Category Archives: Earthquake

USGS Earthquake Swarms Information

There appears to be the beginnings of a small swarm of earthquakes in the Brawley Seismic Zone, this time in the town of Brawley, California. The USGS has a great website on swarms and why they occur.

http://www.scsn.org/index.php/earthquakes/earthquake-swarms/index.html

M5.1 Borrego Springs Earthquake

intensity

http://earthquake.usgs.gov/earthquakes/eventpage/ci37374687#general

Help the USGS with Earthquakes!

How can you help the United States Geological Survey? One simple way is to report to them when you feel an earthquake. This data helps them determine magnitude of the earthquake, how the geology affects that, and how the type of structure reacts to the event. Most earthquakes larger than 4.0 are listed in the “Events”  section of the page. So, help the USGS understand how earthquakes affect our region by contacting them at: “Did You Feel It?

Earthquakes and Movies

Lately, there has been quite a bit of press about the recent “San Andreas” movie. To me, this movie sets back the general public’s knowledge and understanding about how earthquakes create damage in Southern California.

Some basic stereotypes exist in the movie, many of which are completely false. Starting with the magnitude of the earthquake in the movie – No fault line in Southern California is capable of anything larger than about an 8.2. The only one truly capable of such an event, the San Andreas Fault, is also many miles from Los Angeles and is mostly separated from the Los Angeles Basin by the San Gabriel Mountains. Anything larger than a 9.0 is in the domain of “megathrusts” or subduction zones. In California, the only subduction zone is the southern end of the Cascadia Subduction Zone, which ends at the “Mendocino Triple Junction” just offshore of Cape Mendocino. It last produced something close to a 9.2 or so in January 1700.

Tsunamis, especially ones of great height, are also not in the forecast for a large earthquake here in Southern California. Tsunamis are created by the large scale displacement of water, similar to sloshing in a bathtub. Move your hand below the water quickly, you create a wave on the surface. Usually, tsunamis that are related to earthquakes are caused by the movement of the fault itself, typically megathrust faults underneath the ocean. We just don’t have those in Southern California. Even the largest tsunami generated by such a fault may only be tens of feet high, certainly not hundreds of feet.

Big cracks just don’t open up in the land from earthquakes, certainly nothing like those represented in the movie. Fissures are created by earthquakes, however. These fissures are usually the result of settlement or fault movement. They aren’t that large either way.

Structural damage is also not going to be as great as represented. Mind you, a large magnitude earthquake centered in the Los Angeles Basin will do a great deal of damage. Water mains, sewer mains, gas lines, power lines, and other utilities will be compromised in many locations creating shortages and, in some cases, fires. Buildings may collapse or be damaged beyond repair. The underlying geology will determine some of the damage extent. The rest will be determined by building type and its susceptibility to seismic waves. Either way, the skyscrapers in Downtown Los Angeles won’t be toppling like trees anytime soon. I’d still stay away from the area after a major event though, as there would be an immense amount of glass and debris creating hazards for travel.

Keeping all this in mind, and also keeping with the theme that Southern California officials have been doing, use this opportunity to prepare yourself for a major earthquake. They can strike at any time and will create problems for all of us that live, work, and visit this region. The best way to survive a major catastrophe is to be prepared. Part of that preparation is to know your region, know the routes, and know where the problem areas may be following a major earthquake.

For further information, I highly recommend contacting your local Emergency Services agency in your city and county. They have a great deal of resources to help you prepare for an event like a major earthquake.

Image of the Week – 9/15/14

Old alignment of Hwy 2, now offset by about 2 feet horizontally and 5 feet vertically.
Old alignment of Mexico Hwy 2, now offset by about 2 feet horizontally and 5 feet vertically.

M4.6 near Big Bear Lake, CA

At 9:59am on July 5, 2014, a M4.6 earthquake struck near Big Bear Lake. The focus was 5.4 miles deep.  If you felt this earthquake, the USGS wants to know! Watch for debris on the roadways in that area (State Highways 18, 38, 138, 173, 189, and 330).

Shakemap showing intensity.
Shakemap showing intensity.
Map showing area where people felt the quake and at what intensity.
Map showing area where people felt the quake and at what intensity.

April 2010 Baja Quake – Part 2

In July 2010, I was able to go to Baja California with a friend. Part of our route traversed Federal Highway 2 (Mexico), which suffered some damage from the April 2010 quake. Hwy 2 had been repaired but the adjacent old alignment had not been. I was rather amazed at the amount of offset from this earthquake. I observed about 2′ of horizontal and about 5′ of vertical offset at the highway crossing.

East of the fault, bridge embankments on the Hwy 2 Mexicali Bypass show signs of settling.
East of the fault, bridge embankments on the Hwy 2 Mexicali Bypass show signs of settling.
Offset right of way fence next to Hwy 2.
Offset right of way fence next to Hwy 2.
Old alignment of Hwy 2, now offset by about 2 feet horizontally and 5 feet vertically.
Old alignment of Hwy 2, now offset by about 2 feet horizontally and 5 feet vertically.
Side view of the old alignment showing the vertical offset.
Side view of the old alignment showing the vertical offset.
Breaks in the soil to the north. Two distinct scarps can be noted here.
Breaks in the soil to the north. Two distinct scarps can be noted here.
At the break, the old alignment now has a steep ramp and crack.
At the break, the old alignment now has a steep ramp and crack.

April 2010 Baja Earthquake – Part 1

On April 4, 2010, a 7.2 earthquake struck the northern Baja California and Southern California region. I was in Oceanside at a friends house at the time. Initially, I didn’t feel it and thought the others at the party were joking. We had been talking about the Northridge Earthquake earlier in the day. Once I stepped out onto the patio, I felt the ground moving. I knew it was large but farther away. My first thought was – What just happened to Los Angeles? Instead of Los Angeles, it was the Mexicali/Calexico area that got hit the worst as it was much closer to the epicenter.

Map showing the earthquake and affected area.
Map showing the earthquake and affected area.

Wanting to survey the damage to the roadways in that area and see if any of the old bridges were damaged, I headed out the following weekend. As it was also springtime, parts of the desert were in bloom. The ocotillo in particular had a beautiful display of flowers. To get out there, I followed Hwy 80 out to the Desert View Tower. After talking with Ben, the owner, I headed out to Calexico following Hwy 80 and Hwy 98. I was hoping to see cracks in Hwy 98 from any fault movement but did not find any.

Blooming ocotillo along Hwy 98 in the Yuha Desert.
Blooming ocotillo along Hwy 98 in the Yuha Desert.
DSCN0098
Closeup of the blooms.

In Calexico, many buildings were damaged with a large portion of the older downtown area closed off until the buildings could be stabilized. The biggest damage I saw was at a hotel in the northwestern end of downtown. Parts of the walls and roof had collapsed.

An empty and closed off downtown Calexico.
An empty and closed off downtown Calexico.
Partially collapsed roof and wall in Calexico.
Partially collapsed roof and wall in Calexico.
Damaged Hotel De Anza in Calexico.
Damaged Hotel De Anza in Calexico.
Front of Hotel De Anza showing some damage.
Front of Hotel De Anza showing some damage.
Partially collapsed facade of the Hotel De Anza.
Partially collapsed facade of the Hotel De Anza.

Returning from Calexico, I stopped at a few bridges to see the fill on each side had settled, causing some cracking in the pavement. Additional cracks were spotted at the New River crossing on old US 80. Overall, the highways were lightly damaged with some concrete broken at some bridges.

Typical settlement repair at the Westside Canal bridge on Hwy 98.
Typical settlement repair at the Westside Canal bridge on State 98.
Settled dirt at the edge of the Westside Canal at State 98.
Settled dirt at the edge of the Westside Canal at State 98.
Both sides of the New River trench show settlement on US 80.
Both sides of the New River trench show settlement on US 80.
Cracked pavement on old US 80 at the New River.
Cracked pavement on old US 80 at the New River.
Cracking in pavement and soil from settling at the edge of the New River trench.
Cracking in pavement and soil from settling at the edge of the New River trench.