Dynamic evolution patterns of the degree of ground resistivity anisotropy and the seismogenic process

Following a new train of thinking, this paper has explored first the potential information in the ground resistivity data observed by the existing geoelectric observation system, investigated and proposed a new dimensionless geoelectric precursor factor, the degree of ground resistivity anisotropy, S, and studied the characteristics of dynamic evolution pattern of S during the seismogenic process. The results show that, during the seismogenic process, the degree of ground resistivity anisotropy (S) displays a process of 'normal' →'abnormal strengthening (amplitude, range)' →abnormal weakening' → 'earthquake occurrence'→ 'normal'. The earthquake would occur at the time when the S value has entered the late stage of strengthening and turns to weaken and in the gradient belt on the margin of S anomaly region. The dynamic evolution pattern of S reflects the changes of the tectonic stress field during the seismogenic process. Therefore, it would be possible to trace the process of earthquake generation and occurrence from the dynamic evolution pattern of S so as to service earthquake prediction.     

Features and physical process of the dynamic evolution pattern of ground resistivity precursor front

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3D crustal structure and long-period ground motions from a M9.0 megathrust earthquake in the Pacific Northwest region

We have developed a community velocity model for the Pacific Northwest region from northern California to southern Canada and carried out the first 3D simulation of a M_w 9.0 megathrust earthquake rupturing along the Cascadia subduction zone using a parallel supercomputer. A long-period (<0.5 Hz) source model was designed by mapping the inversion results for the December 26, 2004 Sumatra–Andaman earthquake (Han et al., Science 313(5787):658–662, 2006) onto the Cascadia subduction zone. Representative peak ground velocities for the metropolitan centers of the region include 42 cm/s in the Seattle area and 8–20 cm/s in the Tacoma, Olympia, Vancouver, and Portland areas. Combined with an extended duration of the shaking up to 5 min, these long-period ground motions may inflict significant damage on the built environment, in particular on the highrises in downtown Seattle.     

A kind of information on short-term and imminent earthquake precursors—research on atmospheric electric field anomalies before earthquakes

The long-time practice of observational research on earthquake prediction has shown that the information on short-term and imminent earthquake precursors can hardly be detected, but it is very important for practical and effective earthquake prediction. The result of analysis and study in this paper has shown that the anomaly of quasi-static atmospheric electric field may be a kind of reliable information on short-term and imminent earthquake precursors. On such a basis, the 20 years’ continuous and reliable data of atmospheric electric field observed at the Baijiatuan seismic station are used to study the correlation between the anomalies in seismic activity and relative quiet periods bear on the occurrence of near earthquakes within 200 km range around Beijing after the Tangshan earthquake. The observational results recently reported before hand in written form and earthquakes that actually occurred in near field in corresponding time periods are compared and analyzed. The efficacy of these written prediction opinions about near earthquakes in the recent 10 years is tested. From the test results, the brilliant prospect that the anomaly of quasi-static atmospheric electric field may really become a reliable mark for making short-term and imminent earthquake predictions is discussed. Besides, as a preliminary step, some judgment indexes for predicting earthquakes by use of the observational data of atmospheric electric field before earthquakes are put forward. In the last part, it is pointed out that it would be possible to obtain more believable judgment indexes for determining the three elements of near earthquakes before greater earthquakes (M _S≥5) only if a relatively reasonable station network (2–4 stations every 10 000 km²) is deployed and further investigation is made. Contribution No. 97A0040, Institute of Geophysics, State Seismological Bureau, China. This subject is sponsored by Program No. 95-04-05-01-04, State Seismological Bureau, China.     

Temporal and spatial variation characteristics of present stress field in the northern area of North China

From focal mechanism solutions of the earthquakes in the northern part of North China during the period of 2002～2006,the directions of principal stress axes in 4 stress sub-districts are analyzed using a grid test method.The characteristic of present crustal stress directions is discussed.Based on this result and on the focal mechanism solutions calculated for some events in the period of 1977～1998,in combination with some other study results,the temporal variation of present crustal stress directions in the northern part of North China is investigated.The re-sults confirm that the direction of crustal principal stress in some regions had somewhat rotated after the 1976 Tangshan M7.8 earthquake.The mean P axes of the focal mechanism solutions rotated clockwise not only in Tangshan sub-district,but also in Beijing and Xingtai sub-districts after the Tangshan earthquake.In Beijing and Xingtai sub-districts the orientations of principal stress axes in the period of 2002～2006 are consistent with that before the Tangshan earthquake,implying that the stress orientations has rotated back to the state before the Tang-shan earthquake in these two sub-districts.The directions of the mean P axes are nearly E-W in Tangshan sub-dis-trict since the M7.8 earthquake.The present stress field in the sub-district northwest to Beijing,or in the western part of the Zhangjiakou-Bohai fault zone,is relatively stable during the time period concerned in this study.Because of the limitation of data,this paper only states a possible variation of stress field in the northern part of North China in the recent decades.     

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong M=8 earthquake

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed. Foundation item: National important fundamental research “The Basic Research of Important Project in Damage Environment” and The important project “The Seismic Hazard Assessment Research and Anti-earthquake Structure Research” from China Earthquake Administration during the 10th Five-year Plan. Contribution No. 04FE1008, Institute of Geophysics, China Earthquake Administration.     

Relationship between the earthquake sequences of Tangshan and Xingtai and the three dimensional velocity structure

In this paper, based on the results of tomographic image of Tangshan and Xingtai areas, the relations between the characteristics of the two strong earthquake sequences and their three-dimensional velocity structures are studied. The research results indicate that:① Mosaic distribution of low-velocity bodies and high-velocity bodies, especially the existence of high-velocity bodies with large size in crust are the common basis of development of the two earthquake sequences. ②Scale, depth, and heterogeneity of high-velocity and low-velocity bodies are the important factors to effect the characteristic of earthquake sequences.③ The depth of the high-velocity body in Tangshan area is less than that in Xingtai area, which is the principal reason why the dominant focal depth and the biggest focal depth of Tangshan earthquake sequence are less than Xingtai's.④The depth of the high-velocity bodies in Ninghe area is more than that in Tangshan-Luanxian area, which lead to the biggest magnitude and epicentral intensity are lower. These results could be helpful for predicting the main shock of strong swarm-type earthquakes and later strong aftershocks.     

Prediction of long-period ground motions from huge subduction earthquakes in Osaka,Japan

There is a high possibility of reoccurrence of the Tonankai and Nankai earthquakes along the Nankai Trough in Japan. It is very important to predict the long-period ground motions from the next Tonankai and Nankai earthquakes with moment magnitudes of 8.1 and 8.4, respectively, to mitigate their disastrous effects. In this study, long-period (>2.5 s) ground motions were predicted using an earthquake scenario proposed by the Headquarters for Earthquake Research Promotion in Japan. The calculations were performed using a fourth-order finite difference method with a variable spacing staggered-grid in the frequency range 0.05–0.4 Hz. The attenuation characteristics (Q) in the finite difference simulations were assumed to be proportional to frequency (f) and S-wave velocity (V _s) represented by Q = f · V _s / 2. Such optimum attenuation characteristic for the sedimentary layers in the Osaka basin was obtained empirically by comparing the observed motions during the actual M5.5 event with the modeling results. We used the velocity structure model of the Osaka basin consisting of three sedimentary layers on bedrock. The characteristics of the predicted long-period ground motions from the next Tonankai and Nankai earthquakes depend significantly on the complex thickness distribution of the sediments inside the basin. The duration of the predicted long-period ground motions in the city of Osaka is more than 4 min, and the largest peak ground velocities (PGVs) exceed 80 cm/s. The predominant period is 5 to 6 s. These preliminary results indicate the possibility of earthquake damage because of future subduction earthquakes in large-scale constructions such as tall buildings, long-span bridges, and oil storage tanks in the Osaka area.     

河北临城地震序列揭示的一条隐伏断层

2017年9月4日河北临城发生M_L4.4地震,这是邢台地区自2003年以来发生的唯一一次M_L4以上地震。震后大量余震沿条带分布,揭示了一条前人未发现的隐伏断层(根据其经过的地点称之为齐家庄-东双井断裂)。为研究该隐伏断层的几何形状和滑动性质,首先基于河北数字地震台网资料对地震序列进行精定位,利用精定位地震数据拟合发震断层面,计算断层面的走向和倾角,并给出其标准差。然后搜集震中附近历史地震的震源机制解,利用网格搜索法反演区域构造应力场参数,根据构造应力场和断层面的几何形状确定齐家庄-东双井断裂的滑动性质。结果表明,临城M_L4.4地震的发震断层为一条近EW向的隐伏断层,产状为走向约92°,倾角约85°,滑动角约-12°,滑动角标准差约8°,为倾向南的高倾角左旋走滑型断层,延伸深度约10km。区域应力场在齐家庄-东双井断裂上产生的相对剪应力和正应力分别为0.650和0.691,此次地震不是在最大剪应力的断层方位发生,表明该断裂不是现今应力场作用下产生的,而是在复杂的历史地质活动中遗留的,该断裂在现今应力场作用下积累了一定的应力而导致了M_L4.4地震的发生。齐家庄-东双井断裂及其性质的发现为该地区的地质构造和地震孕育环境分析提供了基础。     

The 1986 Dharamsala earthquake of Himachal Himalaya – estimates of source parameters,average intrinsic attenuation and site amplification functions

The 26th April 1986 Dharamsala earthquake (m_b 5.5) occurred in the Kangra region of Himachal Himalaya, which lies in the rupture zone of great Kangra earthquake of 1905. This was the first moderate sized earthquake to be recorded at a few sites of the strong ground motion array in the NW Himalaya. The accelerograms of this earthquake have been used to estimate its source parameters, site amplification functions and to estimate the effective shear wave attenuation factor Q_β in the frontal region of Himachal Himalaya. A double couple fault plane solution for the earthquake has been obtained based on the spectra of the transverse component of the accelerograms. The estimated values of the source parameters are seismic moment: 2.1×10²⁴ dyne-cm, static stress drop (Δσ): 36 bars, source radius (r): 2.8 km and moment magnitude (M_w): 5.4. The estimated average values of effective shear wave attenuation factor Q_β for various sites are in the range of 125 to 300 with an overall spatial average of 239. The influence of local site effects on the observed PGA values have been examined on the basis of site amplification functions.     

Prediction of ground motion in the Osaka sedimentary basin associated with the hypothetical Nankai earthquake

We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with an approximate evaluation by 4 H/V _s where H and V _s are the thickness of the sediment and the average S wave velocity, respectively.     

Ultrasonic modelling research of earthquake response of underground lifeline engineering

Earthquake response of underground lifeline engineering is investigated by the method of ultrasonic model experiments in this paper. From general field conditions, two models of underground lifeline engineering, one for non-uniform field and the other for uniform field, are designed based on the similarity principle. Besides analysis of seismic phases, a series of analyses especially on particle vibration are carried out. The results show that: The shorter the epicentral distance, the greater are the intensity variation and the change rate of intensity variation of earthquake ground motion, so the more disadvantageous to underground pipelines. In soft covering layer, compressional waves mainly cause radial flexures deformation, but shear wave result in axial dilation deformation of the pipelines; when the thickness of the covering layer is smaller (less than seismic wave length), the rhythmic variation of the intensity of earthquake ground motion is controlled mainly by the wave length of seismic waves in the bedrock. The property of the covering layer has considerable effect on earthquake ground motion. For different covering layers, their effect on each component of earthquake ground motion is not the same. Owing to the effect of wave propagation, the ground is in different states of particle vibration at different times, and there is considerable difference in phase and intensity of particle vibration between two different covering layers near their junction line or surface. Because underground lifelines tend to vibrate with the particles of the earth around it, this results in different deformation of underground pipelines under different conditions. So, it is necessary to take corresponding anti-seismic countermeasures for pipelines according to their practical situations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 104–110, 1992. This paper is part of the research supported by Funds of Doctoral Faculty of National Education Committee.     

Design Earthquakes in the U.K.

Three sites in the UK are taken, representative of low, medium and high hazard levels (by UK standards). For each site, the hazard value at 10⁻⁴ annual probability is computed using a generic seismic source model, and a variety of ground motion parameters: peak ground acceleration (PGA), spectral acceleration at 10 Hz and 1 Hz, and intensity. Disaggregation is used to determine the nature of the earthquakes most likely to generate these hazard values. It is found (as might be expected) that the populations are quite different according to which ground motion parameter is used. When PGA is used, the result is a rather flat magnitude distribution with a tendency to low magnitude events (\le 4.5 ML) which are probably not really hazardous. Hazard-consistent scenario earthquakes computed using intensity are found to be in the range 5.8–5.9 ML, which is more in accord with the type of earthquake that one expects to be a worst-case event in the UK. This revised version was published online in July 2006 with corrections to the Cover Date.     

邢台地区长周期地震动特征初步分析

沉积平原中存在地表低速沉积层是长周期地震动产生的关键因素,而长周期地震动会对长周期建筑物造成严重威胁和震害。本文基于邢台地震的历史地震震源模型和含地表沉积层的地壳速度模型,采用离散波数有限元法,对邢台地区进行了长周期地震动的计算分析。研究表明,邢台平原地区在大震中会产生长周期地震波,邢台地震中反应谱峰值区域位于宁晋南,与极震区基本重合。震中距小于55km区域内的周期1.5—4s的放大系数谱超过了抗震设计规范谱,反应谱放大系数值在周期2s附近达到峰值。因此,邢台地区因存在地表软弱沉积层,该区抗震设防可能对长周期地震动估计不足,建议应予以特别考虑。     

Long-period ground motions from the 2003 Tokachi-oki earthquake

We study characteristics of long-period ground motions from the 2003 Tokachi-oki earthquake (Mj 8.0), a large interplate earthquake, based on spatial distribution maps and attenuation relationships for four kinds of peak ground velocity (PGV) value. The first kind (PGV(WB)) is obtained from a maximal value of vector sum of the three-component, wide-band velocity seismograms, and the other three kinds (PGV(BP10), PGV(BP20), and PGV(BP30)) are obtained from a maximal value of vector sum of the three-component, narrow band-pass filtered velocity seismograms (the central periods are 10, 20, and 30 s). The spatial distribution maps for all kinds of PGV value show azimuth dependence; the PGV values in Hokkaido, northern side of the epicenter are larger than those in Tohoku, southwestern side of the epicenter, when compared at a comparable distance. We find that the features result from the radiation pattern of long-period surface waves, that is, the source effect. The attenuation relationships show the following trends: The PGV(WB) values are larger than the sum of the PGV(BP10), PGV(BP20), and PGV(BP30) at distances (D) less than 200 km, while the PGV(WB) values are comparable to the sum of the PGV(BP20) and PGV(BP30) at D > 200 km. This indicates that the PGV(WB) values at D < 200 km are affected by ground motions with periods less than 10 s, while long-period surface waves mainly contribute to the PGV(WB) values at D > 200 km. The basin site effects generate a patchy pattern in the spatial distribution maps and a large scattering in the attenuation relationships for the PGV(WB) and PGV(BP10) values. Finally, we conclude that the PGV(WB) values from the 2003 Tokachi-oki earthquake are controlled by the radiation pattern of long-period S and surface waves and various basin site effects.     

Numerical simulation of spatial-temporal evolution characteristics of subsurface fluid based on strong body seismogenic model

Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we studied the characteristics of "field precursors" and "focus precursors" of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ②dilatancy emerges and anomaly focus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③anomalies spread continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large-scale dilatancy.     

Validation of 3-D basin structure models for long-period ground motion simulation in the Osaka basin, western Japan

We studied the applicability of two types of existing three-dimensional (3-D) basin velocity structure models of the Osaka basin, western Japan for long-period ground motion simulations. We synthesized long-period (3–20 s) ground motions in the Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area, approximately 200 km from Osaka. The simulations were performed using a 3-D finite-difference method with nonuniform staggered grids using the two basin velocity structure models. To study the ground motion characteristics inside the basin, we evaluated the wave field inside the basin using the transfer functions derived from the synthetics at the basin and a reference rock site outside the basin. The synthetic waveforms at the basin site were obtained by a convolution of the calculated transfer function and the observed waveform at the reference rock site. First, we estimated the appropriate Q values for the sediment layers. Assuming that the Q value depends on the S wave velocity V _S and period T, it was set to Q = (1/3V _S)(T ₀/T) where V _S is in m/s and the reference period T ₀ is 3.0 s. Second, we compared the synthetics and the observations using waveforms and pseudovelocity response spectra, together with a comparison of the velocity structures of the two basin models. We also introduced a goodness-of-fit factor to the pseudovelocity response spectra as an objective index. The synthetics of both the models reproduced the observations reasonably well at most of the stations in the central part the basin. At some stations, however, especially where the bedrock depth varies sharply, there were noticeable discrepancies in the simulation results of the models, and the synthetics did not accurately reproduce the observation. Our results indicate that the superiority of one model over the other cannot be determined and that an improvement in the basin velocity structure models based on simulation studies is required, especially along the basin edges. We also conclude that our transfer function method can be used to examine the applicability of the basin velocity structure models for long-period ground motion simulations.     

2011-2014年康定周边地形变场变化与芦山7.0级地震及康定两次中强地震的关系研究

收集康定地震区及周边（99.6°~105.2°E,27.8°~33.0°N范围内）连续GPS观测站的资料求解站速度场,采用刚性-线弹性运动方程计算方法,拟合计算得到研究区域规格网格点（0.4°×0.4°）的速度值和主应变率值。基于该结果分析研究区内的运动特征和应变场变化情况,并讨论其与地震孕育发生的关系。分析结果表明,芦山7.0级地震发生前研究区呈现应变能量积累态势,而地震之后研究区呈应变能量释放调整态势,2014年康定地震的发生就是该区构造运动调整下的产物。     

Atellitic thermal infrared brightness temperature anomaly image—short-term and impending earthquake precursors

Mechanism of satellitic thermo-infrared brightness temperature and temperature increaming is studied. Experiments are made with a gas sample taken around the epicenter area. The gas ample is pmved to contain green house gases such as CH₄, and CO₂ which have increased by tens of thousands of times. In addition, lab research slso pmes that CH₄, and CO₂ can obtain energy under the action of transient electric field and release heat, thus reeulting in a temperature increase of 2–6°C. Also a brief account of practices since 1990 is given; altogether 40 short-tenn and impending earthquake predictions have been made, with 9 precise ones whose three main factors of an earthquake are clearly depicted, and 12 fairly good ones. These predictions include 3 earthquakes ofM.⩾ 7, 4 ofM.⩾ 6.0 and the rest are mundM. 5.0. Yet there are earthquakes left out of prediction. Finally the evolutionwy processing characters of satellitic thermo-infrared brightness temperature and temperature increase before the Lijiang earthquake on Feb. 3, 1996 and Tangshan earthquake on April 14, 1998 are introduced in detail. The conclusion makes a study on the regularities of connection among time, space and stress when there appears the satellitic thermal-inlinred brightness tempera- and temperature increasing anomaly. Project supported by the State 863 High-Tech Project (Grant No. 863-2-7-4-18)     

The space and time distribution characteristics of the shear stress field for the sequence of the Wuding earthquake

Follow Chen and Duda's model of spectral fall-off of (3, the dependence of peak parameters of ground motion, peak displacement dm, peak velocity vm and peak acceleration am, upon the environment stress (0-values are studied using near source seismic digital recordings for the sequence of the Wuding, Yunnan, M = 6.5 earthquake, in which, as a new thought, the peak parameters are assumed to be related to the medium Q-value. Three formulae for estimating the environment stress (0-values by the peak parameters of three types of ground motions are derived. Using these formulae, the environment stress (0-values are calculated for the sequence of the Wuding earthquake. The result show that (0-values calculated by the three formulae are constant largely, the averages of (0 are in the range of 5.0～35 MPa for most earthquakes. It belongs to the high-stress earthquakes sequence: the high-stress values are restricted to the relatively small area closely near to the epicenter of the main shock. The fine distribution structure for the contours of the environment stress (0-values is related closely to the strong aftershocks. The analysis of spatial and temporal feature of (0-values suggests that the earthquakes sequence in a rupture process generated at the specific intersection zone of seismo-tectonics under high-stress background.