Earthquake Prediction and Forecasting

There are two approaches to predicting earthquakes.

• Fist, you can look at the past history of a tectonic area and try to derive a pattern of occurrences from which you can predict future occurrences in a statistical way.
• Second, you can look at what happens as a fault zone builds energy toward an earthquake and try to recognize precursor events that can be used to pinpoint exactly when earthquakes are likely to happen.

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:

• Stress builds up over time, so the longer it builds, the bigger the quake
• Faults that are strong and resist motion produce few quakes, but they are  big quakes
• Faults that are weak produce many quakes, but they are small quakes.
• Many faults have there own characteristic frequency and consistently produce similar sized earthquakes at fairly regular intervals.

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.
 

Historical periodicity

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.

Precursor Events

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.
measures of stress and strain
Electrical

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