High frequency seismic observation at the borehole which reaches an earthquake fault

在1984年日本长野县西部地震断层的钻孔上安装了三个自测仪组件。在频率响应高达1 kHz、动态范围宽达96分贝的观测系统上记录了大量的微震记录，发现微震P波的起始时间比通常的地震台和观测系统探测到的要早得多，说明微震P波的初始上升是相当平稳的，在时间上不起斜坡作用。这一事实不同于以往发表的许多理论所预测的结果，推测在破裂发展初期，微震的震源过程是相当缓慢的。这一缓慢的过程可能包含了断裂生长的关键。

Three components of selsmometers were installed at the borehole which reached the earthquake fault of the 1984 Western Nagano Prefecture, Japan Eartqhauke. A lot of seismograms from microearthqaukes were recorded the observation system which had a frequency response up to 1 kHz and a wide dynamic range of 96 dB.It is found that the onset of P-waves from microeartqhaukes arrives much earlier than that detected with a usual seismic station and observation system.It is made clear that the initial rise of P-waves of microearthquakes is fairly smooth and that it does not act as a ramp in time. This fact is different from that predicted by a lot of theories which had been previously published.It is deduced that the source process of microeathquakes is fairly slow at the beginning of rupture growth. It is possible that this slow process includes the key for the rupture growth.