Earthquake Prediction and Forecasting
There are two approaches to predicting earthquakes.
Historical Patterns and Gap analysis
Why historical patterns work
The basic idea behind using historical patterns is that faults tend to have a repeated and regular history of earthquakes, particularly, that earthquakes tend to occur at regular intervals or with definite patterns in a fault or a system of faults. Therefore, if enough is known about the history of a fault then something can be said for the future of the fault system. Such predictions are not good for pinpointing a time, a day, or even a year that a major event will happen, but they can give us an idea of how likely it is that a major earthquake might occur during the next 30 years.
The relationship between frequency and size
Given that earthquakes represent the release of built up tectonic stresses, it follows that smaller earthquakes occur more often and that larger earthquakes are less frequent. Summarizing:
Looking for Seismic gaps.
Based on the above relationship, a section of fault that has not produced
a significant amount of smaller earthquakes is a likely candidate for
a large earthquake. By mapping the occurrences of smaller earthquakes
we can recognize these seismic gaps, and tag areas as likely to
experience large quakes.
A related approach is to take a long history of fault motions and try to derive a characteristic period. once it is determined that a segment of fault moves more or less every 200 years, and that the last movement was 220 years ago, you can predict another earthquake is likely to occur soon.
The data for such a study must frequently be found by digging trenches
across fault lines.
This field is currently on less firm footing than historical analyses,
but ultimately, it would be desirable to be able to actually see an earthquake
coming by looking at events that occur before an earthquake.
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