煤田物探数字技术讲座 第三讲 数字地震仪

地震仪的发展,经历了三代。第一代:光点地震仪。地震资料记录在照相纸上,不能进行回放和资料处理。第二代:模拟磁带地震仪。地震信息以波形方式记录在磁带上,可以在室内进行回放和资料处理。现在,发展到了第三代:数字地震仪。数字地震仪是数字化地震勘探装备的地震信息野外采集部件,它是数字化地震勘探的核心部分。     

微震台网在地质工作中的应用

微震是指1—3级范围的地震,微震台网则是一组用于记录小于3级地震的地震仪台站.视其需要研究的内容,台网可由几个至数十个台站组成,目前,全世界范围内大约有50余个永久性的微震台网和若干临时设置的流动微震台网在日夜不停地运转.     

青藏高原东部及邻区宽频地震观测初报

利用宽频带数字地震仪在川西高原、云贵高原西部开展了为期一年的地震观测,记录了许多地震波形数据,并对川青地块、川滇地块和华南地块上的5个台站的不同地震纪录进行了频谱试分析。     

慢地震幕式震颤与慢滑移:特征、成因与新进展

<正>普通地震是断层脆性形变破裂并快速释放能量的过程,而慢地震是一种能量释放缓慢的地震,其持续时间比地震矩类似的普通地震长得多,从几分钟到一周,甚至数月,常规的地震仪检波器很难记录到它们,随着数字观测技术的发展,地震仪器频带的增宽、     

MSP在淮南煤田刘庄区勘探中的应用和效果

在我国煤田地震勘探中,长期以来完全采用炸药震源。由于钻井设备笨重,农作物生长季节无法施工,因此,常常是半年工作半年闲。加之所用装备适应环境能力差,使地震勘探使用范围,受到得大程度的限制。为了扩大地震勘探使用范围,不久前,我们用 DFS-V 数字地震仪与 MSP(多源处     

浅层数字地震仪磁带记录格式及解编

一、引言据不完全统计,我国拥有引进的各种型号浅层数字地震仪约300台,地矿部系统占48台。为充分发挥这些设备的作用,数据处理是重要的环节。由于各种型号仪器有不同的磁记录和记录格式,给处理工作造成麻烦。表1为国内常见浅层数字地震仪磁记录器及记录格式。本文论述国内常见的浅层数字地震仪磁带记录格式及数据解编。     

关于数字检波器测定的理论

随着地震勘探技术化的发展,对地震勘探仪器的要求也越来越高。人们总是想尽各种办法去实现较为理想的技术指标,即不失掉任何信息(如由于不适宜的幅频特性响应引起某些有用频谱的遗失),也不增加任何东西(如由仪器的非线性畸变造成的多次谐波)。虽然要达到这些要求困难是很多的,但由于数字地震仪的出现,为实现近于比较理想化的地震勘探仪开拓了良好的前景,有些技术特性已达到比较高的指标。象一般数字地震仪动态范围在120分贝以上;通频带在3—256赫芝范围内;增益精度达0.05％;畸变小于0.05％……等。尽管这些技术指标已经比模拟磁带地震仪提高许多倍,但今后还     

龙门山断裂带WFSD数字地震台网监测能力及动态范围分析

5.12汶川特大地震后,为了监测地震的发展趋势,探讨大范围的构造应力场作用,在龙门山断裂带上及时布设临时数字地震台网。数字台网由11个数字地震台组成,遍布龙门山断裂带的北东缘和南西端。为了分析WFSD数字地震台网监测能力及其动态范围,随机抽取一定数量台站观测数据,通过傅立叶变换和功率谱密度分析,获得台基地动噪声均值,进而分析观测系统的动态范围和台网监测能力。根据计算结果与记录的大量微震对比研究,表明在龙门山断裂带上,WFSD数字地震台网具有监测M_L 1.5级微地震的能力,且与中国地震局台网中心发布的地震结果基本吻合。因此,WFSD数字地震台网可为龙门山断裂带变形机制研究提供基础的观测资料。      

福建数字地震台网与模拟台网记录的震相差异初析

本文通过对数字台网记录的地震震相和波形的分析,初步比较了模拟台网与数字台网记录波形,认为数字台网地震波震相具有高频成份表现突出,及初动清晰的特点,并对此作了进一步的探讨。     

SEG-D数字磁带格式及其解编

一、SEG-D磁带记录格式数字地震仪的SEG-D数字磁带记录格式是美国SEG协会的一种功能强、应用广泛的记录格式。该格式可以是有间隙的也或无间隙的。D格式的划分及其参数定义在它的总头段和扫描类型头段中,其全貌如图1所示。我队1986年从美国引进了ES-2420数字地震仪,该仪器的磁带记录采用了SEG-D格式。格式形式如图1。     

Seismicity of Victoria to 1980

Since 1976 a number of analogue and digital seismographs, which record high frequency seismic waves in the range 4 to 20 Hz, have been installed in Victoria. These enable the detection and location of microearthquakes with Richter magnitude Ml down to less than zero. Because there are many more smaller than larger earthquakes, about 250 events are now being located in Victoria each year, compared with about 25 per year between 1960 and 1975, and an average of two per year between 1840 and 1959. Despite an uneven statewide seismograph coverage, the new instruments and new lithospheric models have led to substantial improvements in earthquake location accuracy. All Victorian earthquakes with reliable depth determinations have been found to lie within the crust, most at a depth of less than 18 km. Some very small but shallow microearthquakes have been felt or heard. The isoseismal map for such an event (of magnitude Ml 1.3) which occurred at Preston during July 1976, is given.

The greater range of magnitudes now recorded permits more reliable estimates of seismicity. On average, the recurrence of earthquakes in Victoria is represented by: log₁₀ (P) = 0.92M_L —2.40, where P is the return period of an earthquake with magnitude greater than M_l in an area of 100 km square. It is suggested that attenuation of seismic wave amplitudes with distance is quite high in Victoria.     

Magnitude Formulae and Intensity–Magnitude Relations for Early Instrumental Earthquakes in the Iberian Region

The magnitudes of early instrumentally recorded earthquakes in the Iberian region (1912–1962) have been studied through processing of digitized seismograms of Wiechert seismograph and analysis of macroseismic information. A magnitude system based on instrumental registrations and macroseismic observations has been proposed. It consists of two compatible magnitude formulae depending on the total duration of seismic oscillations and on the maximum ground amplitude/period ratio of surface waves and includes correspondent intensity–magnitude relationships.     

DFS-Ⅴ型数字地震仪数字AGC的理论分析与探讨

数字AGC(自动增益控制)是数字地震仪中的关键部件之一。本文对DFS-V型数字地震仪中的数字AGC的基本理论进行了深入的理论探讨,建立了严格的工作流程图和工作方框图,对第一乘法器、第二乘法器、数字电平检测器、扩展和压缩发生器进行了深入的电路分析。最后结合主要的时序图,对DFS-V型数字AGC的整体工作过程进行了全面地评述。     

苏门答腊地震对柴达木地方震的触发作用

2004年12月26日印度尼西亚苏门答腊西北海域发生40年来最强烈的地震,造成巨大伤亡和财产损失.大地震在4000km外的柴达木盆地西部地区狮子沟地震台阵网上有长达1000多秒的明显记录,也触发柴西地区地方震的发震频率在大地震之后一天内提高了10倍.从大地震触发的地方震活动分布来看,触发地震的发震断裂是英雄岭南侧花土沟断裂和红柳泉断裂.     

微型检波一体化三分量地震仪及其应用

讨论了一种微型便携式地震仪的设计思路,该仪器具有本安防爆,重量轻、低功耗、高精度、高采样率等特点,内置三分量检波器,采集数据原位数字化且原位存储,能极大限度地抵抗外界干扰,提高采集信号的信噪比,实现了地震勘探检波一体化的理想采集条件。该仪器适用于恶劣环境条件下的高精度浅层多波勘探,如岩土体强度的原位测试、残余煤厚探测与工程检测等。通过实际应用证明该仪器应用范围广阔。     

高密度三维地震勘探在四川复杂山区应用效果

四川山区地形高差大、地层倾角陡、煤层薄、地质情况复杂,过去虽然经过多次探索和试验,地震勘探一直未获得成功。近年来,随着技术的发展、多道数字地震仪的引进、功能齐全的数字处理技术应用的基础上,成功地采用高密度三维地震勘探,获得了较好的地质成果,为矿井建设提供了可靠的地震地质资料。     

Richter magnitudes and site corrections using vertical component seismograms

The definition of the Richter Ml magnitude scale is in terms of seismic wave horizontal components recorded on Wood‐Anderson seismographs. However, at many seismograph sites only the vertical component is available, and at sedimentary sites horizontal components are usually significantly amplified, causing complications in the assignment of a magnitude to an earthquake. Because each earthquake can be recorded at a different subset of sites, each subset having a different combination of site amplifications, the assignment of a magnitude is dependent upon the seismograph site combination that records a particular earthquake. Although there is some amplification of the vertical component at sedimentary foundation sites, it is shown that a reduced spread of values of Ml magnitude, consistent with low amplification (bedrock) site magnitudes, can be achieved using the vertical component to compute the magnitude and adding 0.2 to adjust to the Ml magnitude scale (defined in terms of the horizontal components). This presupposes that the sites used by Richter were on bedrock; however, even if this is incorrect, it appears to be a necessary precondition for the world‐wide unification of the Richter scale along with defining the true gain of Wood‐Anderson seismographs rather than accepting the design gain of 2800. Site corrections would be smaller than those established using the horizontal components. Taking into account the use of only the vertical component in the calculation of Ml and including the 0.2 adjustment to the equivalent horizontal component derived magnitude, the expression for the calculation of magnitudes in the Victoria region becomes:

Ml = logA_z ‐ logS_z + 0.9 + logR + 0.0056Re^‐0.0013R

where A_z is the equivalent Wood‐Anderson seismograph displacement amplitude, S_z is the site amplification (vertical component) and R is the hypocentral distance.     

3-D seismic structure of the Kachchh,Gujarat, and its implications for the earthquake hazard mitigation

Several pieces of studies on the January 26, 2001, Bhuj earthquake (Mw 7.6) revealed that the mainshock was triggered on the hidden unmapped fault in the western part of Indian stable continental region that caused a huge loss in the entire Kachchh rift basin of Gujarat, India. Occurrences of infrequent earthquakes of Mw 7.6 due to existence of hidden and unmapped faults on the surface have become one of the key issues for geoscientific research, which need to be addressed for evolving plausible earthquake hazard mitigation model. In this study, we have carried out a detailed autopsy of the 2001 Bhuj earthquake source zone by applying three-dimensional (3-D) local earthquake tomography (LET) method to a completely new data set consisting of 576 local earthquakes recorded between November 2006 and April 2009 by a seismic network consisting of 22 numbers of three-component broadband digital seismograph stations. In the present study, a total of 7560 arrival times of P-wave (3820) and S-wave (3740) recorded at least 4 seismograph stations were inverted to assimilate 3-D P-wave velocity (Vp), S-wave velocity (Vs), and Poisson’s ratio (σ) structures beneath the 2001 Bhuj earthquake source zone for reliable interpretation of the imaged anomalies and its bearing on earthquake hazard of the region. The source zone is located near the triple junction formed by juxtapositions of three Indian, Arabian, and Iranian tectonic plates that might have facilitated the process of brittle failure at a depth of 25 km beneath the KRB, Gujarat, which caused a gigantic loss to both property and persons of the region. There may be several hidden seismogenic faults around the epicentral zone of the 2001 Bhuj earthquake in the area, which are detectable using 3-D tomography to minimize earthquake hazard for a region. We infer that the use of detailed 3-D seismic tomography may offer potential information on hidden and unmapped faults beneath the plate interior to unravel the genesis of such big damaging earthquakes. This study may help in evolving a comprehensive earthquake risk mitigation model for regions of analogous geotectonic settings, elsewhere in the world.     

Instrumentation for observation of induced seismicity

Instrumentation for observations of seismicity and ground acceleration near artificial reservoirs is evolving rapidly at the present time. Data recorded between 1936 and 1970, generally with only 1–3 seismograph stations, has established that the impounding of a large reservoir may lead to increased seismicity. Occasionally, shallow earthquakes in excess of magnitude 6 have occurred with resulting damage to surface structures and loss of life. Conditions leading to severe earthquakes have not been established but the pattern of enhanced seismicity as the reservoir level rises indicates that it is possible to predict when a dangerous level of earthquake rise is approaching. Increased use is now being made of larger arrays of detectors together with telemetry, storage of data on magnetic tape and even digital recording in the field. Future developments include complete digital recording of a broad range of instrumentation and detection and control of sampling rates by on-line micro-computers. As our instrumental sophistication increases and the relevant parameters for precursor activity are established it would appear that earthquake prediction near reservoirs is a possibility.     

Local tsunamigenic sources in Greece,identified by pattern recognition

Natural Hazards - The horizontal components of S-wave data from 25 events (Mw 2.9–4.2) recorded at five borehole seismograph sites in the Koyna–Warna seismic zone, Maharashtra, India,...