Earthquake Activity Features Before Earthquakes with Ms ≥ 7.0 in the Central-Northern QinghaiXizang (Tibet) Block

We have studied the seismicity features of M_S≥5.0 earthquakes two years before strong earthquakes with M_S≥7.0 occurred in the central-northern Qinghai-Xizang (Tibet) block since 1920. The results have showed that there is an obvious gap or quiescence of M_S5.0～6.9 earthquakes near epicenters. We have also studied statistical seismicity parameters of M_S5.0～6.9 earthquakes in the same region since 1950. The results have showed that earthquakes with M_S≥7.0 occurred when earthquake frequency is relatively high and earthquake time, space accumulation degrees are rising. And the prediction effect R value scores are between 0.4～0.7. We have concluded that, before earthquakes with M_S≥7.0 in the central-northern Qinghai-Xizang (Tibet) block, M_S5.0～6.0 earthquake activity in the whole area increased and accumulated in time and space, but earthquakes with M_S≥7.0 occurred where M_S5.0～6.0 earthquake activity was relatively quiet.     

Earthquake Activity Features Before Earthquakes with Ms ≥ 7.0 in the Central-Northern QinghaiXizang（Tibet） Block

INTRODUCTION Theseismicquiescencebeforelargeearthquakesisoneoftheprecursorsthatattractstheattention ofseismologistsworldwide.Mogi(1969)investigatedthisphenomenonfirst.Ohtake(1981),Wyss(1988)andSongJungao,etal.(1994)proceededwithstudiesinthisarea.Inthispap…     

Application of the Load/Unload Response Ratio Theory to Predictions of Moderate Earthquakes (7.0>M≥6.0)

The variation in load/unload response ratio before some moderate earthquakes is analyzed based on the theory of the load/unload response ratio.The results show that the load-unload response ratio increases noticeably before moderate earthquakes,and there are three kinds of patterns in which the load/unload response ratio varies and the duration of noticeable increase in load/unload response ratio ranges from half a year to two years.     

Characteristics of Strain Release before Large Earthquakes of M≥7. 0 in the Chinese Mainland

The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3～6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. \"decelerating in-accelerating out seismic strain model\".     

Study on the Relationship Between Recent Crustal Deformation and the Temporal-Spatial Distribution of Strong Earthquakes ( Ms ≥6.0) in the Sichuan-Yunnan Region

Analysis of deformation data measured across the faults, regional vertical deformation data and GPS measurements in the Sichuan-Yunnan region made since the 1980s permitted us to conclude that the crustal deformation in the region during this period of time was relatively weak and caused the occurrence of earthquakes (Ms≥6.0), which were not distributed along the major boundary active faults in the region after the 1981 I)awu Ms 6.9 earthquake and that the seismic activity is characterized by quasi-clockwise migration. Thus, it follows that earthquake prediction research should be focused on the central part of the Sichuan-Yunnan region in the coming years. Finally, a concept of temporal division of the region into active blocks is suggested and the preliminary result of the division is given in the paper.     

The Relationship Between Strong Earthquake Activity of Ms≥ 7.0 on the Chinese Mainland and the West Kunlun-A＇nye^maqe^n Secondary Arcuate Tectonic Zone

The active and quiet phenomenon of moderate strong earthquakes one year before the earthquakes with Ms ≥ 7.0, the spatial distribution characteristics of the solid tide modulating and triggering earthquakes and the strong earthquake mechanisms on the Chinese continent have been studied. The secondary arcuate tectonic zone composed of the west Kunlun-A‘nye^maqe^n faults is believed to be a very important boundary to characterize strong earthquake activity of Ms ≥ 7.0 on the Chinese continent, that is, a boundary between the seismically active region and the quiet region of moderately strong earthquakes one year before earthquakes with Ms ≥ 7.0, and a boundary of the spatial distributions between the solid tidemodulating strong earthquakes ( Ms ≥ 7.0) and the non-modulating ones. It might be related with the characteristics of spatial distribution of focal mechanism solutions of strong earthquakes on the Chinese Continent.     

The Relationship Between Strong Earthquake Activity of Ms ≥ 7.0 on the Chinese Mainland and the West Kunlun- A'nyêmaqên Secondary Arcuate Tectonic Zone

The active and quiet phenomenon of moderate strong earthquakes one year before the earthquakes with M S≥7.0, the spatial distribution characteristics of the solid tide modulating and triggering earthquakes and the strong earthquake mechanisms on the Chinese continent have been studied. The secondary arcuate tectonic zone composed of the west Kunlun-Anyêmaqên faults is believed to be a very important boundary to characterize strong earthquake activity of M S≥7.0 on the Chinese continent, that is, a boundary between the seismically active region and the quiet region of moderately strong earthquakes one year before earthquakes with M S≥7.0, and a boundary of the spatial distributions between the solid tide modulating strong earthquakes (M S≥7.0) and the non-modulating ones. It might be related with the characteristics of spatial distribution of focal mechanism solutions of strong earthquakes on the Chinese Continent.     

Relocation of the Ms≥2.0 Earthquakes in the Northern Tianshan Region, Xinjiang, Using the Double-Difference Earthquake Relocation Algorithm

We applied the double-difference earthquake relocation algorithm to 1348 earthquakes with M_S≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these M_S≥2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5≤M_S<2.0. Finally, we obtained the relocation results for 1253 earthquakes with M_S≥2.0, which account for 93% of all the 1348 earthquakes with M_S≥2.0 and includes all the M_S≥3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0≤M_S<3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N-S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 km, with 94% being from 5km to 35 km, 68.2% from 10 km to 25 km. The average hypocenter depth is 19 km.     

Relocation of the Ms≥2.0 Earthquakes in the Northern Tianshan Region, Xinjiang, Using the Double-Difference Earthquake Relocation Algorithm

We applied the double-difference earthquake relocation algorithm to 1348 earthquakes with M_S≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these M_S≥2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5≤M_S<2.0. Finally, we obtained the relocation results for 1253 earthquakes with M_S≥2.0, which account for 93% of all the 1348 earthquakes with M_S≥2.0 and includes all the M_S≥3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0≤M_S<3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N-S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 km, with 94% being from 5km to 35 km, 68.2% from 10 km to 25 km. The average hypocenter depth is 19 km.     

The Relationship Between Strong Earthquake Activity of M_S≥7.0 on the Chinese Mainland and the West Kunlun-A'nyêmaqên Secondary Arcuate Tectonic Zone

1 THESPATIALDISTRIBUTIONCHARACTERISTICSOFMODERATE STRONGEARTHQUAKESBEFORESTRONGEARTHQUAKESWITHMS≥ 7 0　　From 1 90 0to 2 0 0 2 ,6 5largeearthquakeswithMS≥ 7 0tookplaceontheChineseContinent,ofwhich 1 0weretwin quakesorstrongaftershocks.55earthquakecaseshavebeenstudiedinthispaper.ThecharacteristicsofmoderatelystrongearthquakeactivitybeforestrongearthquakeswithMS≥ 7 0wereanalyzed ,andthenotablecharacteristicswerefoundtobetheactiveandquietphenomenaayeefore…     

Deterministic Variability of the Ionosphere on the Eve of Strong (M ≥ 6) Earthquakes in the Regions of Greece and Italy According to Long-Term Measurements Data

Geomagnetism and Aeronomy - Abstract—Specific features of the variation in the electron concentration in the ionosphere in front of strong (M ≥ 6) earthquakes in the most seismically...     

Characteristics of Geoelectric and Geomagnetic Data before Strong Earthquakes in the North China Region

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.     

Spatiotemporal characteristics and trend assessment of Ms ≥ 5.6 earthquakes in the Tianshan area of China based on co-occurrence analysis and commensurability

Based on the complete seismic data of the Tianshan area in the past 118 years,the co-occurrence rate of earthquakes in different fault zones is calculated,the f...     

The Statistical Analysis of Migration of Strong Earthquakes─Taking the North China Region as an Example

INTRODUCTIONMigrationofstrongearthquakesisaphenomenonwherebystrongearthquakestakeplaceinsuccessionincertainspatiallyregularpatterns (ZhangGuomin ,etal,2 0 0 1 ) .Seismologistsintheworldhavenoticedthisphenomenonforalongtime .Manyinstanceswerediscoveredinthepastdecades ,suchasthemigrationofstrongearthquakesalongtheNorthAnatolianFaultinTurkeysince1 939(Richter,1 958)andthemigrationofaseriesofearthquakes (MS ≥ 6 0 )aftertheMS7 9earthquakeinKwandong ,Japan (Utsu ,1 987) .Theexamplesofre…     

Brief Introduction to the Catalogue of Recent Chinese Earthquakes (1912～1990, M_S≥4.7)

This paper briefly introduces the principles and methods for compiling the Catalog of Recent Chinese Earthquakes (1912 ～ 1990, MS≥4.7). This new catalog is compiled by revising and supplementing the 1983 version of the Catalog of Chinese Earthquakes.     

Annual Consultation on the Likelihood of Earthquakes in Continental China： Its Scientific and Practical Merits

Since the 1970s, Chinese seismologists have started to conduct the Annual Consultation on the Likelihood of Coming Earthquakes in the Next Year. This approach has unique scientific and practical merits either as an active response to the social needs in the situation that earthquake prediction research meets many difficulties, or as a real forward prediction test persistently conducted for 1/3 century. It is a pity that such an approach has not been well-known by international seismological community, and the scientific merits of such an endeavor is sometimes regrettably underestimated.     

Deep structural characteristics and seismogenesis of the M≥8.0 earthquakes in North China

Introduction North China is a seismically active area in the eastern part of China, where four M8.0 earthquakes have been recorded in the historical documents and confirmed by the researchers. The first is the M=8.0 earthquake occurred in A.D. 1303 in Hongtong, Shanxi Province. It was the ear-liest M=8.0 earthquake recorded in the historical document in China. The second is the M=8.0 earthquake occurred in A.D. 1556 in Huaxian County, Shaanxi Province. The other two are the M=8.5 earth…     

On the Large Scale Spatial Heterogeneity of Great Shallow Earthquakes and Plate Coupling Mechanism in Chinese Mainland and Its Adjacent Areas

Research on the large scale spatial heterogeneity of great intraplate shallow earthquakes on the Chinese mainland and adjacent areas discussed in this paper shows that(1)there are four main high seismicity areas:the North China seismic area in the eastern part of China(30°-42°N),the Southeastern Coast seismic area in the eastern part of China(19°-25°N),the North-South seismic area in the western part of China and its adjacent areas(Burma-China-Mongolia),and the Central Asian seismic area in the western part of China and its adjacent areas(Pamir-Tianshan Mountains-Baikal);(2)the four intraplate seismic areas that are approximately perpendicular to those sections of the Eurasia plate boundary that surrounds the Chinese mainland and its adjacent areas,where the Eurasia plate has a strong seismic coupling with the North America-Pacific Ocean-Philippine Sea plate and the India plate; and(3)the large scale spatial heterogeneity of intraplate seismicity in China and its adjacent areas that might be control     

Seismic Spatial Distribution Factor ZK and the Features of Its Variation around Moderately Strong Earthquakes

This paper has introduced the spatial distance method to analyze the distribution features of earthquakes quantitatively.The seismic distribution factor ZK defined in this paper can be used to identify the type of seismic spatial distribution better.The spatial distribution of earthquakes features a clustered pattern when the Zg-value approaches to 1; it is stochastic when ZK fluctuates around 0.5; and it may have a network pattern when ZK approaches to 0.From the angle of seismic spatial distribution,the change of the Rvalue reflects to some extent the dynamic variation of the degree of order and complexity of the seismogenic system.Taking 10 earthquakes of Ms≥5.8 in North China since 1970 as an example,the paper has discussed the variation features of ZK around moderately strong earthquakes.Results show that high Rvalue anomalies can generally be detected before moderately strong events.The Zk value of 0.642 can be taken as a criterion for identifying anomalies.Before the 2 strong earthquakes of Ms≥