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观测结果表明,主震之前呈现异常b值。即将来临的主震前b值异常时间与主震震级有关,关系式为log(T)=q+rM,式中q和r为两个常数。本研究将解释这个关系式的内涵。此外,还将探索主震前形成b值异常的机制。根据基于Knopoff-Burridge弹簧—滑块模型的数值模拟结果,Wang(1995)发现b与s之间存在幂律关系,其中参数s是两个滑块之间的弹簧常数(K)和滑块与移动板块之间的常数(L)的比值。累积频度的幂律关系式为b~s~(-2/3),离散频度的关系式为b~s-1/2。因为震源区的L值在很长时段内几乎是常数,所以b直接与K有关。较小(较大)的K导致了较高(较低)的b值。Wang(2012)发现K=ρAV_P~2,式中ρA和VP分别是断裂带的面密度和P波速度。试验结果表明,VP受岩石中含水饱和度的严重影响。由于震源区内含水饱和度随时间而变化,所以VP及K也随时间变化。因此导致了b值也随时间而变化。
The observation shows that the abnormal b value is presented before the main shock. The forthcoming anomalous b-value anomaly before the main shock is related to the mainshock magnitude, and the relation is log (T) = q + rM, where q and r are two constants. This study will explain the meaning of this relationship. In addition, we will also explore the mechanism for the formation of abnormal b values before the main shock. According to the numerical simulation results based on the Knopoff-Burridge spring-slider model, Wang (1995) found that there exists a power law relationship between b and s, where the parameter s is the spring constant (K) between two sliders and The ratio of the constant (L) between moving plates. The power law of the cumulative frequency is b ~ s ~ (-2/3) and the discrete frequency is b ~ s ~ 1/2. Since the value of L in the source region is almost constant over a long period of time, b is directly related to K. A smaller (larger) K leads to a higher (lower) b value. Wang (2012) found that K = ρAV_P ~ 2, where ρA and VP are the areal density and P-wave velocity of the fault zone, respectively. The experimental results show that VP is severely affected by the water saturation in the rock. As the water saturation in the source area changes with time, VP and K also change with time. As a result, the b value also changes over time.