Those Southern California Earthquakes

CAJON PASS - ONE PLACE WHERE THE PACIFIC PLATE AND NORTH AMERICAN PLATE MEET - Even if you are not the biggest newshound you know Worldwide 2014 was not a very good year, but in our place of the World known as Southern California it sure seemed like things were shaking more than usual.



One of the many places in Southern California where the infamous San Andreas Fault runs. Shown for educational purposes only; no copyright infringement intended. Used under a Creative Commons license.

In 2014 several widely "feel-able" minor-to-moderate earthquakes rattled the Los Angeles Basin. The most notable earthquake was the magnitude 5.1 (M5.1) La Habra Earthquake, which was the most damaging earthquake in the area since 2008.

In fact, things have been relatively quiet since the aftermath of the 1994 Northridge Earthquake, but in the last year it seems like things, seismically speaking, have been picking up.

So what gives? Well, as many geologists and seismologists at the United States Geological Survey note, such as "L.A. Earthquake Czar" Doctor Lucy Jones, things are just getting back to normal. In fact, having M4 and M5 earthquakes in Southern California is the normal way of life and we should be having a few them yearly. The problem for some people is that within the 20 years since the Northridge Earthquake many people have moved to Southern California, or been born in the last 20 years and may never had known of a time when these types of earthquakes rattled Southern California on a regular basis (of course they are many others who have been here well beyond 20 years and probably choose to forget we live in earthquake country).

Wait, These Types of Earthquakes Used To Happen All The Time?

Yes, and, by way of The Southern California Earthquake Data Center, here is a list of notable Southern California earthquakes between 1986 and 1994.

July 8, 1986 - North Palm Springs - M5.6
July 13, 1986 - About 32 miles West-Northwest offshore of Oceanside - M5.4
October 1, 1987 - Whittier Earthquake - M5.9
November 23, 1987 - Near Salton Sea and about 90 miles east of San Diego - M6.2
November 24, 1987 - About the same location as above - M6.6
June 26, 1988 - Upland - M4.7
December 3, 1988 - Pasadena - M5.0
January 18, 1989 - Malibu - M5.0
April 7, 1989 - Newport Beach - M4.7
June 12, 1989 - Montebello - M4.9
February 28, 1990 - Upland - M5.4
June 28, 1991 - Sierra Madre - M5.8
April 22, 1992 - Joshua Tree - M6.1
June 28, 1992 - Landers Earthquake - M7.3
June 28, 1992 - Big Bear - M6.4
January 17, 1994 - Northridge Earthquake - M6.7
   
What Happened After 1994?

Well, while there were the always ongoing minor M1-M3 jolts in the region and some M4 earthquakes just outside the area in the desert, along with a series of M5 earthquakes in rural Kern County in 1995-96 (some of which were felt in the L.A. area), notable earthquakes in and around the L.A. basin and Southern California in the aftermath of the Northridge Earthquake had became far, few and in-between.

In fact, outside of large Northridge aftershocks, which mostly faded by 1995, the next noteworthy earthquake would be the 2001 M4.2 West Hollywood Earthquake.

Furthermore, while there was a M5.4 in Big Bear in 2003 it would not be until 2008 that the L.A. basin would experience a damaging M5+ quake, the 2008 M5.4 Chino Hills Earthquake. That is about 14 years since a M5+ earthquake struck the L.A. area.

It is noteworthy to point out on October 16, 1999 in the rural San Bernardino County desert there was a M7.1 earthquake that shook most of Southern California, known as the Hector Mine Earthquake. This earthquake had an epicenter in such a rural area there was very little damage, but it did cause power outages in the Inland Empire, L.A. and Orange County. Despite such a significant earthquake it has been mostly forgotten.
  
Why Did The Lull In Earthquakes Happen?

Simply put, geologists and seismologists believe the Landers and Northridge Earthquakes relieved stress for a time on the fault-lines in Southern California.

In geological time 20 years is less than a blink of an eye.

So, Are We Coming Out of The Earthquake Lull?

Earthquakes in the last couple years would seem to say, "yes," and, much more importantly, in many interviews with the media after some of these shakers Dr. Jones believes we are going back to our normal pattern of earthquakes.

Does This Mean The Big One (Or A Big Enough One) Is Going To Happen?

Who knows?

It could mean something, or it could mean nothing, which is a way of saying there is no way to predict earthquakes.

Or, put another way, a damaging earthquake could happen tomorrow night, or ten years from now.

We Keep Hearing About The Threat of A Big Earthquake Happening, But Will It Ever Really Happen, Or Is It Just Hype?

Recent Southern California earthquake data listed above, along with historic earthquake data and studies going back hundreds of years show that a really big earthquake, or big enough earthquake to cause damage, will hit Southern California again, and again, and again, at some point.

What is most important to understand is Southern California, and much of California for that matter, sits atop two tectonic plate boundaries, the Pacific Plate and North American Plate. Those two plate boundaries in our part of the World create what is known as a transform boundary where the two plates slide past each other.

Image of plate tectonics by USGS via Wikimedia Commons, Creative Commons License.

In California the San Andreas Fault forms the tectonic boundary between the Pacific Plate and the North American Plate, and, simply put, as these boundaries slide past each other many times they become stuck, pressure builds up and you have an earthquake.

Will The Plates Ever Stop Moving Against Each Other So We Can Stop Having Earthquakes?

Nope!

As long as the World is spinning the plates will keep moving, and thus Southern California will continue to always have earthquakes big and small.

When Was The Last Great Big Earthquake in Southern California?

While there certainly have been many "big enough earthquakes" in our lifetime the last great big earthquake in Southern California was in 1857, commonly called The Fort Tejon Earthquake.

This earthquake was on the San Andreas Fault, which many in the Earth science community believe the infamous fault ruptured from the Parkfield area southward to the Cajon Pass. One reason that lead to this belief is the surface rupture along the fault was about 230 miles.

This earthquake is believed to have been M7.9, one of the strongest earthquakes ever recorded in North America, but California was a very sparsely populated place, and so damage and casualties were very limited.

It is believed shaking in Southern California lasted up to three minutes.

A similar earthquake today would profoundly impact Southern California with damage and economic loss going easily into the billions of dollars, according to SCEDC. 

What About The Other Section of The San Andreas Fault?

There is another section of The San Andreas Fault that runs through Southern California, and that section runs between San Bernardino to the fault's terminus in the Salton Sea.

Recent studies have shown the last time this section ruptured was in or around 1690.

For some geologists and seismologists it is this section of The San Andreas Fault they believe will bring us the dreaded Big One.


Video developed by Dr. Robert Graves of the USGS showing a simulation of a major southern San Andreas Fault earthquake. No copyright infringement intended; shown for educational purposes only. 
 
Just Be Prepared!

All you can do is prepare and be prepared. 

There is no way at this time to predict earthquakes. The only earthquakes that can be predicted are aftershocks.

Making The Best of The Faults Below Our Feet 

One way to make the best of all these fault-lines around us is to enjoy the natural beauty they have produced. After all, what gives Southern California its dramatic mountains and hills are earthquakes, and if we did not have earthquakes we would probably be as flat as Kansas.

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.