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实验室和理论研究表明,地震之前会出现一个渐进性的滑动不稳定阶段,在此期间,断层缓慢滑动,而后突然加速并最终导致动态破裂。本文中,我们报道了迄今记录最为完整的大地震之一,即1999年土耳其Izmit MW7.6地震之前出现了持续时间很久的源自震源的地震信号。这种信号包含一连串的地震破裂,破裂随时间和低频地震噪声的增加而加速。这些观测结果表明,此次地震之前在脆性地壳底部出现了44min的缓慢滑动。滑动最初呈缓慢加速,然后在地震发生前2min内又突然加速。
Laboratory and theoretical studies show that a progressive slip instability occurs before the earthquake, during which time the fault slips slowly and then suddenly accelerates and finally leads to dynamic rupture. In this paper, we report one of the most complete large-scale earthquakes hitherto reported by the authors, namely the seismic signal originating from the source for a long time prior to the 1999 Izmit MW7.6 earthquake in Turkey. This signal contains a series of seismic ruptures, which are accelerated with the increase of time and low frequency seismic noise. These observations show that there was a slow slump of 44 minutes at the bottom of the brittle crust before the earthquake. Sliding initially accelerated slowly, then abruptly accelerated within 2 min of the earthquake.