15 January 2005

Lessons from the 1960 Tsunami in Chile, Hawai‘i, and Japan

In 1999, the U.S. Geological Survey published Circular 1187, entitled Surviving a Tsunami--Lessons from Chile, Hawaii, and Japan. It opens with a warning to people living in Cascadia.
Some areas around the margin of the Pacific Ocean are located near subduction zones similar to the one that produced the 1960 Chile earthquake and its tsunami. One of these areas is Cascadia--southern British Columbia, Washington, Oregon, and northern California.

Recently, it has been discovered that the Cascadia Subduction Zone, like the subduction zone off Chile, has a history of producing earthquakes that triggered tsunamis. The most recent of these earthquakes, in 1700, set off a tsunami that struck Japan with waves about as big as those of the 1960 Chilean tsunami in Japan. However, modern Cascadia has had little experience with tsunamis and almost no experience with tsunamis generated close to home. Because of this, people in Cascadia need to look elsewhere for guidance about tsunami survival.

Perhaps the most basic guidance for people in Cascadia comes from the account on the following page. Many people in Cascadia may think that "The Big One"--an earthquake of magnitude 9--will kill them before its tsunami rolls in. So, why bother to prepare for such a tsunami? In the account, all the people in and near the town of Maullín, Chile, survived the biggest earthquake ever measured. The deaths in the area came later, during the tsunami that followed the quake.
Testimony from survivors of the 1960 tsunami in Hilo also demonstrate that survival depends at least as much on public education as it does on mechanical warning devices.
There was plenty of time for evacuation in Hilo, Hawaii, as the Chilean tsunami raced across the Pacific Ocean on May 22, 1960. At 6:47 p.m. Hawaiian time, the U.S. Coast and Geodetic Survey issued an official warning that waves were expected to reach Hilo at about midnight. Around 8:30 p.m., coastal sirens in Hilo sounded and continued to sound intermittently for 20 minutes.

When the first wave, only a few feet high, arrived just after midnight, hundreds of people were still at home on low ground in Hilo. Others, thinking that the danger had passed, returned to Hilo before the highest wave of the tsunami struck at 1:04 a.m. on May 23. One of those who came back too soon was 16-year-old Carol Brown.

Carol was at her family's house on low ground in Hilo when the warning sirens sounded. Carol's parents took valuables to a relative's house in Papa‘ikou, a few miles northwest of Hilo, while Carol and her brother Ernest checked on a niece who was babysitting outside of town.

Later, Carol and Ernest returned to Hilo after hearing on the radio that tsunami waves had already come into town and were only 7 feet high. On the way back, they met a police officer who told them that the danger had passed. Carol and Ernest went to a sister's house in a low part of town. Around 1:00 a.m., they began to hear a low rumbling noise that soon became louder and was accompanied by sounds of crashing and crunching. Moments later, a wall of water hit the house, floating it off its foundation. When the house came to rest, Hilo was dark because the powerplant had been knocked out by the same wave.

Carol and her family survived the 1960 Chilean tsunami without serious injury. However, 61 other people in Hilo died and another 282 were badly hurt. These losses occurred, in part, because the warning sirens in Hilo on the evening of May 22, 1960, were interpreted differently by different people. Although nearly everyone heard the sirens, only about a third of them thought it was a signal to evacuate without further notice. Most thought it was only a preliminary warning to be followed later by an evacuation signal. Others in Hilo were unsure of how seriously to take the warnings, because several previous alerts had been followed by tsunamis that did little damage.
Read the whole thing. It's well written and chock full of informative graphs, maps, photos, and testimony from survivors in Chile, Hawai‘i, and Japan. It also includes a long list of survival tips.

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