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Current tectonic deformation and seismogenic characteristics along the northeast margin of Qinghai -Xizang block

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Acta Seismologica Sinica(English Edition) 2002年第1期15卷 29-38页

作者：王双绪江在森张希陈文胜 second crustal deformation monitoring center China Seismologica Bureau Xi’an China

Based on the data from repeated precise leveling and across-fault deformation measurements carried out in recent 30 years and the analyzed results from GPS observations made in recent years along the northeastern margin of Qinghai-Xizang block, and combined with the geological structures and seismic activities, some characteristics in regional tectonic deformation and strong earthquake development are studied and approached preliminarily. The results show that: a) The space-time distribution of current tectonic deformation in this area is inhomogeneous with relatively intensive tectonic deformation in the vicinity of main boundary faults and weak deformation in the farther areas. The intensity of vertical differential movement and the deformation status vary with time, and the horizontal movement and deformation are characterized by apparent compression and strike-slip. b) The tectonic stress field generated by the NE-trending continuous compressive movement of Qinghai-Xizang block due to the northward press and collision of India plate is the principal stress for the tectonic deformation and earthquake development in this area. The evolution of space-time distribution of tectonic deformation and seismicity is closely related to the block activity and dynamic evolution of regional tectonic stress field. c) The vertical deformation uplift and high-gradient deformation zones and the obvious fault deformation anomaly appeared along the boundaries of tectonic blocks can be considered as the indicators of hindered block motion and intensified tectonic stress field for strong earthquake development. Usually, the above-mentioned phenomena would be followed by the seismicity of M6.0, but the earthquake might not occur in the place with the maximum movement. The zones with the fault deformation anomaly characterized by tendencious accumulation acceleration turning and the surrounding areas might be the positions for accumulation of strain energy and development and occurre

关键词： northeast margin of Qinghai-Xizang block vertical crustal deformation horizontal movement and deformation fault deformation anomaly seismogenic characteristics

Dislocation parameters of Gonghe earthquake jointly inferred by using genetic algorithms and least squares method

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Acta Seismologica Sinica(English Edition) 1999年第3期12卷 314-320页

作者：王文萍王庆良 The second crustal deformation monitoring center China Seismological Bureau Xi’an China

The second crustal deformation monitoring center, China Seismological Bureau, has detected a marked uplift associated with the Gonghe Ms=7.0 earthquake on April 26, 1990, Qinghai Province. From the observed vertical deformations and using a rectangular uniform slip model in a homogeneous elastic half space, we first employ genetic algorithms (GA) to infer the approximate global optimal solution, and further use least squares method to get more accurate global optimal solution by taking the approximate solution of GA as the initial parameters of least squares. The inversion results show that the causative fault of Gonghe Ms=7.0 earthquake is a right-lateral reverse fault with strike NW60°, dip SW and dip angle 37°, the coseismic fracture length, width and slip are 37 km, 6 km and 2.7 m respectively. Combination of GA and least squares algorithms is an effective joint inversion method, which could not only escape from local optimum of least squares, but also solve the slow convergence problem of GA after reaching adjacency of global optimal solution.

关键词： genetic algorithms least squares method Gonghe earthquake dislocation model

deformation datum in source mechanism inversion

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Acta Seismologica Sinica(English Edition) 1996年第2期9卷 299-308页

作者：巩守文王庆良祝意青陈兵 second crustal deformation monitoring center State Seismological Bureau Xi’an China

Based on the analyses of geodetic deformation datum, the concepts of real datum and relative datum of displacements associated with an earthquake are put foward. Introducting a deformation datum parameter into model parameter vector can enable the reference station to be set in the epicentral areas. Two improved inversionmethods, the deformation datum parameter (DDP) method and deformation difference (DD) method, are advanced in this paper. They are further applied to dislocation model inversion of the 1990 Gonghe Ms7.0 earthquake. The inversion results inferred by using the two methods are well consistent with each other, which basically reflect the source geometry and the slip of the causative fault.

关键词： deformation datum focal mechanism inversion levelling survey route, Gonghe earthquake.

Fault deformation anomaly and intermedi-ate and short-term prediction of the Jingtai Ms=5.9 earthquake

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Acta Seismologica Sinica(English Edition) 2001年第2期14卷 156-165页

作者： WANG Shuang-xu The second crustal deformation monitoring center China Seismological Bureau Xi’an China

The time-space distribution characteristics of fault deformation anomaly in the near-source region and its outlying zone in the seismogenic process of the Jingtai Ms=5.9 earthquake occurred on June 6, 2000 in Gansu Province is studied preliminary. The distribution scope of fault deformation anomaly before the earthquake is wide, the anomaly shape is complicated and the pattern anomalous zone of fault deformation (strain) information index is obvious. The shape and amplitude of fault deformation anomaly in different regions differ significantly, which is closely related with the tectonic location of anomaly. The fault deformation anomaly of α β, and γ phases along the western segment of Haiyuan fault zone shows the process from the quasi-linearity to non-linearity of fault movement in the near-source region, matches the high-value anomalous area of fault deformation (strain) information index, and reflects the high strain accumulation in the seismogenic region. However, the anomaly of abrupt jump and cusp with a large amplitude occurred in the areas far from the earthquake, such as Liupanshan fault zone which is the tectonic convergent section does not reflect the strain accumulation of its location, maybe it is a sign that the regional tectonic stress field is strengthened in the seismogenic process. Based on the above-mentioned facts and combined with the preliminary summary of experiences and lessons in the intermediate and short-term prediction of the Jingtai Ms=5.9 earthquake, we study and explore the application of fault deformation anomaly to earthquake judgment.

关键词： Anomaly characteristics Fault deformation Intermediate and short-term earthquake prediction Jingtai Ms=5.9 earthquake

Study on scale dependence of strain value obtained from crustal deformation data

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Acta Seismologica Sinica(English Edition) 2000年第4期13卷 375-383页

作者：江在森张希陈文胜王双绪 second crustal deformation monitoring center China Seismological Bureau Xi’an China

Using statistic analysis, the scale dependence of crustal stain value from crustal deformation data is studied. We found that there exists obvious correlation between strain value and computational figure scale. Along with increasing of figure element scale, the statistic mean value and mean square deviation of strain present power law attenuation. Based on this analysis, the necessity of strain value scale normalization is suggested for calculating strain field using crustal deformation data and the normalization method is proposed in this paper.

关键词： crustal deformation scale relativity normalization

Characteristics of crustal strain associated with M=6.4 Baotou earthquake in 1996

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Acta Seismologica Sinica(English Edition) 2002年第4期15卷 363-373页

作者：郭良迁薄万举胡新康王敏 First crustal deformation monitoring center China Seismological Bureau Tianjin China

Based on the horizontal crustal strain derived from GPS data and the rate accumulation intensity calculated from across-fault vertical deformation, the strain characteristics in the periods of 1992~1995, 1995~1996 and 1996~1999 in Baotou-Datong area is studied in the paper. From the comparison between the crustal strains before and after the M=6.4 Baotou earthquake occurred on May 3, 1996, it is considered that the high-magnitude area with predominant compressive strain might be the seismogenic zone for a coming strong earthquake. The area with the simultaneous higher surface strain, principal compressive strain, shear strain and tendency accumulation might be the place with higher risk of strong earthquakes. Generally, the area with low strain and predominant tensile strain might have a small possibility for strong earthquake development, which belongs to a stable area. The evolution of horizontal strain obtained from GPS measurements carried out in Baotou-Datong area in the period of 1992~1999 reflects the total developing and ending processes of the seismic episode from 1996 to 1998. The area with high and predominant compressive strain and the strain gradient zone can be considered as one of the indicators for determining the strong earthquake risk area in the future.

关键词： crustal deformation Baotou earthquake GPS measurement

Recent crustal horizontal movement in the Chinese mainland

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Acta Seismologica Sinica(English Edition) 2000年第3期13卷 273-279页

作者：黄立人王敏 First crustal deformation monitoring center China Seismological Bureau Tianjin China

According to the results of careful re-proeessing of data obtained from two GPS survey campaigns of crustal movement monitoring network in Chinese mainland carried out in 1994 and 1996, the crustal horizontal movement characteristics in Chinesc mainland are studied in the *** the analysis, a relatively consummate deformation model in which the deformation is described by the relative movement between the tectonic blocks with interior strain and the corresponding analysis method are used. The magnitude of movement along the boundary zones between the tectonic blocks is calculated. And the characters and intensities between the main boundny zones are compared.

关键词： GPS survey crustal horizontal movement tectonic block Chinese mainland

Study　on　the　pattern　and　mode　of　vertical　crustal　deformation　during　the　seismogenic　process　of　intraplate　strong　earthquakes

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Acta Seismologica Sinica(English Edition) 1995年第2期8卷 195-204页

作者：杨国华桂昆长巩曰沐杨春花韩月萍孙东平 First crustal deformation monitoring center State Seismological Bureau Tianjin China

In this paper,the data of vertical crustal deformations associated with the Xingtai,Haicheng,Tangshan and Datong strong earthquakes in North China Block have been processed,analyzed and *** result shows that the seismogenic processes of strong earthquakes are accompanied by an evolution of crustal deformation as follows: ① The area of crustal deformation anomaly should be large in radius and extensive in range. ② There are both the 'field' and 'source' of crustal deformation anomaly,with the 'source' existing inside the'field' but differing from the 'field' distinctly. ③ The evolution process includes a number of ***, movements in the 'field region transform from the normal state to an anomalous state to start the formation of field ***,movements in the 'source' region become outstandingly remarkable. Thirdly,anomalies in the 'field' region that surrounds the 'source' become increasingly ***,the 'source' region enters a state of ***,an earthquake occurs. ④ There are usually one or more areas where the anomaly field forms a special pattern,mostly a four-quadrant *** area which is'activated' first but becomes 'immobilized' afterwards often coincides with the source area.⑤ The appearance of an obviously immobilized area inside the obviously activated area is a precursory feature which suggests that an earthquake is impending.⑥ The longer the duration of immobilized-movement,the higher the magnitude of earthquake would *** above might be the basic mode of vertical crustal deformation during the seismogenic process of strong intraplate earthquakes.

关键词： intraplate earthquake,crustal movement,seismogenic process reactivation

Current horizontal strain field in Chinese mainland derived from GPS data

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Acta Seismologica Sinica(English Edition) 2002年第4期15卷 351-362页

作者：杨国华李延兴韩月萍胡新康巩曰沐 First crustal deformation monitoring center China Seismological Bureau Tianjin China

The current crustal horizontal strain field is given in the paper based on the horizontal movement rates obtained from about 400 GPS stations located in Chinese mainland and its surrounding areas. The results show: a) The horizontal strain in Chinese mainland is strong in the west and weak in the east and the shear strain is larger than the normal strain (absolute magnitude). The general strain magnitude is 10-8/a and in local regions is 10-7/a, but the strain distribution is not homogeneous; b) The regions with the most significant NS-trending strains are the Himalayas belt along the western segment of Chinese southern boundary, the segment of 36N~42N along the western boundary and the northern margin of Qaidam block; c) The EW-trending strain variation along the western margin is the maximum and it is characterized by the alternatively positive and negative variations from the west to the east; d) The regions with larger magnitudes of REN (NE-trending shear strain) and Rmax (maximum shear strain) are Himalayas belt, the segment of 36N~42N along the western boundary, the western part of Qaidam block, Sichuan-Yunnan (Chuan-Dian) rhombic block and the border area of Alxa, Qilian and Tarim blocks; e) The surrounding area of Qinghai-Xizang (Qingzang) block is mainly superfacial contraction and its interior is basically superfacial expansion. The area to its north is mainly superfacial contraction with the maximum magnitude along the western boundary and the minimum magnitude in the eastern part (except Yanshan tectonic zone); f) In the west of the western part, the principal compressive strain is in the SN direction and the principal tensile strain is in the EW direction, while in the eastern margin area of the western part, the principal compressive strain is proximate EW and the principal tensile strain is about SN. The principal strain direction of Chuan-Dian rhombic block has changed greatly. In the northern part, it is compression in the EW and tension in the SN,

关键词： GPS Chinese mainland current strain field strain mechanism