Hi All. The Baja quake taught me one if it taught me nothing else and that is not to believe the moment tensor solution until a real live person gets to look at it. If it was a normal quake then why are all the aftershocks going northwest? The faults in the area are very complex as they can be strike-slip to extensional. There may even be some thrust faults stuck in there somewhere.
From USGS summary:
“The April 4 main-shock occurred along a strike-slip segment of the plate boundary that coincides with the southeastern part of the Laguna Salada fault. Although the location and focal-mechanism of the earthquake are consistent with the shock having occurred on this fault, they still do not have surface rupture or other confirmation.”
“In the vicinity of the 4 April 2010 earthquake, there are several active faults and it has not yet been determined specifically which fault the earthquake occurred on. Within the transition from the ridge-transform boundary in the Gulf of California to the continental transform boundary in the Salton Trough, faulting is complex. Most of the major active faults are northwest-southeast oriented right-lateral strike-slip faults that are common in mechanism to the San Andreas fault and parallel Elsinore and San Jacinto faults, that run north of the Mexico-USA border.”
“Earthquakes having magnitudes as high as 7 have been historically recorded from the section of the Pacific/North American plate boundary on which the 4 April 2010 earthquake occurred. The 1892 earthquake occurred along the Laguna Salada fault system, but significantly farther northwest than today's event epicenter. The 1940 Imperial Valley earthquake approached magnitude 7, though it occurred farther to the north and on the Imperial fault. Both the 1892 and 1940 earthquakes were associated with extensive surface faulting. An event of M 7.0 or 7.1 occurred in this region in 1915, and then a M 7.0 to 7.2 in 1934 broke the Cerro Prieto fault with up to several meters of surface slip.”
The quakes closest to the epicenter are most likely aftershocks, but the further out you go it is more likely the quakes are triggered quakes and not aftershocks. This could weaken the fault and cause it to fail sooner then it would have. The faults most likely affected are the Elsinore fault, and the San Jacinto fault. Can't rule out other faults as there is probably a number of faults in the area we know nothing about. I doubt if we even know they are they. I had one old seismologist tell me you can stand here and spit in any direction you want to and you could hit a fault we don't even know is there. The Northridge quake was one such quake. No one knew there was a fault there. The fault that cause that quake was a thrust fault and they almost never show themselves at the surface. You can dig all you want to but you're not going to find it.
The quake could have increased the stress on some and decreased it on others. It could take another week to fail, or ten more years to fail. Sooner or later they will fail. Sooner or later they will all fail. It is just a matter of time.
From Dr. Lowell Whiteside blog:
http://www.quakecentralforecasting.com/Lowell-Archive-Blog-24.htmlA strong earthquake of M 7.2 hit the region of Baja and Southern California today. We have warned of the possibility of such an earthquake for the past two weeks as unusual seismicity continued to hit around the North American plate. AT least two people were killed and more than 100 were injured in the quake. Damage occurred when sides of buildings were ripped off, telephone poles fell over, roads cracked and goods fell from store shelves. Power outages hit Calexico and other cities. Broken glass, crumbled stucco and bricks littered many streets and at least one store facade fell. Damages are currently being assessed and we will report further in our next report.
Today's event was followed by more than 150 aftershocks of M>3 including at least five of M>5. Most of these were felt in the epicentral areas with intensity IV-V. The mainshock was reported by NEIC to have been felt in Arizona in Phoenix, New River, Mesa, Apache Junction, Casa Grande, Chandler, Gilbert,
Scottsdale, Tempe. Gilbert, Glendale, Avondale, Goodyear, Litchfield Park, Yuma, Surprise, Peoria, Tucson, Lake Havasu City, Fort Mohave, and Bullhead City with intensity II-IV. In Nevada it was reported felt with intensity II-IV in Henderson, Laughlin, North Las Vegas, and Las Vegas. The quake was felt with intensity up to V throughout most of Southern California including up to about 400 km distance. Reports of intensity up to V come from Los Angeles, Hollywood, Beverly Hills, Compton, Culver City, Downey, El Segundo, Hawthorne, Hermosa Beach, Huntington Park, Lawndale, Manhattan Beach, Redondo Beach, Venice, Marina del Rey, Inglewood, Santa Monica, Torrance, Whittier, Buena Park, Altadena, Monrovia, Pasadena, San Diego. Maximum intensity VII was reported from El Cento and Imperial with VII from Ocotillo and Holtville among others. In Mexico the quake was reported with intensity VII in Mexicali and V-VI in Tecate, San Quintin, San Luis Rio Colorado, San Felipe, Primo Tapia, Maneadero, Lazaro Cardenas, La Joya, Guerrero Negro, Ensenada, El Sauzal, Carmalu. Felt reports came from as far away as Abbeville, Alabama (5 reports), New Mexico, Georgia, Tennessee, Texas, Idaho, Montana, Kansas, Colorado, Wyoming, Utah and New Mexico among others. Many of these are probably in error but some may be feeling the surface waves while others may have local sympathetic earth shaking.
O: 04APR2010 22:40:47 32.4N 115.1W MB=7.0 GFZ Calif.-Baja Calif. Border
O: 4APR2010 22:40:41 32.1N 115.3W ML=7.2 NEIC BAJA CALIFORNIA, MEXICO
P: 2MAR2010 52486 32.0N 115.3W 2.5-6.4 AAAAA So. California
In order to provide plenty of warning, beginning about two weeks ago and continuing through yesterday we have been warning about what appeared to be a rotational episode in the North American plate and we had warned of the possibility of a strong earthquake on the rim of the plate at this time. The first indications of a major upcoming earthquake on the edge of the plate (which includes Baja, California) occurred with a light earthquake in Nebraska on March 19. We reported at the time:
"When a series of unusual earthquakes hit this region of the northern Plains and Rocky Mountains it often precedes a strong earthquake on the border of the North American Plate ... This creaking of the North American plate prior to large earthquakes has been documented many times in our report over the past 30 years.
... A large earthquake elsewhere on the western rim of the North American plate is less likely but also possible and we are suggesting a seismic watch ... from Alaska through Mexico." (March 20, 2010)
“A series of moderately strong earthquakes hit around the edge of the North American Plate today ... These earthquakes hint at an attempt of the North American plate to make a significant rotational motion today and it is still possible that a strong earthquake will yet occur from this sudden plate motion." (March 21, 2010)
The first moderate foreshock to today's event occurred on March 21 in Baja. We noted this a one of a pair of antipodal events including a second in the South Indian Ocean.
On March 25 we further noted that a rotational motion of the North American plate was occurring when an earthquake hit near the Euler pole for North America. We noted:
"Two unusual earthquakes of M 4.8 and M 4.9 also hit near the Euler Point for North America in the Central Mid-Atlantic Ocean. The Euler pole is the point on the surface around which a plate appears to rotate. This would seem to confirm that a significant motion of the North American Plate has been occurring." (March 24, 2010)
Less than a week ago on March 29 we continued this argument as follows:
"The activity in New Mexico and West Virginia today continues a creaking of the North American Plate which began about a week ago. Such intraplate events are often followed by a strong earthquake on the plate boundary. There has been a series of unusual earthquake around the North American Plate boundary in the past week but strong geomagnetic/solar/meteorological triggers area generally absent at this time. Because an alignment of the sun earth and moon occurs early on March 30, that would be the most likely time for a larger event in this plate. The sun is increasing activity and this could be a triggering agent under the proper circumstances. The most likely areas for such an unlikely event remain Alaska, Mexico to Guatemala and the northern Caribbean/North America plate boundary." (March 29, 2010)
An earthquake of M 4.5-4.8 than occurred on March 30 in the Sonora, Mexico area southwest of today's epicenter. We noted:
"An earthquake of M 4.5 hit north of Puerto Penasco, Sonora, Mexico today. This is the strongest earthquake within 100 km of this epicenter in the past 20 years. A series of events of M 4.5-5.0 hit about 150 km southwest of this epicenter in October, 2009. This continues the increased activity around the edge of the North America Plate which began about a week ago and is ongoing." (March 31, 2010)
Finally, we reported on the foreshock of M 4.3 which hit the area yesterday in this regard:
"Light earthquakes were felt around the rim of North America in the Cayman Islands of the Caribbean (M 4.2); Baja California (M 4.3) and Oklahoma (M 2.3, 2.5)." (April 4, 2010)
The geomagnetic field was at its most disturbed conditions today since February 15-16 with AP of 13 and Middle latitude index of 11. This storm began three days ago and at the time we forecast "the global seismic activation is likely with this geomagnetic disturbance with the most likely large earthquakes around April 5-6." (April 2-4, 2010)
The earthquake in Baja California was closely related to a strong variation in the geomagnetic Hp field. This variation was recorded by GOES 12 as a decline in the field strength which began about 22:17 UT reaching a minimum value at 22:40 UT before making a strong recovery. The Baja event occurred at the minimum, 22:40 UT. A strong geomagnetic disturbance occurred at the same time with the K-index reaching 4 for only the second day in the past month. The K-index was reached twice today for the first time since
February 16, 2010.
Data from SWPC at:
http://www.swpc.noaa.gov/ftpdir/lists/geomag/30100404_G12mag_1m.txtWe reported on the current sensitivity of the Baja region to solar/geomagnetic effects on March 17 as follows:
"The flare began at about 05:40 UT and was first observed at 05:43. This coincided with a series of shocks in the Baja California area including events of 3.0 and 3.1 at 05:40 and 05:41 UT as well as with an aftershock in Chile of M 4.6." (March 17, 2010)
Such a sensitivity generally indicates an area near rupture as we have previously pointed out here.
"The mechanism by which flares trigger earthquakes can be better understood by studies such as this. In this case the triggered earthquakes appear to be associated with high heat flow due to magma near the surface as in Baja and Mammoth Lakes or at the Geysers which are more related to heated waters. Areas under stress, as the aftershock zone in Chile area also affected." (March 19, 2010)
"Solar activity today was relative light. Four B-class flares were recorded by SWPC. These were associated with earthquakes in Central Mongolia (M 4.
; Baja California (M 2.9, 3.2)" (March 23, 2010)
In preparation for the year 2010 we summarized the historical cycle of earthquakes in Baja California in this report. This summary is repeated below. Note the reference to the quakes occurring at the beginning of the active solar cycle as this did today and the 11-year solar cyclicity (76 years since 1934 (7 times 11); 67 years since lat 1942 (6 times 11); 56 years since 1954 (5 times 11) and 31 years since 1979 (3 times 11), "Earthquakes in this region (Baja) often occur with an 11- or 22-year cyclicity following the beginning of the active solar cycle. The strongest earthquake in the area in the past 100 years occurred almost 75 years to the hour from today's mainshock. This shock and following events with magnitudes up to M 7.1 occurred on December 30 and December 31, 1934. The smaller initial shock of M 6.5 bein followed by a shock of M 7.1-7.3 on December 31, 1934. On January 1, 1927 a similar shock to today's hit the region. In terms of triggering, one of the more interesting shocks in the region was an M 6.0 on April 19, 1906 which occurred only a few hours after the great San Francisco earthquake of M 8.0 hundreds of km to the north. This is a shock many have argued long-distance triggering was clearly involved in. Earthquakes of magnitude near 7 have hit the region in December 1934, May, 1940, October, 1942, October 1954, February, 1956, October 1979. The earthquake today, however is the strongest located in the area in the past 20 years. The last event of M>=5.4 in the area occurred on May 24, 2006 with M 5.4. Other such events occurred on Feb. 22, 2002 (M 5.5-5.7) and Dec. 8, 2001 (M 5.
." (December 31, 2009)
Another of those North American creaking earthquakes occurred early today in West Virginia. This event of M 2.8 was reported by NEIC to have been felt with intensity II in Gassaway and Frametown, West Virginia and II in Bristol, Virginia. As we have previously reported earthquakes of this uncommonality often just precede strong earthquakes on the western rim of the North American plate. A similar earthquake of M 2.8 hit this region on May 6, 2002.
O: 4APR2010 09:19:14 38.6N 80.9W ML=2.8 NEIC WEST VIRGINIA
O: 04APR2010 09:19:14 38.6N 80.9W ML=2.8 CESN Gassaway, WV
P: 4APR2010 52528 40.0N 84.0W 2.0-3.9 ABCAA Ohio/Lake Erie
Global seismicity other than that in California was up a bit from yesterday. The strongest quakes outside Baja California were again located at the far edge of the seismic shadow zone fomr Central Chile (142-148 degrees). Earthquakes in this zone today occurred in the Kuril Islands (M 4.
, Sumatra (M 4.4), Mindanao, Philippines (M 4.7) and the Celebes (M 4.
. The Baja event was at 80.0 degrees from the M 6.7 in Honshu Japan which occurred on March 14. This is an ninth nodal distance (40 times 2 degrees) and some triggering is likely in this situation. The earthquake in West Virginia, like events in New Madrid, MO and Arkansas today occurred at 72 degrees from Chile, the fifth nodal distance. Many unusual earthquakes across the central U.S. in recent weeks have had this distance relation with Chile. At the seventh node from Chile two moderate earthquakes of M 4.7 each hit in central Mexico today (51-52 degrees from Chile). The daily earthquake map today shows the nodal distance from Baja California with forecasts in small pastel shades and earthquakes as bright colors.
https://2img.net/h/i5.photobucket.com/albums/y151/Quakemeister/Bajaquake04-04-2010--04-08-2010.jpg?t=1270748233
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