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Global seismic unrest – Two moderate earthquakes offshore Northern California

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.

Magnitude 5.1
Date-Time
  • Saturday, July 21, 2012 at 01:52:00 UTC
  • Friday, July 20, 2012 at 06:52:00 PM at epicenter
Location 40.382°N, 125.559°W
Depth 10 km (6.2 miles) (poorly constrained)
Region OFFSHORE 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 Uncertainty horizontal +/- 2.7 km (1.7 miles); depth +/- 31.6 km (19.6 miles)
Parameters Nph= 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 ID nc71819391

 

 

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.

 

Magnitude 5.2
Date-Time
  • Saturday, July 21, 2012 at 06:04:21 UTC
  • Friday, July 20, 2012 at 11:04:21 PM at epicenter
Location 40.430°N, 125.234°W
Depth 0.6 km (~0.4 mile) (poorly constrained)
Region OFFSHORE 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 Uncertainty horizontal +/- 1.8 km (1.1 miles); depth +/- 13.6 km (8.5 miles)
Parameters Nph=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 ID nc71819471

 

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

MAG UTC DATE-TIME
y/m/d h:m:s
LAT
deg
LON
deg
DEPTH
km
 Region
4.0 2012/07/21 07:32:44   45.051   145.997 216.9  HOKKAIDO, JAPAN REGION
 4.7   2012/07/21 07:20:01   49.245   156.138 30.7  KURIL ISLANDS
2.5 2012/07/21 06:44:10   36.511  -121.095 5.0  CENTRAL CALIFORNIA
 4.7   2012/07/21 06:37:21   15.496   147.430 35.0  MARIANA ISLANDS REGION
 5.8   2012/07/21 06:11:58  -19.256   173.757 10.0  VANUATU REGION
 5.2   2012/07/21 06:04:22   40.430  -125.234 0.6  OFFSHORE NORTHERN CALIFORNIA
 4.5   2012/07/21 06:00:38   14.440   -93.521 37.9  OFF THE COAST OF CHIAPAS, MEXICO
2.6 2012/07/21 05:43:32   61.438  -150.239 50.6  SOUTHERN ALASKA
 5.8   2012/07/21 04:54:08  -37.755   179.677 20.0  OFF EAST COAST OF THE NORTH ISLAND, N.Z.
3.3 2012/07/21 03:40:34   18.224   -68.654 71.0  DOMINICAN REPUBLIC
 4.9   2012/07/21 03:01:22   37.744   141.894 55.1  NEAR THE EAST COAST OF HONSHU, JAPAN
 4.9   2012/07/21 02:58:43   29.044   142.506 19.0  IZU ISLANDS, JAPAN REGION
 5.1   2012/07/21 01:52:00   40.382  -125.559 10.0  OFFSHORE NORTHERN CALIFORNIA
 4.5   2012/07/21 01:05:23   43.370   82.806 41.9  NORTHERN XINJIANG, CHINA
4.0 2012/07/21 00:34:28   44.199  -128.280 10.1  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 ago 45.05 N 146.00 E 217 4.0  KURIL ISLANDS
2012-07-21   07:20:05.0 1hr 06min ago 49.37 N 156.16 E 60 4.8  KURIL ISLANDS
2012-07-21   07:01:36.4 1hr 24min ago 51.20 N 15.96 E 10 3.0  POLAND
2012-07-21   06:57:43.9 1hr 28min ago 39.69 N 29.44 E 8 2.4  WESTERN TURKEY
2012-07-21   06:50:57.0 1hr 35min ago 21.95 S 68.99 W 95 4.1  ANTOFAGASTA, CHILE
2012-07-21   06:37:21.0 1hr 48min ago 15.50 N 147.43 E 35 4.7  MARIANA ISLANDS REGION
2012-07-21   06:35:33.3 1hr 50min ago 37.23 N 28.16 E 4 2.4  WESTERN TURKEY
2012-07-21   06:12:04.0 2hr 14min ago 19.23 S 173.75 E 60 5.4  VANUATU REGION
2012-07-21   06:04:25.0 2hr 21min ago 40.54 N 125.40 W 10 4.9  OFFSHORE NORTHERN CALIFORNIA
2012-07-21   06:00:40.0 2hr 25min ago 14.60 N 93.21 W 60 4.6  OFFSHORE CHIAPAS, MEXICO
2012-07-21   05:38:23.0 2hr 47min ago 32.71 S 71.41 W 31 2.6  VALPARAISO, CHILE
2012-07-21   05:24:56.6 3hr 01min ago 38.30 N 24.10 E 10 3.1  AEGEAN SEA
2012-07-21   04:54:06.0 3hr 32min ago 37.81 S 179.76 E 10 5.8  OFF E. COAST OF N. ISLAND, N.Z.
2012-07-21   04:33:44.3 3hr 52min ago 49.74 N 18.72 E 10 2.6  POLAND
2012-07-21   03:56:19.5 4hr 29min ago 40.30 N 27.42 E 8 2.9  WESTERN TURKEY
2012-07-21   03:42:02.5 4hr 44min ago 36.63 N 29.24 E 3 3.0  WESTERN TURKEY
2012-07-21   03:01:21.0 5hr 24min ago 37.86 N 141.98 E 52 4.9  NEAR EAST COAST OF HONSHU, JAPAN
2012-07-21   02:58:40.0 5hr 27min ago 29.11 N 142.46 E 2 4.9  IZU ISLANDS, JAPAN REGION
2012-07-21   02:49:27.0 5hr 36min ago 20.88 S 69.83 W 83 3.4  TARAPACA, CHILE
2012-07-21   02:43:46.0 5hr 42min ago 38.70 N 43.29 E 7 2.8  EASTERN TURKEY
2012-07-21   01:52:01.0 6hr 34min ago 40.37 N 125.33 W 2 5.1  OFFSHORE NORTHERN CALIFORNIA
2012-07-21   01:47:27.0 6hr 38min ago 38.75 N 43.34 E 8 2.8  EASTERN TURKEY
2012-07-21   01:06:03.0 7hr 20min ago 36.02 N 4.74 W 60 3.0  STRAIT OF GIBRALTAR
2012-07-21   01:05:22.0 7hr 20min ago 43.38 N 82.79 E 40 4.5  NORTHERN XINJIANG, CHINA
2012-07-21   00:34:27.6 7hr 51min ago 44.20 N 128.28 W 10 4.0  OFF COAST OF OREGON
2012-07-21   00:21:50.4 8hr 04min ago 38.58 N 25.97 E 21 2.4  AEGEAN SEA
2012-07-21   00:20:17.0 8hr 05min ago 38.34 N 22.08 E 9 2.4  GREECE
2012-07-21   00:15:53.5 8hr 10min ago 50.19 N 87.90 E 20 3.9  SOUTHWESTERN SIBERIA, RUSSIA
2012-07-21   00:08:05.0 8hr 18min ago 37.62 N 21.77 E 17 2.6  SOUTHERN GREECE
2012-07-21   00:02:00.1 8hr 24min ago 39.71 N 33.32 E 23 2.2  CENTRAL TURKEY


Featured image: Google Earth +
USGS

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2 Comments

  1. 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.

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