Category Archives: Geology

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.

M5.1 Earthquake hits La Habra

From the USGS – Updated:

http://earthquake.usgs.gov/earthquakes/eventpage/ci15481673#summary

intensity

lahabraci15481673_ciim

Event Time

  1. 2014-03-29 04:09:42 UTC
  2. 2014-03-28 21:09:42 UTC-07:00 at epicenter
  3. 2014-03-28 21:09:42 UTC-07:00 system time

Location

33.919°N 117.944°W depth=7.5km (4.6mi)

Nearby Cities

  1. 1km (1mi) S of La Habra, California
  2. 4km (2mi) W of Brea, California
  3. 5km (3mi) NNW of Fullerton, California
  4. 6km (4mi) E of La Mirada, California
  5. 546km (339mi) W of Phoenix, Arizona

Tectonic Summary

A M5.1 earthquake occurred at 9:09PM on March 28, 2014, located 1 mile easy of La Habra, CA, or 4 miles north of Fullerton, CA. The event was felt widely throughout Orange, Los Angeles, Ventura, Riverside, and San Bernardino counties.  It was preceded by two foreshocks, the larger of M3.6 at 8:03pm.  The demonstration earthquake early warning system provided 4 second warning in Pasadena.

There have been 23 aftershocks as of 10:00PM on March 28, the largest of which was a M3.6 at 9:30PM, and was felt locally near the epicenter. The aftershock sequence may continue for several days to weeks, but will likely decay in frequency and magnitude as time goes by.

The maximum observed instrumental intensity was VII, recorded in the LA Habra and Brea areas, although the ShakeMap shows a wide area of maximum intensity of VI. The maximum reported intensity for the Did You Feel It? map was reported at VI in the epicentral area.

This sequence could be associated with the Puente Hills thrust (PHT).  The PHT is a blind thrust fault that extends from this region to the north and west towards the City of Los Angeles.  It caused the M5.9 1987 Oct. 1 Whittier Narrows earthquake.

Previously, the M5.4 2008 Chino Hills earthquake occurred in this region.  It caused somewhat stronger shaking in Orange County and across the Los Angeles Basin.

The moment tensor shows oblique faulting, with a north dipping plane that approximately aligns with the Puente Hills thrust.

The demonstration earthquake early warning system provided 4 second warning in Pasadena.

Related Links

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.

La Jolla Shores Beach Trip – May 2, 2013

I took a trip out to the beach today (May 2). It has been a while since I’ve gone and I wanted to test out my new zipperless wetsuit. I decided on the beach between La Jolla Shores and Black’s Beach. The scenery is great and the beach is far less crowded. So, I put on my wetsuit, grabbed my bag, and headed out on the motorcycle to La Jolla. Parking is so much easier there when you don’t have to worry about a car. It seems every time I go out there I am left wondering why I don’t go more often.

Scripps Pier
Scripps Pier
Small Sea Arch with muscles
Small Sea Arch with muscles
Tide Pools
Tide Pools
One of the Starfish I found.
One of the Starfish I found.
A Sea Slug? This little creature was quite colorful too.
A Sea Slug? This little creature was quite colorful too.
Another Starfish, this one out of water.
Another Starfish, this one out of water.

The tide was out when I got there, allowing for a very exposed and wide beach. The waves were pretty decent in spots, with the surfers getting plenty of use out of them. Just north of Scripps Pier, there is a rocky area with some tide pools. I stopped by and checked them out on my way. Today was about exploring and having fun, so why not? I found a small sea arch with quite a few muscles clinging to it. I also found a few starfish and some sort of sea slug. Once past the rocks, it was time to find a spot to go swimming. I’ve been wanting to get in the water with my new wetsuit. I’ve heard that zipperless suits are warmer in the water. This style of wetsuit is quite popular with the surfers around here as well. I found a spot to leave my gear, and I headed out to the water. Initially cold, it ended up being quite comfortable in my suit. I didn’t get the cold rush of water into the suit through the rear zipper, this one not having a rear zipper. It felt great to be out in the water. The ocean is cold here, but fairly clear. I think next time I’ll bring my fins and play around some more in the water.

My swim spot. A very wide, yet nearly empty beach in San Diego... this is the life!
My swim spot. A very wide, yet nearly empty beach in San Diego… this is the life!
Heading north along the cliffs.
Heading north along the cliffs.

After my swim, I wanted to explore the beach some more. I headed a bit further north until I reached a canyon that had running water coming from it. I stopped to check out the stream and ended up seeing some surfers with their boards coming out of the canyon. Upon closer investigation, I saw they were using a rope to climb the steep entrance from the beach into the canyon. I decided to explore this canyon a bit. Heading into it was pretty easy, though muddy in places. I was glad to be wearing my wetsuit booties. Much easier to walk in than bare feet. The trail was fairly well worn, though very narrow in places. About 100 yards into the canyon, there was a sizable waterfall. I wondered how I would get past it until I saw a surfer with a long board make it through rather easily. It turns out there was a very well worn series of “steps” in a narrow passage through the sandstone. Once I made my way up these, I got a better view of the upper reaches of the canyon. I decided to head back down, not wanting to end my beach time just yet. Heading down was a little easier than going up.

Surfer on his way down the trail.
Surfer on his way down the trail.
Inside the canyon, deep and narrow.
Inside the canyon, deep and narrow.
A seemingly impenetrable sandstone wall.
A seemingly impenetrable sandstone wall.
"Surfers Steps". Somehow they manage this carrying their boards.
“Surfers Steps”. Somehow they manage this carrying their boards.
Almost back to the beach.
Almost back to the beach.

At the bottom of the canyon, I headed back toward the motorcycle. I stopped for another swim at the same spot I did heading up. I just needed another soak in the ocean. After my swim, I headed over to the rocks where I saw the tide pools earlier. The tide was already coming up, so the outer reaches were flooded. As I got closer to the pier, the beach was a lot busier. It seems like the rocky area is a barrier to some. It sure didn’t stop me today. Overall, it was an enjoyable swim, a fun hike, and I definitely will return sooner. As I live in San Diego, I should at least take advantage of the beautiful beaches we have here in “America’s Finest City”. On my way home I stopped for a burger at the In-n-Out in Mission Valley, where the guy at the counter was rather inquisitive as to why I was wearing a wetsuit. He definitely enjoyed seeing me in my wetsuit. After getting home and doing a bit more research, the canyon I walked up ends at the parking area for the Torrey Pines Glider Port.