2016年1月9日河北怀来ML3.4震群发震构造分析

本文采用模板识别匹配滤波方法检测2016年1月9日河北怀来M_L3.4震群序列目录中遗漏的地震事件,并加入波形互相关信息对震相到时进行校正,采用盖革法进行精确定位。重新定位后震群震中呈NEE向分布,与怀涿次级盆地北缘断裂走向一致,并主要集中在该断裂的小水峪-黄土窑段。震群中最大地震M_L3.4的P波初动解的一个节面走向与精定位后震中展布和断裂的走向基本一致,可推测怀涿次级盆地北缘断裂可能为怀来M_L3.4震群的发震构造。震中集中分布的怀涿次级盆地北缘断裂的小水峪-黄土窑段属5个分段中滑动速率最大的段落,分析认为该震群可能是由断层慢滑动引起的。     

2005年新疆克孜尔震群的重新定位

用双差地震定位法对2005年9月23日克孜尔震群进行重新定位。 从平面上, 重新定位地震集中分布在一个长约14.5 km, 宽约 9.0 km的长方形内, 其长轴为N30°W向, 与克孜尔断裂近乎垂直。 从震源深度来看, 重新定位地震的震源深度全部分布在21 km以内, 集中分布在10~19 km, 平均深度为13.6 km; 震群中绝大部分小震发生在沉积层内, 而震级较大地震基本发生在结晶地壳的上地壳内。 其剖面图显示, 这次震群是从结晶地壳开始沿着N30°W方向向上破裂至沉积层。 根据震区附近断裂性质和该区历史小震震中分布分析认为, 克孜尔水库库区附近可能存在两条共轭断裂, 右翼断裂可能是这次震群的发震构造。     

汶川8.0级地震序列重新定位及其发震构造初探

采用双差定位方法对汶川8.0级地震及其2,216次余震进行了重新定位,得到2,061次地震的震源位置,定位结果在水平向和垂直向的估算误差大致为1～2km和2～3km。8.0级主震的震中位置大致为北纬31.00°,东经103.38°,震源深度13km左右,发震构造为龙门山中央断裂。余震震中沿走向分布的总长度为330km左右,震源深度优势分布在3～20km,表现出明显的分段活动特征。南段以龙门山中央断裂活动为主,后山断裂和前山断裂也有地震发生,这3条断裂自西向东倾角似乎逐渐变缓,形成叠瓦状的破裂分布。北段龙门山中央断裂、平武-青川断裂等多条断裂参与了发震过程,地震破裂既有逆冲推覆,也有右旋走滑方式     

2013-2016年乳山震群b值深度变化特征及意义

利用双差定位方法,对2013年10月—2016年12月乳山震群进行重定位,并计算乳山震群中地震集中活动区域b值,分析其深度分布变化。结果显示：地震重定位后表现为近NW向集中分布;b值在震源深度7.4 km上下最小,反映该深度处应力最强;乳山震群b值并不随震源深度增大而呈系统性减小变化,且深度10.2 km以下无有效b值,进一步证实该震群近NW向发震断裂的存在。根据b值随深度的变化特征,推测断裂活动的高应力区域集中在6.5—10.2 km深度范围内,断裂活动在深度7.4 km处应力最强,且水平分布最广;相比上下两侧地壳介质b值在5.5—6.2 km深度层位明显增大,反映该深度层位介质性质存在明显差异。     

2018年5月6日称多5.3级地震序列重定位及发震构造分析

采用双差定位法对2018年5月6日称多5.3级地震及其余震序列进行重新定位,至2018年7月15日共获取129个地震的重新定位结果。结果显示,称多5.3级地震序列主要呈NWW或NNW向分布,其中长轴沿NWW向展布,长约11 km,震源深度主要分布在6-12 km范围内,优势分布为8-11 km。此次地震的震源机制解为走滑型,最佳波形拟合深度为10.1 km。结合精定位、震源机制等综合分析,认为主破裂面走向呈NNW向,发震构造应为巴颜喀拉山主峰断裂。     

盖州青石岭地震序列发震构造初探

利用双差定位方法对盖州青石岭震群2012年2月至2015年8月的地震活动进行了重新定位,并使用CAP方法和P波初动法计算了M_L≥4.0地震的震源机制解,之后结合盖州地区的地震地质资料,分析了青石岭震群的发震构造.结果表明:青石岭震群在平面上呈NW向分布,地震活动主要分布在6 km×3 km的矩形范围内,震源深度为7—10 km;较大地震的震源机制解的走向与精定位后地震的优势分布方向一致;综合分析双差定位结果、震源机制解和发震区的地震地质等资料,初步认为九寨—盖县北段西北侧存在NW向次级铲式正断层,青石岭震群即为该断层在区域应力场作用下不断地左旋走滑-拉张错动造成的.      

2013年吉林前郭5.8级震群精定位及发震构造分析

利用吉林区域数字地震台网和流动台网的观测数据,采用Hypo DD方法精确定位了2013年10月31日~12月10日发生在吉林前郭地区343次地震事件的震源位置。重新定位结果显示,地震序列优势分布方向为NW向,平行于查干泡-道字井断裂北支。重新定位后的震源分布更趋集中在断裂带附近,且深度多集中在6~14km范围内,表明研究区的孕震层主要集中在中上地壳,与该区的地下介质性质关联明显。以同样的方法修正了5.5级和5.8级地震序列的震中位置和震源深度,重定位后2次序列的优势方向、优势深度和破裂长度均存在明显差异。基于震源机制解及震源深度剖面图初步推测此次地震的发震构造应为NNW向的查干泡-道字井断裂。     

2003年新疆石河子5.4级地震序列重新定位及发震断层与机制分析

利用双差地震定位法对2003年2月14日石河子5.4级地震及其余震进行重新定位。定位结果显示,石河子地震及其余震呈N40°E方向线性展布,与准噶尔南缘断裂近乎垂直;震源深度全部分布在15~30 km范围内,优势分布为15~25 km。石河子5.4级地震震中位置为44.001395°N,85.872175°E,距离新疆地震局测得的震中位置仅1.2 km,而距离宏观考察的震中位置约49 km。分析重定位结果其震源机制解得出,这次地震的发震构造是准噶尔南缘断裂,而不是宏观考察的以连哈比尔尕山断裂;节面Ⅰ是主破裂面,而且其走向与重定位地震序列的展布方向基本一致。     

2019年1月12日新疆疏附5.1级地震序列重定位及发震构造研究

基于新疆区域数字地震台网震相观测报告, 采用双差定位方法对2019年新疆疏附M_S5.1地震序列M_L≥1.0地震进行重定位, 采用CAP波形反演方法, 获得了主震的震源机制解和震源矩心深度, 进而综合分析了本次地震可能的发震构造。 结果表明, 疏附5.1级地震震源位置为39.59°N, 75.57°E, 初始破裂深度为18 km, 震源矩心深度为18 km。 重定位后的地震序列呈两个优势方向展布, 分别为NEE向和NE向分支, NEE向为主要的余震优势分布区域, 呈长约13 km窄带状分布在喀什断裂附近。 另一条优势分布为沿NE向长度约9 km, 这可能与喀什断裂阶区有关。 深度剖面显示, 地震震源深度主要集中分布在8~20 km。 沿NEE走向深度剖面显示, 疏附5.1级地震破裂于深部, 余震沿优势分布的震源深度自SWW向NEE呈现逐渐加深的变化特征。 垂直于震中优势分布的深度剖面显示, 本次地震发震断层面倾向为N倾。 震源机制解显示本次地震断错类型为逆冲型, 结合震源深度剖面特征推断节面Ⅰ为本次地震的发震断层面。 综合地震序列空间分布特征、 震源机制以及震源区地质资料, 推测此次地震的发震构造可能为喀什断裂, 余震向浅部扩展。     

伽师强震群震源特征及震源机制力学成因分析

应用改进的主地震相对定位法对17年伽师强震群3级以上地震进行了精确定位,根据较强地震的空间分布和震源机制解推断出伽师震群的发震构造为北北西向的雁行断裂.根据伽师震群地震的2177个P波初动方向记录,计算了伽师震群的平均震源机制解.基于Silver的震源模型,由震源谱推断了伽师震群主要地震的破裂方向,破裂尺度及应力降.文中最后用右阶雁行断裂的数值模型计算了伽师震群的发震构造所产生的扰动应力场的空间分布图像,用其解释了序列地震震源机制的多样性和低应力降现象,并认为特定的雁行发震构造与强震的多发性有关.     

RELOCATION OF THE HUTUBI MS6.2 EARTHQUAKE SEQUENCE ON 8 DECEMBER 2016 AND ANALYSIS OF THE SEISMOGENIC STRUCTURE

Based on the digital waveforms of Xinjiang Seismic Network, the Hutubi M_S6.2 earthquake sequence (M_L ≥ 1.0) was relocated precisely by HypoDD.The best double-couple focal mechanisms of the main shock and aftershocks of M_L ≥ 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 M_S6.2 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.     

2016年运城4.4级地震序列精定位及发震构造分析

根据2016年运城4.4级地震序列资料,进行余震精定位、主震震源机制和发震构造等研究。地震震中分布结果显示,本次地震的发生构造与以往该地区震群型地震发震构造不同,构造单元相对简单,发生在盐湖北岸断裂附近。余震双差精定位结果显示,余震优势分布呈NNE向,NW向也有零星活动。精定位后震源深度集中分布在15-24 km,平均深度20.2 km,断层剖面深度集中分布在18-23 km,倾向NW,与盆地地形构造吻合。采用Snoke与CAP方法得到的震源机制解基本一致,此次序列的主震错断方式为走滑兼逆冲,节面B参数与中条山山前断裂东段走向和倾向接近。综合认为,本次运城地震序列的余震呈NNE向优势分布,精定位结合地震震源机制结果,推断此次地震序列发震断裂为中条山山前断裂的NNE向隐伏断裂。     

DISCUSSION ON RUPTURE CHARACTERISTICS OF THE 2013 TONGLIAO M5.3 EARTHQUAKE AND ITS AFTERSHOCKS

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 (M_L ≥ 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.     

MECHANISM OF THE 2016 HUTUBI,XINJIANG, MS6.2 MAINSHOCK AND RELOCATION OF ITS AFTERSHOCK SEQUENCES

A strong earthquake with magnitude M_S6.2 hit Hutubi, Xinjiang at 13:15:03 on December 8th, 2016(Beijing Time). In order to better understand its mechanism, we performed centroid moment tensor inversion using the broadband waveform data recorded at stations from the Xinjiang regional seismic network by employing gCAP method. The best double couple solution of the M_S6.2 mainshock on December 8th, 2016 estimated from local and near-regional waveforms is strike:271°, dip:64ånd rake:90° for nodal plane I, and strike:91°, dip:26ånd rake:90°for nodal plane Ⅱ; the centroid depth is about 21km and the moment magnitude(M_W)is 5.9. ISO, CLVD and DC, the full moment tensor, of the earthquake accounted for 0.049%, 0.156% and 99.795%, respectively. The share of non-double couple component is merely 0.205%. This indicates that the earthquake is of double-couple fault mode, a typical tectonic earthquake featuring a thrust-type earthquake of squeezing property.The double difference(HypoDD)technique provided good opportunities for a comparative study of spatio-temporal properties and evolution of the aftershock sequences, and the earthquake relocation was done using HypoDD method. 486 aftershocks are relocated accurately and 327 events are obtained, whose residual of the RMS is 0.19, and the standard deviations along the direction of longitude, latitude and depth are 0.57km, 0.6km and 1.07km respectively. The result reveals that the aftershocks sequence is mainly distributed along the southern marginal fault of the Junggar Basin, extending about 35km to the NWW direction as a whole; the focal depths are above 20km for most of earthquakes, while the main shock and the biggest aftershock are deeper than others. The depth profile shows a relatively steep dip angle of the seismogenic fault plane, and the aftershocks dipping northward. Based on the spatial and temporal distribution features of the aftershocks, it is considered that the seismogenic fault plane may be the nodal plane I and the dip angle is about 271°. The structure of the Hutubi earthquake area is extremely complicated. The existing geological structure research results show that the combination zone between the northern Tianshan and the Junggar Basin presents typical intracontinental active tectonic features. There are numerous thrust fold structures, which are characterized by anticlines and reverse faults parallel to the mountains formed during the multi-stage Cenozoic period. The structural deformation shows the deformation characteristics of longitudinal zoning, lateral segmentation and vertical stratification. The ground geological survey and the tectonic interpretation of the seismic data show that the recoil faults are developed near the source area of the Hutubi earthquake, and the recoil faults related to the anticline are all blind thrust faults. The deep reflection seismic profile shows that there are several listric reverse faults dipping southward near the study area, corresponding to the active hidden reverse faults; At the leading edge of the nappe, there are complex fault and fold structures, which, in this area, are the compressional triangular zone, tilted structure and northward bedding backthrust formation. Integrating with geological survey and seismic deep soundings, the seismogenic fault of the M_S6.2 earthquake is classified as a typical blind reverse fault with the opposite direction close to the southern marginal fault of the Junggar Basin, which is caused by the fact that the main fault is reversed by a strong push to the front during the process of thrust slip. Moreover, the Manas earthquake in 1906 also occurred near the southern marginal fault in Junggar, and the seismogenic mechanism was a blind fault. This suggests that there are some hidden thrust fault systems in the piedmont area of the northern Tianshan Mountains. These faults are controlled by active faults in the deep and contain multiple sets of active faults.     

2015年7月3日皮山6.5级地震发震构造初步研究

基于新疆区域数字地震台网记录,采用CAP（Cut and Paste）方法反演了2015年7月3日皮山6.5级主震和部分M_S3.6以上余震的震源机制解和震源深度;采用HypoDD方法重新定位了序列中M_L2.5以上地震序列的震源位置,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.基于上述研究,综合分析了皮山6.5级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,利用CAP方法得到的最佳双力偶机制解节面I：走向280°/倾角60°/滑动角90°;节面Ⅱ：走向100°/倾角30°/滑动角90°,矩心深度19 km,表明该地震为一次逆冲型地震事件.大部分M_S3.6以上余震震源机制与主震具有一定的相似性.双差定位结果显示,M_L2.5以上的余震序列主要分布在主震的西南方向,深度主要分布在0～15 km范围内,余震分布显示出与发震构造泽普隐伏断裂一致的倾向南西的特征.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104°/倾角34°/滑动角94°,该结果与主震震源机制解中节面Ⅱ的滑动角较为接近,绝大多数余震发生在断层面附近10 km左右的区域.根据本研究得到的震源机制、精定位结果以及利用小震分布和区域应力场拟合得到的断层面的参数,结合震源区地质构造情况,初步给出了此次皮山6.5级地震的发震模式.     

2020年2月18日长清MS4.1地震发震构造研究

本文利用基于波形互相关的双差定位方法对2020年2月18日长清M_S4.1地震序列进行了精定位计算, 共得到33个地震事件的精定位结果。 结果显示, 地震序列主要沿NW向分布, 在水平方向上具有自NW向SE迁移, 在深度上具有由浅向深迁移的特征; 序列震源深度主要集中在2~7 km, 其中, 主震的震源深度约2.8 km。 由于长清地震序列的地震数量较少, 为了更准确地了解长清地震序列的发震构造、 探索该序列的发生和发展过程, 本文采用CAP方法反演了主震的震源机制解, 其中, 节面Ⅰ走向223°、 倾角42°、 滑动角-160°, 节面Ⅱ走向117.9°、 倾角76.8°、 滑动角-49.8°, 最佳拟合震源矩心深度约2.8 km, 矩震级M_W4.2。 结合区域构造特征分析认为, 长清M_S4.1地震的发震断裂为孝里铺断裂和东阿断裂之间发育的一条浅层次生断裂。 在ENE向区域应力场作用下, 发震断裂产生高角度正断滑动, 并伴有左旋走滑分量, 从而引发长清地震序列。     

2021年吴忠—灵武ML3.6震群重新定位及震源机制研究

2021年7月18日—8月7日,宁夏吴忠—灵武地区发生M_L3.6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M_L3.6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M_L3.0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M_L3.6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M_L3.2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M_L3.1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M_L3.0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M_L3.6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M_L3.6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。      

MATCH AND LOCATE FOR SMALL EVENT DETECTION OF NINGXIA SHIZUISHAN EARTHQUAKE SWARM AND INVESTIGATION OF ITS SEISMOGENIC FAULT

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 M_L4.4 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.