Earthquakes were the subject at the Mountain Emergency Services Committee meeting held last Thursday at the Idyllwild Library. Dr. Robert Michael Groot, education programs manager for the Southern California Earthquake Center, focused primarily on the San Jacinto Fault. He included historical data as well as forecast information concerning the probability of a major event that could impact Idyllwild and surrounding areas.
While the San Andreas Fault has always loomed large in the thoughts of many Southern California residents, according to Groot, the 1-million-year-old San Jacinto Fault poses more of a threat. “Something about the San Jacinto Fault that is very interesting is that the one thing we know is that the San Andreas has not had a major quake in this part of the fault in over 300 years but there have been many, many more earthquakes on the San Jacinto Fault.”
Over the years, the San Jacinto Fault has had significant earthquake activity: magnitude 7.3 in 1800, 6.5 in 1892, 6.6 in 1899, 6.6 in 1918, 6 in 1923, 5.9 in 1937, 6 in 1942, 6.2 in 1954, 6.4 in 1968, and two earthquakes, a 6.2 and 6.6, occurring within 11 hours of each other in 1987.
“In 2005, there were a couple of 4.9s and 5 in that range and a mag 4.7 last March in Anza. There will continue to be earthquakes on this fault,” said Groot.
Both faults, while given different names, behave in much the same way. Both are right-lateral, strike-slip faults, meaning that if two people were standing face to face with a fault line running between them, each of them would move to the right.
Some scientists believe the increased activity on the San Jacinto Fault may be having an impact on the San Andreas Fault. “There’s this whole notion that the San Andreas [Fault] may be trying to straighten itself out by essentially having most of the earthquakes or most of the motion going on along the San Jacinto Fault … San Jacinto actually goes all the way through this region up through Hemet, San Jacinto, up into Redlands and San Bernardino. It doesn’t necessarily connect with the San Andreas but it is very close to the San Andreas in the Cajon Pass. It may be nature’s attempt to straighten it out,” explained Groot.
The Uniform California Earthquake Rupture Forecast indicates there is a significant chance that Southern California will have a major quake sometime in the next 30 years. “According to the new forecast, California has a 99.7 percent chance of having a magnitude 6.7 or larger earthquake during the next 30 years. The likelihood of an even more powerful quake of magnitude 7.5 or greater in the next 30 years is 46 percent. Such a quake is more likely to occur in the southern half of the state (37 percent) than in the northern half (15 percent),” he said.
Being prepared is the key to surviving and recovering from a major earthquake. At 10:17 a.m. Thursday, Oct. 17, Californians will be asked to participate in the Great California Shakeout. “Drop, cover and hold-on” is the message and more than 8 million registered participants will take part in a series of drills to be held throughout California. For more information or to register, visit www.shakeout.org.
“A lot of the current recommendations come from real experiences so if you’re in an earthquake and you’re in bed, stay in bed; getting out of bed you’ll probably end up hurting yourself. The doorway is no more safe than anywhere else in the house and it comes from an older idea that in adobe-built structures the doorway was one of the most stable places. You’re not going to be able to drop, cover and hold on all the time. If you have the opportunity to get underneath something, you want to protect your body,” said Groot.
Mountain Disaster Preparedness is planning an “all hands on deck” drill set for Saturday, Oct 19. Certified Emergency Response Teams, will be mobilized, as well as the MDP Medical Group, Mile High Radio Club and the Woodies. The groups will go through a real-case scenarios at each Disaster Aid Station unit. For more information, visit www.mdp-idyllwild.com.
Groot is pleased that MDP is planning its drill just two days after the shakeout, but still encourages participation in the Oct. 17 drill. “I know that folks are planning things for Saturday [Oct. 19] and I think that is perfectly OK, it’s just that the psychological component of doing the shakeout all on the same day with everyone … turns into a conversation,” said Groot. “It’s something that we engage in together. I see my friends doing it and we are all learning to be prepared. We’re going to be able to take care of each other after this,” Groot added.