唐山古冶、滦县地区中小地震活动与构造关系研究

小震活动与断层运动紧密相关,小震定位技术已逐渐成为地震断层破裂、发震构造研究中不可或缺的手段。本文采用双差定位法对唐山地区1978—2011年内发生地震进行重新定位,以地震学与构造地质学为理论基础,着眼于唐山地震构造系统与滦县地震构造系统的交汇区,对连续、丰富的地震数据进行时间、空间综合分析,发现古冶东侧出现一条新生地震带。开滦煤矿地质资料证实了该新生地震带展布与徐家楼—王喜庄基岩断层完全重合,推测2010年MS4.2地震与2012年MS4.8地震均由徐家楼—王喜庄断层活动引起,应加强该区地震监测工作。

华北地区中强震前中小地震活动的动态演化特征研究

应用地震活动加速指数AI算法对华北地区1970年以来ML≥6.0地震进行了回溯性研究。利用该方法统计中强震前的中小地震活动频度,分析结果显示在空间上能够反应出中小震活动频度的异常。另外,应用有关地震活动的频度面积S值方法,对ML6.0级以上强震前后的中小地震活动在时间分布上进行了研究,此方法对AI算法的计算结果在时间上给予了支持。结果表明:AI指数能够量化地给出中强震前中小地震活动的相对增强或减弱程度,中强震的S值在震前表现为高值或低值异常,震后下降或上升。S值的异常点与AI扫描值的异常结果在时空分布上相辅相成。在地震目录完整的情况下,中强震震中区及其附近地区震前1a的中小地震活动与之前3a、5a的活动背景相比,出现明显的"加速"或"减速"现象。利用这两个参量的变化,可为该地区中强震的预测分析提供一定的判定指标。

Research on the Historical Data of the 1585 A. D. South Chaoxian Earthquake and Its Seismogenic Structure

In 1585,a MS5 3/4 earthquake occurred in the south of Chaoxian county,Anhui Province. The parameters of this earthquake were reported differently in various versions of earthquake catalogues. According to detailed textual research on the historic records of this earthquake,the epicenter location of the earthquake was further confirmed by means of seismo-geological field investigations in the Chaohu-Tongling region along the western Yangtze River valleys. Shallow seismic prospecting and drilling methods were applied in studying the buried fault. The possibility of the existence of seismogenic faults and fault activity in the western Yangtze River area were analyzed in depth,and the causative tectonic background of the 1585 MS5 3/4 south Chaoxian earthquake was studied. The results of this study indicate that the Yanjiaqiao-Fengshahu fault,which was active in the early to mid-Pleistocene,is possibly the causative structure of this earthquake. To identifying the seismogenic structure of the 1585 south Chaoxian earthquake will help gain more knowledge about the tectonic background of moderate and small earthquake activity in Eastern China.

Analysis of Small Earthquake Activities before Medium-strong Earthquakes in Northeast China

13 earthquakes with M 〉 5.0 have been recorded in the northeast region of China since 1970, among which eight medium-strong earthquakes are independent in space and time. Studies of seismicity before these eight medium-strong earthquakes show that small earthquake activity was enhanced before the occurrences. Though seismicity increase is a common phenomenon in the northeast China region, we have difficulty in predicting the medium-strong earthquakes by this phenomenon alone. In order to predict medium-strong earthquakes through se｜smicity increase, this paper tries to propose a new method that calculates small earthquake frequency through the changing pattern of small earthquake activities based on the characteristics of small earthquake activity in the northeast China region. The results show that we can get the obvious anomaly frequency of small earthquakes before medium-strong earthquakes through the new method, and can obtain a medium to short term anomaly index for the northeast China region.

Characteristics of Seismic Activity in a 3-Dimensional Space before the Wen'an Earthquake,Hebei Province by Relocation of Small Earthquakes in the China's Capital Area

Characteristics of seismic activity before the M5. 1 earthquake in Wen＇an, Hebei Province on July 4, 2006 are analyzed by relocation of small earthquakes in the China＇s capital area, and some results are obtained as follows：① The seismic activity of ML ≥ 3.0 in the middle part of the Hebei plain seismic belt displayed a feature of strengthening （ lasting 43 months） quiescence （17 months） five years before the Wen＇an earthquake. Simultaneously, the strain release curve showed a variation process of accelerating-flatting. ② A seismogenic gap in a three-dimensional space, located at the depth of 15km - 20km, with 70km long in latitude direction and 90km long in longitude orientation, was formed by M≥2.0 earthquakes four years prior to the Wen＇an earthquake. The initial rupture point of the Wen＇an earthquake is situated at the bottom of the gap. ③ The focal depths of earthquakes with ML ≥ 2. 0 in the middle part of the Hebei plain seismic belt gradually increased from 10km to 30kin during the period from April, 2003 to October, 2004. Meanwhile, the seismic activity obviously strengthened in the middle and lower crust （from 20km to 30km in depth）.

Wavelet Analysis of Earthquake Activity in the West of the Chinese Mainland and Its Adjacent Area1

Wavelets are a useful tool for analyzing the time-frequency of a non-stable series and are widely applied in many fields. The process of earthquake preparation and occurrence is a non-linear process. In the paper, the wavelet method is used to analyze the series of earthquake data for the time period from 1900 to 2003 in the west of the Chinese mainland and its adjacent area (WCMAA), and to obtain the characteristic information for different time scales. In the past 103 years, there were four primary periods of regional earthquake activity in the area with durations of 42, 22, 7 and 14 years, respectively and the intensity of earthquake activity changing with time. It doesn’t make sense to talk about active or quiet periods of earthquake activity unless it is based on a specific time scale. In addition, the tendency analysis of earthquake activity using the primary period of seismic activity and wavelet coefficients of varied time scales indicates that the earthquake activity in this region will be high in the forthcoming years.