Rain slows seismic waves

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The recent occurrence of earthquakes and even heavy rainfall reduce the near-surface velocity of a type of seismic wave responsible for the worst damage during earthquakes.

Nori Nakata and Roel Snieder at the Colorado School of Mines in Golden studied these 'shear' waves using seismic interferometry, which measures how the waves propagate from depth to the surface. The authors analysed the average velocities of shear waves in nearly 112,000 quakes — most of them minor — recorded between 2000 and 2010 by Japan's network of seismic stations. They found that, three months after major earthquakes, wave velocities recorded at nearby stations were 3–4% lower than normal.

In southern Japan, shear-wave propagation was also slower during rainy summers than drier seasons, possibly because of the increase in fluid pressure that occurs when the ground is infiltrated by rainwater.

J. Geophys. Res. (2012)

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