首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 55 毫秒
1.
Selecting three half orbits near the epicenter of Pu'er earthquake, we analyzed the Ne data recorded in their revis-ited orbits during a year before this earthquake, and extracted Ne precursors. The results show that: ① There are significant seasonal variations of ionospheric Ne in night time, which exhibit different shapes respectively in four seasons; ② There are three main shapes of Ne: single-peak, saddle-shaped and even-shaped, all of which may oc-cur in four seasons, but each season with its typical s...  相似文献   

2.
This paper analyzes the characteristics of time sequence changes of gravity points near the epicenter, different changes of measuring lines and gravity changes of measuring areas in point-line-area manner respectively with the 5-period mobile gravity data through densified observation by the South Xinjiang Observation Network after the 2015-2016 Akto earthquake in Xinjiang. The gravity observation results before the earthquake indicate that the Wuqia-Bulungkol area near the epicenter presented the trend of gravity value increasing since 2015, but the gravity value decreased half a year before the earthquake, and witnessed a high gradient zone of gravity changes during some periods before the earthquake. The gravity observation results after the earthquake show that there is a trend of opposite changes in gravity difference on the northern and southern sides of Bulunkou, and good correspondence exists between the characteristics of gravity field changes near the epicenter before and after the earthquake and the geologic structure distribution in the area.  相似文献   

3.
The Qilian Mountain active source network data was processed using the methods of stacking, cross-correlation and interpolation, and the airgun travel time variation characteristics of P and S waves around the January 21, 2016 MS6.4 Menyua, Qinghai earthquake. The results show that about 6 months before the earthquake, the relative travel time of three stations near the epicenter showed a declined change (travel time decrease), and such a change of low value anomaly was recovered about 3 months before the earthquake. The travel time decrease then appeared again, and the earthquake occurred during the recovery process. The maximum decrease of the S-wave travel time was 18ms, and the change in travel time returned to normal after the earthquake. The variation trend of the 3 stations is consistent, including the S-wave travel time change of station ZDY38, which is nearest to the epicenter and changed obviously, and the variation range of the travel time is smaller at the stations afar. This variation pattern is related to the position of the seismic source. The shorter travel time means the velocity increase, which may be related to the regional stress accumulation.  相似文献   

4.
In order to study the spatiotemporal evolution of the precursory anomalies 10 years before the Wenchuan M_S8. 0 earthquake in 2008, the epicentral distance of the precursory anomalies is calculated by using the geometric center of the rupture region and the elliptical centerline of the aftershock region. The result shows, precursor anomalies gradually increased about 2 years before the Wenchuan earthquake. The ratio of abnormal items is greater than 25% in the near source area (about twice the source scale) and 17%-24% in the remote area (about 3-5 times the source scale). There are three different stages of spatiotemporal evolution of precursory anomalies. During the α stage (including α_1 and α_2,between 700 to 3000 days before the main earthquake),the anomalies are mainly distributed in the southwest and northwest area of the Wenchuan aftershocks area. It is shown that the precursors of the far source region and the near source area have the characteristics of outward expansion. During the β stage (between 300 to 700 days before the main earthquake), the anomalies are distributed in the southwest and northern region of the aftershock region, showing a large range of anomalies. During the γ stage (including γ_1 and γ_2, 300 days before the main earthquake),the range of anomaly distribution is wide,and the anomalies are distributed in the southwest and northeast of the aftershock area. The anomalies converged to epicenter (γ_1) in the far source region and expand outwards (γ_2) in the near source region. Results of the experimental study and mechanical analysis of earthquake preparation process indicate that the three-stage characteristics of precursory anomalies in the process of earthquake preparation may be controlled by the seismogenic body,which is a form of expression in the process of earthquake preparation and a universal featureduring the earthquake preparation process,which has a certain guiding role in earthquake prediction.  相似文献   

5.
Shear wave splitting is studied based on the digital waveforms of three seismic stations DJS, SZD and WUJ, which were set up after the Jiujiang-Ruichang MS5.7 earthquake of November 26, 2005 around the epicenter area. The result shows that the time delays of slow shear waves of the DJS station, which is not far from the epicenter and where the distribution of faults is complex near the station, are relatively larger and the polarization directions of fast shear waves are not concentrated; the predominant polarization direction of fast shear waves of WUJ station, with single fault distributed nearby, has a difference of 35° to the strike of the fault and is inconsistent with the direction of regional principal compressive stress. The predominant polarization direction of fast shear waves of SZD station with no faults nearby is in accordance with regional principal compressive stress. There is no obvious regular relationshipship between the delay time and the focal depth.  相似文献   

6.
We discussed the linear and nonlinear character of deformation anomaly before the January 10, 1998 Zhangbei earthquake based on the quantitative analysis by using the tilt observation data. And generalized the three phases character of tilt deformation. ①Before the earthquake in the scale of one year, EW tilt keeps relative stationary on the block of the northern part of Yanshan Mountain; the tilt vector recurs around a point near the epicenter; and the abrupt change appears before the imminent earthquake. ② At a geodesic point, tilts discrete level in two directions have a synchronous property with a decline tendency (that is an entropy reduction) in two years before the earthquake. ③ The anomaly intensity AF value at all geodesic points on the same crustal block appear high value anomaly at least two times within 3 years before the earthquake. Using the simulation experimental results of rock rupture, we interpreted the phenomena of tilt deformation relative stationary or other kinds of stationary (process of entropy reduction), of recurrence of tilt deformation vector, of two times AF high values, and even the earthquake in groups, etc.  相似文献   

7.
A destructive shock with magnitude of 6.3 occurred on 2 June 2007 at 21h34min56s UT in Pu’er region (23.0°N, 101.1°E), Yunnan Province, China. The data from DEMETER satellite during the period from 23 May to 2 June, i.e., ten days before the earthquake and one day just on the day of earthquake occurrence, were analyzed. Among the 284 orbits of DEMETER during the period, 29 orbits with the trace passing through the region within 1 888 km from the epicenter were selected to be studied. Seven anomalous events were found on the dataset of the seven orbits among the 29 ones. There existed synchronous perturbations on the variations of the spectrogram of the electric field and the variations of the density and temperature of the ions and electron, in contrast with the variations of its surround- ing area. And five events appeared in the space within 1 888 km from the epicenter while the other two were out of the studied area. Electrostatic turbulences were also recorded with the synchronous perturbations with that in the electron density and ions density in plasma in the region near the epicenter in the five events, which seems to sug- gest that there be some physical relation between these events and the preparation processes of Pu’er earthquake.  相似文献   

8.
In the moment-ratio imaging algorithm, which is based on the theory of healing of a wound, the energy of each strong earthquake is distributed around the epicenter according to certain rules, and the features of the Moment-ratio value R are analyzed as the space and time change, so that the relationships between the moment-ration value R and strong earthquakes can be found. In the present paper, regions divided, hypocenter depths and events completed magnitude analyses were carried out in the Chinese catalogue. By applying the moment-ratio imaging algorithm in which the parameters are adjusted, the processes of anomaly evolution which correspond to the epicenter and the surrounding value R before earthquakes of M≥7.0 since 1966 in different areas of China were analyzed. It was found that the range area and imminent time of a coming earthquake could be confirmed quantita- tively by analyzing the abnormal temporal and spatial variation of the value R The results showed that the temporal and spatial variation of the value R could quantitatively reflect the temporal and spatial factors of a coming strong earthquake as well as the rule of medium rupture.  相似文献   

9.
To study the crustal movement in the vicinity of the epicenter before the Zhangye MS5.0 earthquake in 2019, the characteristics of crustal deformation before the earthquake are discussed through the GPS velocity field analysis based on the CMONOC data observed from GPS. The baseline time series between two continuous GPS stations and the strain time series of an area among several stations are analyzed in the epicenter area. The resulting time series of baseline azimuth around the epicenter reflects that the energy of the fault in the northern margin of Qilian Mountain is accumulated continuously before 2017. Besides, the movement trend of azimuth slows down after 2017, indicating the stress accumulation on both sides of the seismogenic fault zone has reached a certain degree. The first shear strain and EW-direction linear strain in the epicentral area of the Zhangye MS5.0 earthquake remain steady after 2017, and the surface strain rate decreases gradually after 2016. It is illustrated that there is an obvious deformation loss at the epicentral region three years before the earthquake, indicating that a certain degree of strain energy is accumulated in this area before the earthquake.  相似文献   

10.
Based on a sample of some real earthquakes,we have suggested in previous papers that there is a density-tectonic stress wave with ultra-low frequency which is emitted from the epicenter region for months before earthquakes,and a micro-fracture wave 1 ～ 10 days before earthquakes. The former has been observed by different kinds of measurements and the latter has been observed by a few chance observations which consists of electromagnetic,gravitational and sonic fluctuations. We show real observational results that depict the two waves and they have very different frequencies,which are not difficult to discriminate. The classical elastic-rebound model is one of the most influential theories on earthquakes,and the thermodynamic elastic-rebound model has amended the classical framework. Considering the two waves above,we attempt to further modify the elasticrebound model,and the new framework could be called the "micro-fracture elasticrebound model". We infer that tectonic earthquakes could have three special phases: the accumulation of tectonic stress,micro-fracture,and main-fracture. Accordingly,there would be three waves which come from the epicenter of a tectonic earthquake,i. e. ,the tectonic stress wave with ultra-low frequency a few months before the earthquake,the micro-fracture wave about 1 ～ 10 days before the earthquake and the main-fracture wave (common earthquake wave).  相似文献   

11.
Based on the IDP data from the French DEMETER satellite,global distribution is shown,which corresponds to three precipitation zones:the aural precipitation zone,the mid-high latitude precipitation zone and the South Atlantic precipitation zone.Then the Chili earthquake with M8.8 which occurred on February 27,2010 is taken as an example.The IDP fluxes from repeat orbits are compared and the results show that there is a clear enhancement on February 26,2010,just one day ahead of the Chili earthquake.In the south zone with L=2.1～2.7,the flux on February 26 is higher than that on previous days.However in the north zone with L=2.1～2.7,there is no clear change during the day but great enhancement during the night,which is close to the time of the earthquake.At the same time,the flux on February 26 near the equator is far lower than that on previous days.  相似文献   

12.
Dynamic tracing of space-time evolution pattern of wave velocity ratio before the Lijiang earthquake with M=7.0 occurred on February 3, 1996 in northwestern Yunnan. We compared the Ninglang earthquakes with M=6.7 and M=6.4 which occurred on November 7 and December 13. 1976, 90 km away from the Lijiang earthquake. We found that the space-time evolution patterns of velocity that various authors' studied at different times are very similar.Anomaly areas of wave velocity ratio with high values appeared in the seismogenic areas 5 -7 years before the strong earthquake. Anomalies with low values in large areas appeared 3-4 years before the earthquake. Once again the anomaly areas of wave velocity ratio with high values appear in a lower range 1 ~2 years before. The strong earthquake occurred in the overlapping area of two high value anomaly areas, surrounded by the anomaly areas with low values. The monthly mean values of wave velocity ratio before the two strong earthquakes had maintained low value anomalies  相似文献   

13.
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.  相似文献   

14.
Vertical total electron content （VTEC） time series were obtained from 22 GPS stations near the epicenter of the Lushan earthquake. In this paper, we have adopted a sliding average method to detect and analyze anomalous VTEC associated with the earthquake. The results show that signif- icant, negative ionosphere VTEC anomalies appeared over the 5 days before the earthquake, and on the day when earthquake occurred. The maximum value of VTEC anoma- lies that exceeded the lower bound reached 20 TECU. The spatial distribution of VTEC anomalies showed a conjugate structure, which shifted to the magnetic equator, and subse- quently moved westwards.  相似文献   

15.
The contrast research results show that the number of items and stations with imminent, short and medium term precursor anomalies for the Wenchuan M_S 8. 0 earthquake is less than that of the Menglian earthquake. The number of anomalies and stations associated with the Wenchuan earthquake increased in the early stage of the short-term range,as opposed to the later period for the Menglian and Lijiang earthquakes. Most of the medium term anomalies occurred two to three years before the Wenchuan earthquake,when the number of anomaly stations and items was eleven,and a great change appeared in the observation values in about half of the stations ( items ) . However,for the Menglian earthquake,medium term anomalies happened one to two years before the earthquake, the number of abnormal stations and items reached 20,and a sharp change appeared in the observation values six months to one year before the earthquake in about 30 percent of the stations or items. In the epicenter and the nearby area,the macroscopic abnormalities started 3 years before the Wenchuan earthquake and lasted intermittently until 1 month before the earthquake. Within 2 percent of the total area of the province,the macroscopic abnormalities accounted for 30 to 50 percent of the total number of anomalies of the Province. For the Xingtai,Tangshan,Haicheng,Songpan earthquakes,the macroscopic anomalies started two to three months before,or on the very day of the earthquakes. The common feature of the precursors between the Wenchuan and other strong earthquakes is the appearance of tremendous changes in a certain number of observation values of anomalies in the mid and short terms before all these earthquakes.  相似文献   

16.
This paper introduces relative and absolute gravity change observations in the eastern portion of the Tibetan Plateau. We analyze and discuss a change that occurred in 2010 in the gravity along the eastern margin of the plateau and the relationship between this change and the 2013 Lushan Ms7.0 earthquake. Our results show that： （1） before the Lushan MsT.0 earthquake, gravity anomalies along the eastern margin of the Tibetan Plateau changed drastically. The Lushan earthquake occurred at the bend of the high gradient zone of gravity var- iation along the southern edge of the Longmenshan fault zone. （2） The 2013 Lushan earthquake occurred less than 100 km away from the epicenter of the 2008 Wenchuan earthquake. Lushan and Wenchuan are located at the center of a four- quadrant section with different gravity anomalies, which may suggest that restoration after the Wenchuan earthquake may have played a role in causing the Lushan earthquake. （3） A medium-term prediction based on changes in gravity anoma- lies was made before the Lushan Ms7.0 earthquake, in par- ticular, a prediction of epicenter location.  相似文献   

17.
In order to study the characteristics of crustal deformation around the epicenter before the 2016 MS6.4 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.  相似文献   

18.
汶川8.0级地震前龙门山断裂带能量场变化   总被引：1，自引：0，他引：1  
During the process of preparation and occurrence of a large earthquake,the stress-strain state along the fault zone has close relation with the weak seismicity around the fault zone. The seismic energy release near the fault zone before an earthquake can better reflect the dynamic process of earthquake preparation. Thus,in this paper,the method of natural orthogonal function expansion has been adopted to discuss the time variation about the energy field of the seismic activity along the Longmenshan fault zone before the Wenchuan M_S 8. 0 earthquake,2008. The results show that evident short-term rise changes appeared in the time factors of the typical field corresponding to several key eigenvalues of the energy field along the Longmenshan fault zone before the Wenchuan earthquake,probably being the short-term anomaly message for this earthquake. Through contrastive analysis of earthquake examples such as the 1976 Tangshan earthquake,the authors think that the study of time variation of energy field of seismicity along active fault zone will be helpful for conducting intentional and intensive earthquake monitoring and forecast in active fault regions with high seismic risk based on medium- and long-term earthquake trend judgment.  相似文献   

19.
Based on the waveform data observed by the regional seismic network of Gansu Province,we calculated the apparent stress of 422 earthquakes with M_L≥ 2. 0 occurring in the surrounding area of the Minxian earthquake from January 2010 to July 2014 and obtained the temporal and spatial variation of apparent stress before and after the Minxian earthquake. Results show that( 1) the high value of apparent stress of earthquakes with M_L≥4. 0 was concentrated in the epicenter area before the Minxian earthquake while that of earthquakes with M_L 4. 0 was not;( 2) Apparent stress around the epicenter area showed an obvious increasing process before the Minxian earthquake and the increasing process has continued after the main shock,which means that this study area is still in the danger of strong earthquakes.  相似文献   

20.
Xue Yan 《中国地震研究》2006,20(2):118-126
The characteristics of seismic activity in different time-spatial domain before the Mw9.0 earthquake were studied. The results are as follows ： ① The activity of the deep earthquakes in the north boundary zone of the Australian plate had been evidently strengthened since 1994, showing an increased frequency, magnitude and depth, especially in regards to the heterogeneous distribution of the earthquake depth （namely between 500km and 689km）. Meanwhile the shallow earthquakes of M ≥ 7.0 in the Sumatra island and its vicinity had been obviously strengthened too, and formed a strengthening area with a length of about 1000 km and width 300 km. ②The time distribution of global strong earthquakes with M≥ 7.0 shows that the character of anomalous seismic quiescence-activity one year before the Mw9.0 earthquake and during its active period, the strong earthquakes formed a seismic belt striking in NWW direction. At the same time, there is a seismic gap formed by earthquakes of M ≥ 5.0 in the epicenter and its neighboring region. ③ Two deep earthquakes of M ≥ 7.0 occurred in the west and in the east of the north boundary zone of the Australian plate half year ago. It is notable that one of them occurred in the Sumatra island where no deep earthquake with M ③ 6.0 has occurred in the past thirty years. ④The space distribution of moderate shocks occurring three days ago exhibited a NWW-strike seismic belt along the north boundary zone of the Australian plate. ⑤The activity of volcanoes distributed in the north boundary zone of the Australian plate had been strengthened in the past 4 years, especially several months before the occurrence of the Mw9.0 earthquake.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号