安丘台电磁波观测的震前特征

本文通过对安丘台电磁波仪在安丘境内3.3级地震和辽宁省岫岩5.6级地震前异常反映情况的详细描述,提出了电磁波仪的临震异常特征和发震机理,给出地震预报的时间范围和震震级预测。

断层总面积在祁连山中西段中强地震前的变化特征

用断层总面积理论对祁连山中西段自2000年以来发生的9次中强地震进行了研究,震例表明,在每个强震来临之前若干年∑(t)曲线均有一个显著的"峰"出现。这表明在强震来临之前,地震带或地震区上的地震活动性显著增高。发现在震前断层总面积有明显的∑(t)值高值异常显示,对断层总面积值随时间变化特征的分析表明,断层总面积值对祁连山地区Ms≥5.0级以上地震有较好的中短期预测效果。

玉门5.9级地震前兆异常特征分析

分析了2002年12月14日甘肃玉门MS5.9地震前的地震活动性各项异常指标及地电前兆临震异常特征。结果显示,电阻率和地震活动性频度、C值、b值、GL值、η值在玉门5.9级地震前出现了中、短临多项异常。

断层总面积理论在中强地震预测中的应用

用断层总面积理论对华北地区16例中强地震进行了研究,发现有15例在震前2a左右断层总面积有明显的高值[A(t)≥30]异常显示.对断层总面积值随时间变化特征的分析表明,断层总面积值对华北地区5.5级以上地震有较好的中短期预测效果.将此方法应用于地震趋势预测中,认为2005年度冀鲁豫交界区存在发生5级以上地震的可能.

Seismic analysis of the active character of the Taihang Mountain piedmont fault

The Taihang Mountain piedmont fault is a large-scale structure zone in north and east China which cross Beijing,with the NE-NNE extent spans approximately 620 km.It is very important to determine the fault zone activity due to the close relation of active structures and earthquakes.Regarding the fault activity,there are three different opinions：1） it is a large deep fault zone;2） it is an active fault zone and an earthquake structure belt;and 3） it is not an earthquake structure belt.In order to ascertain the active character of the fault,the deep tectonic setting and the activity since the Quaternary were investigated using recent seismic and drilling data to make a joint interpretation.The investigation results show that the Taihang Mountain piedmont fault is not a large lithospheric fault because the early middle Pleistocene（Q（P2）） layers are offset by the fault and the late middle Pleistocene（Q（P2）） and late Pleistocene layers are not offset by the fault.We determine that the Taihang Mountain piedmont fault in the area is not an active fault and is also not a large lithospheric fault.This study result provides important geological and geophysical data for city planning and construction in Hebei province and, especially,has great significance for seismic hazard assessment of the capital area.

Analysis of Abnormal Characteristics of Regional Crustal Deformation before the Menyuan MS6.4 Earthquake by GPS Continuous Data

In order to study the characteristics of crustal deformation around the epicenter before the 2016 M_S6. 4 Menyuan earthquake,the GPS continuous stations of the period from 2010 to 2016 were selected according to the observation data of the tectonic environment monitoring network in Chinese Mainland. The deformation characteristics of the crust before the earthquake were discussed through inter-station baseline time series analysis and the strain time series analysis in the epicentral region. The results show that a trend turn of the baseline movement state around the epicenter region occurred after 2014,and the movement after 2014 reflects an obvious decreasing trend of compressional deformation.During this period,the stress field energy was in a certain accumulation state. Since the beginning of 2014,the EW-component linear strain and surface strain rate weakened gradually before the earthquake. It shows that there was an obvious deformation deficit at the epicentral area in the past two years,which indicates that the region accumulated a high degree of strain energy before the earthquake. Therefore,there was a significant background change in the area before the earthquake. The results of the study can provide basic research data for understanding the seismogenic process and mechanism of this earthquake.

Variation Characteristics of Focal Mechanisms of Small Earthquakes before Four Strong Earthquakes in Xinjiang

With the point source dislocation model and the velocity structure of a layered medium,focal mechanisms of small earthquakes are calculated using the maximum amplitude of the direct P- and S-waves in the vertical component. By system clustering,and using the vector synthesis method,the average focal mechanism solution is obtained. Using the above method,this paper analyzes the variation characteristics of the source ruptures and the P-axis azimuths of small earthquakes around the seismic zones before four strong earthquakes occurring since 2003 in the western part of north Tianshan and the middle part of Tianshan. The result shows that 2 ~ 3 years before the strong earthquakes,the focal mechanism types of small earthquakes are distributed randomly, and obvious dominant distributions are observed one year before the strong earthquakes. There are obvious changes in the P-axis azimuth.

Analysis of Seismic Activity Characteristics before the Yutian M_S7.3 Earthquake,Xinjiang on February 12,2014

This paper introduces the geological structure background around the 2014 Yutian Ms7. 3 earthquake area, investigates and analyzes the regime of small earthquake activity and the characteristics of regional seismicity pattern in Xinjiang before the earthquake, and compares the characteristics of the regional seismic activity with the 2008 Yutian Ms7.3 earthquake. The results show： ① 2 ~ 3 years before the 2014 Yutian Ms7. 3 earthquake, Xinjiang was in a seismic active state with strong earthquake occurring successively, and before the 2008 Ms 7. 3 earthquake, Xinjiang was in the quiet state of moderate-small earthquakes with M3. 0 ~ 4. 0. ② Before this Yutian Ms7. 3 earthquake, the regional seismic activity showed a short-term anomaly feature, that is, seismicity of M ≥ 5. 0 earthquakes significantly increased on the Altun seismic zone and in the source area three years before the Ms7.3 earthquake, while a five year long quiescence of seismicity of M ≥4. 0 earthquakes appeared on the east of the source area in a range of about 440kin. Six months before this M7. 3 earthquake, there existed seismic gap of M3. 0 ~ 4. 0 earthquakes and near-conjugate seismic belt magnitude 3. 0 and 4. 0 in the source area. ③ The state of strong earthquake activity and the seismicity pattern of small earthquakes before this Yutian Ms7. 3 earthquake were significantly different to that before the 2008 Yutian Ms7. 3 earthquake, and this may be related to the different seismogenic environments of the two Ms7. 3 earthquakes.

The Characteristics of the Precursory Anomaly prior to the Yiliang Earthquakes,Yunnan,China on September 7,2012

An analysis was carried out on the seismic activity and the precursory anomaly prior to the earthquakes in Yiliang on September 7,2012. The characteristics of the seismic activity,the dynamic changes of underground fluid and deformation were investigated. As a result of the investigation,we found that: before the earthquake,the seismicity level of M4. 0earthquakes had enhanced,and seismic gap of a small earthquake had appeared; the precursory anomalies emerged about 1 year before the earthquake; there was phenomenon of short-term anomaly migrating from the periphery to the epicenter area; the imminent anomaly appeared in a relatively concentrated period of time, a week before the earthquake. The research has shown a significant guidance for the analysis and prediction of strong earthquakes( Ml> 5. 0).

Seismic Sequence Characteristics of the March 21,2008,M_S 7. 4 Yutian,Xinjiang Earthquake and Seismological Anomalies before the Earthquake

The parameters, stress field background, geological tectonics and seismic sequence of the March 21, 2008, Ms7.4 Yutian, Xinjiang earthquake are discussed in this paper. The characteristics of seismic activity in the epicenter and its adjacent region before the earthquake are analyzed; and a comparison is made between the Ms7.4 Yutian earthquake sequence, the Wenchuan Ms8.0 earthquake sequence and the Wuqia Ms6.9 earthquake sequence. The results show the Ms7.4 Yutian earthquake occurred in the junction between the Aityn Tagh fault and the western Kunlun fault, resulting perhaps from the tensile fracture of the branch fault located southwest of the Ashikule basin due to left-lateral dislocation of the Aityn Tagh fault; the seismic sequence is of main shock-aftershock type, the strongest aftershock being Ms5.8. The aftershocks attenuated quickly, and occurred in groups; the focal mechanism solutions and epicenter distribution have revealed a unilateral rupture source of this earthquake. Seismic activity shows that there was medium and medium-short term abnormity before the earthquake, but there was not short-imminent abnormity. Seismic activity of this earthquake sequence enhanced before the Ms8. 0 Wenchuan and the Ms6. 9 Wuqia earthquakes, showing the window effect to some extent.

A Study on the Characteristics of Anomalies and Their Dynamic Relationship before the April 14, 2010 M_S 7.1 Yushu Earthquake

The authors studied the seismic activity, precursory anomalies and abnormal animal behavior before the April 14, 2010 Ms 7.1 Yushu earthquake. Analysis showed that anomalies were not rich before the Ms 7.1 Yushu earthquake, but prominent anomalies were observed, such as the long and mid-term trend anomaly characterized by the seismic quiescence of Ms6. 0, MsS. 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.

The Characteristics of Earthquake Swarms in and around Jiangsu Province

This paper systematically analyzed 36 earthquake swarms in and around Jiangsu Province, summarized their characteristics and discussed the relationship between earthquske swarms and subsequent strong earthquakes. It also analyzed the judgment criteria for precursory earthquake swarms. Earthquake swarms in Jiangsu Province are concentrated in several areas. Most of them were of magnitude ML2.0～3.9. For most earthquake swarms, the number of earthquakes was less than 30. Time duration for about 55% of earthquake swarms was less than 15 days. The biggest magnitude of one earthquake swarm was not proportional to the number of earthquakes and time duration. There are 78% of earthquake swarms corresponded to the forthcoming earthquakes of M>4.6 in which there're 57% occured in one year, This shows a medium-and short-term criterion. Distance between earthquake swarm and future earthquake was distributed dispersedly. There were no earthquakes occurring in the same location as earthquake swarms. There was no good correlation between the magnitude and the corresponding rate of future earthquakes and the intensity of earthquake swarms. There was also no good correlation between the number of earthquakes in an earthquake swarm and the corresponding rate. The study also shows that it's better to use U-p or whole-combination to determine the type of earthquake swarm.

Short-term Earthquake Prediction in the Sichuan-Yunnan Region Using the Method of Modulated Earthquakes

By scanning modulated or un-modulated earthquakes spatio-temporally in the region of Sichuan-Yunnan,short-term non-stationary seismic precursory patterns were extracted with significant difference and the characteristic of non-stationary short-term seismic anomalies were analyzed as well as prediction efficiency of modulated small earthquakes before a strong earthquake. Besides,small earthquake modulation ratios near the region of the epicenter were calculated and sorted by time. The results indicated that there were significant effects using the modulated earthquake method to predict earthquakes greater than MS6. 0 in a short time. Before the MS8. 0 Wenchuan earthquake,there were obvious short-term precursory seismicity gap patterns of modulated small earthquakes.

Seismic Sequence Characteristics and Precursory Anomalies of the M_S6.3 and M_S6.4 Da Qaidam Earthquakes in 2008～2009

In this paper,the seismogenic structures of the Da Qaidam strong earthquakes are preliminarily discussed by using the regional seismotectonic data and focal mechanism solutions. Analysis is done on the temporal and spatial distribution characteristics of the two strong earthquake sequences in Da Qaidam in combination with the sequence distribution characteristics of the M6. 6 earthquake of 2003 and the five strong earthquakes of about M5. 0 in 2004 in Delingha. At the same time,the regional characteristics of the historical seismic activity are also investigated. Preliminary analysis is done on the influence of the two M8. 0 earthquakes in the past 10 years on this region. Precursory anomalies and their characteristics are discussed in combination with the analysis of the precursor observation data of Qinghai Province.