Lori Dengler | A souvenir video of the Cape Mendocino earthquakes – Times-Standard

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Why commemorate the events of the past? One, five, 10 or more years of anniversary attention is a relatively modern phenomenon. When I was researching the impacts of the 1906 earthquake in Humboldt County, I was surprised to see no mention of it in the regional newspapers in April 1907 or 1911. It wasn’t until 1956 that I found a column in the Ferndale Enterprise noting the 50th anniversary.

There are many reasons to remember disasters. Although media attention is a 20th century phenomenon, all cultures mark past trauma in one way or another. When I was studying the 2011 tsunami in Japan, many people pointed out the tsunami stones in the Tohoku region that marked the extent of the tsunami floods in 1891 or 1933. The oral history of indigenous people includes Many accounts of floods, eruptions, earthquakes, or other events and world renewal ceremonies include rituals to protect the community from future disasters.

There is a difference between disasters that cause great loss of life and those that have lesser impacts. The 1992 Cape Mendocino earthquake sequence fortunately falls into the latter category. With over $60 million in property losses, it was the costliest earthquake in history, but injuries were mostly minor and everyone recovered. There are still reasons why it deserves a look back.

We’ve had 30 years of relative seismic calm since 1992. Eight earthquakes of at least magnitude 6 have hit the north coast since then, two of them in the magnitude 7 range, but only January 10, 2010, was close enough populated areas to cause significant damage. Many new residents have moved here who have never experienced a strong tremor. Remembering 1992 is a way to remind residents new and old that we live in the most seismically active region of the Coincidental United States, and that preparing for the next earthquake is worth thinking about. before he strikes.

The 1992 earthquakes marked several important turning points in our understanding of seismic risk. It produced the strongest ground shaking ever recorded in a California earthquake at that time. He initiated the approach to intensity studies that would become the USGS “Did You Feel It” site. It produced the first near-source tsunami in the Cascadia area, leading to the National Tsunami Hazard Mitigation Program. And it shed light on the complexity and dangers of the Mendocino triple-junction region and prompted geologists to think about how different fault systems might be connected.

We thought long and hard about how best to remember the 1992 earthquakes. Five years ago, on the 25th anniversary, we held a community gathering at the Wharfinger in Eureka. Over a hundred people attended and we featured short talks by scientists and community members about what happened and how it affected our fields. We even had a birthday cake with the Humboldt Seismogram record in the icing.

We wanted to do something different this year, to use the experiences of 1992 to focus on the front rather than the back and reach a wider audience. The COVID situation was still uncertain, so it made sense to do something easily accessible by anyone, no matter where they were. Web pages and video content were the answer.

The Redwood Coast Tsunami Task Force has been part of California’s Earthquake Country Alliance since 2009, and the ECA has provided annual grants since then. These funds have supported a variety of projects, including KEET public service announcements, interns, and the development of outreach materials. A virtual field trip to the site of the 1992 earthquakes seemed like a good idea.

Completing the task was a great challenge. I was lucky to know who to contact. Thomas Dunklin was an undergraduate in Humboldt’s geology program in the late 1980s and had spent much of his time after graduation at Petrolia. Thomas was a research assistant on several reconnaissance studies of the 1992 earthquakes, measuring coastal uplift and mapping landslides and fissures. In the years following the earthquakes, he became a videographer focusing on the North Coast environment. Much of his work has involved salmonid restoration projects and his underwater films are spectacular. There was no doubt in my mind that Thomas was the only person capable of making the kind of video I had in mind.

We started the project over a year ago and at first we did not associate it with the anniversary. I just thought a video intro to triple junction would be helpful. It was supposed to be finished last year, but delays in paperwork, weather, and a really ambitious set of goals pushed our schedule back, and before we knew it, the anniversary date was fast approaching.

The delay turned out to be a blessing. Thomas used the birthday to frame the video, and it suddenly made so much more sense. We would focus on what happened 30 years ago and how understanding these earthquakes could help people understand the triple junction region and motivate preparedness actions before the next earthquake. earth.

Thomas makes a number of points in the video, and one of the first is that the triple junction is not a point, but rather a complex region. He added Tanya Atwater’s animation of how the Triple Junction formed 30 million years ago and then slowly moved north, growing the San Andreas Rift at the same time. He found other animations to illustrate earth structure and seismicity. The final icing is his extraordinary drone footage offering a unique bird’s eye tour of the triple junction region where three separate but linked faults 30 years ago changed the coastline and contributed new insights to our understanding of the one of the most unusual geological sites on the planet.

The final cut far exceeded my expectations. See if you agree with me https://rctwg.humboldt.edu/capemendo92.

Lori Dengler is professor emeritus of geology at Cal Poly Humboldt, specializing in tsunami and earthquake risk. Do you have questions or comments about this topic, or would you like a free copy of the Living on Shaky Ground readiness magazine? Leave a message at 707-826-6019 or email [email protected]


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