Seismicity anomalies before the great earthquake of M_S=8.1 in the Kunlun Pass and its significance to earthquake prediction

Introduction The MS=8.1 earthquake occurred in west of the Kunlun Pass on November 14, 2001. It is the greatest earthquake occurred in China since the last half of the century and is an important event in recent seismic history of China. Some specialists consider that the earthquake occurred in the area where the earthquake monitoring capability is lowest in Chinese mainland; no striking precursory seismicity was found. The study on the precursory seismicity before the earthquake has not b…     

Horizontal crustal movement in Chinese mainland before and after the great Kunlun Mountain M=8.1 earthquake in 2001

Introduction The great Kunlun Mountain earthquake occurred on November 14, 2001 on the border be-tween Xinjiang and Qinghai in west China (36.2N, 90.9E). It was the largest earthquake oc-curred in Chinese mainland in the last 50 years. The Crustal Movement Observation Network of China (CMONOC) established in 1998 mainly for the purpose of earthquake prediction with only 25 fiducial stations for continuous GPS observations, has recorded the precious information of the crustal movement …     

Multi—scale expression of spatial activity anomalies of earthquakes and its indicative significance on the space and time attributes of strong earthquakes

The noise model based on a trous wavelet algorithm produces a multi-scale expression of image through the combination of wavelet transform and a testing model of statistical significance.This kind of expression not only gives the formation and location of image structure on different scales,but also eliminates the influence of noise Since the algorithm does not need any priori hypotheses,it is suitable for the data with complex structure.The research line is employed in this paper to analyze the spatial activity of earthquake.The method of how to recognize and describe the multi-scale space activity of earthquake is emphatically discussed in this paper.Taking typical sequences in Southwest China as research cases,we systematically study the structure characters of spatial activity of earthquake on different scales.Results show that multi-scale space structure to some extent possesses indicative effect on strong epicenters.And the foreshock anomalies of Songpan seismic sequence also reveal interesting pattem during the spatial-temporal evolvement.     

Discussion on the feature of strong earthquake: Orderly distribution in time, space and intensity before the Western Kunlun Mountain Pass M=8.1 earthquake

Introduction The Western Kunlun Mountain Pass M=8.1 earthquake occurred on November 14, 2001 is the other M=8 earthquake occurred 50 years after Dangxiong, Tibet M=8.0 earthquake in Chinese mainland. The earthquake has caused the attention of the seismologists in the following aspects: 1) The fracture length is more than 400 km, which is far away from the estimated length by the statistic empirical function between the magnitude and the fracture length (WANG, et al, 2002); 2) The aftersh…     

Correlated Features of Horizontal Movement-Deformation on the North and East Margins of the Qinghai-Xizang Block before the Kunlun Earthquake with Ms=8.1

INTRODUCTIONThe Qinghai_Xizang(Tibet)blockis praised as a“piston”in the earth dynamics systemof theChinese mainland,andis regarded asthe hotspot in geoscience study all along.The occurrence of theMS8·1strong earthquake on November14,2001,inside the Qin…     

Damage of 1975 Haicheng Ms7.3 earthquake in the Korean Peninsula and its effect on Kyushu, Japan

The 1975 Haicheng MS7.3 earthquake affected whole Korean Peninsula and even Kyushu,Japan.In this paperisoseismal map of this earthquake was drawn for these areas by sorting out and analyzing data systematically col-lected,furthermore,the characteristics of the earthquake damage were discussed.In the northern Korean Peninsula,the intensity is V in great majority of this area except local area with intensity VI,and the damage is basically inaccordance with typical characteristics of corresponding intensity grade.In the southern Korean Peninsula,theintensity is IV in large part of the area,however,in some big cities such as Seoul etc.,not only high buildingsshook strongly,but also some people appeared perceptions such as feeling dizzy and so on,and electrical servicewas interrupted on one or two districts because of transformer tripping.These phenomena could be caused by theeffect of long-period wave generated from a large earthquake on far-field.     

Estimation of the stress levels in the focal region before and after the 2001 M=8.1 Western Kunlun Mountain Pass earth-quake

Introduction A great earthquake of M=8.1 occurred at 17h26min14.7s (Beijing time) on November 14, 2001 on the eastern Kunlun fault, near Bukadaban mountain peak with an elevation of about 6 866 m in the Qinghai-Xizang (Tibetan) Plateau of western China. The micro-epicenter is at a site of 36.2°N, 90.9°E, and the macro-epicenter is at a site of 35.6°N, 94.1° E, about 300 km west to the Kunlun Mountain Pass.This event is the largest one since 1951 in China, and yet the first su-per-st…     

A discussion on Corioli force effect and aflershock activity tendency of the M=8.1 Kunlun Mountain Pass earthquake on Nov.14, 2001

Following the theory and definition of the Corioli force in physics, the Corioli force at the site of the M=8.1 Kunlun Mountain Pass earthquake on November 14, 2001, is examined in this paper on the basis of a statistical research on relationship between the Corioli force effect and the maximum attershock magnitude of 20 earth-quakes with M≥7.5 in Chinese mainland, and then the variation tendency of attershock activity of the M=8.1 earthquake is discussed. The result shows: a) Analyzing the Corioli force effect is an effective method to predict maximum attershock magnitude of large earthquakes in Chinese mainland. For the sinistral slip fault and the reverse fault with its hanging wall moving toward the right side oftbe cross-focus meridian plane, their Corioli force pulls the two fault walls apart, decreasing frictional resistance on fault plane during the fault movement and releasing elastic energy of the mainshock fully, so the maximum magnitude of aftershocks would be low. For the dextral slip fault, its Corioli force presses the two walls against each other and increases the frictional resistance on fault plane, prohibiting energy release of the mainshock, so the maximum magnitude of attershocks would be high.b) The fault of the M--8. l Kunlun Mountain earthquake on Nov. 14, 2001 is essentially a sinistral strike-slip fault,and the Corioli force pulled the two fault walls apart. Magnitude of the induced stress is about 0.06 MPa. Alter a comparison analysis, we suggest that the attershock activity level will not be high in the late period of this earth-quake sequence, and the maximum magnitude of the whole aftershocks sequence is estimated to be about 6.0.     

Gravity variation before Kunlun mountain pass western Ms=8.1 earthquake

The relation between the gravity variation features and Ms=8.1 earthquake in Qinghai-Xizang monitoring area is analyzed preliminarily,by using spatial dynamic variation results of regional gravity field from absolute gravity and relative gravity observation in 1998 and 2000.The results show that:1)Ms\8.1 earthquake in Kulun mountain pass westem occurred in the gravity variation high gradient near gravity‘s high negative variation;2)The Main tectonic deformation and emnergy accumulation before MS=8.1 earthquake are distributed at south side of the epicenter;3)The range of gravity‘s high negative variation at east of the MS=8.1 earthquake epicenter relatively coincides with that rupture region according to field geology investigation;4)Gravity variation distribution in high negative value region is just consistent with the second shear strain‘s high value region of strain field obtained from GPS observation.     

Source process of the 14 November 2001 western Kunlun Mountain M S=8.1 earthquake

Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain M _S=8.1 (M _W=7.8) earthquake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The second stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position. Foundation item: Joint Seismological Science Foundation of China (103066) and Foundation of the Seismic Pattern and Digital Seismic Data Application Research Office of Institute of Earthquake Science of the China Earthquake Administration.     

Preliminary analysis on characteristics of coseismic deformation associated with M S=8.1 western Kunlunshan Pass earthquake in 2001

Based on the analysis of coseismic deformation in the macroscopic epicentral region extracted by Differential Interferometric Synthetic Aperture Radar (D-InSAR), and combined with the seismic activity, focal mechanism solutions of the earthquake and field investigation, the characteristic of coseismic deformation of M _S=8.1 western Kunlunshan Pass earthquake in 2001 was researched. The study shows that its epicenter lies in the northeast side of Hoh Sai Hu; and the seismogenic fault in the macroscopic epicentral region can be divided into two central deformation fields: the west and east segments with the lengths of 42 km and 48 km, respectively. The whole fault extends about 90 km. From the distribution of interferometry fringes, the characteristic of sinistral strike slip of seismogenic fault can be identified clearly. The deformations on both sides of the fault are different with an obviously higher value on the south side. In the vicinity of macroscopic epicenter, the maximum displacement in look direction is about 288.4 cm and the minimum is 224.0 cm; the maximum sinistral horizontal dislocation of seismogenic fault near the macroscopic epicenter is 738.1 cm and the minimum is 551.8 cm. Foundation item: National Natural Science Foundation of China (40374013) and “Researching on the Disaster Earthquake” (2003) of Public Welfare Research Item, Ministry of Science and Technology of China.     

Horizontal crustal movement in Chinese mainland before and after the great Kunlun Mountain M =8.1 earthquake in 2001

The continuous GPS observation at the fiducial stations in the Crustal Movement Observation Network of China (CMONOC) recorded the crustal movement of Chinese mainland before and after the great Kunlun Mountain earthquake of M=8.1 on November 14, 2001, especially the horizontal crustal movement in the western part of China. Based on the datum defined by a group of stable stations with small mutual horizontal displacements for a few years, the time series of horizontal displacements at fiducial stations were obtained. Significant anomalous horizontal displacements had appeared at the fiducial stations in the western part of China since early November 2000 and several earthquakes with the magnitudes about 6.0 had occurred in Yunnan and Sichuan Provinces. The northward components of the horizontal displacement at the fiducial stations in west China had decreased significantly and even changed in the opposite sense since mid April 2001. After the earthquake, the northward displacements still decreased and there were significant westward displacements. The process of the crustal movement in the western part of Chinese mainland (in reference to east China) suggests that the main force source for this earthquake came from the northward pushing of the Indian plate. The great earthquake released a large amount of energy, as a result, the action applied by the Indian plate to Chinese mainland diminished significantly and after the great earthquake, the seismic activity in Chinese mainland decreased considerably until the end of 2002. Foundation item: The National Development and Programming Project for Key Basic Research (95-13-03-07).     

Study on rupture zone of the M =8.1 Kunlun Mountain earthquake using fault-zone trapped waves

The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface. Foundation item: Joint Earthquake Science Foundation of China (201001). Contribution No. RCEG200305, Research Center of Exploration Geophysics, China Earthquake Administration.     

Estimation of the stress levels in the focal region before and after the 2001 M =8.1 Western Kunlun Mountain Pass earthquake

A method estimating the stress level in the focal region of an earthquake is proposed here. Taking the 2001 M=8.1 Western Kunlun Mountain Pass earthquake as an example, we estimate its stress level in the focal region before and after it by this method. The results show that the stress level in the focal region just prior to the initiation of this event is approximately 6.3–8 MPa, and about 5–6.7 MPa remained in the focal region after its occurrence. The stress in the focal region decreased by roughly twenty percent after this event. Contribution No. 05FE3026, Institute of Geophysics, China Earthquake Administration.     

2001年昆仑山口西8.1级大震预报的再讨论

由立交模式、静中动判据和高山峰指标讨论了2001年昆仑山口西8．1级大震的地点骤报。由74年周期性、三性法和倍九律讨论了这个8．1级大震的时间预报。倍九律包括热红外异常、6级地震活动和K＝8的大磁暴在震前出现的倍九天时间特征。