How can seismology be used to detect and map the presence of magma chambers beneath Kilauea Volcano?
The Hawaiian Volcano Observatory operates an array of seismometers
over the surface of Kilauea which allows them to locate earthquakes
beneath and within the body of the volcano. Earthquakes define a
conduit which rises from 60 km depth to about 5 km below the
volcano's summit where there is a large diffuse area with only very
small earthquakes. This diffuse zone is inferred to be the magma
chamber. Earthquakes also define dike intrusion zones which extend
down the southwest and east rifts of the volcano.
With a lot of earthquakes and a lot of stations, it is possible also
to determine the rough three-dimensional seismic velocity structure
of the volcano. As you might expect, the feeder conduit, the magma
chamber, and the axes of the rift zones all show lower velocities,
indicating the presence of magma.
Active seismology (setting off explosive charges and listening) could
be used to refine our models of Kilauea's structure, but little such
work has been done for two reasons. First, the area is
environmentally sensitive (it is a National Park); second, the
attenuation is so high that large charge size is needed to see more
than about ten kilometers. Natural sources (earthquakes) are abundant
and work almost as well.
Dr. Gerard Fryer
Hawaii Inst. of Geophysics & Planetology
University of Hawaii, Honolulu, HI 96822
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