Santa Barbara May Be at Greater Risk of a Major Earthquake and Tsunami, But It’s the Ventura Fault



05/10/2015 - 12:00am to 11:45pm


Jamison Steidl

Recent studies point to evidence of regional hazards, but wary officials cite community’s attention to tsunami readiness

By Lara Cooper, Noozhawk Staff Writer | @laraanncooper | 

A tsunami hazard zone sign at the Santa Barbara Harbor is part of the city’s readiness preparations. A recent geological study stated that the Ventura Fault, which passes under downtown Ventura and continues into the Santa Barbara Channel, connects with other faults in the area — a network that could cause larger earthquakes than previously thought, and have tsunami implications for coastal cities. (Lara Cooper / Noozhawk photo)

Recent studies that have linked the Ventura Fault to a network of nearby geological fault lines could have major earthquake and tsunami implications for Santa Barbara County’s coastal areas, including the possibility of a higher magnitude quake than previously thought likely.

The fault line that runs underneath downtown Ventura and then northwest through the Santa Barbara Channel adjacent to offshore Carpinteria and Santa Barbara is connected to other fault lines in the area, according to a paper published last year in the Bulletin of the Seismological Society of America.

The study states that the Ventura Fault connects with other regional faults, including the San Cayetano and Red Mountain faults. If the faults slipped at the same time, the impact could result in an earthquake with a magnitude as large as 8.“Because of local geography and geology, such events would be associated with significant ground-shaking amplification and regional tsunamis,” the paper states.  The paper says the last earthquake of such size struck what is now Ventura about 800 years ago.

UC Santa Barbara seismologist Jamie Steidl broke down some of the studies’ findings for Noozhawk, noting that the data suggest the South Coast could be at risk of large earthquakes that might rupture the length of the Santa Barbara Channel and “potentially generate a significant tsunami.”

Steidl said that the seismological community has known about the local hazard, and has always agreed that significant quakes are possible in the area.

What has changed is the length of the fault that is needed — and, thus, the magnitude of the earthquake — to support the new data that suggest there could be an uplift of 15 feet or more during a single quake, he said.

“Santa Barbara has recently been certified as tsunami-ready,” he said. “Hence the signs that denote tsunami evacuation routes, which if this new data is correct, might come in handy.”

Steidl said the evidence indicates there have been four of these type events in the last 10,000 years.

“I think that the more likely event is a magnitude 6 to 6.5 event under Santa Barbara or Ventura on this same fault system,” he said, close to what was experienced in the 1925 Santa Barbara earthquake and, more recently, in the 1994 Northridge earthquake.

That magnitude can cause a significant disruption to normal life, Steidl said, but he added that area residents should be ready at all times to face an earthquake.

“We need to be prepared regardless of if it’s a M6 event or a M8 event,” he said.

“The main differences between these two sizes of earthquakes is just the length of the fault that is rupturing, and thus the number of affected cities and people.”

An earthquake’s size is determined by measuring the energy released by the quake and assigning a magnitude number to quantify it.

Steidl said a larger earthquake could mean the potential for a larger tsunami, while a smaller quake would make a tsunami more focused in a smaller area.

Rick Wilson, of the California Geological Survey’s tsunami program, told Noozhawk that the tsunami inundation maps won’t be changed yet.

“The report on the Ventura Fault came out about a year ago, and we did do preliminary tsunami modeling that incorporated the data it contained to ensure our maps are useful,” he said, adding that no changes to the inundation maps are planned currently.

“Of course, our primary concern is the safety of coastal communities,” he said. “If additional new information becomes available, we certainly can incorporate that into our maps.”

Yolanda McGlinchey, manager of the City of Santa Barbara’s emergency services office, said the city got its tsunami maps in 2009 and officially became a “tsunami-ready” community in 2011.

At the time, California Geological Survey officials conducted a walk-through of the coastal area, she said.

Being “tsunami-ready” means that a plan is in place about how to best evacuate Santa Barbara’s waterfront area. The city also worked with several agencies to create the evacuation plan, including the California Highway Patrol, county agencies and the American Red Cross Santa Barbara County.

McGlinchey said the city gets a chance to practice a large-scale “evacuation” every Fourth of July, when tens of thousands of people descend on the waterfront area for the fireworks show — and then leave all at once when it’s over.

The National Weather Service maintains offshore buoys that measure sea rise and fall, which generate estimate times of when wave action would reach the area, McGlinchey said, giving people warning time to evacuate.

She said Santa Barbara’s community plan will be updated again in 2016.