Stress triggering effect on the 2022 Honghe M_(S)5.0 earthquake with historical strong earthquakes

The 2022 Honghe M_(S)5.0 seismic event is intriguing due to its occurrence in the south of the Red River Fault,an area historically lacking seismic activities greater than M_(S)5.0.To elucidate the seismogenic mechanism and scrutinize stress-triggered interactions,we calculated co-seismic and post-seismic Coulomb stress alterations induced by nine historical seismic events(M≥6.0).The analysis reveals that these substantial seismic events provoked co-seismic stress augmentations of 1.409 bar and postseismic stress increments of 0.159 bar.Noteworthy seismic events,such as the 1833 Songming,1877Shiping,1913 Eshan,and 1970 Tonghai earthquakes,catalyzed the occurrence of the Honghe earthquake.Areas of heightened future seismic risk include the southern region of the Red River Fault and the eastern segments of the Shiping-Jianshui and Qujiang faults.Additionally,we assessed the correlation between the spatial distribution of aftershocks and the Coulomb stress shift triggered by the mainshock,taking into account the influence of calculation parameter settings.

基于PI方法的华北2019年以来3次M_(S)≥5.0地震回溯性预测研究

本文应用图像信息(PI)方法对2023年山东平原M_(S)5.5地震、2021年江苏大丰海域M_(S)5.0地震和2020年河北古冶M_(S)5.1地震进行了回溯性预测研究。以华北局部(32°N~42°N,114°E~122°E)为研究区域,在网格尺度分别为0.5°×0.5°和1.0°×1.0°且预测窗长为5 a的两组参数模型下,获取2019—2027年逐年滑动的预测窗热点演化图像。结果显示,当网格尺度为1.0°×1.0°时,PI热点效果优于0.5°×0.5°网格,且对平原地震和大丰海域地震的发震位置指示作用较好。当时间窗长和归一化阈值绝对值同时增大,个别窗口存在古冶地震的有效热点,但未找到热点能同时覆盖3个地震震中所在网格的参数模型。不同参数模型下的PI热点显示,未来3~4 a郯庐断裂带渤海段存在发生M_(S)≥5.0地震的风险。本文研究结果对于华北局部地区M_(S)≥5.0地震危险性分析具有一定的参考意义。

2019年四川威远东两次M_(S)>5.0地震序列活动特征及震源区体波速度结构

自2015年以来,四川威远及邻区的地震活动强度显著增强,其中2019年9月8日和12月18日在威远东发生了M_(S)5.4和M_(S)5.2地震,刷新了威远地区有记录以来历史地震震级上限.本文利用2019年8月至2020年3月期间威远及邻区25个流动台和17个固定台记录到的5638次M_(L)≥1.2地震Pg和Sg波到时以及连续波形资料,采用双差层析成像方法获得了威远东这两次地震序列的重定位结果和震源区浅层地壳高分辨率三维体波速度结构.重定位结果显示震源区地震震源深度主要集中在3~4 km.基于两次M_(S)>5.0地震震后10天余震序列空间展布,本文推测两次地震的发震构造均为NNE走向且倾向SE(倾角40°左右)的盲冲断层.三维体波速度结构反演结果揭示:震源区V_(P)异常变化较V_(S)异常变化显著,V_(P)/V_(S)比背景值普遍低4%~10%.在深度小于5 km的浅层内,地震多分布在V_(P)低速异常和V_(S)弱高速异常以及二者的高低速异常过渡带内;在5~7 km深度范围,地震基本上都发生在V_(P)低速异常区.上述速度结构特征揭示震源区附近可能发育着富含气体的孔隙和裂缝且存在流体活动.此外,2019年11月7日以后的地震活动具有明显的流体扩散驱动地震迁移特征,沿两次地震发震断层走向和倾向的流体扩散系数分别为1.5 m~2·s^(-1)和0.1 m~2·s^(-1).两次地震的发生机理很可能是流体扩散引起的孔隙压力上升.

2022年云南红河县M_(S)5.0地震震害特征

2022年11月19日云南省红河县(23.37°N,102.26°E)发生M_(S)5.0地震,打破了红河哈尼族彝族自治州21世纪以来未发生5级以上地震的记录。本文结合地震现场灾害损失调查和灾情资料收集整理,详细阐述了灾区的建筑物震害、生命线工程震害、地震地质灾害特征及原因分析,并与云南相近震级历史地震震害特征进行对比,结果表明,本次地震灾区受灾规模小,余震少,灾害损失相对较轻。

The Seismogenic Structure of the 2010 Suining Ms 5.0 Earthquake and its Geometry,Kinematics and Dynamics Analysis

In January 2010, the Suining Ms5.0 earthquake occurred in central Sichuan Basin, with the epicenter in Moxi-Longnvsi structural belt and a focal depth of 10 km. Based on structural interpretations of seismic profiles in this area, we recognized a regional detachment fault located at a depth of 9-10 km in the Presinian basement of the Suining area, transferring its slipping from NW to SE orientation. This detachment fault slipped from NW to SE, and underwent several shears and bends, which caused the basement to be rolled in and the overlaying strata fold deformation. It formed a fault-bend fold in the Moxi area with an approximate slip of 4 km. Correspondingly, the formation of the Moxi anticline is related to the detachment fault. With the earthquake＇s epicenter on the ramp of the detachment fault, there is a new point of view that the Suining earthquake was caused by re-activation of this basement detachment fault. Since the Late Jurassic period, under the influence of regional tectonic stress, the detachment fault transfered its slip from the Longmen Mountains （LMS） thrust belt to the hinterland of the Sichuan Basin, and finally to the piedmont zone of southwest Huayingshan （HYS）, which indicates that HYS might be the final front area of the LMS thrust belt.

Landslides triggered by the 1970 Ms 7.7 Tonghai earthquake in Yunnan,China: an inventory, distribution characteristics, and tectonic significance

The 1970 Tonghai earthquake, which occurred on January 5, 1970, in Tonghai County, Yunnan Province, China, triggered a large number of landslides. Since the occurrence of the earthquake, there have been a huge number of research reports on the seismogenic structure and earthquake mechanism, but rare reports on the seismic landslides. As the largest earthquake recorded in the Qujiang fault zone, the study on the coseismic landslides triggered by this earthquake are of great significance to the prevention and mitigation of earthquake-induced landslides in this region. In this study, we established a coseismic landslide inventory for the VⅢ–X seismic intensity areas of the Ms 7.7 Tonghai earthquake, and conducted spatial analysis on the coseismic landslides, mainly having analyzed the effect of the topographic factors, geological factors, and seismic factors on the development of the coseismic landslides. To enhance the understanding of this earthquake, we converted the earthquake epicenter and magnitude with empirical formulas based on the distributions and areas of the coseismic landslides. Comparing with coseismic landslides in other earthquake-hit areas, we found the capability that this earthquake could induce landslides is low. This study provides a useful supplement to the global coseismic landslide inventories and could be the basic data for seismic landslide assessment in this earthquake-prone region.

Using Airgun Source Signals to Study Regional Wave Velocity Changes before and after the Yunlong M_S5.0 and Yangbi M_S5.1 Earthquakes

On the basis of the airgun source signals recorded by the stations from January,2016 to June,2017,we use cross-correlation detection technology to obtain the characteristics of the stable phase travel time change of each station.We used the Yunlong MS5.0 and Yangbi MS5.1 earthquakes as samples.According to regional characteristics,13 stations with high signal-to-noise ratios and complete data were selected(including 3 fixed stations and 10 active source stations).They are divided into four regions,and on the basis of the GNSS baseline data,the characteristics of regional wave velocity changes before and after the earthquake are analyzed.The results show that the station phase travel time change and the regional stress characteristics represented by the GNSS baseline data have good correlation in the short-term.Due to different degrees of regional stress,there are differences in the travel time changes of different stations in the four regions.Before the Yunlong MS5.0 and Yangbi MS5.1 earthquakes,with regional stress adjustment,there is an upward trend in the travel time changes of related stations in the adjacent areas of up to 0.02 s.The difference is that there are differences in the time nodes and duration of the travel time anomalies,and there is a reverse descent process after the Yangbi MS5.1 earthquake.There are different degrees of travel time fluctuations in the relevant stations before and after the two earthquakes,but the fluctuation range before and after the earthquake was small.Compared with the water level change of the reservoir,the adjustment of the regional stress is more likely to have a substantial impact on the travel time changes of the relevant stations.

Gravity anomaly before the Leshan M5.0 earthquake?

The North-South Seismic Belt was analyzed using gravity observation data from 2011 to 2015, and the nontidal analysis results show that there was a nonlinear gravity change at both the Chengdu and Guza seismostations one month before the Leshan M5.0 earthquake.

Analysis of Anomalous Characteristics of Regional Crustal Deformation before the September 16^th,2019 Zhangye MS5.0 Earthquake,Gansu,China

To study the crustal movement in the vicinity of the epicenter before the Zhangye MS5.0 earthquake in 2019, the characteristics of crustal deformation before the earthquake are discussed through the GPS velocity field analysis based on the CMONOC data observed from GPS. The baseline time series between two continuous GPS stations and the strain time series of an area among several stations are analyzed in the epicenter area. The resulting time series of baseline azimuth around the epicenter reflects that the energy of the fault in the northern margin of Qilian Mountain is accumulated continuously before 2017. Besides,the movement trend of azimuth slows down after 2017,indicating the stress accumulation on both sides of the seismogenic fault zone has reached a certain degree. The first shear strain and EWdirection linear strain in the epicentral area of the Zhangye MS5.0 earthquake remain steady after 2017,and the surface strain rate decreases gradually after 2016. It is illustrated that there is an obvious deformation loss at the epicentral region three years before the earthquake,indicating that a certain degree of strain energy is accumulated in this area before the earthquake.

Tectonic Mechanism of the Suining(Ms5.0) Earthquake,Center of Sichuan Basin,China

On Jan.31 of 2010,the Suining earthquake occurred at Suining City whch is located the center of Sichuan Basin.It is unusual for the strong earthquake to occur at the center of Sichuan Basin with a stable geotectonic environment and a low-level historical seismicity.The macro-epicenter of the earthquake is located at Moxi town of Suining city,Sichuan province,China.The earthquake intensity of the epicenter area is degree VII,and the long axis of the isoseismal line trends in NE orientation.The Suining earthquake caused the collapse or destruction of 460 family houses.The earthquake focal mechanism solution and records of the near-field seismographic stations showed the earthquake occurred at the reverse fault at a depth 34 km.Based on the waveform and focal mechanism,we consider the Suning earthquake is triggered by the reverse fault and not by the gravitational collapse or man-made explosive sources.Basing on seismic refraction profile and borehole,we consider that the earthquake is triggered by the backthrust fault of Moxi anticline rooted in detachments at a depth 3-4 km.Furthermore,we infer that tectonic mechanism of the Suining(Ms5.0) Earthquake is driven by the horizontal crustal shortening and stress adjustment on a shallow detachment after the Wenchuan(Ms 8.0) earthquake.

The Characteristics and Cause of Seismic Damage of the Jinghe M5.0 Earthquake in Xinjiang on October 16, 2011

The epicenter of the M5.0 earthquake occurring in Jinghe County, Xinjiang on October 16, 2011, is located in Tuoli Township. The intensity of the meizoseismal area is VI. The seismic damage investigation shows that the houses are mainly mud-clay style and the seismic damage characteristics take on an obvious regional nature. The damage degree varies relative to the field conditions.

2022年11月19日红河M_(S)5.0地震前云南地区异常特征

通过梳理2022年11月19日红河M_(S)5.0地震前云南地区地震活动和定点地球物理观测异常,发现:此次红河M_(S)5.0地震发生在2019年以来持续活动的滇东北至滇南—滇西南M_(L)≥4.0地震条带上,震前1年快速形成新的3级以上地震条带、峨山地震窗开窗、震群活动等地震活动异常,可以作为判定滇南—滇西南未来半年内5级以上地震发生的依据;震中附近地区200 km范围内的定点形变、流体观测异常显著,石屏倾斜和水位、思茅水温和气氡等测项异常出现时间晚于快速形成的3级地震条带,可作为判定发震紧迫程度的依据。

2018年通海5.0级地震前黄草坝台四分量钻孔应变临震异常特征分析

2018年8月13日、8月14日通海两次5.0级地震前,黄草坝台四分量钻孔应变仪记录到异常信号.重点从异常干扰排查、异常形态、同震应变阶跃等特征进行分析,讨论应变异常的可信度及其与通海地震的相关性.结果表明:2018年8月8日-8月12日应变异常不受环境干扰,临震异常可信度高;异常特征为加速压性转张性后发震,其中北西向压性变化幅度最大,变幅达1.29×10^(-7);黄草坝台位于此次通海地震震中北西向,计算这2次5.0级地震震源机制解反演得到主压应力方向为北西-南东向,与北西向压性变化吻合,认为钻孔应变异常的变化幅度对地震预测地点的方向具有指向性;第一次5.0级地震时,北西向同震应变阶跃显示震后压应力减小,认为这个方向的应变能得到释放,进一步佐证北西分量压性变化与此次通海5.0级地震具有较高的相关性,第二次5.0级地震时,北西向同震应变阶跃小,认为这个方向的应变能得到充分释放,初步判定后续发生更大地震的可能性小.

2018年通海M_(S)5.0地震显著异常时空演化特征分析

通过对2018年8月13—14日通海2次M_(S)5.0地震前,玉溪市、红河州所属的滇南地区地震活动和定点形变、流体等异常进行分析.结果表明:发现震前出现滇南M_(S)≥6.0地震平静、M_(S)≥5.0地震平静、M_(L)≥4.0地震空区、M_(L)≥4.0和M_(L)≥3.0地震积累频度增加、低b值、高水位等背景异常,以及峨山窗口地震、滇东南M_(L)≥3.0地震活跃、高大地温、曲江水氡、石屏水平摆、蒙自CO_(2)、绿春CO_(2)、黄草坝钻孔应变等中短临15条异常.其中,测震学异常7条,占总异常的47%;微观前兆异常8条,占总异常的53%.中短临异常8条,占总异常的53%.对显著前兆观测异常时空演化特征进行分析,可为后续地震预测预报提供可借鉴的经验.

2023年2次肃北5级及以上地震的PI和LURR特征回溯性研究

2023年10月24日和12月1日在甘肃省肃北县分别发生M_(S)5.5和M_(S)5.0地震,震中位于祁连山地震带西段,采用图像信息(PI)和加卸载响应比(LURR)探查2次地震孕育过程中应力状态和震后地震活动趋势,为分析祁连山地震带地震活动趋势提供参考。结果显示:①PI热点计算结果显示,肃北地区存在显著的背景应力异常,其幅度指示该区域在未来1年存在发生6级左右地震的可能;②LURR的时空演化特征进一步显示,2023年3月起LURR时序曲线呈显著上升异常变化,且异常空间分布持续向震源区迁移,表明在中短期内有发生强震的可能;③2次地震发生后,震源区LURR异常的时空特征仍呈现持续发展状态,尚未恢复到小于1的正常水平。因此,仍需关注祁连山地震带西段发生6级左右地震的可能。

临震微波动现象回溯性研究——以青海地区为例

为进一步检验临震微波动异常跟踪指标,基于兰州临震微波动实时监控与跟踪系统的数据资料,对青海地区2020~2022年5.0级及以上地震震中距150 km以内台站的波形资料进行分析。结果表明,震中距150 km以内的台站几乎都能记录到临震微波动事件;达到临震微波动异常指标的台站不是震中距最小的测震台站,这可能与区域构造应力、发震断层走向及地震破裂过程等有关;主震震级越大,震前出现临震微波动异常指标的可能性越大。

2018年云南通海2次M_(S)5.0地震震源机制解及深度测定

准确的震源机制解和震源深度是深入理解地震发震机理的基础。针对2018年8月13、14日在云南通海发生的2次M_(S)5.0地震,利用云南地震台网30多个宽频带地震仪的波形记录,采用3个不同的区域速度模型和CAP方法获得了2次地震的震源机制解及矩心深度,并选取方位角约为300°的不同震中距的多个台站记录到的sPn深度震相准确测定了2次地震的初始破裂深度。结果表明:(1)基于数量更多、方位角覆盖较好的近台宽频带地震波形,在不同频率域内利用3个速度模型反演得到了2次地震的矩心深度分别为8 km和7 km;(2)利用震中距大于260 km、方位角约300°的多个地震台记录波形的sPn和Pn震相的到时差,测定2次地震的初始破裂深度约为10 km, 2种深度的差异可能是反映了主震沿断层面自下向上扩展的破裂过程;(3)结合双差重定位及CAP反演结果,初步认为2次M_(S)5.0地震的震源机制解应该是一致的,2018年2次通海M_(S)5.0地震的发震断层应该为同一条左旋走滑型断层,其断层面走向/倾角/滑动角约为20°/75°/-10°。

2018年云南通海5.0级地震前区域地壳水平形变特征分析

利用1991—2015年GPS观测地壳长期水平运动速度场,研究了2018年8月13,14日云南通海2次5. 0级地震前附近区域地壳水平形变背景特征,结合构造分析认为:(1)通海地震发生在区域地壳水平运动受阻,应变快速积累部位,即面应变率和最大剪应变率的高值区。该部位亦是小江断裂带和曲江—石屏断裂带的交汇部位,从背景形变特征来看,该区域及其附近未来稍长一段时间再次发生中强地震的危险性依然存在。(2)个旧与弥勒之间为另一个应变快速积累部位,应警惕未来发生中强地震的可能。

2018年云南通海Ms5.0和墨江Ms5.9地震前地磁垂直强度极化异常时空特征研究

利用云南11个地磁台站的秒采样观测数据,计算和分析了地磁垂直强度极化值Yzh在2019年8月13日、14日通海MS5.0地震前及2019年9月8日墨江MS5.9地震前的时空变化特征。研究表明,地磁台站Yzh值的幅度在震前会出现同步增强现象。而与以往的极化震例研究相比,Yzh值的高值异常在震前出现时间要更早些,可能会在震前2~5个月出现,距发震时间越近,产生的异常幅值可能越大,异常持续时间也越长。同时,研究还发现2次地震主要发生在异常空间等值线的高值区内,尤其在零值阈值线附近,这可能对今后发震地点的预测有一定的指示意义。对比异常产生时段内的Dst指数,认为该高值异常并非由空间电流体系所引起。

云南水温异常与M_S≥5.0地震关系研究

选取2009—2015年云南地区观测连续、稳定的水温观测资料共34项,采用异常过程和从属函数分析方法联合提取异常,分析水温异常与M_S≥5.0地震的关系。结果表明:该方法提取的单项异常,具有短期指示意义,与地震有较好的对应关系,但地震的漏报率较高;采用异常频次和权重集成方法提取的全省群体异常与全省的M_S≥5.0地震对应较好,减少了漏报,并可以通过置信度为97.5%的R值评分检验。按构造和地震活动进行分区后,提取小区域的水温群体异常,并只考虑对应本区的地震,则各区域内出现异常的虚报和漏报率均显著增加。分析其原因,认为水温异常和地震都是区域构造活动增强的产物,群体异常能更好地刻画区域构造活动增强,在构造活动增强的背景下是有利于地震发生的,因此区域的群体异常有更好的对应效能;异常过程和从属函数方法提取的水温异常能较好地表达震前水温变化加剧的特征,区域的群体异常可以作为云南地区有M_S≥5.0地震的短期时间判据。