Volcano Watch — Earthquake preparedness
"Volcano Watch" this week is written by seismologist Carl Johnson of the University of Hawaii at Hilo's Geology Department and the Center for the Study of Active Volcanoes. His topic of earthquake preparedness in Hawaii is a prelude to an upcoming symposium at UHH on "Earthquakes and Personal Safety."
Hawaii is a land of rugged beauty and untamed natural forces swathed in a beguiling gentleness that is unmatched anywhere else on Earth.
Most of us are aware of the lava flows that build the island upon which we live while, at the same time, destroying everything in their path. Although capable of great destruction, the advancing lava flows rarely endanger human life. A more sinister danger, however, lurks beneath the surface.
From time to time, the insides of the volcanoes are wrenched by seismic forces that split the Earth and send rolling waves of destruction across the land. Both the spectacular eruptions and devastating earthquakes arise from the the same source--the "Hawaiian hot spot."
Magma from hundreds of miles within the Earth slowly rises to form the Hawaiian Islands. Only about half of this magma makes it to the surface to appear as fountains and rivers of fire; the rest remains and cools within the volcano. As new space is made to accommodate the magma that cools within, the structure of the volcano is torn and stressed until the strength of rock is overcome and an earthquake occurs.
An earthquake is actually a very loud, exremely low-pitched sound produced by rocks breaking deep within the Earth. While this cracking lasts less than a few seconds, the resulting sound reverberates within the volcanic edifice like thunder in a canyon.
Since it is the sound that we experience, it seems that earthquakes last much longer than they actually do. Indeed, at the source of an earthquake, fault motion has generally stopped completely by the time we begin to feel the ground shake as earthquake waves radiate outward at the speed of sound in rock (roughly 3 to 4 miles per second).
Although the goal of accurately predicting earthquakes continues to elude scientists, there is still much that can be done to reduce losses when earthquakes do occur. Most of these efforts involve careful planning and an awareness of the effects earthquakes have on our homes, buildings, and critical facilities. The first line of defense lies in the adoption and compliance with appropriate building codes.
Because major damaging earthquakes are a relatively rare phenomenon, the appropriate level of preparedness is sometimes hard to determine. If the hazard is underestimated, the costs resulting from an earthquake can easily exceed the savings from inadequate lower-cost structural design.
On the other hand, building beyond the needs of the hazard is simply a waste of money. The trick is to find the "sweet spot" where construction costs closely match the expected savings from earthquake-resistant construction.
The Hawaii State Earthquake Advisory Board (HSEAB) was founded in 1990 under the auspices of Hawaii State Civil Defense to advise state policy makers regarding appropriate preparations for the damaging earthquakes that lie in Hawaii's future.
Another way of bracing for the next "big one" lies closer to home. Indeed, there is much that can be done in and around your home to protect your loved ones and possessions. The first step is to walk through your home and imagine what would happen during a large earthquake. Heavy bookshelves in children's bedrooms, water heaters without adequate bracing, and heirlooms precariously perched on a high shelves could pose problems that can easily be addressed.
During construction, a small increase in ties and shear panels can result in a substantial increase in resistance to the lateral loads from earthquakes, and the importance of an adequate foundation cannot be overlooked.
In addition, every family should have a plan for getting together after a quake when lifelines, communications, and roadways are destroyed.
Earthquake preparedness in the home will be the topic of a public symposium, "Earthquakes and Personal Safety," sponsored by the UHH Center for the Study of Active Volcanoes (CSAV) and the UH Geology Department, in cooperation with the Hawaiian Volcano Observatory, the Hawaii State Earthquake Advisory Board, and Hawaii State and County Civil Defense.
The symposium is scheduled for Saturday, July 8, from 8:30 a.m. to 12:30 p.m., at the UHH Theatre. Brief presentations by scientists, architects, and engineers, together with county and federal officials, will cover such areas as the causes of earthquakes in Hawaii, structural aspects of earthquake-resistant homes, and resources available after an earthquake has occurred.
Following the panel discussion, you, the public, will have the opportunity to discuss your concerns with scientists, engineers, and government officials with hands-on demonstrations of things you can do in and around your own homes to prepare for the next earthquake. Come and talk with us.
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