Know Your Faults: The Whittier Fault

(This is an occasional series exploring the many earthquake fault lines in and around Southern California. This series is not intended to be a scholarly, scientific review of earthquake faults throughout Southern California, but hopefully will be a jumping off point for you to understand and further explore the fault lines that cross Southern California. )

BREA - Standing in the parking lot of the Brea Mall turning your head from the southeast to the north and slowly to the northwest you see vivid brown hills dotted with trees and homes lining the landscape. These hills provide a natural border between Orange County and the Inland Empire, and Orange and Los Angeles Counties. Like many of the hills and mountains that provide a majestic backdrop for Southern California there is a hidden danger in the hills, which resulted in the creation of these hills.

As geologists and seismologists have pointed out, anytime you see a hill or mountain in California chances are very good you are looking at an earthquake fault. If you are in Orange County looking at the hills above Brea, Yorba Linda and La Habra, or in the San Gabriel Valley checking out the hills that sort of parallel State Route 60, you are looking at the work of the Whittier Fault.

How Often Do Big Quakes Happen?

Like many earthquake faults in Southern California there are some things known about the Whittier Fault, but a lot that is not known about the fault. One of the most important things not known about this fault is the interval between major ruptures. What is known are United States Geological Survey studies showing the Whittier Fault is capable of producing an earthquake between 6 to 7.2 on the moment magnitude scale. 

What all that means is this, the USGS currently has no data on how often the Whittier Fault produces a major earthquake, and that is rather unfortunate, because that would give seismologists a rough forecast of when the next major quake may strike. 

About the only thing USGS knows about the last major earthquake on the Whittier Fault is that it occurred sometime in the last 10,000 years, otherwise known as the current Holocene era. As well, the slip rate is about 2.5 and 3.0 millimeters per year, according to USGS.

Where Is The Whittier Fault?

The fault line is a branch of the quiet giant Elsinore Fault, and going east-to west the fault begins just north of SR 91, up and above Gypsum Canyon Road at Bryant Ranch Park near Bryant Ranch Elementary School in Yorba Linda. Going in a west-northwest direction the Whittier Fault runs on the southwest section of Chino Hills State Park, crossing through Carbon Canyon Regional Park and crossing Carbon Canyon Road/Lambert Road. The fault continues to run in a northwest direction in the hills above Lambert Road and crossing very close to Brea Olinda High School, then crossing SR 57, crossing into the Humble Reservoir, crossing Brea Boulevard, and going in a more northwest direction into the hills above La Habra, crossing Harbor Blvd just south of Vantage Pointe Drive.

From that point the fault continues to run in a gentle northwest direction crossing "E" Road north of the Hacienda Golf Club into La Habra Heights, crossing Hacienda Road at about Skyline Drive going into Arroyo Pescadero Trail and then crossing Colima Road just south of Casino Drive. The Whittier Fault makes a more sudden northwest turn into Turnbull Canyon, crossing Turnbull Canyon Road/Beverly Blvd. and ending at Hellman Wilderness Park in the hills above Whittier.

Just How Bad Could A Big Quake Be?

A major rupture on the Whittier Fault could end up being a historic American disaster.

A scenario by USGS predicts that if a M6.8 occurred at 5 p.m. on the Whittier Fault there would be 9.450 injuries and fatalities, and predictions of building damage to be nearly $20 billion.


USGS Whittier Fault earthquake scenario map. Shown for educational and informational purposes only; no copyright infringement intended.

It is important to understand that anytime you get at or above a magnitude 6 that occurs in an urbanized area you begin to see structural damage, even in a place like Southern California, which is suppose to be "built" to withstand a major earthquake.

Also, remember that the Whittier Fault runs near several of Southern California's older neighborhoods and old downtown areas, such as Fullerton, Orange and Whittier, and a major event on the Whittier Fault could severely impact those places and older neighborhoods in the San Gabriel Valley. Depending on the dynamics of a major earthquake on the Whittier Fault it is certainly possible the old downtown areas of Pomona, Claremont and Ontario could see structural damage.

Again, depending of the dynamics of a major rupture on the Whittier Fault, it is very possible that even L.A. proper could see structural damage. 

What it comes down to is the Whittier Fault has the potential to cause major damage in the four county L.A. metro area.

Possible Major Freeway Damage

Let us not forget if there is a major rupture on the Whittier Fault that breaks on the surface the 57 freeway could see major damage. You add major damage on the Orange Freeway, along with possible major damage on the streets that connect L.A. and Orange Counties through the hills, and perhaps possible damage on the Riverside Freeway, you have the makings of a major commuter nightmare that could result in more economic losses. 

The 60 freeway, which seems to be the choice of truckers shipping goods from the Port of L.A. and Long Beach to the Inland Empire and points east, could also be structurally impacted by a major Whittier Fault event. It is not far fetch to say damage on the Pomona Freeway could reverberate throughout the nation.

Not At Fault

If you grew up in Southern California you probably remember the 1987 Whittier Narrows Earthquake, but it is worthy to note that earthquake was not on the Whittier Fault, but rather ruptured a small and previously unidentified, gently north-dipping,west-striking thrust fault, according to USGS. Seismologists originally thought this earthquake was caused by the Elysian Park Fault. 

Furthermore the somewhat recent 2008 Chino Hills Earthquake, which was the last magnitude 5-plus to occur in the L.A. basin, is not believed to be the work of the Whittier Fault nor Chino Fault.

What Can You Do?

All you can do is prepare. Prepare for the next major earthquake on whatever known or unknown fault it occurs on in Southern California.

No One Knows When!

At this time, and unfortunately probably for many years to come, there is no accurate way to predict when any earthquake is going to strike. The only earthquakes that can be predicted are aftershocks, and sometimes those can take geologists and seismologists by surprise.

Despite what any person or any group claims about predicting earthquakes at this time, quite frankly, there have been no proven concrete methods to accurately predict earthquakes.

The bottom line, you just need to prepare.

Knowing Your Faults: The Elsinore Fault

(This is the first in an occasional series exploring the many earthquake fault lines in and around Southern California.)

ALONG THE EASTERN EDGE OF THE CLEVELAND NATIONAL FOREST - Today, like everyday before and after, the Earth keeps spinning and tectonic plates keep slowly sliding by each other. In our part of the world it is the Pacific Plate slowly sliding north along the North American Plate, and sometimes the sliding and grinding of those two plates make its presence known in Southern California in the worst way possible.

(As the Pacific Plate slowly inches its way north in many millions of years from now Southern California will become apart of the Bay Area, and finally have a NFL football team).

It has now been over 20 years since the Los Angeles Basin experienced a severely damaging earthquake, and nearly 15 years since a magnitude 7 earthquake occurred within Southern California. Aside from the passing minor jolt here and there the ground under Southern California has been quiet, and that worries some seismologists at the United States Geological Survey. Now they are not worried that all this quietness means a big quake, or "the big one," is coming. Rather, since it has been so quiet and Southern California has not had any real notable earthquake in many years USGS officials are worried that some people may not be taking earthquake preparedness seriously.

We know Southern California brings in transplants from all over the country and the world, and hopefully they learn a little bit of history on their new home and realize historically Southern California is disaster prone.

In this Knowing Your Faults series since it has been so seismically quiet we figured the best way to start this series is to explore one of the "quietest" faults in Southern California, The Elsinore Fault.

The Elsinore Fault is a major fault system, and in fact it is one of the largest faults in Southern California capable of producing a major earthquake, but for such a large fault it has been very seismically inactive. 

Why So Quiet? 

Well, geologists and seismologists are not entirely sure. There are a lot of working theories why the Elsinore Fault may be so quiet. One of the floating theories is the San Jacinto Fault and Newport-Inglewood Fault may possibly be taking stress off The Elsinore Fault. It is one of many mysteries of earthquakes that have yet to be solved.

Where Can You Find the Fault?

Going from south-to-north The Elsinore Fault starts at the southern section of Anza-Borrego Desert State Park, just a few miles north of Interstate 8, and runs in a northwest direction skirting the northeast side of Cuyamaca Rancho State Park, through Palomar Mountain State Park, through Temecula, crossing I-15 and seemingly paralleling I-15 a couple miles west of the freeway with the fault going through Murrieta, Wildomar, Lake Elsinore, and into southwest Corona. 

It is in Corona where the Elsinore Fault splits into two separate faults, the Chino Fault going northwest and the Whittier Fault going in a west-northwest direction. Both faults cross State Route 91.

It is the Elsinore Fault that helped create the Cleveland National Forest, and what amounts to a natural, mountainous border between Riverside and Orange Counties.


NASA Photograph. Shown for educational purposes only; no copyright infringement intended.

Just How Bad Would Such a Quake Be?

Should the day come when the Elsinore Fault decides to wake up with a bang seismologists at the Southern California Earthquake Data Center believe the fault is capable of producing up to a magnitude 7.5 earthquake.

As USGS Doctor Lucy Jones told the San Diego Union-Tribune in 2005, "In Temecula, the 7 on the Elsinore will be much worse than the 8 on the San Andreas."

Should there be a major rupture of the Elsinore Fault at around magnitude 6.8 heavy damage is expected along the I-15 cities through Riverside County, and moderate to major damage is expected in central Orange County, according to studies by the Southern California Earthquake Data Center. The same study shows injuries and fatalities to be at 9,495, and damage to be near the $20 billion mark. 

If a large earthquake occurs there is also the possibility of major damage along the Riverside Freeway through the Santa Ana Canyon, which would bring extraordinary havoc to the entire Southern California freeway system.

Of course freeway problems may be the least of problems as a large earthquake could possibly break Diamond Valley Lake's 284-foot-high dam, and within ten minutes could flood the Riverside County cities of Menifee, Winchester and French Valley, according to Riverside County Emergency Service Director Mary Moreland.

The above is presuming The Elsinore Fault ruptures on its own fault in western Riverside County. There have been scenarios floated by USGS that the north end of The Elsinore Fault could rupture in Corona and the rupture could continuing "moving" along the either Chino Fault or Whittier Fault.  
  
The Elsinore Fault Earthquake History  

So, just how often does the Elsinore Fault move? According to USGS studies the interval between ruptures is about 250 years. 

Just when was the last rupture, well, USGS studies put it somewhere in the 18th Century.

The last notable earthquake on the Elsinore Fault was a magnitude 6 near Temescal Valley in 1910. 

Based on these studies it is believed the Elsinore Fault, like so many earthquake faults in Southern California, is likely overdue for a major earthquake.

When Is It Going To Happen?

With any basic knowledge and understanding of earthquakes your guess, quite frankly, is about as good as those at USGS. 

When it is going to happen nobody knows, and at this time there is no accurate way to predict earthquakes.

All you can do is be prepared, and know the hazards of where you live and work.

Editors Note: While this series is not intended to be a scholarly, scientific review of earthquake faults throughout Southern California, we hope this series will be a jumping off point for you to understand and further explore the fault lines that cross Southern California.