California State Route 178, southwest of Trona, following the 7.1 magnitude earthquake Friday, July 5. The road is now closed for repairs. 
Photo courtesy of the U.S. Geological Survey

After a year in which two natural disasters — fire and floods — have threatened the hill and disrupted living patterns, the Fourth of July and the evening of July 5 raised concerns of a third disaster, earthquakes.

While Idyllwild only experienced the tremors from two distance quakes to the north, Ridgecrest — near the Mojave Desert and just east of the Sequoia National Forest — experienced two earthquakes greater than 6.4 in magnitude. Both were felt as far south as San Diego.

The first occurred about 10:30 a.m. on July 4 during Idyllwild’s Fourth of July Parade. Most parade spectators only detected it after reading news bulletins on their cell phones.

This map shows the intensity of the Friday evening quake and how far it was felt from Ridgecrest. 
Map courtesy of the U.S. Geological Survey

However, the second quake was at about 8:20 p.m. on Friday, July 5 and many local residents felt their floors quivers, the walls stretch and heard the vibration. No local damage or injuries occurred.

The second quake was measured at 7.1 magnitude. The damage around Ridgecrest was reported as much greater than Thursday’s quake.

On Saturday, U.S. Geological Survey (USGS) Seismologist Dr. Lucy Jones wrote on Twitter that there was a 10% chance that Searles Valley, the actual site of the two quakes, would experience another earthquake greater than 7.0.

But she calmly added, “That is a nine in 10 chance that tonight’s magnitude 7.1 was the largest.”

No crack was apparent in this driveway on the hill before the 7.1 magnitude Ridgecrest earthquake Friday, July 5.  Photo by Jenny Kirchner

Looking into the future Jones wrote, “Like any quake, today’s magnitude 7.1 has a one in 20 of being followed by something even bigger. Smaller quakes – magnitude 5s are likely and a magnitude 6 is quite possible.”

After Friday’s 7.1 magnitude quake, three quakes greater than 5.0 magnitude occurred in the Ridgecrest Little Lake area in a 16-hour period. Twelve greater than 4.5 magnitude shook the area and another 22 between 4.0 and 4.5 magnitudes were recorded. 

A total of more than 270 quakes occurred in Southern California during that period. In total, thousands of quakes in magnitude from less than one to over five have occurred since the first 6.4 magnitude quake on Thursday.

“The number of aftershocks goes down with time, but not the magnitudes! The ratio of large to small quakes is constant,” Jones wrote on Twitter. “The big ones just become much less frequent. Large, late aftershocks show up in most sequences. The last magnitude 5 aftershock to 1994 Northridge was in 1997.”

Saturday morning, the USGS posted the following probabilities: “The chance of an earthquake of magnitude 6 or higher is 27%, and it is most likely that as few as zero or as many as two such earthquakes may occur... The chance of an earthquake of magnitude 7 or higher is 3%, such an earthquake is possible but with a low probability.”

By the afternoon on July 4, Gov. Gavin Newsom had declared a state of emergency for the Ridgecrest area. Shortly after midnight Saturday, he issued a state of emergency for all of San Bernardino County and wrote President Donald Trump requesting federal assistance for Kern and San Bernardino counties.

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