The unusual event prompted U.S. Geological Survey researcher Emily Montgomery-Brown and her colleagues to look back through 33 years of seismic and water records for the region. They found that rates of shallow seismicity were about 37 times higher during very wet periods versus dry periods. Although scientists have linked earthquakes to heavy rainfall or heavy runoff before this, the evidence connecting the two has been relatively weak or ambiguous, says Montgomery-Brown. In the Long Valley Caldera case, she says, “we’re seeing phenomenal correlation between the seismicity and the stream discharge, and we are seeing about 37 times the number of earthquakes during the wet season as during the dry season.”