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实验和理论研究表明,地震发生之前存在断层失稳扩展阶段,在此过程中断层缓慢滑动直至加速至动态破裂。本文研究的地震是迄今为止记录最好的大震之一,即1999年土耳其伊兹米特MW7.6地震。此次地震之前出现了源于震源的地震信号,并持续了较长时间。这些信号由一连串随时间不断加速的重复地震的爆发和逐渐增加的低频地震噪声组成。结果表明,在地震发生前的44min里,脆性地壳的底部存在着缓慢滑动阶段。起初滑动加速非常缓慢,但在震前2min内迅速加速。
Experiments and theoretical studies show that there is a fault-failure propagation stage before the earthquake, during which the fault slips slowly until it accelerates to dynamic fracture. The earthquake studied in this paper is one of the best-recorded large earthquakes so far, namely the Izmit MW7.6 earthquake in Turkey in 1999. Earthquake signals originating from the source appeared before the earthquake and lasted for a long time. These signals consist of a series of repeated seismic explosions that are accelerating over time and increasing low frequency seismic noise. The results show that there is a slow slip phase at the bottom of the brittle crust in 44 min before the earthquake. Sliding acceleration was slow at first, but quickly accelerated within 2 minutes before the earthquake.