柴达木盆地低頻地震探測的基岩首波和大角度反射波

1958年6月开始,在柴达木盆地进行低頻折射地震的試驗工作,目的在于探測埋藏很深的基岩,以及基岩以上的主要沉积岩界面。根据地貭資料的推測,盆地中部基岩埋藏的深度可达10公里以上,利用其他的地震勘探方法是不容易得到效果的.所用检波器的固有頻率为13周/秒,最远两个相遇炮点相距約90公里,接收距离达100公里.关于仪器的性能与工作方法,已在前文叙述,对于低頻地震波性貭的研究,仅有簡短的报导.

THE BASEMENT HEAD WAVES AND WIDE-ANGLE REFLECTED WAVES IN CHAI-DA-MU BASIN BY LOW-FREQUENCY SEISMIC REFRACTION WORK

The low-frequency refraction work has been applied in Chai-Da-Mu Basin for detecting the depth and relief of the basement. The crystalline basement in Chai-Da-Mu Basin is very deep. It is estimated to be buried more than ten kilometers under the ground surface. Moreover, in the upper medium, there are several layers with sufficiently high elas'ic velocities; namely 5500-6500 m/sec. These conditions have made the basement head waves to be recorded as la'er arrivals even as the profiles were extended to about 100 kms. Criterions have been acertained to discriminate the basement head waves from reflected waves and multiple waves. Because of the complexity of basement structure, the head waves of the basement boundary possess some particular properties making themselves distinguishable from head waves arising in the sedimentary boundaries above. Strong wide-angle reflected waves were recorded also. Similar methods have been applied to distinguish them from head waves and multiple waves. Some characteristics of these reflected waves are described.