Geotimes: Earthquake Predictions

September 2002 — Web Extra, Wednesday, September 18

Izu Islands' Stresses

During the summer of 2000, more than 7,000 earthquakes rumbled beneath the Pacific Ocean, 75 miles south of Tokyo amidst the Izu Islands volcanic chain. One of the most dense networks of GPS receivers and seismometers in the world registered each centimeter of earth shifting and shaking.

A team of geophysicists capitalized on this rich data set to test a theory about what causes earthquakes, especially prolonged swarms associated with volcanism. Their results, published in Nature on September 5, 2002, helped validate Jim Dieterich's 1994 seismicity-rate theory.

The findings show that earthquake frequencies increase as stress rates on the Earth's crust increase.

Dieterich's theory proposed that the rate of earthquake nucleation is controlled by the rate at which stress accumulates on faults. The Izu Islands swarm provided a rare natural laboratory: a concentrated burst of seismicity captured by dense instrumentation, allowing researchers to correlate stress-rate changes with earthquake frequency in near real time.

The validation carried implications beyond volcanic settings. If seismicity rates respond predictably to stress changes, the same physics could inform hazard assessments in tectonic environments worldwide — a line of inquiry that continues to shape USGS research on earthquake probability modeling.