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1.
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   

2.
Based on the waveform data of 5,076 local earthquakes recorded at 25 stations in Xinjiang during the period from 2009 to 2014 and the observation reports provided by the Xinjiang Digital Seismic Network,a data set of 19,140 attenuation factors t*is obtained by fitting the high-frequency attenuation of S-wave spectra with a genetic algorithm. The spatial distribution of Q_S is determined by inverting the t*data with seismic tomography. The results show that the average Q0 in eastern Tianshan is 520,and there is a significant correlation between the Q_S value distribution or attenuation characteristics it disclosed and the surface structure of the study area. The Q_S value is lower in the intersection area of the mountain basin which is located on the north and south sides of the Tianshan Mountains,and the high Q_S distribution is more concentrated inside the Tianshan orogenic belt. The M≥6. 0 earthquakes have been basically located in the Low-Q_S region since 1900. 24 high heat flow points in eastern Tianshan are located at the north and south of Tianshan Mountains where low Q_S exists,indicating a negative correlation. In addition,there is a positive correlation between the velocity structure and the attenuation structure in the study area,which reflects the consistency of the 2-D attenuation structure with the velocity structure and the two-dimensional density structure.  相似文献   

3.
2-D crustal structure and velocity ratio are obtained by processing S-wave data from two wide-angle reflec-tion/refraction profiles in and around Jiashi in northeastern Pamir,with the result of P-wave data taken into con-sideration.The result shows that:1)Average crustal velocity ratio is obviously higher in Tarim block than in West Kunlun Mts.and Tianshan fold zone,which reflects its crustal physical property of “hardness“and stability.The relatively low but normal velocity ratio(Poisson‘s ratio)of the lower crust indicates that the “downward thrusting“ of Tarim basin is the main feature of crustal movement in this area.2)The rock layer in the upper crust of Tian-shan fold zone is relatively“soft“,which makes it prone to rupture and stress energy release.This is the primary tectonic factor for the concentration of small earthquakes in this area.3)Jiashi is located right over the apex or the inflection point of the updoming lower crustal interface C and the crust-mantle boundary,which is the deep struc-tural background for the occurrence of strong earthquakes.The alternate variation of vp/vs near the block bounda-ries and the complicated configuration of the interfaces in the upper and middle part of the upper crust form a par-ticular structural environment for the Jiashi strong earthquake swarm.vp/vs is comparatively high and shear modulus is low at the focal region,which may be the main reason for the low stress drop of the Jiashi strong earthquake swarm.  相似文献   

4.
Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June, 2016, arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5 and MS4.0 earthquakes on February 8, 2016, as well as the epicenter of the Yunlong MS5.0 and Eryuan MS4.6 earthquakes on May 18, 2016 through the waveform cross-correlation technique. The wave velocity ratio of the four stations was calculated using the single-station method. At the same time, the b-value and the focal mechanism consistency parameters of the study area were also calculated. The results show that:(1) the wave velocity ratio of each station experienced a process of decline-recovery-fast rise before the two strong earthquakes, and a significant quasi-synchronous rapid rise occurred within 3-12 days before the earthquake; (2) the timing of the rapid rise of the wave velocity ratio of the four stations before the Yunlong MS5.0 and Eryuan MS4.6 earthquakes were related to the epicentral distance. The station which observed the earliest increase in rapid rise is the farthest one from the epicenter, and the station where the rapid rise appeared in the latest is closest to the epicenter; (3) the form of change of the wave velocity ratio before the earthquake was different between stations located at different directions in the epicenter area; (4) the b-value and the focal mechanism consistency parameter which is commonly used to characterize the stress level both showed a downward trend before the two strong earthquakes, and were consistent with the change in the wave velocity ratio. According to the preliminary analysis, the wave velocity ratio obtained by using airgun source can better reflect the change in the stress state of the underground medium.  相似文献   

5.
An Ms6.8 strong earthquake took place in Jiashi, Xinjiang on February 24 of 2003. The digital wave form data recorded in Kashi and Wushi stations are selected to inverse the moment tensor solutions for the strong earthquake and the moderate and small earthquakes before and after it （ 108 earthquakes in 2001 - 2004）. 67 focal mechanism solutions have been calculated, and the results agree with those from Harvard University and USGS. The analysis reveals that before the strong earthquake, the moderate and small earthquake distribution was dispersed, and after the event the distribution was mainly concentrated around the strong earthquake. Before the strong earthquake, the seismic faults of the mid and small events had the character of strike-slip and normal faulting, and after the event, they exhibit strike-slip and thrust faulting. The region is dominated by near-NS horizontal compression from the southern block after the strong earthquake.  相似文献   

6.
In this paper,the process of dynamic variation of the wave velocity ratio that occurred at a single station,such as Lancang,Tengchong,and Eryuan stations,8 years before the Lancang-Gengma earthquakes(Ms=7.6 and 7.2),is studied by applying the synthetic method as a whole.It is found that the moderately strong and strong earthquakes 250 km away that occurred since 1983 may lead to mutation anomalies of the wave velocity ratio in the Lancang region.The mutation amplitude is increased with the approaching time and distance of a large event.The reliability of mutation data for the wave velocity ratio has been demonstrated in many ways.The application of mutation of the wave velocity ratio to earthquake prediction and its physical explanation are discussed.  相似文献   

7.
Based on the Gauss linear frequency-modulated wavelet transform, a new characteristic index is presented, namely time-frequency energy attenuation factor which can reflect the difference features of waveform in earthquake focus mechanism, wave traveling path and its attenuation characteristics in focal area or near field. In order to test its validity, we select the natural earthquakes and explosion or collapse events whose focus mechanisms vary obviously, and some natural earthquakes located at the same site or in a very small area. The study indicates that the time-frequency energy attenuation factors of the natural earthquakes are obviously different with that of explosion or collapse events, and the change of the time-frequency energy attenuation factors is relatively stable for the earthquakes under the normal seismicity background. Using the above-mentioned method, it is expected to offer a useful criterion for strong earthquake prediction by continuous earthquake observation.  相似文献   

8.
In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. 8 in 2015 and MS5. 0 in 2016 in this area. The results show that:① Before the MS5. 8 earthquake,the seismic stations located near the epicenter in Wuhai,Dongshengmiao,and Shizuishan recorded seismic waves that showed the phenomenon of spectrum shift from high to low frequency.② The low frequency signals recorded by different stations have obvious difference.③ According to the data recorded by the station closest to the epicenter,low-frequency signals were recorded about120 hours before the earthquake and had obvious anomalies. This may reflect slow slip before the earthquake.  相似文献   

9.
Using the digital telemetric seismic waveform data of Chengdu and Kunming, this article studies the focal mechanism solutions and the apparent stress values of a large number of small earthquakes, and then analyzes the dynamic variation of regional stress fields and the spatio-temporal distribution of apparent stress values. The annual variation values of the azimuth of average principal stress field before the May 12, 2008 M_S8.0 Wenchuan earthquake in the Sichuan-Yunnan region were 58° from 2003 to 2004, 85° from 2003 to 2005,61° from 2006 to 2007 and 90° from 2006 to April 2008 respectively. In recent years, deflection or disturbances occurred in the azimuth of the average principal stress field in the Sichuan-Yunnan region. Analysis shows that this may be related to the change of stress field states of crustal blocks before and after the December 26, 2004 M_S9.0 Sumatra earthquake and the 2008 M_S8.0 Wenchuan earthquake. The ratio of thrust-type earthquakes in the Sichuan-Qinghai block was on the higher side in the period from 2006 to 2007, and the source faulting type of the regional moderate and small earthquakes had changed before the M_S8.0 Wenchuan earthquake. The change of state of the stress field is consistent with the changes in block displacement fields revealed by GPS data and the crustal shortening velocity vertical to the Longmenshan fault zone. Based on the radiation energy calculated from all bands of the seismic waveform, the value of apparent stress σ_app is obtained. The fluctuation shape of the fitting trend of the apparent stress is related to the intensity of regional seismicity. It reveals that the micro-dynamic fluctuation process of the regional stress value is similar to the azimuth transition of the regional principal compressive stress field, which can be used to probe for pregnant physical processes. Areas with a higher value of apparent stress σ_app are possible areas of potential seismic risk. It can be seen from the spatial distribution of the medium and short-term apparent stress σ_app before the M_S8.0 Wenchuan earthquake, the Longmenshan fault zone is in a low stress distribution area, and the relatively high apparent stress is in the peripheral area. These images may show medium and short-term locking phenomena near the seismogenic tectonics of the M_S8.0 Wenchuan earthquake. For example, changes with time of the focal parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces, continual increase of thrust-type earthquakes in the Sichuan-Qinghai block and the appearance of spatial distribution areas of high apparent σ_app stress. The work on this aspect was continued after the M_S8.0 Wenchuan earthquake, and the results seem to be shown a clearer relationship between these phenomena and future great earthquakes.  相似文献   

10.
The earth resistivity and geomagnetic observation data of the Z component from many stations in near-epicentral areas of strong earthquakes are combined and calculated by using a spatial linearity method and a new characteristic value, the spatial linearity a, describing the precursory field in near-epicentral area of strong earthquake, is obtained. The analysis and calculation results of geoelectric and geomagnetic observation data prior to 8 earthquakes with M≥5.5 occurring in the North China region show that a value near the epicentral area tendsto decrease significantly half a year before strong earthquakes.  相似文献   

11.
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12.
2013年2月6-8日圣克鲁斯群岛发生6次强震,琼中地震台的重力仪记录都有同震响应出现。本文从重力仪记录的面波的延迟时间、最大变形幅度、同震持续时间3个方面研究了6次强震的同震响应特征。  相似文献   

13.
The determination of the coefficient of viscosity of eruptive products gives useful elements to the knowledge of possible variations of composition and physical conditions of the magmas.  相似文献   

14.
As is known, the secular deceleration of the Earth's diurnal rotation is explained mainly by the tidal friction in the ocean. Below we consider this mechanism in some detail, taking into account also elastic deformations of the mantle under the action of ocean loading and the interaction between the tide-generating body, ocean tidal wave, liquid outer core, and solid inner core. It is shown that elastic displacements of the core-mantle boundary under the action of ocean loading are of about the same amplitude and phase as the elastic loading displacements of the Earth's outer surface. As a result, side by side with the mechanism of secular deceleration of diurnal rotation of the mantle, there are also (1) the opposite mechanism of secular acceleration of diurnal rotation of the outer liquid core and of the solid inner core and (2) the mechanism of excitation of differential rotation in the liquid core. Taking these effects into account, we compare theoretical and modern observed data on the eastward drift of the solid inner core. It is shown that the best agreement may be obtained if the turbulent viscosity of the liquid core is about 2 × 10 3 Poise  相似文献   

15.
The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth.  相似文献   

16.
Studia Geophysica et Geodaetica -  相似文献   

17.
地震激励下处于深水中的桥墩和周围水体的相互作用将对桥梁结构的动力响应产生较大影响。首先对地震作用下水-桥墩的相互作用理论做了概括,给出了动水压力对桥墩的作用效应及各自的适用范围;对主要的三种考虑流固耦合效应的分析方法做了对比,探讨了地震作用下影响水-结构相互作用的主要因素,并对今后的研究提出了建议。  相似文献   

18.
Geomagnetism and Aeronomy - The magnetic evolution of the active region of the Sun at the level of the photosphere has been studied. Magnetic synoptic maps of the 2007 Kitt Peak Observatory were...  相似文献   

19.
Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary.  相似文献   

20.
The geodynamic interpretation of the results of GPS observations among the permanently operating stations which establish the frame for defining and conserving the coordinate system and simultaneously for describing the fundamental tendencies of dynamics in the area represented by them, should be deprived of the effects of geodynamic phenomena, which can be either periodic or short-term (even non-periodic) so that secular changes may be found. Some of these influences are included in scientific processing software, others have to be modelled later. The purpose of this project is to determine the influences of the indirect effect of ocean tides and the direct deformational effect of the atmosphere on the results of GPS observations, performed at stations Pecný (Czech Republic), Wettzell (FRG) and Graz (Austria), and also for the GPS stations of the Central Europe Regional Geodynamic Project (CERGOP) in the region of Central and East Europe. On the basis of analyses and results it is possible to claim that at the present accuracy of GPS observations the influence of ocean loading and atmospheric pressure effects for geodynamic campaigns in the region of the Czech Republic is negligible. For campaigns in larger regions (i.e. Central Europe) atmospheric corrections will have to be applied to height differences. These corrections, however, due to their periodicity have negligible influence on secular changes.  相似文献   

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