1976年唐山地震前土层水平最大剪应变的时空分布

土层应变仪观测网的观测结果表明:土层水平最大剪应变在唐山地震前有异常,异常后便发生了主震;异常时间等值线从震中向外围传播,其传播速度为每天0.1—6.6公里,从震中区向外围加快,以沿着通过唐山主震震中区的北东和北西向断裂带的传播速度为最快;最高等值线圈闭震中或在震中附近

TIME-SPACE DISTRIBUTION OF MAXIMUM HORIZONTAL SHEARING STRAIN IN SOILS BEFORE THE 1976 TANGSHAN EARTHQUAKE

The results observed network by of strainmeters in superficial soils show that the maximum horizontal shearing strain in soils had produced abnormal variation before the 1976 Tangshan earthquake and the principal earthquake would have happened after this abnormal variation. The contour lines of equal duration of maximum horizontal shearing strain abnormaly in the soils propagated outward in all directions from the epicenter of the earthquake at a velocity of 0.1-6.6 km per day. This velocity of propagation increases with distance from the epicenter and the epicenter is enclosed by the maximum contour line or situated near it.The epicentral distance of an earthquake can be determined from the abnormal duration curves recorded at the stations as well as the epicentral distance-abnormal duration curves which correspond to the earthquakes of same magnitude. To illustratethis, three or more circles are drawn. Each station is the center of a circle, and the radii are equal to their relative distances to the epicenter. These circles then intersect at the epicentral area