A STUDY OF THE RELATION BETWEEN ACOUSTIC EMISSION AND ANIMAL UNUSUAL BEHAVIOR PRIOR TO EARTHQUAKES

This paper is an analysis of some observed results of acoustic emission prior to earthquakes, occurred in the last ten years in China for the temporal and space distribution pattern of such acoustic emission before large earthquake events and an estimation of the transmitted sound pressure above the bed rock and in surface water. The distribution pattern was then compared with that of the animal unusual behaviors before earthquakes. Besides, the threshold values of sensation to hearing and vibration of human and some animals have also been compared. Finally, a cross-correlation analysis of the observed acoustic emission and the activities of fishes during the aftershock period of the Tangshan earthquake for the same time intervals was made. The results are as follows:1. The pattern of temporal and space distribution of acoustic emission and animal anomalous behavior before earthquakes are generally similar. They are commonly referred to as the earthquake short-term precursors.2. Transmitted sound pressure of acoustic emission before an earthquake of the magnitude around 3 near the epicentral region above the bed rock and in the surface water equals respectively to 23-19 db and 90-86 db in the frequency band of 150-250 Hz. It can be seen that human ears, are not able to sense this sound pressure level on ground surface, but possibly cats, dogs and pheasants living on ground surface and usually rates living in holes, can sense it, and perhaps teleost fishes are superior to ground animals in sensing acoustic emission prior to earthquakes. At the same time, the vertical amplitude of displacement of the bed rock surface amounts to about 10-7cm. Although this value is about 3 orders of magnitude lower than the amplitude thresholds of sensation to vibration for some animals, we might infer that the vertical amplitude of ground surface displacement before strong earthquakes can be of the order of microns or more, so that they should be able to sense the vibrations.3. When the observational sites for the activities of fishes and acoustic emission are about 20 km apart, the results show not only that they reflect the aftershock activity of the same regions in Tangshan but also certain cross-correlation between the sequences of daily frequency of activities of fishes and acoustic emission.