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.

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