Global seismic unrest - Two moderate earthquakes offshore Northern California

Global seismic unrest - Two moderate earthquakes offshore Northern California

According to USGS a 5.1 magnitude earthquake hit offshore Northern California on July 21, 2012 at 1:52 UTC. Recorded depth was 10 km and epicenter located 108 km (67 miles) W (274°) from Petrolia, CA at 40.382°N, 125.559°W.

Magnitude5.1
Date-Time
  • Saturday, July 21, 2012 at 01:52:00 UTC
  • Friday, July 20, 2012 at 06:52:00 PM at epicenter
Location40.382°N, 125.559°W
Depth10 km (6.2 miles) (poorly constrained)
RegionOFFSHORE NORTHERN CALIFORNIA
Distances
  • 108 km (67 miles) W (274°) from Petrolia, CA
  • 112 km (70 miles) W (259°) from Ferndale, CA
  • 121 km (75 miles) WSW (252°) from Humboldt Hill, CA
  • 126 km (78 miles) WSW (249°) from Eureka, CA
  • 397 km (247 miles) NW (318°) from San Francisco City Hall, CA
Location Uncertaintyhorizontal +/- 2.7 km (1.7 miles); depth +/- 31.6 km (19.6 miles)
ParametersNph= 37, Dmin=104 km, Rmss=0.22 sec, Gp=256°,
M-type=regional moment magnitude (Mw), Version=A
Source
  • California Integrated Seismic Net:
  • USGS Caltech CGS UCB UCSD UNR
Event IDnc71819391
 


 
The second one struck the same area at 6:04 UTC with preliminary magnitude of 5.8 which was downgraded to 5.2 couple of hours later. Poorly constrained depth of this one was 0.6km. Epicenter was located 81 km (50 miles) W (279°) from Petrolia, CA at 40.430°N, 125.234°W.

 
Magnitude5.2
Date-Time
  • Saturday, July 21, 2012 at 06:04:21 UTC
  • Friday, July 20, 2012 at 11:04:21 PM at epicenter
Location40.430°N, 125.234°W
Depth0.6 km (~0.4 mile) (poorly constrained)
RegionOFFSHORE NORTHERN CALIFORNIA
Distances
  • 81 km (50 miles) W (279°) from Petrolia, CA
  • 84 km (52 miles) W (259°) from Ferndale, CA
  • 93 km (58 miles) WSW (249°) from Humboldt Hill, CA
  • 99 km (62 miles) WSW (246°) from Eureka, CA
  • 382 km (238 miles) NW (321°) from San Francisco City Hall, CA
Location Uncertaintyhorizontal +/- 1.8 km (1.1 miles); depth +/- 13.6 km (8.5 miles)
ParametersNph=151, Dmin=76 km, Rmss=0.57 sec, Gp=230°,
M-type=regional moment magnitude (Mw), Version=6
Source
  • California Integrated Seismic Net:
  • USGS Caltech CGS UCB UCSD UNR
Event IDnc71819471
 


Earthquake-report.com had very interesting analysis of whats going on there:

While looking into the details about these earthquakes, we found a number of coincidences which may be realated to each other. The series started with a M4.0 earthquake at a depth of 10.1 km (6.3 miles) along the ridge fault in front of the Oregon coast. Nothing special as the stress in the part of the fault is generating regular earthquakes up to M6.0.
1 hour and 18 minutes later a more powerful M5.1 earthquake occurred along the same ridge fault (separating plates), bt this time more to the south in the Californian sector. The depth was set to 10 km or 6.2 miles but this is the usual depth which is set if the data are not accurate enough.

Finally (at least up to now) a M5.2 earthquake  occurred at a depth of 0.6 km approx. in the same sector than the earlier M5.1 earthquake. The depth of the last M5.2 earthquake (even poorly constrained) is attracting our attention.  We do not sea anything special on the sea floor except some stress scars and ridges (red lines on the three maps below).

There is certainly no proved relation in between the Oregon and California events, but if ER detects patterns, we like to share them with our readers.
Only few people at the Eureka coast have reported the shaking at USGS. All of them reported a weak to very weak shaking. ER

Global seismic unrest

California earthquakes are just part of global unrest taking place as we write this. New Zealand had 5.8 today, Japan is responding with double 4.9 eq's, Kuril Islands are still very active and we just saw 4.7 there...  Lets take a look at listings for today:

Recorded by USGS - Update time = Sat Jul 21 8:12:36 UTC 2012
MAGUTC DATE-TIME
y/m/d h:m:s
LAT
deg
LON
deg
DEPTH
km
 Region
4.02012/07/21 07:32:44  45.051  145.997216.9 HOKKAIDO, JAPAN REGION
 4.7  2012/07/21 07:20:01  49.245  156.13830.7 KURIL ISLANDS
2.52012/07/21 06:44:10  36.511 -121.0955.0 CENTRAL CALIFORNIA
 4.7  2012/07/21 06:37:21  15.496  147.43035.0 MARIANA ISLANDS REGION
 5.8  2012/07/21 06:11:58 -19.256  173.75710.0 VANUATU REGION
 5.2  2012/07/21 06:04:22  40.430 -125.2340.6 OFFSHORE NORTHERN CALIFORNIA
 4.5  2012/07/21 06:00:38  14.440  -93.52137.9 OFF THE COAST OF CHIAPAS, MEXICO
2.62012/07/21 05:43:32  61.438 -150.23950.6 SOUTHERN ALASKA
 5.8  2012/07/21 04:54:08 -37.755  179.67720.0 OFF EAST COAST OF THE NORTH ISLAND, N.Z.
3.32012/07/21 03:40:34  18.224  -68.65471.0 DOMINICAN REPUBLIC
 4.9  2012/07/21 03:01:22  37.744  141.89455.1 NEAR THE EAST COAST OF HONSHU, JAPAN
 4.9  2012/07/21 02:58:43  29.044  142.50619.0 IZU ISLANDS, JAPAN REGION
 5.1  2012/07/21 01:52:00  40.382 -125.55910.0 OFFSHORE NORTHERN CALIFORNIA
 4.5  2012/07/21 01:05:23  43.370  82.80641.9 NORTHERN XINJIANG, CHINA
4.02012/07/21 00:34:28  44.199 -128.28010.1 OFF THE COAST OF OREGON
 

Recorded by EMSC - Update time = Sat Jul 21 8:28 UTC 2012
































2012-07-21   07:32:44.0 53min ago45.05N146.00E2174.0 KURIL ISLANDS
2012-07-21   07:20:05.0 1hr 06min ago49.37N156.16E604.8 KURIL ISLANDS
2012-07-21   07:01:36.4 1hr 24min ago51.20N15.96E103.0 POLAND
2012-07-21   06:57:43.9 1hr 28min ago39.69N29.44E82.4 WESTERN TURKEY
2012-07-21   06:50:57.0 1hr 35min ago21.95S68.99W954.1 ANTOFAGASTA, CHILE
2012-07-21   06:37:21.0 1hr 48min ago15.50N147.43E354.7 MARIANA ISLANDS REGION
2012-07-21   06:35:33.3 1hr 50min ago37.23N28.16E42.4 WESTERN TURKEY
2012-07-21   06:12:04.0 2hr 14min ago19.23S173.75E605.4 VANUATU REGION
2012-07-21   06:04:25.0 2hr 21min ago40.54N125.40W104.9 OFFSHORE NORTHERN CALIFORNIA
2012-07-21   06:00:40.0 2hr 25min ago14.60N93.21W604.6 OFFSHORE CHIAPAS, MEXICO
2012-07-21   05:38:23.0 2hr 47min ago32.71S71.41W312.6 VALPARAISO, CHILE
2012-07-21   05:24:56.6 3hr 01min ago38.30N24.10E103.1 AEGEAN SEA
2012-07-21   04:54:06.0 3hr 32min ago37.81S179.76E105.8 OFF E. COAST OF N. ISLAND, N.Z.
2012-07-21   04:33:44.3 3hr 52min ago49.74N18.72E102.6 POLAND
2012-07-21   03:56:19.5 4hr 29min ago40.30N27.42E82.9 WESTERN TURKEY
2012-07-21   03:42:02.5 4hr 44min ago36.63N29.24E33.0 WESTERN TURKEY
2012-07-21   03:01:21.0 5hr 24min ago37.86N141.98E524.9 NEAR EAST COAST OF HONSHU, JAPAN
2012-07-21   02:58:40.0 5hr 27min ago29.11N142.46E24.9 IZU ISLANDS, JAPAN REGION
2012-07-21   02:49:27.0 5hr 36min ago20.88S69.83W833.4 TARAPACA, CHILE
2012-07-21   02:43:46.0 5hr 42min ago38.70N43.29E72.8 EASTERN TURKEY
2012-07-21   01:52:01.0 6hr 34min ago40.37N125.33W25.1 OFFSHORE NORTHERN CALIFORNIA
2012-07-21   01:47:27.0 6hr 38min ago38.75N43.34E82.8 EASTERN TURKEY
2012-07-21   01:06:03.0 7hr 20min ago36.02N4.74W603.0 STRAIT OF GIBRALTAR
2012-07-21   01:05:22.0 7hr 20min ago43.38N82.79E404.5 NORTHERN XINJIANG, CHINA
2012-07-21   00:34:27.6 7hr 51min ago44.20N128.28W104.0 OFF COAST OF OREGON
2012-07-21   00:21:50.4 8hr 04min ago38.58N25.97E212.4 AEGEAN SEA
2012-07-21   00:20:17.0 8hr 05min ago38.34N22.08E92.4 GREECE
2012-07-21   00:15:53.5 8hr 10min ago50.19N87.90E203.9 SOUTHWESTERN SIBERIA, RUSSIA
2012-07-21   00:08:05.0 8hr 18min ago37.62N21.77E172.6 SOUTHERN GREECE
2012-07-21   00:02:00.1 8hr 24min ago39.71N33.32E232.2 CENTRAL TURKEY

Featured image: Google Earth +
USGS

Comments

adexter 7 years ago

when checking the past on USGS it finds there were clearly a lot more earth quakes last year than this year. In every sense too, like intensity. My question. Why are so many earthquakes reported in areas not put on, or recorded by USGS this year? Why? Looks like some one is trying to keep the numbers down.

Randall Bass 7 years ago

Where is this in relation to the huge underwater crater west of San Francisco?

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