The earthquakes displayed on these maps and associated web pages have been detected and located by the seismographic network of the U.S. Geological Survey, Hawaiian Volcano Observatory.

Seismic signals are telemetered in real-time by radio and land lines from over 60 seismic stations on the islands of Hawai`i and Maui. Real-time computer systems continuously monitor the Earth for the occurrence of earthquakes.

When an earthquake occurs, seismic waves are created, which propagate away from the focus or hypocenter. The fastest waves, the P-wave, travels outward at a speed of about 3 to 5 miles/second. As the P-wave passes each seismic station, its arrival time is detected and noted by the real-time computers. The computers use the list of arrival times to determine the location of the earthquake. The location is typically available within a minute or less after the occurrence of the earthquake.

Once the location of the earthquake is known, a signal is sent to the computer that updates these web pages. Initially the magnitude may not be known, in which case the updated maps may show the earthquake location with a white box with an X through it. Only the index map and the zoomed-in or special maps displaying this new earthquake are updated at this time.

The magnitude of an event is determined from the strength of the seismic waves detected at each station. We use several different formulas to determine the magnitude. Most formulas depend on a measure of the shear, or S-waves, which have the largest amplitude and carry most of the seismic wave energy. S-waves travel more slowly than the P-waves used to locate the earthquake, at about 2 to 3 miles/second, so a particular magnitude may not be available until a few minutes after the earthquake.

Once a reliable magnitude is available, the relevant maps and text files are updated to replace preliminary magnitude estimates. This process is typically completed within about five minutes of the occurrence of the earthquake.

Earthquakes are routinely reviewed by a seismic data analyst and updates posted to this web site. Due to limitations of our automatic processing programs and manpower constraints, we will endeavor to maintain a catalog of earthquakes with magnitude of 2.0 and greater. Automatically processed earthquakes that drop below magnitude 2.0 upon review will be deleted, and missing earthquakes determined to be at least magnitude 2.0 will be added to the web page, provided they fall within the confines of our maps.

All reliably located earthquakes from the last fourteen days are shown on these maps. The index map and relevant zoomed-in maps are updated whenever new information about an event becomes available. Approximately once an hour, the time stamp on all maps containing earthquakes is updated, whether or not an earthquake has occurred. If the time stamp on a particular map is much older than one hour, you should try to reload the maps into your browser using the reload/refresh button (possibly holding down the shift key at the same time). If a new map does not appear, there may be computer problems at our end. (We hope not, but they do happen!)