Earthquake Measurements

EARTHQUAKE MEASUREMENTS

Measuring earthquakes is important to understanding what is happening to the earth's crust. It also helps to construct infrastructure and buildings that will withstand potential future earthquakes.

There are parts of California that are basically shaking continually. Most people don't feel anything at all. Historically, the magnitude of an earthquake was only based on measurement of the seismogram. Nowadays, the magnitude is adjusted to account for the damage the earthquake does in general as well as the seismographic report.

There is a worldwide network of seismographs that can say when and where there is seismic activity. The graph is digital and plotted over time. Figure 49 shows what a seismogram reading looks like:

Figure 49.

There will be background waves over time so that you won't ever see a flat line. You see these from nearby traffic or from wind activity. These are very sensitive machines after all. There are tiny dots or marks to indicate each minute. These are necessary because each seismogram is different.

There are different kinds of waves, broadly categorized as body waves and surface waves. Body waves will go through the "body" of the earth. You can have P waves,