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Possible　dynamics　of　normal－fault　earthquakes　in　the　upper　crust　of　the　south　part　of　the　Qinghai－Xizang　Plateau

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Acta Seismologica Sinica(English Edition) 1995年第2期8卷 233-239页

作者：张东宁许忠淮 Institute of Geophysics State Seismological Bureau Beijing China

A numerical model for generating normal fault earthquakes in the Qinghai-Xizang Plateau′S upper crust is constructed with 3-D elasto-viscous finite element method. Based on the numerical simulation calculation,some conclusions were got:If the effective viscosity of the upper crust material is less than that of lower strata of the crust in the Qinghai-Xizang Plateau, even under the strong push of India continent,the stress state of the upper crust can still be extensional in south part of the Qinghai-Xizang *** simulations show that the stress state changes with the depth of the lithosphere,from extensional stress state in upper crust to compressive in the lower *** stress state may exist mainly in the upper crust of the south part of the Qinghai-Xizang Plateau.

关键词： Qinghai-Xizang subplate normal fault seismic activity finite element effective viscosity

Research　on　the　completeness　of　earthquake　data　in　the　Chinese　mainland（I）──North　China

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Acta Seismologica Sinica(English Edition) 1994年第3期7卷 351-359页

作者：黄玮琼李文香曹学锋 Institute of Geophysics State Seismological Bureau Beijing China

In terms of the temporal-spatial distribution features of earthquakes, we study the completeness of historical data in North China where there is the most plenty historical data and with the longest record history by some meth ods of analysis and comparison. The results are obtained for events with Ms≥4 are largely complete since 1484 in North China (except Huanghai sea region and remote districts, such as Nei Mongol Autonomous region), but quakes with Ms≥6 are largely complete since 1291 in the middle and lower reaches of the Yellow River.

关键词： completeness earthquake data record capability mean annual rate proportionality factor

On unified analysis of uncertainty in seismic hazard assessment

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Acta Seismologica Sinica(English Edition) 1994年第4期7卷 629-636页

作者：胡聿贤陈汉尧 Institute of Geophysics State Seismological Bureau Beijing China

In this paper, firstly the current analysis methods of uncertainties in seismic hazard assessment (SHA) are systematically reviewed, and the existing problems are pointed out. At the same time, it is proposed that the uncertainties can be divided into three kinds, namely, randomness, fuzziness and incompleteness of knowledge, and they can be treated in a unified way. Then, based on marked point process theory, a general equation for SHA is obtained, and a general equation for uncertainty analysis is also given on the basis of total probability theorem. Finally, the relationship between the proposed analysis method with those currently used both at home and abroad is discussed. The analysis shows that they are just the special case of the proposed method.

关键词： seismic hazard assessment randomness fuzziness incompleteness of knowledge uncertainty

Promoting　effects　of　1975　Haicheng　foreshocks　on　theoccurrence　of　the　mainshock

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Acta Seismologica Sinica(English Edition) 1994年第3期7卷 409-414页

作者：李兴才 Institute of Geophysics State Seismological Bureau Beijing China

Assuming that principal axis of the distribution of the 1975 Haicheng mainshocks and aftershocks means that there is already a fault (a1 ) on N67°W, which together with Dayanghe fault (a3) on its right side with the orien tation of N50°W form a left step and left lateral fault system. The calculation indicates that the energy release rates G3 corresponding to a3 is greater than that of G1 corresponding to a1, which indicate that a3 will extend first as compared to a1, this results can illustrate qualitatively the observations of Haicheng foreshock distribution along a3′s orientation and in its northwest extending part; analyses also show that there may exist two types of secondary cracks in the step zone between a1 and a3, tensile cracks and shearing cracks, which may provide space and channels for fluid transportation on one hand and may transform slip between the two faults on the other hand. otherwise because the variations of foreshock locations with time have the spreading tendency to north west direction along a3 and the fractals for the foreshocks are much less than for aftershocks, therefore the fractures for foreshocks may have relatively uniform orientations and may connect with each other as the evolution process of the foreshock series, the effects of which may be considered as that of a3′s growing to the northwest,for this case the variations of the mean stresses C, and the maximum shearing stresses Sm, near a1 are then calculated, the results that tensile Cm, increase mean the local confining pressure or frictional stress decrease as the development of the for eshocks, and at the same period the Sm increases, the combining effects of the two types of variations may help the occurrence of slip or initial fracture on the end part of a1, that is the occurrence and the development of foreshocks may have the promoting function to the occurrence of the main shock if the stress level in the source area has already been high enough, furthermore if another fau

关键词： energy release rate mean stress maximum shearing stress

In　search　of　potential　earthquake　source　regions　in　the　Chinese　mainland　in　the　light　of　ambient　shear　stress　field

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Acta Seismologica Sinica(English Edition) 1995年第3期8卷 365-370,370-377页

作者：陈培善白彤霞肖磊 Institute of Geophysics State Seismological Bureau Beijing China

Earth media are incomplete *** exist many cracks in it. The achievements of fracture mechanics showthat the strength of the incomplete materials will be much lower than that of the complete materials. We consider that earthquake occurrence is the result of unstable propagation of a crack in crust media in proper conditionand the earthquake rupture is the phenomenon of a failure by fast fracture under applied low shear stress. It hasalready been explained by fracture *** occurrence of failure by fast fracture is necessarily associated with the presence of high level concentration of local stress and strain. The elastic/plastic stress analysis in cracked pieces by Dugdale indicates that thestate of stress at the tip of a crack takes a very important role to crack propagation. A plastic zone has necessarilyformed in the tip of a crack due to stress concentration. Therefore, the dislocations st the tip of a crack are naturally a plastic displacement, rather than elastic one. The plastic displacement, where τ0 is appliedshear stress which is equivalent to initial or tectonic shear stress when the quake occurs, a is the half length of acrack, It is the rigidity,τy is the yield stresses in shear. The main seismic dislocations take place exactly at theends of the crack where the plastic zone had been formed. SO, a critical assumption is adopted, i. e. we assumethe dislocation D(1,,t) as formula (5) in text. The maximum earthquake dislocation, whereL is the fault length. If p is taken the value in the upper crust, μ=33 GPa; and τy is taken the average valuegiven from laboratories,τy= 30 MPa. Thus, according to observation values of Dmax and L, using the formula,one can estimate the initial shear stresses for large earthquakes. Computations show that the initial shear stressesfor large earthquakes all over the world are about 5-20 MPa which have some differences between *** further research the characteristics of source spectra and have derived the de

关键词： seismic rupture potential earthquake zone seismic risk region,tectonic shear stress,ambientshear stress

A kind of informationon short-term and imminent earthquake precursors-research on atmospheric electric field anomalies before earthquakes

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Acta Seismologica Sinica(English Edition) 1998年第1期11卷 116-126页

作者：郝建国唐天明李德瑞 Institute of Geophysics State Seismological Bureau Beijing China

The long time practice of observational research on earthquake prediction has shown that the information on shortterm and imminent earthquake precursors can hardly be detected, but it is very important for practical and effective earthquake prediction. The result of analysis and study in this paper has shown that the anomaly of quasi static atmospheric electric field may be a kind of reliable information on short term and imminent earthquake *** such a basis, the 20 years′ continuous and reliable data of atmospheric electric field observed at the Baijiatuan seismic station are used to study the correlation between the anomalies in seismic activity and relative quiet periods bear on the occurrence of near earthquakes within 200 km range around Beijing after the Tangshan earthquake. The observational results recently reported before hand in written form and earthquakes that actually occurred in near field in corresponding time periods are compared and analyzed. The efficacy of these written prediction opinions about near earthquakes in the recent 10 years is tested. From the test results, the brilliant prospect that the anomaly of quasi static atmospheric electric field may really become a reliable mark for making short term and imminent earthquake predictions is discussed. Besides, as a preliminary step, some judgment indexes for predicting earthquakes by use of the observational data of atmospheric electric field before earthquakes are put forward. In the last part, it is pointed out that it would be possible to obtain more believable judgment indexes for determining the three elements of near earthquakes before greater earthquakes ( M S5) only if a relatively reasonable station network (2～4 stations every 10 000 km 2) is deployed and further investigation is made.

关键词： atmospheric electric field judgment index monthly report form

Evolution characteristics of seismic intensity in Tangshan seismic zone

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Acta Seismologica Sinica(English Edition) 1998年第5期11卷 124-127页

作者：王泽皋乔子云 seismological bureau of Hebei Province China Seismological Bureau Shijiazhung China

１ＴｈｅｕｓｅｄｄａｔａＴｗｏｃｏｐｉｅｓｏｆＣｈｉｎａＥａｒｔｈｑｕａｋｅＣａｔａｌｏｇｕｅｓｅｄｉｔｅｄｂｙＰｒｏｆｅｓｏｒＧＯＮＧＸＵＧＵｗｅｒｅｕｓｅｄｆｏｒｔｈｅｄａｔａｂｅｆｏｒｅ１９７９；ＣｈｉｎａＥ... 详细信息

１ＴｈｅｕｓｅｄｄａｔａＴｗｏｃｏｐｉｅｓｏｆＣｈｉｎａＥａｒｔｈｑｕａｋｅＣａｔａｌｏｇｕｅｓｅｄｉｔｅｄｂｙＰｒｏｆｅｓｏｒＧＯＮＧＸＵＧＵｗｅｒｅｕｓｅｄｆｏｒｔｈｅｄａｔａｂｅｆｏｒｅ１９７９；ＣｈｉｎａＥａｒｔｈｑｕａｋｅＣａｔａｌｏｇｕ...

关键词： Tangshan earthquake long term activity intensity evolution

Comparison　and　analysis　of　the　stress　field　in　the　source　region　of　Tangshan　and　Lancang　earthquake　sequences

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Acta Seismologica Sinica(English Edition) 1995年第3期8卷 379-386页

作者：刁桂苓于利民李钦祖 seismological bureau of Tianjin Tianjin China seismological bureau of Hebei Province Shijiazhuang China seismological bureau of Yunnan Province Kunming China

The state of the stress fields in the source region is analysed systematically, on the basis of the focal mechanismsof 167 events with Ms≥4. 0 of Tangshan sequence and 163 moderate-small events of Lancang sequence respectively. The result indicates that the directions of the stress field in the source region are generally stable and thevariation is not obvious after the occurrence of strong shock. The dominant orientations of focal mechanisms ofthe aftershocks are consistent with that of the mainshock, there is still a small difference between some mechanisms of aftershocks and the mechanism of mainshock, and the difference decreases as time goes on. The numbers of solutions with dominant direction of Tangshan and Lancang sequences are similar to each other, it indicates that the controls of the strong earthquake sequences from the tectonic stress field are similar to each othertoo. Through the hierarchical clustering analysis of focal mechanism,it is found that the number of clusters ofTangshan sequence is larger than that of Lancang sequence,and their orientations are relatively disordered. Itmay be the cause that the tectonics in the Tangshan region are more complicated than those in the Lancang region.

关键词： focal mechanism stress field Tangshan earthquake sequence Lancang earthquake sequence

Velocity　structure　of　the　crust　and　upper　mantle　in　Xingtai　earthquake　region　and　its　adjacent　area

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Acta Seismologica Sinica(English Edition) 1995年第3期8卷 405-412页

作者：祝治平张称康盖玉杰张建狮聂文英石金虎张成科阮红 Geophysical Prospecting Brigade State Seismological Bureau Zhengzhou China

Two seismic refraction profiles which are perpendicular to each other, running through Xingtai earthquake region,reveal the anomalous variations of crust-mantle velocity structure and deep tectonics. Pg wave attenuatesrapidly with distance in the earthquake region. A group of strong reflections from a depth of 21. 0 km can be identified along the section from Longyao to the piedmont of Taihang Mountain, but P. waves characterized generally by strong amplitude are not obvious. Under the earthquake region and its western neighboring region, thecrustal velocity structure features high and low velocities changed alternatively. From North China plain toShanxi plateau, the velocity at the top of the upper mantle decreases progressively, while crustal thickness increases by 11 km. Moho uplifts locally in the earthquake region. The crustal fault stretching deeply to Moho andthe discontinuous sections of Moho in the earthquake region are supposed to be the channels and zones for magmatic intrusion. The uplifting of upper mantle and magmatic intrusion are responsible for the formation ofanomalous crust-mantle structures and extending basins, and for the occurrence of Xingtai earthquake as well.

关键词： velocity structure lower crust upper crust upper mantle refraction