日本兵库县南部地震和关东地区强震前正负地震的演变特征及其对地震预测的意义

通过对日本兵库县南部7.2级地震和关东地区强震前的正、负地震演变过程的研究发现:大部分强震震源及附近地区内,震前某一时段、某一震级以上地震主要为正地震,形成正地震集中时段,主震一般位于正地震分布区内或边缘;在主震前数个月内一般发生负地震(不排除正地震）,同时响应比值在震前存在降低的过程,这可能是孕震过程进入短期阶段的一种表现．这些特征对未来地震的发生区域和发生时间预测可提供一些参考,并对日本关东地区1996年9月11日6.6级地震的发生区域和发生时间的特征进行了初步研究．      

内陆直下型地震的发生与断层的关系——日本兵库县南部7.2级地震的启示

讨论了与1995年1月17日日本兵库县南部7.2级地震相应的余震及灾害的分布、内陆直下型地震的发生与断层的关系及强震动等基本特征．地表断层系同地下断层系的构造可能存在着较大的差异,地震不一定受既存活断层系（地表断层系）构造活动的制约,强震动域不与震源断层位置直接相对应,而多出现于稍偏离断层两端的区域或断层单侧稍远处的区域内．对强震动的机理也进行了一些探索性的讨论．      

1995年1月17日日本兵库县南部7.2级地震的特征

叙述了１９９５年１月１７日发生在日本兵库县南部７．２级地震的主震和余震分布、发震断层、震前的空区现象、震源机制解及区域应力场等特征，并对该次地震的发生与周围地体应力环境的关系等问题进行了探讨。     

景谷6.6级、鲁甸6.5级地震序列应力降变化对比研究

利用云南2014年10月7日景谷6.6级、8月3日鲁甸6.5级地震序列的波形与震相资料,消除区域地震波衰减与台站场地响应后,计算得到2次地震序列的应力降。结果显示,在研究所涉及的震级范围内,应力降呈现随震级增大而增大的趋势。为尽可能消除震级对应力降的影响,对比了相同震级档地震的应力降,结果显示,景谷地震序列的平均应力降明显高于鲁甸地震,这可能与2次6.5级左右地震后震源区的应力状态有关。从序列余震应力降的时、空变化对比来看,景谷6.6级地震后至2014年12月6日5.8、5.9级强余震发生前,应力降变化呈现先缓慢下降、进而转折升高并持续高值的变化过程;同时,高应力降地震在空间上主要集中于5.8级强余震区域。这表明,主震发生后经过一个较短期的调整之后,5.8级强余震震源区的应力环境可能持续增强。5.8、5.9级强余震发生后,地震序列应力降快速下降至相对稳定状态。研究表明,2次6级左右强余震发生后,震源附近区域应力得到一定程度的释放,应力环境降低,地震序列活动也趋于结束。对于后续没有强余震发生的鲁甸地震序列,余震应力降小于景谷地震序列相同震级档地震的平均应力降,同时,主震后余震序列的应力降在时间上几乎未发生太大的变化;结合主震能量释放特点推测,震源区的应力在主震破裂过程中已得到较多的释放,主震后震源区应力变化呈现逐渐恢复的过程,这可能是鲁甸地震余震活动明显较弱,后续亦未有较强余震发生的原因之一。     

日本兵库县南部地震和关东地区强震前正负地震的演变特征及其对地震预测的意义

通过对日本兵库县南部７．２级地震和关东地区强震前的正、负地震演变过程的研究发现：大部分强震震源及附近地区内,震前某一时段、某一震级以上地震主要为正地震,形成正地震集中时段,主震一般位于正地震分布区内或边缘;在主震前数个月内一般发生负地震（不排除正地震）,同时响应比值在震前存在降低的过程,这可能是孕震过程进入短期阶段的一种表现．这些特征对未来地震的发生区域和发生时间预测可提供一些参考,并对日本关东地区１９９６年９月１１日６．６级地震的发生区域和发生时间的特征进行了初步研究．     

2003年青海德令哈M6.6地震序列的活动特征

分析了2003年4月17日青海省德令哈6.6级地震序列活动的空间和时间变化特征及其发震构造,得到以下结果:①主震发生在地震活跃区与相对平静区的分界带上;②主震后半个多月内余震快速衰减,初期余震持续到7月底,以后平静了4个多月,接着震源区东部又发生第2期余震活动,连续发生5次5.0级以上地震,最大余震震级5.9;③震源区...     

汶川地震前地震活动特征的普遍性及其机理探讨

汶川地震前地震活动较为显著的异常是：1970—2008年汶川地震前,从云南北部至甘青川交界形成规模巨大的5.5级以上地震活动增强区（或称环形分布）;1970—1999年围绕龙门山断裂带形成5级以上地震背景空区,汶川地震发生在增强区内的背景地震空区里;2001—2007年形成M_L4.0以上地震孕震空区,震前1年孕震空区内部及其两端相继发生多次M_L 4.0~5.0地震,空区打破.上述地震活动增强区、背景空区和孕震空区是大地震前普遍出现的现象.为对比分析,本文系统研究了2001年以来我国大陆及邻区4次M_S≥7.8级地震和全球10次M_W≥8.0级地震前类似地震活动异常,并给出统计特征.结果显示：地震增强区规模为850~2700 km,持续时间13—38年,增强区长轴对数与主震震级呈正相关关系.增强区与余震区规模之比为2.3~7.7,其对数与主震震级呈负相关.背景空区长轴300~1100 km,持续时间10—32年,其长轴对数与主震震级呈正相关关系.孕震空区长轴为370~780 km,持续时间1—7年,孕震空区长轴对数与主震震级呈正相关关系.对于板内地震,构成增强区的最低震级为5.0级或5.5级,构成背景空区和孕震空区的最低震级分别为5.0级和4.0级.而对于板间地震,构成增强区和背景空区的最低震级为6.0级或6.5级,构成孕震空区的最低震级为5.0级或5.5级.基于坚固体地震孕育模型,认为地震活动增强区的环形分布是由于震源区的破裂强度高于周围介质造成的,地震孕育过程中体应变的范围和强度存在逐渐增大和变小的过程,这是地震活动增强区出现三阶段特征的原因.从包体弹性理论可以推导出增强区尺度的对数与主震震级、增强区与震源体比值的对数与主震震级存在线性关系.     

2010年4月14日玉树MS7.1地震对余震的触发研究

研究了2010年4月14日青海玉树7.1级地震产生的静态库仑破裂应力变化对余震及区域地震活动空间分布的影响.在考虑震源区附近区域构造应力场的基础上,由震源区构造应力和主震破裂产生的应力叠加,计算得到最容易破裂的余震断层面,进而计算玉树主震在上述余震断层面上产生的库仑破裂静态应力变化.结果表明,库仑应力变化图像与余震分布较为吻合,说明玉树主震对大部分余震有触发作用.利用相同方法计算了玉树主震对周边更大范围内地震的应力触发影响,发现大部分区域地震活动空间分布与库仑应力变化图像基本一致,中小地震大多发生在正向触发区域,但量值较小.对余震断层面与主震完全一致的情形进行了同样的计算,与前述方法计算结果的对比显示,考虑区域应力场的计算方式所得库仑破裂应力变化图像,能够更好地与余震及区域中小地震空间分布图像相吻合.     

广西北流与靖西地区地震的应力触发现象分析

2019年广西相继发生北流5．2级和靖西5．2级地震,两次地震间隔仅一个多月,为广西陆区有地震记载以来之少见现象.分别计算广西北流4．2级前震对其5．2级主震、靖西5．2级主震对其 4．3级最大余震,以及北流5．2级地震对靖西5．2级地震的库仑破裂应力变化作用大小.结果显示:北流4．2级前震对5．2级主震可能存在明显的动态与静态应力触发作用;靖西5．2级主震对4．3 级最大余震地震可能存在动态应力触发作用和静态库仑应力抑制作用,靖西4．3级余震的发生可能是构造应力场和其5．2级主震动态应力触发共同作用的结果.由于震级较小且距离较远,北流 5．2级地震对靖西5．2级地震的库仑应力触发作用不明显.     

2021年5月21日云南漾濞地震及5月22日青海玛多地震的支持向量机震级估算

2021年5月21日及5月22日,云南漾濞县与青海玛多县分别发生破坏性地震,主震震级分别为M_s6.4级与M_s7.4级。本文基于机器学习中的支持向量机方法,以多类型特征参数为输入建立地震预警震级估算模型SVM-M,离线模拟云南漾濞M_s5.6级前震、M_s6.4级主震以及青海玛多M_s7.4级主震的连续震级估算。结果表明:对于云南漾濞M_s5.6级前震,支持向量机方法在首台触发后1s可估算震级为5.6级,且随着首台触发时间的增加,估算震级一直在实际震级附近波动;对于云南漾濞M_s6.4级主震和青海玛多M_s7.4级主震,随着首台触发时间的增加,支持向量机方法对于大震低估问题得到了有效的改善,且震级估算结果逐渐接近实际震级。同时,这3次地震的震级估算离线模拟表明:引入震源距的支持向量机方法（SVM-M1模型）对于震级估算有更好的稳定性,且在地震预警系统的震级估算中有着潜在的应用前景。     

强震观测网、高灵敏度地震观测网、地中强震观测网、宽频带地震观测网

阪神·淡路大震灾后 ,日本着手对原有的地震观测体制作彻底改革 ,多项全国性配置地震计的计划同时开始启动。地震引起的地面晃动的程度不尽相同 ,无感微小地震引发的晃动仅有 0 .0 0 1 μm,频率为1 0 Hz;巨大地震引起的地面晃动的幅度高达 2～ 3 m,周期也有几十秒。虽说都称之为地震计 ,但由于地震动的振幅和频率涉及的范围太大 ,所以应针对观测对象选用不同类型的地震计。下面介绍不同类型的观测网。1　强震观测网 ( K- NET)无论大地有多大的晃动都能将其准确记录下来的地震计称之为强震计。它构造坚实 ,信号明确 ,通常设置在地表 ,对了…     

Age, geology, geophysics, and geochemistry of Mahukona Volcano, Hawai`i

The size, shape, and magmatic history of the most recently discovered shield volcano in the Hawaiian Islands, Mahukona, have been controversial. Mahukona corresponds to what was thought to be a gap in the paired sequence (Loa and Kea trends) of younger Hawaiian volcanoes (<4?Ma). Here, we present the results of marine expeditions to Mahukona where new bathymetry, sidescan sonar, gravity data, and lava samples were collected to address these controversies. Modeling of bathymetric and gravity data indicate that Mahukona is one of the smallest Hawaiian volcanoes (～6,000?km³) and that its magmatic system was not focused in a long-lived central reservoir like most other Hawaiian volcanoes. This lack of a long-lived magmatic reservoir is reflected by the absence of a central residual gravity high and the random distribution of cones on Mahukona Volcano. Our reconstructed subsidence history for Mahukona suggests it grew to at least ～270?m below sea level but probably did not form an island. New ⁴⁰Ar–³⁹Ar plateau ages range from 350 to 654?ka providing temporal constraints for Mahukona’s post-shield and shield stages of volcanism, which ended prematurely. Mahukona post-shield lavas have high ³He/⁴He ratios (16–21?Ra), which have not been observed in post-shield lavas from other Hawaiian volcanoes. Lava compositions range widely at Mahukona, including Pb isotopic values that straddle the boundary between Kea and Loa sequences of volcanoes. The compositional diversity of Mahukona lavas may be related to its relatively small size (less extensive melting) and the absence of a central magma reservoir where magmas would have been homogenized.     

The Yecheng,Xinjiang, China,earthquake of February 14, 1980

In this study, we have checked the location and focal depth of the Yecheng earthquake (m _b = 6.0, maximum intensity VII) of February 14, 1980. The result shows that this is an intermediate event with a focal depth of 90 km. The microepicenter is located at 36. 4°N, 76, 9°E, while the macroepicenter is at 37.3°N, 76.9°E, 90 km to the north of the microepicenter. This is the first destructive intermediate event in China which led to a damage as severe as of intensity VII. The focal mechanism of the event is determined to be of thrust type. Combined with the analysis of seismological and geological data in surrounding area, the possible relation between the event and plate movement has been discussed. The result in this paper indicates that in some particular place, the destructive effect of intermediate event should be considered in seismic hazard assessment.     

Physical properties,vitrinite reflectance,and microstructure of coal,Taiyuan Formation,Qinshui Basin,China

In this study, we experimentally established the relationship between physical properties, vitrinite reflectance, and microstructure of coal, Taiyuan Formation, Qinshui Basin, China using representative coal samples collected from three different mines via the rock mechanics testing system (MTS). We analyzed the organic macerals, vitrinite reflectance, and microstructure of 11 coal samples using petrography and scanning electron microscopy (SEM). The experimental results suggest that (1) the elastic parameters can be described by linear equations, (2) both P-and S-wave velocities display anisotropy, (3) the anisotropy negatively correlates with vitrinite reflectance, and (4) the acoustic velocities and Young’s modulus are negatively correlated with the volume of micropores. The derived empirical equations can be used in the forward modeling and seismic inversion of physical properties of coal for improving the coal-bed methane (CBM) reservoir characterization.     

山西高平地震

阐述了发生在山西高平的地震和对高平有影响的地震，分析了高平市的地震灾害，通过分析得出高平地震与晋获断裂带活动有关的结论。     

Spatial distribution,source apportionment,and associated risks of trace metals (As,Pb, Cr,Cd, and Hg) from a subtropical river,Gomti, Bangladesh

Sediment samples from the Gomti River basin were investigated to determine and evaluate trace metal concentrations,their biological effect,and potential ecological and human health risks for adults and children.The mean concentrations of trace metals were organized in the descending order of mercury(Hg)(0.08 mg/kg)>chromium(Cr)(0.06 mg/kg)>lead(Pb)(0.05 mg/kg)>arsenic(As)(0.02 mg/kg)>cadmium(Cd)(0.01 mg/kg).The current study illustrated that metals were attributed to the area from natural sources and different anthropogenic sources especially from industries.However,the concentration levels were lower than the sediment quality guidelines(SQGs)based on the effect-range classifications of threshold effect concentration(TEC)and probable effect concentration(PEC).Therefore,the concentration of the elements showed no adverse biological effects on aquatic organisms.The evaluated potential ecological risk index also revealed the low toxicity to the aquatic environment.Moreover,the applied sediment quality indices,geo-accumulation index(Igeo),contamination factor(CF),and contamination severity index(CSI)suggested that the contamination levels of the elements were in the acceptable range,and the contamination had not notably impacted on the sediment quality.The risk index(HI)concerning age groups was significantly less than the threshold limit of 1 indicating that the contamination had no non-carcinogenic risk effect.The total carcinogenic risk(TCR)was less than a risk value of 1×10⁴.Hence,the current study suggests that immediate remediation is not required due to an absence of alarming conditions in the study area.Proper monitoring of the attribution of the metal elements should be done for the betterment of human and environmental health。     

Seismicity at Fuego,Pacaya, Izalco,and San Cristobal Volcanoes,Central America, 1973–1974

Seismic data collected at four volcanoes in Central America during 1973 and 1974 indicate three sources of seismicity: regional earthquakes with hypocentral distances greater than 80 km, earthquakes within 40 km of each volcano, and seismic activity originating at the volcanoes due to eruptive processes. Regional earthquakes generated by the underthrusting and subduction of the Cocos Plate beneath the Caribbean Plate are the most prominent seismic feature in Central America. Earthquakes in the vicinity of the volcanoes occur on faults that appear to be related to volcano formation. Faulting near Fuego and Pacaya volcanoes in Guatemala is more complex due to motion on a major E-W striking transform plate boundary 40 km north of the volcanoes. Volcanic activity produces different kinds of seismic signatures. Shallow tectonic or A-type events originate on nearby faults and occur both singly and in swarms. There are typically from 0 to 6 A-type events per day withb value of about 1.3. At very shallow depths beneath Pacaya, Izalco, and San Cristobal large numbers of low-frequency or B-type events are recorded with predominant frequencies between 2.5 and 4.5 Hz and withb values of 1.7 to 2.9. The relative number of B-type events appears to be related to the eruptive states of the volcanoes; the more active volcanoes have higher levels of seismicity. At Fuego Volcano, however, low-frequency events have unusually long codas and appear to be similar to tremor. High-amplitude volcanic tremor is recorded at Fuego, Pacaya, and San Cristobal during eruptive periods. Large explosion earthquakes at Fuego are well recorded at five stations and yield information on near-surface seismic wave velocities (α=3.0±0.2 km/sec.).