Analysis of foreshock sequence of the 1975 Haicheng earthquake of Ms 7.3

Ａｎａｌｙｓｉｓｏｆｆｏｒｅｓｈｏｃｋｓｅｑｕｅｎｃｅｏｆｔｈｅ１９７５ＨａｉｃｈｅｎｇｅａｒｔｈｑｕａｋｅｏｆＭｓ７．３Ｚｈａｏ－ＲｏｎｇＺＵＯ（左兆荣）；Ｊｉａｎ－ＰｉｎｇＷＵ（吴建平）ａｎｄＺｈｉ－ＬｉｎｇＷＵ（巫志玲）（Ｉｎｓｔｉｔｕｔｅｏｆ...     

Damage of 1975 Haicheng Ms7.3 earthquake in the Korean Peninsula and its effect on Kyushu, Japan

The 1975 Haicheng MS7.3 earthquake affected whole Korean Peninsula and even Kyushu,Japan.In this paperisoseismal map of this earthquake was drawn for these areas by sorting out and analyzing data systematically col-lected,furthermore,the characteristics of the earthquake damage were discussed.In the northern Korean Peninsula,the intensity is V in great majority of this area except local area with intensity VI,and the damage is basically inaccordance with typical characteristics of corresponding intensity grade.In the southern Korean Peninsula,theintensity is IV in large part of the area,however,in some big cities such as Seoul etc.,not only high buildingsshook strongly,but also some people appeared perceptions such as feeling dizzy and so on,and electrical servicewas interrupted on one or two districts because of transformer tripping.These phenomena could be caused by theeffect of long-period wave generated from a large earthquake on far-field.     

The mechanism of the effects of the upwelling mean on the ENSO event mature phase locking

The mechanism of the effects of the upwelling mean on the ENSO event mature phase locking is ex-amined by using a mixed-mode model. The results show that the positive feedback process of the ef-fects of the seasonal variation of the upwelling mean on the Kelvin wave is the mechanism of the locking of the event mature phase to the end of the calendar year. The memory of the Rossby waves for the sign-shifting of the sea surface temperature anomaly from positive to negative 6 months before the cold peak time is the other mechanism of the locking of the La Nia event mature phase to the end of the calendar year. The results here are different from previous ones which suggest that the balance between cold and warm trends of sea surface temperature anomaly is the mechanism involved. The cold trend is caused by the upwelling Kelvin wave from upwelling Rossby wave reflected at the western boundary, excited by the westerly anomaly stress over the central Pacific and amplified by the seasonal variation of the coupled strength in its way propagating westward. The warm trend is caused by the Kelvin wave forced by the western wind stress over the middle and eastern equatorial Pacific. The cause of the differences is due to the opposite phase of the seasonal variation of the upwelling mean to that in the observation and an improper parameterization scheme for the effects of the seasonal varia-tion of the upwelling mean on the ENSO cycle in previous studies.     

Regional characteristics of the effects of the El Niño-Southern Oscillation on the sea level in the China Sea

Based on coastal tide level, satellite altimetry, and sea surface temperature (SST) data of offshore areas of China’s coast and the equatorial Pacific Ocean, the regional characteristics of the effects of the El Niño-Southern Oscillation (ENSO) on the sea level in the China Sea were investigated. Singular value decomposition results show a significant teleconnection between the sea level in the China Sea and the SST of the tropical Pacific Ocean; the correlation coefficient decreases from south to north. Data from tide gauges along China’s coast show that the seasonal sea-level variations are significantly correlated with the ENSO. In addition, China’s coast was divided into three regions based on distinctive regional characteristics. Results obtained show that the annual amplitude of sea level was low during El Niño developing years, and especially so during the El Niño year. The ENSO intensity determined the response intensity of the annual amplitude of the sea level. The response region (amplitude) was relatively large for strong ENSO intensities. Significant oscillation periods at a timescale of 4–7 years existed in the sea level of the three regions. The largest amplitude of oscillation was 1.5 cm, which was the fluctuation with the 7-year period in the South China Sea. The largest amplitude of oscillation in the East China Sea was about 1.3 cm. The amplitude of oscillation with the 6-year period in the Bohai Sea and Yellow Sea was the smallest (less than 1 cm).     

Numerical simulation for 1975 Haicheng and 1999 Xiuyan earthquake processes by DDA+FEM

Introduction The Xiuyan earthquake(MS=5.4)on Nov.29,1999,occurred between Hushan town and Pi-anling town at the southeast end of the aftershocks of Haicheng earthquake(MS=7.3).These two earthquakes′sequences are highly similar in the way that the foreshocks are very frequent,focal mechanisms of the main shocks are about the same and fault strikes are approximately in the same direction.It is important to study these earthquakes for further research on seismogenesis to fore-cast earthquake…     

Study of a model for correcting the effects of horizontal advection on surface fluxes measurement based on remote sensing

As well known, the methods of remote sensing and Bowen Ratio for retrieving surface flux are based on energy balance closure; however, in most cases, surface energy observed in experiment is lack of closure. There are two main causes for this: one is from the errors of the observation devices and the differences of their observational scale; the other lies in the effect of horizontal advection on the surface flux measurement. Therefore, it is very important to estimate the effects of horizontal advection quantitatively. Based on the local advection theory and the surface experiment, a model has been proposed for correcting the effect of horizontal advection on surface flux measurement, in which the relationship between the fetch of the measurement and pixel size for remote sensed data was considered. By means of numerical simulations, the sensitivities of the main parameters in the model and the scaling problems of horizontal advection were analyzed. At last, by using the observational data acquired in agricultural field with relatively homogeneous surface, the model was validated.     

Damage spectra for the mainshock–aftershock sequence-type ground motions

Strong aftershocks have the potential to increase the damage state of the structures due to the damage accumulation. This paper investigates the damage spectra for the mainshock–aftershock sequence-type ground motions with Park–Ang damage index. A method of simulating the mainshock–aftershock sequence-type ground motions is proposed based on the modified form of Bath's law and NGA ground motion prediction equation. The damage spectra are computed using the recorded and simulated sequence-type ground motions, and the effects of period of vibration, strength reduction factor, site condition, seismic sequence, damping ratio and post-yield stiffness on damage spectra are studied statistically. The results indicate that the effect of aftershock on structural damage is significant and recorded sequence-type ground motions may underestimate the damage of long-period structures due to the incompleteness of dataset. A simplified equation is proposed to facilitate the application of damage spectra in the seismic practice for mainshock–aftershock sequence-type ground motions.     

Modeling the ML4.7 mainshock of the February–July 2001 earthquake sequence in Aegion, Greece

An earthquake sequence comprising almost 2000 events occurred in February–July 2001 on the southern coast of the Corinth Gulf.Several location methods were applied to 171 events recorded by the regional network PATNET. The unavailability of S-wave readings precluded from reliable depth determination. For the mainshock of April 8, M_L= 4.7, the depth varied from 0 to 20 km. The amplitude spectra of complete waveforms at three local stations (KER,SER, DES; epicentral distances 17, 26 and 56 km) were inverted between 0.1 and 0.2 Hz for double-couple focal mechanism and also for the depth. The optimum solution (strike 220°, dip 40°, rake ‒160°, and depth of 8 km) was validated by forward waveform modeling.Additionally, the mainshock depth was further supported by the P- and S-wave arrival times from the local short-period network CRLNET (Corinth Rift Laboratory).The scalar seismic moment was 2.5e15 Nm,and the moment rate function was successfully simulated by a triangle of the 0.5 second duration. This is equivalent to a 1–1.5 km fault length, and a static stress drop 2–6 MPa. This value is important for future strong ground motion simulation of damaging earthquakes in Aegion region, whose subevents may be modeled according to the studied event. The T axis of the mainshock (azimuth 176° and plunge 67°), is consistent with the regional direction of extension N10°. However, none of the nodal planes can be associated to an active structure seen at the surface. The relationship of this earthquake sequence with deeper faults (e.g. possible detachment at about 10 km) is also unclear.     

Several effects of baroclinic currents on the three‐dimensional propagation of inertial‐internal waves†

A ray theory is applied to the problem of three‐dimensional propagation of inertial‐internal waves in the presence of a mean baroclinic current which does not vary in the downstream coordinate. As time increases, the Doppler‐shifted wave frequency, or intrinsic frequency, tends to a limiting value determined by the horizontal and vertical variations of the mean current and density fields. The limiting value of the intrinsic frequency determines critical surfaces where energy is transferred to the mean motion. Also, the group velocity tends to the mean current velocity, and the phase velocity tends to be oriented towards or away from the core of the mean current, depending upon whether the wave is either initially propagating with a wave number component antiparallel or parallel to the mean current.     

Observations on the effects of barite on the gill tissues of the suspension feeder Cerastoderma edule (Linné) and the deposit feeder Macoma balthica (Linné)

Barite, an important component of offshore drilling muds, is shown to adversely affect the ctenidia of the suspension feeding bivalve, Cerastoderma edule and the deposit feeder, Macoma balthica. SEM observations showed that exposure to barite caused cilia to shorten and coagulate, and, in some extreme cases, cause the disintegration of the gill structure itself. Using a simple ciliary condition index (CCI) the impact of the barite was quantified and damage rates expressed. The bivalves were treated with daily doses of 1, 2, and 3-mm depth equivalents of barite. In all treatments significant damage to the gills was recorded although, in the case of the 1-mm dose rate, this did not occur for 4 days. In the other two treatments, damage was apparent within a day of exposure with 100% mortality occurring within 12 days. Macoma balthica appeared slightly more tolerant of exposure to barite than C. edule.     

前震或广义前震识别的频谱偏移法及其应用研究

在前期研究的基础上,本文提出了一种前震或广义前震识别的频谱偏移法。其判定指标为,正常背景的中等震级地震事件频谱较宽,而具有前震或广义前震性质的中等震级地震具有频带变窄且向低频端偏移集中的特征。究其根源可能与强震前震源区或主震相关区域亚稳态扩展破裂或区域介质破碎损伤、裂隙扩展成核等过程有关。对2010年4月14日青海玉树7.1级、2014年2月12日新疆于田7.3级等地震前震的计算结果显示,2次前震的频谱都发生了偏移,且与非前震性同等震级地震频谱差异明显。     

海城地震预报过程的回顾及地震预报发展的思考

通过1975年海城地震预报过程的回顾,结合国内外地震监测预报研究的进展,提出了发展我国地震预报研究的建议。     

Identifying the occurrence time of an impending mainshock:a very recent case

The procedure by means of which the occurrence time of an impending mainshock can be identified by analyzing in natural time the seismicity in the candidate area subsequent to the recording of a precursory seismic electric signals(SES) activity is reviewed. Here, we report the application of this procedure to an MW5.4 mainshock that occurred in Greece on 17 November 2014. This mainshock(which is pretty rare since it is the strongest in that area for more than half a century) was preceded by an SES activity recorded on 27 July 2014, and the results of the natural time analysis reveal that the system approached the critical point(mainshock occurrence) early in the morning on 15 November 2014.     

Research on geomagnetic tectonic characteristics of the crust in Haicheng seismic area

In this paper, the two metnods, rectangular spectrum (RS) and maximum entropy power spectrum (MES), have been used in calculating the geomagnetic structures of the crust in Haicheng and its adjacent areas and carrying out the geomagnetic stratification of the crust. The result of the research indicates that the crust can be devided into such three layers as nonmagnetic layer, magnetic layer and regressive magnetic layer from the top to the bottom. It is also found the distribution of the geomagnetic bottom interface (Curie surface) is consistent with the lower interface of the upper crust and the top interface of the middle crust of the velocity structure of the crust. It is very interesting that the Haicheng earthquake of Feb. 4, 1975,M 7.3 occurred at the depth gradient belt of the Curie isotherm surface. So, to research on the geomagnetic layers and the distribution characteristics of the Curie isotherm surface is meaningful in judging potential seismic foci. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 448–454, 1993. The data of velocity and electricity materials used in this paper are as reference from the related materials of the maps and directions etc. of Donggou-Haicheng-Dong Ujimqin Qi Geoscience Transect by Prof. Zao-Xun LU, Huai-Kuan XIA and others.     

Analysis of foreshock sequence of the 1975 Haicheng earthquake of M S 7.3

The “earthquake nucleation” is discussed in this paper. The acceleration is a property of the nucleation phase and is a necessary condition of earthquake instability too. If the acceleration property of this nucleating process is described by the equation dΘ/dt=C/(t _f−t) ⁿ , the process can be summarized briefly that the rate of cumulative seismic release is proportional to the inverse power of the remaining time to failure. Based on this principle, the foreshock sequence of the 1975 Haicheng earthquake withM _S7.3, was analysed backward. It is stated clearly that the time-to-failure and magnitude of the mainshock can be predicted successfully if the coefficientr ² attains to the maximum. In the estimation of mainshock time, the error can generally be less than, or far less than, one-half the remaining time between the time of the last used data point and the mainshock. Contribution No. 95A0024, Institute of Geophysics, SSB, China. This study is the "Eighth-Five" contract project ofSSB.     

1975年海城MS7.3地震强地面运动模拟

地震强地面运动预测对工程的抗震设计,地震危害性分析以及减轻特定地区可能发生的大地震所造成的灾害具有重要的作用.本文根据辽宁省海城地区的地质资料和发生于1975年2月4日辽宁省海城市的M_S7.3地震资料,分别构造了海城地区的地下速度结构和海城地震的震源模型,并且使用可以准确描述地形起伏的曲线网格有限差分方法计算了海城地震的波场传播过程.通过对计算得到的波场快照、合成理论地震图以及地震烈度的分析表明：（1）震源模型、地下的速度结构和地形起伏对海城地震的波场传播模拟具有重要的影响,它们所产生的近断层效应、方向性效应和盆地效应明显;（2）通过计算得到的海城地震的理论烈度分布与通过震后调查得到的烈度分布大体符合,验证了本文所构造的震源模型和速度结构的合理性.

     

1975年海城地震和1976年和林格尔强震与1976年唐山大震的关系讨论

从北纬40°纬向地震带活动的关系探讨了华北3次强震发生的同时性的原因,这条EW向地震带首先发生的地震传递的能量促使唐山积累了发震能量,而另一条由邢台、河间NE走向的下地壳蠕滑断层的能量传至唐山断层后,解锁了该孕震断层,从而发生了唐山大震。地震波的触发作用也是同步的另一个原因,除了震动的断层面的直接触发之外,对组合模式中单地震波的积累与调整也会产生触发作用而改变其性质。另外还从中国8级大地震发生的25年周期讨论了同步性。     

在二维应力状态下土体地震动偏应力的特征

地震作用在土体中产生的动偏应力包括动水平剪应力τｖｈ 和动正应力差［σｐ － σｈ］ ／２ 。本文讨论了这两种动偏应力分量之间相互变化的关系     

在二维应力状态下地震触发砂土液化动应力条件

在二维应力状态下,地震在土体中不仅产生动水平剪应力τｈｄ,而且也引起在一般情况下不可忽略的竖向与水平动正应力关「σｖｄ－σｈｄ」／２,二者定义为动偏应力之二分量,均应是评估土体或土工结构物变形及其稳定性的主要因素。本文给出了在地震动偏应力二分量共同作用下,土单元中最大往返剪切作用面及其上最大动剪应力比「τｄ／σｓ」ｍａｘ的确定方法。据此,提出了地震触发砂土液化的应力条件及液化判别准则。