基于微动H/V谱比法的土石分界面探测研究——以济南中心城区为例

土石分界面对城市抗震设防和地下工程建设具有重要意义.城市中复杂的干扰限制了常规地球物理勘探方法的使用,本文选用环境友好且抗干扰能力强的微动H/V谱比法对济南中心城区的土石分界面展开研究.在济南中心城区开展三分量微动测量,得到了400多个测点的微动数据,计算了对应的H/V谱比曲线.将得到的H/V曲线划分成单峰、宽峰、双峰和无峰四种类型,分析了不同类型曲线与地质结构的关系.根据基岩性质不同,将研究区的基岩划分为灰岩和岩浆岩两种类型,总结出了基岩为灰岩时的深度-频率关系式,同时发现当基岩为岩浆岩时无法得到可靠的关系式.根据关系式计算得到了济南部分测线的土石分界面深度分布,另外,关系式的计算结果与钻孔资料十分吻合,能满足工程探测的精度要求.本方法为在城市强干扰环境中确定土石分界面深度提供了快速准确的解决方案.     

二维微动剖面探测"孤石":以深圳地铁7号线为例

"孤石"是花岗岩不均匀风化所残留的风化核,在我国南方沿海地区普遍发育."孤石"埋藏分布随机,形状大小各异,给地铁盾构施工带来重大安全隐患,探测"孤石"一直是地铁工程勘察面临的难题.我们首次尝试利用二维微动剖面技术探测"孤石",在深圳地铁7号线车公庙—上沙段区间实测二条剖面,结合少量钻孔资料进行岩性层划分和"孤石"解释.实测结果显示,在二维微动视S波速度剖面上,素填土、粉质粘土、砾质粘性土等岩土层、全风化、强-中风化、微风化和未风化的花岗岩层,视S波速度值各不相同,剖面特征也存在较大差异,利用少量钻孔结果标定,易于划分;在强-中风化花岗岩层中,视S波速度(岩性)横向变化剧烈,局部发育"团块状"高速体,本文将其解释为未风化的花岗岩"孤石".本文结果表明,二维微动剖面技术探测"孤石"是有效的微动视S波速度剖面除能直观显示岩性的纵、横向变化,提供工程基岩面的埋深及起伏形态信息外,还可给出岩土层风化程度的判断信息,为高层建筑的桩基设计提供地球物理依据.作为一种全新的"孤石"探测手段,二维微动剖面技术尤其适用于交通繁忙、建筑物密集的、各种场源干扰严重的闹市区.     

基于微动HVSR法的基岩面探测研究——以深圳16号线共建管廊项目为例

盾构掘进穿越上软下硬地层属于高风险工程,在盾构施工前需根据基岩面特征优化掘进参数的设置,管控施工风险,保障经济效益.灰岩地区易受溶蚀作用影响,部分区域形成溶洞,部分区域发育溶沟溶槽,导致基岩面的深度变化大,对盾构施工造成重大影响,我们亟待寻找一种能快速准确识别岩溶区基岩面的解决方案.微动HVSR法是一种简单有效的被动源地震勘探方法,已被广泛应用于场地类型评价、地震放大效应评估等方面.本文以深圳16号线共建管廊项目为依托,将HVSR法用于快速地层分界面识别,通过对比分析不同的HVSR法界面深度估计经验公式,总结出一套快速准确识别基岩面的方法,经实际钻孔验证,达到了95％的识别准确率.微动HVSR法可以快速准确地识别基岩面,满足城市地下空间精细探测的需求,具有绿色环保、经济、施工便捷等优点,值得推广应用.     

地铁线路采空区微动剖面法探测研究——以广州地铁14号线二期为例

煤层开采留下大范围采空区,可能引发地面沉降和塌陷,危害地面建筑物和地下设施安全,查明采空区的空间位置与结构形态,对矿区环境治理、土地资源开发利用和确保地铁、铁路等大工程建设地质安全具有重要意义.然而,采空区探测一直是公认的行业难题,尤其是当采空区位于城镇等复杂强干扰环境下,传统的采空区物探面临诸多挑战.本文采用微动剖面探测新方法研究广州地铁14号线二期乐嘉路站—岗贝站区间的煤层采空区,介绍在城区交通要道开展地铁线路采空区微动剖面法探测的方法技术.探测查明2#、4#煤层采空区、六处岩巷与二处竖井,与钻孔揭露情况和历史记载的煤矿开采水平巷道吻合,探测结果为地铁设计建设提供了可靠的物探依据和地质安全保障.

     

微重力和微动法相结合的隐伏岩溶探测效果分析——以长宁某页岩气钻井平台为例

微重力测量相较于传统重力测量方法,其观测研究的对象是在尺度规模上越来越细小、在重力信息上反应越来越微弱的密度异常体,更加突出“微”的性质与特点.利用该方法能精准识别地下岩溶的平面位置,但推测目标体的垂向埋深需结合其他先验信息进行反演;微动法采用天然源信号,具有抗电磁干扰、抗振动干扰能力强、纵向分辨率高等优点,可准确识别地下岩溶的空间位置,特别适用于强干扰环境下的地质勘察.将微重力和微动两种方法相结合进行岩溶探测,优势互补,能准确确定地下岩溶的空间位置和形态规模.本文通过微重力、微动两种测量方法在长宁页岩气区块某钻井平台场地岩溶探测的具体实例,来分析两种方法组合在工程场地隐患排查中的效果.实践证明,应用微重力、微动方法组合在探测近地表的溶洞、地下河、孔穴以及规模较小的地质构造等异常体方面有广泛的应用前景．     

用微动台阵记录联合反演场地浅层速度结构——以唐山响嘡台3#场地为例

目前,利用台阵观测记录反演浅地表土层波速剖面的研究一般单独进行面波频散曲线(Dispersion Curve,简称DC)或微动水平与竖向谱比(Microtremor Horizontal-to-Vertical Spectral Ratio,简称MHVSR)反演,但其反演的速度结构往往存在明显的多解性。鉴于此,文中发展了DC与MHVSR联合反演方法,提出了一种新的反演策略。区别于已有的反演方法,文中方法首先利用微动台阵记录获得面波频散曲线,进而采用改进的半波长法获得场地初始速度结构,最后通过DC和MHVSR的联合反演得到场地最佳速度结构。该反演方法的优势体现在2个方面:1)在面波频散曲线提取环节,综合应用修正空间自相关(MSPAC)法和频率-波数(F-K)法,拓宽了采用单一方法提取频散曲线的频率范围; 2)在初始速度结构确定环节采用了改进半波长法,可较好解决当前其他反演方法依赖一定先验信息的难题。文中分别以一理论算例及台阵观测算例验证了新反演策略的有效性及稳定性。结果表明,单独的DC反演模型的理论MHVSR在峰值频率之后(特别在高频段)与理论算例模型的MHVSR有差异,单独的MHVSR...     

基于回声探测监测沉水植物盖度的插值方法研究:以杭州西湖沉水植物盖度监测为例

沉水植物作为水生态系统的重要组成成分,在水生态系统物质循环和能量流动中发挥着重要作用,其覆盖度和生物量是评价湖泊等浅水水体系统稳定性的关键参数随着高效和无损伤监测的回声探测仪在沉水植物盖度监测中的应用,其精确度算法也受到了越来越多的关注本研究以成功恢复沉水植物的浅水湖泊杭州西湖为研究对象,利用BioSonics便携型回声探测仪——MX采集沉水植物回声样本同时结合人工样方设置,采集与回声探测对应位点的沉水植物样本,验证回声探测结果的精确性通过建立回归模型分析回声探测得到的沉水植物体积百分比(PVI)与人工样方获得的对应平均鲜重关系,结果表明二者具有较好的相关性分别采用普通克里金法、反距离权重法、径向基函数法3种插值方法对同一季节的不同湖泊和同一湖泊的不同季节未采集区域沉水植物的盖度数据进行插值分析,并对插值结果进行交叉验证,以确定方法的精确度交叉验证结果表明,插值精确度反距离权重法径向基函数法普通克里金法研究结果为回声探测与插值分析方法结合在大尺度浅水水体中沉水植物监测应用提供了技术支撑.     

微动多阶瑞雷波SPAC系数反演方法及应用研究

为充分利用微动信号中基阶和高阶模式瑞雷波,本文研究了基于多阶瑞雷波SPAC系数直接反演的方法.该方法首先基于地层介质响应计算多阶瑞雷波的能量占比,考虑实际观测台阵有限台站个数对SPAC系数影响,正演计算多阶瑞雷波SPAC系数,再采用快速模拟退火算法对其反演以获得地下介质横波速度结构.在此基础上,本文通过数值模拟验证该方法的可靠性,分别选取三种典型地质模型,基于模式叠加算法合成理论微动信号,采用本文方法计算其理论多阶瑞雷波SPAC系数并反演,给出反演结果与真实模型对比.我们将该方法应用于上海中心城区的地质调查中,通过与钻探结果对比,进一步验证该方法的有效性.本文理论与实际应用研究表明,基于多阶瑞雷波SPAC系数直接反演的微动探测方法有助于提高反演结果的可靠性,尤其对含软硬夹层的复杂地层介质,可提高探测精度.     

High-resolution flood hazard mapping based on nonstationary frequency analysis: case study of Ho Chi Minh City,Vietnam

Flood modelling inputs used to create flood hazard maps are normally based on the assumption of data stationarity for flood frequency analysis. However, changes in the behaviour of climate systems can lead to nonstationarity in flood series. Here, we develop flood hazard maps for Ho Chi Minh City, Vietnam, under nonstationary conditions using extreme value analysis, a coupled 1D–2D model and high-resolution topographical data derived from LiDAR (Light Detection and Ranging) data. Our findings indicate that ENSO (El Niño Southern Oscillation) and PDO (Pacific Decadal Oscillation) influence the magnitude and frequency of extreme rainfall, while global sea-level rise causes nonstationarity in local sea levels, having an impact on flood risk. The detailed flood hazard maps show that areas of high flood potential are located along river banks, with 0.60 km² of the study area being unsafe for people, vehicles and buildings (H5 zone) under a 100-year return period scenario.     

太湖典型地区工矿企业废水中主要污染物排放特征研究——以江苏溧阳市为例

在调查了江苏省溧阳市化工、纺织等18家典型工矿企业废水中TN、TP、 CODMn等主要污染物质排放强度及特征基础上,估算了溧阳市工业行业的万元产值排污系数及TN、TP、CODMn的年排放量. 2000年度溧阳市全市工业行业年排放TN 479.9t, TP 40.8t, CODMn的1529.7t,约占太湖外源性污染负荷的2%-3%. 造纸、印染、化工、纺织等行业的万元产值排污系数较其它行业为高.被调查企业排污口废水中TN、TP、CODMn等污染物排放强度具有夜间高于白天等日变化特征.     

城市微动高阶面波在浅层勘探中的应用: 以苏州河地区为例

土耳其东部是由碰撞引起的挤压变形区域,而西部为俯冲引起的爱琴海伸展变形区域,土耳其中部作为两者之间的过渡拥有很复杂的地质情况,尤其是具有火山活动和长远的俯冲、大陆碰撞等构造历史,因此获得此区域岩石圈可靠的速度结构对认识俯冲末期的板块状态、岩浆活动等现象意义重大。为了更好地了解此区域的岩石圈速度结构,本研究使用了（31°E—38.8°E,34.5°N—42.0°N）范围内172个台站的背景噪声数据,通过互相关方法获得经验格林函数;之后利用频率-贝塞尔变换法得到了5—80 s周期范围内的基阶瑞雷波频散曲线,并在个别区域获得了高阶模式频散曲线;最后利用基于Broyden-Fletcher-Goldfarb-Shanno算法校正的拟牛顿迭代反演方法得到地表至124 km深的三维剪切波速度结构。结果表明：土耳其中部的速度横向变化剧烈（最大变化可达400 m/s）,且与地质边界和缝合带区域密切相关,中安纳托利亚火山区及部分金牛座山脉东部的速度在0—100 km深度均小于4.3 km/s,因此推测此区域不存在岩石圈地幔;从塞浦路斯海沟开始俯冲的非洲大洋岩石圈,以近垂直俯冲在金牛座山脉中部下方,表现为明显的高速特征;土耳其中部在70—100 km深度广泛存在与上升软流圈物质相关的低速带,因此大部分研究区域的岩石圈波速小于全球平均剪切波速度,并且此区域岩石圈整体较薄、厚度多变。此外,本研究还发现在金牛座山脉中部和东部约13—23 km深度存在一个明显的低速带,推测可能与地块破裂导致的地层部分熔融有关。     

城市微动高阶面波在浅层勘探中的应用：以苏州河地区为例

频率-贝塞尔变换方法(Frequency-Bessel Transform method,简称F-J方法)是一种分析微动信号的新方法,由于该方法采用频率矢量波数变换处理水平层状各向同性弹性模型中时空平稳随机分布的微动信号,所以从理论上可以提取出清晰的瑞利波基阶和高阶模态频散曲线,但是目前还没有相关的野外实验对此进行研究和应用.本文首先采用该方法对上海市苏州河地区采集的城市微动信号进行处理获得了频率-相速度谱,然后提取了多模态瑞利波频散曲线,最后通过粒子群算法对频散曲线进行联合反演,得到了浅地表0~70 m深度范围的S波速度结构,并且利用钻孔数据对反演的速度结构进行了验证.另外,本文还通过对比F-J方法和传统的SPAC(SPatial AutoCorrelation method)方法分别提取的频散曲线,展示了F-J方法在处理城市微动信号方面的优势.本文研究结果表明:(1)F-J方法可以从少量台站(21个台站)短时记录(1小时)的微动信号垂直分量中提取出清晰的基阶和高阶模态瑞利波频散曲线;(2)F-J方法提取的高阶模态频散曲线比传统SPAC方法提取的更加清晰,高频部分(>13 Hz)优势更为明显;(3)联合基阶和高阶模态频散曲线反演的浅地表速度结构更加精确,可以分辨出第四系沉积层中物性相差较小的速度界面和低速异常,在城市浅地表精细结构成像方面具有较好的应用前景.     

Site amplification of S-waves in Bursa City and its vicinity, Northwestern Turkey: comparison of different approaches

Microearthquake recordings of local events have been used to quantify the site effects in the vicinity of Bursa City, northwest Turkey. Since the city is located near the southwest branch of the western extension of the North Anatolian Fault (NAF) zone, the importance of the seismic hazard in the region becomes progressively more important. The accelerograms of 69 earthquakes that were recorded on different geologic units, massive limestone, slope deposit and Quaternary sediment were analyzed to estimate the response of the recording sites. Site amplification functions were obtained by using three different approaches (standard spectral ratio, SSR; horizontal to vertical, H/V ratio and generalized inversion method, GIM) and the differences between the methods were also evaluated. We found large discrepancies between the SSR and H/V ratio methods, specifically; the former yields almost three times higher amplitudes than those obtained in the latter approach. Station located within the Bursa Quaternary basin (SCKR) is characterized by the largest estimates of the amplification amplitudes (8.0, 4.5 and 4.0 for SSR, H/V ratio and GIM, respectively) in all the three methods. On the other hand, stations located on deep limestone geological unit (SIGD and SKAY) show the least amplification level, ranging between 1.0 and 1.6. Three methods are able to identify resonant frequencies of the sites, although the absolute amplitudes of the amplification function are obtained different from each method.     

Cosmogenic nuclide burial dating of an alluvial conglomerate sequence: An example from the Hexi Corridor,NE Tibetan Plateau

The thick alluvial conglomerate sequences around the Tibetan Plateau have been notoriously difficult to date. Here we use the cosmogenic nuclide burial dating method to date the Yumen and Jiuquan formations, a ∼900 m thick fanglomerate found in the Hexi Corridor, the foredeep of the Qilian Shan, and exposed in the Laojunmiao anticline. We date 16 sites with simple burial dating and 2 sites with isochron burial dating, and use these dates to reinterpret the magnetostratigraphy of the section. We suggest that the bottom of the Yumen Formation, defined by a progressive unconformity, is around 5 My. Taking this timing as the initiation of anticline growth, the long-term crustal shortening rate at the ramp zone in western Qilian Shan is about 0.72 mm/yr, consistent with those obtained from middle and eastern Qilian Shan. The boundary between the Yumen and Jiuquan Formations is near ∼1.2 My. Three other angular unconformities are dated to ∼2.6–3.1, ∼2.2–2.5, and ∼1.2–1.7 My, respectively. Burial dating offers a robust chronology for these deposits, and when combined with paleomagnetic stratigraphy offers much tighter precision.     

Geochemistry of caldera-forming and resurgent magmas in the Pliocene Hiwada caldera,northeast Japan: An example of a monotonous intermediate system

The 2.9-Ma Hotokezawa Ignimbrite, which was ejected from the Aizu caldera cluster in the northeast Japan arc, is a typical monotonous intermediate ignimbrite, with 40–50 vol% crystals and an eruptive volume of >140 km³ dense-rock equivalent. This ignimbrite filled Hiwada caldera and was deformed by post-caldera plutonic intrusions that formed a resurgent dome. The Hotokezawa Ignimbrite is a calc-alkaline, medium-K dacite to rhyolite with SiO₂ contents of 67.9–71.3 wt%, and has homogeneous trace-element abundances and Sr–Nd isotopic ratios. These geochemical features suggest that the Hotokezawa magma was formed by partial melting of amphibolitic crustal rocks. This crystal-rich magma did not appear during the post-caldera stage. Therefore, it is plausible that the chamber of eruptible magma was emptied by the caldera-forming eruption. In contrast, post-caldera plutonic rocks exhibit a variety of compositions and have a clear SiO₂ gap corresponding to the caldera-forming magma: the early pluton (tonalite) and later ones (quartz porphyry, granite porphyries, and granite) contain 62.0–66.6 and 71.2–76.5 wt% SiO₂, respectively. The tonalite and the Hotokezawa Ignimbrite form a continuous trend in their major-element variations. The Sr–Nd isotopic ratios of the ignimbrite and tonalite overlap, but those of the porphyries and granite are more enriched. The early tonalite represents the more basic part of the Hiwada caldera system that was held in small pockets separate from the main magma chamber, because its trace-element abundances are varied and distinct from those of the Hotokezawa Ignimbrite. The distinct compositional change from the Hotokezawa Ignimbrite to the late porphyries and granite indicates that the partial melting crust generating felsic magma was renewed by the subsequent intrusion of the mantle melts. The new felsic magma ascended through subsidence-related faults into the shallow caldera system and emplaced as laccoliths forming the resurgent dome.     

洞庭湖区湖洲生态建设初探─以沅江市湖洲为例

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