Saturday’s magnitude 7.1 earthquake near Ridgecrest, California, was nothing to sneeze at. The shake, which triggered gas leaks, power outages, and fires, was felt from San Diego to Sacramento. And it ripped open a new fissure in the Earth that didn’t escape the notice of humanity’s ever-growing satellite fleet.
Before-and-after imagery captured by Planet Labs Inc. on July 4 and 6, respectively, shows a gash appearing in the ground roughly 16km northeast of Ridgecrest, California, pretty much exactly above the location of the magnitude 7.1 quake.
The shake, which occurred at 8:19pm local time on Friday, July 5 (1:19pm Saturday, July 6 AEST), is the largest quake to occur inside the state of California since 1999, according to the Los Angeles Times.
The United States Geological Survey (USGS) says the earthquake occurred at a depth of about 8 kilometres, and was the result of strike-slip faulting (plates grinding against each other in a roughly horizontal fashion) at a juncture of the Pacific and North American tectonic plates known as the Eastern California shear zone.
It’s part of a sequence of earthquakes that began rippling across the region last week and was preceded, less than 36 hours earlier, by a magnitude 6.4 foreshock on July 4.
Because of the logarithmic nature of the earthquake magnitude and energy scales, the July 5 quake released approximately 11 times more energy than its magnitude 6.4 predecessor. (It also released substantially more energy than the atomic bomb at Hiroshima, per this handy USGS graphic.)
It’s unsurprising, then, that the ground around the epicentre cracked up a bit, although it still speaks to the awesome power of the event that this is so clearly visible from orbit.
The sequence that these two quakes belong to now includes over 3000 earthquakes, according to CalTech seismologist Lucy Jones.
That includes more than 350 earthquakes of magnitude 3.0 or greater, which are strong enough to be felt, and five magnitude 5.0 or higher earthquakes which are capable of causing damage, according to the USGS. Aftershocks are on the decline but haven’t let up yet, with 55 to 120 magnitude 3.0 or greater anticipated over the coming week.
The USGS now places the chance of another earthquake of magnitude 7.0 or higher at just 1 in 100 – a small probability, to be sure, but then again Friday’s quake was a low probability event.