基于现代地震资料确定汾渭地震带分区及其地震活动性参数

汾渭地震带是我国东部一个强震活动带,其分段特征及地震活动趋势一直是研究热点,过去利用历史地震和地震地质资料,已得到许多有价值的结果.本文以第五代区划图中最新划分的汾渭地震带为研究区域,收集整理1970至2010年ML2.0～5.0级的现代地震资料,计算中小地震能量密度值,定量分析了该带中小地震空间分布图像特征,据此,确定了汾渭地震带的分区,并给出了各分区的地震活动性参数.对比分析表明,对汾渭地震带进行精细分区,可以更加真实地反映区域的地震活动水平,同一地震带的精细分区,可得到代表不同地震活动水平的地震活动性参数.同时,本研究也为地震带的精细划分提供了一种定量分析方法,对地震区划、工程场地地震安全性评价、地震活动中长期预测均有重要意义.     

东北地震区小震资料完整性分析及其对地震活动性参数的影响研究

以东北地震区为例,基于G-R关系的震级·频度分布原理,研究了东北地震区最小完整性震级MC的时间分布特征和各时段的空间分布特征,统计了研究区内的地震活动性参数,探讨了小震资料完整性分析对地震活动性参数和地震危险性计算结果的影响.研究表明,对区域小震资料进行完整性分析,可以在低水平地震活动地区获得较准确的地震活动性参数,更好地反映了该区未来的地震活动趋势.本文的研究方法和结论可供地震资料完整性分析和地震活动性分析时参考.     

利用远震接收函数揭示的喜马拉雅东构造结台阵下方地壳结构及其动力学意义

在喜马拉雅造山带的东缘,雅鲁藏布江缝合带在这里发生急剧转折,南迦巴瓦变质体快速隆起,然而关于东构造结的形成机制一直未有定论.利用围绕南迦巴瓦峰的48个宽频带地震台站记录的远震数据提取P波接收函数,采用改进的H-κ叠加方法和共转换点叠加方法综合研究了东构造结的地壳厚度、波速比分布和地壳结构特征.结果表明：研究区平均地壳厚度为64.03 km,大部分台站介于60.48~66.55 km范围;平均波速比为1.728,主要集中范围为1.696~1.742.东构造结地壳厚度横向变化剧烈,构造结西端和北端厚而中间薄,东构造结核部Moho面呈现上隆的构造形态,东西向上隆幅度约为6~7 km,南北向的上隆超过9~10 km.东构造结核部地壳上隆减薄可能由高密度、高波速的岩石圈撕裂残片拆沉到上地幔软流圈后重力失衡所致.平均波速比超过1.8的高值异常展布于东构造结的两侧,推测为环东构造结的壳内部分熔融体.东构造结地壳上隆减薄和壳内部分熔融的存在很可能均与幔源热物质的上涌有关,而软流圈地幔的上涌则可能由印度板片的撕裂引起.

     

Processing and preliminary interpretation of noisy high-resolution seismic reflection/refraction data across the active Ostler Fault zone,South Island,New Zealand

In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1–2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N–S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ～ 800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ～ 50° west-dipping primary fault plane.     

地震与测井数据综合预测裂缝发育带

章针对前新生代海相残留盆地碳酸盐岩裂缝识别这一难题提出一种利用地震与测井数据综合预测裂缝发育带的方法.用测井资料标识出裂缝发育层段,同时利用地震资料具有空间上数据点多、分布均匀的特点通过地震多属性的人工神经网络方法将测井与地震数据结合起来综合预测裂缝发育带,充分利用测井资料和地震资料的各自优势,达到在剖面上和区域上预测裂缝发育带的目的.本方法经过实际资料的处理与预测证实比常规方法预测精度高.     

Modulus defect,velocity dispersion and attenuation in partially-saturated reservoirs of Jurassic sandstone,Indus Basin,Pakistan

Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus defect and velocity dispersion in real seismic data. The main attenuation and dispersion phenomenon is wave induced fluid flow due to the heterogeneity in pore fluids or porous rock. The identification of pore fluid type, saturation and distribution pattern within the pore space is of great significance as several seismic and petrophysical properties of porous rocks are largely affected by fluid type, saturation and fluid distribution pattern. Based on Gassmann-Wood and Gassmann- Hill rock physics models modulus defect, velocity dispersion and attenuation in Jurassic siliclastic partially-saturated rocks are studied. For this purpose two saturation patterns - uniform and patchy - are considered within the pore spaces in two frequency regimes i.e., lower frequency and higher frequency. The results reveal that at low enough frequency where saturation of liquid and gas is uniform, the seismic velocity and bulk modulus are lower than at higher frequency where saturation of fluid mixture is in the form of patches. The velocity dispersion and attenuation is also modeled at different levels of gas saturation. It is found that the maximum attenuation and velocity dispersion is at low gas saturation. Therefore, the dispersion and attenuation can provide a potential way to predict gas saturation and can be used as a property to differentiate low from high gas saturation.     

基于大数据技术的地震数据处理新思路

现代地震观测积累了大量、种类繁多的地震前兆数据和震后数据,但数据中隐含的地震规律及趋势无法用经典的算例、数学公式、物理公式进行定量解释、分析和预测,需要探索新方法、新技术。案例表明,大数据分析具有预测事物发展趋势、改变传统观念和发现新事物的功能,有助于从错误信息中挖掘有价值信息。本文由此提出基于大数据技术处理地震数据的新思路,对地震监测预报新思路进行探索;通过在大数据平台上基于地震目录的余震预测研究,给出大数据技术在地震数据处理方面的一个应用实例,验证该思路的可行性。     

Investigation into regional thermal structure of the Thrace Region, NW Turkey, from aeromagnetic and borehole data

The aeromagnetic values over the study region are relatively uniform except for a few anomalies in the northeastern and southwestern areas. Analyses of aeromagnetic data were performed in NW Turkey, in order to have a look into the subsurface regional thermal structure of the region. For this purpose, power spectra, reduced to pole (RTP), and band-pass filtered anomalies were produced using geophysical techniques. Band-pass filtered data were produced from the RTP aeromagnetic anomalies to isolate near surface and undesired deep effects. Based on the aeromagnetic data interpretation, the thickness of the magnetized crust, named the Curie Point Depth (CPD), in the study area lies between 9.7 and 20.3 km. The CPD estimates in the Thrace region of Turkey indicate two shallow CPD (SCPD1 and SCPD2) zones (the Istranca Massif and the Saros Graben area). The deep CPD are located within the Thrace Basin with sediment thickness of about 9 km. The corresponding heat flow map prepared from the averaged thermal conductivities and thermal gradients from the CPD reveals the existence of one low heat flow zone (75 mW/m²) over the center of Thrace Basin, and two high heat flow zones over the Istranca Masif (100–125 mW/m²) in the northern side and Saros Graben (125–135 mW/m²) areas in the southern side of the Thrace Basin.     

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters. In process of data processing, we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such as filtering, edition surgical blanking, prediction deconvolution, fitting static correlation of first arrival time, and velocity analysis. Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75–80 m, in the Middle Pleistocene deposits dated to be about 220 ka BP. The continuity, discontinuity, increasing and decreasing amount of reflection wave groups and change of their configurations, in combination with geological columns of drills, permitted us to know that the width of upper termination of the fault zone is 100 m. It can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is 200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene. No tectonic movement, which offset the covering deposits, had occurred since the late stage of Middle Pleistocene. Foundation item: A High-new Technique Project by State Development and Planning Commission of China (2001977).     

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Introduction Artificial seismic sounding is a geophysical exploration technique developed in prospectingfor oil and gas and other mineral resources and consists of reflection wave and refraction waveexploration methods. With rapid development of computer techniques and sounding instruments,the reflection wave method became a high-resolution imagery technique for underground struc-tures and is widespreadly used in detection of underground caves and in engineering exploration.In previous se…     

Deep structure of the Racha earthquake source zone from seismic tomography data

The Racha earthquake of 1991 was the strongest of the earthquakes recorded in the Caucasus. It was studied by an international epicentral expedition. Unique data gathered by this expedition included records of aftershocks whose swarm was very intense. A 3-D velocity model is obtained from analysis of these data by the method of local earthquake tomography. The ancient crystalline basement and the sedimentary-volcanic Mesozoic-Cenozoic cover could be identified from cross sections of the P wave field. The eastern and western boundaries of an uplift in the basement of the Dzirulskii Massif are delineated. Linear low velocity heterogeneities correlating with the active Kakheti-Lechkhumi fault zone and two Trans-Caucasian linear fault zones are discovered in the basement. The cloud of aftershock hypocenters is shown to correlate with a reflector coinciding with the cover-basement interface.     

广义地震数据合成及其偏移成像

根据地震波场的线性叠加原理,提出了对地震共炮道集及其震源进行线性叠加的一般方案——广义地震数据合成的方法.利用这个方法,可以根据不同的地质情况和要求得到各种不同的人工合成地震数据道集和震源,如平面波数据道集和震源、局部平面波（束）数据道集和震源以及面向目标的人工合成地震数据道集和震源.对于人工合成地震数据道集的偏移成像可应用单平方根方程实现.不同的合成地震数据道集具有不同偏移成像特性：平面波数据道集具有很高的计算效率,局部平面波数据道集具有很好的方向性,面向目标的合成地震数据道集具有很好的面向目标特性.     

Characteristics of seismic wave attenuation in the Kishtwar and its adjoining region of NW Himalaya

Journal of Seismology - We investigate the attenuation characteristics of high frequency seismic waves in the Kishtwar and its adjoining region of NW Himalaya using 161 local earthquakes (M...     

Probabilistic seismic hazard analysis for the city of Quetta,Pakistan

Seismic hazard assessment for Quetta is carried out using probabilistic seismic hazard analysis technique based on area sources and augmented by line source used for the first time in Pakistan. Seismic data has been collected and analyzed in spatial and temporal domains. Five Seismic Zones have been modeled in line with tectonics of the region with b-value of 1.14 using regression. The b-value is slightly higher, which is attributed to the fact that aftershocks were not removed as it distorted the dataset. Five fault sources are modeled, with three as reverse and two as strike-slip with 7.8 as maximum magnitude. Mach Structure is included in the tectonics for the first time. The attenuation relation used in the present study is recommended by various researchers. The expected Peak Ground Acceleration for 500-year return period is 4.79 m/s² for rock outcrop and characterized as very high. Furthermore, variation in spectral acceleration within Quetta city is observed, for which spectral curves are developed for four different places.     

Monitoring of TDS and conductivity in groundwater in the seismically active region in NW Himalayas,India

<正>The earthquake precursors and earthquake prediction are the burning issue among the community of earth scientists and engineers. Studies of earthquake precursory phenomena since the last several decades have shown that significant geophysical and geochemical changes may occur prior to intermediate and large earthquakes (Hartmann and Levy, 2005; Yang et al, 2005;     

New insights into the age and formation of the Ankarokaroka lavaka and its associated sandy cover (NW Madagascar,Ankarafantsika natural reserve)

Lavaka represent a typical erosional landform in Madagascar. The chronology of their formation remains, however, under discussion. Our research focuses on the Ankarokaroka lavaka, a spectacular landform located in NW Madagascar (Ankarafantsika natural reserve), which is characterized by the presence of sandy units of regional extension at its top. The two main units correspond to white and red sands, and are closely associated with specific vegetations (dry dense forest for the white sands, savannah grasslands for the red sands). We applied a geochronological approach based on Optically Stimulated Luminescence (for the coversands) associated with radiocarbon dating performed on archaeological remains found at the contact between the sands and the lavaka. The combination of this approach with field work and sedimentological analyses makes it possible to show that the sands experienced a complex history, both in terms of sedimentation and post‐sedimentary pedogenesis (podzolization of the white sands, rubefaction of the red sands). The numerical ages furthermore indicate that the Ankarokaroka lavaka formed between 18.5 ± 2.3 ka ago and the 14th century AD. The present study demonstrates that this lavaka has a climatic origin, and highlights the potential of OSL to date sediments associated with Madagascar lavaka. Copyright © 2014 John Wiley & Sons, Ltd.     

地震数据正交投影分解方法的研究与应用

地震记录正交分解是值得研究的重要问题.本文将人工神经网络自组织学习算法引入到地震数据处理中,提出地震数据神经网络正交分解方法.在分解后的特征子空间中进行特征提取来消除相干和随机噪声,提高地震记录的信噪比.研究结果表明,这种实现方法是可行的,因特征滤波或数据压缩一般只需为数不多的主分量,本文的方法可根据滤波需要自适应提取所需主分量,可免去大量无用的计算,因此,本方法可降低滤波的计算成本,参与分解的道数越多效果越明显.最后,给出了对实际资料进行特征滤波的一个应用实例.     

南北地震带地区地震烈度衰减关系研究

收集了我国南北地震带地区1970年~2012年的85次地震事件的烈度等震线资料,建立了震中烈度与震级之间的经验关系,利用长轴和短轴椭圆模型拟合得到了该地区的地震烈度衰减关系。同时还搜集整理了近年来基于我国各地区的地震资料,研究得到的地震烈度衰减关系,并将其中与南北地震带存在地域重合的研究结果与本文结果进行对比分析。该研究结果能够较好地反映南北地震带地区的地震烈度衰减规律,对该地区的地震灾害快速评估具有一定的参考意义。     

New data on the structure of the Eastern Mediterranean basin from seismic reflection

The Avanavero Dolerite intruding the Guiana Shield in western Suriname is a quartz gabbroic mass yielding a Rb-Sr isochron age of 1603 ± 27 Ma, while the mass has invaded basement with a Rb-Sr isochron age of 1810 ± 40 Ma (λ = 1.47 × 10^?11/a; errors with 95% confidence level). From 61 K-Ar measurements on whole-rocks, sieve fractions of whole-rocks, density fractions and separated minerals it is evident that nearly all investigated samples, fractions and minerals (except microcline which suffered some argon loss) contain excess⁴⁰Ar. This excess⁴⁰Ar is very inhomogeneously distributed through the gabbroic mass. The bulk is stored in the plagioclase, in which mineral the excess⁴⁰Ar attains unusually high values ranging from about 14 × 10^?6 to around 150 × 10^?6cm³ NTP/g. The excess⁴⁰Ar contents of biotite, hornblende and the pyroxenes are comparable to published data.Two samples from a core drilling were studied in some detail. In graphs of radiogenic⁴⁰Ar versus K, four mineral separates from one sample display a fairly good, but geochronologically meaningless linear arrangement roughly passing through the origin. Most density fractions from the other sample show a tendency towards an array parallel to the 1603 Ma reference isochron.It is assumed that the excess⁴⁰Ar was acquired by the Avanavero Dolerite during a moderate tectonothermal event 1200 ± 100 Ma ago, when the⁴⁰Ar partial pressure was much higher in the environmental basement complexes than in the basic mass.