The latest version of Volcweb was launched December 20, 2013. Based on
feedback from our users (you), we have made the following adjustments:
- Auto-refresh: The webpage now automatically refreshes when the page has been
inactive for 10 minutes. If you move your mouse on the webpage, the timer restarts.
- Earthquake list: The earthquake list has been moved to a tab behind the control panel
on the left. This frees up more space for the map on small screens (particularly tablets).
Simply click on the Earthquake List tab to see the earthquake list.
- Number of Earthquakes: Due to popular demand, the number of earthquakes is now shown
at the bottom of the earthquake list. The number of earthquakes only counts earthquakes
that are within the current map frame.
The dots presented in this map represent earthquake location calculated by
the Hawaiian Volcano Observatory and its partners.
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 web display
of earthquakes with magnitude of 1.7 and greater.
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 speeds between 3 and 5 miles/second. As the P-wave passes each seismic
station, its arrival time is detected and noted by HVO's real-time computers.
The computers use the arrival times to triangulate the location of the
earthquake. The location is typically available within a couple minutes after
the occurrence of the earthquake. When an earthquake occurs in an area of the
seismic network that is relatively sparse, its possible that the automatic location
will have large errors and not be plotted automatically. These earthquakes are
usually found by analysts on the next working day.
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.