龙马溪页岩弹性各向异性与矿物分布之间的关系探讨

岩石弹性各向异性特征是普遍存在的,但导致岩石弹性各向异性的原因复杂且仍然存在一定争议.本研究以龙马溪页岩为例,试图建立页岩弹性各向异性和矿物分布之间关系.研究使用无损超声波探测获取岩石弹性各向异性参数,并使用背散射技术获取岩石矿物分布特征.研究通过引进变异系数来描述矿物或孔裂隙在不同方向的差异性,并通过2个正交方向的变异系数建立微观异质性指标,用于表征微观尺度上矿物或孔裂隙在不同方向的差异程度.微观背散射图像显示,龙马溪组页岩主要由石英和伊利石构成,且这两种矿物和孔裂隙在X和Y面上都有定向排列特征.相应地,它们的变异系数在X面和Y面上均表现出随角度增大而降低的特征;而在Z面,石英、伊利石和孔裂隙变异系数变化不明显,这与Z面上矿物和孔裂隙无明显方向性的特点一致.无损超声波探测结果显示,波速在X和Y面上随角度增加而减小,这与主要矿物和孔裂隙变异系数变化趋势相同;而在Z面,波速变化不大,与主要矿物和孔裂隙变异系数变化不明显的特征一致.以上观测结果说明,宏观波速与矿物的微观变异系数明显相关,暗示岩石弹性各向异性与矿物分布直接相关.     

Response of A Gravel - Bed River To Dam Closure: Insights From Sediment Transport Processes And Channel Morphodynamics

This work deals with the impacts of dams on large gravel -bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics. Using data collected by a tracer -based monitoring programme carried out in a 4 -km -long study sector of the Parma River (Italy), located downstream from a relatively recently established dam, we applied a virtual velocity approach to estimate the coarse bed material load at four river cross -sections. Monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 -month calculation period. A longitudinal gradient of effects was observed along the study sector. Sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream. Sediment mobility here is strongly altered, especially in the highly armoured main channel, and the overall bed material load is extremely low. A partial recovery of sediment dynamics was observed at the sections located further from the dam, where estimates indicate higher sediment yield. The observed longitudinal trend in the coarse sediment transport regime matches the morphology, as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one. The novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments. © 2019 John Wiley & Sons, Ltd.     

汶川地震震前龙门山以西地壳垂直隆升机理分析

结合流动GPS观测速度场及层析成像结果,构建跨龙门山断裂剖面的二维有限元分层模型,分两种情况讨论汶川地震前龙门山前缘地壳垂直隆升的物理机制,以及中、下地壳软物质垂向和横向的不均匀性对地壳隆升作用的影响。分析认为：川西高原相对四川盆地的差异抬升和龙门山以西地壳缩短的共同作用是汶川地震震前龙门山前缘地壳垂直隆升的可能原因。     

非饱和土中剪切S波的传播特性分析

基于对非饱和多孔介质的研究成果,考虑孔隙中的液相和气相的相互影响,研究非饱和土地基中剪切S波的传播特性。通过非饱和土中固相、液相和气相的质量平衡方程、动量平衡方程和非饱和土有效应力原理,建立问题的弹性波动方程,经过理论推导给出非饱和土中剪切S波的弥散特征方程。通过数值算例分析剪切S波的波速和衰减系数随饱和度、频率和固有渗透系数等因素的变化规律。结果表明,剪切S波的波速几乎不受饱和度的影响,但其随着频率的增大而减小,随着固有渗透系数的增大先不变后增大;剪切S波的衰减系数随着饱和度和频率的增加均增大,而随着固有渗透系数的增大先不变后增大最后减小。     

利用爆破事件分析不同速度模型下常规定位方法定位结果

地震定位对速度模型的依赖性很强.四川地区地形复杂,常规工作中可选取多种速度模型进行定位.川西龙门山断裂带为东南部四川盆地和西北部青藏高原东部山区的明显分界线,近年在此断裂带上发生多次较大地震.对发生在该断裂带附近的6个爆破事件和15个天然地震重新定位,并对比结果.研究表明,相同台站包围情况下,川滇3D速度模型稳定性最好,但对浅表爆破不太准确.相比HypoSat(一维速度模型)组合,台站分布对Hypo2000(一维速度模型)和Hypo2000(赵珠速度模型)组合的定位结果影响较大.     

水动力条件对沉积物-水界面氧通量的影响

氧环境决定了水体沉积物中各种生命所需元素的最终归趋,沉积物-水界面是水相与沉积物相氧传递的重要场所,而水动力条件是影响沉积物-水界面氧传递的重要因素.选择三峡库区一级支流御临河为研究对象,根据长年监测数据建立实验室模型,采用声学多普勒流速测试仪及微电极测试系统构建了非侵入式涡度相关测试系统,探究了不同水动力条件对沉积物-水界面氧通量的影响.结果表明：水体静止状态下沉积物-水界面溶解氧浓度随时间的增加而减少,非静止状态下随时间的增加而增加;沉积物-水界面氧通量随水体流速的增加而增加.根据氧通量求解对应流速下垂直涡动扩散系数并进行线性拟合,当水体流速为0.01~0.14 m/s时,垂直涡动扩散系数与水体流速的相关性最好,此时沉积物-水界面氧通量的传递以涡动扩散为主导.     

双向环形水槽模拟变化水位和流速下洞庭湖沉积物氮释放特征

浅水湖泊生态系统中的沉积物—水界面是湖泊内源氮释放的重要界面,而水动力因素是改变沉积物氮释放的重要因素.三峡大坝修建以后,长江中下游通江湖泊的水动力条件发生了明显的变化.通过采集洞庭湖湖口区域的沉积物和水样,在双向环形水槽动力模拟装置内模拟湖泊水位和流速的变化,探讨湖泊沉积物氮在沉积物和水系统中的二次释放特征.结果表明,随着扰动强度的增加,上覆水悬浮物浓度增大,上覆水中总氮浓度增加,沉积物向上覆水释放氮的强度增强,水动力条件的改变所引起的沉积物内源氮释放不容忽视.在该模拟实验条件下,沉积物存在最适扰动水位(20cm),此水位下上覆水中悬浮物浓度最低,总氮浓度最小.水动力条件的改变对上覆水和沉积物—水界面处铵态氮和硝态氮浓度的影响并不明显,孔隙水中铵态氮与硝态氮之间发生形态的转化.     

三峡澎溪河水-气界面温室气体模型估算及其敏感性分析

模型估算法是水-气界面温室气体通量监测的主要方法,所得成果也不胜枚举.然而监测过程中诸多环境因素会对最终结果产生不确定的影响.结合三峡库区澎溪河背景条件,利用模型估算法进行水-气界面温室气体通量(以CO_2为例)估算,并且采用修正Morris筛选法尝试分析模型估算法中各个参数对温室气体扩散通量(以CO_2为例)的局部敏感性.研究结果表明:利用模型估算法计算三峡澎溪河流域水-气界面温室气体通量具有较高的可行性和可靠性;风速、水温以及pH值会对监测结果产生影响,且风速越强、水温越高、pH值越小,CO_2扩散通量就越大;pH值是高灵敏参数,风速和水温是灵敏参数.在三峡库区澎溪河监测过程中更应注意pH值的精确性,每次采样前需校正仪器.     

VARIATION OF THE TRAVEL TIME DIFFERENCE BETWEEN TELESEISMIC PS CONVERTED WAVE AND PP TRANSMITTED WAVE IN FOCAL REGION BEFORE AND AFTER WENCHUAN MS8.0 EARTHQUAKE

When P waves from distant earthquakes meet a velocity discontinuity in the earth's crust and upper mantle, they give rise to a series of converted PS waves besides PP refracted waves. It is possible to monitor the variation of the physical properties of the medium in the limited formation space above the transition zone of the seismogenic zone by measuring the time difference between the teleseismic PS converted wave and the first arrival P wave, that is, time-variation Δt_PS=t_PS-t_P. The advantage of this method is that the transition point of the teleseismic source with similar source is relatively stable at the transition interface, and the accuracy of the measured relative time is high, and the change of the medium in a small range of the seismogenic zone above the conversion interface can be monitored. This paper studies the variation of the travel time difference Δt_PS in focal region before and after Wenchuan M_S8.0 earthquake. We select 2001 to 2012 as the research period, use teleseismic waveforms which occurred in the southern region of Sumatra and Hindu Kush area recorded by Sichuan station YZP and JJS. These teleseisms satisfy 5.0 ≤ M ≤ 6.5, and their waveform signal-to-noise ratio is high with clear initial P-wave motion. The epicentral distance of teleseisms is less than 3 degrees. Then we obtain the variation of the travel time difference Δt_PS between teleseismic PS converted wave and PP transmitted wave recorded during the study period in the two stations. The results show that there is a slow increasing trend of Δt_PS before 2006, and an obvious low value process of Δt_PS appeared in the period about 2 years before the Wenchuan earthquake. The maximum decline was about 0.2~0.3s, more than 4~5 times the measurement error. The low value has a certain degree of return about 2~3 months before the earthquake. The change of arrival time difference indicates that the medium is in different states in different periods of seismogenic process. The sharp decrease in Δt_PS from 2006 to January 2008 may be due to the strong disturbance caused by the stress accumulation of the medium. At this stage, the velocity of P wave and S wave increases with the increase of stress, and the increase of S wave velocity will result in the decrease of Δt_PS. The change of Δt_PS is greatly affected by S wave velocity, so Δt_PS appears to decrease rapidly. Regarding the low value that has a certain degree of return about 2~3 months before the Wenchuan earthquake, the possible reason is that the release of stress is much higher than the accumulation of stress in meta-instability stage. At this stage, the velocity of S wave decreases and the decrease of S wave causes Δt_PS to increase. Then, the Wenchuan earthquake of magnitude 8.0 occurred. It is shown that the teleseismic converted wave method in this paper can monitor the variation of medium's wave velocity before large earthquakes, and it has a good prospect in seismic monitoring and worth further experimental study.