Abstract
A temporary observation of near-by microearthquakes was made with Ultra Sensitive Seismometers at Matsushiro. The purpose of this experiment was to see the relation between the frequency of near-by microearthquakes and the annual number of near-by shocks felt at Matsushiro.
The results and conclusions are as follows. An average of one microearthquake occurs every hour. The average annual number of earthquakes felt at Matsushiro is about 1.2. As M of the microearthquakes are from less than -l to 0, and M of near-by felt earthquakes are about 4-5, we have an equation,
log N=3.6-0.77M,
where N is the annual number of earthquakes whose M are between M-0.5 and M+0.5. This equation holds good in the relation between N and M of earthquakes with M from -1 to 5 occurring in the vicinity of Matsushiro (area≈60×60kmkm2).
As the equation is valid in such a wide range of M, it will be possible to determine the seismicity of a certain region within a rather short period of time through observing microearthquakes.
The E of the minimal recorded earthquake was about 109ergs in this experiment. Its M was approximately -2.
