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1.
Just after the occurrence of anM=5.2 earthquake in Shimian, Sichuan, two three-component seismometers were set up near the epicenter of the earthquake. Field observations were made for the four-year period from 1989 to 1992. Analysis of the data recorded from either aftershocks following theM=5.2 earthquake or from small earthquakes scattered in this region indicates the presence of shear wave splitting. And shear wave splitting varies with time. The mean direction of polarization of the faster shear waves is N18°W during the period of aftershock activity, which is consistent with the strike of the faulting plane of the mainshock; but has turned to N46°W from 1990 to 1992, which is consistent with the regional maximum compressive stress. The time delays between split shear waves measured on records from 1990 to 1992 are about half of that in 1989. The results obtained from observations at two temporary stations are similar. This indicates that the temporal changes may be related to the occurrence of theM=5.2 mainshock. This study was supported by the Chinese Joint Seismological Science Foundation. The English version is improved by Prof. Xin-Ling QIN, Institute of Geophysics, SSB, China.  相似文献   

2.
Turkey was struck by two major events on August 17th and November 12th, 1999. Named Kocaeli (Mw=7.4) and Düzce (Mw=7.2) earthquakes, respectively, the two earthquakes provided the most extensive strong ground motion data set ever recorded in Turkey. The strong motion stations operated by the General Directorate of Disaster Affairs, the Kandilli Observatory and Earthquake Research Institute of Bogazici University and Istanbul Technical University have produced at least 27 strong motion records for the Kocaeli earthquake within 200 km of the fault. Kocaeli earthquake has generated six motions within 20 km of the fault adding significantly to the near-field database of ground motions for Mw>=7.0 strike–slip earthquakes. The paper discusses available strong motion data, studies their attenuation characteristics, analyses time domain, as well as spectral properties such as spectral accelerations with special emphasis on fault normal and fault parallel components and the elastic attenuation parameter, kappa. A simulation of the Kocaeli earthquake using code FINSIM is also presented.  相似文献   

3.
Just after the occurrence of anM=5.2 earthquake in Shimian, Sichuan, two three-component seismometers were set up near the epicenter of the earthquake. Field observations were made for the four-year period from 1989 to 1992. Analysis of the data recorded from either aftershocks following theM=5.2 earthquake or from small earthquakes scattered in this region indicates the presence of shear wave splitting. And shear wave splitting varies with time. The mean direction of polarization of the faster shear waves is N18°W during the period of aftershock activity, which is consistent with the strike of the faulting plane of the mainshock; but has turned to N46°W from 1990 to 1992, which is consistent with the regional maximum compressive stress. The time delays between split shear waves measured on records from 1990 to 1992 are about half of that in 1989. The results obtained from observations at two temporary stations are similar. This indicates that the temporal changes may be related to the occurrence of theM=5.2 mainshock.  相似文献   

4.
The 17 August 1999 Kocaeli earthquake in Turkey produced a majorsurface rupture. We traced this surface rupture from Gölcük toDüzce and located it accurately by using GPS. The closest distancefrom the surface rupture to the strong motion observation sites weredetermined. Then the attenuation characteristics of the observed peakground acceleration were compared with the attenuation relation given byFukushima and Tanaka (1992), which is suitable for the near-fault zone inJapan and gives results that closely match data recorded during the 1995Hyogo-ken Nanbu earthquake in Japan. Although this attenuation relationwas developed for Japan, we found that it agreed well with the KOCAELIearthquake. Furthermore, the observed spectral acceleration of 5%damping was compared with the building design code of Turkey and theobserved level was lower than the code.  相似文献   

5.
Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters (i.e., the polarization direction of fast shear wave and the time delay of slow wave) to perform a systematic analysis of the crustal seismic anisotropy around the Longmenshan fault in the 2013 MS7.0 Lushan earthquake region. We observed apparent spatio-temporal characteristics in the shear wave splitting parameters. The spatial distribution of fast polarization directions showed a clear partitioning in the characteristics from northwest to southeast in the focal region, which changed from NW-SE to NE-SW. In the northwest of the focal region, the fast polarization direction was oriented to NW-SE, which was parallel to the maximum horizontal compressive stress direction. However, the NE-SW fast polarization direction in the southeast of the focal region was parallel to the Longmenshan fault strike. For station BAX on the Central fault in the middle of the focal region, the distribution of fast polarization directions showed a bimodal pattern, with one dominant in the NE-SW direction and the other in the NW-SE direction. With regard to the temporal variation, the time delays were large in the initial stage after the mainshock but then gradually decreased over time and tended to be stable in the later period. This indicated that stress in the focal region increased to a maximum when the main shock occurred, with the stress release caused by the mainshock and aftershock activity, and the stress gradually decreased after a period of time. The scatter of fast polarization directions was large after the main shock, but over time the scatter gradually decreased, indicating that the Lushan earthquake caused a large perturbation in the local stress field. As the stress gradually decreased and was adjusted by the aftershock activity, the perturbation gradually weakened.  相似文献   

6.
Abstract Seismometers were installed at three depths in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone, southwest Japan. The waveforms recorded by these seismometers are rather simple compared with those recorded at the DPRI 800 m borehole or on the ground surface. These data should be well suited for detecting fault zone-trapped waves and estimating the fault zone structure and its temporal variation related to the healing process of the ruptured fault. Typical waveforms trapped in the fault zone were observed by a surface seismographic array across the Nojima Fault just after the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). Among the wave data recorded in the DPRI 1800 m borehole, however, clear evidences of fault zone-trapped waves have not yet been found, and further studies are continuing. The present study outlines the observation system in the DPRI 1800 m borehole, which will make it easier to access and analyze the borehole data.  相似文献   

7.
The 2010 Yushu MS7.1 earthquake occurred in Ganzi-Yushu fault, which is the south boundary of Bayan Har block. In this study, by using double difference algorithm, the locations of mainshock (33.13°N, 96.59°E, focal depth 10.22 km) and more than 600 aftershocks were obtained. The focal mechanisms of the mainshock and some aftershocks with MS>3.5 were estimated by jointly using broadband velocity waveforms from Global Seismic Network (GSN) and Qinghai Seismic Network as well. The focal mechanisms and relocation show that the strike of the fault plane is about 125° (WNW-ESE), and the mainshock is left-laterally strikeslip. The parameters of shear-wave splitting were obtained at seismic stations of YUS and L6304 by systematic analysis method of shear-wave splitting (SAM) method. Based on the parameters of shear-wave splitting and focal mechanism, the characteristics of stress field in seismic source zone were analyzed. The directions of polarization at stations YUS and L6304 are different. It is concluded that after the mainshock and the MS6.3 aftershock on April 14, the stress-field was changed.  相似文献   

8.
四川宜宾地区S波分裂特征   总被引：1，自引：0，他引：1  
本文采用纵横比与偏振分析相结合的方法测定了2013年4月25日~2015年12月31日四川宜宾地区10个台站S波分裂参数,即快波偏振方向和慢波延迟时间。结果表明,华蓥山断裂两侧台站呈现不同的快波偏振优势方向,断裂带以西的台站偏振优势方向为NW向,与区域应力场方向一致;位于断裂带以东的台站优势偏振方向为NE向,与断裂走向一致。在地震密集分布区域内的CNI台的优势偏振方向为NE向,与台站附近的断裂带走向基本一致。研究区域南段的3个台站(JLI、YAJ、XWE)优势偏振方向近NS向。各个台站平均慢波延迟时间在3.07~11.95ms/km范围内,慢波延迟时间最大的台站是CNI台,距离2013年4月25日06时10分M_L5.2地震震中位置最近,这反映出震源区地震波各向异性程度较强。CNI台站的慢波延迟时间显示,在2015年2月7日M_L4.8地震前观测到慢波延迟时间有明显的上升趋势。  相似文献   

9.
In this paper, variations of shear wave splitting in the 2013 Lushan Ms7.0 earthquake sequence were studied. By analyzing shear wave particle motion of local events in the shear wave window, the fast polarization directions and the delay time between fast and slow shear waves were derived from seismic recordings at eight stations on the southern segment of the Longmenshan fault zone. In the study region, the fast polarization directions show partition characteristics from south to north. And the systematic changes of the time delays between two split shear waves were also observed. As for spatial distribution, the NE fast polarization directions are consistent with the Longmenshan fault strike in the south of focal region, whereas the NW fast direction is parallel to the direction of regional principal compressive stress in the north of focal region. Stations BAX and TQU are respectively located on the Central and Front-range faults, and because of the direct influence of these faults, the fast directions at both stations show particularity. In time domain, after the main shock, the delay times at stations increased rapidly, and decreased after a period of time. Shear-wave splitting was caused mostly by stress-aligned microcracks in rock below the stations. The results demonstrate changes of local stress field during the main shock and the aftershocks. The stress on the Lushan Ms7.0 earthquake region increased after the main shock, with the stress release caused by the aftershocks and the stress reduced in the late stage.  相似文献   

10.
王伶俐  洪敏  高涵  徐良叶  王岩  牛甜 《中国地震》2023,39(1):116-127
基于云南省内及邻区2009—2020年GNSS观测数据解算结果,在各个测点时间序列和速度场的基础上,采用克里金插值方法估计区域应变率场;以连续基准站时间序列为约束,获取漾濞MS6.4地震近场区域的块体应变时间序列。分析发现:漾濞地震发生在前期最大剪应变高值区以及面应变高梯度带的张压转换区,发震的时间处于区域应变积累速率逐渐降低的过程之后。震中近场区域均以NW向断层的右旋走滑应变积累为主,且大多呈现持续增强趋势,与漾濞地震的发震断层走向及其破裂特征一致。震前震区东部块体出现了短期应变趋势转折及反向加速的异常现象,反映了应力-应变积累在接近临界破裂状态时的非线性调整。  相似文献   

11.
To study the crustal movement in the vicinity of the epicenter before the Zhangye MS5.0 earthquake in 2019, the characteristics of crustal deformation before the earthquake are discussed through the GPS velocity field analysis based on the CMONOC data observed from GPS. The baseline time series between two continuous GPS stations and the strain time series of an area among several stations are analyzed in the epicenter area. The resulting time series of baseline azimuth around the epicenter reflects that the energy of the fault in the northern margin of Qilian Mountain is accumulated continuously before 2017. Besides, the movement trend of azimuth slows down after 2017, indicating the stress accumulation on both sides of the seismogenic fault zone has reached a certain degree. The first shear strain and EW-direction linear strain in the epicentral area of the Zhangye MS5.0 earthquake remain steady after 2017, and the surface strain rate decreases gradually after 2016. It is illustrated that there is an obvious deformation loss at the epicentral region three years before the earthquake, indicating that a certain degree of strain energy is accumulated in this area before the earthquake.  相似文献   

12.
Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF-MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR-0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo-ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.  相似文献   

13.
王鹏  侯金欣  吴朋 《中国地震》2017,33(4):453-462
中强地震序列的主震发生后,短时间内受台站距震中较远、尾波干扰和波形重叠等因素的影响,往往会遗漏大量的地震,而地震目录的完整性会直接影响到震后趋势判定和余震序列特征分析的科学性和可靠性。本文利用基于GPU加速的模板匹配方法对2017年8月1～12日的连续波形进行扫描计算,检测九寨沟MS7.0地震前后遗漏的地震事件,选取台网目录中信噪比较高的1033个地震事件作为模板,在主震前7天至震后5天期间识别出4854个检测地震事件,为台网可定位目录的3.3倍,除去对台网单台地震事件的修正外,还检测到1797个遗漏地震事件,将完备震级从1.6级降低到1.4级。基于补充了遗漏地震的完整地震目录,对2017年8月8日九寨沟MS7.0地震序列活动特征进行分析。结果表明,前震序列在主震前短时间内出现了地震活动的密集增强,b值也显示为低值状态,可能是深部断层发生破裂之前的加速蠕动的结果。随着时间的推移,余震序列的完备震级逐渐下降并趋于稳定,b值存在缓慢升高的趋势,未来较长时期内余震序列仍将处于持续衰减的状态。  相似文献   

14.
Using seismic data of the aftershocks sequence of the April 20, 2013 Lushan earthquake recorded by seismic temporary and permanent stations in the source region, with the visual inspection of particle motion diagrams, this paper preliminarily contains the polarization directions of fast shear wave and the time-delays of split shear waves at every station, and analyzes the crustal anisotropic characteristics in the source region. In the study area, the polarization directions at stations BAX, TQU, L132, L133, L134, and L135 are northeast, which is consistent with the strike of Dachuan–Shuangshi fault. There are two polarization directions at MDS and L131, which are northeast and southeast. The scatter of polarization directions suggests the complex stress field around these two stations where two faults intersect. For the normalized time-delays at every station, the range is 1.02–8.64 ms/km. The largest time-delay is from L134 which is closest to the mainshock, and the smallest one is from L133. The variations in time-delays show the decreasing at stations BAX, L134, and L135 because of the stress–relaxation after earthquake.  相似文献   

15.
An earthquake with MS5.8 occurred on 10 March 2011 in Yingjiang county, western Yunnan, China. This earthquake caused 25 deaths and over 250 injuries. In order to better understand the seismotectonics in the region, we collected the arrival time data from the Yunnan seismic observational bulletins during 1 January to 25 March 2011, and precisely hand-picked the arrival times from high-quality seismograms that were recorded by the temporary seismic stations deployed by our Institute of Crustal Dynamics, China Earthquake Administration. Using these arrival times, we relocated all the earthquakes including the Yingjiang mainshock and its aftershocks using the double-difference relocation algorithm. Our results show that the relocated earthquakes dominantly occurred along the ENE direction and formed an upside-down bow-shaped structure in depth. It is also observed that after the Yingjiang mainshock, some aftershocks extended toward the SSE over about 10 km. These results may indicate that the Yingjiang mainshock ruptured a conjugate fault system consisting of the ENE trending Da Yingjiang fault and a SSE trending blind fault. Such structural features could contribute to severely seismic hazards during the moderate-size Yingjiang earthquake.  相似文献   

16.
采用双差定位方法,利用中国地震台网的数据对2017年8月9日精河6.6级地震的余震序列进行了重新定位。截至2017年8月14日16时,共获得209个余震的重新定位结果。结果显示,余震主要呈近EW向或NWW向分布,余震区长约50km,宽约17km。余震分布在主震的西侧,推断此次地震单侧破裂。余震震源深度为1～25km,其中,震级较大余震深度为8～17km。精河地震序列的余震活动随时间呈起伏状衰减,震后2天内比较活跃,此后出现较快衰减。随时间推移,余震区呈现中西部衰减慢、东部衰减快的特点。此次地震震中距2011年精河5.0级地震震中21km,相比2011年精河地震,其震源更深,震级更大,但震源机制解相近,均为逆冲型。结合区域构造背景分析认为,库松木契克山前断裂为此次地震发震构造的可能性较大。  相似文献   

17.
孙冬军  刘芳  毕波 《中国地震》2022,38(1):112-119
本文选取2013年芦山地震和2017年九寨沟地震波形,重新量取垂直向振幅,计算宽频带面波震级MS（BB）,分析各台站实测震级出现方向性差异的原因。其中,通过572个宽频带台站实测芦山地震震级MS（BB）7.1,通过603个宽频带台站实测九寨沟地震震级MS（BB）6.9。芦山地震实测震级大于MS（BB）7.3的台站呈现WN-ES向分布,与断层倾向一致;实测震级小于MS（BB）7.0的台站呈现NE-WS向分布,与其所在断层走向一致。九寨沟地震实测震级大于MS（BB）7.0的台站分布呈现NE向分布,与断层倾向一致;实测震级小于MS（BB）6.8的台站总体分布较为离散,大体呈现NW-SE向分布,与树正断裂走向一致。实测震级偏大的台站方向性分布与多普勒效应和P波辐射花样联系不明显。对比分析芦山地震和九寨沟地震,去除场地响应和仪器自身影响,台站实测震级差异性仍然存在,因此,台站实测震级差异性是由于受到了多普勒效应、辐射花样、仪器和场地响应之外的因素影响。综合考虑地震震级涉及的影响因素,芦山地震和九寨沟地震的台站实测震级差异性可能与地震波的传播路径有关。  相似文献   

18.
The Stone Canyon earthquake sequence started during August 1982 and lasted for about four months. It contained four mainshocks withM L 4, each with an aftershock zone about 4 km long. These mainshocks, progressing from southeast to northwest, ruptured a segment of the fault approximately 20 km long leaving two gaps, which were later filled by theM L =4.6 mainshocks of January 14, and May 31, 1986. The equivalent magnitude of the sequence isM L =5.0.Precursory seismic quiescence could be identified in: (1) the northernmost 10 km of the aftershock zone which contained three of the mainshocks; and (2) the southern gap in the aftershock zone. The fault segment containing the first mainshock and its aftershocks did not show quiescence. This pattern of precursory quiescence is very similar to two cases in Hawaii where the rupture initiation points of the mainshocks (M S =7.2 and 6.6, respectively) were located in volumes of constant seismicity rate, surrounded by volumes with pronounced precursory quiescence.The precursory quiescence before the August 1982 Stone Canyon earthquakes lasted for 76 weeks, amounted to a reduction in rate of about 60%, and could be recognized without any false alarms. That is, the anomaly was unique within the 60 km study segment of the fault and in the years 1975 through August 1982. Eighteen foreshocks occurred between July 27 and August 7, 1982. We conclude that the August 1982 mainshocks could have been predicted, based on seismic quiescence and foreshocks.  相似文献   

19.
Following the theory and definition of the Corioli force in physics, the Corioli force at the site of the M=8.1 Kunlun Mountain Pass earthquake on November 14, 2001, is examined in this paper on the basis of a statistical research on relationship between the Corioli force effect and the maximum attershock magnitude of 20 earth-quakes with M≥7.5 in Chinese mainland, and then the variation tendency of attershock activity of the M=8.1 earthquake is discussed. The result shows: a) Analyzing the Corioli force effect is an effective method to predict maximum attershock magnitude of large earthquakes in Chinese mainland. For the sinistral slip fault and the reverse fault with its hanging wall moving toward the right side oftbe cross-focus meridian plane, their Corioli force pulls the two fault walls apart, decreasing frictional resistance on fault plane during the fault movement and releasing elastic energy of the mainshock fully, so the maximum magnitude of aftershocks would be low. For the dextral slip fault, its Corioli force presses the two walls against each other and increases the frictional resistance on fault plane, prohibiting energy release of the mainshock, so the maximum magnitude of attershocks would be high.b) The fault of the M--8. l Kunlun Mountain earthquake on Nov. 14, 2001 is essentially a sinistral strike-slip fault,and the Corioli force pulled the two fault walls apart. Magnitude of the induced stress is about 0.06 MPa. Alter a comparison analysis, we suggest that the attershock activity level will not be high in the late period of this earth-quake sequence, and the maximum magnitude of the whole aftershocks sequence is estimated to be about 6.0.  相似文献   

20.
通过对2014年8月3日云南省昭通市鲁甸县发生的MS6.5地震的震源机制解、余震空间分布、活动断裂组合样式和区域构造背景等特征的综合分析表明:(1)根据主震及4级以上强余震的震源机制解、余震空间分布、烈度长轴方向,判断本次地震的发震断裂为NW向的包谷垴—小河断裂;(2)根据地表GPS水平运动速率及水平缩短速率的差异性、断裂组合样式和历史余震深度,判断发震断裂具有薄皮-同向差异逆冲型捩断层的特征;(3)包谷垴—小河断裂活动可能主要受深部的"管道流"控制,"管道流"自NW向SE方向运动,在昭通断裂带处受到华南板块的差异阻挡,造成包谷垴—小河断裂西侧管道流运动速率大于东侧管道,从而驱动包谷垴—小河捩断层的左旋滑动,导致了鲁甸地震的发生。  相似文献   

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