基桩均震动测法工程实践

基桩均震动测法的均震与聚束特性，在工程检测实践中展示了其独特优越性。在对比“均震”与“偏震”检测完整桩、缺陷桩的基础上，重点介绍该方法在超长桩、超粗桩检测中的应用范例。

秸秆还田机刀片及刀片优化排列的研究

对秸秆还田机工作部件—刀片部分的受力和在刀轴上的排列方式进行了理论分析和总结。在“均力免震假设”的基础上,推导出常用刀片类型的结构参数优化方程,并利用计算机高级语言对优化方程求解,得出了相应机型秸秆还田机的刀片优化排列,为今后秸行还田机的设计提供了直接理论依据。

利用震级均值特性建立有上限震级概率模型对2017年九寨沟7.0级地震的余震概率预测

震级均值ma是震级m以上事件的震级平均值.研究了九寨沟7. 0级地震余震序列的震级均值ma之后,发现两个与ma有关的线性关系:(1) lg N'=a'-b'ma,(2) ma=c+dm.第一个关系式不仅与G-R关系的形式相同,并且也可以用来估计完备震级Mc.令ΔN=lg N-lg N',lg N从目录统计得到,lg N'是(1)式给出的预测值.在ΔN与ma的散点图上,ΔN第一次突破0轴对应的ma值可以很好地估计完备性震级Mc.第二个关系式称为震均关系(A-M关系),只能从实际目录统计,不能从已有的统计关系推导出来.若震级是连续随机变量且G-R关系在完备震级Mc以上的任意的震级范围[m,∞]成立,将A-M关系代入极大似然法求b值的Aki-Utsu公式,可得到b值函数B(m)=-r/[c-(1-d) m].对B(m)积分可得(3) lg N=p+klg(c-qm),其中q=1-d.从(3)式可导出(4) F(M≥m)=[(cqm)/(c-qm0]k.(3)和(4)分别是有上限的震级-频度关系及其条件概率分布函数.按以下步骤确定参数c、q、p、k:第一步,拟合线性关系(1) lg N'=a'-b'ma,用ΔN=lg N-lg N'确定完备震级Mc,并统计Mc以上余震序列的震级均值mca.第二步,利用余震序列的最大震级不可能超过主震震级Mm的特点,假定余震序列震级上限mu=Mm+0. 5,通过点(mu,mu)和点(Mc,mca)求解A-M关系(2) ma=c+dm,获得参数c、q.第三步,拟合lg(c-qm)和相应的lg N,确定参数p、k.根据以上步骤,用震后2 h的余震目录拟合各项参数,获得概率分布函数F(M≥m)=[(0. 62-0. 0827m)/(0. 62-0. 0827m0]8. 8602.据此估计在后续累计发生0级以上余震10000次的条件下,至少发生一次的概率为63%、10%和1%对应的的震级分别为4. 8、5. 4、5. 9级.据蒋海昆等(2006)的多震型序列定义,后续须至少发生一次6. 4级以上地震,才能认为九寨沟7. 0级余震序列是多震型序列,而6. 4级以上地震至少发生一次的概率仅为4. 02E-4.根据这些概率计算,在震后2 h可以作出的预测意见为:九寨沟7. 0级地震的余震序列类型为主震-余震型,最大余震震级可能在5级左右或5～6级.迄今为止的事实表明,虽然随着余震的不断发生,以后的参数c、q、p、k会发生一定的波动,但不至于改变震后2 h作出余震预测意见.这表明将A-M关系和G-R关系结合起来,可以在震后最短时间内为预测余震序列类型和最大可能震级提供可靠判据.

Seismic random noise suppression using an adaptive nonlocal means algorithm

Nonlocal means filtering is a noise attenuation method based on redundancies in image information. It is also a nonlocal denoising method that uses the self-similarity of an image, assuming that the valid structures of the image have a certain degree of repeatability that the random noise lacks. In this paper, we use nonlocal means filtering in seismic random noise suppression. To overcome the problems caused by expensive computational costs and improper filter parameters, this paper proposes a block-wise implementation of the nonlocal means method with adaptive filter parameter estimation. Tests with synthetic data and real 2D post-stack seismic data demonstrate that the proposed algorithm better preserves valid seismic information and has a higher accuracy when compared with traditional seismic denoising methods （e.g., f-x deconvolution）, which is important for subsequent seismic processing and interpretation.

Interpolation of near offset using surface-related multiples

In this research, we present a seismic trace interpolation method which uses seismic data with surface-related multiples. It is different from conventional seismic data interpolation using information transformation or extrapolation of adjacent channels for reconstruction of missing seismic data. In this method there are two steps, first, we construct pseudo-primaries by cross-correlation of surface multiple data to extract the missing near- offset information in multiples, which are not displayed in the acquired seismic record. Second, we correct the pseudo-primaries by applying a Least-squares Matching Filter （LMF） and RMS amplitude correction method in time and space sliding windows. Then the corrected pseudo-primaries can be used to fill the data gaps. The method is easy to implement, without the need to separate multiples and primaries. It extracts the seismic information contained by multiples for filling missing traces. The method is suitable for seismic data with surfacerelated multiples.

Estimation of active earth pressure based on pseudo-dynamic approach and discretization technique

A method combining the pseudo-dynamic approach and discretization technique is carried out for computing the active earth pressure.Instead of using a presupposed failure mechanism,discretization technique is introduced to generate the potential failure surface,which is applicable to the case that soil strength parameters have spatial variability.For the purpose of analyzing the effect of earthquake,pseudo-dynamic approach is adopted to introduce the seismic forces,which can take into account the dynamic properties of seismic acceleration.A new type of micro-element is used to calculate the rate of work of external forces and the rate of internal energy dissipation.The analytical expression of seismic active earth pressure coefficient is deduced in the light of upper bound theorem and the corresponding upper bound solutions are obtained through numerical optimization.The method is validated by comparing the results of this paper with those reported in literatures.The parametric analysis is finally presented to further expound the effect of diverse parameters on active earth pressure under non-uniform soil.

Post-earthquake Rainfall-triggered Slope Stability Analysis in the Lushan Area

The ＂4.20＂ Lushan earthquake in Sichuan province, China has induced a large amount of geological hazards and produced abundant loose materials which are prone to post-earthquake rainfall- triggered landslides. A detailed landslide inventory was acquired through post-earthquake emergent field investigation and high resolution remote sensing interpretation. The rainfall analysis was conducted using historical rainfall records during the period from 1951 to 2010. Results indicate that the average annual rainfall distribution is heterogeneous and the largest average annual rainfall occurs in Yucheng district. The Stability Index MAPping （SINMAP） model was adopted to assess and analyze the post- earthquake slope stability under different rainfall scenarios （light rainfall, moderate rainfall, heavy rainfall, and rainstorm）. The model parameters were calibrated to reflect the significant influence of strong earthquakes on geological settings. The slope stability maps triggered by different rainfall scenarios were produced at a regional scale. The effect of different rainfall conditions on the slope stability is discussed. The expanding trend of the unstable area was quantitatively assessed with the different critical rainfall intensity. They provide a new insight into the spatial distribution and characteristics of post- earthquake rainfall-triggered landslides in the Lushan seismic area. An increase of rainfall intensity results in a significant increase heterogeneous distribution strongly correlated with of unstable area. The of slope instability is the distribution of earthquake intensity in spite of different rainfall conditions. The results suggest that the both seismic intensity and rainfall are two crucial factors for post- earthquake slope stability. This study provides important references for landslide prevention and mitigation in the Lushan area after earthquake.

Applications of fluid substitution effect analysis on seismic interpretation

The root mean square(RMS) difference of time-lapse seismic amplitudes is routinely used to identify the substituted fluid type in a reservoir during oil field production and recovery. By a time-lapse seismic method, we study the effects of fluid substitution in a physical model, which is an analogy of the three-dimensional inhomogeneous reservoir. For a weak inhomogeneous medium, gas/oil substitution results in positive anomalies in the reservoir layers, and negative anomalies below the bottom of the reservoir layers; while water/oil substitution causes only weak variations in the reservoir layers, but positive anomalies below the bottom of the reservoir layers. For the strong inhomogeneous medium, no matter what kind of fluid substitution(gas/oil or water/oil), there are significant anomalies in seismic amplitude difference attributes both in and below the reservoir layers. Therefore, for weak inhomogeneous media, such as tight sandstone or thin interbedded layers, the RMS amplitude difference attributes can be used to monitor fluid changes and predict the drilling direction; for inhomogeneous medium with karst carves or fractures, it is difficult to accurately determine the distribution of fluids with the RMS amplitude difference attributes.

Study on the Attenuation Features of Earthquake Intensity in the Yunnan Region

This research on the attenuation features of intensity in the Yunnan region has been conducted by using intensity isoseismals of 127 earthquakes, and the following three conclusions have been put forward: (1) The average ratio value of long axis to short axis of innermost isoseismals in the Yunnan region is larger than that of eastern China and smaller than that of western China. The velocity of intensity attenuation varies in different directions; (2) The zoning feature of intensity attenuation in the Yunnan region is obvious; (3) In Northwest China and North China, the ratios of long axis to short axis of low magnitude isoseismals are larger than those of high magnitude ones. Compared with that phenomenon, the ratios in the Yunnan region are more complicated. Finally, some relevant questions are discussed.

Study on Focal Mechanism Changing Characteristics of the 2013 Zogang-Markam Ms6. 1 Earthquake Sequence

The M_S6. 1 earthquake was a foreshock-mainshock-aftershock type which occurred in the boundary region between Zogang and Markam counties on August 12,2013. Within 9hours before the main shock seven earthquakes of greater than M_L2. 0 occurred,with a maximum of M_L4. 7. In this paper,the earthquake focal mechanism changing process of the Zogang-Markam M_S6. 1 earthquake sequence is studied by calculating the correlation coefficient of body wave spectral amplitudes,and the result shows that the correlation coefficients of spectral amplitude of foreshocks present high value fluctuation with an average value of 0. 86,which shows that the focal mechanism of foreshocks are similar;and the correlation coefficients of spectral amplitude of aftershocks present low value,which shows that the possibility of a large earthquake is not high after a time.

Study of Crustal Thickness and Poisson Ratio of Hebei and Its Adjacent Areas by Teleseismic Receiver Function

We collected waveforms of a teleseismic event which occurred from January 2007 to October 2011 from 174 broadband seismic stations deployed in Hebei and its adjacent areas. Using the H-k stacking method,the average thickness and Poisson's ratio of the crust are acquired. In order to obtain reliable receiver functions, the broadband seismograms of 488 teleseismic earthquakes occurring in the epicentral distance range from 30° to 90° with magnitudes larger than Mb6. 0 are collected. The results show that crustal thickness have conspicuous lateral heterogeneity and have good correlation to the regional geological tectonic features. Poisson ratio's value is equated with the global models estimates which fluctuate at about 0. 25. Crustal thickness has positive correlation to the topography and the Taihang Mountains form the transition zone of thick and thin crustal thickness. There is an obvious difference in crustal thickness beneath the north and south of the Shanxi earthquake zone and the Poisson ratio of Datong,Ningwu and Anze basins is greater than 0. 3. The crustal thickness beneath the Zhang-Bo( Zhangjiakou-Bohai Sea)earthquake zone decreases from west to north and its Poisson ratio shows conspicuous lateral heterogeneity. The thin crust and low Poisson ratio in the Huabei( North China)basin may correlate with the delamination of the North China craton.

Statistical Analysis of the Dynamic Parameters of Silty Clay in the Beijing Area

Soil dynamic parameters,including dynamic shear modulus ratio and damping ratio,have important effects on the results of layered soil earthquake response. In this paper,the mean parameter values of silty clay in different depths are obtained after statistical analysis of the experimental soil dynamic data from 20 recent site seismic safety evaluation reports in the Beijing area. Furthermore,based on two typical engineering sites,the influence of four different soil dynamic parameters,the statistic mean values,experimental values, values recommended by Yuan Xiaoming,and the values recommended in the code for seismic safety evaluation of engineering sites( DB001-94) are analyzed. The result shows that mean statistical values are applicable to seismic safety evaluation work in the Beijing area,especially for some inter-layered silty clays whose undisturbed soil samples are hard to obtain.

Methods for Estimating Mean Annual Rate of Earthquakes in Moderate and Low Seismicity Regions

Two kinds of methods for determining seismic parameters are presented, that is, the potential seismic source zoning method and grid-spatially smoothing method. The Gaussian smoothing method and the modified Gaussian smoothing method are described in detail, and a comprehensive analysis of the advantages and disadvantages of these methods is made. Then, we take centrai China as the study region, and use the Gaussian smoothing method and potential seismic source zoning method to build seismic models to calculate the mean annual seismic rate. Seismic hazard is calculated using the probabilistic seismic hazard analysis method to construct the ground motion acceleration zoning maps. The differences between the maps and these models are discussed and the causes are investigated. The results show that the spatial smoothing method is suitable for estimating the seismic hazard over the moderate and low seismicity regions or the hazard caused by background seismicity; while the potential seismic source zoning method is suitable for estimating the seismic hazard in well-defined seismotectonics. Combining the spatial smoothing method and the potential seismic source zoning method with an integrated account of the seismicity and known seismotectonics is a feasible approach to estimate the seismic hazard in moderate and low seismicity regions.

A Study on Average Velocity Ratios(V_P/V_S) in the Hohhot-Baotou Area

The geological structure is complex in the Hohhot-Baotou area.Several earthquakes with MS≥6.0 have occurred in the area in history.This article selected the Hohhot-Baotou area as the study region and divided it into 2 sub-regions,each with a spatial scope of 3°×2°,according to the spatial distribution of ML≥1.0 earthquakes occurring between January 2001 and April 2010,and the layout of the seismic network in the study region.Average velocity ratios of respective sub-regions were calculated,and comparative analysis was made on their temporal and spatial variations.Results show that there are slight differences between sub-regions in the variation amplitude of average velocity ratio curves over time,which mostly remains between 2.5% to 2.584%.In the Hohhot area,the average velocity ratio is 1.722,significantly lower than the average velocity ratio of 1.733 in the Baotou area.We preliminarily concluded that this was related to the distribution of fault structures and properties of underground media in the Hohhot area.

Study on the Recent Tectonic Stress Field in the “Huoshan Seismic Window” Region

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the ＂ Huoshan seismic window＂ region are calculated with the method developed recently by Snoke, combining the use of the first motion of P, SV and SH waves with their amplitude ratios. Based on these abundant focal mechanisms, the mean tectonic stress field in the ＂Huoshan seismic window＂ region is inverted with the average stress tensor method, and the result shows that the ＂Huoshan seismic window＂ region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction, which is in accord with statistical results of focal mechanism parameters. We estimate the difference （also referred to as consistency parameter 0） between the force axis direction of the focal mechanism solution and the mean stress tensor, then further analyze the variation characteristics of 0 versus time, and the relationship with moderately strong earthquakes in the east China region. The result indicates that 0 in the ＂ Huoshan seismic window＂ region is in good correspondence with moderately strong earthquakes in the East China region. When 0 is lower than the mean value, corresponding moderately strong earthquakes may occur in the East China region.

Effect of Heterogeneities in Soil on Spatial Variation of Peak Ground Acceleration

In the proximity of an active fault, spatial variation of peak ground motion is significantly affected by the faulting mechanism. It has been observed that near fault ground motions consists of different characteristics compared to the far fault ground motions. Near fault records, in the distance range of less than 100 m from the faults are not available except for few cases. Therefore numerical simulation of ground motions for such near-fault situations is necessary. In addition to the understanding of the phenomenon of near fault ground motion there is a need to enhance our understanding of the possible potential hazard that can be caused due to the future rupture activity by understanding the phenomenon of surface faulting. In this paper we propose numerical simulation based on discrete modeling to investigate the fault rupture propagation and its effect on the surface peak ground acceleration. In the present two dimensional study rupture propagation due to bedrock motion has been observed for different shear wave velocity. A model of size 1000× 150 m is selected for this purpose. It has been observed that as the stiffness of the media is decreasing, the affected surface is decreasing and also width of the shear crack zone is decreasing. Secondly, we attempted to study the ground motion on the surface due to the bedrock motion in presence of boulders in the soil media by keeping the boulder at different positions. We find that there is an increase in the shear zone as well as the PGA on the surface when the boulder is present on the foot wall and in the vicinity of the rupture zone. Finally, we performed the analysis using layered media and studied the affect of crack propagation and also the variation of peak accelerations. Findings from the study can be utilized to assess the damage potential of the near fault areas.

A Simple Model for Earthquake Instability

Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.

The Preliminary Research on Rupture and Factors Affecting Rupturing of the Hoh Sai Hu Segment in Eastern Kunlun

On November 14, 2001, an extraordinarily large earthquake (MS8.1) occurred on the Hoh Sai Hu segment of the Eastern Kunlun Fault, in the northern Qinghai-Tibetan Plateau. The seismogenic fault, the Hoh Sai Hu segment, is a left-lateral fault with a high slip rate in geological history, with the average slip rate reaching(14.8±2.8)mm/a since the late Pleistocene. Different slip rates of the Hoh Sai Hu segment can affect fault motion in the future. Therefore, this paper analyzes the effect of different slip rates and different initial friction coefficients on the fault plane of the Hoh Sai Hu segment of the eastern Kunlun Fault on the rupture behaviors of the fault. In this research, we apply the single degree of spring block model controlled by the rateand state-dependent frictional constitutive laws. Using the fault dislocation model and based on ancient earthquake research, historical earthquakes data and the achievements of previous researchers, we obtained the parameters of this model. Through numerical simulation of the rupturing motion of the Hoh Sai Hu segment in the next 6500 years under different slip rates, we find that a faster annual slip rate will shorten the recurrence interval of the earthquake. For example, the earthquake recurrence interval is 2100a at a slip rate of 0.014m/a, which agrees with previous research, but, the recurrence interval will be 1000~1500a and 2100～2500a, corresponding to the slip rates of 0.018m/a and 0.008m/a, respectively. The fault slip rate has no regular effect on the coseismic slip rate and fault displacement in an earthquake. The initial friction coefficient on the fault surface has an effect on the earthquake recurrence interval. A smaller initial friction coefficient will lengthen the earthquake recurrence interval. At the same time, the smaller initial friction coefficient will lead to larger slip rates and fault displacement when earthquakes occur.

Comparison of Design Response Spectrum for Long Period Structures Based on Scenario Earthquakes

Two kinds of determining methods for scenario earthquakes are presented in this paper,namely the weighted average method and maximum probability method. This paper briefly introduces the two methods,then taking a high-rise building in the Yantai area as a case study,we use the weighted average method and maximum probability method to realize seismic hazard analysis, determine earthquake magnitude, the epicenter and specific space position,and then give two response spectrums of the two methods. By comparing the differences of response spectrums between the two methods,we find that the weighted average method is more suitable for long period structures,while considering long period safety. The maximum probability method is more suitable for short period structures. It is reasonable to choose a corresponding different method when the structures have different natural vibration periods.

Two types of changes in apparent resistivity in earthquake prediction

Two types of changes in apparent resistivity (AR) have been linked to earthquake occurrences. This paper studies the changes and their causes, in detail with the ultimate purpose of developing and assessing a method of earthquake (EQ) prediction. The AR changes of the first type (CFT) are considered to be precursors related to earthquakes (EQs); these appear mostly in the medium-term period before EQs and in the short-term period preceding EQs. The changes of the second type (CST) are characterized by a turning anomaly of a long-trend AR variation or the drastically descending/ascending anomaly superimposed on such a variation; these appear synchronously in large areas, such as the Chinese mainland, and northern and northwestern China, ect. Their spatio-temporal clusters correspond well to high seismicities in the areas and distant great EQs around the Chinese mainland. Based on the behaviors of the two types of changes, the AR changes observed prior to the Ms8.0 Wenchuan EQ of 2008 are studied. The results show that in the medium-term period before the EQ, noticeable anomalies appeared synchronously at four stations around the Songpan-Ganzi active block, but only weak upward changes were observed in the short-term period preceding the EQ, which caused the prediction of the imminent EQ to fail.