Earthquake Swarm Southern California

Powerful earthquake swarm in Southern California / Mexico border – Minor damage

Last update: August 26, 2012 at 11:48 pm by By

Update 23:42 UTC :
– New M4.7 aftershock, one more of an impressive number of aftershocks
– Some trailers are simply being knocked off from their foundations

Click on the image for the normal size

Update 22:17 UTC :
Minor damage is being reported in Brawley. No houses have collapsed and we do not expect to find such damage, however some structural damage has been reported in a number of buildings. Click on the Thumbnail to watch the image in the local Imperial Valley Press

Update 22:06 UTC
– Power has been restored in some Brawley areas but not yet everywhere.
– The earthquakes were also registered on the seismographs in Los Angeles. ABC7 network has a live Quake cam on the Internet. Click here to watch it Live

Update 21:46 UTC
– The last comparable seismic swarm in Brawley dates from 1970. Another one occurred in the 1930′s
– Some buildings in Brawley were evacuated after the first stronger quakes. People will probably stay outside for a while which is good in case other even stronger quakes would strike.
– The Brawley zone is a complex seismic area of smaller faults. The San Andreas main Fault runs from near Palm Springs to enter Mexico just west of Yuma.

Update 21:38 UTC
– Damage assessments are currently being executed in the Brawley area.
– Imperial County has begun operating a “County Emergency Headquarters”
– Brawley has a population of 24,953 (latest census), not a small village. The town has a significant cattle and feed industry, and hosts the annual Cattle Call Rodeo. Year-round agriculture is an important economic activity in Brawley.
– Brawley has also a Geothermal power plan

Update 21:26 UTC
– Based on the reports we receive from our readers, the shaking seems to have lasted only a few seconds. Short shaking is seldom damaging. The longer the shaking is lasting the more chance on damages.
– 17 aftershocks in between M2.5 and M4.3 in only 26 minutes

Shaking map of the latest M5.4 earthquake at 21:57 UTC

Update 21:16 UTC
– The last strong earthquake has currently been labeled M5.4 at a shallow depth of 8.9 km. Epicenter 5 km North of Brawley
– Intensities of MMI IV to VI are reported in the epicenter area

Update 21:10 UTC
– There are scattered power outages in the Brawley area and out at Naval Air Facility El Centro, said Marion Champion, spokeswoman for the Imperial Irrigation District. More than 1,000 customers were out of power temporarily. Crews are out checking for damage.
– Pioneers Memorial Hospital has been evacuated, and patient have been moved to the wound care center.  Though there has not been reports of major damage at the hospital, patients had asked to be evacuated because they were scared. Glass had been broken inside the hospital.
(messages courtesy Imperial Valley press)

Important Update 21:03 UTC
A new strong M5.4 earthquake (preliminary value) had happened a few minutes ago
– The National Weather Service reports a preliminary Magnitude of M5.6!
– Epicenter a few km NNW of Brawley

Update 20:53 UTC :
– Residents in the San Diego area reported feeling the quake in places including downtown San Diego, Mission Valley, Santee and Chula Vista.
– Authorities in San Diego reported NO damage or injuries
– The Brawley seismic zone is very well known by seismologists for earthquake swarms. More M3 to M5 earthquakes can be expected, but it is unlikely that stronger earthquakes will appear. Of course stronger are possible but based on historic facts would be very abnormal.

Update 20:40 UTC :
– As you can see on the picture below, Brawley is a farming community with a patchwork of farming grounds. This kind of area can be very vulnerable for earthquake waves.
– SSN, the Mexican seismological agency has reported a M5.7 for the strongest quake (vs 5.3 USGS) and M5.2 vs M4.9 for the second quake.

Update 20:36 UTC :
USGS has updated the calculation of the intensity and reports now that 28000 people will probably have experienced a strong shaking (MMI VI).

Update 20:27 UTC :
– Not less than 19 earthquakes did struck in Southern California before the first M4.6 earthquake. It all started at 15:33 UTC
– When the first powerful M4.6 earthquake happened, this quake was followed by 7 earthquakes in only 13 minutes. The last 2 of this range measured M5.3 and M4.9
– Since the mainshock and in less than an hour, the area was struck by 22 aftershocks ranging from 2.5 until 4.3. This is only the total of M2.5 or greater as the real number will be far higher.

Update 20:19 UTC : The area is really rattled by aftershocks, most of them in the M3.0 to M3.9 range
– The earthquakes was felt as a very weak shaking as far as the Greater Los Angeles area in the North and as far as Ensenada to the south.
– Our Mexican correspondent reports that in Mexicali live has returned to normal and no damage has been reported or noticed.
– The strongest reported shaking so far was MMI V (moderate shaking), si after all this earthquake looks to be luckily harmless.

Update 19:59 UTC : The list of strongest quakes has been reduced by USGS to the following quakes : 4.6, 4.7, 5.3, 4.9, 4.5. Most of these quakes were very well felt in a north-south range Brawley to Mexicali.
The area is very well known by people following earthquakes and is a little north from the epicenter of the massive earthquake from a couple of years ago.
– The hospital in Mexicali has been partly evacuated and personnel is inspecting the building for eventual damage.
– Theoretical calculations from USGS are stating that 19000 people will have experienced a MMI VI strong shaking.
– The epicenter of the strongest shock is just north-west of Brawley
– The area has a lot of fault zones

Shaking map courtesy USGS

Update : Up to now, the strongest earthquakes had values of 4.6, 4.7, 5.3, 5.3, 5.3; 4.5 – thats really a lot of earthquakes in a short time. USGS has a hard time to follow the many strong earthquakes as they have to be monitored by seismologists

Update : The hospital in Mexicali is currently being evacuated

Since 15:33 UTC this afternoon a big number of earthquakes started in Southern California
The most powerful ones (4 in total) started at 19:20 UTC

The epicenter of these earthquakes are south of the Salton Sea and a north of Calexico / Mexicali.
We will start up an in-depth article soon as this earthquake needs more attention than a normal one

Most important Earthquake Data:
Magnitude : M5.3 + many more
UTC Time : Sunday, August 26, 2012 at 19:32:59 UTC
Local time at epicenter : Sunday, August 26, 2012 at 12:32:59 PM at epicenter
Depth (Hypocenter) : 4.6 km
Geo-location(s) :
9 km (5 miles) E (83°) from Brawley, CA
17 km (10 miles) SSE (158°) from Calipatria, CA

from:    http://earthquake-report.com/2012/08/26/powerful-earthquake-swarm-in-southern-california-mexico-border/