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.

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.

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.

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 group’s apparent success in predicting the magnitude 8.1 earthquake in Hokkaido, Japan in September 2003 and last December’s 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."