共查询到20条相似文献，搜索用时 453 毫秒
1.
The time-frequency analysis and anomaly detection of wavelet transformation make the method irresistibly advantageous in non-stable
signal processing. In the paper, the two characteristics are analyzed and demonstrated with synthetic signal. By applying
wavelet transformation to deformation data processing, we find that about 4 months before strong earthquakes, several deformation
stations near the epicenter received at the same time the abnormal signal with the same frequency and the period from several
days to more than ten days. The GPS observation stations near the epicenter all received the abnormal signal whose period
is from 3 months to half a year. These abnormal signals are possibly earthquake precursors.
Foundation item: Joint Seismological Science Foundation of China (604021) and National Natural Science Foundation of China (40074024). 相似文献
2.
Three-dimensional coherent cube is an extremely effective new technique for interpreting seismic data. It has obvious advantages in many aspects compared with the conventional 3D data volume, such as recognizing faults and fractures, interpreting ancient channels, and edge detection of oil-gas reservoir. Coherent cube is to condense and extract information around a certain point in 3D data volume, and then highlight the original characteristics of the geologic body at this point. Therefore, in terms of its essence, coherent cube is a special seismic attribute cube and those points having rather small coherent value are related to the discontinuity of geologic body. In practical production, people often interpret horizontal slices or layer slices of coherent cube, and this provides advantageous foundations for resolving special problems in oil-gas exploration. 相似文献
3.
Due to the particularity of the seismic data, they must be treated by lossless compression algorithm in some cases. In the
paper, based on the integer wavelet transform, the lossless compression algorithm is studied. Comparing with the traditional
algorithm, it can better improve the compression rate. CDF (2, n) biorthogonal wavelet family can lead to better compression ratio than other CDF family, SWE and CRF, which is owe to its
capability in canceling data redundancies and focusing data characteristics. CDF (2, n) family is suitable as the wavelet function of the lossless compression seismic data.
Contribution No.04FE1019, Institute of Geophysics, China Earthquake Administration. 相似文献
4.
We tried to apply the dual-tree complex wavelet packet transform in seismic signal analysis. The complex wavelet packet transform
(CWPT) combine the merits of real wavelet packet transform with that of complex continuous wavelet transform (CCWT). It can
not only pick up the phase information of signal, but also produce better “focalizing” function if it matches the phase spectrum
of signals analyzed. We here described the dual-tree CWPT algorithm, and gave the examples of simulation and actual seismic
signals analysis. As shown by our results, the dual-tree CWPT is a very effective method in analyzing seismic signals with
non-linear phase.
Foundation item: Cultural Heritage Protection Program of State Administration of Cultural Heritage (200001). 相似文献
5.
A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows
Abstract A wavelet-neural network (WNN) hybrid modelling approach for monthly river flow estimation and prediction is developed. This approach integrates discrete wavelet multi-resolution decomposition and a back-propagation (BP) feed-forward multilayer perceptron (FFML) artificial neural network (ANN). The Levenberg-Marquardt (LM) algorithm and the Bayesian regularization (BR) algorithm were employed to perform the network modelling. Monthly flow data from three gauges in the Weihe River in China were used for network training and testing for 48-month-ahead prediction. The comparison of results of the WNN hybrid model with those of the single ANN model show that the former is able to significantly increase the prediction accuracy. Editor D. Koutsoyiannis; Associate editor H. Aksoy Citation Wei, S., Yang, H., Song, J.X., Abbaspour, K., and Xu, Z.X., 2013. A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows. Hydrological Sciences Journal, 58 (2), 374–389. 相似文献
6.
Karem Chokmani Kristell Dever Monique Bernier Yves Gauthier Lisa-Marie Paquet 《水文科学杂志》2013,58(4):649-660
Abstract The snow mapping algorithm SNOWMAP was adapted to Landsat-TM data and to the context of eastern Canada. Six Landsat-5 TM scenes were used. It was found that the original version of SNOWMAP greatly underestimates snow cover extent. The modification made to the original algorithm, by cancelling the minimum threshold of 0.1 on the NDVI value, allows gaps to be filled in. In addition, a spatial correction procedure applied to the modified SNOWMAP algorithm results improves snow detection under coniferous forests. Based on a limited data set of ground-based observations (only 40 sites were available), the modified SNOWMAP seems to perform better in snow detection than the original version of the algorithm. An application case is presented in order to demonstrate the relevance of the modified SNOWMAP results as a high spatial-resolution reference for the validation of historical snow maps derived from medium spatial-resolution satellite data. Citation Chokmani, K., Dever, K., Bernier, M., Gauthier, Y. & Paquet, L.-M. (2010) Adaptation of the SNOWMAP algorithm for snow mapping over eastern Canada using Landsat-TM imagery. Hydrol. Sci. J. 55(4), 649–660. 相似文献
7.
地面磁共振是一种新的地球物理探测方法,能够通过探测地下水中氢质子丰度获取地下水含量、孔隙度等水文地质信息.然而,磁共振信号甚为微弱,仅达到纳伏级(10~(-9)V),极易受到噪声干扰.其中,尖峰噪声对磁共振信号影响最为严重,亟待研究有效的噪声抑制方法.小波多尺度分解硬阈值是近两年国际磁共振领域专家提出的尖峰噪声有效消除方法,但硬阈值算法设定阈值的固有缺陷会引发信号震荡,出现伪吉布斯效应,导致信号损失.基于此,本文提出压缩小波变换(Synchrosqueezing Wavelet Transform,SWT)和非线性國值处理(Nonlinear Thresholding,NT)算法联合消除磁共振信号尖峰噪声干扰.首先选择Morlet小波作为基小波,使得信号与噪声数据具有更高的时频集中性,利于尖峰噪声消除.其次,基于压缩小波系数进行非线性处理,可以弥补利用硬阈值和软阈值进行噪声消除时所引起的信号损失.仿真数据和实际数据结果表明,SWT联合NT方法可以利用单次采集数据有效消除尖峰噪声干扰并还原信号.本文提出的消噪方法将为磁共振数据后续反演解释,如多指数弛豫反演,奠定坚实的基础. 相似文献
8.
The research on relationship between wavelet transform on vertical deformation and moderate earthquakes in hexi region, Gansu Province 总被引：1，自引：0，他引：1
ＴｈｅｒｅｓｅａｒｃｈｏｎｒｅｌａｔｉｏｎｓｈｉｐｂｅｔｗｅｅｎｗａｖｅｌｅｔｔｒａｎｓｆｏｒｍｏｎｖｅｒｔｉｃａｌｄｅｆｏｒｍａｔｉｏｎａｎｄｍｏｄｅｒａｔｅｅａｒｔｈｑｕａｋｅｓｉｎＨｅｘｉｒｅｇｉｏｎ,ＧａｎｓｕＰｒｏｖｉｎｃｅＹＯＮＧ－ＺＨ... 相似文献
9.
Abstract This study applies the discrete wavelet transform (DWT) to decompose the unit hydrograph, thereby generating parsimonious reparameterizations of the unit hydrograph. A model compression method is then employed to significantly compress the unit hydrograph requiring that fewer coefficients be estimated. Moreover, a wavelet-based linearly constrained least mean squares (WLCLMS) algorithm is also used to estimate on-line the wavelet coefficients of the unit hydrograph. The updated wavelet coefficients of the unit hydrograph, convoluted with effective rainfall input in the wavelet domain, allow for accurate prediction of one-step-ahead runoff in the time domain. The proposed approach allows the unit hydrographs to vary in time and accurately predicts runoff from a basin in Taiwan, thus making it highly promising for flood forecasting. 相似文献
10.
Based on the results from seismogeological study,aeromagnetic inversion and deepseismic sounding(DSS),it is found that the M≥8.0 earthquakes in North China have three common deep structural characteristics,i.e,they all took place above the ultra-crustal deep faults or on the edges of the tectonic blocks with higher intensity,and there are low-velocity,low-density and high-conductive layers deep in the epicentral regions.The origins of the earth-quakes are also discussed and the two possibilities of seismogenesis are proposed,i.e,tectonic movement and intracrustal explosion. 相似文献
11.
In the moment-ratio imaging algorithm, which is based on the theory of healing of a wound, the energy of each strong earthquake is distributed around the epicenter according to certain rules, and the features of the Moment-ratio value R are analyzed as the space and time change, so that the relationships between the moment-ration value R and strong earthquakes can be found. In the present paper, regions divided, hypocenter depths and events completed magnitude analyses were carried out in the Chinese catalogue. By applying the moment-ratio imaging algorithm in which the parameters are adjusted, the processes of anomaly evolution which correspond to the epicenter and the surrounding value R before earthquakes of M≥7.0 since 1966 in different areas of China were analyzed. It was found that the range area and imminent time of a coming earthquake could be confirmed quantita- tively by analyzing the abnormal temporal and spatial variation of the value R The results showed that the temporal and spatial variation of the value R could quantitatively reflect the temporal and spatial factors of a coming strong earthquake as well as the rule of medium rupture. 相似文献
12.
ABSTRACTIn this study, a data-driven streamflow forecasting model is developed, in which appropriate model inputs are selected using a binary genetic algorithm (GA). The process involves using a combination of a GA input selection method and two adaptive neuro-fuzzy inference systems (ANFIS): subtractive (Sub)-ANFIS and fuzzy C-means (FCM)-ANFIS. Moreover, the application of wavelet transforms coupled with these models is tested. Long-term data for the Lighvan and Ajichai basins in Iran are used to develop the models. The results indicate considerable improvements when GA selection and wavelet methods are used in both models. For example, the Nash-Sutcliffe efficiency (NSE) coefficient for Lighvan using FCM-ANFIS is 0.74. However, when GA selection is applied, the NSE is improved to 0.85. Moreover, when the wavelet method is added, the performance of new hybrid models shows noticeable enhancements. The NSE value of wavelet-FCM-ANFIS is improved to 0.97 for Lighvan basin.
Editor D. Koutsoyiannis Associate editor E. Toth 相似文献
13.
In order to understand the site soil response of the Xiangtang borehole seismic array under real strong ground motion, reveal the site response, verify the technique of borehole exploration, and improve the precision of in-situ test and laboratory test, this paper presents a new approach, which is composed of two methods. One is the layered site seismic response method, whose layer transform matrix is always real. The other is a global-local optimization technique, which uses genetic algorithm (GA)-simplex method. An inversion of multi-component waveforms of P, SV and SH wave is carried out simultaneously. By inverting the records of three moderate and small earthquakes obtained from the Xiangtang borehole array (2# ) site, the soil dynamic characteristic parameters, including P velocity, damping ratio and frequency-dependent coefficient b, which has not been given in previous literatures, are calculated. The results show that the soil S wave velocity of the Xiangtang 2# borehole is generally greater than that obtained from the 1994 in-situ test, and is close to the velocity of the 3# borehole, which is more than 200 m away from the 2# borehole. Meanwhile, perceptible soil nonlinear behavior under peak ground motion of about 60×10-2m/s2 is detected by the inversion analysis. The presented method can be used for studying the soil response of other borehole array sites. 相似文献
14.
Coseismic stress-triggering is becoming a new hot spot of research. Coseismic strain steps recorded by borehole strainmeters are particularly valuable in studying coseismic stress-triggered fault slips. Based on the theory of dis location, one can invert the triggered fault slips with such data if he/she has a well understanding about the local faults. Genetic algorithm can be applied to significantly raise the efficiency of searching a best solution among all possibilities in this kind of inversion. A testifying check of the program and analyses of each parameter＇s influence may further enhance the reliability of inversion results. Taking complexity of geological structure into account, the inversion results should be regarded as the predominant property or a comprehensive effect of triggered local faults＇ activities. As an attempt, we inverted the assumingly active faults＇ slips triggered by the Ms=8.1 Kunlun Mountain earthquake over Beijing area. 相似文献
15.
In this study, we collected 1 156 broadband vertical components records at 22 digital seismic stations in Xinjiang region,
ürümqi station, and 7 stations in the adjacent regions during the period of 1999–2003. The records were firstly processed
by the stacked spectral ratio method to obtain Q
0 (Q at 1 Hz) and the frequency correlation factor η corresponding to each path. Based on the results, the distribution images
of Q
0 and η in 1°×1° grids for Xinjiang region were gained by the back-projection technique. The results indicate that Q
0 is high (300–450) in the Tarim platform and marginal Siberian platform, while Q
0 is low (150–250) in the southern regions as west Kunlun fold system and Songpan-Ganzi fold system. In the northern regions
as Junggar fold system and Tianshan fold system, Q
0 is also low (250–300) and η varies between 0.5 and 0.9.
Foundation item: National Natural Science Foundation of China (49974012) and Joint Seismological Science Foundation of China (604004). 相似文献
16.
According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic
shear modulus, which shows the relation of G
max (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (e
min). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical
shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes,
which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth.
Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic
triaxial tests.
Foundation item: State Natural Science Foundation (59678020) and Natural Science Foundation of Zhejiang Province (RC9609). 相似文献
17.
Two rock samples with different structures and materials were deformed under a biaxial loading system, and multipoint strain
measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability
process were analyzed by using C
v value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of C
v value and to explore its physical meaning experimentally. The result shows that the change of C
v value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity
of precursor distribution. C
v value increases firstly and then decreases before the instability, and the instability occurs when C
v value decreases to the level before increasing. This indicates that C
v value may be a useful parameter for earthquake prediction.
Foundation item: Chinese Joint Earthquake Sciences Foundation (9507435). 相似文献
18.
Based on the three-dimensional ela stic inclusion model proposed by Dobrovolskii, we developed a three-dimensional rheologic
inclusion model and theory to study the earthquake preparation process. By using correspondence principle in the theory of
rheologic mechanics, we derived the analytic expression of the viscoelastic displacement at an arbitrary point (x, y, z) in three directions of x, y and z-axes (i.e., U(r, t), V*(r, t) and W(r, t)) produced by a three-dimension inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model.
Foundation item: Chinese Joint Seismological Science Foundation (101105) 相似文献
19.
IntroductionThenortheasternregionofQinghai-Xizangplateauisthejunctionregionofthethreeblocks,ie.,Qinghai-Xizang,AIxaandordosblock.TianandDing(l998)studiedtheclockwisetypequasi-trijunctionaroundHaiyuan-YinchuaninnortheasternregionofQinghai-Xizangplateau.Thethreet6ctonicbranchesofthequasi4rjunctionareQiIianshanfaultzone,Yinchuan-Jedai-Linhe(YJL)fractureddepressionbasinandLiupanshanfaultzone.TheQilianshanfaultzoneshowssin-istraIandcompressionalmovement,themovementofYJLbasinisofdextraland… 相似文献
20.
We collect 1974 broad-band velocity records of 94 earthquakes (ML=2.8~4.9, △=13~462 km) from seven stations of the Fujian Seismic Network from March 1999 to March 2007. Using real-time simulation, we obtain the corresponding acceleration and then adopt different models to analyze the seismic data. As a result, a new attenuation relationship between PGA and PGV of the small and moderate earthquakes on bedrock site in Fujian region is established. The Yongchun earthquake occurred recently verifies the attenuation relationship well. This paper provides a new approach for studying the ground motion attenuation relationship using velocity records. 相似文献