Abstract

The issue of whether tidal forces really affect seismicity has been raised many times in the literature. Nevertheless, even though there seems to be a kind of consensus that such effects do exist, no quantitative estimates are available to relate tide parameters to changes in the level of seismic activity. Such estimation for aftershocks of large earthquakes near Kamchatka is the goal of the present study. We consider the influence on seismicity due to ocean tides only, because their effects are stronger than those of solid earth tides. Accordingly, we only consider earthquakes that occurred in the ocean. One important feature that distinguishes the present study from most other such research consists in the fact that we study the height of ocean tides and its derivative rather than tidal phases as the decisive factors. We considered 16 aftershock sequences of earthquakes near Kamchatka with magnitudes of 6 or greater. We also examined shallow background earthquakes along the coast of Kamchatka. Our basic model of aftershock rate was the Omori–Utsu law. The background seismicity distribution was assumed to be uniform over time. In both of these cases we used the actual distributions in space. The heights of sea tides were estimated using the FES 2004 model (Lyard et al., 2006). The variation in activity from what the basic model assumes in relation to tidal wave height and its time derivative was estimated by the method of differential probability gain. The main practical result of this study consists in estimates of averaged differential probability gain functions for aftershock rate with respect to both of the considered factors. These estimates can be used for earthquake hazard assessment from aftershocks with ocean tides incorporated. The results of our analysis show a persistent tendency of aftershock rate increasing during periods when the ocean tide decreased at a high rate. For the background events, we found a typical tendency of events rate increasing when the ocean tide decreased with high tidal amplitudes. The difference in the main factors that affect aftershocks and background seismicity suggest the inference that the effects of tides on aftershocks are more likely to be direct dynamic initiation of events during high strain rates, while the effects on the background events were static in character.

中文翻译：

---

潮汐对余震活动影响的定量估计：堪察加半岛

摘要

文献中已经多次提出了潮汐力是否真正影响地震活动的问题。但是，即使似乎确实存在这样的影响，也没有定量的估计可将潮汐参数与地震活动水平的变化联系起来。堪察加半岛附近大地震余震的这种估算是本研究的目标。我们仅考虑海洋潮汐对地震活动的影响，因为它们的影响要比固体地球潮汐的影响强。因此，我们仅考虑海洋中发生的地震。使本研究与大多数其他此类研究区别开来的一个重要特征在于，我们研究洋潮的高度及其派生而不是潮汐期是决定性因素。我们考虑了堪察加附近16级以上6级以上地震的余震序列。我们还研究了堪察加半岛沿岸的浅背景地震。我们的余震发生率的基本模型是大森－宇津法则。假定背景地震活动性分布随时间变化是均匀的。在这两种情况下，我们都使用了实际的空间分布。使用FES 2004模型（Lyard等，2006）估算了海潮高度。通过微分概率增益的方法估算了基本模型所假设的活动变化与潮汐高度及其时间导数的关系。这项研究的主要实际结果是针对两个考虑因素，估计了余震率的平均微分概率增益函数。这些估计值可用于包含海潮的余震的地震危险评估。我们的分析结果表明，当海潮以高速率下降时，余震率呈持续上升趋势。对于背景事件，我们发现当潮汐以高潮幅减小时，事件发生率增加的典型趋势。影响余震和背景地震活动性的主要因素的差异表明，在高应变率下，潮汐对余震的影响更可能是事件的直接动态引发，而对背景地震的影响则是静态的。我们的分析结果表明，当海潮以高速率下降时，余震率呈持续上升趋势。对于背景事件，我们发现当潮汐以高潮幅减小时，事件发生率增加的典型趋势。影响余震和背景地震活动性的主要因素的差异表明，在高应变率下，潮汐对余震的影响更可能是事件的直接动态引发，而对背景地震的影响则是静态的。我们的分析结果表明，当海潮以高速率下降时，余震率呈持续上升趋势。对于背景事件，我们发现当潮汐以高潮幅减小时，事件发生率增加的典型趋势。影响余震和背景地震活动性的主要因素的差异表明，在高应变率下，潮汐对余震的影响更可能是事件的直接动态引发，而对背景地震的影响则是静态的。