Depth Distribution of Aftershocks in the China Mainland and Its Rheological Mechanism

The relationship between aftershock depths and surface heat flow in the source areas of five great earthquakes(M≥7.0)in the China mainland has been studied in this paper.The result shows that the higher the surface heat flow,the shallower is the aftershock depth,and that the distribution of aftershock depths is controlled by the rheological mechanism of brittle-ductile transition of rocks in the crust.     

Effect of Aftershocks on Assessment of Seismic Hazard for Hebei Seismic Zone,China

In this paper,the earthquake hazard parameters(λm,b and Mmax) from the maximum likelihood method for the raw catalogue and declustered catalogues have been used to discuss the effect of the aftershocks on the earthquake hazard estimation.The declusterd catalogues have been compoiled from the raw catalogues by deleting the aftershocks in different time interval after main shock according to the criteria for the aftershock activity period.As an example,Hebei seismic zone is taken to show the effect of the aftershock on the earthquake hazard assessment because three strong earthquakes with the aftershocks occurred from 1966,to 1976,The results have been shown that the effect of the aftershocks on the parameters λm,b is significant.The difference between the clustered and declustered catalogues has reached in seismic activity rate and recurrence period,at most,45% and 90%,respectively,But the diffeence in Mmax is smaller,Based on this,the suggestion that the aftershocks should be omitted in the estimation of the earthquake hazard could be made,but how long the aftershocks activity duration is still left to the future research.     

自适应滤波器在地磁数据噪音处理中的应用

利用自适应信号处理的原理，尝试消除地磁观测数据中的干扰噪音。结果显示这种方法能有效地抑制包括随机噪音，大幅度突跳偏离和阶跃各种形式的干扰。对于和信号频率相重的干扰能给予有效抑制，且能保持信号基本不变。     

余震区长度与震级关系的模糊神经元网络模型

本文试图将模糊人工神经元网张及模糊信息分析理论引入到余震区长度与震级关系的识别之中，采用信息扩散与ＢＰ型人工神经元网络相结合的方法建立模型，该模型有较强的自适应能力及处理矛盾样本的功能。最后将该模型的识别结果与统计结果瑟统计结果进行了比较，结果表明该模型具有一定的优越性。     

唐山几次强余震前地震活动标度的异常特征分析

本文计算了1980年1月——1987年4月唐山老震区余震序列的地震活动标度值。通过数据处理,分折讨论了在此期间所发生的4次强余震前,地震活动标度的异常特征。     

A quantitative study of some aftershock sequences in greece

Temporal features of the aftershock activities following twelve moderate shallow earthquakes in Greece have been studied quantitatively, by making use of the modified Omori's formula and Akaike's Information Criterion (AIC).Although the earthquake sequences occurred in different seismotectonic regions in Greece, similar seismic patterns before the occurrence of large aftershocks have been observed. Aftershock activity shows an appreciable decrease from the level expected from the modified Omori formula before the occurrence of the large aftershock. Also in some cases, the aftershock activity recovers to a normal level or increases beyond it prior to the occurrence of the large aftershock, if the aftershock activity is monitored immediately after the occurrence of the main shock. In such case, the observed pattern may be useful in predicting a large aftershock.     

Seismicity anomaly scenario prior to the major recurrent earthquakes off the east coast of Miyagi Prefecture, northern Japan

This paper is concerned with the intermediate-term prediction of the forthcoming M7.4–8.2 earthquake on the plate boundary, off the east coast of Miyagi Prefecture, northern Japan, which has the highest occurrence probability among the long-term forecasted events announced to the public. Seismicity and aftershocks in the regions of stress-shadow preceding each of the previous ruptures in 1936 and 1978 shows significantly lower activity than the predicted rate by the ETAS model (the relative quiescence) during some years preceding the events, whereas the seismicity is normal or even activated in the regions of neutral or increasing Coulomb failure stress (CFS), which leads to the scenario based on the likely precursory slip within or near the source. Assuming such a scenario, a number of sequences of earthquakes or aftershocks during 1979–2004 from various regions in northern Japan are selected to analyze them by fitting the ETAS model. Then the results are examined in relation to the CFS increments in the considered regions using the source models of the 1793, 1936 and 1978 interplate ruptures, and additionally the source model of recently occurred 2003 Miyagi-Ken-Oki intra-slab earthquake of M7.1. It is likely that the results of the normal activity and relative quiescence in the respective activities are due to the preslip of the intra-slab earthquake rather than the preslip of the expected rupture on the plate boundary.     

Imaging the heterogeneous source area of the 2003 M6.4 northern Miyagi earthquake, NE Japan, by double-difference tomography

A shallow M6.4 inland earthquake occurred on 26 July 2003 in the northern part of Miyagi Prefecture, northeastern Japan. This earthquake was a typical inland thrust earthquake, a type that is common in NE Japan. We obtained a detailed seismic velocity structure in the focal area of this earthquake by the double-difference tomography method. Arrival-time data came from temporary seismic stations deployed above the mainshock fault plane. Both the P-wave and S-wave velocities in the hanging wall were lower than those in the footwall. Aftershocks were aligned along a zone where the seismic velocity changes rapidly. This is consistent with the interpretation that the 2003 northern Miyagi earthquake occurred along a fault that acted as a normal fault in the Miocene and has been reactivated as a reverse fault under the present compressional stress regime. The large slip area by the main shock rupture (asperity) corresponds to an area with relatively high P- and S-wave velocities. A zone with low V_p/V_s was detected along the aftershock area. One of the possible causes of this low-V_p/V_s zone is the existence of high-aspect-ratio pores that contain water. Hypocenters of the main shock, largest foreshock, and largest aftershock are also located within the low-V_p/V_s zone.     

震后趋势判定技术系统CAAFs震后余震预测效果评价

自2019年正式运行以来,震后趋势判定技术系统CAAFs为震后应急与趋势研判及时提供数据和技术支撑。本文梳理总结CAAFs系统持续4.5年产出的数据,从全国和不同地区两个方面评价系统产出的震后余震预测结果,得到以下三点认识:①震级上限预测(发生某震级以上地震的可能性不大)的正确率大多为90 %及以上,显著优于震级区间预测(存在发生同等大小地震的可能或存在发生某震级左右地震的可能),各分区预测情况差异不大; ②震级区间预测震级普遍比地震实况偏高,实际7日内发生的最大余震震级与预测震级的差值(震级偏差)落入[-0.5,0.5]区间的地震比例约为44 %,落入[-1,1]区间的地震比例约为69 %,越靠近[-0.5,0.5]区间,地震的比例越高; ③震级区间预测中,各分区有一定差异,西南地区优于西北、华南和华北东北三个地区,总的来看4~5级地震预测情况不如其他震级区间,可能与该震级区间内地震的最大余震震级变化范围较大有关。