The Haichenghe strike-slip blind fault, which experienced the M 7.3 Haicheng earthquake in 1975, is one of the most active seismic zones in eastern China. To better understand the fault structures, we deployed a dense array of 23 broadband seismic stations in the area in 2022, with an average distance interval of ~ 6 km. Combining the automatic workflow LOC-FLOW with manual review, we detect 1339 events with a completeness of magnitude ~ M L -0.1 using data recorded at the dense array and the Liaoning regional Seismic Network from Oct. 1 to Oct. 31 in 2022. Of these, we relocated 877 earthquakes using Hypoinverse and HypoDD. The relocations finely delineate the NWW-striking Haichenghe fault, including the NW and SE segments, and its NE-trending conjugate fault. They also clearly feature two seismic gaps, one corresponding to the fragmentation zone generated by the M 7.3 Haicheng earthquake and the other being consistent with the low-velocity zone between NW and SE segments. Based on relocations, we further identify 10 clusters of recurrent events with a median magnitude of M L 0.8. We observed a phenomenon that several clusters are occurred right after the M L 3.7 event, the largest event during the observation. We suggest that, as a larger-magnitude earthquake, the M L 3.7 event resulted in the stress change along the fault plane and triggered the small-magnitude repeaters. Our results indicate that dense array observation in the study area could provide an abundant seismological basis for studying the Haichenghe blind fault.

In this paper, we use the observation data of the Haicheng area in Liaoning, China, from 2021 to 2023 to investigate the velocity variation in the Haicheng area using the coda wave of the repeating microearthquakes. To minimize the velocity perturbation caused by source location variations, the double-difference location method is used to obtain the precise location of small earthquakes. Combined with the seismic rupture scale, the repeating microearthquakes with overlapping rupture zones are strictly selected. A total of 91 repeating microearthquakes in 38 sequences are finally identified in the study area, which is temporally concentrated in three series. The relative velocity variations between the first and subsequent events in each sequence are calculated using the coda wave interferometry technique. We found that differences in the velocity change in different time clusters. Three earthquakes with M ≥ 3.0 occurred in the study area during the observation period. The results indicate a preseismic increase in velocity of approximately 0.2%. Additionally, the postseismic velocity changes measured by the S coda of the repeating events also demonstrate an increase, which suggests that the faults are healing. For an ML 3.0 earthquake, this process takes no more than 10 months.

利用sPL深度震相对1999～2020年海城老震区ML≥3.0地震震源深度进行重新测定,共识别出146次地震事件的sPL震相,其中sPL震相与P波到时差在1.2～3.2 s之间,震源深度在5～15 km范围内.研究发现,1999年岫岩MS5.4主震发生前地震序列的震源深度保持在8 km附近,与主震的震源深度相当;临近主震发生时,在5.5 km深度处出现破裂,随后震源深度从5.5 km开始变深,逐渐逼近主震震源深度,存在震源深度由浅及深的迁移过程;岫岩MS 5.4主震发生后,震源深度破裂范围扩展,浅部依然有地震发生,更深的位置也发生地震.

北京时间2021年5月21日21时48分36秒,云南省大理州漾濞县发生Ms 6.4地震.利用云南数字地震台网2021年5月18日至8月22日的震相报告,采用双差地震定位法,对漾濞Ms6.4地震序列进行重新定位.重新定位结果显示序列呈NW向优势分布,破裂长约20 km,宽约7 km,对重新定位结果进行误差分析,水平方向定位误差约为0.8 km,垂直方向定位误差约为1.0 km,定位结果具有较好的稳定性.依据震中分布的走向将序列划分为NW向的主断层与NNW向的分支断层,主断层存在较为明显的分段现象,分支断层呈雁列状分布.根据小震丛集性发生在大震断层面及其附近的原则,利用重新定位后的小震震源位置反演得到漾濞Ms 6.4序列主断层走向约320°,倾角约89°,深度范围3～13 km.根据拟合得到的断层在地表的投影位置,推测本次地震的发震断层为维西-乔后断裂西侧的草坪断裂.基于断层滑动量分布识别出3个凹凸体,结合序列时空演化特征,分析了漾濞Ms 6.4地震序列的破裂过程,结果显示断层中段的凹凸体发生初始破裂,触发相邻的凹凸体发生主震,随后破裂沿断层走向传播,最终导致相邻的数个凹凸体全部发生破裂.

1 研究背景 地电场主要包括大地电场和自然电场,大地电场的场源是高空电离层、磁层、对流层的电流体系的电磁感应,其影响分布于整个地表.20世纪70年代后,希腊、法国、日本等国家把地电场应用于地震等自然灾害的监测预警.我国地电场观测与地震预测研究始于1966年3月22日邢台MS 7.2 地震后,并记录到不少震前异常变化.例如:1975年辽宁海城地震前,海城虎庄邮电支队和冶金102队应用观测地面两点间地电流异常,成功预报此次地震;20世纪80年代希腊学者Varotsos(1984)应用多极距观测法,解决了地电场观测系统噪声问题;席继楼等(2020)应用传统的时间序列统计法,分析了2019年四川长宁 MS 6.0 地震前后仙女台方位角异常变化.

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.

利用金州地震台跨断层形变观测资料分析金州断裂现今活动特征.长趋势分析结果表明,金州断裂以右旋兼正断为主,活动水平总体较弱.断裂活动分段分析结果表明,北段活动速率高于南段.GPS资料分析表明,2011-03-11日本MW9.1地震对东北地区应力积累具有缓解作用,结合金州断裂跨断层数据认为,金州断裂在2011～2014年活动速率明显减弱,2014年至今断层活动与其背景资料一致,但活动水平较弱.

以2020年7月12日唐山古冶Ms5.1地震为研究震例,选取反映地下介质、地震强度、时空特征等信息的多种地震活动性参数,筛选参数特征,应用因子分析的方法进行多参数综合分析,所得综合参数W曲线在古冶Ms5.1地震发生前有明显的异常变化.同时,不同单因子参数曲线在震前的不同时段出现了时间差异变化.

获取了2020年4-7月新疆于田Ms6.4地震区周边约400 km范围内连续的中国气象卫星FY-2G遥感热红外资料,选取北京时间凌晨1:00～5:00时的分钟值数据,经过小波变换和功率谱估计法进行处理,得到研究区地震前后相对功率谱异常演化过程,对比分析了 2019年相同频率同期的相对功率谱幅值,并讨论了异常时间演化过程及异常空间分布特征的可能原因.结果表明:从2020年4月初开始相对功率谱在塔里木盆地南缘出现零星高值异常,显著特征周期为13 d;随后,异常面积沿着盆地边缘断裂逐渐扩大并向阿尔金南缘断裂区域扩展.4月下旬异常区域进一步扩大并形成跨发震断裂的异常带,异常在2020年5月下旬和6月初达到峰值;随着地震的临近,异常区域开始收缩,异常幅度也开始减小,至地震发生时震中区附近异常已经消失;对比分析2019年同期同频率研究区的相对功率谱值后,认为此次热红外亮温异常可能是地震前的短临异常现象.

The Dunhua-Mishan fault is a component of the Tanlu fault zone, and it is also a major regional fault structure in Liaoning area. The study area is located in Fushun area of the Dunhua-Mishan fault. In order to study the crustal velocity structure in this region, we used 60 sets of three-component short-period seismographs and lay out two temporary profiles in Fushun, Liaoning from Nov. 3 to 25, 2019. Each temporary profiles is about 12km long that is composed of 30 seismometers, which nearly vertically cross the Dunhua-Mishan fault where the survey lines are 6km apart. The installation stations spacing distance from 200 to 400m use the external GPS time service to record frequency range of 0.2 to 150Hz in the instrument. The crustal structure characteristics of the fault zone are studied by ambient noise cross-correlation method. In order to efficiently extract high and low frequency surface wave dispersion signals at the same time, we adopt the Extended Range Phase Shift (ERPS) method. Finally, we use ERPS method to process the collected data and invert the S-wave velocity structure. We initially obtained the S-wave velocity structure of the upper crust below 5 km in the area, which matches well with the local geological data. The S-wave velocity structure has significant lateral inhomogeneity of the Dunhua-Mishan fault in Fushun area. The S-wave velocity is obviously lower on the Dunhua-Mishan fault, while with the existence of ancient mixed granite the velocity on both sides of the fault is obviously higher.

郯庐断裂带是贯穿中国东部的一条巨型断裂带,总体呈NNE向延伸,总长度达 2400 km,南起长江北岸湖北广济,经安徽庐江、江苏宿迁、山东郯城和渤海,过沈阳后分为西支的依兰—伊通断裂带和东支的密山—敦化断裂带.郯庐断裂带北段是中国大陆历史强震活跃区和现今地震重点危险区之一.前人从地震地质、地球物理及地震活动性等方面开展基础性研究工作,获得系列研究成果,如:郯庐断裂带分支依兰—伊通断裂全新世以来存在7级历史强震活动;区域岩石圈速度结构具有明显的横向不均匀性等(卢造勋,2005;闵伟等,2011).但关键构造部位地质资料较少、速度结构分辨率不高,限制了对区域构造环境及强震孕育动力学机理的认识.

基于地电场潮汐波岩体裂隙水(电荷)渗流(移动)模型计算辽宁地区大地电场优势方位角α,并对比分析降雨、温度、磁暴等典型干扰对大地电场优势方位角a的影响程度.结果 表明,大地电场优势方位角α受典型干扰的影响较小.结合2013-01-23辽宁灯塔Ms5.1地震前后优势方位角α的动态变化研究发现,多个同一或相邻地质构造地电场台站准同步的岩体裂隙电荷移动方位的长时间突变可认为是中强地震的前兆异常.

In this paper, we use the brightness temperature data of the Chinese stationary meteorological satellite and wavelet transform and power spectrum estimation methods to investigate the thermal infrared anomalies of these three greater than M S4.5 earthquakes in Songyuan area around 2017. The results show that the anomalies gradually expanded along the strike of Yilan-Yitong fault and Mishan-Dunhua fault zone before the M S4.9 earthquake on July 23, 2017 and the M S 5.7 earthquake on May 28, 2018. The anomalies existed in the eastern margin of the Songliao Basin, but the epicenter of the earthquake was not in that area. The abnormality was not obvious before the M S5.1 earthquake on May 18, 2019. It is a possibility that greenhouse gases, such as CO2 and CH4, were released in the greatest amount in the basin, before and after the previous two earthquakes.

作为中国东部的一条巨型走滑型断裂带,郯庐断裂带具有漫长的发育历史,对我国东部矿产资源分布、地质灾害的形成与发生具有重要的控制作用.作为辽宁地区主要区域性活动构造断裂,郯庐断裂沈阳段与周围其他构造体系相互作用,共同控制着该地区强震活动.2013年灯塔MS 5.1地震打破了辽宁地区长达13年的5级地震平静,标志着该区进入新一轮地震活跃期,郯庐断裂带沈阳段的地震危险性备受关注.开展郯庐断裂带沈阳段的小震精定位工作,获取地震事件的空间分布图像,有利于分析地震活动与断裂构造的关系,进而深入研究断裂带几何展布,为辽宁地区的断裂带活动性与地震危险性研究提供新的地震学依据.

Deep slip rates at depths along the northern segment of the Red River fault zone were estimated using repeating microearthquakes between 1999 and 2015 recorded by the Yunnan Seismic Network (YSN). Due to the sparsity of the network stations in the study area, we used an empirical method to constrain the relative distance between event pairs based on S-P differential times measured at subsample accuracy. Using this method, we finally identified a total of 23 sequences of repeating microearthquakes. In each sequence, the occurrences of the earthquakes are rather aperiodic. Based on the spatial-temporal distribution of repeating sequences, we found that the changing of the stress field caused by large earthquakes occurred near the repeating sequences may cause the reduction of recurrence intervals. Some repeating sequences are located closely, the interactions between these sequences are tied to the irregularity of earthquake recurrence. Based on the magnitudes and recurrence intervals of the repeating sequences, we computed the fault slip rates along the northern segment of the Red River fault zone varies from 2.3 to 10.0 mm . a(-1) at the depth range of 6. 0 similar to 13. 4 km, and shows substantial difference at different seismogenic depths.