二维地震波模型试验的振源

本文討論二維模型試驗所用的二种振源:扩张中心型的振源和垂直集中力型的振源。扩张中心型的振源系用压电钛酸鋇短柱体的径向伸縮,以柱面为发射面而得到的。实驗証明,柱面上的伸縮主要是由直径决定的单頻振动。因此,用寬度相应于径向振动周期的矩形电脉冲来激发晶体时,可以消除由晶体自由振动所造成的“余震”,从而得到短暫的声脉冲。单力型振源是一个用钛酸鋇晶体和黄銅棒制成的杆状发射器。这种发射器在工作頻率范围內,实际上是一个非周期性器件,因此不存在器件的自由振动問題。在实驗中研究了三种不同直径杆状发射器的发射强度与波形同发射方向角间的关系。

ON THE TRANSMITTING SOURCES IN TWO-DIMENSIONAL SEISMIC MODEL EXPERIMENTS

The character of a transmitting source plays an important part in seismic model experiments for obtaining a distinct wave form with short duration on the receiving record. The present paper describes two kinds of transmitting sources: the source of central expanding force and the source of normally concentrated force. A cylindrical piezo-electrical crystal of barium titanate inserted in the central hole of a circular plate was used as the source of a central expanding force. It is found when the initiating electrical pulse has a time duration corresponding to one cycle of the radial resonant frequency of the crystal,the received seismogram shows the most distinct wave form with short duration. A rod type transducer of barium titanate in contact with the edge of a semi-circular plate with a thickness of 2mm was used as a source of normally concentrated force. It is found that when the diameter of the transducer is less than 5mm,the directional effect of intensity is similar to that of a point source. In general,this kind of transducer will produce a satisfactory wave form in the receiving record. The detector consisting of a barium titanate cylinder attached to the end of a brass rod with the same diameter were used in all the experiments.