California’s deadliest tsunami, though, came thousands of miles away. But scientists say they have identified more wave stimulators closer to home. An earthquake following a strike crash could produce potentially dangerous waves in some contexts, a new model shows – and the fault immediately occurred off the coast of Golden State.
If confirmed, the findings described in the Proceedings of the National Academy of Sciences could influence future local tsunami risk assessments for coastlines along California and others.
Tsunamis can be caused by events including landslides, volcanic eruptions, and generally earthquakes.
But not every earthquake can create a rogue wave. An earthquake follows an underwater repulsion where one side is pushed higher than the other is a major culprit, as the vertical motion can cause waves in the water above.
Earthquakes following strike faults such as San Andreas, where two tectonic plates slide across each other, are not thought to induce tsunamis on their own because they cause mostly horizontal movement.
The 2018 Sulawesi earthquake and the Indonesian tsunami raised eyebrows by geologists.
On Sept. 28 of that year, waves, expected to reach 13 to 23 feet, struck the provincial capital, Palu, after a magnitude 7.5 earthquake followed a strike sled. Combined, the two events killed thousands of people.
Scientists were amazed by the power of the waves, suggesting that perhaps it could cause landslides with vertical movements that can produce waves.
“We don’t think so,” said Ares Rosakis, a solid mechanics expert engineer and one of the senior authors of the study. His suspicion rests on one offense: “Unzipping the ocean floor in the Palu area… would be enough to explain the formation of the tsunami.”
As Rosakis and his team, which combine experts in all aspects of the process including seismology, and fluid dynamics, begin investigating potential solutions to the Palu mystery, they begin to see evidence that An earthquake crack is not your average unzipping. It fits the details of the “supershear” event, where the true physical rupture travels faster than the seismic waves that travel through the material. That creates a triangular shock wave called the Mach Cone (it’s very similar to a sonic boom that occurs when a very fast plane travels faster than the speed of sound).
They entered this data into powerful computer models that took into account seismic waves, seismic cracks, the shape of the Palu Bay bottom, and the dynamics of the waves themselves.The result: earthquakes from strike-like faults as well. With that devastating Palu could cause a tsunami.
“This is an interesting study in terms of physics,” said Eric Geist, a research geophysicist at the US Geological Survey based at California’s Moffett Field. “It’s a new way of looking at tsunami formation.”
Such complex models that combine both earthquake and tsunami dynamics require powerful computers. But that tends to become the norm, he added.
Part of the cause of the Sulawesi tsunami is the very narrow Palu Bay, Rosakis compared to the intensity you might see after shaking the tall and skinny glass compared to the softer movements that would be seen in the container. Widening
Rosakis and his colleagues pointed to areas along the northern California coast that are well-profile, including San Francisco Bay and Tomales Bay in Marin County.The San Andreas offenses are located off the coast of both areas. And both of them are narrow enough to see some very harsh parts.
Other bays around the world also fit in profiles such as the Gulf of Izmit in Turkey and the gulf formed by the Gulf of Aqaba in Egypt.
“This is the first time it has been accepted,” Rosakis said, “so a lot of work has to be done to put it into the hazard assessment map. At this point, these areas have been declared safe.”
Diego Arcas, director of the NOAA Center for Tsunami Research, called the authors’ conclusions “interesting.”
The study helps explain how earthquakes following a strike error might trigger a tsunami and why the resulting risk could be underestimated, he said. But, he added: “ I don’t think it will change the way we do things in terms of tsunami forecasts or hazard assessments. ”
That’s because basically a tsunami hazard map is made by estimating the impact of the largest and possibly the most damaging tsunami.
For California, these were likely large waves triggered by a magnitude 9 earthquake from thousands of miles across the Pacific, or similarly large earthquakes from the Cascadia sub-zone north of Cape Mendocino, geologist Rick Wilson. Senior engineering said. From the California Geological Survey, which has updated the state’s tsunami hazard map. It is unlikely that the additional tsunami risk, if confirmed, would cause damage in those worst-case scenarios.
“We will continue to review documents like these to see if we really need to update anything, but based on our experience and all the large data sources we include in the map, we are very comfortable with the available maps. That is safe Nice and nice to use, ”Wilson said.
The results of the study may influence the assessment of the hazard probability that not only But consider the worst case But also the possibility of earthquakes of various magnitude, Arcas said.
Ultimately, many scientists will have to spend time independently testing whether they can produce results, said Lori Dengler, geophysicist and professor emeritus at Humboldt State University.
“I guess this article will give many tsunami modelers a closer look,” said Dengler, in the role of slippage-based oscillations. Any condition that allows a supershear to occur, if the concept is more carefully considered, will be incorporated into the next generation of tsunami maps. ”
Although it is important to understand the potential tsunami risks posed by these local sources. But it is unlikely to affect tsunami forecasts, as data on ground cracking is not available in real time, Arcas said.
Even if that was the case, he added. “Many of these mechanical failures can be found near the coast and while potentially dangerous in the area. But there will be no local warning time because it is close to the source.
Dengler said that in these situations, the earthquake itself is a warning.
“As far as public safety is concerned – whenever you feel an earthquake near a coast, especially when it hits a long time, assume a tsunami and evacuate the coastal area,” she said. Palu had a festival during the time of the earthquake that brought many people from the sea to the bay, many of whom may not know that the shaking was a warning to them to get off the coast.
This story originally appeared in the Los Angeles Times.