新疆天山地区与川滇地区中强地震震源机制解对比分析

利用1970年以来新疆天山地区和川滇地区中强地震震源机制解,对两区中强地震的错动性质做了对比分析,得出以下两点结论:(1)新疆天山地区中强地震断错性质复杂多样,主要以逆断层型和走滑型地震为主;而川滇地区强震主要以走滑型地震为主。(2)新疆天山地区走滑型地震大多包含倾滑分量,单纯的水平错动地震数量极少;而川滇地区走滑型地震的错动方式主要以水平错动为主,倾滑分量较小。     

CHARACTERISTICS OF FOCAL MECHANISMS IN THE DOWNSTREAM RESERVOIR AREAS OF JINSHA RIVER

We select the Xiluodu-Wudongde reservoir area in the downstream of Jinsha River as the research area, and use the CAP and GPAT method to obtain focal mechanisms of M_L ≥ 2.0 earthquakes from 2016 to 2017 in this region. Then, we analyze the spatial distribution characteristics of focal mechanism solutions in each local region and investigate the relationship between seismicity and regional structures. According to 414 focal mechanism solutions we get following conclusions:1)The Xiluodu dam began to impound water on May 4, 2013, and seismicity increased significantly after impoundment. We get 49 focal mechanisms in the Xiluodu dam and its adjacent area which are dominated by thrust faulting and next by strike-slip faulting, which are mainly distributed near the middle section of the Ebian-Jinyang fault zone. The distribution of nodal planes striking in NNW to NE direction is consistent with that of regional faults, and some large earthquakes are controlled by regional structures. 2)There are 39 and 24 focal mechanisms obtained in the unimpounded Baihetan and Wudongde dams and adjacent areas, and the spatial distribution of focal mechanism solutions are relatively consistent, dominated by strike-slip faulting with a small amount of thrust and normal faulting. The sinistral strike-slip earthquakes are consistent with the activity of Xiaojiang fault zone and Puduhe-Xishan Fault. The strikes of the nodal planes are distributed discretely, and many groups of faults intersect with each other in the area, suggesting that the seismogenic environment is relatively complex. 3)The seismicity in Ludian continues to be active after the Ludian M6.5 earthquake. By the end of 2017, we got 260 focal mechanism solutions in the aftershock area of the Ludian M_S6.5 earthquake of Aug 3rd, 2014, which show an "L-shape" in distribution and are dominated by thrust and strike-slip faulting. The long axis is distributed in EW direction, and the short axis is distributed in near NNW direction. The strikes of nodal planes are mainly near EW and near NE, and the nodal planes in the NW direction are less. According to characteristics of a large number of focal mechanism solutions, we deduce that there may exist a buried structure in the EW direction, the seismicity is controlled by different types of faults and the seismogenic structure is very complex. 4)The centroid depth in each region is concentrated in the range of 5~15km, indicating that the seismogenic layer in the study area is 5~15km deep in the middle and upper crust.     

Relative location and source mechanism of inland earthquakes in Northern Egypt

We have relocated 259 inland earthquakes in northern Egypt using the double-difference hypocenter technique. Among this dataset we are able to determine source mechanisms of 200 events using P-wave polarities and amplitude ratios as well. The studied earthquakes have been recorded by the Egyptian National Seismological Network from October 1997 to December 2006 with local magnitude (M_L) varies between 1.5 and 5.0. Three earthquake dislocations have been defined namely: Dahshour, southeast Beni-Suef, and Cairo-Suez district. Earthquake activities tend to occur in clusters along the first dislocation (Dahshour) however, relatively scattered along the second (southeast Beni-Suef) and the third (Cairo-Suez district) dislocations. At Dahshour dislocation three distinct clusters have been distinguished. Source mechanism solutions of Dahshour earthquakes displayed normal faulting with a strike-slip component to strike-slip faulting with a minor normal dip-slip component. Most of earthquake focal mechanism orientations are varying from NE-SW to NW-SE. The fault plane solutions of Beni-Suef earthquakes represented normal faulting with a strike-slip component. If the NNW-SSE striking plane has been chosen to be the actual fault plane, some solutions would indicated normal faulting with a sinistral strike-slip motion and other reflect normal faulting with a dextral strike-slip component. The fault plane solutions of Cairo-Suez district earthquakes are compatible with E-W to ENE-WSW striking normal fault with a dextral strike-slip motion.     

Analysis on the Characteristics of the Kalpin MS5.3 Earthquake Sequence of December 1, 2013 and Anomalies before the Earthquake

This paper introduces the basic parameters, focal mechanism solutions and earthquake sequence characteristics of the Kalpin M_S5.3 earthquake sequence of December 1, 2013, and analyzed seismic activity before the earthquake, the adjacent tectonic features and the precursory anomaly at fixed points within a range of 200km. Research indicates:(1) The earthquake occurred on Kalpin fault, the source rupture type is thrust faulting with sinistral strike-slip component. (2) The earthquake sequence is mainshock-aftershock type, with the aftershock distribution attenuating quickly and trending NE. (3) Abnormal seismic activity before the earthquake was characterized by seismically nesting quiescence of M_S2.0-4.0 earthquakes, seismic quiescence of M_S4.0 earthquakes and seismic belts of M_S3.0 earthquakes in the Kalpin block, abnormal enhancement zone of moderate earthquakes on Puchang fault and seismological parameters. (4) Anomalies of precursory observation data at fixed stations are mainly characterized by mutation. Apart from the borehole tiltmeter in Halajun, the spatial distribution of other abnormal precursors showed a phenomenon of migration from the near field to far field and from the epicenter to the peripheries.     

Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy)

The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting (pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with horizontal σ ₃ (plunge 0°, trend 230°) and subvertical σ ₁ (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators.     

2008年6月10日内蒙古鄂伦春自治旗M5.2地震的震源机制、震源深度和发震构造

2008年6月10日14时5分,内蒙古鄂伦春自治旗发生M5.2地震,该地震处于大兴安岭梯度带北段,是内蒙古东北部地区近年来发生的最大地震。基于内蒙古地震台网观测资料,使用TDMT方法、CAP方法、PTD方法和sPn-Pn等方法测定此次地震的震源机制解和震源深度。结合已有数据资料,分析震源区域地震的时空分布特征和构造应力特征,并探讨该地震的发震构造。此次地震震源深度较浅,位于上地壳,结合震源机制解结果、地震分布特征和构造背景分析认为,此次地震为右旋走滑类型,走向NNE,主压应力方向为SWW。     

SPATIO-TEMPORAL STRESS FIELD VARIATION IN THE CENTRAL LONGMENSHAN FAULT ZONE AFTER THE 2008 WENCHUAN EARTHQUAKE FROM FOCAL MECHANISM SOLUTIONS OF SMALL EARTHQUAKES

We determined the focal mechanism solutions(FMS)of aftershocks of the 2008 Wenchuan earthquake using the waveform data recorded by the Western Sichuan movable seismic array. We further obtained the spatio-temporal variation of the stress field by inverting the stress tensors from these data. The results show that the FMSs of the small earthquakes are primarily reverse faulting with considerable number of normal and strike-slip. The proportion of reverse type earthquakes clearly increases with time, and the spatial distribution of the FMSs is closely related with local geology and the characteristics of the deep faults. The stress tensor inversion results reveal that the orientations of the maximum horizontal compressive stress(S_H)shortly after the mainshock in each area are mainly in EW to NWW-SEE directions, while in the area along Xiaoyudong-to-Lixian aftershock branch it is in NE-SW direction in shallow crust. This implies that the stress field at the early stage after the Wenchuan earthquake is mainly controlled by the dynamic stress change caused by the rupture propagation, and the conspicuous factor determining the S_H direction is the characteristics of the rupture plane. Temporal variations of the stress tensors show that the stress regimes at depth changed from a mixture of reverse and strike-slip faulting to pure reverse, implying that local Coulomb stress caused by the main shock is released through strike-slip faulting and gradually recovers into the background stress field. The change of stress in the shallow subsurface follows that in the deep subsurface with observable time delay.     

涿鹿4.3级地震前后应力场变化特征

采用目前普遍接受的基于初动符号和振幅比的HASH方法,计算了2008年10月至2018年10月张渤带西段中小地震震源机制解;在获得震源机制解的基础上,进一步利用震源机制解一致性参数研究了涿鹿4.3级地震前后的应力场变化特征。结果表明:该区域震源机制解以正断型和走滑型为主,逆冲型次之,涿鹿4.3级地震后走滑型地震较震前略有上升,表明该区域的剪切作用增强;主压应力轴方位大致为NEE-SWW,主张应力轴为SSENNW向;涿鹿4.3级地震发生在震源机制一致性参数的低值边缘附近,发震时间也在一致性参数的低值时段。     

川滇交界东段昭通、莲峰断裂带的地震危险背景

川滇交界东段NE向昭通、莲峰断裂带的研究程度较低.为了了解该断裂带是否存在发生强震/大地震的危险背景,我们基于区域活动构造与动力学、重新定位的小震分布和震源机制解、历史地震破裂区、GPS形变场、现代地震活动及其参数图像等多学科的信息进行综合研究.结果表明:昭通、莲峰断裂带是川滇-华南活动块体/地块边界带的一部分,也是活动及变形的大凉山次级块体与相对稳定的华南地块之间的边界带;结构上表现为2个平行展布、朝南东推覆的断裂带,现今运动为带有显著逆冲分量的右旋走滑性质.沿昭通断裂带无大地震的时间至少为1700 余年,目前存在地震空区.GPS变形图像反映昭通、莲峰断裂带已不同程度闭锁.另外,昭通断裂带的鲁甸附近以及莲峰断裂带的南段分别存在异常低b值区或高应力区.已由低b值区和小震空白区识别出昭通断裂带上的鲁甸-彝良之间存在高应力闭锁段,并估计出其潜在地震的最大矩震级为M_W7.4.本研究因此认为昭通断裂带存在发生强震/大地震的中-长期危险背景, 而莲峰断裂带的危险性还需进一步研究.     

2022年7—9月中国大陆地区M≥4.0地震震源机制解测定

利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法得到2022年7月1日—9月30日发生在中国大陆地区的M≥4.0共18次地震的震源机制解以及2022年9月5日四川泸定M6.8地震的矩心位置和矩心偏移时间。结果显示逆断型6次,走滑型7次,正断型4次,未知型1次。      

1997～1998年伽师强震群小地震震源机制解系统聚类分析

用P、S波最大振幅比法计算1997~1998年伽师强震群MS2.5~3.7小地震震源机制解,对小地震震源机制解进行系统聚类分析。结果表明,伽师小地震主要以走滑和正断层为主,与该时段发生的伽师6级强震具有相似的断错性质。1997年伽师小地震主压应力P轴方位为北东或近南北向,与1997~1998年6级强震主压应力P轴方位一致。1997年4月6日6.4级和1998年8月2日6.1级两次6级正断层地震前出现地震空段现象。     

2014年11月22日康定M6.3级地震序列发震构造分析

2014年11月22日在NW向鲜水河断裂带中南段四川康定县发生M6.3级地震,11月25日在该地震震中东南约10km处再次发生M5.8级地震.基于中国国家数字地震台网和四川区域数字地震台网资料,采用多阶段定位方法对本次康定M6.3级地震序列进行了重新定位;利用gCAP(generalized Cut And Paste)矩张量反演方法获得了M6.3和M5.8级地震的震源机制解与矩心深度,分析了本次地震序列的发震构造,并结合历史强震破裂时空分布和2001年以来小震重新定位结果,对鲜水河断裂带中段强震危险性进行了初步探讨.获得的主要结果如下:(1)M6.3级主震震中位于101.69°E、30.27°N,震源初始破裂深度约10km,矩心深度9km;M5.8级地震震中位于101.73°E、30.18°N,初始破裂深度约11km,矩心深度9km.gCAP矩张量反演结果揭示这两次地震双力偶分量占主导,M6.3级地震的最佳双力偶解节面Ⅰ走向143°/倾角82°/滑动角-9°,节面Ⅱ走向234°/倾角81°/滑动角-172°.M5.8级地震最佳双力偶解节面Ⅰ走向151°/倾角83°/滑动角-6°,节面Ⅱ走向242°/倾角84°/滑动角-173°.依据余震分布长轴展布与断裂走向,判定节面Ⅰ为发震断层面,M6.3和M5.8级地震均为带有微小正断分量的左旋走滑型地震.(2)序列中重新定位的459个地震平均震源深度约9km,地震主要集中分布在6~11km深度区间,余震基本发生在M6.3和M5.8级地震震源上部.依据余震密集区展布范围,推测本次康定地震的震源体尺度长约30km、宽约4km、深度范围约6km.M6.3级主震震源附近的余震稀疏区可能是一个较大的凹凸体(asperity),在主震中能量得以充分释放.(3)最初3天的余震主要分布在M6.3级地震NW侧;而M5.8级地震之后的余震主要集中在其震中附近.M6.3级地震以及最初3天的绝大部分余震发生在倾角约82°近直立的NW走向色拉哈断裂上;M5.8级地震与其后的多数余震发生在倾角约83°近直立的NW走向折多塘断裂北端走向向北偏转部位,M5.8级地震可能是M6.3级地震触发相邻的折多塘断裂活动所致.(4)康定M6.3与M5.8级地震发生在鲜水河断裂带乾宁与康定之间的色拉哈强震破裂空段,本次地震破裂尺度较小,尚不足以填补该强震空段.色拉哈段以及相邻的乾宁段7级地震平静时间均已超过其平均复发周期估值,未来几年存在发生7级地震的危险.康定M6.3级地震序列基本填补了震前存在于塔公与康定之间的深部小震空区,未来强震发生在塔公至松林口段深部小震稀疏区内的可能性很大.     

濮阳小震集中区地震丛集特征分析

利用濮阳小震集中区1970年1月—2019年12月地震目录,基于最邻近事件距离算法计算地震丛集率,分析该区地震丛集特征。结果发现:(1)在中强地震前,濮阳小震集中区地震丛集率存在高值现象,而后出现不同程度的低值,与强震前地震活动从增强到平静的过程相吻合,对地震危险区判定有一定指示意义;(2) 1997年以来,4级以上地震主要分布在聊城—兰考断裂西侧,且小震出现相对“稀疏”异常,应给予关注。     

云南地区现代构造应力场研究

利用云南及周边地区中强地震震源机制解资料,采用对震源机制参数进行统计的方法,详细分析了地震断层类型和云南地区的现代构造应力场特征.结果表明,云南地区发生的中强地震走滑型地震占绝大多数,比例为80%,正断型和正走滑型与逆断型和逆走滑型地震所占的比例相当,分别约为8%.云南地区应力场接近水平,地震错动面的倾角较陡.云南地区...     

长宁地区复杂地震活动的力学成因分析

长宁地区地震活动复杂,发生在长宁背斜轴部的长宁Ms6.0地震及其后续中强余震的震源机制与相距仅十几公里的南部向斜区内的中强震具有显著差异;这种差异仅仅是由于发震断层构造不同所造成的,还是孕育地震的应力场本身也存在局部变化?为了回答这一问题,本文在通过双差层析成像反演修正小震定位和波速结构的基础上,利用小震综合震源机制解...     

FOCAL MECHANISM AND SEISMOGENIC STRUCTURE OF THE M5.0 YUEXI EARTHQUAKE ON 1 OCT. 2014, SOUTHWESTERN CHINA

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 M_L≥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 M_W5.1.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 M_L ≥ 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.     

2009年7月24日西藏尼玛西南MS5.6地震研究

主要研究2009年7月24日西藏尼玛西南MS5.6地震的基本参数、地震序列特征、震源参数、发震构造等;利用震中附近600km范围内台站测定参数研究地震的震源机制解,与哈佛大学给出的震源机制解较一致,且与通过现场考察的发震断层走向具有一致性。研究认为本次地震发生在冈底斯山—拉萨块体内部,断裂为NNW向,主要受张应力作用产生左旋走滑正断层活动。此外还分析了震前地震学条带异常特征,结束表明,震前1年出现NW向条带非常显著,研究结论为该地区今后地震预测提供科学依据。     

2022年10月—2023年2月中国大陆地区M≥4.0地震震源机制解测定

利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法得到2022年10月1日—2023年2月28日发生在中国大陆地区的M≥4.0共46次地震的震源机制解以及2023年1月30日新疆沙雅M6.1地震的矩心位置和矩心偏移时间。结果显示逆断型15次,走滑型15次,正断型14次,未知型2次。     

2021年12月中国大陆地区M≥4.0地震震源机制解测定

为了填补测震台网地震震源参数目录常规数据产出方面的空白,本文利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法对2021年12月1—31日发生在中国大陆地区的M≥4.0共6次地震进行震源机制反演。结果显示逆断型3次,走滑型2次,未知型1次。      

Study on the Anomaly of Small Earthquake Activity Before Moderate-strong Earthquake in the Northeast Margin of the Qinghai- Xizang （Tibet） Block

26 earthquakes with MS ≥5. 0 have been recorded in the northeast margin of the Qinghai- Xizang (Tibet) block since 1980,22 of which were relatively independent of other moderate- strong earthquakes. Research on the increase of small earthquake activity before the 22 moderate-strong earthquakes has indicated that small earthquake activity was enhanced before 17 of the moderate-strong earthquakes. Though the increased seismicity is a common phenomenon in the northeast margin of the Qinghai-Xizang ( Tibet ) block,we have difficulty in predicting the moderate-strong earthquakes by this phenomenon. In order to predict the moderate-strong earthquakes through the increased seismicity of small earthquakes,this paper attempts to propose a new method, which calculates small earthquake frequency through the change of distribution pattern of small earthquakes, based on the characteristics of small earthquake activity in the northeastern Qinghai-Xizang (Tibet) block,and then make primary applications. The result shows that we are able to obtain obvious anomalies in the frequency of small earthquakes before moderate strong earthquakes through the new method,with little spatial range effect on the amplitude of this small earthquake frequency anomaly. We can obtain mid to short-term anomaly indices for moderate-strong earthquakes in the northeast margin of the Qinghai-Xizang (Tibet) block.