数字地震仪的发展历史及展望

地震仪经历了光点，模拟和数字的变化，数字地震仪本身由16位发展到24位，其附属设备（电缆，检波器）也是到了不同程度的发展。近年来，I／O等公司利用MEMS技术研制了新型地震检波器，这一新的发展对于地震采集尤其是多分量采集带来重要影响。     

涡流地震检波器的特性及测试方法的研究

本文介绍了涡流地震检波器的工作原理、结构及其频率响应特性--涡流检波器的输出特性在固有频率之上是按外界激励频率的平方递增。高频灵敏度随着激励频率的增加而增高有助于弥补高频信号通过地层传播时的急剧衰减,从而提高了地震勘探的分辨率。在固有频率之下,则加强了低频滤波作用。 本文还以对单自由度线性振动系统的动态分析为基础,研究了利用实验幅频特性曲线来求该系统的固有频率和阻尼系数的方法,推导出必要的计算公式。最后举出一个应用实例,并检验了这种方法的可信度。     

用于微动探测的低成本自存储式数字地震检波器

微动探测是利用地球表面的天然震动信号进行探测的被动源探测方法.相对于传统的物探方法,微动探测野外施工灵活,阵列形状多样,受施工场地限制小,对施工环境影响小.目前进行微动探测所用的地震检波器大多成本较高、重量和体积大,不便于运输与大规模布设.本文由微动探测方法的特点出发,优化改造了自行研发的低成本自存储式数字地震检波器,使其性能满足微动探测的需要.通过对地震计系统噪声的详细分析、微动探测原理的讨论,结合现场试验数据,探讨了该检波器应用于大规模微动探测的可行性.     

Surface and downhole shear wave seismic methods for thick soil site investigations

Shear wave velocity–depth information is required for predicting the ground motion response to earthquakes in areas where significant soil cover exists over firm bedrock. Rather than estimating this critical parameter, it can be reliably measured using a suite of surface (non-invasive) and downhole (invasive) seismic methods. Shear wave velocities from surface measurements can be obtained using SH refraction techniques. Array lengths as large as 1000 m and depth of penetration to 250 m have been achieved in some areas. High resolution shear wave reflection techniques utilizing the common midpoint method can delineate the overburden-bedrock surface as well as reflecting boundaries within the overburden. Reflection data can also be used to obtain direct estimates of fundamental site periods from shear wave reflections without the requirement of measuring average shear wave velocity and total thickness of unconsolidated overburden above the bedrock surface. Accurate measurements of vertical shear wave velocities can be obtained using a seismic cone penetrometer in soft sediments, or with a well-locked geophone array in a borehole. Examples from thick soil sites in Canada demonstrate the type of shear wave velocity information that can be obtained with these geophysical techniques, and show how these data can be used to provide a first look at predicted ground motion response for thick soil sites.     

Geophone‐ground coupling with flat bases

Seismic acquisition can be costly and inefficient when using spiked geophones. In most cases, such as the desert, the most practical solution is the use of flat bases, where geophone‐ground coupling is based on an optimal choice of the mass and area of contact between the receiver and the ground. This optimization is necessary since areas covered by sand are loose sediments and poor coupling occurs. Other cases include ground coupling in stiff pavements, for instance urban areas and ocean‐bottom nodes. We consider three different approaches to analyse coupling and model the geophone with a flat base (plate) resting on an elastic half‐space. Two existing models, based on the full‐wave theory, which we refer to as the Wolf and Hoover‐O'Brien models, predict a different behaviour with respect to the novel method introduced in this work. This method is based on the transmission coefficient of upgoing waves impinging in the geophone‐ground contact, where the ground is described as an anelastic half‐space. The boundary conditions at the contact have already been used to model fractures and are shown here to provide the equation of the damped oscillator. This fracture‐contact model depends on the stiffness characteristic of the contact between the geophone base plate and the ground. The transmission coefficient from the ground to the plate increases for increasing weight and decreasing base plate area. The new model predicts that the resonant frequency is independent of the geophone weight and plate radius, while the recorded energy increases with increasing weight and decreasing base plate area (as shown from our own experiments and measurements by Krohn) which is contrary to the theories developed by Wolf and Hoover‐O'Brien. The transient response is obtained by an inverse Fourier transform. Optimal geophone‐ground coupling and energy transmission are required, the first concept meaning that the geophone is following the motion of the ground and the second one that the signal is detectable. As a final example, we simulate seismic acquisition based on the novel theory, showing the differences between optimal and poor ground‐to‐geophone energy transmission.     

地震检波器的横向灵敏度特性

地震检波器受到地面横向运动激励时的输入输出关系定义为检波器的横向灵敏度特性.本文对检波器线圈受到横向激励时产生的轴向振动进行了分析.可以看到,当悬挂线圈的弹簧片悬丝发生动力失稳时,检波器的横向灵敏度突然增大;在线圈横向振幅很小的情况下,失稳频率接近悬丝的横向固有频率.利用谱分析技术可以准确地从检波器噪声中检测出检波器的横向灵敏度和失稳频率,即检波器假频.     

Research on the middle-of-receiver-spread assumption of the MASW method

The multichannel analysis of surface wave (MASW) method has been effectively used to determine near-surface shear- (S-) wave velocity. Estimating the S-wave velocity profile from Rayleigh-wave measurements is straightforward. A three-step process is required to obtain S-wave velocity profiles: acquisition of a multiple number of multichannel records along a linear survey line by use of the roll-along mode, extraction of dispersion curves of Rayleigh waves, and inversion of dispersion curves for an S-wave velocity profile for each shot gather. A pseudo-2D S-wave velocity section can be generated by aligning 1D S-wave velocity models. In this process, it is very important to understand where the inverted 1D S-wave velocity profile should be located: the midpoint of each spread (a middle-of-receiver-spread assumption) or somewhere between the source and the last receiver. In other words, the extracted dispersion curve is determined by the geophysical structure within the geophone spread or strongly affected by the source geophysical structure. In this paper, dispersion curves of synthetic datasets and a real-world example are calculated by fixing the receiver spread and changing the source location. Results demonstrate that the dispersion curves are mainly determined by structures within a receiver spread.     

灰岩裸露区检波器三自由度耦合系统理论的研究

中国南方海相碳酸盐岩沉积盆地的分布幅员辽阔,地下油气等资源极为丰富,但是由于大面积坚硬灰岩的出露,给检波器完好耦合带来了很大困难,从而降低了地震采集资料的品质,严重制约了该地区未来的油气勘探.目前野外检波器耦合试验缺乏较为合适的理论指导,带有较大的盲目性.为此,本文考虑到检波器与灰岩耦合时增加了耦合介质（石膏、泥饼等）的实际情况,提出了检波器-灰岩三自由度耦合系统的理论,研究了耦合介质、尾锥和阻尼等耦合因素对检波器-灰岩耦合系统传输函数的影响规律.发现检波器-灰岩耦合系统是具有三个谐振频率的谐振系统,通过增加耦合介质的弹性模量、减小耦合介质的底面积和高度、选用介质密度较小的尾锥、减小尾锥的高度、增加尾锥的底面积等,可以提高耦合谐振频率.通过适当增加耦合系统的阻尼,可以减小耦合系统的窄频带“带通滤波”的影响.最后,通过振动台实验初步验证了检波器-灰岩三自由度耦合系统理论模型.     

固体液体分界面处P波和S波波场的分离

在地震勘探中,Ｐ波和Ｓ波入射到一固体液体分界面处时,在该分界处的水平检波器和垂直检波器将接受到相位的响应垂直的响应。垂直检波器的响应与在自由界面处的垂直检波器 响应大概相同,而水平检波器对Ｐ波的响应相对于对Ｓ波的 来说要强。     

Application of an impact plate – Bedload transport measuring system for high-speed flows

To achieve the sustainable use of dams, the development of methods for sediment management in reservoirs is required. One such method includes the use of Sediment Bypass Tunnels (SBTs) to divert sediment around a dam, thereby preventing sedimentation in the reservoir. However, SBTs are prone to severe invert abrasion caused by the high sediment flux. Therefore, it is necessary to establish a measurement system of the sediment transport rate in these tunnels. One system to measure sediment transport in rivers is the Swiss plate geophone, which can register plate vibrations caused by particle impact. In Japan, the Japanese pipe microphone is used, and sediment transport is measured based on the sound emitted by the particle impact. In this study an attempt was made to optimize the advantages of both systems by fixing a microphone and an acceleration sensor to a steel plate. The results of calibration experiments with this new system are presented and compared with the existing methods. It was found that the acceleration sensor can detect sediment particles larger than 2 mm in diameter. Moreover, a new parameter, referred to as the detection rate, was introduced to describe the correlation between the actual amount of sediment and the registered output. Finally, two parameters - the saturation rate and hit rate - are introduced and exhibit strong correlation with the detection rate.