All FAQs
Common Myths about Earthquakes
- Can you predict earthquakes?
- Can animals predict earthquakes?
- Can some people sense that an earthquake is about to happen? (earthquake sensitives)?
- Is there earthquake weather?
- Are there more earthquakes in the morning/in the evening/at a certain time of the month?
- Can the ground open up during an earthquake?
- Will California eventually fall off into the ocean?
- Do earthquakes cause volcanoes?
- Can you prevent large earthquakes by making lots of small ones, or by "lubricating" the fault with water or another material?
- Why are we having so many earthquakes? Has earthquake activity been increasing? Does this mean a big one is going to hit? OR We haven't had any earthquakes in a long time; does this mean that the pressure is building up?
- What is the "Triangle of Life" and is it legitimate?
- Where can I buy a Richter scale?
Earthquakes, Faults, Plate Tectonics, Earth Structure
- Can we cause earthquakes? Is there any way to prevent earthquakes?
- What do we know about the interior of the Earth?
- Can earthquakes be predicted?
- What is plate tectonics?
- What is a fault and what are the different types?
- What is the relationship between faults and earthquakes? What happens to a fault when an earthquake occurs?
- How do we know a fault exists?
- Where can I go to see the/a fault?
- Where can I get seismic hazard maps?
- Where can I find information about faults in my area?
- How can I find out about earthquakes in my area?
- Where can I find information about volcanoes?
- How can I find out about tsunamis?
- What is an earthquake and what causes them to happen?
- At what depth do earthquakes occur?
- What is surface faulting or surface rupture in an earthquake?
- Foreshocks, aftershocks - what's the difference?
- Can the position of the moon or the planets affect seismicity?
- Two earthquakes occurred on the same day. Are they related?
- Where can I get a fault map?
- Do earthquakes occur in Antarctica?
- What is the significance of the depth of an earthquake?
Current Earthquake Information
- Can I get on a list to receive an e-mail message when there is an earthquake?
- How can I report an earthquake experience or related observation?
- Where can I see current or past seismograms?
- How do I find what I want?
- What pages should I bookmark?
- Why are squares used for the earthquakes?
- How were the symbol sizes chosen?
- How were the colors chosen?
- Why do so many earthquakes occur at a depth of 10km?
- What do "last hour", "last day" and "last week" mean?
- How do the earthquakes get to the webpages?
- Why do some earthquakes disappear?
- Why isn't the distance to the nearest fault provided?
- How did you decide which places to use for computing the distance to individual earthquakes?
- What is the reference point for the places?
- How did you decide which places to plot on the maps?
Measuring Earthquakes
- Where can I buy a Richter scale?
- Why are there often different magnitudes reported for the same earthquake?
- What is moment magnitude?
- What are the earthquake magnitude classes?
- When was the first instrument that actually recorded an earthquake?
- What is a P wave? An S wave?
- What does an earthquake look like?
- What is intensity? What is the Modified Mercalli Intensity Scale?
- What is the difference between intensity scales and magnitude scales?
- What is acceleration, velocity, and displacement?
- What is spectral acceleration?
- What are those beachball figures?
- How much energy is released in an earthquake?
- What are UTC and GMT (in reference to the time of an EQ)?
- What does it mean that the earthquake occurred at a depth of 0 km?
- How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
- What are the different magnitude scales, and why are there so many?
- How do you give a Richter magnitude to earthquakes that occurred prior to the scale?
- What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?
- How do seismologists locate an earthquake?
Earthquake Effects & Experiences
- Where can I find photographs of earthquake damage?
- Why do earthquakes in other countries seem to cause more damage and casualties than earthquakes in the U.S.?
- How do you classify/measure the shaking that you feel during an earthquake? Sharp jolts versus rolling motion?
- What are isoseismal maps?
- What is liquefaction?
- What are the effects of earthquakes?
- Where have tsunamis occurred historically?
- At what magnitude does damage begin to occur in an earthquake?
- What are earthquake lights? Are they real?
- What does an earthquake feel like?
- What are those booms I sometimes hear before or during an earthquake?
- How can an earthquake effect groundwater or changes in wells?
Seismographs
- What is a seismometer? What are seismographs? How do they work?
- What are seismograms? How do you read them?
- How is the movement of the seismometer converted into a seismogram?
- How can I make my own seismometer?
Historic Earthquakes and Earthquake Statistics
- What is the biggest earthquake ever?
- What is the biggest earthquake in the United States?
- Which States in the United States have the most earthquakes?
- Which State has the most damaging earthquakes?
- Which States have the smallest number of earthquakes?
- How many earthquakes worldwide occur each day? Each year?
- Where can I find a list of the largest earthquakes near my town?
- Where can I find a list of the most destructive earthquakes in the world?
- Where can I find a list of the largest earthquakes in the United States?
- Where can I find other lists of earthquakes?
- Can I do an earthquake catalog search to get my own list of earthquakes?
- Where do earthquakes occur?
- I want to move to a place that doesn't have earthquakes. Where can I go?
- Which Country has the most earthquakes?
Probabilities, Seismic Hazard & Earthquake Engineering
- Are earthquake probabilities or forecasts the same as prediction?
- What is the probability that an earthquake will occur in the Bay Area?
- What is the probability that an earthquake will occur in the LA Area?
- What is seismic hazard and how is it determined?
- Where can I find seismic hazard maps?
- How do earthquakes affect buildings?
- How will my house hold up in an earthquake? Can the USGS send someone out to evaluate my property?
- How are engineers working to make roads and buildings safer?
- What are the Guidelines for evaluating and mitigating seismic hazards in California?
- What is the USGS doing to mitigate and respond to earthquake hazards?
- How do I decide whether or not to get earthquake insurance?
- What is the probability that an earthquake is a foreshock to a larger earthquake?
- Is it safe to go to X since they've been having a lot of earthquakes lately?
- What are the earthquake risks where I live?
Nuclear Explosions and Seismology
- What is the Comprehensive Test Ban Treaty (CTBT)?
- What is the role of seismology in monitoring a CTBT?
- What are the differences between explosions and earthquakes?
- Can nuclear explosions cause earthquakes?
- Can we use alot of explosives to cause small earthquakes in order to prevent having large ones?
Earthquake Preparedness
- During an EQ should you head for the doorway?
- What emergency supplies do I need?
- How can I plan ahead for an EQ?
- What should I do during an EQ?
- Things NOT to do during an EQ?
- What can I expect in my house when an EQ occurs? How do I identify it? What can be done?
- What do I do after an earthquake?
- What are the steps to EQ safety/awareness?
California
- Why are there so many earthquakes in the Geysers area in Northern California?
- Will California eventually fall off into the ocean?
- Why are there no faults in the Great Valley?
Other Resources
- What are some good books on earthquakes and geology?
- Where can I find educational materials?
- Where can I find other online resources on earthquakes?
Did You Feel It?
- Why don't you have the earthquake I felt?
- I accidentally filed an unknown report before the earthquake I felt was in the system. Can I go back and change my report?
- Why isn't my zip code on the map?
- Why don't you use Canadian zip codes?
- How do you calculate Global DYFI?
- The earthquake was in my area, but I didn't feel it. Should I still fill out this form?
- What is intensity?
- What is geocoding?
- What time is GMT?
- Do you have a printable version of the report form for those without access to the Internet?
- How is my personal information used? Can others access my personal information?
- How do you filter erroneous responses?
- This earthquake was a rolling one, but the one the other day was a jolt. Why the difference?
- How long was the shaking?
- Can people predict earthquakes? Will there be more after this one? Is there a pattern?
- Where can I find information about seismicity in my area?
- What can I do to prepare for an earthquake? How can I keep my family safe?
- How is my “Did you feel it?” input used?
- My question is still unanswered. Where do I go now?
PAGER
- Is there a concise, printable version of PAGER results?
- Which earthquakes are analyzed by the PAGER system?
- How long after the earthquake are the PAGER results available?
- What is the modified Mercalli Intensity scale and how is it different from magnitude?
- How are the estimated ground motion intensities calculated?
- Why doesn't PAGER estimate loss of life or property?
- Does PAGER provide tsunami warnings?
- Are PAGER results available by e-mail?
National Seismic Hazard Maps
- General Questions
- Why are there different probability maps, and which one do I use?
- I am having problems logging into your FTP site. Is this my problem or yours?
- I am publishing a book (journal article, thesis, pamphlet, poster, postcard, T-shirt, etc.), and I wish to use one of the NEHRP national hazard maps as an illustration. Who do I contact to obtain permission to do this?
- What is probabilistic ground motion?
- I need a simple description of what the maps are about.
- How do I use these maps?
- I am trying to calculate the ground motion effect for a certain location in California. I obtained the design spectrum acceleration from your site, but I would like to identify the soil type of this location, how can I reach it?
- What is the likelihood of a large earthquake at location X?
- Why aren't these maps 0, 1, 2, 3, 4 Zone maps?
- What do the ground-motion parameters on these maps mean?
- What is "Peak Acceleration" or "Peak Ground Acceleration" (PGA)?
- What is "% g"?
- If I were to use an accelerometer to measure seismic events, how could I convert the acceleration data (in g's) to the magnitude numbers you folks use?
- What is "probability of exceedance" or PE?
- What is "spectral acceleration" or SA?
- What is percent damping?
- Your map is for ground motions having a 2% probability of exceedance in 50 years. Are those values the same as those for 10% in 250?
- Your map values show ground motions that have a probability of being exceeded in 50 years of 10, 5 and 2 percent. What is the probability of their being exceeded in one year (the annual probability of exceedance)?
- What is the relationship between peak ground acceleration PGA and "effective peak acceleration," Aa, or between peak ground velocity and "effective peak velocity," Av, as these parameters appear on building code maps?
- A certain ground motion has an x percent probability of being exceeded in Y years. What is the probability, w that that same ground motion is exceeded in Z years? See the next FAQ.
- Ground Motion Parameter Calculator
- After downloading the application, how do I install it?
- When I run the application I get an error message saying "Could not find the main class. Program will exit." What is wrong?
- When I run the application I get an error message saying "Could not establish a connection to the server. Our server may be temporarily down..." What should I do?
- I downloaded the file and unzipped it, but I can't find an executable. How do I run the application?
- How do I know which version of Java I am using?
- I input incorrect proxy information and now the application does not prompt me to correct it. How can I change this?
- Our proxy server requires authentication (username and/or password), how can we set this information?
- I am still having problems, who can I contact for assistance?
- I have a miscellaneous map question.
US Seismic Design Tool
- How should batch mode data be formatted?
- What is the upper bound on the number of locations that can be handled by the Webtool batch mode?
- What does the error “Given lat/lon pair (lat/lon) failed to return data.” mean?
- Where can I find more information about the 2009 NEHRP Recommended Provisions and the ASCE 7-10 Standard?
- Which data sets are used to support this tool?
- Why have the 2008 USGS National Seismic Hazard Maps data changed from those included in the 2002 Maps?
- How has the 2008 hazard data update affected my results?
- For what grid spacing are the data reported?
- How are the acceleration values interpolated?
- With which building codes are the provided spectral acceleration values compatible?
- Why does the Webtool produce results that conflict with those given by the USGS Java Ground Motion Parameter Calculator? Which approach should govern?
- What is the significance of the 0.2 second and 1.0 second periods used in this Webtool?
- Why was this Webtool created?
