新疆天山地区的波速比异常分析     

张琳琳  高朝军 《中国地震研究》2017,31(1):39-50

Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using the multi-station method in Tianshan,Xinjiang.This paper analyzes the variation of the wave velocity ratio disturbance value to highlight the abnormal,and also back-traces 7 moderate earthquakes at the research area.The results show that:(1)the background value of the wave velocity ratio is almost 1.70,the wave velocity ratio obviously decreases in the middle-eastern part of Tianshan and the region near the Puchang fault;(2)the wave velocity ratio disturbance value is mostly low in the epicenter before four earthquakes of M≥5.0 from 2011 to 2013 in the study area;(3)before 7 moderate strong earthquakes,the earthquake events with low value of the wave velocity ratio account for over 60% of corresponding total events near the epicenters,and the low value of the wave velocity ratio is relatively obvious before moderate earthquakes.  相似文献   

Late Quaternary Activity of the Chuxiong-Nanhua Fault and the 1680 Chuxiong MS6 ¾ Earthquake     

Chang Zufeng  Chang Hao  Li Jianlin 《中国地震研究》2017,31(3):431-440

In this paper, according to the results of the satellite imagery interpretation and field investigation, we study the active features and the latest active times of the Chuxiong-Nanhua fault, the Quaternary basins formation mechanism, and the relationship between the fault and the 1680 Chuxiong M_S6 ¾ earthquake. Several Quaternary profiles at Lvhe, Nanhua reveal that the fault has offset the late Pleistocene deposits of the T2 and T3 terraces of Longchuan river, indicating that the fault was obviously active in late Quaternary. The Chuxiong-Nanhua fault has been dominated by dextral strike slip motion in the late Quaternary, with an average rate of 1.6-2.0mm/a. Several pull apart Quaternary basins of Chuxiong, Nanhua, and Ziwu etc. have developed along the fault. The 1680 Chuxiong M_S6 ¾ earthquake and several moderate earthquakes have occurred near the fault. The Chuxiong-Nanhua fault are the seismogenic structure of those earthquakes, the latest fault movement was in the late-Pleistocene, and even the Holocene. In large area, the Chuxiong-Nanhua fault and the eastern Qujiang fault and the Shiping fault composed a set of NW-trending oblique orientation active faults, and the motion characteristics are all mainly dextral strike slip. The motion characteristics, like the red river fault of the Sichuan-Yunnan Rhombic Block southwestern boundary, are concerned with the escaping movement of the Sichuan-Yunnan Rhombic Block.  相似文献   

青藏高原东缘的地壳流及动力过程   总被引：13，自引：6，他引：7       下载免费PDF全文

朱介寿  王绪本  杨宜海  范军  程先琼 《地球物理学报》2017,60(6):2038-2057

黏滞性地壳流对地壳及上地幔变形作用及动力机制,是大陆新生代造山带的一个重要研究内容.青藏高原中下地壳存在部分熔融或含水物质的黏滞性流体,已为一系列地球物理及岩石学研究所证实.为研究青藏高原东缘地壳流的动力作用,本文用密集的被动源宽频带地震台的观测数据,反演了地壳上地幔精细速度结构和泊松比.研究表明,川西及滇西北高原的中地壳内普遍存在低速层,而高泊松比的地壳只分布在川西北地区.位于中地壳的黏滞性地壳流从青藏高原腹地羌塘高原流出,自北西向南东流入青藏高原东缘.这些黏滞性地壳流带动了上地壳块体水平移动,当它们受到刚强的四川盆地及华南地块阻挡时将发生分层作用,地壳流将分为二或更多分支不同方向的分流,向上的一支地壳流将对上地壳产生挤压,引起地面隆升,向下的一支地壳流将使莫霍面下沉加厚下地壳·黏滞性地壳流的运动在地壳中产生应变破裂发生强烈地震活动,地震的空间分布与震源机制也受到地壳流动力作用控制.  相似文献   

青藏高原东北缘及周边地区基于程函方程的面波层析成像   总被引：7，自引：2，他引：5       下载免费PDF全文

钟世军  吴建平  房立华  王未来  范莉苹  王怀富 《地球物理学报》2017,60(6):2304-2314

利用"中国地震科学台阵探测"在南北地震带北段布设的670套宽频带地震台站记录到的面波资料,使用新近发展的程函方程面波层析成像方法,获得了青藏高原东北缘及周边地区12~60 s周期范围比以往成像结果具有更高分辨率的瑞利面波相速度分布图像.青藏高原东北缘的祁连褶皱系西段、秦岭褶皱系西段和松潘一甘孜褶皱系,在16~60s周期范围内均显示出明显的低速异常分布,表明该地区的地壳力学强度较低,在强烈的构造应力作用下易发生形变.与西段不同,祁连褶皱系东段和秦岭褶皱系中段的相速度分布特征揭示,其中下地壳的速度明显高于高原内部区域.鄂尔多斯块体整体上表现为稳定块体具有的高速特征,但其西部边缘在中上地壳的速度比块体中部地区偏低,且存在一定的不均匀性.鄂尔多斯块体西北缘的临河断陷盆地和西缘的银川断陷盆地,在较短的周期范围内(12~20 s)表现为局部低速特征,但与银川断陷盆地不同,临河断陷盆地的低速特征可一直延续至60 s周期以上,表明该盆地下方地壳及上地幔速度明显偏低,可能与深部热作用有关.阿拉善块体与其北部地区的速度差异主要表现在中上地壳,这一现象值得今后进一步探讨.基于程函方程面波层析成像方法给出了青藏高原东北缘及周边地区高分辨率的成像结果,揭示了以往面波层析成像难以获得的深部细节特征,为该地区的深部构造研究提供了新的信息.  相似文献   

CSAMT法三维分辨能力及其物理机制          下载免费PDF全文

王显祥  底青云  邓居智  许诚 《地球物理学报》2017,60(3):1143-1157

随着CSAMT法探测应用需求的日益增多,其分辨能力及其物理机制的研究成为人们不得不面对的问题.在CSAMT勘探中,几何效应、电流效应和感应效应是引起电磁场变化的三种物理机制,本文详细介绍了与地下电性结构密切相关的电流效应和感应效应.首先,利用CSAMT法对100 m×100 m×100 m的异常体进行了探测,研究表明存在两个畸变区域.利用电流效应对存在的两个畸变区域进行了解释,进一步研究表明当收发距为10 km时电流效应占据主要地位,感应效应位居次要地位,当收发距增大时电流效应比重下降,感应效应比重增大.选取坐标原点位于电偶极子中心,x方向为电偶极矩方向,z轴垂直向下,随后,研究了CSAMT法对异常体沿x、y及z方向长度变化时的探测灵敏度,研究表明CSAMT法对异常体沿x方向的变化最为灵敏、y方向变化次之、z方向最为迟钝,最后对以上现象给出了解析.  相似文献   

场地效应研究的传递台站线性反演法——以芦山地震为例   总被引：1，自引：0，他引：1       下载免费PDF全文

李红玉  于湘伟  章文波 《地球物理学报》2017,60(1):198-211

采用线性反演法研究了地震动的场地效应,并针对线性反演法的局限性,提出了"传递台站"的方法来扩展其应用.通过传递台站,地震事件不再局限于必须被参考台记录到,台站也不再局限于须与参考台站同时获取到地震记录,改进后可大大增加数据样本,使得结果更趋稳定.同时,对于原来难以参与分析的台站,也可得到其场地反应.研究中,还采用了基于遗传算法的非参考台方法,进一步分析了场地反应和验证所提方法的合理性.将所提方法应用于2013年芦山7.0级地震周边区域,分析了这一地区的强震台站的场地反应和地震波衰减因子Q_s值.研究结果显示,当采用一个和二个传递台站进行分析时,所能利用的地震事件和所能求解场地反应的台站数目逐步增加,随着数据样本的增加,分析结果趋于稳定.研究区域的Q_s值拟合结果为Q_s(f)=334.16f~(0.73).遗传算法结果表明,线性反演法中所选取的参考台站有其自身的场地反应.当利用遗传算法获得的参考场的场地反应去校正线性反演法的结果时,对于多数场地,两者的结果符合得很好,说明了遗传算法的结果可以合理地认为是场地较为真实的反应.  相似文献   

岩石加速破裂行为的物理自相似律   总被引：4，自引：0，他引：4       下载免费PDF全文

杨百存  秦四清  薛雷  陈竑然  吴晓娲  张珂 《地球物理学报》2017,60(5):1746-1760

掌握岩石变形破坏过程中体积膨胀点至峰值强度点之间加速破裂行为的演化规律,是实现地质灾害物理预测的关键.本文考虑裂纹张开和闭合两种情况,基于断裂力学建立了三轴应力作用下裂纹扩展临界尺度与等效应力的关系.对微元体破坏概率,分别采用以等效应力表达的Weibull分布函数和裂纹尺度分形函数,通过对比导出了形状参数m与裂纹分布分维D_f关系的表达式.一个有趣的发现是,岩石峰值强度点与体积膨胀点应变比仅与m或D_f有关.对岩石蠕变或准蠕变破坏,合理的m值范围为[1.0,4.0],在此范围内应变比近似为常数1.48,该常数是描述不同尺度岩石加速破裂规律的物理自相似常数.实例分析表明,基于岩石加速破裂规律构建的多锁固段脆性破裂理论,其适用性广,尤其在崩滑和大地震预测领域,具有良好应用前景.此外,本文给出了b值与m值定量关系,以解释b值的物理意义,并探讨将其用于地震预测的可行性.  相似文献   

Investigating Bermuda's pollution history through stable isotope analyses of modern and museum-held gorgonian corals     

David M. Baker  Thaddeus J.T. Murdoch  Inga Conti-Jerpe  Marilyn Fogel 《Marine pollution bulletin》2017,114(1):169-175

For centuries, Bermuda has been challenged with wastewater management for the protection of human and environmental health. By quantifying the δ¹⁵N of the common sea fan Gorgonia ventalina sampled from 30 sites throughout Bermuda we show that sewage-derived nitrogen is detectable on nearshore coral reefs and declines across the lagoon to the outer rim. We also sampled gorgonians from two museum collections representing a 50y time-series (1958–2008). These samples revealed an increase in δ¹⁵N of > 4.0‰ until the mid-1970s, after which δ¹⁵N values slowly declined by ~ 2.0‰. A δ¹⁵N chronology from a gorgonian skeleton exhibited a similar decline over the last 30–40 years of approximately 0.6‰. We conclude that policies have been effective in reducing sewage impacts to Bermudian reefs. However, significant sources of sewage pollution persist and are likely have a strong impact on harbor and nearshore coral communities and human health.  相似文献   

鲜水河断裂带炉霍段的震后滑动与形变   总被引：5，自引：0，他引：5       下载免费PDF全文

杜方  闻学泽  张培震 《地球物理学报》2010,53(10):2355-2366

1973年2月在鲜水河断裂带炉霍段发生了M7.6地震破裂.自那以来,先后在炉霍县虾拉沱布设了若干横跨该地震断层(1973年破裂带)的地壳形变观测系统,包括断层近场的短基线、短水准、蠕变仪、人工构筑物等,以及断层近-远场的GPS观测站.利用这些观测系统的长期观测资料,本文分析了鲜水河断裂带炉霍段的震后滑动/变形及其时、空变化特征,并建立起解释这些特征的动力学模式.研究表明:(1)1973年地震后的头5年,地震断层在虾拉沱场地表现为开放性质,近场的断层震后滑动以无震左旋蠕滑为主,速率达到10.27 mm/a,且伴有微量的拉张性蠕动作用;1979年以来,左旋蠕滑速率由5.3 mm/a逐渐减小到2.27 mm/a,减小的过程呈对数函数型,反映此阶段断层面已逐渐重新耦合、正朝闭锁的方向发展,并伴有部分应变积累.(2)1999年以来,地震断层两侧远场的相对左旋位移/变形速率为10 mm/a,远大于同时期断层近场(跨距40~144 m)的左旋蠕滑速率0.66~2.52 mm/a;远-近场位移/形变速率的显著变化发生在地震断层两侧各宽约30 km的范围,显示出这是与大地震应力应变积累-释放相关的断裂带宽度.(3)结合动力学背景与深部构造信息,本文对这里断层的震后位移/变形及其时、空变化的机理进行初步解释,要点是:震后约5年之后,由于逐渐增大的断层滑动/摩擦阻抗,上地壳脆性层中的断层面由震后初期的开放性质逐渐转向重新耦合、并朝闭锁的方向发展,但其两侧地块深部持续的延性相对运动拖拽着浅部脆性层发生相应的弹性位移/变形.(4)可估计再经历15~25年,研究断裂段将完全"闭锁",即进入积累下一次大地震应力应变的震间闭锁阶段.  相似文献   

Longitudinal variations of phytoplankton compositions in lake-to-river systems     

《Limnologica》2017

To test the hypothesis of longitudinal variations in phytoplankton compositions from a eutrophic lake to its river downstream and determine the length of the transition zone, we applied functional groups as well as taxonomical methods to this coupled aquatic system, which is composed of the Dianchi Lake upstream and the Tanglang River downstream, by sampling at 9 stations during Microcystis blooms in the Dianchi Lake in 2013. The longitudinal variations in phytoplankton compositions from lacustrine species to fluvial species were reflected by: (1) the shift from Microcystis to Chlorococcales green algae and centric diatoms; (2) the shift from the dominance of codon M to the coexistence of a variety of coda without one outstanding codon; and (3) except for codon M, the shift from lacustrine coda (H1, L_O, T) towards coda that are adapted to both lacustrine and fluvial circumstances (MP, X1, X2). The prominent difference of phytoplankton compositions between the Dianchi Lake and the lower reaches of the Tanglang River revealed that there was a transition zone in between. The upper and middle reaches of the Tanglang River with a length of approximately 26.4 km were considered the transition zone because: (1) the dominant lentic codon M in the Dianchi Lake disappeared at the lower reaches of the river; (2) the amount of codon P that is sensitive to stratification rose at the beginning of the river; and (3) the codon T, which is well adapted to the persistently mixed layer or epilimnia of lakes, lost a large number of biomass at the upper and middle reaches of the Tanglang River. In this study, we found that the eutrophic lake had a significant influence on the river downstream. In addition, we found that functional groups were sensitive to the changes of external aquatic conditions and helpful in determining the length of the transition zone.  相似文献