​The "Earthquake DOC" is an ongoing question-and-answer session mostly about earthquakes. It is the public's opportunity to ask questions about California earthquakes and geology of the California Geological Survey (CGS). E-mail responses by geologists and seismologists to your questions will likely be issued on a monthly basis. CGS will maintain an active list of selected recent questions for you to browse. Your question and answer could be posted next! Also you may browse previous sessions of the "Earthquake DOC". We have listed some Web page links at the end of this page for additional earthquake information.

We apologize if we are not able to get to all of the questions asked. Please try again. Thank you for your participation and we hope you enjoy this interaction as much as we do! Staff - CGS.

Cartoon of the Earthquake DOC 

The Earthquake DOC is in!

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That's a good question!

Q1: I would like to know if there are any counties or cities in California that don't experience earthquakes?

A1: Thanks for the question. Basically, all parts of California have "experienced" shaking from earthquakes at one time or another, but the amount of shaking varies based on the distance from the fault or source generating the earthquake. As you can tell from the map at the following link (, active and potentially faults cover most of California. Areas will feel shaking from earthquakes differently based on: 1) the size of the earthquake, 2) the distance from the earthquake, and 3) the type of geologic material on which the area in question is located (another link:

Since all portions of California can experience shaking from and be impacted by earthquakes, it is important that Californians (and people who visit California) learn to live with "our faults" and be prepared before, during, and after an earthquake one more link:

: Could you give me some information about the great earthquake that hit Winters, California in 1892?

A2: This year (2006) is the 100-year anniversary of the 1906 Great San Francisco Earthquake. The California Geological Survey (CGS) published a special 70-page edition of California Geology devoted to basic facts about earthquakes, and focusing on earthquakes in northern California. In that publication, we devoted a couple articles to the 1892 Vacaville-Winters Earthquake due to its significance to the Central Valley of California. Below are web links to articles referenced in the magazine that provide some detailed information about that specific earthquake:

You can purchase a copy of the new California Geology, "Earthquakes of the San Francisco Bay Area and Northern California," for only $6. If you are interested, please contact the CGS publications department at (916) 445-6199.

Q3: I watched the miniseries "10.5 Apocalypse." I know it is just a movie but can a large city like Las Vegas really sink into the ground like they showed? What about some of the other parts of the miniseries...are they true?

A3: For the most part, the answer to your question(s) is no: the way the miniseries portrays sinkholes in Las Vegas is incorrect. An engineering geologist with CGS provided a "geo-logical" movie review that looks at what is fact and fiction in the "10.5 Apocalypse" miniseries; here is link to the movie review:
10.5 Apocalypse Movie (

Q4: After the 1989 Loma Prieta earthquake, what was determined could have been done to better prepare for and/or prevent the damage that occurred?

A4: Good question. There were many things that could have been done, things that are now being done, and things that we can still do. One of the things that has been done was the passage of the California Seismic Hazard Mapping Act in 1990. This law establishes that the California Geological Survey (CGS) produce maps showing areas where potential earthquake-induced landslide and liquefaction hazards exist (many maps have been completed for the San Francisco Bay and Southern California areas). Cities and counties must require "special studies" to identify if these hazards exist prior to certain types of land development/construction. Here is a link to the CGS program that produce these maps:

Here is another web publication that discusses "lessons learned" from the Loma Prieta Earthquake:

Q5: When measuring the magnitude of an earthquake, it is often expressed in Mw. I understand that is the moment magnitude and is based on displacement at the fault. But I've also seen earthquakes expressed in terms of ML. What is ML?

A5: Thanks for your question. Your explanation of the moment magnitude, Mw, is correct. It is the most common scale used for measuring moderate to large earthquakes and is based on the area of rupture along the fault and the amount of displacement caused by the earthquake.

The ML is the Richter magnitude. It has been in use since 1932 and is derived from the measure of earthquake vibrations recorded on seismogram. The letter designation "L" is for "local." Richter (local) magnitudes should only be used for earthquakes within 400 miles of the recording seismographs.

Here is some more information on different types of earthquake magnitudes:

Q6: I am moving to Hemet, CA in about a month and a half. I was told that it was NOT on the San Andreas fault. Now however, I am hearing information that it is on the fault. I am terrified of earthquakes and this has me scared to death. Is Hemet on the fault? MSNBC had a news segment on the other night stating that the southern part of the fault was due to "blow" at any time. Please advise.

A6: You are correct that Hemet is not located on the San Andreas fault. Hemet is located approximately 20 miles southwest of the San Andreas fault. Having said that, Hemet is located close to other active faults, namely the San Jacinto fault which crosses portions of the city.

The following two links will give you more information regarding the earthquake hazards that exist in the Hemet area. The first link is for the County of Riverside Safety Element. It contains text and maps indicating where the potential hazards exist and what the hazards mean. The second link is for the Southern California Earthquake Center which keeps on-line information about faults in Southern California.

There is no doubt that California is "Earthquake Country." At CGS, we believe that Californians have to learn to live with their "faults," that it is good idea for the public to understand faults, earthquakes, and their hazards. The following link will give you more information about earthquakes and earthquake hazards in Southern California, and it will help give you ideas of how you can be better prepared when they happen.

We hope this information is helpful.

Q7: Where can I find a map of northern California (Sonoma County) fault lines?

A7: We found several websites with the information that might help you.

The first one is the Sonoma County website that has a map of geologic hazards for the entire county:

These next websites are our (California Geological Survey) websites that contain information about active fault zones in the area:

This last website is a detailed map of geology in western Sonoma County from the USGS:

Q8: I need to find information on an earthquake on October 8, 1865 in the Santa Cruz Mountains. I need to find the local time for this quake and if there was loss of life. Can you maybe direct me to a web site for this information.

A8. This reference is from our (California Geological Survey) California Geology gives the time as 1:18pm:

In the following reference, Mark Twain says it was "just after noon":

Here is a reference from the USGS for the earthquake:

The USGS reference states that property loss was about $500,000 but no "loss of life" estimate is given.

Q9: I live in Ventura, Calif. and I am taking out earthquake insurance to protect my property. My agent tells me that in my area, zip 93003, we must pay perhaps the highest rate in the entire state. Please let me know, or refer me on to another website.

A9: All parts of California may be subject to potential earthquake hazards, and it is true that Ventura is in an area of increased hazard relative to other parts of the State. Below I have listed some information/links that CGS produces regarding earthquake hazards:

As CGS does not directly address earthquake insurance questions, I have listed the following links to possibly help you:

Q10: I have a question regarding which areas around the world are most vulnerable to earthquakes and why? Any help with this question would be appreciated.

A10: Most earthquakes around the world occur along or near "plate tectonic" boundaries. For California and the rest of the west coast of the United States, the boundary is the eastern edge of what is known as the "Ring of Fire." The following links will help explain more about earthquakes in California, plate tectonics, and the Ring of Fire:

Q11: Hi. I would like to find out the magnitude of the following earthquakes: Italy 1980, China 1976, Pakistan 1935, Japan 1995, and Peru 1970. Please help me with this, I don't know where to search for the answer to this kind of question. Thank you.

A11: Here is a link that gives magnitude and casualties for the post-1900 earthquakes:

Q12: We live on Landing Hill in Seal Beach, in a two-story home (in good condition) constructed in the mid-1960's on a concrete foundation (no crawl space). We would like to prepare our home for the inevitable large earthquake. Our question concerns the pros and cons of earthquake retrofitting the home versus tearing the home down and building a new two-story to modern codes (caissons, steel frame, etc.). Any insights that you could provide would be appreciated.

A12: That is a great question. It is difficult to say just how at risk your present structure is without having an expert (architect or structural engineer) look at it. Having said that, consider that many injuries in the home related to earthquake shaking are not caused by structural collapse. They are a product of falling objects such as heavy bookcases, light fixtures, mirrors, pictures, and even televisions. So, there are things you can do to your existing house to help prevent some problems. The following links will help you identify some of those problem areas, show how to minimize them, and provide you with other valuable earthquake preparedness information:

Another thing to investigate is whether your home is located in an area of seismic hazards other than ground shaking. The California Geological Survey maps Seismic Hazard Zones where potential earthquake-induced landslides or liquefaction might occur. The following link shows the Seismic Hazard Zone map for the Seal Beach area:

Your local city or county building or planning departments might have additional information for identifying hazards and helping to take care of them. The following link goes to the City of Seal Beach's General Plan and Safety Element:


Browse previous sessions with the Earthquake DOC:

Browse these links for more earthquake information: