There was only one earthquake greater than magnitude 1.0 in the past week in the area of the quake swarm in northwest Arizona until Saturday night when a magnitude 3.7 event struck just after 9 p.m. local time, followed by three apparent aftershocks in less than an hour. The main event is the largest one yet in the swarm of the past few weeks, surpassing the previous one of M=2.7. [Right, orange star marks the epicenter of the M=3.7 quake, with contours showing distribution of shaking. Red lines are active faults. Credit, USGS]
There are reports of the earthquake being felt in the sparsely populated region.
[Below, magnitudes, location, and time of Saturday night quakes in the swarm area.]