The United States Geological Survey’s (USGS) Earthquake Hazards Program through its National Earthquake Information Center (NEIC), established in 1966, provides information on earthquakes with magnitude greater than 2.5 within the United States and adjacent areas, and greater than 4.5 in the rest of the world. This information is disseminated in form of summaries, maps, scientific and technical information, RSS feeds, near-real-time maps of ground motion and shaking intensity following significant earthquakes and real-time maps in google maps. USGS’s Prompt Assessment of Global Earthquakes for Response (PAGER) system provides fatality and economic loss impact estimates following significant earthquakes worldwide, available on their website and by email to pre-registered users.

USGS’s Earthquake Notification Service (ENS) disseminates earthquake information through emails and cellphone messages in case of an earthquake. Notifications are sent out 5 minutes after an earthquake in the US and 30 minutes after an earthquake elsewhere. Information provided by ENS includes magnitude, date and time, location, depth, region, distances to major cities and location uncertainty. The list of data sources and contributing networks is available online. The data is analyzed within minutes in the USGS National Earthquake Information Center (NEIC) in Golden, Colorado, and then disseminated. Main users are scientists and government officials responsible for emergency response, staff of U.S. embassies, the United Nations Department of Humanitarian Affairs, as well as national and international news media and citizens.

References:
USGS Websites (http://pubs.usgs.gov/fs/1997/103/pdf/FS-103-97.pdf, http://earthquake.usgs.gov/earthquakes/recenteqsww/, http://earthquake.usgs.gov/earthquakes/catalogs/, http://earthquake.usgs.gov/monitoring/gsn/, accessed on February 13, 2012)
V. Grasso and A. Singh, UNEP (Dec 2011, forthcoming): Early Warning Systems: State-of-Art Analysis and Future Directions.