Lori Dengler | In 1992 the Co-Seismic UPS and depths of the country highlighted-his-Times standards

Did I miss important details about the 1992 quake in my last column? Of course I did it and it was intended. The room is always a restriction, but the main reason was my own limited awareness at that time. I didn't mention a tsunami because on April 25, 1992 I did not link a 7.2 earthquake with a potential tsunami. And I also didn't think about changes at the land level.

It took about a week for me to hear murmens that drift over the department that the coast near the mouth of the Mattole had changed in the earthquake. It looked like at low tide all the time, and some people could now wade in knee -deep water and harvest abalons. Petrolia Old-Timer noticed the change immediately, but it took about a week for the rest of us to have decay into the sea wall life to believe that the coastal sea level “falls”.

When I visited the area almost three weeks later, a comprehensive research project started. Gary Carver in the geology department had teamed up with Bob Rassmussen in Biology to map the survey and to bring a number of students, former students and colleagues in both disciplines.

One of them was Thomas Dunklin, who lived in Petrolia at the time (and still does). Thomas' geology background and knowledge of the triple junction area made him the perfect field assistant for geological studies on earth, and he was quickly moved into the Coastal Upper Project.

Measuring the relative sea level is easy if you have a tidal knife. There are no tidal measuring devices near Petrolia. How can scientists measure the change of height? There were no previously defined benchmarks in the area of ​​interest. The team developed a unique method that was based on marine life itself and measures the “vertical extent of mortality”, the distance between the dead organisms and where they had survived.

More than a dozen organisms were included in the study, but Seeigel proved to be particularly useful. They are plentiful on our coast and crouch small bags on the rocks to anchor themselves. Thomas and others spent weeks to measure the distance between the highest “dead” dimension mark on which a diuses had once lived, and the top of the still living sea angel zone.

The result was a detailed graphic, as the coast had turned up as a result of the 1992 error slip. The survey could be recognized over 15 miles between Cape Mendocino and Punta Gorda. The largest survey was a little more than 4.5 feet in the middle of the profile and gradually decreased both in the north and in the south.

This survey should not have surprised me. Geomorphologists who examine the coastal area of ​​Cape Mendocino have identified at least eight other increased former beach areas. We call them marine terraces, a flat surface that marks the former surf abrasion platform. If you stand on the Mattole Road and look down on Singley apartment, you can significantly engraved these surfaces in the landscape. If you don't want to drive, see Thomas Dunklin Mendocino Triple Junction video for a virtual tour of the place (

Each of these raised terraces marks an earlier earthquake in the last 10,000 years. Some of them show a similar amount of buoyancy as in 1992, which indicates earthquakes in the area of ​​size 7. However, others are more extensive and indicate larger quakes. Of course, it is not just the coast that rises in these quakes. The royal area is one of the fastest uplifting areas on the west coast, and the repetition of large earthquakes is an important factor.

The 1992 earthquake slide did not stop on the coast. While the break on land under Petrolia started, it grew up and in the west and created a diagonal fault aircraft about 10 miles wide and 15 miles long. The error fell into the west and possibly broke the sea floor surface on the continental shelf. We will never find out because no offshore education was carried out after the earthquake.

We know that the entire rock mass was pushed to the west over the error during the earthquake. This means that a 10 miles long stain of the sea floor has moved the ocean over it, and the elevation produced a tsunami. I hadn't known anything about the tsunami for a few weeks. No tsunami warning was issued, and at that time Tide -Messengeräte were not online.

Tsunami protocols were different in 1992 and the local tsunami threat was not well recognized. The initial size of 6.9 put it below the threshold to spend an alarm, and the local emergency officials were not for the fact that they mentioned them. If the earthquake had taken place today, a tsunami warning would have been spent, and we would see that the scenario on December 5, 2024, but a lot more damage.

It took the Californian state of geologist Jim Davis to come to ask NOAA about a possible tsunami. This was pulled by the tide measuring device not only a tsunami in Humboldt County, but also on other instruments from the coast of Central California to Port Orford and in Hawaii. In Crescent City it was a little more than 1.5 feet high and had performed with a higher flood, could have affected ports and low areas.

In 1992 we also had no robust post-tsunami field frages system. The first international tsunami survey team would be used about four months later to examine a tsunami in Nicaragua. Since then, groups of national and international scientists have quickly mobilized to examine the physical characteristics and effects of moderate to important tsunami events shortly in their opinion.

When we were aware of the 1992 tsunami, Wave Action would have deleted all the physical traces. We published the request for the request for the observation of unusual water level activities on April 25, 1992. A group on College Cove near Trinidad reported on a sudden increase in the water level of about three feet and several surfers described unexpected turbulence.

The 1992 earthquake is a history of Kosteismische (during earthquake). This week was released this week in the Proceedings of the National Academy of Sciences on Coseismic during large earthquakes in Cascadia. The paper under the direction of Tina Dura from Virginia Tech examines the potential of a sudden lowering of the land surface, which is connected to earthquakes in the area of ​​the upper size from 8 to 9 in the Cascadia region from Cape Mendocino to Vancouver Island, Canada.

How can earthquakes be raised a coast like the area of ​​Cape Mendocino in 1992 and let other areas fall? It all depends on the type of earthquake fighter, where they are relative to the earthquake deflection slides and how much load was saved before the quake. I had the opportunity to increase and to lower both the field examinations according to Earth/Tsunami. For earthquakes such as Indonesia 2004, Chile 2010 and Japan, the main signature is the country that falls off.

The Cascadia -Subsidence study this week estimates that the coastal country height could fall between 1.5 feet and 6 feet in our next large earthquake at Humboldt County to South British Columbia. We have given a lot of attention to shaking ground and tsunami dangers that are associated with great earthquakes and not enough attention to changes in the soil. Take a look at the column of the next week to take a closer look at the effects of the study on the north coast.

Lori Dengler is an emeritus professor of geology at Cal Poly Humboldt, an expert in tsunami and earthquake. Questions or comments about this column or a free copy of the on -call magazine “Living on Shaky Ground”? Leave a message under 707-826-6019 or send an email to kamome@humboldt.edu.