Physics Department, Solid State Section and Solid Earth Physics Institute, University of Athens, 157 84 Athens, Greece.
Proc Natl Acad Sci U S A. 2013 Aug 20;110(34):13734-8. doi: 10.1073/pnas.1312740110. Epub 2013 Aug 5.
It has been shown that some dynamic features hidden in the time series of complex systems can be uncovered if we analyze them in a time domain called natural time χ. The order parameter of seismicity introduced in this time domain is the variance of χ weighted for normalized energy of each earthquake. Here, we analyze the Japan seismic catalog in natural time from January 1, 1984 to March 11, 2011, the day of the M9 Tohoku earthquake, by considering a sliding natural time window of fixed length comprised of the number of events that would occur in a few months. We find that the fluctuations of the order parameter of seismicity exhibit distinct minima a few months before all of the shallow earthquakes of magnitude 7.6 or larger that occurred during this 27-y period in the Japanese area. Among the minima, the minimum before the M9 Tohoku earthquake was the deepest. It appears that there are two kinds of minima, namely precursory and nonprecursory, to large earthquakes.
已有研究表明，如果我们在自然时间 χ 域中对复杂系统的时间序列进行分析，就可以揭示出其中隐藏的一些动态特征。在这个时间域中引入的地震活动性序参量是 χ 的方差，加权为每个地震的归一化能量。在这里，我们通过考虑一个由几个月内发生的事件数量组成的固定长度滑动自然时间窗口，来分析 1984 年 1 月 1 日至 2011 年 3 月 11 日（即 9 级东日本大地震发生的那一天）的日本地震目录。我们发现，在日本地区这段 27 年期间发生的所有震级为 7.6 级或更大的浅层地震之前的几个月，地震活动性序参量的波动会出现明显的极小值。在这些极小值中，9 级东日本大地震之前的极小值是最深的。看来，大地震之前存在两种类型的极小值，即前兆性极小值和非前兆性极小值。
