 1–2 km of crystalline crust with reflection seismics is the drilling required for explosive sources. By reducing the charge size to a minimum, shallow inexpensive shotholes can be drilled with handheld equipment. Here, we present results from a full-scale test using small charges for high-resolution seismic surveying over a nuclear waste disposal study site (not an actual site). Two 2–2.5-km-long crossing profiles were acquired in December 1999 with 10-m shot and geophone spacing in the Laxemar area, near Oskarshamn in southeastern Sweden. After standard processing, including dip moveout (DMO), several subhorizontal to moderately dipping reflections are imaged. Many of the dipping ones can be correlated to fracture zones observed in a ca. 1700-m-deep borehole where the profiles cross and/or to fracture zones mapped on the surface. The imaged fracture zones form a complex 3D pattern illustrating the necessity of having 3D control before interpreting seismic reflection data. Analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole (granite/greenstone reflection coefficient is +0.065). These greenstones may contribute to the reflectivity when associated with fracture zones. In some cases, where they are present as larger subhorizontal lenses, they may be the dominant source of reflectivity. A set of north-dipping (10°) reflectors at 3–3.5-km depth can be correlated to a similar set observed below the island of Ävrö about 3 km to the east.     

煤层陷落柱多波地震数值模拟与成像研究

陷落柱是煤田勘探开发中常见的地质灾害体,陷落柱的精确探测一直是煤田安全生产研究的重点,单纯依靠常规纵波地震勘探技术难以满足现阶段煤田精细勘探的需求。多波地震勘探技术能够获得纵波和转换波地震资料,提供更丰富的波场信息,且转换波对于埋深较浅的小幅度构造有更高的分辨率,充分利用多分量地震资料可以有效的提高地震勘探的精度。本文将多波地震技术应用到煤层陷落柱研究中,利用数值方法对煤层陷落柱进行多波地震勘探模拟研究,采用弹性波有限差分方法对构建的陷落柱模型进行多分量正演模拟,然后分别对波场分离后的PP波和PS波地震数据进行叠前深度偏移成像测试。通过对两个小尺寸陷落柱模型进行多波地震数值试算表明,多波地震勘探技术是一种有效的煤层陷落柱探测方法,充分利用多波地震资料有利于查明煤层陷落柱构造,对陷落柱取得更好的勘探效果。     

井中地震粘声逆时偏移成像影响因素分析

当前油气勘探目标已由简单构造油气藏转向深层复杂构造油气藏,其具有的储层薄、分布广、赋存状态隐蔽等特点对地震偏移成像技术提出了巨大挑战。与地面地震相比,井中地震震源位于井中,靠近目的层,且波场少一次经过低降速带,因此理论上具有资料信噪比高、储层识别力强等优点,能够实现井周储层精细成像的目的。然而,井中地震特殊的观测方式使得成熟的地面地震成像技术难以直接应用。此外,井中地震震源能量弱,地层的吸收衰减效应的影响强于地面地震。因此,需要发展针对性的井中地震偏移成像方法。鉴于上述因素,本文将粘声逆时偏移成像方法应用至井中地震,通过模型试算探讨多种因素对井中地震偏移成像效果的影响,为井中地震技术在实际中的应用提供理论支持和技术指导。     

地震波逆时偏移中两种成像条件应用效果对比

成像条件是实现地震波场准确成像的关键环节,而优化逆时成像条件在改善逆时成像应用效果中的作用尤为明显。为此,从零井源距和非零井源距脉冲响应出发,系统对比了常规相关法逆时成像条件和基于行波分离法逆时成像条件的逆时偏移脉冲响应波场差异,分析了逆时偏移低波数噪声的成因机理及波场规律,同时以复杂断陷理论模型和SZ工区实际三维地震资料为例,系统对比了两种逆时成像条件的成像应用效果。研究结果表明,采用基于行波分离法逆时成像条件的成像结果能够有效衰减逆时偏移低波数背景噪声,恢复掩盖在这种背景噪声之下的有效地震成像信息,地层细节刻画更加清晰,这可为当前复杂波场和复杂构造高精度地震成像提供方法指导。     

Detailed seismic imaging of a chemical munition dumpsite in the Bornholm Basin,south-western Baltic

Very high resolution seismic investigations were carried out over a munition dumpsite in the Bornholm Basin, south-western Baltic Sea. After WW2 over 32,000 tons of chemical weapons were dumped in this area. The aim of the investigations was to image the internal structure of the dumpsite and to identify possible natural hazards with regard to the dumped war material. Two geophysical surveys were carried out in the summers of 2006 and 2007. During the surveys, acoustic sources with a distinct frequency spectrum (parametric echosounder, sparker, boomer) were deployed simultaneously. This approach proved very fruitful as it allowed to study the sediments in a wide depth range and in the highest possible detail. In total, seven seismic–stratigraphic units have been identified, related to different stages in the Holocene and late glacial history. Water depths range roughly between 96 m in the north and 70 m in the south where the basin shallows and older glacial sediments are outcropping. The seafloor topography at the dumpsite is generally quite flat, locally marked by small pit-like features that are probably related to the dumping impact. Small-scale fluid escape features are present throughout the dumpsite area. Large-scale doming occurs locally and is possibly linked to the migration of deep thermogenic gas. A large number of buried objects were identified on the acoustic data. Their burial depth is generally less than 1 m. The data confirm the wide variety of dumped war material, ranging from bombs and shells to encasements and containers. The distribution of the objects seems to be very heterogeneous, with locally high concentrations and areas of low object density. Four different shipwrecks were identified but their relation to the dumped warfare is not clear.