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本文根据对1976年5月29日龙陵7.3级与7.4级地震和同年7月28日唐山7.8级地震中民房倒塌率的调查,发现覆盖有松散土层的山间盆地多为震害高异常区,并从盆地边缘到盆地沉积中心,随着覆盖土层的逐渐增厚和地下水位逐渐变浅,震害不断加重。通过对不同盆地的比较发现,在其它因索(震中距、土质等)近似的条件下,盆地中的震害分布除受土层厚度影响外,还与盆地中土层之下的基岩界面坡度有关。也就是说坡度陡,震害较重。这种现象可能是由地震波的折射作用引起的。当地震波传播至盆地底部界面时,由于界面两侧分别为基岩和土层两种不同的介质,从而出现波的折射,并在盆地中心产生波的聚焦作用。
Based on the investigation of the collapse rates of 7.3 and 7.4 earthquakes in Longling on May 29, 1976 and the 7.8 magnitude Tangshan earthquake on July 28, 1976, it is found that most of the mountain basins covered with loose soil are mostly high anomalies And from the margin of the basin to the sedimentary center of the basin, with the gradual thickening of the covering soil layer and the gradual shallowing of the groundwater table, the earthquake damage is aggravated. Based on the comparison of different basins, the distribution of seismic damage in the basin is affected by the thickness of the soil layer under the conditions of other factors such as epicenter distance and soil quality, but also with the bedrock interface Slope related. That is steep slope, heavier earthquake damage. This phenomenon may be caused by the refraction of seismic waves. When the seismic waves propagate to the bottom interface of the basin, the wave refraction occurs due to the two different media of bedrock and soil respectively on both sides of the interface, and the focus of the wave is produced in the center of the basin.