| In this article, we analyze stress triggering effect between strong earthquakes as well as regional seismic activity in Xinjiang area; discuss how focal depth and parameters of fault plane, which includes strike, dip and slip, influence the stability of static stress triggering model.During the study of triggering effect between strong earthquakes, we select medium and strong earthquakes in Xinjiang since 1944. According to regional geology structure and difference of seismic activity, we divide Tianshan into north Tianshan, east section of south Tianshan, Keping block and Kashi—Wuqia mixing region, study triggering effect between medium and strong earthquakes within 150km respectively. Of all the selected 45 pairs since 1944, whose magnitudes are no less than 5.5, 32 pairs happened in the area of |ΔCFS|>0 made by focus earthquakes, the coulomb stress produced by most medium and strong earthquakes maybe promote or delay their following shocks. TheΔCFS in north Tianshan and east section of south Tianshan are generally small, sized 10-3Mpa, effect in these two areas are not remarkable. TheΔCFS in Keping block and Kashi—Wuqia mixing region are bigger, most reach 10-2Mpa, effect in these two areas are remarkable. The relationship between the coulomb stress change generated by 45 pairs and spatial distance shows that magnitude of coulomb stress decreases with the increase of distance, especially when the two earthquakes in one pair apart each other between 40~60km. When they apart less than 100km, specially less than 50km, coulomb stress can reach 10-2Mpa. When they apart more than 100km, coulomb stress generally counts 10-3Mpa.During the study of regional earthquakes, those in the condition of Ms≥6.0 or close to 6.0 under better monitoring ability are selected as focus earthquakes. Deduction of possible foreshocks and aftershocks, we analyze velocity rate of small-moderate earthquakes activity before and after two years of focus earthquakes within 300km; quantitatively discuss small-moderate earthquakes activity half year before focus earthquakes. The results shows increase or decrease of small-moderate earthquakes is not significant for the former, their rate are 0.47(8/17)å'Œ0.29(5/17) respectively; however, small-moderate earthquakes activity half year before focus earthquakes largely changed to 0.76(13/17). The analysis shows that regional earthquake activity level's up and down may has certain precursor meaning. Trough comparative analysis on positive and negative coulomb stress change zones, we find that small-moderate earthquakes activity levels in these two zones are almost the same before or after two year of focus earthquakes. Increase or decrease of seismic activity is not obvious. The change in those two zones remarkable increased when it comes to half year before focus earthquakes, both reach 0.71(12/17). This result may have some meaning on deepening study and practice of earthquake prediction.Studying the appearance of Ms≥5.0 earthquakes after focus earthquakes. The result shows that of the selected 17 focus earthquakes, 15 has following Ms≥5.0 earthquakes after they happened 2～3 years. The number in positive coulomb stress change zones are more than that in negative zones, 35 and 25 each.Select collected 15 Ms≥6.0 earthquakes since 1970 in Xinjiang as"focus earthquakes", Ms≥4.0 aftershocks as"tragic seismic". By change focal depth and parameters of fault plane, which includes strike, dip and slip, quantitatively analyze the effect of those factors on static coulomb stress model's stability. The result shows that when focal depth changes 5km and dip changes 10°, they have little effect on the model's stability, when focal depth changes 10km and dip changes 20°, they have more effect on the model's stability, when strike and slip change 10°～20°, they also has little influence on the model's stability. |
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