Interpreting the Distribution of Earthquakes (Grades 7-8)
The movement of magma can be tracked by mapping the distribution of
earthquakes. Earthquakes can precede an eruption by years, months, days,
and, in a few cases, hours. Activity 14 shows the migration of
epicenters preceding and accompanying dike emplacement and the onset of
the current eruption of Kilauea Volcano in January 1983. Students must
interpret the distribution of the earthquakes to answer the following
questions.
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for a copy of Activity 6.
- Where did the seismicity begin?
Seismicity began in the upper east rift zone near Makaopuhi Crater.
- In what direction did the seismicity migrate?
Seismicity migrated down rift to the east.
- How do you interpret the seismic patterns for 00 hours on
January 1 to 00 hours on January 3?
The pattern suggests intrusion and migration of a dike of magma to the east.
- How do you interpret the seismic patterns for 00 hours on
January 3 to 00 hours on January 8?
The seismic patterns are due to continued intrusion of magma and the
start of the eruption.
- When does seismicity begin at the summit?
After the onset of the eruption on January 3.
- How do you interpret the seismicity at the summit?
The seismicity at the summit suggests deflation and the migration of
magma down the rift, probably due to a decrease in pressure by the eruption.
- Based on the data presented in the graphs, outline the geologic
events preceding and accompanying the onset of the current
eruption.
- Magma migrates upward from a deeper part of the east rift zone near
Makaopuhi, causing a local swarm of low magnitude earthquakes.
- The magma forms a dike that migrates down the east rift zone. The
path of the dike is marked by the location of the earthquakes. The
number and magnitude of earthquakes increases.
- The dike continues to migrate down the east rift zone.
- The dike grows vertically until it reaches the surface and generates
an eruption. The summit responds to the decrease in pressure by
deflating and sending magma down the rift. Pressure exerted by magma in
the rift generates small earthquakes in the south flank of the volcano.
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