We were jolted by a large earthquake very early Friday morning. The temblor hit at 1:04 a.m. and was centered near Borrego Springs, about 17 miles south of us.
There was an initial shock, followed by shaking that increased to a second large jolt. The shaking gradually tapered off after that. The entire quake lasted for about 35 seconds or so and was accompanied by a loud sound, sort of like a rumbling. We did not notice the aftershocks that occurred after the initial quake.
CREDITS: Both of the maps below are from the USGS web site www.USGS.gov
Here in the Golden State, small earthquakes are not unusual and occur often. Most of them are not even noticeable.
This one registered 5.2 on the Richter scale, and was definitely big enough to notice.
The Coachella Valley region is bordered and criss-crossed by a number of fault lines and shear zones, including the San Jacinto Fault Zone where this earthquake occurred. As a result, there are signs of geologic activity all around.
South of us at the Salton Sea there are boiling, bubbling pots of mud that break through a thin part of the earth's surface to form mini "volcanos" up to 6 feet high. The area has a number of geothermal plants that are piping super heated brine steam to the surface, and using it to boil water that spins turbines to generate electricity.
The famous San Andreas Fault starts at the Salton Sea and runs north and east through our valley. The fault zone continues in a northerly direction through California for over 800 miles and exits the state near Mendocino, north of San Francisco. The San Andreas is the dividing line between the Pacific Plate and the North American Plate, two huge sections of the earth's crust that are grinding past each other at the average rate of a fingernail's growth - about 2-1/2" a year. This is not a continuous motion, and sometimes there are snaps and jolts which we feel as earthquakes.
The mountains along the north side of the valley were created by this strike-slip motion. And at the foot of these mountains is a line of palm oases. Rain water and ground water are forced to the surface between the two tectonic plates, and this provides the constant moisture that palm trees need to flourish. If you drive along Interstate 10 in this area and look to the north, the palm oases are visible as dotted lines of green.
We did a walk through of our house after the quake, and there was no damage. Only one mirror had been knocked very slightly askew. Each earthquake has its own "personality", and as long-time California residents we have experienced a variety of quakes that rolled gently like being on a boat, others that rattled and shook, and some that were a series of sharp jolts.
When a larger earthquake does hit, there is always the question while the shaking is happening... is this going to be The Big One? Our southern section of the San Andreas Fault historically ruptures approximately every 150 years or so. Right now, we are 300 years overdue.
"Opinion has caused more trouble on this little earth than plagues or earthquakes."