Monitoring Volcano Seismicity
Moving Magma and Volcanic Fluids Trigger Earthquakes
Earthquake activity beneath a volcano almost always increases before an eruption because magma and volcanic gas must first force their way up through shallow underground fractures and passageways. When magma and volcanic gases or fluids move, they will either cause rocks to break or cracks to vibrate. When rocks break high-frequency earthquakes are triggered. However, when cracks vibrate either low-frequency earthquakes or a continuous shaking called volcanic tremor is triggered.
Most volcanic-related earthquakes are less than a magnitude 2 or 3 and occur less than 10 km beneath a volcano. The earthquakes tend to occur in swarms consisting of dozens to hundreds of events. During such periods of heightened earthquake activity, scientists work around the clock to detect subtle and significant variations in the type and intensity of seismic activity and to determine when an eruption is occurring, especially when a volcano cannot be directly observed.
Networks of Seismometers are Needed to Monitor Volcanoes
A seismometer is an instrument that measures ground vibrations caused by a variety of processes, primarily earthquakes. To keep track of a volcano’s changing earthquake activity, we typically must install between 4 and 8 seismometers within about 20 km of a volcano's vent, with several located on the volcano itself. Seismic networks are made up of several instruments. Having enough of the right instruments located in strategic places is especially important for detecting earthquakes smaller than magnitude 1 or 2; sometimes, these tiny earthquakes represent the only indication that a volcano is becoming restless. If a seismometer is located more than 50 km away, these tiny earthquakes could go undetected.
Advances in Volcano Seismology Lead to Better Eruption Warnings
Dramatic improvements in computer technology and increased scientific experience with volcano seismicity from around the world have improved our ability to provide eruption warnings and to characterize eruptions in progress. New technologies have enabled us to locate earthquakes beneath a volcano faster and with greater accuracy than we could in the past. We can determine in real time the changing character of a volcano's earthquake activity. And we can better “map“ subsurface structures such as fault zones and magma reservoirs.
More About Volcano Seismicity
- Earthquakes and other ground vibrations "write" unique seismic signatures
- Current earthquake activity beneath selected volcanoes
- Magnitude 7.2 earthquake on November 29, 1975, on the Island of Hawai`i triggers a tsunami, remarkable ground movement, and an eruption in the summit caldera of Kilauea Volcano.
