## 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.

1. Where did the seismicity begin?
Seismicity began in the upper east rift zone near Makaopuhi Crater.

2. In what direction did the seismicity migrate?
Seismicity migrated down rift to the east.

3. 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.

4. 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.

5. When does seismicity begin at the summit?
After the onset of the eruption on January 3.

6. 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.

7. 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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