Analysis of seismoionospheric disturbances at the Chain of Japanese stations for vertical sounding of the ionosphere

Seismoionospheric disturbances in the parameters of the ionospheric F ₂ and sporadic E layers at the chain of the Japanese stations for vertical sounding of the ionosphere before strong crustal earthquakes with M>6.5 during the period from 1968 to 1992 have been considered. The dependence of the disturbance time of appearance in the ionospheric parameters on the earthquake magnitude and epicentral distance, obtained for each specific earthquake using the selected series of ionospheric stations, made it possible to consider these disturbances among medium-term precursors of earthquakes. The velocity of the disturbance front apparent motion has been determined based on the model of horizontal radially-isotropic disturbance propagation from the projection of the impending earthquake epicenter to the ionospheric altitudes. The conclusion has been made that the distinguished seismoionospheric disturbances follow the boundary of the earthquake preparation region, expanding on the Earth’s surface.     

2007年3月3日长时间持续Pc5 ULF波的多点联合观测分析

2007年3月3日位于磁层昏侧THEMIS的5颗卫星、同步轨道晨侧和午前的GOES 3颗卫星和地面地磁台站同时观测到了持续近4 h的Pc5 ULF波.我们用交叉小波相关分析计算脉动的传播速度,用MVA分析求解脉动的传播方向,然后结合两者的计算结果获得了Pc5相速度矢量信息.THEMIS卫星观测到Pc5具有压缩特性,且向阳传播,速度约在6~20 km/s左右,相比于磁层中阿尔芬速度(1000 km/s)较低.这些Pc5 ULF波动可能产生于磁尾或磁层内部不稳定性.GOES 3颗卫星观测到不同情况的Pc5 ULF波,极向模占主要成分,且具有波包结构,具有阿尔芬驻波特性,可能产生于K-H(Kelvin-Helmholtz)不稳定性.地面台站观测到ULF波扰动幅度随纬度升高而增强,Pc5脉动在地理纬度60°附近达到最大值, Dumont durville台站观测到的脉动与THEMIS观测到波形有很好的相似性.     

Dynamics of the large-scale ULF electromagnetic wave structures in the ionosphere

The present article displays the results of theoretical investigation of the planetary ultra-low-frequency (ULF) electromagnetic wave structure, generation and propagation dynamics in the dissipative ionosphere. These waves are stipulated by a spatial inhomogeneous geomagnetic field. The waves propagate in different ionospheric layers along the parallels to the east as well as to the west and their frequencies vary in the range of (10–10⁻⁶) s⁻¹ with a wavelength of order 10³ km. The fast disturbances are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field. The large-scale waves are weakly damped. They generate the geomagnetic field adding up to several tens of nanotesla (nT) near the Earth's surface. It is prescribed that the planetary ULF electromagnetic waves preceding their nonlinear interaction with the local shear winds can self-localize in the form of nonlinear long-living solitary vortices, moving along the latitude circles westward as well as eastward with a velocity different from the phase velocity of the corresponding linear waves. The vortex structures transfer the trapped particles of medium, as well as energy and heat. That is why such nonlinear vortex structures can be the structural elements of the ionospheric strong macro-turbulences.     

Comparison of variations in the <Emphasis Type="Italic">F</Emphasis>2 layer critical frequency before the strong Italian earthquakes and during the magnetic storm: Data of the stations for ground-based vertical sounding of the ionosphere

The possible seismic ionospheric effects before two strong earthquakes in Italy, which took place near Rome station (January 7, 1962, M = 6.0; April 5, 1998, M = 5.3), have been studied using the data of several European stations for ground-based vertical sounding of the ionosphere. An analysis of the behavior of the foF2 critical frequencies for the earthquake that occurred on January 7, 1962, made it possible to simultaneously consider the effects, originating during earthquake preparation under quiet geomagnetic conditions and caused by the magnetic strom that began on January 10, 1962, using a unified technique. It has been indicated that the distinguished precursor effects of two considered earthquakes with magnitudes not more than 6.0 are localized in the region with an epicentral distance of about 400 km, whereas the disturbances caused by the magnetic storm are of a planetary character. The amplitude of foF2 seismic ionospheric disturbances is much smaller than the maximal variations caused by the magnetic storm; however, the absolute value of this amplitude is a factor of 1.5 as large as the standard deivation from the monthly median.     

Anomalous variations in the foF2 critical frequency above Japan prior to the earthquake of March 9, 2011

Based on data from the Japanese Kokubunji and Wakkanai stations of vertical sounding of the ionosphere, the variations in the foF2 critical frequency prior to the strong earthquakes of March 9 and 11, 2011 (M 7.2 and 9.0, respectively), are analyzed. It is found that significant positive disturbances of foF2 had been recorded approximately one day before the first earthquake. Notably, at the Irkutsk reference station, which is located about 3300 km from the earthquake epicenters, there were no significant disturbances of foF2. This suggests that the effects of increased foF2, observed at the Kokubunji and Wakkanai stations, were probably caused by the earthquake preparation processes. The seismo-ionospheric manifestations of the stronger earthquake on March 11, 2011, even if they took place, were hidden by the geomagnetic storm’s effects.     

DEMETER卫星观测的超低频电场扰动 预处理方法及震例应用分析

基于法国DEMETER卫星观测的超低频(ULF)电场波形, 本文提出了更简单易实施的ULF电场扰动预处理方法. 利用该方法, 对文献中已报道的2010年2月27日智利M_S8.8地震前的ULF电场扰动进行了更全面的分析. 结果表明: 已报道的20°S—40°S地磁纬度带内的ULF电场扰动并非仅出现在最靠近震中的半轨道, 而是出现在较大的经度范围内. 大范围ULF电场扰动的区域正好位于南大西洋异常区, 很可能受到该区域异常磁场的影响. 南大西洋异常中心区域的ULF电场扰动表现出共轭特征, 即在南北地磁纬度20°—40°范围内ULF电场均出现约5 mV/m的扰动, 北纬地区的ULF电场扰动幅度相比南纬地区更小. 而在南大西洋异常中心区域外的ULF电场扰动则仅在20°S—40°S地磁纬度带内出现, 在其共轭区并未观测到ULF电场扰动. 这可能是由于南大西洋异常中心区域外的ULF电场扰动幅度比中心区域更小所致, 在电离层中由于碰撞效应更易被衰减, 因此ULF电场扰动无法传播至其共轭区. 本文的方法和结果可为后续更全面地分析卫星在电离层高度记录的ULF电场扰动提供参考.      

青藏高原北部地区中强震前地磁低点位移特征研究

分析了1994年以来青藏高原北部地区中强震前地磁低点位移的分布特征后,发现在该区中强震前均出现地磁低点位移异常。表明根据地磁低点位移异常对地震三要素（时间、地点和震级）的短临预报有一定的指导作用。     

On the onset and meridional propagation of the ionospheric F2-region response to geomagnetic storms

The meridional propagation velocities of the ionospheric F2-region response to 268 geomagnetic storms are calculated. Ionospheric vertical sounding data of 1 h time resolution from several stations located in a longitude sector approximately centred along the great circle that contains both the geomagnetic poles and the geographic poles are used.Most meridional propagation velocities from high to low latitudes are less than 600 m/s. The smaller velocities are typical of global neutral meridional wind circulation and the larger are representative of traveling atmospheric disturbances.Simultaneous disturbances at several locations are more frequent during positive phases than during negative phases. Negative phase meridional propagation velocities associated with meridional neutral winds are less frequent in the southern hemisphere when compared with corresponding velocities observed in the northern hemisphere. This may be related to the fact that the distance between the geomagnetic pole and the equator is smaller in the northern hemisphere.Most negative phase onsets are within the 06–10 LT interval. For middle geomagnetic latitudes a “forbidden time interval” between 11 and 14 LT is present. The positive phase onsets show the “dusk effect”.     

3-D Velocity Structure of the Middle and Upper Crust in the Yunnan Region,China

Using short-period (1–18 s) surface wave data recorded by 23 stations of the Yunnan Digital Seismic Network of China we determined phase velocities of the fundamental Rayleigh wave along 209 paths by the two-station narrowband filtering and cross-correlation method, followed by an inversion for phase velocity distributions at various periods using the Ditmar-Yanovskaya method. We then obtained a 3-D S-wave velocity structure of the middle and upper crust in the Yunnan region using the genetic algorithm. The results show strong lateral variation of phase velocity in the region. The short-period phase velocity variation is closely related to thickness variation of sedimentary layer in the shallow crust. Within the depth range of 26–30 km, the S-wave velocity in the Sichuan-Yunnan rhombic block is lower than in the surrounding areas. Most large earthquakes of M > 6.0 in Yunnan occurred in the transition zones between low and high velocities.     

云南地区地壳中上部横波速度结构研究

根据云南地区的基阶瑞利波相速度频散资料，用面波层析成像方法反演得到该区域中上地壳S波速度结构. 给出了研究区域内在4个深度上的S波速度水平分布图像和沿100.5°E、24°N、25°N、26°N及27°N的S波速度-深度剖面图. 结果表明：在小江断裂与红河断裂围成的川滇菱形块体内，26～30km深度处的速度明显低于周边地区，其南段从地表到15km深度均为明显的低速区域. 云南地区的强震（M＞6.0）震中位置与S波速度分布图像具有明显的相关性，主要分布于高速与低速的过渡区域.     

Geomagnetic field effects of the Chelyabinsk meteoroid

An analysis was conducted of time variations in geomagnetic field components on the day of the Chelyabinsk meteorite event (February 15, 2013) and on control days (February 12 and 16, 2013). The analysis uses the data collected by magnetic observatories in Novosibirsk, Almaty, Kyiv, and Lviv. The distance R from the explosion site to the observatories varies in the range 1200–2700 km. The flyby and explosion of the Chelyabinsk cosmic body is found to have been accompanied by variations mainly in the horizontal component of the geomagnetic field. The variations are quasi-periodic with a period of 30–40 min, an amplitude of 0.5–2 nT for R ≈ 2700?1200 km, respectively, and a duration of 2–3 h. The horizontal velocity of the geomagnetic field disturbances is close to 260–370 m/s. A theoretical model of wave disturbances is proposed. According to the model, wave disturbances in the geomagnetic field are caused (a) by the motion of the gravity wave generated in the atmosphere by the falling space body and (b) by traveling ionospheric disturbances, which modulate the ionospheric current at dynamo altitudes. The calculated amplitudes of the wave disturbances are 0.6–1.8 nT for R ≈ 2700?1200 km, respectively. The estimates are in good agreement with the observational data. Disturbances in the geomagnetic field level (geomagnetic pulsations) in the period range 1–1000 s are negligible (less than 1 nT).     

Seismic Precursors to Space Shuttle Shock Fronts

—?Seismic precursors to space shuttle re-entry shock fronts are detected at TXAR in Southwest Texas when the ground track of the orbiter vehicle passes within ～150–200?km of the observatory. These precursors have been termed “shuttle-quakes” because their seismograms superficially mimic the seismograms of small earthquakes from shallow sources. Analysis of the “shuttle-quake” seismograms, however, reveals one important difference. Unlike ordinary earthquakes, the propagation azimuths and horizontal phase velocities of the individual phases of the “shuttle-quakes” are functionally related. From a theoretical model developed to account for the origin of these precursors it is found that the seismic phases of “shuttle-quakes” are “bow” waves. A “bow” wave originates at the advancing tip of the shock front trace (i.e., intersection of the re-entry shock front with the surface of the earth) when the ground speed of the orbiter vehicle exceeds the horizontal phase velocity of a particular seismic phase. “Bow” waves are shown to differ in two important respects from the ordinary seismic phases. They vanish ahead of the advancing tip of the shock front trace and their propagation azimuths and horizontal phase velocities are functionally related. The ground speed of the orbiter vehicle exceeds the horizontal phase velocities of crustal seismic phase over much of the re-entry flight profile. As a result, P,S, and R _g “bow” waves will be seen as precursors to the re-entry shock front at stations located within a few hundred km of its ground track.     

地磁绝对测量大台距差值法对强震的反应

在应用地磁绝对测量预测地震中,为适应我国大陆地磁台距大的状况,充分利用地磁场等变线有规则分布特征,使原来仅限于小台距的差值预报法扩大到大台距,并取得了一定的预报效果,自1996年以来已获得M_s ≥ 6. 0震例6组次,并在震前做了一定程度的预测。     

Studying the spread <Emphasis Type="Italic">F</Emphasis> effect before earthquakes

The observations of spread F during the nighttime hours (0000–0500 LT) have been statistically analyzed based on data of Tokyo, Akita, Wakkanai, and Yamagawa Japan vertical ionospheric sounding stations for the time intervals a month before and a month after an earthquake. The disturbances in the probability of spread F appearance before an earthquake are revealed against a background of the variations depending on season, solar activity cycle, geomagnetic and solar disturbances. The days with increased solar (Wolf number W > 100) and geomagnetic (ΣK > 30) activity are excluded from the analysis. The spread F effects are considered for more than a hundred earthquakes with magnitude M > 5 and epicenter depth h < 80 km at distances of R < 1000 km from epicenters to the vertical sounding station. An average decrease in the spread F occurrence probability one-two weeks before an earthquake has been revealed using the superposed epoch method (the probability was minimal approximately ten days before the event and then increased until the earthquake onset). Similar results are obtained for all four stations. The reliability of the effect has been estimated. The dependence of the detected effect on the magnitude and distance has been studied.     

新疆伊犁及邻区地磁谐波振幅比异常特征分析

本文利用新疆伊犁及邻区温泉和克拉玛依红浅两个地磁台站2008年至2015年FHD分钟值观测数据, 采用地磁谐波振幅比计算方法, 选取台站300 km范围区域内, 震级M≥5.0的震例进行映震效果分析。 结果表明, M5.0以上地震发生前后, 温泉和克拉玛依红浅台站的地磁谐波振幅比异常变化特征主要表现为“下降—转折—恢复上升”。 异常持续总时间约为1～3年, 地震发生在趋势性下降变化后的转折期或者恢复上升阶段, 其中, 6.0级地震异常持续总时间为2～3年, 震前为1～2年。 温泉台谐波振幅比异常存在较为明显的长周期向短周期迁移现象, 意味着对应的未来地震震中距一般在100 km以上。 温泉和克拉玛依红浅台均发现不同测项之间或者同一测项不同周期之间存在不同步现象, 并且地震发生在同步性变差的阶段。     

地电阻率瞬时突变序列变化与临震预报

本文采用断裂力学观点，分析研究了一些临震预报实验结果与地电实际观测资料。发现在强震与部分中强震前，震中附近的台站，除能预测到有关地震的地电阻率日突变序列的短期异常变化外，在瞬时突变序上还能看到临震前明显的突变现象，还是震前三个月里的最大瞬时突变，从它的出现至发震所需的时间，将随震中距的减少而缩短，且与震级有关，对于强震多集中出现在震前一个月内，中强震为十天内，并有由外围向震中收缩的趋势，其平均收缩     

Upper crustal structure of the western Corinth Gulf, greece, inferred from arrival times of the January 2010 earthquake sequence

The western part of the Corinth Gulf attracts attention due to its seismically active fault system and considerable seismic hazard. A moderate size earthquake occurred close to the town of Efpalio on January 18, 2010, followed by a sequence of smaller earthquakes. In the present paper we use this sequence to derive a local structural model for the region in the vicinity of Efpalio. The model is based on the minimization of traveltime residuals. In particular, we used arrival times from 51 selected events recorded on January 19 and 20 by at least 5 stations at epicentral distances less than about 25 km. A variant of the method of conjugate gradients has been used for this purpose. In comparison with several previous models, the new model is characterized by higher velocities to a depth of about 8 km. The velocity ratio in the model is v_P / v_S = 1.83. The hypocentres of the selected earthquakes lay at depths between about 5 and 9 km, but their distribution is rather irregular.     

云南地区地壳上地幔三维S波速度与径向各向异性结构研究

云南地区地处青藏高原东南缘,一直是地球科学研究的热点地区.目前,一些热点问题,如云南地区是否存在中下地壳低速流及其空间分布,仍有一定的争议.通过建立云南地区精细的地壳上地幔速度与各向异性结构,可为深入认识上述问题提供重要信息.本文利用天然地震波形记录,采用双台法提取了12~60 s周期的Rayleigh和Love波相速度频散,并进一步反演获得了云南地区10~100 km的三维地壳上地幔SV和SH波速度及径向各向异性结构.结果表明：S波速度与径向各向异性结构在横向和垂向均存在显著变化.在20~30 km深度,存在两个低速条带,且条带内呈现出正径向各向异性（V_SH>V_SV）特征,暗示了中下地壳低速物质的水平向运动.在80~100 km深度,云南西南和东南部显示为低速异常和正径向各向异性特征,暗示了软流圈物质的水平流动.在云南北部的丽江、攀枝花和昭通地区,岩石圈地幔中则存在明显的负径向各向异性（V_SH<V_SV）,可能反映了地幔物质的上涌痕迹.历史强震多发生在地壳低速区域或高低速过渡带,且地震附近的径向各向异性为负或者较弱.一些地震震源下方存在低速层,地壳低速层可能会促进强震发生.     

Upper mantle structure beneath central Western Europe from data on phase velocities of surface waves

The deep structure of the upper mantle is determined from data on phase velocities of Love and Rayleigh waves measured by a differential method on traces between two stations in central Western Europe. One-dimensional velocity structures are first constructed from data of each pair of stations, after which two-dimensional distributions of SH and SV velocities are calculated by the method of two-dimensional tomography from S wave velocities at fixed depths. The results are presented in the form of 2-D vertical structures of the average S wave velocity (S = (SV + SH)/2) constructed along profiles crossing the region in directions of the best resolution. The main structural features are a higher velocity zone at depths of 60–80 km in the area (48°–50°N, 9°–11°E) and a lower velocity zone in the western part of the region at depths of 100–150 km, probably extending farther beyond the studied area.     

Oscillations of the geomagnetic field caused by the flight of Vitim bolide on September 24, 2002

The results of observation and analysis of oscillations of the geomagnetic field within the 1–1000 s range that followed the flight of a bolide with a mass of 50 t, diameter of about 3 m, and initial kinetic energy of 1013 J at a distance of 4850 km are given. Spectral analysis of the time variations of the geomagnetic field oscillation level was performed using three integral transformations. Four groups of disturbances to which the transport velocities of 7–8 km/s, 800–850, 300–400, and 260–280 m/s corresponded were detected and identified. The enumerated velocities are close to the velocities observed in geomagnetic pulsations after rocket launchings from the Plesetsk and Baikonur rocket sites. The magnetometer data were confirmed by the results of analysis of the recordings at a microbarograph located at a distance from the flight trajectory of the bolide of 4350 km.