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

Abstract

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 studied. The 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 steps. Firstly, movements in the “field” region transform from the normal state to an anomalous state to start the formation of field precursors. Secondly, movements in the “source” region become outstandingly remarkable. Thirdly, anomalies in the “field” region that surrounds the “source” become increasingly intense. Fourthly, the “source” region enters a state of immobilized-movement. Finally, an earthquake occurs. (4) There are usually one or more areas where the anomaly field forms a special pattern, mostly a four-quadrant distribution. The 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 be. The above might be the basic mode of vertical crustal deformation during the seismogenic process of strong intraplate earthquakes.