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Volcano's Deadly Warning

Seismic Signals


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Hybrid image  

Hybrid Event

Sometimes a volcano-tectonic (VT) event triggers a long-period (LP) event, and vice versa. A seismic signal that contains a mixture of both types is called a hybrid.

This hybrid event is a VT event that triggered an LP event. Notice how the signal is bunched up more at the beginning than it is later on. The first part of this signal shows the VT event; later, the less-bunched (lower frequency) signal of the LP event appears.


Hybrid seismograph image

Because LP events often begin with signals that look very similar to those at the beginning of a hybrid, it is usually difficult for seismologists to distinguish between the two.

To tell one from the other, seismologists look closely at several seismograms of a single event, as recorded by seismographs placed at various locations. If the first part of the signal looks similar on all of the seismograms, they probably have an LP event.

Volcano-Tectonic Event | Long Period Event | Tremor | Hybrid


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