Why do some earthquakes disappear from the map/list?
The USGS and networks contributing to the Advance National Seismic System (ANSS) take great effort to provide accurate and timely earthquake information. Occasionally our systems produce erroneous information that is released to the public via our web pages or Earthquake Notification System. These mistakes are generally promptly identified by seismologists, removed from our web pages, and “delete” e-mails are sent through ENS. We also have an Errata page when we correct information that is newsworthy and out of the ordinary.
In the interest of rapidly providing earthquake information to the public, most of the information about earthquakes that occur in the USA is automatically posted to the web and ENS if it meets quality standards. There is a trade off between the speed of our earthquake notifications and number of false alarms in the same way that any kind of "breaking news" story may have substantial changes or corrections as more information is received. The faster we release earthquake locations and magnitudes, the more likely it is that the information may be erroneous. Experience demonstrates that imposing more restrictive quality standards prevents the release of legitimate earthquake information.
There are multiple causes of false alarms. Automatic systems are particularly prone to errors following large earthquake when earthquake location algorithms misidentify reflected and refracted seismic waves created by a single earthquake. In this case, one earthquake can turn into "events" located in areas far from the earthquake. In other cases, noise in legacy analog telephone circuits that bring the data from seismometers to computers can be misidentified as earthquakes. Software optimized to locate local earthquakes by ANSS “regional” seismic networks in the USA occasionally may mislocate a large earthquake occurring on the other side of the Earth (e.g., China) deeply beneath the seismic network. Adding to this complexity, there are multiple seismic monitoring networks that contribute their earthquake locations and magnitudes to the ANSS system. These networks use different data and algorithms to locate the earthquakes, and sometimes the spatial separation of the contributed locations is so large that our systems interpret the independent solutions as distinct earthquakes of similar magnitude and location. In this situation, a delete message will be sent for one of the earthquake solutions but an earthquake did occur.
We are continuously improving our automatic systems and manual procedures to reduce the number of false alarms. However, with the advent of rapid distribution methods like RSS/ATOM feeds and the re-distribution of our alerts through social media sites, our errors are more widely seen and more difficult to retract completely. For these reasons, it is very important to remember that this data is preliminary and users should check our web site for the most recent updates.
How fast does the earthquake information get posted to the website, get sent out via the Earthquake Notification Service (ENS), ATOM feeds, etc?
Can I get on a list to receive an email message when there is an earthquake? How do I sign up for earthquake notifications? Are there any Feeds I can subscribe to?
The USGS Earthquake Hazards Program recently released a new strategic plan for earthquake monitoring entitled the “Advanced National Seismic System – Current Status, Development Opportunities, Priorities, 2017-2027.”
The Hawaiian Volcano Observatory’s 1912–2012 Centennial—100 Years of Tracking Eruptions and Earthquakes
HAWAI‘I ISLAND, Hawaii —The history of earthquakes and seismic monitoring in Hawai‘i during the past century will be the topic of a presentation at the University of Hawai‘i at Hilo on Thursday, January 26, at 7:00 p.m.
More than $7 million in cooperative agreements will be awarded for earthquake monitoring by the U.S Geological Survey in 2010. This funding will contribute to the development and operation of the USGS Advanced National Seismic System (ANSS).
USGS will Grant Universities $5 Million to Beef Up Public Safety Grants totaling $5 million under the American Recovery and Reinvestment Act are being awarded to 13 universities nationwide to upgrade critical earthquake monitoring networks and increase public safety.
Example of results returned when searching the USGS Earthquake Catalog. The ANSS Comprehensive Earthquake Catalog (ComCat) contains earthquake source parameters (e.g. hypocenters, magnitudes, phase picks and amplitudes) and other products (e.g. moment tensor solutions, macroseismic information, tectonic summaries, maps) produced by contributing seismic...
This map shows earthquakes above magnitude 4.0 in the eastern United States since 1973, the first year with a complete catalog. There are 184 earthquakes recorded. An earthquake of magnitude 4.0 or greater can cause minor or more significant damage. The circle sizes correspond to earthquake magnitude, ranging from 4.0 to 5.9 (the largest was in the Gulf of Mexico).