Scientists confirm a rare type of earthquake thought impossible

In the early hours of February 24, 1979, seismographs at the University of Utah picked up an earthquake beneath a small town called Randolph, near the Idaho and Wyoming borders. It registered magnitude 3.8 – substantial enough that people should have felt it. Nobody did. And when a young postdoctoral researcher named George Zandt looked more closely at the data, he found out why: the earthquake had originated 90 kilometers below sea level. It did not originate in the crust, but deep in the upper mantle – where earthquakes simply aren’t supposed to happen.

Scientists confirm a rare type of earthquake thought impossible. In the early hours of February 24, 1979, seismographs at the University of Utah picked up an earthquake beneath a small town called Randolph, near the Idaho and Wyoming borders. It registered magnitude 3.8 – substantial enough that people should have felt it. Nobody did. And when a young postdoctoral researcher named George Zandt looked more closely at the data, he found out why: the earthquake had originated 90 kilometers below sea level. It did not originate in the crust, but deep in the upper mantle – where earthquakes simply aren’t supposed to happen. “The deep depth explained why it wasn’t felt by people at the surface,” Zandt said. “I did some other analysis that convinced me of the reality of the deep depth but it was hard to convince others of the highly anomalous ma...