云南地区双震型地震序列中第二主震的前震识别

本文通过对双震型地震序列的地震波动力学特征的研究，提出了识别双震中第二主震前震的可能性。结果表明、在双震第一主震发生后，序列地震的Ｐ波垂直分量初动一致时，可依据波形来识别第二主震的前震；而初动不一致时有三种情况：１、两组初动中有一组Ｐ、Ｓ波振幅比仍保持为过原点的直线而另一组离散，２、两组初动的振幅比分别为过原点的直线；３、两组初动的振幅比共同组成过原点的直线，对前两种情况可识别第二主震的前震，最后一种情况难以识别。总体达６０－７０％的可识别率。     

The Tongliao MS5.3 Earthquake and Its Foreshock Determination

Taking the 2013 Tongliao MS5. 3 earthquake as a research subject, on the basis of statistical analysis of earthquake sequence using the HypoDD location method and focal mechanism solutions,the paper analyzes and discusses the relationship between the ML4. 4 and MS5. 3 earthquakes. The results show that the Tongliao MS5. 3 earthquake occurred under the background of medium-small earthquakes long-term quiescence and short-term enhancement in the epicentral area. The results of accurate seismic location shows that the Tongliao MS5. 3 earthquake sequence is distributed in the NW direction,extending 10 km,and the ML≥3. 0 aftershocks are concentrated south of the mainshock. The distance between the MS5. 3 mainshock and the ML4. 4 foreshock is about 1. 8 km,with a focal depth of 7. 208 km and 7. 089 km,respectively,their focal location is very close,and may have occurred on the same fault plane. The results of focal mechanism shows that the Tongliao MS5. 3 earthquake is of the strike-slip type,the focal mechanism of aftershocks are disordered,and with time lapse,the type is changed from strike-slip to thrust and normal faulting. The bigger foreshocks had similar focal mechanism and were all normal fault types,which exhibits to some extent,an obvious crustal medium anisotropy in the epicentral area before macroscopic rupturing,as represented by alignment fractures,with stress action enhanced,this"consistency"of seismic precursor regime would gestate the mainshock. According to the characteristics of temporal-spatial distribution of earthquake sequence and similarity of focal mechanism,we judge that the Tongliao MS5. 3 earthquake sequence is a foreshock-mainshock-aftershock type.     

新丰江水库6.1级地震前震序列分析

裂纹由初始的亚临界扩展到发生非线性动力学失稳这一整个物理过程呈加速释放征兆；加速是失稳的一个必要条件。若以方程ｄΩ／ｄｔ＝Ｃ／（ｔｆ－ｔ）ｎ表征这一加速过程，则可将该过程简要地概括为地震释放速率比例于失稳破裂前剩余时间的负幂。根据这一原理，对１９６２年３月１９日广东河源新丰江水库６．１级地震的前震序列进行回顾性分析，并推算出库区于３月下旬发生７级以上大地震。与实测主震相比，发震时间有所推迟，震级也偏高，但却能提前２０多天发出警报，有利于防震减突对策的布署。     

2010年4月14日玉树7.1级地震前异常特征及强震动力学关系探讨

The authors studied the seismic activity, precursory anomalies and abnormal animal behavior before the April 14, 2010 MS7.1 Yushu earthquake. Analysis showed that anomalies were not rich before the MS7.1 Yushu earthquake, but prominent anomalies were observed, such as the long and mid-term trend anomaly characterized by the seismic quiescence of MS6.0, MS5.0 and MS4.0 earthquakes, and the anomalies in precursor observation of surface water temperature in Yushu and Delingha and electromagnetic measurement in Pingan. There were a large number of animal behavior anomalies appearing one week before the earthquake. An M4.7 earthquake occurred 130 minutes before the main shock. In this paper, we studied the dynamic process of the Yushu earthquake preparation using the earthquake focal mechanism solutions on the Bayan Har block boundary since 1996. The results show that the Kalakunlun M7.1 earthquake in 1996, the Mani M7.5 earthquake and the Yushu MS7.1 earthquake have the same dynamic process. Long and mid-term trend anomalies may be related to the dynamics of evolution of different earthquakes. This paper also discusses the recurrence interval of strong earthquakes, foreshock identification and precursor observation of the Yushu MS7.1 earthquake.     

前震序列的图像特征研究

地震丛集在时间和空间上分布具有不同的特征,2个特殊的例子就是前震序列和震群。基于对1966~1996年中国大陆8个前震序列的分析,本研究提取了如下前震序列的图像特征:1前震序列的震中在空间上密集集中;2前震的震源机制与主震的震源机制相似,而这种与主震震源机制的一致性在余震序列和震群中并不存在;3这30年在中国大陆我们尚未发现主震之前的前震丛集的震源机制不一致。最后,我们发现中国大陆5%的主震前发生前震序列。     

关于1999年岫岩偏岭5.6级地震前震群序列性质的研究

利用经验类比的方法,对１９９９年１１月２９日岫岩偏岭５．６级地震前群序列及以往在辽宁地区发生的典型具有预报意义的１９８８年２月２５日彰武４．８级地震前岫岩偏岭兆震群和１９７５年２月４日海城７．３级地震前序列进行了详细研究。结果显示,１９９９年１１月２９日岫岩偏岭５．６级地震前震群序列与１９７５年２月４日海城７．３级地震前震序列的统计特征及性质相同,因此,认为该序列属于前震序列。同时, 将序列的表象     

Statistical parameters of Bhuj earthquake sequence of January 26th, 2001

An intraplate earthquake of magnitude (M _c) 6.9 (Anon 2001a) struck Bhuj and the adjoining region of Kachchh in Gujarat on January 26th, 2001 at about 0316 hrs (GMT) and was followed by a number of aftershocks. The epicentre of this earthquake was located at 23.4‡N and 70.28‡E close to the Kachchh mainland fault. The intensity observed around the epicenter was X on the MSK scale. A study of 531 aftershocks, in the magnitude range of 3.0–5.7, recorded at Vadodara Seismological Observatory till March 31st, 2001 has been carried out and various statistical parameters calculated. The total energy released during the study period is calculated to be 8.2 × 10¹⁴ joule. Sudden occurrence of the main shock without any foreshock in the same tectonic system is a unique feature of this sequence. Theb- value (0.86), value of M₀-M₁ (1.2), high M₁/M₀ (0.89) and high value of the decay constanth (0.91), all support the tectonic origin of the present study.     

Discrimination Between Foreshocks and Earthquake Swarm from the Change of First Motion Sign

Based on the data of first motion of 11 earthquake sequences with ML ≥ 3.0 recorded by the Telemetric Seismic Network of Shanxi since the 1980s, the first motion characteristics of each earthquake sequence were studied. It is known that earthquake sequences of different types have different consistency characteristics of focal mechanism. The decrease and increase of the first motion contradictory sign ratios could be taken as an index to judge whether there would still be a larger earthquake to come after the earthquake sequence.     

后续地震发生时间估计及序列性质判定--以海城7.4级、巴楚-伽师6.8级地震序列为例

在前人研究的基础上,给出利用参数k判定序列性质及利用前期地震预测后续地震发生时间的方法.理论分析表明,参数k以0为界,不同的取值表征了不同的地震活动状态,这与地震趋势估计及后续地震预测密切相关.k<0表明地震间时间间隔逐渐增长,呈现一种类似余震序列逐渐衰减的活动特征;k=0意味着地震间时间间隔不变,地震活动表现为以T为周期的准周期性活动;k>0表明地震间时间间隔逐渐缩短,呈现一种类似前震序列或地震累积频次指数增长的异常活动特征.如果k值在正、负区间随机分布,则该组地震之间无相关性可言.利用1975年2月4日海城7.4级地震前、余震序列及2003年2月24日巴楚-伽师6.8级地震序列对上述方法进行了检验并对有关问题进行了初步讨论.     

一种短期前震标志

根据对云南、四川5995次地震资料的研究,本文提出了一种新的前震序列的判别方法。以某点为园心,50公里为半径,在10天内所发生的M_L≤4.8的地震归为同一序列。在所有1192次地震序列中,序列发生后在250天时间200公里范围内有M_S≥4.8级地震发生的共计481个序列。对比481个序列按其序列中地震的震级差M_1-F_1或M_1-A_1进行统计,发现当序列内震级差大于等于1.0时,其后中强震发生的概率极高,约为0.82。由此我们选取震级差大于等于1.0的序列为短期前震标志,从而建立一种人机结合进行地震预报的方法。