Before Wangqing Ms7.2 deep earthquake occurred on June 29 of 2002, a group of tendency and short-term precursory anomalies were observed by part wells of the subsurface fluid observing net in Jilin.
The frequency of deep earthquakes was far higher than that of shallow earthquakes during the years 1986— 1987.The global seismicity exhibited a small peak value in the years 1985—1987.
In this paper, the relationship between deep earthquake and the regional tectonic activity background in Jilin Province was introduced based on the research about the relationship between formation of deep earthquakes and plate tectonic activity.
After shallow earthquakes controlled by the eastern stress field and intermediate and deep focus earthquakes quieted for about 20 a,the Huichun M7.0 deep focus earthquake and the Taiwan M7.6 earthquake may be a signal of aggravation of action of the Pacific plate and beginning of relative seismic activity in China.
Firstly, spatial and temporal distribution, dominant direction of principal compressive stress of deep focus earthquakes in northeast of China and volcanic activity in deep shock area are discribed.
Making use of history earthquake data,space-time features relating to deep focus earthquakes of the Japan trench and the Sea of Japan and shallow shocks in NortheastChina have been studied in this paper,The risk tendency of shallow earthquake in Northeastchina is also analysed according to correlation between deep and shallow earthquakes.
The relation between the shallow earthquakes in North China and the deep focus earthquakes in western part of Sea of Japan and in Northeastern China has been analyzed in the paper. We consider that the deep earthquakes in above mentioned seismic area has undergone five relative active periods in this century,and the active periods correspondently have influence on the shallow shocks activity in North China.
We assume that subduction process of Japan trench is cause of deep seated earthquakes but is not important cause to give rise to shallow shockes in Northeast China.
The very deep earthquake of March 8, 1990 has a complex focal mechanism with a long source time function (1.2 s) and two different fault-plane orientations.
The appearance of a zone of anomalousVp/Vs values with linear dimensions of the order of 100 km was noted at least 4 years before a deep earthquake of magnitude 7.
The sources for thirteen deep focus earthquakes ofmb≥5.5 andh>amp;gt;400 km in Northwest Pacific region were studied using waveform fitting and shear fracture source model.
The strike direction of faulting plane for most deep focus earthquakes coincides with that of the subduction zone, especially in the deep part of the subduction zone, it results in the tendency of reducing the dip angle of the subduction zone.