高性能水下地震数据采集系统设计与实现

针对高分辨海上石油勘探中的水下地震信号的特点和采集要求,采用Σ-Δ结构ADC和数字抽取滤波器设计了高性能、高可靠性的水下拖缆数据采集系统。FPGA逻辑实现了对分布式数据采集的实时控制和流水线结构的远距离数据传输。

水下节点地震仪在陆地主动源探测中的应用

主动源激发的精确时刻非常重要,为了获取更加精确的激发时刻,我们通过在刘家峡主动源调试安装水下节点地震仪观测系统,记录激发数据。实验证明,该水下节点地震仪观测系统能够清晰记录到气枪震源激发信号。同时对平静时观测数据进行背景噪声分析,噪声功率谱密度低于NHNM噪声曲线,各分项背景噪声值小于-120 dB,与岸边架设仪器背景噪声进行比较,水下地震仪记录噪声略高于岸边陆地地震仪噪声,这可能与水浪、风以及船舶航行等有关。对激发数据进行频谱分析,优势频率在2~8 Hz范围内,与前人研究结果一致,可以作为刘家峡主动源激发信号记录的参考台之一。水下节点地震仪在陆地主动源探测中的应用,将对提高气枪主动源观测精度以及气枪主动源地震监测系统建设和数据处理有一定的价值。

Study on the Rainfall and Aftershock Threshold for Debris Flow of Post-earthquake

Due to the special condition of provenance and disaster environment after "5·12" Earthquake, the probability and conditions of the occurrence of gully debris flow change greatly after the event, which make it difficult to prevent disaster effectively. In this study the hydrological model of ground water table in loose sediment is established. According to infinite slope theory, the safety factor of deposits is defined as the ratio of resistance force to driving force. The starting condition of post-earthquake gully debris flow is clearly studied by analyzing the effects of rainfall intensity, seismic strength, slope gradient and mechanical properties on the balance of accumulation body. Then the formulas of rainfall and aftershock threshold for starting of gully debris flow are proposed, and an example is given to illustrate the effect of rainfall, aftershocks and their coupling action on a debris flow. The result shows the critical rainfall intensity decreases as the lateral seismic acceleration and channel gradient increases, while the critical intensity linearly increases as the friction angle increases.

Some Problems Related to the Construction of Groundwater Wells for Earthquake Monitoring

This paper discusses technical requirements for location selection,structure design,and drilling of groundwater monitoring wells for earthquake studies on the bases of national and earthquake-prediction specific technical standards as well as practical experience from construction of such wells.

Co-seismic Water Level and Temperature Responses of Some Wells to Far-Field Strong Earthquakes and Their Mechanisms

The observation of water temperature in deep wells has been carried out for more than 20 years in China.However,study on the mechanism of water temperature response to earthquakes is inadequate.During the study of the co-seismic response characteristics of water level and temperature in 121 wells within the China subsurface fluid monitoring network at the time of the December 26,2004,M-S8.7 Indonesia earthquake,we found regular response characteristics,that is,when the water level in a deep well oscillates,the water temperature in the same well will mostly experience a cycle from dropping to restoration at the same time.The process will continue for dozens of minutes to several hours.In order to confirm the observed phenomenon,we collected the digital water level and temperature observation data for 39 far-field strong earthquakes from the Tangshan well in Hebei Province(with the data set beginning in 2001).The same response characteristics were observed.Based on the analysis of the influencing factors that may cause the water temperature drop,the authors suggest the gas escape mechanism for co-seismic water temperature drop and posit two main factors that influence the water temperature drop during the process of gas escape.Finally,the authors provide a rational explanation of some observed phenomena based on the mechanism.

Characteristics and Mechanisms of Co-seismic Groundwater Responses in Tayuan Well

Co-seismic responses of the groundwater level and temperature in the Tayuan well of 68 earthquakes （Ms ≥ 7.0） from January 2004 to September 2007 were analyzed. Results show that the Tayuan well has a strong ability to record large earthquakes worldwide, and the coseismic response shows a pattern of water level oscillation →temperature decrease→ oscillation stop → temperature resumption. Further analyses indicate that the amplitude of the water level and temperature change is not ouly concerned with the epicenter distance and magnitude, but is also related to the temporal state of aquifer while the seismic wave arrives. Mechanisms of water level oscillation, temperature decrease, water level oscillation stop and temperature resumption are discussed, with the results from previous research on the co-seismic response mechanisms analyzed. These include gas escape, heat diffusion and cold water seepage. Results show that a single mechanism could not explain the co-seismic response of the Tayuan well water level to multiple earthquakes; the results were garnered from a variety of jointly acting mechanisms.

Application Study on Correction Method for Lag of Water Level Response to Earth Tide and Atmospheric Pressure

The water level in a deep well instantly responds to the earth’s tide and atmospheric pressure, and varies accordingly, not only in terms of amplitude but also in the phase lag. Therefore, phase lag correction is used in analyzing digital groundwater observation data in eastern China. Calculation results presented by the authors in this paper show that the correction method is effective in the identification of anomalous changes for short-term seismic precursors. The correction method can also be applied to the processing of observed deformation and tilt data.

Rainfall and Obtaining Information Regarding Earthquake Development Processes from Groundwater Level

Many factors can cause changes of groundwater level,such as the development process of an earthquake,rainfall,solid earth tides etc.Among these we are interested in information regarding earthquake development processes.Eliminating the influence of various disturbance factors is an effective way to obtain seismic development process information contained in the groundwater level.This paper provides two different ways to remove the rainfall effect,and compares the two methods by means of correlation analysis.Furthermore,based on these a logistic regression model is established to describe the seismicity level.

Study on Critical Slowing Down Phenomenon before the Two Medium-strong Earthquakes in Xinjiang

We study the critical slowing down phenomenon in deformation and groundwater observations before the Nilka-Gongliu MS6. 0 earthquake on November 1, 2011 and Xinyuan-Hejing M S6. 6 earthquake on June 30,2012. Firstly,we remove the annual variation and tendency change of basic data by means of wavelet transform analysis.Secondly,we calculate the autocorrelation coefficients and variance of the critical slowing down phenomenon. Lastly,we try to verify the critical slowing down phenomenon before an earthquake. The result indicates that there was obvious critical slowing down of the records at different stations before earthquakes.

The Jinsha River Groundwater Observation Network and Discussion about Its Earthquake Precursor Monitoring Capability

A groundwater observational network for monitoring seismic precursors has been established at the reservoirs on the lower reaches of the Jinsha River in southwestern China, where a series of hydropower stations are under construction. It is the second network in China that is operated by enterprises with the purpose to observe and study earthquake precursors in reservoir areas. This paper presents the layout and technical constitution of the network, features of its observational wells and aquifers and the preliminary result of its experimental operation. Its capability to monitor seismic precursor is evaluated based on an analysis of the well-aquifer system as well as the multiple-monthly, monthly, daily and hourly variations of water levels and water temperatures observed by this network.

Groundwater Dating and Its Application to Earthquake Monitoring

Monitoring and study of dynamic characteristics of groundwater are significant methods of earthquake monitoring and forecasting. For research on groundwater dynamics,groundwater dating can qualitatively and quantitatively provide scientific analysis on the characteristics of groundwater recharge and runoff as well as renewal capacity. This article illustrates the methods used globally and summarizes the main advances and achievements in groundwater dating. It also focuses on the relationships between groundwater renewal capacity and seismic monitoring,groundwater movement and seismic activity,shallow groundwater recharge and abnormal interference elimination. The studies show that groundwater dating plays an important role in water-rock interaction,and geological tectonic and seismic activity evaluation. Therefore,groundwater dating can be widely used to monitor and analyze the precursor information in seismic underground fluid observations in the near future.

地震和波流作用下海底悬跨管线模型实验研究

利用水下地震-波流联合模拟实验系统研究了海底管线在波浪、水流和地震作用下的动态响应特征。实验中考虑了有无地震作用、悬跨长度、波浪高度、水深、水流速度以及是否满管状态等因素。通过DDP动态数据后处理软件对实验结果进行处理分析,得到海底悬跨管道的动态响应特性。实验结果表明:在浅海海域,悬跨管线的动态反应受波浪及水深变化的影响不明显,悬跨长度是影响管道动态响应的主要影响因素;悬跨管线在地震与波流共同作用下的反应与仅地震作用下的应变存在差别;在波浪力作用下,空管时管线的应变要小于满管时的情况。

Research and Practice on the Crustal Deformation Mobile Monitoring Network Layout in the Hydropower Station Reservoir Area

According to the construction project of the crustal deformation mobile monitoring network in the cascade hydropower stations built in the lower reaches of Jinsha River,this paper analyzes the design ideas and layout principles of crustal deformation mobile monitoring used in the monitoring of reservoir induced earthquakes. This paper introduces three types of monitoring networks used in the Xiluodu reservoir and Xiangjiaba reservoir, as well as the work already undertaken,in order to provide a kind of reference for the related engineering construction and comprehensive monitoring of reservoir induced earthquakes.

Removing barometric pressure effects from groundwater level and identifying main influential constituents

Changes in barometric pressure can affect the micro-dynamic state of groundwater level.The groundwater level data carry a lot of important information of tectonic activity and earthquakes.It is very significant to eliminate the barometric pressure effects from the groundwater level data in order to recognize seismic anomalies effectively.With the analysis of the main influential constituents of barometric pressure and their changes,we can have a better understanding of the changes of the aquifer medium,which can provide useful information for earthquake prediction.Taking the May 12,2008 Wenchuan earthquake as an example,this paper deals with the influence of barometric pressure on groundwater level based on observational data from Nanxi,Qionglai and Chaohu wells.The methods of the linear regression and the deconvolution regression were employed to remove the barometric pressure from the groundwater level data.The harmonic analysis and the spectral analysis were used to recognize the main influential waves of barometric pressure effect.A comparison was conducted on the main influential waves before and after the earthquake.The results showed that the main influential waves of barometric pressure effect changed and the amplitudes of all constituents also changed.This phenomenon may result from the characteristics of the influential constituents of pressure,or from the changes of the aquifer medium,which were caused by the earthquake.

Relationship between the Earth tidal factor and phase lag of groundwater levels in confined aquifers and the Wenchuan M_s8.0 earthquake of 2008

This work focuses on variations of the Earth tidal factor and phase lag derived from groundwater observations before and after major earthquakes.It is based on an analysis of the data from four observational wells at boundaries between distinct active blocks of China mainland.These wells are also situated on several active fault zones and have exhibited considerable responses to the Wenchuan Ms8.0 earthquake of 2008 in China.We collected hourly records of water levels of these wells from 2007to 2009 and processed these data for analysis.The tidal factors,phase lags,and phase-difference changes of tidal residuals of each well were calculated.We found that when the Wenchuan quake happened,the tidal factors of the 4 wells were changing rapidly,while their phase lags and phase differences of tidal residuals declined swiftly,which may reflect the stress and strain changes of the well-aquifer system during the seismic generation.