Listening to Multiple Earthquakes

If you haven't done the Fault Length Effects and Distance Effects topics yet, you should do them first.

After the 1992 Landers earthquake in southern California many areas around the western United States experienced increased numbers of small earthquakes. Here is a seismogram recorded at the Long Valley Caldera, a volcanic center near Mammoth Lakes, California, which was one of the areas that had a large number of triggered earthquakes.

Landers seismogram

In this seismogram the earliest triggered events we can see are several minutes after the shaking from the mainshock arrives. But there could be earlier events that we can't see because they are covered up by the shaking of the mainshock.

It may be easier to hear the small triggered earthquakes than it is to see them. The Landers earthquake is far from the seismometer so most of its high frequencies have died away before the waves reach the seismometer. But the small earthquakes have small fault areas and therefore produced high frequency energy and because they are near the seismometer this energy has not died away.

Landers geometry

Listen to the seismogram recorded at the Long Valley Caldera and see if you can hear the small earthquakes (high frequency bursts) despite the low rumble of the distant large earthquake. Click the sideways triangle (or play button) to hear the sound.

If you are having trouble picking out the small nearby earthquakes, listen for the two very close to the end and then listen to the seismogram again.

Listen to the seismogram recorded at the Long Valley Caldera and see if you can hear the small earthquakes (high frequency bursts) despite the low rumble of the distant large earthquake. Click the sideways triangle (or play button) to hear the sound.

Long Valley Caldera Seismogram

If you are having trouble picking out the small nearby earthquakes, listen for the two very close to the end and then listen to the seismogram again.


Here are two more seismograms of the Landers earthquake. One is recorded at Parkfield near Paso Robles and the other is recorded at the Geysers north of San Francisco. Only one of these areas had small earthquakes triggered by the Landers event. Can you tell which one?

Parkfield Seismogram

Geysers Seismogram

Which area had small triggered earthquakes: Parkfield or the Geyers?

Location Map