There have been more than a hundred aftershocks since Friday's magnitude 5.1 quake in the La Habra area, and while these lesser jolts can be unnerving, they also help geologists map the fault responsible for the shaking, says Kate Hutton with the U.S. Geological Survey.
"The aftershocks occur along where the fault rupture was," Hutton said.
Each aftershock is logged on a map, and by drawing a line through them, a picture of the larger fault emerges.
In this case, Hutton said, it's becoming clear Friday's quake did not occur on the potentially dangerous Puente Hills Thrust Fault that runs under downtown Los Angeles. But the fault responsible was close by, she said.
"It’s perpendicular, more or less, from the Puente Hills fault," she said.
Like many of the smaller faults in the region, Hutton said this new fault doesn’t appear to have been mapped yet.
If the quake ruptured to the surface, Hutton said her team could trace it much more accurately.
She said seismologists will continue gathering evidence on this new fault over the next few days.