Acta Seismologica Sinica 

About: Acta Seismologica Sinica is an academic journal. The journal publishes majorly in the area(s): Fault (geology) & Aftershock. It has an ISSN identifier of 1000-9116. Over the lifetime, 1559 publications have been published receiving 6652 citations.

Interpretation of seismic reflection profiling data for the structure of the san andreas fault zone

Abstract: A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the true-amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly non-unique, is consistent with the various lines of evidence on the fault zone structure.

Stochastic models for earthquake occurrence

Abstract: Seismic data for the period 1446-1969 in the North China seismic active region have been used in this study. We selected 36 earthquakes which occurred at the points of inflection and at the main peaks of the active periods. Hermitian interpolation was made between the energies of two consecutive earthquakes. In this way, a curve of equal sampling intervals showing the variation of the activity of the North China seismic region during the past 500 years was obtained.This curve may be assumed to consist of two parts, namely, the deterministic part and the stochastic part. A periodic model and an auto-regressional model of stationary stochastic process were respectively proposed for carrying out extrapolation and prediction.By posteriori-test analysis, we mean the interceptions of the recent data 15 times, each followed by computing, extrapolating and predicting separately. Again, by summing up the number of time intervals predicted to be earthquake dangerous, a curve of prediction could be obtained.Based on these results of posteriori-test we predicted in April 1974 the appearance during the time interval from 1975 to 1977 a seismic active period in North China, within which the Haicheng earthquake of 1975 and the Tangshan earthquake of 1976 actually occurred. Moreover, the said curve is still significant for predicting future earthquakes in North China. It seems that the seismic active period of North China starting from the Haicheng earthquake would last for a certain length of time, till about 1980, but it would be again active at around the year 2001.

A present-day tectonic stress map for eastern Asia region

Abstract: Based on the data of earthquake centroid moment tensor (CMT) solution, P-wave first motion focal mechanism solution and deep hole breakouts, a present-day tectonic stress map for eastern Asia region is compiled. The original stress data are smoothed for every 200 km × 200 km area by taking the average of all stress indicators within each sub-region. The stress map shows the spatial distribution of the orientation of principal stress axes and the stress regimes. An earthquake focal mechanism map for the eastern Asia is also given. The maps of orientation of principal stress axes show that, apart from the strong influence of the collision between the Indian Ocean plate and Eurasian plate, the present-day tectonic stress in eastern Asia is significantly affected by the back-arc extension of the subduction zones. The joint effect of the continental collision at the Himalaya arc and back-arc extension in the Burma arc region may be responsible for the remarkable rotation of the principal stress orientations in southeastern part of the Tibet plateau. The joint action of the collision between the Philippine Sea plate and Eurasian plate at Taiwan Island and the back-arc extension of the Ryukyu arc affect the stress field in eastern part of China. There are no strong earthquakes in the present day in the vast back-arc region of the Java trench subduction zone. The back-arc extension there may create a condition favorable to the southward flow of the lithosphere material in southeastern Asia. In the inner part of the Tibet plateau region, roughly demarcated by the Kunlun mountain, the northern and northeastern part is a broad intracontinental compressive zone, while the southern and southwestern part is generally in a normal-faulting stress state.

A study on 3-D velocity structure of crust and upper mantle in Sichuan-Yunan region, China

Abstract: Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others show the characteristic of tectonic boundary, indicating that the faults likely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the India and the Asia plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

An equivalent-boundary method for the shell analysis of buried pipelines under fault movement

Abstract: A new shell finite element method (FEM) model with an equivalent boundary is presented for estimating the response of a buried pipeline under large fault movement. The length of affected pipeline under fault movement is usually too long for a shell-mode calculation because of the limitation of memory and time of computers. In this study, only the pipeline segment near fault is modeled with plastic shell elements to study the local buckling and the large section deformation in pipe. The material property of pipe segment far away from the fault is considered as elastic, and nonlinear spring elements at equivalent boundaries are obtained and applied to two ends of shell model. Compared with the fixed-boundary shell model, the shell model with an equivalent boundary proposed by the study can remarkably reduce the needed memory and calculating time.