Previous Question and Answer Session
The "Earthquake DOC" -
Thanks for asking these great questions!
Q1: I understand that there are "zones" for earthquakes, ie. 1, 2, 3, and 4. I am trying to locate a map of these zones for the US or portions of. Thanks for any help.
A1: : You can find a seismic zone map of the United States from the 1997 Uniform Building Code at the top of the following Web page:
Q2: How much ground shaking occurred in the Woodside-Portola Valley area during the 1989 Loma Prieta earthquake? Where were the closest monitoring stations in 1989? Are there more stations in the area now? Thanks.
A2: You can find a shaking intensity model by the Association of Bay Area Governments for the 1989 Loma Prieta earthquake on:
The peak ground acceleration (PGA) map for the Loma Prieta Earthquake is on:
Values of PGA instruments in your area of concern were in the range of 0.08g (gravity) to 0.29g.
California Integrated Seismic Network's Rapid Instrumental Intensity Map for the Loma Prieta Earthquake is on:
(Click on the "Scientific Background" tab for explanation of symbols and to identify stations.)
Seismic network maps and lists of stations (for Northern California Seismic Network see "Station List Format" link for dates stations have been active) are available on:
Q3: Which civil authorities have the most information, or are in charge of response activities to an earthquake event?
A3: Please refer to the Governor's Office of Emergency Services' document, "Emergency Management in California" on the following link. See page 33 for a discussion of California's Standardized Emergency Management System (SEMS) to see which agencies respond and in what order. In short, the local agencies (cities) respond first, but county, state, or federal assistance could be requested, depending on the need.
For specific geologic information about recent earthquakes, go to the Earthquake Engineering Research Institute (EERI) Web site:
http://www.eeri.org/ Information is also available one the U.S. Geological Survey site,
http://earthquake.usgs.gov/ and the California Department of Conservation, California Geological Survey site, http://www.consrv.ca.gov/cgs/index.htm . For the Southern California area, go to the Southern California Earthquake Center site at
Q4: Why are some faults referred to as a "fault zone," while others are not? Has anyone attempted to standardize these terms...such as fault, fault zone, fault system? Thanks!
A4: Though general fault terms are often used interchangeably by some people, some dictionaries make distinctions among the terms. A popular reference book is the American Geological Institute's
Glossary of Geology, available for purchase at:
Here are simplified definitions for the terms you have listed from A Dictionary of Mining, Mineral, and Related Terms (1968) by the U.S. Bureau of Mines:
fault -- A fracture or a fracture zone in crustal rocks along which there has been displacement of the two sides relative to one another parallel to the fracture.
fault set -- A group of faults that are parallel, or nearly so, and that are related to a particular deformational episode.
fault system --Two or more fault sets that were formed at the same time.
fault zone -- A fault that is expressed as a zone of numerous small fractures or of breccia or fault gouge. A fault zone may be as wide as hundreds of meters.
Q5: I have searched all afternoon for information - I was told of, somewhere in California, an area of the earth opened resulting in a gigantic split. The bit of news which did show a picture did not say the exact location, nothing more than it happened in California. This would have been shown in the last 3-4 weeks. What can you tell me about this? Many thanks.
A5: I did not see the picture so I'm not sure what the subject was, but I can refer you to a photo of the San Andreas Fault trace in the Carrizo Plain area in central California. It certainly looks as if the earth opened up, but it didn't. Go to
http://pubs.usgs.gov/gip/ and click on "The San Andreas Fault."
Also, the picture you are referring to might be a fake of some sort or from a movie. There are some pictures floating around regarding the recent NBC TV miniseries "10.5" that show the ground opening up and swallowing people, buildings, and even a train. For more information concerning "10.5", see our "geo-logical" movie review at the following link:
Q6: As a result of my web page and its wake-up call about the coming "New Madrid" earthquake, scores of people, including myself, have been left wondering "How bad will it really get?" If you are so inclined,
http://www.cusec.org was the site that woke me up. At their home page on the left side, (the last time that I looked at it), had a link called "New Madrid Seismic Zone", (http://www.cusec.org/S_zones/NMSZ/nmsz_home.htm). After clicking on the second link you will come to a page with a drawing of the projected damage, not only in the number of states involved, but in magnitude as well. The "6.0 magnitude" just crosses the Ohio border from Indiana. Dayton and Cincinnati are not far from that border, and concern is becoming an issue.
So as concerned Ohioans, this is what we would like to know... "How can we compare the probable 5.5 to 6.0 magnitude quake in SW Ohio to a Californian earthquake?" Since you may have a 5.1 earthquake and little damage is done there, it gets people's hopes up that it will not be that bad here. That is a misleading conclusion, because your state has sufficient building codes, while ours are lacking. (It is not a one-to-one comparison.) But, I believe that a comparison can be made with the Earthquake Engineering Staff, in California, expert assessment.
Is it possible to reasonably say, for example... that there is a difference of 1.5 magnitudes when comparing damage-for-damage? Meaning, if you have a 7.0 in California, it would be the same amount of damage if we had a 5.5 earthquake here. I would not be surprised that the 1.5 magnitude difference would not be able to be applied in all of the New Madrid situations, because, some people may have a 6.0 -7.0, and other people may experience a 7.0 - 8.0. But in an effort to try to keep things simple, let's stick to SW Ohio. (After all, Dayton Ohio is one of the nation's top 90 minute markets, meaning that you can reach Millions of people with a 90 minute drive.) Also, other cities fit into the same magnitude range as Dayton. Thus, you can see that an expert reply that I can post on my Web site, will go a long way in helping to get the facts out, about what people can expect, and what if any precautions that we should make. Please reply!
A6: Earthquake size is described by magnitude and intensity. I think the map you are referring to is showing the Modified Mercalli Intensities (MMI) that might be expected from a magnitude 8 earthquake in the New Madrid Seismic Zone. The Roman numerals you see refer to the intensity of an earthquake as determined from the visible effects of the event. If you click on the link below the caption you'll be able to see what kinds of damage to expect in each intensity zone. For example, dishes and windows might break in the MMI V areas, while heavy furniture might move and plaster fall in the MMI VI areas. The maximum MMI expected is VIII, so in that area you might see some chimneys and walls fall, with greater damage in poorly built structures.
http://pasadena.wr.usgs.gov/shake/cus/html/background.html in the section called "What is Intensity" that California's 1994 magnitude 6.7 Northridge earthquake had intensities as high as IX. The magnitude 8.3 New Madrid earthquake's highest intensity was VIII. This demonstrates that magnitude is not always a good measure of how an earthquake affects things on the earth's surface.
Also of interest on the CUSEC website is the map accessed by clicking on "(see the differences in affected areas here)" which leads to this page:
http://www.cusec.org/S_zones/NMSZ/Areas.htm. On this map, A Comparison of Areas of Damage from the New Madrid and San Francisco Earthquakes, you can see the intensities for the December 16, 1811 magnitude 8.6 New Madrid and April 18, 1906 magnitude 8.3 San Francisco earthquakes. This map shows that southwestern Ohio had MMI VI, which means that there was more serious damage in Ohio during the 1811 earthquake might be expected from a future magnitude 8.0 earthquake, possibly because buildings are built better now. Perhaps CUSEC could offer more information about the maps and information that are on their website. You can contact them through
Note also that there is more information about earthquake intensity and how individuals can report what they felt during an earthquake so that community internet intensity maps can be created. The following link is to a U.S. Geological Survey site about the science behind the maps:
http://pasadena.wr.usgs.gov/shake/cus/html/background.html. You can click on "Unlisted quake" near the top of the page to report details about what you felt during a new earthquake. Also, you can click on your geographic area near the top of the page to see recent earthquake intensity maps.
More Ohio earthquake information is at
I'm glad you take earthquakes seriously, it's good to be prepared!
Q7: I am looking for the map that shows the effect of California falling into the ocean. At one time there was a rendering of how the United States would be affected and the coastlines etc. if such a catastrophic event occurred. Can you help me locate it?
A7: The recent NBC-TV miniseries "10.5" showed part of California "falling" into the Pacific....really, becoming an island...and someone asked if that could happen. Please read my explanation of Question and Answer #4 from my previous session of July 2004 at:
In short, California will NOT fall into the ocean.
Q8: A condo I am considering buying is in a liquifaction area (Greenfield Ave, L.A., between Wilshire and Santa Monica Blvd). How bad is this?
A8: Please see Question and Answer #14 from the Earthquake DOC's previous session of May 2005 -
Click here. You have already discovered that the condo is in a potential liquefaction zone, but you would need to read a liquefaction study done on the property to find out if the hazard exists at that specific site. A good resource is a geology, soils, or geotechnical report for the condo property that the City of Los Angeles, the property tract developer, or a previous homeowner might have. These reports may have been completed for your home or subdivision as a requirement prior to construction and might contain evaluations for liquefaction. Though these reports might be hard to track down, they will be the most site-specific and informative to help you with your questions about your property.
Q9: I have been told, and I am skeptical, that underneath Simi Valley lies an enormous underground lake (maybe aquifer) that is said to be one of the largest bodies of fresh water in the United States! Is this true? If so, what is its depth and how might the lake or the city of Simi Valley be affected during an earthquake event on the local fault? Thanks.
A9: Simi Valley covers an area of about 22 square miles. In contrast, Lake Mohave Reservoir (between Hoover and Davis dams) has about twice the surface area; Lake Tahoe covers about 190 square miles; and Lake Mead, 250 square miles. Lake Superior covers 31, 700 square miles.
Simi Valley contains up to 700 feet of alluvium, and because there's no outlet for the accumulated ground water, it rises close to the surface in some places. But this is not an underground lake, only saturated sediment.
It's hard to say how Simi Valley would be affected during an earthquake. Some factors include the magnitude and distance from the origin of the earthquake, the type of rock at the site, and the type of building construction. Earthquakes can cause ground failures that can break water and gas pipelines in and around structures triggering additional hazards. You can open CGS's Seismic Hazard Zone Map for the area (quadrangles Simi East and Simi West), at http://gmw.consrv.ca.gov/shmp/download/pdf/ozn_simve.pdf and
http://gmw.consrv.ca.gov/shmp/download/pdf/ozn_simvw.pdf to see where there is a potential for landslides or liquefaction might occur during an earthquake. Keep in mind that just because these areas are in hazard zones doesn't mean that the hazard exists...it just means that it potentially exists (site-specific analysis is needed for confirmation).
Q10: What would be a good basic "checklist" for items to have on hand in case of an earthquake, sufficient to maintain one's existence for a period of five days maximum?
A10: Please refer to the Red Cross and Earthquake Country Web sites below. They have suggestions for food, first aid, tools, sanitation, clothing, bedding, baby items, and important documents.
Q11: I live in Lancaster and I just heard on the news that Lancaster is considered an Earthquake zone, my zip code is 93535, is this an earthquake area?
A11: You probably heard news of the August 11 release of CGS's Preliminary Seismic Hazard Zone Maps for parts of Antelope Valley. You can see and read about these maps on our Web site
http://gmw.consrv.ca.gov/shmp/ To see the liquefaction and landslide zones for an area, click on the green map under "Quick View/Download PDF Maps." For southern California, click on the grey box at the top of the page, then on the quadrangle of interest. For your area, try Lancaster West, near the top of the map. The Lancaster West zone map shows some green areas that indicate where liquefaction is possible. Back up a page and click on the Del Sur Quadrangle, to the west, to see some blue areas that indicate where seismically-induced landslides could occur.
In answer to your question, yes, this is an "earthquake area." The San Andreas fault runs parallel to the hills that border Antelope Valley on the south. If you zoom in on the southwest part of the Del Sur Quadrangle, you can probably read "SAN ANDREAS RIFT ZONE" on the topographic base map just above "LEONA VALLEY." If you've driven north on the Antelope Freeway (Highway 14) into Palmdale, you've probably noticed contorted rock in a big roadcut just north of the Avenue S offramp. The San Andreas fault is at the south end of the roadcut; the Little Rock fault is north of the northern end of the roadcut.
Also of interest might be the California Geological Survey's Official Maps of Earthquake Fault Zones, which are discussed on
http://www.consrv.ca.gov/CGS/rghm/ap/index.htm. These maps show the surface traces of active faults. An index map is at
This section of the San Andreas fault ruptured in 1857, causing the magnitude 7.9 Fort Tejon earthquake, though the epicenter was likely further northwest along the fault. For a discussion of this event, click on http://earthquake.usgs.gov/regional/states/events/1857_01_09.php and to see a map of the probable epicenter and effects of the earthquake, click on "Isoseismal Map" near the top of that Web page. During the Fort Tejon earthquake, Lancaster was within the VII-IX intensity range on the Modified Mercali scale of I to XII. For example, at level VII, people have difficulty standing; at IX, well-built buildings are damaged. See
http://www.seismo.unr.edu/ftp/pub/louie/class/100/mercalli.html for more on isoseismal maps and earthquake intensities.
No one knows when or where another such earthquake will occur, but all Californians should do their best to prepare. See these and other Web sites for safety tips:
Q12: I've never heard of an earthquake occurring in the immediate Sacramento area. Are there any active faults in the Sacramento metropolitan area that could produce a damaging earthquake? Is the Sacramento area at any risk from local or regional earthquakes? Also, do you know what amount of shaking and damage the Sacramento area experienced during the 1906 San Francisco earthquake, which occurred approximately 100 miles away from downtown Sacramento? Thanks!
A12: The U.S. Geological Survey has records of 10 earthquakes of magnitude 5 or greater within 100 kilometers (about 62 miles) of Sacramento (try earthquake searches at
The towns of Vacaville, Winters, and Dixon suffered damage from the Vacaville (magnitude 6.5) and Winters (magnitude 6.2) earthquakes of 1892. In Sacramento, statues fell and plaster cracked in the Capitol. The following link gives a brief description of this earthquake:
For 1906 earthquake effects, see an isoseismal map:
http://earthquake.usgs.gov/regional/states/events/1906_04_18_iso.php. Note that Sacramento was in the intensity V area, where almost everyone would have felt movement during the earthquake, and damage would have consisted of broken dishes and such. See the following Web page for more on earthquake intensities:
For a comparison to a more recent earthquake, see an isoseismal map for the 1989, magnitude 6.9, Loma Prieta earthquake:
http://pasadena.wr.usgs.gov/shake/STORE/XLoma_Prieta/ciim_display.html. Note that shaking was mostly light to moderate in Sacramento, with very little damage.