Mapping sediment thickness of Islamabad city using empirical relationships: Implications for seismic hazard assessment

Soft sediments make an important component of the subsurface lithology, especially in areas underlain by river/stream basins. Occupying a position directly above the bedrock up to the land surface, these soft sediments can range in thickness from few centimeters to hundreds of meters. They carry a special nuisance in seismic hazards, as they serve as a source of seismic amplification that may enhance the seismic shaking of many folds. Determination of the thickness of the soft sediments is therefore crucial in seismic hazard analysis. A number of studies in recent years have demonstrated that frequency and amplitude spectrum obtained from the noise measurements during the recording of natural seismicity can be used to obtain thickness of soft sediments covering the bedrock. Nakamura (1989) presented a technique to determine such spectrum using ratio of horizontal to vertical components of the Rayleigh waves. The present study is based on an extensive set of microtremor measurements carried out in the Islamabad city, Pakistan. Fundamental frequencies were obtained from weak motion sensors and Tromino Engy Plus instruments to show that the correlation is clearly valid for a wide range of sediment thickness. A simple formula was derived for the investigated area to determine directly the thickness of sediments from the main peaks in the H/V spectrum for seismometer and Tromino data separately. A comparison is made between sediment thicknesses derived from empirical relations developed in this study with those given in literature to demonstrate a positive correlation. The correlation of instrumental resonant frequencies with calculated resonant frequencies (theoretical) suggests that the relation derived from the noise measurements mostly depends on the velocity depth function of the shear wave. The fundamental frequency of the main peak of spectral ratio of H/V using the both instruments correlates well with the thickness of sediments at the site obtained from the borehole data. It is found out that there is a wide variation in soft-sediment thickness in the Islamabad area, but as a general rule, soft sediments are thicker adjacent to stream courses compared to the areas intervening the streams. The distribution of sediments in the studied area is illustrated by means of cross sections constructed from results of the microtremor analyses and available borehole data, which provides a visual distribution of the soft sediments underlying the Islamabad city.     

高密度电阻率成像法与微动谱比法探测岩溶区塌陷的地质背景——以广东省高要市蛟塘镇塱下村塌陷区为例

塌陷已成为岩溶区最主要的地质灾害。本文以广东省高要市蛟塘镇塱下村岩溶塌陷区为例,结合钻探资料,应用高密度电阻率成像法与微动谱比法联合探测塌陷区背景地质结构和构造。通过区内外14个已知钻孔旁的微动测量,建立了微动特征频率与覆盖层厚度的数学关系,并应用于塌陷区覆盖层厚度的估算。高密度电阻率成像反映出岩土电阻率在水平方向和垂直方向上的变化,揭示了地下地质结构;微动谱比法揭示了探测场地的基岩起伏形态,结合地层岩性推断了古河道的存在并确定了其边界及延伸方向,与高密度电阻率成像法联合进行地质解译,推断了基岩内断层发育的空间位置、走向等特征。综合该两类物探技术探测成果和钻探资料表明,塌陷位于古河道内,并沿古河道方向发育,其方向与区域北东向构造走向方位一致。     

珠江三角洲地壳稳定性分区及其特征

分析研究珠江三角洲地区的新构造运动、活动断裂、地壳厚度、地壳沉降、地热分布、地震活动等资料，其呈现出比较明显的空间分异。认为珠江三角洲区域稳定性划分为稳定区和次稳定区，区域地壳稳定性活动程度中等，次稳定区主体在地质构造区划上属于珠江三角洲断陷区及三角洲沿海区域，次稳定区范围之外的相对隆起地带为稳定区。     

Seismic microzonation study in Doon valley, northwest Himalaya, India

Fundamental frequency map of site amplification at different sites in Doon valley, Uttarakhand, India is prepared from microtremor (ground ambient noise) using Horizontal to Vertical Spectral Ratio (HVSR) technique. The fan deposited alluvium filled synclinal valley of Doon lies between Main Boundary Thrust (MFT) and Himalayan Frontal Thrust (HFT) in the Himalayan active seismic belt and experienced many earthquakes in the past. The HVSR at different sites in the Doon valley ranges between the predominant frequencies 0.13 and 12.77 Hz. The HVSR in lower frequencies indicates that the site has either thick sediment covers or less compact rocks with fractures. Based on information on fundamental frequency and soft soil thickness, site classification map is generated. Results indicate that degree of compactness of rock types and presences of sediments vary significantly, which may play a major role in seismic hazard. The use of microtremor, therefore, constitutes an effective and inexpensive approach to site response and soft soil thickness estimation for preliminary microzonation.     

珠江三角洲平原区第四纪沉积物地球化学特征及其控制因素

在珠江三角洲经济区多目标区域地球化学调查基础上,根据珠江三角洲第四纪地质、基底地形、水系走向等方面的资料,在珠江三角洲布署了6条钻孔剖面,共44个第四纪地质钻探,对其晚更新世以来沉积物的地球化学特征进行了系统分析。结果表明:珠江三角洲平原区重金属元素富集,特别是以Cd、Hg、Cu、Pb、Zn、Ni、As为代表的重金属元素较为富集,形成高背景区。不同区域富集元素类型及富集程度呈现较大差异,其中以西北江三角洲各元素最为富集,而潭江三角洲仅U、Al2O3富集,其Cl、Cd、Cu、Sb、CaO等元素含量明显低于全区平均含量,东江三角洲Mo、S、Th、Tl、U等元素富集,Cd、Cl、Co、Cr、Hg、Mn、Ni、Sb、Sr、Ti、V、MgO、CaO、Na2O等元素含量明显低于全区平均含量。元素空间分布差异的控制因素是三角洲平原物质来源差异及沉积体系变迁。     

Characterizing site response in the Attock Basin,Pakistan, using microtremor measurement analysis

The Attock Basin is situated close to the northwest of Pakistan. Recent seismic event of October 2015 (7.5M_w) near the Pakistan Afghanistan border has proved that the area of interest is seismically active and triggered a series of aftershocks of magnitude even greater than 6.5M_w. This seismic activity has posed danger to the future of the people and infrastructure especially to the northwestern part of the country. Therefore, site response analysis is essential for estimating local site conditions in response to seismic events. Ambient noise recordings were made at 50 sites within urban and semi-urban settlements in the Attock Basin to analyze the site response of the small but densely populated basin. At each of these sites, the fundamental frequency of the soft sediments (f ₀), the amplitude (A ₀) of corresponding H/V spectral ratios, the thickness of soft sediment (H) lying over competent lithology, and the soil vulnerability index (K _g) were studied. Results were correlated with sparsely available borehole data to enhance the credibility of the study conducted for microzonation and predicting the site response to earthquake seismicity in the Attock Basin. The soil vulnerability index was found to range from moderate to high. Results clearly showed that the study area exhibits low to moderate fundamental frequency with greater soft sediment thicknesses distributed throughout the study area. Moreover, higher impedance contrasts were found at most of the sites within the central part of the Attock Basin, thus reflecting a moderate to high susceptibility of damage in those regions in response to seismic events.     

天水黄土地区覆盖层厚度的反演研究

基于天水黄土地区现场测试的539个地脉动测点数据,分析得到了其H/V频谱特征和场地卓越频率。结合该区59个钻孔编录和波速测试结果,运用1/4波长和覆盖层厚度与卓越频率统计等两种方法反演了该区黄土覆盖层厚度。结果表明,1/4波长法在黄土覆盖层较厚、且地层较为单一的III、IV级阶地具有较好的适应性;覆盖层厚度与卓越频率统计法得出了较高精度的覆盖层厚度与卓越频率之间的幂函数关系,简化了剪切波速的影响,在整个研究区域具有较好的适应性。     

珠江三角洲经济区农业地质与生态地球化学调查成果综述

2005年中国地质调查局与广东省人民政府联合开展珠江三角洲经济区农业地质与生态地球化学调查项目。通过开展多目标区域地球化学调查、区域生态地球化学评价、局部生态地球化学评价和总体综合评价,系统完成了珠江三角洲经济区47954 km2(包括10 m水深以浅的近岸海域)的生态地球化学调查与评价。按照双层网格化方法系统采集了陆域土壤、近岸海域和珠江水系主要河流沉积物表层和深层样品,测试了71项元素和指标,建立了珠江三角洲经济区土壤、沉积物地球化学背景值和基准值,全面查明了珠江三角洲经济区土壤环境质量状况。定量计算了镉、铅、汞等主要异常元素经河流、成土过程等自然来源和大气干湿沉降、施肥、灌溉、使用农药等人为来源贡献量,阐明了其迁移转化途径及生态安全性。项目紧密结合本地区特点,在国内首次开展了三角洲形成演化过程地球化学研究、区域辐射环境质量评价、酸雨对土壤质量影响的模拟实验、土壤环境质量地方标准研究与制订等工作。     

HVSR technique as tool for thermal-basin characterization: a field example in N-E Italy

The Euganean thermal basin, located in the Eastern Po plain (Italy), is one of the most important thermal districts of Italy (Euganean–Berician Thermal District). The presence of hot water in the basin has brought about its exploitation over time. The thermal area has been known since the Roman Empire and is still of crucial interest for the profitable use of its hydro-geological resources. For these reasons the water cycle of the thermal area has been thoroughly studied, in particular with regard to its chemical and hydrogeological properties. The effects of well pumping, such as subsidence and water temperature steadiness, have been monitored over time. In the present work, the Horizontal to Vertical Spectral Ratio (HVSR) single station microtremor technique was applied as a non-invasive geophysical tool for the characterization of a part of the Euganean–Berician thermal district involving the municipalities of Abano and Montegrotto towns. This study represents the first correlation between the results from microtremor geophysical surveys and the thermal basin geological structure, including remote sensing data and thermal well information. More than 50 HVSR measurements from single stations were collected and analysed, in close correlation with the vast amount of available borehole logs, well exploitation data and SAR interferometry measurements collected for the monitoring of land subsidence induced by thermal water pumping. The aim of the work was to evaluate the suitability of the microtremor technique for the preliminary characterization of a thermal basin, in terms of resonance properties of the alluvial deposits covering the rocky bedrock, evaluated by means of HVSR methods. HVSR results were interpreted in terms of regional geological setting and hydrogeological properties of the subsoil. Our field results confirmed the existence of significant correlations between the resonance behaviour of the basin determined by the HVSR technique and the geological structures, suggesting that single station measurements are a promising tool for creating a rapid and preliminary non-invasive contribution to the characterization of the geothermal basin.     

谱分解技术在煤层厚度预测及沉积环境方面的应用

谱分解技术是通过短时窗离散傅里叶变换(DFT)将地震资料从时间域转换到频率域,得到振幅谱及相位谱调谐体的一项处理技术。通过谱分解顺层相位与频率切片可以较清晰地了解区内煤层的岩性特征及沉积环境,从而预测煤厚。基于该项技术,以山西省沁水盆地某研究区山西组3煤层为例,研究了3号煤层厚度与下伏砂岩厚度的对应关系,发现3煤层厚度与基底分流河道砂岩厚度呈负相关关系,即煤层厚度随基底砂岩厚度增大而减小。由此认为在三角洲平原沉积环境下,在钻孔较少且分布不均匀时,可通过谱分解属性切片对煤层基底砂岩厚度的预测来推断煤厚。该区利用谱分解技术预测的煤厚趋势与振幅法获得的煤厚趋势相比,其精度较高,因此,谱分解技术不失为一种较好的煤层预测方法。     

珠江三角洲水资源可持续利用综合评价分析

按照复合系统理论。水资源可持续利用系统是一个由水资源、社会经济和环境等子系统组成的复合系统．且各子系统包含多个要素。由此，本文构建珠江三角洲水资源可持续利用评价层次结构多指标体系．采用主成分分析法和层次分析法对珠江三角洲水资源可持续利用进行综合评价，评价结果客观地反映了珠江三角洲各地区的水资源可持续利用状况。在评价结果的基础上，对珠江三角洲各地区的水资源可持续利用问题提出了相应的建议。     

珠江三角洲经济区生态地球化学评价

土壤重金属污染是珠江三角洲地区主要的生态环境问题之一,直接影响到区域生态系统的稳定和食品安全。通过开展多目标区域地球化学调查、区域生态地球化学评价、局部生态地球化学评价和总体综合评价,系统完成了珠江三角洲经济区47954 km²(包括10 m水深以浅的近岸海域)的生态地球化学调查与评价。按照双层网格化方法系统采集了陆域土壤、近岸海域和珠江水系的主要河流沉积物表层和深层样品,测试了71项元素和指标,建立了珠江三角洲经济区土壤、沉积物地球化学背景值和基准值,首次对珠江三角洲地区区域地球化学特征进行了系统全面的调查,全面查明了珠江三角洲经济区土壤环境质量状况,区内一级和二级土壤分别占总面积的19.9%和57.3%,三级和三级以上土壤占22.8%。定量计算了镉、铅、汞等主要异常元素经河流、成土过程等自然来源和大气干湿沉降、施肥、灌溉、使用农药等人为来源贡献量,阐明了其迁移转化途径及生态安全性。结合研究区特点,系统开展了三角洲形成演化过程的地球化学研究,并在国内首次制定了符合地区特点的珠江三角洲经济区土壤环境质量地方标准。     

微动HVSR法在岩溶区探测地下河管道和溶洞的有效性研究

微动HVSR（Horizontal-to-Vertical Spectral Ratio）法是一种简单有效的被动源地震勘探方法,当测点下方介质存在明显的速度变化时,HVSR曲线会呈现相应的异常形态。为探索该方法在岩溶区探测地下河管道和溶洞的有效性,选择桂林毛村地下河流域内的大岩前村作为研究区,并在此开展野外试验。研究区发育有一条地下河管道,通过精准的洞穴测量,获得了此地下河管道的平面位置和洞高等信息。在研究区的地下河管道上方地面布设3条物探测线,均进行微动HVSR法测量,并用探地雷达法测量作对比。结果表明,两种物探方法的异常位置与测线下方地下河管道的实际平面位置基本一致,证明微动HVSR法可作为一种有效的地下河管道和溶洞探测方法。     

Estimation of the compound hazard severity of tropical cyclones over coastal China during 1949–2011 with copula function

The site effect plays very important role for planning design of structures and estimating seismic damage of existing structures, especially in seismicity active regions. Alia?a, located in the northern region of the ?zmir City, is high seismically active region in western Turkey. We identified the dynamic properties of shallow soil for Alia?a district (western Turkey) in terms of the average shear-wave velocity for the top 30 m of soil (Vs₃₀), predominant period (T ₀) and vulnerability index (Kg). We created the microzonation map that classes the shallow soil according to National Earthquake Hazards Reduction Program (NEHRP). Shear-wave velocity (Vs) was evaluated using the 1-D multichannel analysis of surface waves at 34 sites. The microtremor measurements were taken at 58 stations with a grid spacing of 1000 m in Alia?a district. The acquired HVSR results show that the T ₀ values change from 0.1 to 1.9 s, while the amplification factor (A ₀) values change between 1.5 and 12. Soil classification results illustrate that northern part of the study area, located in alluvial unit, has lower Vs₃₀ values. These values are observed within the range of 100–300 m/s. This part was classified as the D and E types according to NEHRP. In addition, the weak zones of the study area due to the local site effects were indicated by the Kg values which vary from 5 to 55. The northern part of the study area is high vulnerability index zone (Kg > 20). Last of all, we can mention that the northern part of our study area is the weakest zone according to the results of geophysical and geological data.     

多道瞬态面波法与微动法联合推断岩溶塌陷区覆盖层的结构和厚度分布

为了大尺度范围内获取岩溶塌陷典型调查区覆盖层的结构和厚度分布,采用多道瞬态面波法与微动法,对柳州市柳城县东泉公社幅岩溶塌陷重点调查区进行了野外观测,根据微动法提取的特征频率与地层厚度的关系,结合已知钻孔资料,得出覆盖层厚度与特征频率的函数关系,获取了覆盖层的厚度分布,根据面波的频散特性,得出覆盖层的横波速度分布,获取了覆盖层的结构分布,结合得出的覆盖层结构和厚度分布,推断出测区内发育4条断层或溶沟等局部构造。研究表明,利用微动法提取的特征频率和面波的频散特性,可以有效地推断出塌陷区覆盖层的结构和厚度分布。      

从沉积速率和沉积物粒度看冰后期海侵以来珠江三角洲西江大鳌沙的形成

大鳌沙处于珠江三角洲西江河口的近口段,洪季西江河口的潮区界西线在其顶端附近。冰后期海侵以来,大鳌沙顶端的PRD05和中部的PRD04两个钻孔的沉积速率和沉积物粒度有着极大的差别。7 630 a BP以前,PRD04孔的沉积速率小于PRD05孔的沉积速率;但7 630 a BP以来,PRD04孔的沉积速率大于PRD05孔的沉积速率。从粒度分析看,埋深12.28 m以下,PRD04孔沉积物比PRD05孔的粗,分选性比PRD05孔的差;埋深12.28 m以上,PRD04孔的沉积物比PRD05孔的细,分选性相对比PRD05孔的好。分析表明,9 000～4 200a BP, 沉积物由南（中部）向北（顶部）输运,涨潮流冲蚀老沉积物,在喷出磨刀门通道后,流速迅速降低,粗颗粒泥沙先沉积,而细颗粒泥沙被涨潮流搬运至更北的区域沉积。近3500年以来,河流动力占优势,沉积物由北（顶部）向南（中部）输运。大鳌沙的形成与涨潮射流密切相关。涨潮射流口的位置在蛇地山和右岸纵向山地之间,宽约2200 m。     

珠三角沿海地区土壤硒的来源和富集成因初探

本文总结了珠三角沿海地区土壤硒含量的分布特征及其与成土母质的关系,探讨了该区域土壤中硒的来源及富集影响因素,提出珠三角地区土壤富硒是亚热带季风性气候湿热条件下花岗岩类强烈化学风化和富集改造的结果,土壤富硒作用的实质是杂质元素从成土母质中大量活化并分离移出,从而使硒元素发生相对富集的过程。本文对珠三角沿海地区土壤硒富集规律的总结显示该地区硒资源具有巨大潜力,具有广阔的开发富硒资源前景。     

Dissolved trace elements in river water: spatial distribution and the influencing factor, a study for the Pearl River Delta Economic Zone, China

Twenty-nine water samples were collected from different river channels of the Pearl River Delta Economic Zone, China. An inductively coupled plasma-mass spectromonitor (ICP-MS) was used to measure concentrations of the trace elements in these samples. The results suggest that the average concentrations of rare earth elements in river water show an increasing trend from the West River, the North River, the rivers of the Pearl River Delta, and the Shenzhen River to the East River. Relatively high concentrations of heavy metals appear in the East River, the rivers of the Pearl River Delta and the Shenzhen River, while the West River and the North River have relatively low heavy metal concentrations. Trace element concentrations in samples collected near urban or industrial areas are much higher than those of samples collected from distant areas, away from urban and industrial areas. After natural conditions, human activities have significant influence on the trace element concentrations in river water. This trace element concentration’s spatial distribution in the river water from the Pearl River Delta Economic Zone is actually an integrated effect of natural conditions and human activity.     

珠江三角洲中部大鳌平原晚第四纪古生物记录及环境演化

珠江三角洲是中国最主要的三角洲之一,人口密集,在未来极易受到海平面上升的影响,因此该地区的海平面变化研究尤为重要。有孔虫、介形类等微体动物是半咸水中最重要的生物类群,对海平面变化非常敏感,虽然已有许多涉及研究区微体化石的研究,但该地区微体化石定量分析还未开展,详细的古环境演化过程亦有待阐明。本文利用取自珠江三角洲中部大鳌子平原的5个钻孔的岩芯进行分析,对其中PRD05和PRD04钻孔进行详细的微体动物群定量分析和宏体动物群分析,结合各钻孔沉积学及磁化率特征及其他3个钻孔测年样品的微体、宏体动物群分析,讨论了珠江三角洲中部的环境演化过程。微体动物根据已有水深分布资料,划为两种类型分别代表近岸和远岸两种类型,借以讨论海平面变化。结果显示,珠江三角洲中部晚第四纪的古环境由钻孔中从下到上7个层位的划分体现为3个沉积阶段: 1)低地沉积阶段(14340cal.aB.P.前),包括基岩及其风化层(层位A),末次冰期前和期间的河流沉积环境(层位B); 2)全新世海侵阶段(14340~2860cal.aB.P.),包括障壁后沉积(层位C,14340~6480cal.aB.P.)和河口湾沉积(层位D,6480~2860cal.aB.P.); 3)高地沉积阶段(2860cal.aB.P.至今),包括砂坝环境(层位E,2860~230cal.aB.P.)和三角洲平原沉积(层位F,230cal.aB.P.至今)。其中全新世海侵阶段的河口湾沉积,主要由微体动物群特征反映了更高分辨率的环境演化,包括全新世伊始的快速海侵(D1亚层); 海侵速率降低(D2亚层); 海平面显著上升(D3亚层); 海平面范围最大(D4亚层),海平面最高(约5700cal.aB.P.); 海平面快速降低(D5亚层); 小规模海平面波动(D6亚层)。     

珠江三角洲环境地质控制性因素及问题分析

珠江三角洲经济区地处广东省中南部,濒临南海,海陆相互作用较强烈,新构造运动活跃,侵蚀和剥蚀作用明显,第四系广布,地貌类型多样,是地质环境的过渡带和敏感带,独具特色的区域地质环境必然产生相应的环境地质问题。本文基于现代调查并综合以往研究成果,从地形地貌、新构造运动、海平面变化、第四纪沉积的角度分析了控制珠三角城市群地质环境的重要因素,提出了对可持续城市化进程具有广泛影响的灾害性环境地质问题:地震灾害,软土区地面形变,岩溶塌陷,海岸异常变迁叠加海平面上升等问题。从地质环境的角度分析了这些问题的成因并提出了针对性的对策建议。