The city sits near a boundary between two tectonic plates – they shift, we shake. What about places that aren’t along tectonic plate boundaries?
Seismicity on the North American plate occurs as far afield as southern Missouri, where earthquakes between 1811 and 1812 estimated at around magnitude 7 caused the Mississippi River to flow backward for hours.
While earthquakes along tectonic plate boundaries are caused by motion between the plates, earthquakes away from fault lines are primarily driven by motion beneath the plates, according to a new study published by USC scientist Thorsten Becker in Nature on Aug. 27.
That convective process, interacting with the ever-changing motion of the plates at the surface, is driving intraplate seismicity and determining in large part where those earthquakes occur.
Previously, scientists had suggested that the varying density of the plates was the main cause.
“This study shows a direct link between deep convection and shallow earthquakes that we didn’t anticipate, and it charts a course for improved seismic hazard mapping in plate interiors,” said Tony Lowry, co-author of the paper and associate professor of geophysics and geodynamics at Utah State University.