If You Felt Monday's ELB Quake, Seismologists May Want To Hear From You
(August 17, 2004) -- LBReport.com has received a number of emails from readers who felt the light ELB earthquake at 12:56 a.m. on August 16...and thanked us for reporting it. Here's what the shaker looked like monitored by the Southern CA Earthquake Center.
If you were among those who felt Monday morning's mild but memorable temblor, the U.S. Geological Survey's seismologists may be interested in hearing from you. USGS has an earthquake web section that says in part:
DID YOU FEEL IT? REPORT IT HERE! You can help provide information about the extent of shaking and damage for earthquakes in the United States, and you may provide specific details about how your area may respond to future earthquakes," says the USGS page, adding "USGS scientists may use the information you enter in this form to provide qualitative, quantitative, or graphical descriptions of damage in USGS publications.
Of course, there was no damage from the 2.3 magnitude quake...but to report what you felt to the U.S. Geological Survey, click USGS "Did You Feel It?" Web Page.
We also noticed something interesting on the fault map (right) on the Southern CA Earthquake Center's web site. We're not a seismologist, but it looks to us like the August 16 quake might have something to do with that little purple diagonal fault line, running from the 605/405 area northwest and ending up (it looks like) near LB Airport.
Compare the purple diagonal fault line to these descriptions on the CA Earthquake Center's web site regarding the location of the August 16 mini quake: 3 miles east (96 degrees) from LB, 3 miles ESE (107 degrees) from Signal Hill, 3 miles NNW (346 degrees) from Seal Beach...and 2 miles W (263 degrees) from Rossmoor.
The purple line fault is described by the So. Cal. Earthquake Center's web site as follows:
TYPE OF FAULT: uncertain
LENGTH: 11 km
NEARBY COMMUNITIES: Los Alamitos, Lakewood, Bellflower
MOST RECENT SURFACE RUPTURE: Late Quaternary [last two million years of Earth history]
OTHER NOTES: Age uncertain; fault indistinct. May be part of a larger fault system -- the Compton-Los Alamitos fault.
Others have speculated that the small temblor might be related in some way to the longer green fault line: the notorious Newport-Inglewood fault. It last ruptured on March 10, 1933, flattening parts of LB. The Southern CA Earthquake Center indicates the Newport-Inglewood fault can generate probable magnitudes between of 6.0 and 7.4. "[T]he fault zone can easily be noted...by the existence of a chain of low hills extending from Culver City to Signal Hill. South of Signal Hill, it roughly parallels the coastline until just south of Newport Bay, where it heads offshore..."
So...was the August 16 light quake associated with the Newport-Inglewood fault, or some other identifiable fault? John Marquis of the Southern CA Earthquake Center tells LBReport.com:
For an earthquake as small as this one, there is no way to definitively
pin it on a single causative fault. That's because the size of the fault rupture that produced the earthquake (maybe 5 meters square) is far less than the error in the earthquake's location (roughly .5 km).
To correlate an earthquake with a specific fault, the earthquake generally needs to be at least magnitude 5 in size. (In terms of energy released, that's well over 1,000 times larger!) Thus, trying to say that this M 2.3 earthquake was on any specific fault would be misleading at best. There are many, many, tiny unnamed faults that could have produced a quake of this size, so it was most likely not on the trace of the Newport-Inglewood
or any other named fault.
And if you don't have enough to worry about, the USGS web site notes that a prediction has been made by the Keilis-Borork research team for a "magnitude 6.4 or greater earthquake to occur between January 5 and September 5, 2004, within a 12,440 sq. miles area of southern California that includes portions of the eastern Mojave Desert, Coachella Valley, Imperial Valley (San Bernardino, Riverside and Imperial Counties) and eastern San Diego County..."
The site notes:
The Keilis-Borork team has just begun the test of this prediction technique and has not yet issued enough predictions to evaluate whether or not the approach is successful. It's notable because of the groupís apparent success in predicting the magnitude 8.1 earthquake in Hokkaido, Japan in September 2003 and last Decemberís magnitude 6.5 San Simeon quake. However, those predictions also covered very large areas so there was some chance the earthquakes would have happened anyway...
The prediction method the Keilis-Borok team uses is based on identifying patterns of small earthquakes as precursors to large ones. These small earthquakes occurred last fall and the prediction window is 9 months from the end of that earthquake cluster.
...The work of the Keilis-Borok team is a legitimate approach to earthquake prediction research. However, the method is unproven, and it will take much additional study, and many additional trial predictions, before it can be shown whether it works, and how well...
In February, experts from U.S. Geological Survey, California Geological Survey, the Southern California Earthquake Center and others reviewed the Keilis-Borok prediction. Dr. Keilis-Borok and his colleagues presented their methods and findings and engaged in frank discussion with about 30 invited scientists and public officials. The California Earthquake Prediction Evaluation Council attended and concluded that the Keilis-Borok methodology is a legitimate approach in earthquake prediction research, but that, while the prediction serves as a reminder for vigilance in earthquake-prone areas, "the results do not at this time warrant any special public policy actions in California."
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