Specific User Questions

Why are there so many earthquakes in Southern Ca. in the area of the Cochella (sic) Valley?
Is is because of the number of instruments in the area, or are there really that many more quakes in that area as opposed to other areas in Ca.?

September 17, 2007

The northern Coachella Valley extends southeast from the San Gorgonio Pass to the north end of the Salton Sea. The area is traversed by multiple strands of the San Andreas Fault Zone, including the Mission Creek Fault, with the main trace of the fault zone approximately 2 miles east of the intersection of Route 86 South and Interstate 10 East, just to the north of the town of Coachella (click to view a schematic map of the region). Recent studies have suggested that the valley is a region undergoing contraction, developing over the last one million years due to movements along the various strands of the San Andreas Fault Zone. These movements are the cause of the earthquake activity in the area.

The number of instruments in the area does not affect the frequency of earthquake detection. Although this region is quite active, other parts of the San Andreas Fault Zone are more so, including the village of Parkfield in central California and the town of Anza which lies on the San Jacinto Fault Zone, a 200km long branch of the San Andreas system.

More information:

- Rob Newman

Please help me with these questions? Have the recent small earthquakes been anyway related to the Rose Canyon Fault. Also I just moved out of Clairemont due to that scare. Is there any faults close to Rancho Bernardo??? Do you believe that these small earth quakes are a good thing? relieving pressure? Or building up for a big one?? Also about the Big one do you believe that San Diego is overdue for a major earthquake? and also do you believe that the new laws for builders that most of the newer houses will have no problem standing a good size earthquake??? I have been seriously thinking about moving back to the east coast. But I was also told that the biggest earthquake recorded was on the east coast. Is that true??? Also do you still believe the safest place to stand is in the door frame of the home??? Please help me with any info. I am scared to death that we are going to have the "big one" and float out to sea...Am I just paranoid? Thank you

September 10, 2007

The recent spate of earthquakes off the coast of San Diego have occurred on a variety of offshore fault zones, notably the San Diego Trough Fault Zone and the Coronado Bank Fault Zone. They have not occurred on the Rose Canyon Fault Zone, with the exception of the magnitude 1.8 that occurred at 12:35PM on Sunday September 9th, 2007, and that would have most likely been too small to have been felt by anything except instrumentation. For a detailed view of faults offshore San Diego see http://eqinfo.ucsd.edu/faq/faults_sd_coast.php. For an interactive map of earthquakes where you can view the major fault zones in relation to earthquake epicenters, see http://eqinfo.ucsd.edu/tools/southern_california_recent_earthquakes.php

There is the Rose Canyon Fault Zone ~15km to the west, and the Elsinore Fault Zone ~35km to the east of Rancho Bernardo. Both these fault zones are quite close to you. The Rose Canyon Fault Zone is not particularly active, with movements on the order of ~1.1mm/year (http://www.data.scec.org/fault_index/rosecany.html).

The Elsinore Fault Zone has movements ~4.0mm/year (http://www.data.scec.org/fault_index/elsfault.html) and has had several large earthquakes in recorded history - a magnitude 7 on the southern extension of the fault zone, called the Laguna Salada fault, ruptured on February 23rd, 1892 in an uninhabited area of Baja California, Mexico. This event caused cracks in large buildings in San Diego, although no fatalities occurred (http://www.data.scec.org/chrono_index/lagsalad.html). The main trace of the Elsinore Fault Zone has only ever seen one event greater than magnitude 5.2 (http://www.data.scec.org/chrono_index/elsinore.html) and that occurred in 1910 and was a magnitude 6 that occurred near Temescal Valley. No surface rupture occurred and there was little damag

There is currently no general consensus on whether small earthquakes relieve pressure. Some scientists believe that a number of small earthquakes can relieve pressure, but others believe a high frequency of small earthquakes can lead to a larger one, and are 'foreshocks'. See http://quake.wr.usgs.gov/prepare/factsheets/QuakeForecasts/ for more information.

In my own opinion I would not suggest that the county of San Diego is overdue for a major earthquake, but that Southern California as a whole has not had a large event for over 300 years, and studies have shown that certain areas (such as the Coachella Valley) experience large events every 150 years. The whole region is possibly overdue, but I would not just single out San Diego county. There are certain regions in Southern California that are more likely to experience a large earthquake, such as areas lying on the San Andreas Fault Zone (including communities such as Parkfield, Palmdale and San Bernardino) and the San Jacinto Fault Zone (including communities such as San Bernardino, Loma Linda, San Jacinto, Hemet, Anza, and Borrego Springs).

If you are referring to the 2006 FEMA 232 Homebuilders' Guide, then I must admit that I have not studied it in any great detail. I am not an expert on building codes and I suggest that if you are seriously concerned you should contact the Building Seismic Safety Council (BSSC) in Washington, D.C (http://www.bssconline.org/ab/contactus.html). Earthquake insurance is available, and provides additional coverage in the event of a catastrophic event.

The largest earthquake recorded in the United States since 1900 was the magnitude 9.2 Alaska event that occurred on March 28th, 1964 in Prince William Sound near Anchorage. Historically, the largest event know to have occurred in the 'lower 48' United States occurred on January 26th, 1700 in the Cascadia Region (northern California, Oregon, Washington and southern British Columbia) and was estimated to have been magnitude ~9.

"Only if you live in an old, unreinforced adobe house. In modern homes doorways are no stronger than any other parts of the house and usually have doors that will swing and can injure you. YOU ARE SAFER PRACTICING THE DUCK, COVER, AND HOLD under a sturdy piece of furniture."
Reference: http://earthquake.usgs.gov/learning/faq.php?categoryID=14&faqID=76

I would recommend positioning yourself under a strong desk or dining room table.

You are not paranoid, although it is highly unlikely that parts of California will float out to sea if an earthquake does occur! It is good to have a healthy respect for earthquakes. They are a natural phenomenon and part of living in California. The more you can understand and prepare for them, the less frightening they will become. With careful planning, you can limit the effects a large earthquake will have on you and your family. Being properly prepared is critical. Please follow the links below for more information.

More information and resources:

- Rob Newman

Is there any reason to believe that there is a connection between the underground nuclear testing in Korea and the earthquake in Hawaii?

October 16, 2006

You ask an interesting question -- unraveling what triggers earthquakes is a subject of great interest to me, and one a topic that the seismological community has devoted a great amount of effort and research.

To begin to answer your question the first bit of information we need is what the time and distance separation is between the nuclear test in Korea and the Hawaii earthquake.

There is a lot of information available on the Hawaii earthquake, for example researchers here at Scripps Institution of Oceanography recorded this earthquake on EarthScope's USArray network, see:

http://anf.ucsd.edu/spevents/2006/288/a/index.php

Information about the North Korea nuclear test can be found, for example, here on the CNN website:

http://www.cnn.com/2006/WORLD/asiapcf/10/08/korea.nuclear.test/

From this simple data gathering we can determine:

Korea Test:
    Time: October 9 1:36AM GMT
    Location: North Korea (~41.3N, 129.1E)
    Equivalent to a magnitude ~4 earthquake

Hawaii Earthquake:
    Time: October 15, 2006, 17:07 UTC
    Location: Hawaii: 19.8, -156
    Magnitude: 6.6

To find out approximately how far apart these two locations are you can use this tool:

http://www.timeanddate.com/worldclock/distance.html

After a few computations, we can estimate:

Time separation between events: ~6 days
Distance separation between events: ~7400 km or 4600 miles

The other information we need to gather is how common are magnitude 4 earthquakes and how common are magnitude 6 earthquakes. We can find that information here:

http://wwwneic.cr.usgs.gov/neis/eqlists/eqstats.html

So, a magnitude 4 earthquake occurs about 13,000 times a year and a magnitude 6.6 earthquakes occurs about 134 times a year. Ah-ha this is an important bit of information! What this tells us is that we have ~13,000 magnitude 4 earthquakes every year and it is very unlikely that they routinely trigger larger earthquakes because there are only 134 of the larger earthquakes every year (a factor of 100 smaller!).

Based on this information I conclude that there is not any connection between the Korea test and the Hawaii earthquake. The two strongest bits of evidence for this is that: (1) the supposed triggering event (the Korea test) is relatively speaking very very small; and (2) the distance between the two events is very very large.

Let me know if anything is unclear or if we can help you with any other questions.

– Debi Kilb

Do you use some kind of heavy microwave equipment on your Toro Peak station? I live on El Toro road in Anza and I feel the "shooting" that is about to burn my TV set. This "shooting" is constant and of course somewhat bothersome, but tolerable in the name of science.

October 13, 2005

Actually we while we do use several microwave frequency radios on Toro Peak, they are all extremely low power. All of our radios transmit using less than 1 Watt of power, which is much less than the power a standard 40 Watt light bulb radiates.

– Frank Vernon

I am seeking info regarding ground motion vs distance for locations in Carlsbad and Mira Mesa

May 25, 2005

The best information available is probably at:

http://www.data.scec.org/general/PhaseII.html

and historical seismicity can be found at:

http://www.data.scec.org/clickmap.html

Your question is hard to answer, since there are several faults in the region which can sustain "major" earthquakes. But in general if we have a magnitude 6 or larger inside San Diego county, there probably will not be much difference in the level of shaking between your Carlsbad and Miramar sites. To give you an example of the shaking from the 1994 Northridge earthquake, you should look at;

http://pasadena.wr.usgs.gov/shake/ca/STORE/XNorthridge/ciim_display.html

– Frank Vernon

What does the negative (-0.34ML) mean?

May 11, 2005

Magnitude is a measure of the energy released by an earthquake, or the size of the earthquake. The magnitude scale is logarithmic so that each increase of one unit of magnitude corresponds to a ten-fold increase in the amplitude on a seismogram. In terms of energy released, an increase of one magnitude unit corresponds to approximately a 32 fold increase in energy. The magnitude scale is not a 1 to 10 scale. Negative magnitude earthquakes occur very frequently (although because of the definition of magnitude, negative magnitude does not correspond to negative energy released).

Different magnitude scales are discussed here:

http://eqinfo.ucsd.edu/glossary/glossary.html#diff

– Rob Newman

It is 9:40 pm on Wed. April 6. I just heard on the radio that So. Cal. near the LA area and San Diego area experienced some jolts. To make it interesting, the east coast, No. East area just experienced a shaker as well. Any relation betwen the two?

April 06, 2005

Thanks for your question, unfortunately the answer is rather complicated. It is currently debated in the seismology community how, and if, earthquakes relatively far from each other can be causally related. Ten years ago the typical rule of thumb was that 'aftershocks' (any earthquake caused by a previous earthquake) only extended out to a region that was 1- or 2-times the fault length of the causative mainshock. But, following the 1992 Landers earthquake it was clearly observed that aftershocks occurred up to 12-17 fault lengths away. This observation drastically changed the theories of earthquake source physics, and spurred seismologist to ask questions similar to yours below. Because the two earthquakes you ask about are relatively small earthquakes (below magnitude 5) it is very difficult to show a causative relation between them because there is too much uncertainty -- for example other nearby earthquakes, these earthquakes happening just by random chance etc. If we apply the 12-17 fault length rule to these events the causative region would be at maximum 20 km and therefore much too short a distances in comparison with the distance between the east/west coasts. I would conclude that a correlation can not be proved and that because the earthquakes are so small the correlation is unlikely, but that said, we can not rule it out as a possibility.

One of the more interesting correlations that has been found recently is this:

The recent recording of water level changes up to ~3 feet in a 450-foot-deep well in western Virginia following the 26 December 2004 Mw 9.0 Sumatra earthquake (~15,500 km away from the mainshock event!) helps support the idea that fluids re-equilibrate after the passage of seismic waves (see http://www.rense.com/general61/dssde.htm).

– Debi Kilb

URL: http://eqinfo.ucsd.edu/faq/specific.php [Last updated: 2015-10-22 (295) 23:07:44 UTC]