Physics of Seismic Source Ⅱ. Mechanics of Seismic Source

An earthquake is regarded as a fracture from the viewpoint of continuum mechanics, in which stress and strain play key roles in understanding the nature of a seismic source. This review briefly outlines the mechanics of a seismic source in terms of the dislocation model and crack model. The introduction includes the Coulomb failure criterion, static stress drop, dynamic stress drop, the Griffith criterion, and the scaling of source parameters. The selection of topics in the introduction emphasizes the application of seismic data, i.e., in practice, the mechanical parameters introduced here are measurable in the interpretation and analysis of seismic waveform data.     

Seismic Network,Seismic Activity and Seismological Research of Vietnam

In this paper,a historical review of the seismic network of Vietnam and the ability of the network to monitor earthquakes is presented.The seismic activity of Vietnam as a country of high seismictiy in the last century and since the beginning of the new century is described.The current state of seismological research in Vietnam and cooperation with institutions outside of Vietnam is outlined.     

Effect of Aftershocks on Assessment of Seismic Hazard for Hebei Seismic Zone,China

In this paper,the earthquake hazard parameters(λm,b and Mmax) from the maximum likelihood method for the raw catalogue and declustered catalogues have been used to discuss the effect of the aftershocks on the earthquake hazard estimation.The declusterd catalogues have been compoiled from the raw catalogues by deleting the aftershocks in different time interval after main shock according to the criteria for the aftershock activity period.As an example,Hebei seismic zone is taken to show the effect of the aftershock on the earthquake hazard assessment because three strong earthquakes with the aftershocks occurred from 1966,to 1976,The results have been shown that the effect of the aftershocks on the parameters λm,b is significant.The difference between the clustered and declustered catalogues has reached in seismic activity rate and recurrence period,at most,45% and 90%,respectively,But the diffeence in Mmax is smaller,Based on this,the suggestion that the aftershocks should be omitted in the estimation of the earthquake hazard could be made,but how long the aftershocks activity duration is still left to the future research.     

New Physical Measures of Seismic Intensity

The physical measures of macroscopic seismic intensity have been extensively studied based on the new understanding of seismic intensity and the new analytical method and new database of strong ground motion.New physical measures of seismic intensity have been proposed.     

Seismic Signatures of Rock Pore Structure

Rock pore structure is one of the important parameters in controlling both seismic wave velocity and permeability in sandstones and carbonate rocks. For a given porosity of two similar rocks with different pore structures, their acoustic wave speeds can differ 2 km/s, and permeability can span nearly six orders of magnitude from 0.01 mD to 20 D in both sandstone and limestone. In this paper, we summarize a two-parameter elastic velocity model reduced from a general poroelastic theory, to characterize the effect of pore structures on seismic wave propagation. For a given mineralogy and fluid type of a reservoir, this velocity model is defined by porosity and a frame flexibility factor, which can be used in seismic inversion and reservoir characterization to improve estimation of porosity and reserves. The frame flexibility factor can be used for quantitative classification of rock pore structure types (PST) and may be related to pore connectivity and permeability, using both poststack and prestack seismic data. This study also helps explain why amplitude versus offset analysis (AVO) in some cases fails for the purpose of fluid detection: pore structure effect on seismic waves can mask all the fluid effects, especially in carbonate rocks.     

Dynamic Method of Seismic Casualty Assessment

The concept of Initial Casualty Matrix is introduced. Using some probability distribution functions, the initial casualty matrix of masonry is determined. The dynamic method of seismic casualty assessment is established and then applied to the Tangshan earthquake data, with some conclusions drawn.     

Wavenumber response of Shanghai Seismic Array

Seismic array can be traced back to 1950s when it mainly aimed at detecting and distinguishing the signals of nuclear explosion and seismic signals. The research on seismic array includes seismic array techniques and applications of array in geophysics. Array techniques involve array design and data processing methods (Anne, 1990). Nowadays, the continuous development of seismic array(s theory could relate to many scientific issues in geophysical field (Tormod, 1989; Mykkeltveit, Bungum, 198…     

Seismic risk analysis of coastal area of Pakistan

Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized in five seismic provinces as potential hazard sources. Maximum magnitude potential for each of these sources is calculated. Peak ground acceleration (PGA) values at the seven coastal cities due to the maximum credible earthquake on the relevant source are also obtained. Cities of Gwadar and Ormara with acceleration values of 0.21g and 0.25g respec-tively fall in the high seismic risk area. Cities of Turbat and Karachi lie in low seismic risk area with acceleration values of less than 0.1g. The Probabilistic PGA maps with contour interval of 0.05g for 50 and 100 years return period with 90% probability of non-exceedance are also compiled.     

The Seismic Risk Assessment and Seismic Zoning of the Hong Kong Region

The Hong Kong-Kowloon Block,which has been uplifted continually and is stable since the late Cretaceous-Paleogene period,is identified and determined as a potential source with a maximum credible magnitude of M=5.5,while the late Cretaceous-Paleogene fault basins located around the Hong Kong-Kowloon Block are determinated as a potential source with a maximum credible magnitude of M≥6.0 based on the characteristics of seismo-tectonic activities in Hong Kong and its adjacent regions.The attenuation law of peak ground acceleration(PGA)and standard response spectra of acceleration(β)with damping 5% underlain by basement were determined by comparing the Chinese continent with the western U.S.A.in the similarity of tectonic environment of continental earthquakes,potential source with credible seismic magnitude of 5.0-7.5,and considering ground motion saturation near the source.The near source attenuation model of acceleration and response spectrum also reflect the field of Intensity distribution in East Chi     

Analysis of Geological Background of Seismic Activity in the Chengdu Plain from Data of Seismic Prospecting for Oil

Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in‘ the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum organizations in Sichuan and of the results of seismic prospecting and detailed exploration in Chengdu depression during the last 20 years permitted us to studythe types and distribution of hidden structures in Chengdu depression and its adjacent areas, in particular, to identify in, detail the “hidden faults” in the Chenngdu-Deyang area on the one hand; The obtained data indicate that the NE-trending Xinjin fault ruus northward and dies out in the south of Penzhen town of Shuangliu County; Meanwhile, we studied genetic relations of seismic activity to active faults and their corresponding movernent charaeteristics on the other hand, Moreover, the Surface faults and deep-seated faults are clearly defined and outlined,and 5 types of seismogenic faults suggestd. The knowledge thus obtained enables us to delimit the focal zones for potential strong earthquakes in Chengdu depression. The study suggests that a zone of 40 km wide and more than 100 km long on sides along the Chengu Deyang lim bas a stable seismogeological background and good engineering-seismological conditions.     

Seismic features of vibration induced by train

Introduction Collisions can be generated continuously by the passage of trains due to the surface irregu-larities of wheels and rails. When a fully loaded train or freight with weight of thousands tons runson deformed rails, it may induce strong vibrations. Such vibrations may transmit several kilome-ters to result in building damage. For instance, the famous Longmen Grottoes near the Luoyangcity in China has been seriously damaged by the ground trembling by trains pasting near it(http:…     

Analysis of Seismic Activity in the Middle Part of the North-South Seismic Belt—Joint Study on Deep Seismic Sounding Profile and Seismicity Parameters

Using the rich deep seismic sounding data recorded in the middle part of the North-South Seismic Belt in China, the horizontal and vertical profiles are constructed to obtain the seismic velocity structure, analyze the seismic distribution and calculate the seismic energy and the thickness of the seismogenic layer at the same time. On this basis, the seismicity parameters are calculated using the earthquake catalogue of the study area for the past 40 years, and the relationship between the b-value distribution and the velocity structure is analyzed. The results show an uneven b-value distribution in the study area and a segmented feature along the Longmenshan fault zone. Most of the earthquakes occur in the transition zone anomalies from the positive to the negative. In addition, the thickness of the crust drops from ~60 km to ~48 km from the Southeastern to the Northeastern Qinghai-Tibetan Plateau, but the thickness of the seismogenic layer increases gradually. It is speculated that the crustal composition of the Northeastern margin contains more felsic materials and has relatively stronger seismic activities than the Southeastern Qinghai-Tibetan Plateau, possibly associated with the subduction and compression of the Indian Ocean Plate.     

Physics of Seismic Source Ⅲ. Statistical Mechanics of Earthquakes

The statistical mechanics of earthquakes adopts the concepts and methodology of statistical mechanics, especially the theory of critical phenomena, in studying the preparation, initiation, propagation and healing of earthquake rupture, which forms a new branch in the physics of seismic source in recent years. This article introduces to the fundamental concepts of the statistical mechanics of earthquakes. The introduction includes the seismic Hamiltonian, percolation model, earthquake rupture nucleation, and Burridge-Knopoff spring-block model. It is pointed out that some of the statistical mechanical models of earthquakes have a sound seismological basis. There is a smooth "transition" from the "classical" theory to the "modern" theory of seismic source.     

Seismic Studies of the Earth’s Core

Izvestiya, Physics of the Solid Earth - Abstract—The paper presents the review of the conceptually most important results of seismological studies of the Earth’s core and their...     

Features of Seismic Waves Observed by Downhole Seismometers

In this paper,the authors have summarized the kinematic and dynamic features of seismic waves observed by downhole seismometers in China.The features of seismic waves recorded on ground and downhole as well as in soil layer and bedrock layer,including amplitude,traveltime,spectrum and wave field are discussed individually and then explained integrally in term of the effects of soft covering layer.This research result has been applied to the establishment of downhole seismic stations,the location of fractures in oil fields and the measurement of seismic focus parameters and structural parameters of media.     

Methods of Determining the Seismic Spatial Distribution Functions

Several factors are selected to reflect the temporal and spatial features of seismicity in Southwest China.The measurements of the factors are all taken from the statistical relation between the factors and actual earthquakes,and make the factors possess a certain probabilistic prediction meaning and the base for mutual contrast.The effects of prediction of part of the factors have been evaluated and used to correct the factors.Three sets of seismic spatial distribution functions have been calculated by using three different methods and discussed in detail.     

Study and Practice of Wide-Angle Seismic Data Processing

This paper presents the special processing methods used for wide-angle land seismic data through both theoretical study and model testing. They are different from conventional ones in the following aspects: separation of reflection and refraction waves, long offset NMO and stacking and forward modeling and inversion. These processing techniques have been applied for the first time to land seismic data from Liaohe areas, resulting in greatly improved quality of the deep formation and better imaging of the shallow layer obtained in the volcanic-shielded area. Wide-angle reflection and refraction seismic surveys were carried out in the Liaohe area using the maximum offset of 6500m and with the target around 2000ms. In the processing, we adopted the τ-p transform and the high-order normal moveout correction.     

Seismic Intensity and Earthquake Damage Rate of Buildings

Based on the analysis of the three current seismic intensity scales,the authors maintain that there are still some shortcomings in the present seismic intensity evaluation and propose a method which takes the damage rate of structures such as houses to determine the seismic intensity.Also,it is pointed out that the proposed method is favorable to the combination of seismic investigation,seismic damage forecast and hazard reduction counter-measures.