关键词: 大陆岩石圈, 塑性流动网络, 地震迁移, 塑性流动波, 走时等值线, 起波年份, 波峰带

Abstract: The studies of the phenomena about earthquake migration and ground deformation diffusion have long been carried out by many seismologists (Richter,1958; Bott et al .,1973; Kasahara, 1979; Mogi, 1986; Sato, 1989; Babazade et al ., 1991; Ma et al ., 1992; Zhao et al ., 1995), and show that the velocities of these migrations range roughly between 1～1,000 km/a. The suggestion of the idea about plastic-flow waves is also closely related with the study of earthquake migration (Wang et al ., 1994b, 1995). However, it differs from those mentioned above in the following aspects: it focuses on the migration of earthquakes along plastic-flow belts, considering that the large-scale seismic belts are controlled by the netlike plastic-flow in the lower lithosphere (including the lower crust and lithospheric mantle) and the earthquake migration is a manifestation of wave propagation in the lower layer; this kind of waves is different from the waves along elastic or viscoelastic layer and is mainly a kind of viscous gravity waves in the lower lithosphere, in short, it can be called network waves in consideration of the closed relation between the plastic-flow waves and the plastic-flow network. According to the viewpoints of plastic-flow network and plastic-flow wave in the lower lithosphere, the migration of earthquakes along the plastic-flow belts (Fig.2 and 3), velocity field (Fig.4 and 5) and wave-generating stages at driving boundary (Fig.7) are investigated by means of the method used previously for the network waves in the major area of the central eastern Asian continent. Moreover, the travel-time contour map of the network waves (Fig.6) and the map of wave-crest belts (Fig.8) for the southeastern region of China are compiled, preliminarily showing the seismic energy background controlled by the network waves and providing the basis for further studies and the physical prediction of seismic energy background in this region. The studies indicate that in addition to the network waves corresponding to the Central Eastern Asian plastic-flow network system stated previously (Wang et al ., 1994b), there are also the waves corresponding to the Southeastern China network system. They are originated from the Himalayan and Taiwan driving boundaries, respectively, and propagate into the continent at different periods and velocities. The former includes mainly the "centenary wave" with average period of 93.4 a and velocities of about 1～10 km/a and the "decadal wave" with 10.8 a and about 20～60 km/a. The latter (Fig.8) includes mainly the "twenty year wave" with average period of 23 a and velocities of about 10～20 km/a and the "decadal wave" with 12a and about 30～50 km/a. As indicated by the experimental models of plastic-flow waves in the lithosphere, the quasi periodicity of the network waves is mainly related to the pulsative or intermittent actions at driving boundaries. Note that some simplifications and assumptions have been made in this study, such as the linear assumption of the migration of earthquakes along plastic-flow belts, the rough estimation of the migration lines in the time-distance distribution charts of earthquakes, etc. The obtained results, therefore, should be considered only as an "initial approximate value" for further studies, and should be examined in the practice of earthquake prediction and revised progressively for approximating the "optimum value" of the seismic energy background. The network waves in the southeastern China region have been examined and revised by the actual seismic activity in 1999 and 2000. The much better understanding about network waves will be gained through a number of "prediction-feedback-revision-prediction" cycles.

Key words: continental lithosphere, plastic-flow network, earthquake migration, plastic-flow wave, travel-time contour, wave-generating year, wave-crest belt