Many people draw their own conclusions about earthquakes based upon a very few occasions that stand out in their memory. These oversimplified observations are akin to the comment that "the phone always rings when you're in the shower". This isn't really true, but since people only tend to note the events that fit a certain pattern and forget about the mundane ones, it has a "ring" of truth. To avoid creating or supporting similar myths about seismicity, it's important that we not only consider all the appropriate data (in the example above, all showers and phone calls, not just those that coincide), but that we have enough data to reach an accurate conclusion. Otherwise, chance or bias can influence that end result.
One currently popular myth about the timing of earthquakes in southern California is that big earthquakes always happen in the morning. This is primarily due to the fact that most people only remember the last few large earthquakes that have occurred, perhaps just from the past decade. Farther back in time than that, their knowledge of when earthquakes happened is less complete. Since two of the most recent damaging earthquakes, Landers and Northridge, struck in the morning hours, many people now have the impression that big earthquakes will always happen in the morning. But were those same people alive in 1941, it's possible they'd think big earthquakes happen only in the evening, since the two most destructive earthquake prior to that time were the Long Beach and Imperial Valley earthquakes, both of which struck in the evening hours.
What other problems might you find while making these kinds of comparisons? The activity below should get you thinking about the pitfalls you may run into while attempting to draw conclusions from seismological data about what factors, if any, can influence the distribution of earthquakes in time.
Is Earthquake Timing Influenced?
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In comparing earthquake records to various factors,
can you find a connection? |
It's difficult for people to admit that the timing of earthquakes is something complex and potentially beyond our ability to anticipate. That's why myths develop so easily -- we want them to be true, because we want to feel like we have some control or understanding of earthquakes, to make them less terrifying. The truth is that we are only beginning to understand what influences the occurrence of earthquakes. And despite the fact that we are making gains in our knowledge, we still have a long way to go.
