The 2024 Mw 7.0 Wushi earthquake is the largest earthquake within the seismically active Tian Shan during the past three decades. Through integrated analyses of seismic, geodetic, and geologic data, here we investigate the fault structure corresponding to the Wushi mainshock and subsequent aftershocks. Our work reveals (i) a moderately-dipping, oblique-reverse main-fault rupture and (ii) numerous steeply to vertically-dipping subfault ruptures that align obliquely in cross-section to the main fault. The subfaults made clear aftershock concentrations while the main fault did not, and a shallowly-buried subfault generated clear surface rupture despite the main fault being totally blind. This fault network, misoriented with the prevailing background stress field, likely forms through a reactivation of inherited planes of weakness. These results demonstrate the significant control of structural inheritance on fault geometric architecture and highlight the complexity of seismic activity and rupture behavior of the yielding fault network.

Based on the seismic magnitude-frequency relationship observed for earthquakes with a local magnitude (M-L) of 2.0 or higher in North China between 1970 and 2022, a maximum cutoff magnitude of M(L)7.3 is projected under long-term conditions. Based on a three-year-scale scanning, we forecast the maximum cutoff magnitude for the year 2023 as M(L)5.5, with a seismic activity intensity of M(L)5.0. This paper provides seismic frequencies and probabilities for earthquakes with M(L)4.0 and M(L)5.0 or higher in North China, Yanshan-Bohai Seismic Belt, Shanxi Seismic Belt, Hebei Plain Seismic Belt, and Yishu Seismic Belt in 2023. The analysis indicates that the Hebei Plain Belt is likely to have the highest probability of earthquakes with M(L)4.0 or higher. In the long-term background, the maximum cutoff magnitude for Shandong and its neighboring areas is estimated to be M(L)6.0. Through a three-year-scale scanning approach, it is forecasted that the maximum cutoff magnitude for the year 2023 in the areas will be M(L)4.9, with seismic activity intensity at M(L)4.3. Additionally, this paper divides Shandong and nearby regions into seven tectonic regions for seismic magnitude-frequency calculations and provides seismic probability forecasts for each region.

On August 6, 2023, an M5.5 earthquake occurred in Pingyuan County, Dezhou City, Shandong Province, which was the largest earthquake in North China since 2000. This earthquake broke the 626 days of M5.0 seismic quiescence in North China after the M5.0 earthquake in a sea area in Dafeng District, Jiangsu Province, on November 17, 2021. In this study, the geological structure of the epicenter was analyzed and the seismological anomalies in Shandong and adjacent areas before the earthquake occurred were sorted out.

On 21 May 2021, the MS 6.4 earthquake struck Yangbi County, Dali City, Yunnan Province. Minor seismic activities were common both before and after the earthquake; the foreshock sequence activity characteristics of this earthquake were studied to gain a better understanding and more perspective. First, between May 18 and 5 July 2021, we collected data of the seismic events from the Yangbi MS 6.4 earthquake sequence, determined the minimum magnitude of completeness of the sequence based on the magnitude-frequency relationship, filtered out the more complete earthquake sequences, and performed double-difference earthquake relocation using the HypoDD method. Then, we improved the nearest-neighbor distance algorithm and used it in conjunction with the Gaussian mixed model fitting method to conduct a comprehensive multiple factor analysis of the Yangbi MS 6.4 earthquake sequence. The main findings of our preliminary analysis are as follows: 1) We distinguished the foreshocks, mainshocks, and aftershocks of the Yangbi earthquake sequence as well as their higher-order aftershocks, using the method described in this paper, and we can obtain clear intergenerational relationships between them. We identified eight “foreshocks” with statistically greater physical significance than the others and found that majority of the shocks occurred shortly after the mainshock were direct aftershocks, with secondary or higher-order aftershocks gradually increasing in the later stage of the sequence. 2) Combining the double-difference earthquake relocation and the event distribution on the fault plane, we found that the b-value of the Yangbi foreshock sequence was clearly on the lower end of the spectrum, with an obvious nonlinear amplification process, and can be divided into three foreshock sub-sequences: sub-sequence I with the lowest b-value and a concentrated spatial distribution, which is an F-value foreshock sequence; subsequence II with an overall shallower source depth and an obvious rebound in b-value, which is an explosive aftershock sequence; subsequence III with a lower b-value and a rapid rupture spread, which is a typical U-F-ρ foreshock. 3) We constructed a topological tree of the Yangbi foreshock sequence in Yunnan Province using the nearest-neighbor distance algorithm, combining the correlation between earthquake sequence type and fault rupture intensity. We analyzed the distribution and topology of the three sub-sequences (combined) of the Yangbi MS 6.4 foreshock sequence and found the following: the topology of subsequence I was more linear than the sequence II, each was the parent event of the subsequent event, and its rupture mode was similar to the fluid intrusion rupture in a specific channel; sequence II had a relatively simple topology, exhibiting a spray topology, and independently formed a main-aftershock mini-sequence, probably triggered by its shallow brittle rupture, which caused the fluid intrusion rupture to spread faster and eventually triggered the Yangbi MS6.4 mainshock.

基于2023年2月6日土耳其卡赫拉曼马拉MW7.8地震和MW7.5地震的有限断层破裂模型,计算了两次强震在周围地区产生的位移场、应力场以及同震库伦应力变化对MW＞4.0的余震的应力触发.结果表明:(1)两次强震在地表产生了较大的位移,其中,MW7.8地震产生的最大水平位移约为3.1m,最大隆升约为0.4m,最大沉降约为0.6m.MW7.5地震产生的最大水平位移约为4.3m,最大隆升约为1.9m,最大沉降约为0.8m.两次强震后地表的最大水平位移约为4.15m,最大隆升约为1.9m,最大沉降约为0.8m.(2)MW7.8地震震中南北两侧为面膨胀区,东西两侧为面压缩区,震中区域的主压应力方向为近南北向,主张应力方向为近东西向.MW7.5地震震中北东和南西侧为面膨胀区,南东和北西侧为面压缩区,震中区域的主压应力方向为近东西向,主张应力方向为近南北向.(3)MW7.8地震在MW7.5地震震中处的库伦应力增加约为0.28MPa,说明MW7.8地震对MW7.5地震的发生是有触发作用的.两次强震的发生使得有限断层周围出现较大范围的应力卸载,库伦应力增加的区域主要出现在两个地震的有限断层的两端,应该注意库伦应力增加区域发生地震的危险性.(4)MW7.5地震对MW7.8地震所在断层的南段和北段上MW＞4.0的余震是有促进作用的,14～25km深度上的MW＞4.0的余震主要发生MW7.8地震所在断层北段与MW7.5地震所在断层东段的交叉区域,MW7.5地震震中西侧的MW＞4.0的余震是由MW7.5地震所触发.

Coal mining in thick-hard roof areas leads to frequent high-energy seismicity and may even induce coal–rock dynamic disasters such as rockburst. It is important to explore the focal mechanism of mining-induced seismicity to understand the failure behaviour of the coal–rock mass and the characteristics of the stress field. It is helpful to propose a seismic absorption method. Taking the 6306 working face of the Dongtan coal mine as the study area, the rupture type, focal mechanism, characteristics of the local stress field, and main controlling factors of the mining-induced 22 high-energy seismic events were investigated using the probabilistic full-waveform optimization inversion and the stress field inversion. The main conclusions were as follows: (1) the rupture types of 22 seismic events were shear, tensile, compression, and mixed failure, and the corresponding number of events was 11, 4, 1, and 6, respectively; (2) the focal mechanism of the above events was eight strike-slips, twelve reverse fault slips, and two normal fault slips; and (3) the stress field using the inversion of focal mechanisms was discovered. There was no significant variation of the maximum compressive stress σ 1 and minimum compressive stress σ 3 directions in the seismicity concentration area, fold 1, and fold 2. The principal stresses σ 1 and σ 3 were the main controlling factors inducing seismicity. This study is helpful in revealing the mechanism of the mining-induced high-energy seismicity and proposing corresponding prevention measures in the future.

对1586年以来的西太平洋火山带VEI≥5 级火山大喷发与中国大陆东部M≥6强震的相关性进行了分析,结果表明,随着西太平洋火山带大喷发,大陆东部一般滞后半年至5年开始强震丛集,且火山连续性大喷发后大陆东部可能出现强震活动高潮或丛集活动时间增长及频度增加现象;强震平静时段一般在火山间歇期内,且强震最长平静期与火山最长间歇期同步.由此认为,火山的大喷发——间歇性活动,显示了西太平洋火山带相关板块运动及上地幔热对流的微动态(10～20年左右尺度)的韵律性活动过程,这可能是大陆东部强震韵律性活动的"节拍器",西太平洋火山带大喷发是大陆东部强震丛集活动的警报"哨声",但不是"触发"或"诱发"了大陆东部的强震丛集活动.对火山带大喷发后强震丛集活动预测方法进行了探索,估计了2022年1月15日汤加火山VEI 5 级大喷发后中国大陆东部强震活动趋势.

为深度剖析2021年云南漾濞MS6.4地震对周围断层的影响以及地震序列间的静态库仑应力影响关系,文章基于主震的破裂模型和Okada给出位移对空间偏导数的解析式,首先计算了主震在周围断层上产生的静态库仑破裂应力,结果表明维西—乔后断裂带中段、澜沧江断裂带北端、红河断裂带北端以及怒江断裂带中段库仑应力均有千帕量级的增加.其次,计算了此次地震对周围地区产生的水平应力场及位移场,发现震中东西两侧物质向外流出,南北两侧向震中汇聚;震中南北两侧沉降,东西两侧隆升;产生的应力场呈EW向挤压,NS向拉张,在一定程度上抵消了该区域背景构造应力场.最后计算了前震-主震-余震序列间的静态库仑应力影响,结果表明前震产生的静态库仑应力促进了主震的发生;在2 km、13 km和18.5 km深度附近,触发的余震(前震和主震产生的库仑应力变化为正)比例很高,但在7 km深度处(同震破裂模型中滑移量最大)大部分余震分布在库仑应力负值区(应力影区),考虑到该深度余震与主震震源机制相差较大,因此通过模拟最易错动的断层面作为余震接受断层面,从而计算出最大静态库仑破裂应力,发现应力影区的余震仍有被触发的可能.

Yishu fault zone is the Shandong section of the Tanlu fault zone,and it is the structural boundary between the Luxi fault block and the Ludong fault block.In history,the Tancheng M S 8? earthquake in 1668 and the Anqiu M S 7.0 earthquake in 70BC occurred with serious casualties and property losses.The Anqiu-Juxian Fault is a Holocene active fault in the Yishu fault zone.Predecessors have conducted a lot of research on the fault by means of field geological survey,magnetotelluric measurement,small earthquake activity analysis,GPS velocity field,etc.and found that the north section of the Yishu fault zone is currently in the locking stage and has the potential for strong earthquakes with M S ≥7.The mobile gravimetry is an effective means for medium and long-term prediction of strong earthquakes.The gravimetry along the Yishu fault zone was conducted using the LCR-G and CG-5relative gravimeters every half year from 2010 to 2020.The mobile gravimetry anomalies occurred in the north section of the Yishu fault zone in 2019,and the area was delineated as an earthquake risk area based on the mobile gravimetry anomaly.Then the anomaly was confirmed to be caused by groundwater decrement.Therefore,it is necessary to make clear whether the mobile gravimetry anomalies are caused by tectonic or non-tectonic background field variations.In order to provide effective mobile gravimetry data for medium and long-term forecasting of earthquakes,we divide the Yishu fault zone area into plain area and mountainous hilly area according to the different geographical landforms to study the tectonic background and characteristics of stratum lithology,geomorphology and hydrogeology of the two types of areas.Based on the 22 periods of highprecision mobile gravity data from 2010 to 2020,the high temporal-spatial resolution GPS images and the distribution variation characteristics of groundwater are analyzed,the influence of groundwater and vertical crustal deformation on gravimetry is calculated quantitatively using the infinite plane layered model and the approximate proportional relationship between gravity and vertical crustal deformation,and the spatial distribution of gravity effects of groundwater and vertical deformation and the corrected gravity variation image are obtained.Then,combined with the leveling and GPS research results in recent years,the possibility of earthquake in the near future in the Yishu fault zone is judged.Finally,the time-sequence curve of gravity and gravity effects of groundwater and vertical deformation of Guangrao,Shouguang and Changyi stations are drawn to summarize the time-varying characteristics and synchronization of groundwater,vertical deformation and gravity.Through the above correction processing,we find that:（1） The multi-year gravity anomaly in the north section of the Yishu fault zone since August 2010has a strong correlation with the decline of groundwater level and land subsidence in the region.The maximum impact of groundwater lowering on gravity is-102.21μGal,and the maximum impact of land subsidence is 190.56μGal.The superposition effect is 195.72μGal.The gravity field after correction is stable as a whole,and the variation in the positive and negative transition regions is not dramatic,indicating that there is no large differential movement of underground materials.Combined with the leveling and GPS research data,it is speculated that there is less possibility of strong earthquakes in the north section of the Yishu fault zone in the near future.（2） The influence of groundwater and land subsidence on the mobile gravimetry mainly occurs in the north section of the Yishu fault zone,which is distributed in Quaternary strata,and there is little such interference in the bedrock-outcropped middle and south section of the Yishu fault zone.When gravity anomaly occurs in the plain area due to the variation of non-structural background field,it is likely to misidentify it as an earthquake precursor.Therefore,in the study of gravity anomaly,groundwater and vertical crustal deformation correction should be carried out first to eliminate the gravity anomaly caused by the variation of the non-tectonic background field.（3） Deep confined water funnel area is often accompanied by land subsidence and obvious gravity variations.Phreatic decline generally does not cause land subsidence,but water loss will cause negative gravity change to a certain extent.（4） In the daily correction of mobile gravimetry data,the mean annual correction constant can be calculated according to the magnitude variation law of groundwater and vertical crustal deformation in recent years,which has certain positive significance for the analysis,application and related research of mobile gravimetry data.

利用四川宜宾及周边地区布设的30个临时台站连续44天的波形记录,采用背景噪声互相关方法提取了周期为1—15 s的瑞雷面波相速度频散曲线,然后使用基于面波射线路径追踪的瑞雷面波直接成像方法得到0—10 km深度范围内三维S波速度模型,最后利用该模型作为初始模型采用相同的反演框架得到该地区的方位各向异性结构.结果表明:浅层S波波速横向分布不均匀,随着深度增加呈不均一性减弱,在2 km深度左右,筠连—高县—珙县—长宁背斜一带的S波速度呈高速分布,可能与该区域地层经历褶皱、抬升和地表风化剥蚀有关;从5 km深度起,随着深度增加狮子滩—双河场—长宁背斜区域的S波速度在西北部较东南部相对较低,而低速的分布反映出区域内介质力学性质较弱,因此可能是2019年长宁地震序列沿近北西向破裂的原因之一.方位各向异性结果表明:在孔滩背斜附近,快波方向与背斜走向近似平行,随着深度增加各向异性强度变弱,而且快波方向逐渐向北收敛向西南撒开,呈帚状分布;在区域地质构造作用、主压应力场等的共同影响下,局部区域的方位各向异性快波方向在不同深度处呈现出复杂的特征.

Earthquakes can occur in one or several periods, and by analyzing the period spectrum and its synthetic probability, the trend of seismic activity in a certain area in the future period can be studied. In this paper, namely, the seismic period spectra and their linear synthetic probability values were calculated in three regions using earthquake data of magnitude https://www.w3.org/1998/Math/MathML"> M ≥ 4 3 3 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003308584/bebb6986-3d8f-445c-9ce0-332068e7a6e9/content/inline-math111_1.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> (all magnitudes are M in the text without special notes) from 1480-2000 and M≥4 since 1970 in Shandong and nearby areas (34–38.5°N, 114–123°E, no further hints below), and a certain time period in each region according to the characteristics of different subregions, The actual seismic prediction tests were conducted for each partition according to the characteristics of each partition. The results show that the method has good results in retrospective verification of moderate to strong earthquakes in Shandong and neighboring areas, except for the earthquake period spectrum of magnitude https://www.w3.org/1998/Math/MathML"> M ≥ 4 3 3 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003308584/bebb6986-3d8f-445c-9ce0-332068e7a6e9/content/inline-math111_2.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> since 1480 in the Yishu zone, which shows no dominant period, and makes a reasonable analysis of seismic activity trends in Shandong based on synthetic probability out-test predictions, there is a possibility of a magnitude 4 earthquake in Shandong and nearby areas in the next year.

2020年2月18日山东济南长清发生M4.1(Ms 4.1)地震,基于中国地震台网中心的观测报告,使用双差定位法对济南长清地震序列进行重定位,利用重定位后的地震参数拟合了断层面的走向及倾角.利用P波初动方法求取了 5个震源机制解,并反演了震源区的局部应力场,根据局部应力场和断层面参数计算了滑动角.得到以下初步结论:长清地震序列从SE向NW延伸、倾向NE;断层面拟合得到断层面走向NW(320.5°),倾角接近垂直(84.8°),滑动角为15.7°,本文推断发震断层为走向NW、倾角近垂直且具有左旋走滑性质的隐伏次级断裂.主震震源机制解是正走滑型地震,其节面Ⅰ走向111°、倾角65°、滑动角-45°,5个震源机制解按时间顺序呈正断走滑型与走滑型地震相互交替出现.震源区局部应力场呈正断兼少量走滑的应力机制,与山东背景应力场不同.本文认为在太平洋板块自东向西推挤作用背景下,鲁中隆起与其西北凹陷区垂向运动差异,是济南长清发生地震的根本原因.

An M(s)6. 4 earthquake occurred on May 21st, 2021 in Yunnan Yangbi country. In order to analyze the seismogenic fault and structure deeply, and discuss the difference of seismogenic structure and background between the 2013 Eryuan, 2017 and 2021 Yangbi earthquakes. The earthquake sequence is relocated by double-difference method with the observation report from the China Earthquake Networks Center (CENC). And the tectonic stress field is calculated with nine focal mechanism solutions from the Global Centroid Moment Tensor (GCMT) catalogue and the United States Geological Survey (USGS) in seismic source region. The initial conclusions are as follow: (1) The Yangbi earthquake sequence is distributed in the direction from NW to SE. More aftershocks are located in the part of SE segment than that in NW segment of earthquake cluster. Few aftershocks occurred around the earthquakes with magnitude larger than 5.0 because of heterogeneity release of crustal stress. Initial rupture depth of four events with magnitude larger than 5.0 are deeper than their centroid depth, their rupture process of seismogenic faults are beginning from fault bottom to fault upper. (2) Two unknown faults F2 and F3 are the seismogenic faults of the Yangbi earthquake sequence, which are lying down southwestern of Weixi-Qiaohou-Weishan fault. Both of them are similar with nearly vertical dip, tending to SW direction, trending from NW to SE direction and sliding in right-lateral strike-slip. The length of F2 is about 30 km, another one (F3) is shorter with the length of nearly 11 km and intersecting with F2 fault in the middle of earthquake cluster. (3) The tectonic stress field is strike-slip regime in seismic source region. The principal compressive stress axis is tended in SSE direction (174.57 degrees) with lower plunge (18.79 degrees). And the principal extensional stress axis is tended in SWW direction (-93.65 degrees) with nearly horizontal plunge (5.21 degrees). The seismogenic structure in seismic source region is controlled by right-lateral strike-slip boundary between Sichuan-Yunnan Block and Southern Yunnan Block. (4) All the three earthquakes occurred under the background of strike-slip regime in southwestern boundary of Sichuan-Yunnan Block with right-lateral strike-slip movement. The seismogenic structure of the 2013 Eryuan earthquake is controlled mostly by local structure with vertical movement. The 2017 Yangbi earthquake is controlled only by Sichuan-Yunnan Block boundary with right-lateral strike-slip movement. The 2021 Yangbi earthquake sequence is controlled mostly by right-lateral strike-slip movement on the boundary of Sichuan-Yunnan Block and little vertical movement from local structure crust.

通过计算1976年唐山7.8级地震、滦县7.1级地震、宁河6.9级地震产生的库仑破裂应力,得到这3次地震在唐山地区的库仑破裂应力演变过程;将研究区域(39.0°～40.5°N,117.0°～119.0°E)1979年以来的1.0级及以上地震双差重定位结果同库仑破裂应力分布对比分析,认为历史大震对现今地震的调制作用变弱;通过分析2002—2020年部分中强地震受库仑破裂应力作用情况,认为历史大震可能对蓟运河断裂附近区域触发作用较明显,而对唐山断裂附近区域的触发作用不明显,2020年7月12日古冶5.1级地震、2021年4月16日滦州4.3级地震受到了历史大震的抑制作用.

通过限定震群集中区范围,剔除同一台站记录的震中位置相近且具有相同路径的地震波,使用双差波速比两次差分的方法,对2017～2018年长岛地区发生的2个震群的波速比值开展特征分析.通过对震相数据敏感性分析得出,双差波速比方法对Pg波到时较为敏感,资料处理时需要将Pg、Sg波震相误差分别控制在0.02 s和0.20 s以内.最终分析结果显示,长岛震群波速比值在1.69～1.78范围内波动,波速比变化与震群活动过程密切相关;震群几次较大余震发生前,波速比呈现低值状态;主震和余震的波速比变化存在差异,可能反映二者发震机理有所不同.

1 研究背景 2010年8月金钟水库蓄水活动开始之后,福建仙游地区地震活动性增强,小震频发.截至2014年12月31日,共记录地震3471次,其中4级以上地震5次,3级以上地震20次,2级以上地震101次,最大地震为2013年9月4日4.8级地震.

1 研究背景 波速比是特征化描述岩石成分和流体饱和度的重要参数,可用来反映地下介质性质改变以及间接反映断层活动情况.波速比研究是地震学领域重要的研究方向,常用多台或者多震方法计算平均波速比(黎明晓等,2004;张小涛等,2012;王林瑛等,2014).但在震群活动过程中,震中较为集中,传统波速比计算方法不能准确反映震源区地下介质情况.Lin等(2007)提出,基于P波、S波的双差思想,将距离同一台站相近的2个地震组成一组,通过扣除这2个地震射线的相同路径,获得震群震源区波速比.该方法首次讨论和检验了应用2次差分来计算震源区波速比的可行性,随后诸多学者做了相关研究( Dahmet al, 2014;Bachura et al,2016;贾漯昭等,2017;郑建常等,2018).双差波速比方法是,基于误差分布和概率密度,借鉴双差定位程序中2次差分技术,使用台站S与P震相到时差和台站对的2次差分,扣除地震射线相同路径, 实现震群活动波速比值求解.

为研究2022年门源MS6.9地震的发震构造及构造应力场特征,文章先搜集了1月8—30日M≥1.9地震事件的P波初动符号,基于P波初动极性反演震源机制解的方法,得出66个地震的震源机制解,参考水平应变花面应变对地震震源机制的划分原则进行分类,虽然震源机制分布类型较广,但走滑类震源机制超过半数,表明此次地震序列以走滑为主;然后基于得到的震源机制解,利用网格搜索法反演该区构造应力场,得到研究区内呈NEE-SWW向挤压,NNW-SSE向拉张;主震震源机制P和T轴与所处的应力区应力方向相近;最后模拟研究了主震震源机制与应力体系的关系,得到此次地震是在构造应力场作用下沿最优节面破裂的,可视其为该区域应变能积累后的一次正常释放.该研究对后续的发震机制和地球动力学分析具有参考意义.

收集2008—2018年3036个地震的20395个P波初动资料,应用综合震源机制解法对晋陕豫交界应力场进行反演计算,得到研究区浅部0.15°×0.15°的精细应力场分布状态.结果显示:(1)晋陕豫交界大部分地区主要受走滑和拉张应力体系的作用,整体压应力轴方位表现为NE-NEE向,张应力轴方位表现为近NS向,表明山西断陷盆地为典型走滑拉张的产物;(2)华山山前断裂周边及洛阳盆地出现挤压型应力场作用的特征,反映出逆冲作用机制在这两个地区占主要成分;(3)夹于封门口—五指岭断裂带和新安—郏县断裂带的地区出现了P波矛盾比最大值,表明应力场在该区域的复杂性,该地区受拉张和走滑双重作用控制;(4)晋陕豫交界应力场存在明显的非均匀性特征,隆起和坳陷的过渡区往往是应力场非均匀性特征的主要体现.