Both of the two largest earthquakes in the past 50 years occurred in November, making this month an ideal time for both long-time kama`aina and newcomers alike to remember that they live in earthquake country, and be aware of the high seismic hazard in the islands notably on the Big Island.
On November 29, 1975, a magnitude-7.2 earthquake beneath the south flank of Kilauea Volcano violently shook the island and was felt as far away as Oahu. Only eight years later, on November 16, 1983, a magnitude-6.6 earthquake beneath the southeast flank of Mauna Loa Volcano caused considerable damage on the island.
These two earthquakes were the result of the volcanoes’ expanding to accommodate an increased volume of magma within them. The volcanoes expand by pushing out their flanks and inflating their summits. Generally, these actions take place slowly, and the rocks bend, but over time, the strain becomes too great, and the rocks break. This is an earthquake.
As long as the Hawaiian hotspot supplies magma to the volcanoes, there will be large earthquakes on the island. We have to live with them, so it is never too late to take steps to mitigate the damage that an earthquake can incur or to learn how to avoid being engulfed by a locally generated tsunami.
The November 1975 earthquake, commonly referred to as the Kalapana earthquake, resulted in two fatalities. Both deaths were caused by the tsunami that formed when the land subsided and moved seaward to disrupt the ocean water. The tsunami attained a height of 14.6 m (48 ft) and crashed ashore within minutes.
When you are at the beach and feel an earthquake so strong that it is difficult to stand, head immediately for high ground. Don’t wait for a tsunami warning announcement from Civil Defense. The violently shaking ground is your warning. Just remembering this advice and acting accordingly may save your life one day.
What can you do to prepare for an earthquake? Most personal injuries during an earthquake are from falling objects. In your home or office, you can secure bookcases to the wall. You can rearrange items, such that heavier objects are on lower shelves and breakables are in low or closed cabinets. You can have a structural engineer inspect your house and recommend ways to improve it to withstand the shaking of an earthquake. On your own, you can install shear walls and metal clips that will help, not only during an earthquake but also during a hurricane.
Fire is often the result of an earthquake. Be sure to secure your water heater so it won’t topple over and start a fire at the exposed electrical connection or the severed gas line. Learn how to turn off your utilities. Have flexible connectors between your gas supply and appliances. Secure your large kitchen appliances to the floor. Move your propane tank from under your house, or, if it is located away from the house, secure it so it won’t roll to the house during the earthquake.
During an earthquake, the safest place to be is outdoors on open ground. If indoors, try to get under a table, desk or bed; move to a corner away from windows or into a strong doorway. Stay away from windows and large mirrors, which might shatter. Watch out for large appliances, such as refrigerators that may topple or computer/television monitors that may “walk” off their stands and fall. If outside, stay away from buildings where facades can fail, overhangs fall, and display windows break. Avoid standing near power poles and lines.
When the earth starts to shake, remain calm and don’t panic. Have an emergency plan in place, where family members will know what to do and where to gather after the shaking stops. Teach everyone how to turn off the electricity, water, and gas to your home. Have a three-day supply of food and water in your pantry. Have a flashlight and battery-powered radio handy.
The Hawai`i State Civil Defense and the Federal Emergency Management Agency have pamphlets outlining ways that you can prepare for an earthquake. You can pick them up at the Hawai`i County Civil Defense office at 920 Ululani Street or have them mailed to you by calling the nearest CD office. The U.S. Geological Survey’s Earthquake Hazards program has an excellent web site (http://quake.wr.usgs.gov) with a section on earthquake preparedness.
Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Low spatter fountaining from the West Gap Pit section of the cone was reported seen from Highway 11 near Hirano Store. This activity produced multiple short pahoehoe lobes spreading down the west shield. Breaches in the tube system and the rootless shields near the top of the Mother’s Day flow supply small flows in the area. Lava was not seen on Pulama pali or the coastal flat below Paliuli. No lava is entering the ocean.
One earthquake was reported felt in the week ending on November 20. Residents of Ahualoa, Papa`aloa, and Waimea felt an earthquake at 36 minutes after midnight on Friday, November 14. The earthquake responsible was a magnitude-3.0 event located 3 km (1.8 mi) southwest of Pa`auilo at a depth of 14 km (8.4 mi).
Mauna Loa is not erupting. The summit region continues to inflate. Seismic activity remains very low, with only two earthquakes located in the summit area during the last seven days. Visit our website (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time earthquake information.
This article was written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory and is republished by HawaiiNews.com with permission.