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1.
Many small earthquakes occurred intensively and continuously and formed an earthquake sequence after the ML3.8 earthquake happened at Rushan County, Shandong Province on October 1, 2013. Up to March, 2017, more than 13 000 events have been recorded, with 3 429 locatable shocks, of which 31 events with ML ≥ 3.0. This sequence is rarely seen in East China for its extraordinary long duration and the extremely high frequency of aftershocks. To track the developing tendency of the earthquake sequence accurately, 20 temporary seismometers were arranged to monitor the sequence activities around the epicenter of the sequence since May 6, 2014. Firstly, this paper adopts double difference method to relocate the 1 418 earthquakes of ML ≥ 1.0 recorded by temporary seismometers in the Rushan earthquake sequence (May 7, 2014 to December 31, 2016), the result shows that the Rushan earthquake sequence mainly extends along NWW-SEE and forms a rectangular activity belt of about 4km long and 3km wide. In addition, the seismogenic fault of Rushan earthquake sequence stretches along NWW-SEE with nearly vertical strike-slip movement and a small amount of thrust component. Then we apply the P-wave initial motion and CAP to invert the focal mechanism of earthquakes with ML ≥ 1.5 in the study area. The earthquakes can be divided into several categories, including 3 normal fault earthquakes (0.9%), 3 normal-slip earthquakes (0.9%), 229 strike-slip earthquakes (65.8%), 18 thrust fault earthquakes (5.2%), 37 thrust-slip earthquakes (10.6%)and 58 undefined (16.6%). Most earthquakes had a strike-slip mechanism in Rushan (65.8%), which is one of the intrinsic characteristics of the stress field. According to the focal mechanism solutions, we further utilized the LSIB method (Linear stress inversion bootstrap)to invert the stress tensor of Rushan area. The result shows that the azimuth and plunge of three principal stress (σ1, σ2, σ3) axes are 25°, 10°; 286°, 45°; 125°, 43°, respectively. Based on the stress field inversion results, we calculated the focal mechanism solutions consistency parameter (θ)and the angle (θ1)between σ1 and P axis. The trend lines of θ and θ1 were relatively stable with small fluctuation near the average line over time. Furthermore, the earthquake sequence can be divided into three stages based on θ and θ1 values. The first stage is before September 16, 2014, and the variation of the θ and θ1 values is relatively smooth with short period. All focal mechanism solutions of the three ML ≥ 3.0 earthquakes exhibited consistence. The second stage started from September 16, 2014 to July 1, 2015, the fluctuation range of θ and θ1 values is larger than that of the first stage with a relative longer period. The last stage is after July 1, 2015, values of θ and θ1 gradually changed to a periodic change, three out of the four ML ≥ 3.0 earthquakes (strike-slip type)displayed a good consistency. Spatially, earthquakes occurred mainly in green, yellow-red regions, and the focal mechanism parameters consistency θ was dominant near the green region (around the average value), which presents a steady state, and the spatial locations are concordant with the distribution of θ value. Moreover, all of ML ≥ 3.0 earthquakes are located in the transitional region from the mean value to lower value area or region below the mean value area, which also indicates the centralized stress field of the region. 相似文献
2.
Based on the digital waveforms of Xinjiang Seismic Network, the Hutubi MS6.2 earthquake sequence (ML ≥ 1.0) was relocated precisely by HypoDD.The best double-couple focal mechanisms of the main shock and aftershocks of ML ≥ 4.0 were determined by the CAP method. We analyzed the characteristics of spatial distribution, focal mechanisms and the seismogenic structure of earthquake sequence. The results show that the main shock is located at 43.775 9°N, 86.363 4°E; the depth of the initial rupture and centriod is about 15.388km and 17km. The earthquake sequence extends unilaterally along NWW direction with an extension length of about 15km and a depth ranging 5~15km. The characteristics of the depth profiles show that the seismogenic fault plane dips northward and the faulting is dominated by thrusting. The nodal planes parameters of the best double-couple focal mechanisms are:strike 292°, dip 62° and rake 80° for nodal plane I, and strike 132°, dip 30° and rake 108° for nodal plane Ⅱ, indicating that the main shock is of thrust faulting. The dip of nodal planeⅠis consistent with the dip of the depth profile, which is inferred to be the fault plane of seismogenic fault of this earthquake. According to the comprehensive analysis of the relocation results, the focal mechanism and geological structure in the source region, it is preliminarily inferred that the seismogenic structure of the Hutubi MS6.2 earthquake may be a backthrust on the deeper concealed thrust slope at the south of Qigu anticline. The earthquake is a "folding" earthquake taking place under the stress field of Tianshan expanding towards the Junggar Basin. 相似文献
3.
FOCAL MECHANISM AND SEISMOGENIC STRUCTURE OF THE M5.0 YUEXI EARTHQUAKE ON 1 OCT. 2014, SOUTHWESTERN CHINA 
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下载免费PDF全文 The Oct.1,2014 M5.0 Yuexi earthquake occurred on the Daliang Shan fault zone where only several historical moderate earthquakes were recorded.Based on the waveform data from Sichuan regional seismic network,we calculated the focal mechanism solution and centroid depth of the M5.0 Yuexi earthquake by CAP (Cut and Paste) waveform inversion method,and preliminarily analyzed the seismogenic structure.We also calculated the apparent stress values of the M5.0 earthquake and other 14 ML≥4.0 events along the Shimian-Qiaojia fault segment of the eastern boundary of the Sichuan-Yunnan block.The result indicates that the parameters of the focal mechanism solution are with a strike of 256°,dip of 62°,and slip of 167° for the nodal plane Ⅰ,and strike of 352°,dip of 79°,and slip of 29° for the nodal plane Ⅱ.The azimuth of the P axis is 121° with dip angle of 11°,the azimuth of T axis is 217° with dip angle of 28°,and the centroid depth is about 11km,and moment magnitude is MW5.1.According to the focal mechanism solution and the fault geometry near the epicenter,we infer that the seismogenic fault is a branch fault,i.e.,the Puxiong Fault,along the central segment of the Daliang Shan fault zone.Thus,the nodal plane Ⅱ was interpreted as the coseismic rupture plane.The M5.0 Yuexi earthquake is a strike-slip faulting event with an oblique component.The above findings reveal the M5.0 Yuexi earthquake resulted from the left-lateral strike-slip faulting of the NNW Dalang Shan fault zone under the nearly horizontal principal compressive stress regime in an NWW-SEE direction.The apparent stress value of the Yuexi earthquake is 0.99MPa,higher than those of the ML ≥ 4.0 earthquakes along the eastern boundary of the Sichuan-Yunnan block since 2008 Wenchuan M8.0 earthquake,implying a relatively high stress level on the seismogenic area and greater potential for the moderate and strong earthquake occurrence.It may also reflect the current increasing stress level of the entire area along the eastern boundary,and therefore,posing the risk of strong earthquakes there. 相似文献
4.
2021年7月18日—8月7日,宁夏吴忠—灵武地区发生ML3.6显著震群活动。本文利用多阶段定位方法对该震群进行了重新定位,并根据gCAP方法反演了2021年7月20日灵武ML3.6地震的震源机制及震源矩心深度,采用Snoke方法计算了震群中3次ML3.0以上地震的震源机制,测定了同一地震多个震源机制的中心解。结果表明,该震群中最大的地震即7月20日02时40分ML3.6地震的震源机制为节面Ⅰ走向289°,倾角72°,滑动角?22°,节面Ⅱ走向26°,倾角69°,滑动角?161°,震源矩心深度为12 km,初始破裂深度为12.5 km;7月20日03时15分ML3.2地震的震源机制为节面Ⅰ走向290°,倾角82°,滑动角?2°,节面Ⅱ走向20°,倾角88°,滑动角?172°,初始破裂深度为11.9 km;7月21日04时55分ML3.1地震的震源机制为节面Ⅰ走向285°,倾角53°,滑动角2°,节面Ⅱ走向194°,倾角88°,滑动角143°,初始破裂深度为11.6 km,这些地震震源机制的主压应力轴主要为NE向。该震群序列的震源深度主要相对集中在7—15 km之间,其中ML3.0以上地震的震源深度主要介于11—13 km,震源深度剖面显示震群相对集中的区域由深到浅大体呈现近似于陡立的展布。本文进一步研究发现区域应力场在灵武ML3.6地震震源机制NNE向节面产生的相对剪应力为0.393,而在NWW向节面产生的相对剪应力为0.945。结合地质构造和已有断层资料初步分析认为,若NNE向的崇兴隐伏断裂为灵武ML3.6地震的发震断层,则表明崇兴断裂可能是一条断裂薄弱带,地震破裂方式主要为右旋走滑;若NWW向的未知隐伏断裂为发震断层,则表明NWW向断裂可能为该地震在区域应力场下的剪应力相对最大释放节面,其破裂方式为左旋走滑。 相似文献
5.
Based on the phase report of Xinjiang Seismic Network, the Hutubi MS6.2 earthquake sequence ML ≥ 1.0 was relocated by the HypoDD method. The results show that the aftershocks were distributed along NE and NW direction. The aftershocks were in the depths of 5~15km. In addition, by using the digital waveforms of Xinjiang Seismic Network, the best double-couple focal mechanism of the main shock and some aftershocks of MS ≥ 3.8 were determined by the CAP method. Based on the above studies, the source depth, focal mechanism and aftershock distribution of the Hutubi MS6.2 earthquake were analyzed and the seismogenic structure was discussed. The nodal plane parameters of the best double-couple focal mechanism are strike 144°, dip 26°, rake 118°, and strike 293°, dip 67°, rake 77°, respectively. The moment magnitude MW is about 5.9, with centroid depth of 15.2km. These show that the main shock was a thrust type. Most focal mechanism solutions of the aftershocks were shown as a thrust type, which are similar to the main shock. It is speculated that the possible seismogenic fault of this earthquake is the Huorgosi-Manas-Tugulu Fault. 相似文献
6.
Based on the seismic data collected from regional permanent stations and 6 temporal stations, we analyzed the seismic activity from October 2008 to July 2011 in Rongchang area. On the basis of HypoDD relocated results, we used Match&Locate method to detect and located the micro-earthquakes. We obtained the focal mechanism solutions of some earthquakes with ML ≥ 3.5 by using CAP method. Then we analyzed the temporal-spatial distribution of earthquakes and discussed the characteristics of micro-seismicity before the ML5.1 earthquake occurring on September 10, 2010. We totally detected 3 354 micro-earthquake events, which are nearly 5 times of the earthquakes in the seismic catalog issued by China Earthquake Networks Center. The magnitude of the detected events is mostly from ML-1 to 1, and the focal depth is from 2 to 4km. The magnitude-frequency analysis shows that the catalog completeness is obviously improved after adding the detected earthquakes, with the lowest magnitude decreasing from ML1.0 to 0.3. The earthquakes hypocenters are mainly clustered along faults or buried faults and in a dominant depth range consistent with the depth of injection wells, and also show a tendency of lateral extension from injection wells. The focal mechanism solutions of 9 earthquakes of ML ≥ 3.5 presented reverse faulting, as the same as the preexisting faults, indicating that earthquakes were surely related to reactivation of the faults. The strike, dip and rate of the causative faults separated in wide ranges, which indicates not only obvious changes in structure and strike of preexisting faults but also the effect of increasing pore pressure on the local stress field. Before the ML5.1 earthquake on September 10 of 2010, seismicity firstly showed clustering in time and covered the most part of the seismogenic fault in space. Then an obvious seismic quiescence occurred and lasted about 3 months. The phenomenon is consistent with the mechanism of creep sliding and resistance-uniformization along the fault zone, suggested on the basis of laboratory experiments, and it may be one of patterns of sub-instability along fault zone. However, such explanation needs to be further confirmed. 相似文献
7.
On two velocity models, the HypoDD method is used to accurately locate the Tongliao M5.3 earthquake sequence, then the CAP method is used to invert the focal mechanism solutions. The parameters of the seismogenic fault plane are fitted quantitatively by the small earthquake distribution and the regional stress field. The geometry, rupture features and possible seismogenic structure of the Tongliao M5.3 earthquake are comprehensively determined. The HypoDD relocation results show that this earthquake is located at 42.95°N, 122.37°E, the whole sequence trends in NW and major aftershocks (ML ≥ 3.0) strike in NEE direction. With the time elapsed, the aftershocks extended to the shallow crust gradually. Comparing the focal mechanism solutions and relocation results, we determine that the fitted causative fault based on NNW-trending aftershock distribution is reliable, which has the top left corner (43.00°N, 122.35°E, depth 3.3km), lower left corner (43.00°N, 122.35°E, depth 8.9km), upper right corner (42.92°N, 122.37°E, depth 3.3km), lower right corner (42.92°N, 122.37°E, depth 8.9km), extending range 3km×7km, trending in 349° (NNW), dip angle 86° (nearly vertical), and slip angle 15°. It is inferred that whole process of main shock rupture is from the source to the NW and SE sides as a shear. The rupture degree is larger in southeast where the late rupture concentrated, and did not reach the surface. 相似文献
8.
基于中国国家和四川区域数字地震台网记录,采用HypoDD方法精确定位了四川芦山ML2.0级以上地震序列的震源位置,采用CAP方法反演了36次ML4.0级以上地震的最佳双力偶震源机制解,并利用小震分布和区域应力场拟合了可能存在的发震断层面参数,从而综合分析了芦山地震序列的震源深度、震源机制和震源破裂面特征,探讨可能的发震构造.结果显示,7.0级主震的震源位置为30.30°N、102.97°E,初始破裂深度为15 km左右,震源矩心深度为14 km左右,最佳双力偶震源机制解的两组节面分别为走向209°/倾角46°/滑动角94°和走向23°/倾角44°/滑动角86°,可视为纯逆冲型地震破裂,绝大多数ML4.0级以上余震的震源机制也表现出与主震类似的逆冲破裂特征.ML2.0级以上余震序列发生在主震两侧,集中分布的长轴为30 km左右,震源深度主要集中在5～27 km,ML3.5级以上较大余震则集中分布在9～25 km的深度上,并揭示出发震断层倾向北西的特征.利用小震分布和区域应力场拟合得到发震断层参数为走向207°/倾角50°/滑动角92°,绝大多数余震发生在断层面附近10 km左右的区域.综合地震序列分布特征、主震震源深度和已有破裂过程研究结果,可以推测主震破裂过程自初始点沿断层的两侧扩展破裂,南侧破裂比北侧稍长,滑动量主要集中在初始破裂点附近,可能没有破裂到地表.综合本文研究成果、地震烈度分布和现有的科学考察结果,初步推测发震构造为龙门山山前断裂,也不排除主震震中东侧还存在一条未知的基底断裂发震的可能性. 相似文献
9.
STUDY ON THE SEISMOGENIC FAULT AND DYNAMICS PARAME-TERS OF THE 2014 MS6.6 JINGGU EARTHQUAKE IN YUNNAN 下载免费PDF全文
下载免费PDF全文 On October 17, 2014, a MS6.6 earthquake occurred in Jinggu, Yunnan. The epicenter was located in the western branch of Wuliang Mountain, the northwest extension line of Puwen Fault. There are 2 faults in the surrounding area, one is a sinistral strike-slip and the other is the dextral. Two faults have mutual intersection with conjugate joints property to form a checkerboard faulting structure. The structure of the area of the focal region is complex. The present-day tectonic movement is strong, and the aftershock distribution indicates the faulting surface trending NNW. There is no obvious surface rupture related to the known fault in the epicenter, and there is a certain distance from the surface of the Puwen fault zone. Regional seismic activity is strong. In 1941, there were two over magnitude 7.0 earthquakes in the south of the epicenter of Jinggu County and Mengzhe Town. In 1988, two mainshock-aftershock type earthquakes occurred in Canglan-Gengma Counties, the principal stress axes of the whole seismic area is in the direction of NNE. Geological method can be adopted to clarify the distribution of surficial fracture caused by active faults, and high-precision seismic positioning and spatial distribution characteristics of seismic sequences can contribute to understand deep seismogenic faults and geometric features. Thus, we can better analyze the three-dimensional spatial distribution characteristics of seismotectonics and the deep and shallow tectonic relationship. The focal mechanism reveals the property and faulting process to a certain extent, which can help us understand not only the active property of faults, but also the important basis for deep tectonic stress and seismogenic mechanism. In order to study the fault characteristic of the Jinggu earthquake, the stress field characteristics of the source area and the geometric parameters of the fault plane, this paper firstly uses the 15 days aftershock data of the Jingsuo MS6.6 earthquake, to precisely locate the main shock and aftershock sequences using double-difference location method. The results show that the aftershock sequences have clustering characteristics along the NW direction, with a depth mainly of 5~15km. Based on the precise location, calculations are made to the focal mechanisms of a total of 46 earthquakes including the main shock and aftershocks with ML ≥ 3.0 of the Jinggu earthquake. The double-couple(DC)component of the focal mechanism of the main shock shows that nodal plane Ⅰ:The strike is 239°, the dip 81°, and the rake -22°; nodal plane Ⅱ, the strike is 333°, the dip 68°, and the rake -170.31°. According to focal mechanism solutions, there are 42 earthquakes with a focal mechanism of strike-slip type, accounting for 91.3%. According to the distribution of the aftershock sequence, it can be inferred that the nodal plane Ⅱ is the seismogenic fault. The obtained focal mechanism is used to invert the stress field in the source region. The distribution of horizontal maximum principal stress orienation is concentrated. The main features of the regional tectonic stress field are under the NNE-SSW compression(P axis)and the NW-SE extension(T axis)and are also affected by NNW direction stress fields in the central region of Yunnan, which indicates that Jinggu earthquake fault, like Gengma earthquake, is a new NW-trending fault which is under domination of large-scale tectonic stress and effected by local tectonic stress environment. In order to define more accurately the occurrence of the fault plane of the Jinggu earthquake, with the precise location results and the stress field in the source region, the global optimal solution of the fault plane parameters and its error are obtained by using both global searching simulated annealing algorithm and local searching Gauss-Newton method. Since the parameters of the fault plane fitting process use the stress parameters obtained by the focal mechanism inversion, the data obtained by the fault plane fitting is more representative of the rupture plane, that is, the strike 332.75°, the dip 89.53°, and the rake -167.12°. The buried depth of the rupture plane is 2.746km, indicating that the source fault has not cut through the surface. Based on the stress field characteristics and the inversion results of the fault plane, it is preliminarily believed that the seismogenic structure of the Jinggu earthquake is a newly generated nearly vertical right-lateral strike-slip fault with normal component. The rupture plane length is about 17.2km, which does not extend to the Puwen fault zone. Jinggu earthquake occurred in Simao-Puer seismic region in the south of Sichuan-Yunnan plate. Its focal mechanism solution is similar to that of the three sub-events of the Gengma earthquake in November 1988. The seismogenic structure of both of them is NW-trending and the principal stress is NE-SW. The rupture plane of the Jinggu main shock(NW direction)is significantly different from the known near NS direction Lancang Fault and the near NE direction Jinggu Fault in the study area. It is preliminarily inferred that the seismogenic structure of this earthquake has a neogenetic feature. 相似文献
10.
2019年黄海ML4.6地震序列发生在NW向苏北—滨海断裂带附近，历史上该断裂带附近曾多次发生破坏性地震。为了判断此次地震序列的发生是否与苏北—滨海断裂带活动有关，本文基于黄海ML4.6地震震中附近400 km范围内的测震台站记录，采用CAP方法计算了此次黄海地震序列中ML4.6和ML4.1地震的深度和震源机制解参数，并使用双差定位方法对该地震序列进行了重新定位。研究结果显示:2019年12月8日黄海ML4.6和12日黄海ML4.1地震的震源深度分别为20 km和21 km，位于发震区域的脆韧转换带内；黄海ML4.6地震震源机制解节面Ⅰ的走向、倾角、滑动角分别为123°，74°和61°，节面Ⅱ的走向、倾角、滑动角分别为6°，33°和149°；黄海ML4.1地震震源机制解节面Ⅰ的走向、倾角、滑动角分别为135°，77°和32°，节面Ⅱ的走向、倾角、滑动角分别为37°，59°和165°。两次地震的震源机制解节面参数与苏北—滨海断裂带的几何参数并不一致，表明此次黄海地震序列的发生与苏北—滨海断裂带的主断裂活动没有直接关系。黄海地震序列震中的重新定位结果显示该地震序列呈NW向分布。由上述反演所获的两次黄海地震的震源机制和地震序列的重新定位结果推测，黄海ML4.6和ML4.1地震的破裂方向可能为NW向，黄海ML4.6地震序列可能是发生在区域壳内脆韧转换带的左旋走滑地震事件。 相似文献
11.
RELOCATION OF THE 23 NOVEMBER 2017 WULONG MS5.0 EARTHQUAKE SEQUENCE AND ANALYSIS OF ITS SEISMOGENIC FAULT 下载免费PDF全文
下载免费PDF全文 LI Cui-ping TANG Mao-yun GUO Wei-ying HUANG Shi-yuan WANG Xiao-long GAO Jian 《地震地质》2019,41(3):603-618
The Wulong MS5.0 earthquake on 23 November 2017, located in the Wolong sap between Wenfu, Furong and Mawu faults, is the biggest instrumentally recorded earthquake in the southeastern Chongqing. It occurred unexpectedly in a weak earthquake background with no knowledge of dramatically active faults. The complete earthquake sequences offered a significant source information example for focal mechanism solution, seismotectonics and seismogenic mechanism, which is helpful for the estimation of potential seismic sources and level of the future seismic risk in the region. In this study, we firstly calculated the focal mechanism solutions of the main shock using CAP waveform inversion method and then relocated the main shock and aftershocks by the method of double-difference algorithm. Secondly, we determined the seismogenic fault responsible for the MS5.0 Wulong earthquake based on these calculated results. Finally, we explored the seismogenic mechanism of the Wulong earthquake and future potential seismic risk level of the region.
The results show the parameters of the focal mechanism solution, which are:strike24°, dip 16°, and rake -108° for the nodal plane Ⅰ, and strike223°, dip 75°, and rake -85° for the nodal plane Ⅱ. The calculations are supported by the results of different agencies and other methods. Additionally, the relocated results show that the Wulong MS5.0 earthquake sequence is within a rectangular strip with 4.7km in length and 2.4km in width, which is approximately consistent with the scales by empirical relationship of Wells and Coppersmith(1994). Most of the relocated aftershocks are distributed in the southwest of the mainshock. The NW-SE cross sections show that the predominant focal depth is 5~8km. The earthquake sequences suggest the occurrence features of the fault that dips northwest with dip angle of 63° by the least square method, which is largely consistent with nodal planeⅡof the focal mechanism solution. Coincidentally, the field outcrop survey results show that the Wenfu Fault is a normal fault striking southwest and dipping 60°~73° by previous studies. According to the above data, we infer that the Wenfu Fault is the seismogenic structure responsible for Wulong MS5.0 earthquake.
We also propose two preliminary genetic mechanisms of "local stress adjustment" and "fluid activation effect". The "local stress adjustment" model is that several strong earthquakes in Sichuan, such as M8.0 Wenchuan earthquake, M7.0 Luzhou earthquake and M7.0 Jiuzhaigou earthquake, have changed the stress regime of the eastern margin of the Sichuan Basin by stress transference. Within the changed stress regime, a minor local stress adjustment has the possibility of making a notable earthquake event. In contract, the "fluid activation effect" model is mainly supported by the three evidences as follows:1)the maximum principle stress axial azimuth is against the regional stress field, which reflects NWW-SEE direction thrusting type; 2)the Wujiang River crosscuts the pre-existing Wenfu normal fault and offers the fluid source; and 3)fractures along the Wenfu Fault formed by karst dissolution offer the important fluid flow channels. 相似文献
12.
利用双差定位方法对2018年松原MS5.7地震序列中ML≥1.0地震重新定位，之后使用CAP方法求解松原MS5.7地震序列中强地震的震源机制解，再借助MSATSI软件包反演得到松原地区的区域应力场。综合分析以上研究结果得到如下结论:① 松原MS5.7地震序列发生在NW走向的第二松花江断裂与NE走向的扶余—肇东断裂交会处，将地震精定位结果沿两条断层走向作剖面分析，NW向剖面主轴长度约为5 km，震中分布均匀，NE向剖面主轴长度亦约为5 km，震中呈倾向NE的高倾角分布；② 该序列中的4次ML≥3.7地震的震源机制解具有良好的一致性:节面Ⅰ走向为NE向，节面Ⅱ走向为NW向，均为高倾角走滑断层。中强地震的震源机制节面解与第二松花江断裂性质基本一致，由此推断第二松花江断裂是本次松原地震的发震断层；③ 松原地区的主压应力方位角为N86°E，倾角为7°，主张应力方位角为N24°E，倾角为71°。松原地区的区域应力场既受到大尺度的板块构造运动的控制，又受到区域构造运动的影响。在太平洋板块对北东亚板块向西俯冲作用下，东北地区产生了近EW向的主压应力，受周边地质构造控制，松辽盆地内NE向断裂与NW向断裂交会处易发生走滑型地震，2018年松原MS5.7地震正是在这种构造作用控制下发生的中强地震。 相似文献
13.
An ML4.7 earthquake occurred on February 2,2012 in Liaoning Gaizhou (40.56°N,122.36°E),since then,small earthquakes are frequent in this area,and until now the seismic activity does not stop,several earthquakes with magnitude larger than 4.0 have occurred.As of October 30,2014,1223 earthquakes have happened in the Gaizhou area,including 934 earthquakes with the magnitude ML1.0~1.9,247 with the magnitude ML2.0~2.9 and 45 with the magnitude ML3.0~3.9.Meanwhile,earthquakes are continuously active in Haicheng area where the MS7.3 earthquake happened in 1975,and there are over 1100 earthquakes (ML ≥ 1.0) having occurred since the Gaizhou earthquake swarm activity.Because the polarization direction of the fast shear wave is very sensitive to the variation of the principal stress environment,the shear wave splitting parameter can reflect the regional stress state and the local structural features,especially effective for the analysis of small-scale stress environment characteristics.So based on the seismic activities of the two earthquake clusters,this study analyzes the characteristics of shear-wave splitting in Gaizhou-Haicheng area.Preliminary results show that predominant polarization direction of fast shear-waves in the old earthquake region of Haicheng is stable,consistent with the direction of regional stress field.Due to presence of active fault below the Gaixian station (GAX),the predominant polarization direction of fast shear-waves is more complicated.There are two predominant polarizations,consistent respectively with Jinzhou Fault strike which is below the station and the maximum principal stress direction in this area.In addition,Gaizhou earthquake swarm activity increased after December 22,2013,and after the time node,the predominant polarization direction of fast shear-waves in Gaixian station is SEE,which is close to the predominant polarization direction of fast shear-waves in Yingkou station,at the same time consistent with the maximum principal stress direction of this region.Thus it can be inferred,the enhanced activity of Gaizhou earthquake swarm since December 22,2014 may be related to local enhancement of regional stress.In addition,the average time-delays of slow waves in station YKO and GAX show that there are no obvious changes before and after the time point of December 22,2013,which is different greatly with the previous related researches on the variation of slow wave time-delays,and there is no possibility that the Gaizhou earthquake swarm evolved into foreshock sequences from current preliminary results.We should do more work to study the details of the time delay variation of shear wave splitting parameter. 相似文献
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RESTUDY ON HYPOCENTRAL LOCATION AND SEISMOGENIC TECTONIC OF THE JIUJIANG-RUICHANG MS5.7 EARTHQUAKE SEQUENCE,JIANGXI PROVINCE 下载免费PDF全文
下载免费PDF全文 We collected seismic records of 228 ML≥1.0 Jiujiang-Ruichang MS5.7 earthquake sequence from Dec.26, 2005 to Jun. 30, 2006. By using double-difference method combined with waveform cross-correlation, those earthquakes were relocated and finally the accurate source parameters of 224 earthquakes were obtained. The errors are about 0. 5km in horizontal and less than 2km in vertical direction, respectively. It was found that the depth of earthquake sequence concentrates in 8~14km range, and the epicenters are distributed along both NW and NE direction, and dominantly along NW direction. Combined with the focal mechanism, the distribution direction and the tectonic setting, we infer that the rupture of the NW-trending fault caused the MS5. 7 main shock, and then the rupture probably encountered an asperity and triggered the MS4. 8 strong aftershock. The NE-trending fault came into a seismically quiet period by stress adjustment in a short time, while the NW-trending fault released stress for a long time which caused a series of aftershocks. The MS5. 7 main shock is caused by the NW striking Yangjisshan-Wushan-Tongjiangling Fault and the MS4. 8 aftershock occurred on the NE striking Liujia-Fanjiapu-Chengmenshan Fault. 相似文献
15.
MATCH AND LOCATE FOR SMALL EVENT DETECTION OF NINGXIA SHIZUISHAN EARTHQUAKE SWARM AND INVESTIGATION OF ITS SEISMOGENIC FAULT 下载免费PDF全文
下载免费PDF全文 In this paper, a new method for small event detection named Match & Locate(M&L)is used to detect and locate the small earthquakes that are missing in the catalogue of the February 28, 2014 Shizuishan ML4.4 earthquake swarm. A total of 34 earthquakes were detected, which is nearly 3 times as much as the number(13)of earthquakes from Ningxia seismic network. The number of earthquake swarm sequence is greatly increased. Then, it provides the possibility for the fine study of the earthquake swarm activity and seismogenic fault. The best double couple solution of the main shock obtained by the cut and paste method is strike 354°, dip 70° and slip 166° for nodal plane I, and strike 89°, dip 77° and slip 21°for nodal plane Ⅱ. The main shock is a dextral strike-slip earthquake with a small amount of thrust component. And, the depth of the main shock is 7~8km, which is a shallow earthquake, derived from the results of the double difference relocation and the best fitting depth of focal mechanism. Together with the results of deep 3-D seismic tomography of the Yinchuan Basin, our results show that the main shock and the largest aftershock more likely occurred in the upper crust, and the rest of earthquakes mainly occurred at the bottom of sedimentary layer or on the top of the upper crust crystallization basement. We find some interesting phenomena on the pattern of time-space evolution of the earthquake swarm. The distribution of earthquake swarm is in the near north-south direction. Aftershocks are mainly concentrated in the north region of the main shock, which show an obvious trend of extending gradually from the south to the north. Also, the result shows the general trend of shallower focal depth with the development of aftershocks to the north. The results of distribution and depth profile of the earthquake swarm and the focal mechanism of the main shock all show that the sequence probably occurred in the fault at the east foot of Helan Mountain with an eastward dip and a larger dip angle. Surface projection image of the earthquake sequence shows that the epicenter distribution extends northward from the northern end of the fault. This may suggest that the deep part of the fault is likely to extend northward. 相似文献
16.
THE SOURCE PARAMETERS AND SEISMOTECTONIC IMPLICATIONS OF THE SEPTEMBER 4, 2017 ML4.4 LINCHENG EARTHQUAKE 下载免费PDF全文
下载免费PDF全文 LI He XIE Zu-jun WANG Yi-xi WANG Xiao-shan DONG Yi-bing ZHANG Hui PENG Zhao LIU Wen-bing GAO Ye WANG Li-xia 《地震地质》2019,41(3):670-689
At 3:05, September 4, 2017, an ML4.4 earthquake occurred in Lincheng County, Xingtai City, Hebei Province, which was felt obviously by surrounding areas. Approximately 60km away from the hypocenter of Xingtai MS7.2 earthquake in 1966, this event is the most noticeable earthquake in this area in recent years. On the one hand, people are still shocked by the 1966 Xingtai earthquake that caused huge disaster, on the other hand, Lincheng County is lack of strong earthquakes. Therefore, this quake has aroused widespread concerns by the government, society and seismologists. It is necessary to clarify whether the seismogenic structure of this event is consistent with the previous seismicity and whether it has any new implications for the seismic activity and seismic hazard in this region. Therefore, it is of great significance to study its seismogenic mechanism for understanding the earthquake activity in Xingtai region where a MS7.2 earthquake had occurred in 1966.
In this study, the Lincheng earthquake and its aftershocks are relocated using the multi-step locating method, and the focal mechanism and focal depth are determined by the "generalized Cut and Paste"(gCAP)method. The reliability of the results is analyzed based on the data of Hebei regional seismic network. In order to better constrain the focal depth, the depth phase sPL fitting method is applied to the relocation of focal depth. The inversion and constraint results show that aftershocks are mainly distributed along NE direction and dip to SE direction as revealed by depth profiles. Focal depths of aftershocks are concentrated in the depths of 6.5~8.2km with an average of about 7km. The best double-couple solution of the mainshock is 276°, 69° and -40° for strike, dip and slip angle for nodal plane I and 23°, 53° and -153° for nodal plane Ⅱ, respectively, revealing that it is a strike-slip event with a small amount of normal-fault component. The initial rupture depth of mainshock is about 7.5km obtained by the relocation while the centroid depth is 6km derived from gCAP method which was also verified by the seismic depth phase sPL observed by several stations, indicating the earthquake is ruptured from deep to shallow. Combined with the research results on regional geological structure and the seismic sequence relocation results, it is concluded that the nodal plane Ⅱ is the seismogenic fault plane of this earthquake.
There are several active faults around the hypocenter of Lincheng earthquake sequence, however, none of the known faults on the current understanding is completely consistent with the seismogenic fault. To determine the seismogenic mechanism, the lucubrated research of the MS7.2 Xingtai earthquake in 1966 could provide a powerful reference. The seismic tectonic characteristics of the 1966 Xingtai earthquake sequence could be summarized as follows:There are tensional fault in the shallow crust and steep dip hidden fault in the middle and lower crust, however, the two faults are not connected but separated by the shear slip surfaces which are widely distributed in the middle crust; the seismic source is located between the hidden fault in the lower crust and the extensional fault in the upper crust; the earthquake began to rupture in the deep dip fault in the mid-lower crust and then ruptured upward to the extensional fault in the shallow crust, and the two fault systems were broken successively. From the earthquake rupture revealed by the seismic sequence location, the Lincheng earthquake also has the semblable feature of rupturing from deep to shallow. However, due to the much smaller magnitude of this event than that of the 1966 earthquake, the accumulated stress was not high enough to tear the fracture of the detachment surface whose existence in Lincheng region was confirmed clearly by the results of Lincheng-Julu deep reflection seismology and reach to the shallower fault. Therefore, by the revelation of the seismogenic mechanism of the 1966 Xingtai earthquake, the seismogenic fault of Lincheng earthquake is presumed to be a concealed fault possessing a potential of both strike-slip and small normal faulting component and located below the detachment surface in Lincheng area. The tectonic significance indicated by this earthquake is that the event was a stress adjustment of the deep fault and did not lead to the rupture of the shallow fault. Therefore, this area still has potential seismic hazard to a certain extent. 相似文献
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利用地震科学探测台阵在云南、 贵州地区的17个流动台站的地震记录, 采用双差定位法对2012年9月7日云南彝良MS5.7和MS5.6地震及其余震序列(ML≥1.0)进行重定位． 在获得精确的震源位置后, 采用CAP法反演了MS≥4.0地震的震源机制解． 结果显示, 彝良MS5.7主震位于(27.509°N, 103.971°E), 震源深度为9.7 km, 震源机制解节面Ⅰ走向251°、 倾角66°、 滑动角150°, 节面Ⅱ走向354°、 倾角63°、 滑动角27°; 彝良MS5.6主震位于(27.563°N, 104.034°E), 震源深度为10.0 km, 震源机制解节面Ⅰ走向235°、 倾角39°、 滑动角147°, 节面Ⅱ走向352°、 倾角70°、 滑动角56°． 反演结果显示断层的几何形态、 余震分布特征、 震源机制解特征及构造应力场等均有很好的一致性． 综合断层的运动学特征、 地震活动规律和地质构造背景, 推测彝良地震的发震断裂为昭通断裂带的前缘断裂, 即NE走向的石门断裂． 导致震区受灾严重的主要原因是由于彝良地震震源深度较浅, 能量释放多发生在地壳浅部所致． 相似文献
18.
MECHANISM OF THE 2015 PISHAN,XINJIANG, MS6.5 MAINSHOCK AND RELOCATION OF ITS AFTERSHOCK SEQUENCES 下载免费PDF全文
下载免费PDF全文 Using the digital broadband seismic data recorded by Xinjiang network stations, we obtained focal mechanism of the July 3 Pishan, Xinjiang, MS6.5 earthquake with generalized Cut and Paste(gCAP)inversion method. The strike, dip and rake of first nodal plane are 97°, 27°, 51°, and the second nodal plane are 318°, 70°, 107°. The centroid depth and moment magnitude are calculated to be 12km and 6.4. Combining with the distribution of aftershocks, we conclude that the first nodal plane is the seismogenic fault, and the main shock presents a thrust earthquake at low angle. We relocated 1014 earthquakes using the double-difference algorithm, and finally obtained 937 relocated events. Our results show that the earthquake sequences clearly demonstrate a unilateral extension about 50km nearly in NWW direction, and are mainly located above 25km depth, especially the small earthquakes are predominately located at the shallow parts. Furthermore, the focal depth profile shows a southwestward dipping fault plane at the main shock position, suggesting listric thrust faulting, which is consistent with the dip of the mainshock rupture plane. The spatial distribution of aftershocks represents that the Tarim block was thrust under the West Kunlun orogenic belt. In addition, the dip angle of the fault plane gradually increases along the NWW direction, possibly suggesting a gradual increase of strike-slip component during the NWW rupturing process. From above, we conclude that the Pishan MS6.5 earthquake is the result of Tibet plateau pushing onto the Tarim block from south to north, which further confirms that the continuous collision of India plate and Eurasia plate has strong influence on the seismic activity in and around the Tibet plateau. 相似文献
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利用广东新丰江锡场2012和2013年2次MS4.8地震震中附近的2009年1月至2015年6月精定位小震资料,依据小震丛集发生在大震断层面及附近的原则,采用模拟退火算法和高斯-牛顿算法相结合的方法,反演得到了锡场附近2条相交断层的详细参数及地理分布。NEE向断层F1的走向为78.5°,倾角为87.7°,长度约8.2km,以右旋走滑错动为主;NW向断层F2的走向为137.3°,倾角为87.9°,长度约5.9km,以左旋走滑错动为主。用断层附近ML3以上地震的震源机制解证明反演结果是可靠的,并由2次4.8级地震的震源机制解判断出各自的发震断层。 相似文献
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本文研究了兴都库什及帕米尔地区地震的空间分布.发现h<70km的地震分布广泛,h≥100km的地震形成-S形的倾斜中源地震带.在71.5°E以西,中源地震带倾向接近正北,倾角随深度变化,在深部接近垂直,且倾角自西向东逐渐变陡,在71.5°E以东,倾向逐渐由东南变为正南. 分析了121个mb≥5.0地震的机制解.浅源地震机制解的P轴大多位于NS和NNW-SSE方向,且多近水平,反映此区受到NS或NNW-SSE方向挤压.各剖面应力轴分布规律性强,在150km以下,总的趋势是机制解的T轴接近于倾斜的中源地震带的下倾方向,而P轴倾角较小且垂直于倾斜的中源地震带的走向. 相似文献