Hi All,

This past week I've been keeping an eye out for far field aftershock events following he Lake Tanganyika 6.8 earthquake. This is an event which doesn't occur very often in which the 140° line sat/sits just along our California west coast. So what occurred that would be unusual?

Let's start with my hometown of Encinitas (San Diego County). The area normally has off shore events, yet this one was onshore:
1.7 2005/12/09 13:46:48 33.072N 117.234W 1.7 5 km ( 3 mi) NE of Encinitas, CA

I've driven past Temelec dozens of times. It's a subdivision just off Arnold Drive in Sonoma. But this earthquake didn't occur in Temelec at all, but about 2 miles S/E of it. It sits behind the Rodgers Creek fault on the Sonoma side, but this earthquake happened where the land is totally flat. It's very close to Turkey Farm Road off Hwy 116. It is very unusual to have an earthquake there.
1.0 2005/12/06 06:40:02 38.232N 122.464W 6.5 4 km ( 3 mi) SE of Temelec, CA

However, what about this profusion of earthquakes in the North Bay? This is highly unusual. But something which is important to remember is most of the places on this list are volcanic in nature, which is frequently denoted as something caused by FFA events. There are 13 quakes which are definitely in a volcanic zone. Lake Pillsbury seems to run hot and cold, but this week it perked up. This list clearly demonstrates seismicity which is way above the normal of about 5 or less quakes during the same time period. I know, I read them every day.

map 1.5 2005/12/11 00:27:30 38.589N 122.770W 2.9 6 km ( 4 mi) NNE of Windsor, CA
map 1.9 2005/12/09 10:28:05 37.787N 122.598W 9.6 9 km ( 5 mi) S of Muir Beach, CA
map 1.7 2005/12/09 10:02:13 37.596N 121.984W 6.6 5 km ( 3 mi) E of Union City, CA
1.4 2005/12/09 05:55:58 37.742N 122.555W 7.0 5 km ( 3 mi) WNW of San Francisco Zoo
map 1.8 2005/12/08 09:30:50 38.688N 122.899W 4.7 8 km ( 5 mi) NNW of Healdsburg, CA
map 1.3 2005/12/08 07:31:47 38.571N 122.657W 6.9 7 km ( 4 mi) W of Calistoga, CA
map 2.0 2005/12/08 05:49:00 39.377N 122.882W 3.5 7 km ( 5 mi) ESE of Lake Pillsbury, CA
map 2.1 2005/12/08 05:45:07 39.374N 122.898W 12.2 6 km ( 4 mi) SE of Lake Pillsbury, CA
map 2.1 2005/12/08 05:14:44 39.382N 122.897W 7.7 6 km ( 4 mi) ESE of Lake Pillsbury, CA
map 2.2 2005/12/08 03:57:02 39.404N 123.335W 2.6 1 km ( 1 mi) E of Willits, CA
MAP 3.8 2005/12/08 01:47:08 40.372N 125.074W 8.7 67 km (42 mi) W of Petrolia, CA
map 1.7 2005/12/07 23:38:09 38.684N 122.898W 6.7 8 km ( 5 mi) NNW of Healdsburg, CA
map 2.6 2005/12/07 08:01:27 39.810N 123.447W 7.3 15 km (10 mi) NNE of Laytonville, CA
map 1.9 2005/12/07 07:20:54 38.523N 122.623W 2.1 7 km ( 5 mi) SSW of Calistoga, CA
map 2.0 2005/12/06 19:44:24 38.551N 122.521W 8.4 4 km ( 3 mi) WNW of Deer Park, CA
map 2.2 2005/12/06 06:51:37 38.550N 122.521W 8.9 4 km ( 3 mi) WNW of Deer Park, CA
map 1.3 2005/12/06 01:43:02 38.547N 122.521W 7.9 4 km ( 3 mi) WNW of Deer Park, CA
map 1.8 2005/12/05 10:44:53 38.486N 122.281W 5.8 12 km ( 7 mi) NE of Yountville, CA

Regarding the list below of 47 quakes. I removed all Geysers events as those would be difficult to distinguish between background seismicity. But what of Parkfield and San Simeon? I attribute them to the FFA events because there are more quakes than normal. But one could take them out if they wanted to.

Due to the size of this earthquake and the distance from the epicenter to our west coast, I don't believe anyone would expect even a moderate quake, but these little popper stoppers are exactly clear examples of what FFA events are all about......Petra

A strong earthquake occurred at 12:19:57 (UTC) on Monday, December 5, 2005. The magnitude 6.8 event has been located in the LAKE TANGANYIKA REGION, CONGO-TANZANIA. (This event has been reviewed by a seismologist.)

MAG DATE LOCAL-TIME LAT LON DEPTH LOCATION
y/m/d h:m:s deg deg km

map 1.1 2005/12/11 06:39:00 36.869N 121.420W 3.0 3 km ( 2 mi) NW of Hollister, CA
map 1.2 2005/12/11 06:05:38 36.466N 121.043W 6.0 12 km ( 7 mi) SE of Pinnacles, CA
map 1.7 2005/12/11 05:33:30 35.895N 120.445W 11.2 1 km ( 1 mi) WSW of Parkfield, CA
map 1.1 2005/12/11 03:25:57 36.453N 121.035W 9.0 13 km ( 8 mi) SE of Pinnacles, CA
map 1.5 2005/12/11 00:27:30 38.589N 122.770W 2.9 6 km ( 4 mi) NNE of Windsor, CA
map 1.5 2005/12/10 14:14:58 36.859N 121.586W 6.2 5 km ( 3 mi) WNW of San Juan Bautista, CA
map 1.6 2005/12/10 13:17:15 36.043N 120.603W 6.0 22 km (14 mi) NW of Parkfield, CA
map 1.4 2005/12/10 09:24:43 35.797N 120.336W 11.1 14 km ( 9 mi) SE of Parkfield, CA
map 2.2 2005/12/09 18:59:54 36.819N 121.410W 7.6 3 km ( 2 mi) SSW of Hollister, CA
map 1.7 2005/12/09 13:46:48 33.072N 117.234W 1.7 5 km ( 3 mi) NE of Encinitas, CA
map 1.9 2005/12/09 10:28:05 37.787N 122.598W 9.6 9 km ( 5 mi) S of Muir Beach, CA
map 1.7 2005/12/09 10:02:13 37.596N 121.984W 6.6 5 km ( 3 mi) E of Union City, CA
1.4 2005/12/09 05:55:58 37.742N 122.555W 7.0 5 km ( 3 mi) WNW of San Francisco Zoo
map 1.1 2005/12/09 05:26:03 35.926N 120.475W 5.3 5 km ( 3 mi) NW of Parkfield, CA
map 1.1 2005/12/08 16:06:23 36.124N 120.787W 4.7 16 km (10 mi) NE of San Ardo, CA
map 2.1 2005/12/08 13:17:43 32.227N 116.779W 6.0 26 km (16 mi) ESE of Rosarito, Baja California, Mexico
map 1.8 2005/12/08 09:30:50 38.688N 122.899W 4.7 8 km ( 5 mi) NNW of Healdsburg, CA
map 1.3 2005/12/08 08:09:10 36.570N 121.162W 3.4 5 km ( 3 mi) NNW of Pinnacles, CA
map 1.3 2005/12/08 07:31:47 38.571N 122.657W 6.9 7 km ( 4 mi) W of Calistoga, CA
2.1 2005/12/08 06:36:55 35.615N 120.882W 6.3 14 km ( 8 mi) S of Lake Nacimiento, CA
map 2.0 2005/12/08 05:49:00 39.377N 122.882W 3.5 7 km ( 5 mi) ESE of Lake Pillsbury, CA
map 2.1 2005/12/08 05:45:07 39.374N 122.898W 12.2 6 km ( 4 mi) SE of Lake Pillsbury, CA
map 2.1 2005/12/08 05:14:44 39.382N 122.897W 7.7 6 km ( 4 mi) ESE of Lake Pillsbury, CA
map 2.2 2005/12/08 03:57:02 39.404N 123.335W 2.6 1 km ( 1 mi) E of Willits, CA
MAP 3.8 2005/12/08 01:47:08 40.372N 125.074W 8.7 67 km (42 mi) W of Petrolia, CA
map 1.7 2005/12/07 23:38:09 38.684N 122.898W 6.7 8 km ( 5 mi) NNW of Healdsburg, CA
map 1.6 2005/12/07 23:28:08 36.086N 120.641W 5.4 25 km (15 mi) ENE of San Ardo, CA
map 0.7 2005/12/07 21:03:05 36.674N 121.298W 6.3 13 km ( 8 mi) S of Tres Pinos, CA
MAP 3.1 2005/12/07 20:58:56 36.678N 121.301W 4.8 13 km ( 8 mi) S of Tres Pinos, CA
map 1.0 2005/12/07 18:13:11 36.748N 121.416W 7.2 10 km ( 6 mi) WSW of Tres Pinos, CA
map 1.4 2005/12/07 17:52:43 36.648N 121.268W 4.8 16 km (10 mi) SSE of Tres Pinos, CA
map 1.5 2005/12/07 08:41:22 36.468N 121.044W 5.8 11 km ( 7 mi) SE of Pinnacles, CA
map 2.6 2005/12/07 08:01:27 39.810N 123.447W 7.3 15 km (10 mi) NNE of Laytonville, CA
map 1.9 2005/12/07 07:20:54 38.523N 122.623W 2.1 7 km ( 5 mi) SSW of Calistoga, CA
map 2.0 2005/12/06 19:44:24 38.551N 122.521W 8.4 4 km ( 3 mi) WNW of Deer Park, CA
map 1.6 2005/12/06 18:10:23 36.803N 121.268W 8.3 5 km ( 3 mi) ENE of Tres Pinos, CA
map 2.3 2005/12/06 11:54:08 35.723N 121.124W 1.1 11 km ( 7 mi) NE of San Simeon, CA
map 1.4 2005/12/06 11:45:47 36.960N 121.587W 5.9 6 km ( 4 mi) S of Gilroy, CA
map 1.7 2005/12/06 11:12:57 35.725N 121.076W 4.6 14 km ( 9 mi) NE of San Simeon, CA
map 2.8 2005/12/06 09:38:25 40.321N 124.599W 20.8 27 km (17 mi) W of Petrolia, CA
map 2.2 2005/12/06 06:51:37 38.550N 122.521W 8.9 4 km ( 3 mi) WNW of Deer Park, CA
map 1.0 2005/12/06 06:40:02 38.232N 122.464W 6.5 4 km ( 3 mi) SE of Temelec, CA
map 1.2 2005/12/06 05:35:09 36.650N 121.277W 6.8 16 km (10 mi) SSE of Tres Pinos, CA
map 1.3 2005/12/06 01:43:02 38.547N 122.521W 7.9 4 km ( 3 mi) WNW of Deer Park, CA
3.1 2005/12/06 00:28:29 35.792N 120.346W 10.0 14 km ( 9 mi) SSE of Parkfield, CA
map 1.8 2005/12/05 10:44:53 38.486N 122.281W 5.8 12 km ( 7 mi) NE of Yountville, CA
map 1.5 2005/12/05 06:39:46 36.836N 121.441W 2.7 4 km ( 2 mi) WSW of Hollister, CA

http://neic.usgs.gov/neis/eq_depot/2005/eq_051205_ggai/neic_ggai_t.html

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