【摘要】 声波透射实验表明 ,对于板状材料 ,声音的一部分能量可以透射到空气中。另一部分能量在板中产生简正波 ,使板产生较大的振幅 ,在空气中产生能被话筒接收到的声音信号 ,而信号的简正频率与板的尺寸有关。另外 ,破裂过程中的声发射实验证实 :随着微破裂的集结和裂纹的扩展 ,所辐射波的频谱会逐渐向低频移动 ,而且当频率很低时 ,可以透射出岩石 ,被话筒接收到。根据尺度相似性原理 ,推广到野外 ,强地震前破裂集结可能会辐射出超低频波 ,这种超低频波不能被常规的地震仪记录到 ,但可以被超低频传感器或次声接收器记录到。在地震前 ,产生前兆的源非常复杂 ,大多数情况下可能并非脆性破裂 ,而是塑性蠕滑或者有流体的参与。而后两种情况产生的波的周期会更长 ,而且缺乏脆性破裂所固有的高频成分 ,这可能就是多数地震前缺乏前震的原因。更多还原

【Abstract】 It is demonstrated that some of the energy of the sonic wave in a plate material can transmit into the air. At the same time, the normal vibration in the plate can give rise to large amplitude vibration on the surface of the plate, generating measurable sound in the air. The characteristic frequency is related to the size of the plate. From the experiment of AES in the process of fracture, it is demonstrated that with the nucleation and propagation of the fracture, the spectrum of the radiated wave will transfer to lower band. When the frequency becomes very low, the wave can transmit through the rock and be received by the microphone. According to the theory of size comparability, there will be ultra-low-frequency waves occur before strong earthquakes because of nucleation, which cannot be received by ordinary earthquake detection instruments but can be received by special ultra-low-frequency transducer or infrasonic receiver. Before earthquakes, the sources of precursors could be very complicated. They might be produced by plastic creep or can attribute to liquids but not crisp fracture in most cases. So the periods of the produced waves will be longer. This perhaps account for the lack of foreshocks.更多还原