Photography by Baron Sekiya | Hawaii 24/7

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

The Volcweb interface offers a wide range of ways to view seismic data from Hawaii.

Recently the Hawaiian Volcano Observatory (HVO) launched Volcweb, an interactive portal for exploring earthquake information on the Hawaiian Islands. This interface provides the public significantly expanded access, not only to earthquake information, but also to continuous seismic data for each station operated HVO.

The old Web pages, found at tux.wr.usgs.gov, have been working faithfully for more than a decade and were used at several other seismic networks across the country to display earthquake information. Since the old Web pages were developed, several online mapping tools (e.g., Google Maps) have become available to make map data exploration much more flexible and interactive. Volcweb combines these tools with a design specifically for volcanic environments to give the user rapid access to more information than was previously possible.

Volcweb is divided into three pieces. The front page (http://hvo.wr.usgs.gov/earthquakes/new) should be the most familiar to those individuals comfortable with the old Web pages. The new map initially has the same boundaries, time span, and earthquake color scheme as the old web-page maps. In addition, this new page has the capability of coloring the earthquakes, based on depth, and of selectively viewing earthquakes in limited-magnitude ranges. With a user-defined line segment, one can also plot a cross section of seismicity (distance versus earthquake depth), time versus depth, cumulative number of earthquakes, and cumulative magnitude of earthquakes that fall within a selectable distance of the line segment.

The second part of the Web site displays Webicorders for each station that HVO maintains (select Webicorders on the left side of the Volcweb display). A Webicorder is a continuous plot of seismicity that commonly spans many hours and is the digital version of a drum helicorder. It is read much like the pages of a book and is a useful way of quickly looking at the activity at a particular seismometer. On the Volcweb Webicorders page, each seismometer is located on a Google map of Hawai`i Island. Users can identify stations closest to point of interest, like their house, and select it to see a Webicorder record of recent seismicity there. Continuous data for the last 3 days are available and updated approximately every 10 minutes.

When interpreting Webicorders, it is important to note that seismometers are very sensitive to a variety of cultural and atmospheric noise (e.g., people walking, nearby construction, helicopters, cars, wind, thunder, etc.). Because of this, only signals that show up on two or more stations should be considered seismically significant.

The third part of Volcweb brings together earthquake hypocenters and continuous seismic data into one place. On the Volcweb page, each active Hawai`i volcano has its own page, selectable in a panel on the lower left corner, from which the user can look at seismic hypocenters up to a year old. Having access to such a long time period of seismic data is a significant improvement over the old Web pages and gives the user a longer perspective of the seismicity in a given region than was available on the older pages. All of the new tools on the front page of Volcweb are available in the individual volcano view.

On the individual volcano pages, the user can view the continuous seismic data from HVO seismometers by toggling to view the stations (upper left). For volcanoes, the range of seismic activity is often not fully represented by the earthquakes plotted in this interface. In particular, the occurrence of seismic tremor is not well represented on a plot of individual earthquakes; however, variations in tremor are often conspicuous on Webicorders from stations surrounding lava lakes at Halema`uma`u and Pu`u `O`o. Local earthquakes that are too small to be accurately located may are also visible in the Webicorders.

Taken together, the suite of tools provided by Volcweb provide the amateur seismologist or volcanologist with many of the same basic tools that seismologists at HVO use to understand volcanic and tectonic processes. HVO looks forward to your comments and suggestions at hvowebmaster@usgs.gov