July 12, 2002

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

A Reminder That We Live in Earthquake Country

For years, scientists have tried to understand what causes earthquakes. They have recorded, catalogued, and analyzed them.

Instruments and telemetry systems are constantly upgraded, enabling us to collect greater amounts of data from a single earthquake. Techniques have been developed to better understand the complicated effects the soil and rock beneath us have on the destructiveness of an earthquake. Modern computers have become increasingly proficient at testing realistic models of an earthquake and its effects.

Despite these advances, accurate earthquake prediction has remained elusive, and we are unable to prevent an impending earthquake from happening. Instead of prediction, recent efforts have focused on mitigating seismic hazards by determining locations and types of structures where damage is most likely to occur. Thus, we can minimize the impact of a large earthquake by carefully planning the placement of future roads, bridges, utilities, homes, and other buildings. In addition, appropriate standards for earthquake-resistant construction can also be adopted.

While designing to the most earthquake-resistant standard may minimize the risk, it is also the most costly mitigation measure. In some countries, current building codes are ignored due to poor economic conditions, lack of understanding, or bureaucracy.

In September 1993, a magnitude-6.3 earthquake struck the Latur area of southern India, killing nearly 10,000 people and destroying several dozen villages. Most homes were of stone construction, with only mud used as mortar. Mud and timber were used for roofs, which easily collapsed on the inhabitants while they slept at night. The larger, magnitude-6.7 earthquake in Northridge, California, less than four months later was economically devastating, yet killed only 60 people.

On Hawai`i Island, over a decade has passed since an earthquake resulted in considerable damage or casualties. A magnitude-6.2 earthquake in the Kalapana area injured several people, destroyed five homes, and damaged about 100 other homes on June 25, 1989. Other damaging earthquakes in the past 30 years were the 1973 Honomu (M6.2), the 1975 Kalapana (M7.2), and the 1983 Ka`oiki (M6.7) earthquakes. The 1975 earthquake caused over $4 million (nearly 14 million in 2002 dollars) in property damage. Two people were killed as the tsunami generated by the earthquake struck a low-lying beach campground at Halape.

In 1993, Hawai`i County approved adoption of the 1991 Uniform Building Code (UBC). Seismic provisions in the UBC set standards for earthquake-resistant design. More recent studies by the U.S. Geological Survey convinced the Hawai`i State Earthquake Advisory Committee (HSEAC) that zonation for Hawai`i County should be upgraded from zone 3 to 4, the highest seismic hazard zone considered by the UBC. Thus, the International Council of Building Officials incorporated Hawai`i County into seismic zone 4 in the 1997 publication of the UBC. The successor to the 1997 UBC was drafted as the 2000 International Building Codes (IBC). Provisions of the 2000 IBC have already been adopted by several jurisdictions on the mainland. Hawai`i County has amended the 1991 UBC to assign seismic zone 4 to the entire island.

Successful implementation of new building codes requires proper training of government officials, building inspectors, architects, contractors, and engineers. Many older post-and-pier houses are not tied to a solid foundation. Such homes have had a history of sliding off their foundations during earthquakes, resulting in major structural damage. There are means to retrofit such post-and-pier foundations and other structural elements in a home to increase their resistance to strong shaking.

Citizens can also prepare for the next "big one" by having emergency supplies ready and knowing what to do in case of a large earthquake. To assist residents, the Center for the Study of Active Volcanoes at UH-Hilo produced a 30-minute video entitled, "Earthquake and Volcano Hazards on the Island of Hawai`i." This video, which has been shown on public access television, can be borrowed from libraries, community associations, and many video rental stores free of charge. Information about the video can be found at http://www.uhh.hawaii.edu/~nat_haz/video/video.html.

Benefits to adopting current building codes and educating about natural hazards may not be immediately apparent, but they will eventually result in reduced human and economic losses from earthquakes, hurricanes, and other natural disasters.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. The "Mother's Day" flow is spreading and inflating in the coastal flats beyond the base of Paliuli. The flow's advance toward the Chain of Craters road has stagnated, but another lobe is now moving to the southeast and is about 500 m (1,600 ft) from the old "High Castle" turnout. The National Park Service allows visitors to hike out to a great viewing area near the active flows.

The Boundary flow emanating from the "rootless" shields is still active on Pulama pali within the Royal Gardens subdivision. Field observations last week found no activity along the mauka HALP flow.

Two earthquakes were reported felt during the week ending on July 11, but no earthquakes were recorded on or about the stated times.