- Why don't you have the earthquake I felt?
If the earthquake just happened a few minutes ago, you may have arrived at the webpage before our system has finished locating the earthquake and updating the web pages. If this is so, please fill out an "unknown" event questionnaire and check back in a few minutes to see if your event is now in place.
If the earthquake you felt occurred several years ago, chances are that it will not be in the database. CIIM was put online mainly as an information tool for current earthquakes and future damaging earthquakes. Some larger, "historic" events were added to the database as a calibration of the system, but some historic and past earthquakes are not on the list. Be sure to thoroughly check the "Archives".
It may also be that you felt an earthquake just below the magnitude cutoff for automaticf triggering. Generally, new maps are automatically made for quakes of magnitude 3.8 and greater (2.8 in certain urban areas). However, if you felt a smaller earthquake that is not on our site, please send in an "unknown" report. We review and associate the unknown reports regularly and will post maps if we receive reports on smaller quakes.
There is also the possibility that what you felt was not an earthquake. It is not uncommon for users to fill in unknown reports for sonic booms, trucks, explosions, mine blasts, and other events, thinking it was an earthquake.
- I accidentally filed an unknown report before the earthquake I felt was in the system. Can I go back and change my report?
No, you can't go back and change data you've already submitted. However, your information will be automatically associated with the correct event based on time and location.
- Why isn't my ZIP code on the map?
The maps are automatically generated to cover a preset distance from the epicenter of the earthquake. If you felt an earthquake but were some distance from the epicenter, your ZIP code may be off the borders of the map (although still counted in the total number of responses). If the earthquake is felt by a sizable number of people outside the original map range, a zoomed-out map may be made manually.
Also, our ZIP code database is always slightly out of date, even though it is periodically updated. It is possible that you may be in a ZIP code close to the epicenter, but it may not appear in our database. Please realize that updating the database with the newest ZIP code boundaries is not as simple as going to the US Postal Service. We have to go through a commercial source to get the coordinates of the ZIP code boundaries.
- Why don't you use Canadian ZIP codes?
We've been working with our colleagues at the Canadian Geological Survey to implement Canadian Postal Codes and that will be available soon for earthquakes felt in Canada. Until then, Canadian responses will be calculated as part of Global DYFI.
- How do you calculate Global DYFI?
We have recently expanded CIIM to a global scale. Users from all over the world can now contribute their earthquake experiences. Since ZIP codes do not exist or are not available in most countries, we have simplified the system to base location on the approximate latitude and longitude of the city which the respondent was closest to. On the map, it is displayed as a filled circle, the size of which is dependent on the population of the city. Since we need to know the city's location to map it, only cities in our database can be selected by observers.
- The earthquake was in my area, but I didn't feel it. Should I still fill out this form?
Yes. The more questionnaires that are received for your ZIP code, the more reliable the average intensity assigned to that ZIP code will be. In areas of lighter shaking, the "not-felt" responses are needed to prevent the average ZIP code intensities from being too high. The "non-felt" area is also useful to delimit in order to understand the full extent of shaking effects.
- What is intensity?
See: Scientific Background
- What is geocoding?
See: Scientific Background
- What time is GMT?
GMT stands for "Greenwich Mean Time" and is the time kept near the Prime Meridian. It is 5 hours ahead of Eastern Standard Time, and is also known as Universal Coordinated Time (UTC). For more information, visit the NEIC's time information website.
- Do you have a printable version of the report form for those without access to the Internet?
We've purposely avoided encouraging non-Web based contributions since we do not have the resources (people) to manually enter the amount of data that might entail. While we have set up a nearly fully automated system to do the intensity collection online--a huge resource savings--even this requires time in responding to inquiries. We encourage friends and family members to help fill out questionnaires online for others not having internet access.
Formerly, we collected data from postal surveys, a long slow, tedious process, which only solicited information from ZIP code post-masters, not the general public. Given the incredible response via the Internet, we're certainly getting more folks involved.
- How is my personal information used? Can others access my personal information?
This Citizen Science tool relies fundamentally on the good will of Internet uses like you, and we appreciate and respect the valuable data you provide. Rest assured we have obligations to keep all personal information private and secure. The personal information is automatically processed and summarized (devoid of any personal information) in our final products, the ZIP code map, for example. We do allow government researchers to use the data for scientific studies, but again, they are obligated to strip out any personal information prior to quoting or characterizing it. For example, we might say, "an observer in San Jose noted..."
While a very common, popular request is to see other's entries, we obviously cannot do so without potentially sacrificing personal information. This request comes from the media as well, but we politely decline such access.
As a side note, street addresses, when provided, allow us to make a more detailed map than from ZIP codes alone, and typically 90% of the entries contain that information.
- How do you filter erroneous responses?
Occasionally, we receive bad responses from people who think it might be amusing to throw off the map with an unnaturally high response. We reserve the right to manually exclude such responses from the final product, but we also have several built-in filters. For example, the responded intensity must make sense for the distance and magnitude. It would not make sense for a magnitude 3.9 earthquake to produce Intensity VIII shaking, even at the epicenter. However, our best filter is to have multiple responses per ZIP code to give a reliable average of the shaking over the area. The wisdom of the crowd usually outweighs individual eccentricities, but not always.
- This earthquake was a rolling one, but the one the other day was a jolt. Why the difference?
The shaking you feel from an earthquake depends on the distance you are from the epicenter of the earthquake, the structure you are in, the type of material under the structure, and a variety of other factors. If you are close, the shaking will be more violent and "faster" (higher frequency). If you are further away, the high-frequency "fast" shaking will have been "absorbed" by the earth's crust, and all that you will feel are the longer-period, more rolling motions. Furthermore, hard rock tends to shake less than softer sediment. Focusing and de-focusing of seismic energy can cause dramatic differences in the shaking between areas also. So it could have been any number of these factors or a combination of them that contributed to the difference in your experience of the earthquake.
- How long was the shaking?
The actual time it takes for a fault to slip depends on the size of the earthquake. A magnitude 5 earthquake slips for about a second; a M6 for a few seconds; a M7 for several seconds. The duration of shaking you actually feel from an earthquake depends in part on the distance you are from the epicenter of the earthquake. If you are close, the shaking will be more violent, "faster", and may not last as long. If you are further away, the high-frequency "fast" shaking will have been "absorbed" into the earth's crust, you will feel are the longer-period, more rolling motions, and they may be of longer duration. In short, the duration is different in different places, even for the same earthquake. In addition, observers in the nearby locations may describe different directions depending on the type of building they are in, and how each perceives the shaking.
- Can people predict earthquakes? Will there be more after this one? Is there a pattern?
The answer to these and other, similar questions can be answered in USGS Earthquake FAQ: Myths.
- Where can I find information on seismicity in my area?
If you are moving to a new area or want to know more about your current area, the USGS US Earthquake Information website is an excellent resource.
- What can I do to prepare for an earthquake? How can I keep my family safe?
See the Earthquake Preparedness FAQ and Preparedness Information websites for detailed information.
- My question is still unanswered. Where do I go now?
Send us a Comment or check out the USGS General Earthquake FAQ.
