July 26, 2001
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Surfing Cyberspace for Hawaiian Earthquakes
Surfers of our Hawaiian Volcano Observatory (HVO) web site might have noticed that, earlier this year, we rolled out a modified web presentation of earthquake activity in Hawai`i. An "After Dark in the Park" evening talk at Hawai`i Volcanoes National Park in June also described our new web pages and their operation.
Those familiar with earthquake web pages served from other U.S. Geological Survey (USGS) offices should recognize similarities between our "Recent Earthquakes in Hawai`i" web pages and these other pages. These similarities are by no means coincidental.
Last fall, we installed a suite of computer programs to update our earthquake web pages. This package was originally developed by Robert Simpson of the USGS Earthquake Hazards Team in Menlo Park, California. While the templates came from California, HVO staff dedicated a great deal of effort toward implementing and customizing these utilities for our use in Hawai`i. This allowed us to use a set of programs common to a number of other seismic networks and to conform to a USGS style of earthquake web page appearance.
Underlying all of the web page postings are the seismographic field networks that provide data in continuous and real-time fashion to our networks' operational centers. Ground vibrations, whether generated by earthquakes, man-made sources, cultural disturbances, or ambient conditions, are converted by our field hardware to electrical signals. These electrical signals are then converted to radio transmissions to carry information to HVO from as far away as Maui.
Once the radio signals are received and decoded at HVO, our computers take over. The first step is to convert the seismic signals into digital streams for computer processing and archiving. Following the analog-to-digital conversion, we apply automated algorithms to detect signals that might be produced by earthquakes. Additional programs then attempt to estimate the arrival times of the principal seismic waves. If these procedures are successful, an earthquake message, including time, location and magnitude, is automatically generated. Literally gigabytes of seismic data are scanned, processed, and recorded at HVO each day.
The Recent Earthquakes programs receive the computer-generated message and manipulate it so that an earthquake symbol, a text message, and several seismograms can be posted on the web page. This is routinely done within one or two minutes of the time of the earthquake. From our Recent Earthquakes base map showing the island of Hawai`i, the maps and earthquake symbols are programmed to provide additional information for any given earthquake or to look at earthquakes from different regions with appropriate mouse clicks. When a significant earthquake occurs, our web pages should provide a reasonable look at the current activity.
While the overwhelming majority of earthquakes occur beneath the island of Hawai`i, we also provide links to maps of Maui County and O`ahu for the relatively infrequent, but still possible, seismicity there. Once we have interactively reviewed the data, we update the web page posting to include information drawn from other sources, possibly even adding or deleting earthquakes the automated computer programs have misinterpreted.
The web pages hold two weeks of earthquake information. Data older than two weeks automatically scroll off the web pages and are replaced by the most recent activity. Interested parties can watch the earthquakes and volcanoes themselves by surfing to http://hvo.wr.usgs.gov.
Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. Lava moves away from the vent toward the ocean in a network of tubes and descends Pulama pali in two separate areas. Small surface flows, primarily ooze-outs from inflated areas, are occasionally observed in the coastal flats. Lava continued to enter the ocean in the area east of Kupapa`u throughout the week. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the new land. The steam cloud is extremely hot, highly acidic, and laced with glass particles.
Updated: July 30, 2001 (pnf)