Lori Dengler | A 60-Year Perspective of the Great Alaska Earthquake of 1964 – Times-Standard

At 5:36 PM EDT on Good Friday 60 years ago, a small crack formed about 16 miles underground near Prince William Sound on the southern coast of Alaska. Over the next four minutes, the rupture would grow toward the surface and laterally, displacing rocks 500 miles long and 125 miles wide, raising some areas more than 30 feet and dropping others nearly 8 feet.

The entire time and area where the fault ruptured, it was generating seismic waves. It was felt by almost everyone in Alaska, from Ketchikan in the southeast to the eastern Aleutian Islands, and even as far north as the Brooks Range, an area of ​​more than 800,000 square miles. If you centered the same felt map near Humboldt Bay, you would feel it from Los Angeles to Seattle and into Utah and Idaho.

Remembering what happened on March 27, 1964, is not only of historical importance. Very large earthquakes are rare, and one of the few places on the planet where earthquakes occur is right under your feet, if you live in coastal Northern California, Oregon, or Washington. Examining what happened in Alaska provides clues to what could happen here.

I have read and heard many accounts of people who were in Alaska that day. There is a unique one. Bob Pate was a salesman for radio station KHAR in Anchorage and aspired to be an on-air reporter. He carried a portable tape recorder with him, and whenever anything interesting happened around him, he would turn it on and describe what was happening. This is what he did from his home that evening.

“Hey, we're going through the ground (audio tracks), hey boy, this sure is an earthquake… Woo-ee, that's a good idea, oh boy oh boy oh boy,” the recording begins. Because of the narrator's shortness of breath, he is very afraid. You can hear everything in the house rattling and crashing. Pat stumbles over words as he tries to describe what is happening and repeats himself frequently. Recording begins about five seconds after the vibration begins. By then, the vibrations are already violent. This strong shaking phase lasts for over a minute and some swaying continues until the end of the recording, over three minutes later.

While Pat is afraid, he does not panic. The process of operating the recorder is rational and his attempts to describe what is going on may help focus his thoughts. He describes moving the TV off the table, so it doesn't fall. After the strongest tremors pass, he tours his house to check the damage. And just like I probably would have done, he kept pressing the light switch to be reminded that the power was off.

There were about 100,000 people living in Anchorage in 1964, and all of them, like Bill Pate, were in the area of ​​the strongest tremors. The modified Mercalli scale (MMI) is a qualitative measure of vibration intensity that ranges from zero to twelfth. We often use Roman numerals to differentiate between intensity and magnitude. Intensity V is the level at which some elements turn over and are felt by everyone inside. The docking area ranges between 8th and 10th, and is strong enough to throw objects into the air and damage even some well-built structures.

Despite the intense level of shaking, only nine deaths were directly caused by the earthquake. Four of them were in Turnagin Heights, a middle-class suburb of new homes built on the gentle hillside above Cook Inlet. When the shaking began, the friction melted some of the frozen ground, liquefying and causing the 130 acres to slide a third of a mile toward the sea. The Earth did not move uniformly. It split into pieces, forming large gaps between them. Some of the 75 houses above the slippery ground were also destroyed.

The liquefaction process also played a role in other parts of Anchorage. The airport control tower collapsed, killing the air traffic controller. Several areas of downtown subsided, damaging a Penny's Department Store, where two people died, and Government Hill Elementary School collapsed in half. Fortunately, it was a holiday, and no one was in school at that time.

The Good Friday holiday and the early evening hours contributed to the lower death toll. Schools and businesses were closed, and most people were at home. But the built environment also contributed; The houses were built of wood, and outside the liquefaction zones, they sustained little structural damage despite their proximity to the fault rupture zone.

Less than one hundred percent of the population died from the tremors. But like Bill Butte, they were without electricity or other services. Areas of Anchorage were isolated from each other due to landslides and damage to roads and bridges. Severe weather prevented outside relief efforts for several days. More remote areas were left alone for weeks.

In those early hours and days, neighbors helped neighbors. Alaskans are resilient by nature, and have established informal centers in neighborhoods to help each other, sharing food and emergency first aid. One radio station was back on the air within 24 hours, providing a soothing sound and what little information was available. Lyndon Johnson, just four months into his presidency, declared a state of emergency, but it took days for help to reach Anchorage.

Details of what happened on Good Friday will not be known for years. It has taken painstaking field investigation and re-examination of the data, some of which is still in progress, to paint a more complete picture. The year 1964 was the dawn of the Neotectonic Epoch and the “subduction zone” did not enter the literature for another six years. A very large earthquake occurred nearly four years ago along the coast of southern Chile, and the magnitude scale used at the time gave a value of 8.6. Using this old estimate of earthquake size, the 1964 Alaska magnitude was 8.4, barely larger than the 1906 San Francisco earthquake, which then had a magnitude of 8.3.

It would take 15 years before a moment scale was developed and the true magnitude of these great earthquakes could be accurately compared. The 1960 Chile earthquake still tops the list with a magnitude of 9.5, Alaska is second with a magnitude of 9.2, and the 1906 San Francisco earthquake, revised to a magnitude of 7.9, doesn't even make the top 100 list. But these changes were not the case. This was not done until later. For the people in Alaska, they knew something unusual had happened.

We still use a variation of the MMI today, although it has now been augmented with instruments that measure ground acceleration and the responses of people exposed to the USGS “Did you feel it?” website.

In case you haven't noticed, there is no mention of a tsunami in what I wrote above. Tune in next week's column to find out what happened next and how it might happen differently if it happened again today.

Note: You can find a link to Bill Butt's recording at https://kamome.humboldt.edu/activities/6-8/sounds-quake-grades-6-8. It is part of the online Earthquake Sounds curriculum activity which all teachers are welcome to use.

Lori Dengler is professor emeritus of geology at Cal Poly Humboldt and an expert in tsunami and earthquake hazards. Questions or comments about this column, or want a free copy of the “Living on Shaky Ground” preparedness magazine? Leave a message at 707-826-6019 or email [email protected].

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