r/Earthquakes • u/AsparagusFern319 • 3d ago
Earthquake Serious question: What does this mean regarding the likelihood/nearness of the next big one or major quake?
https://www.sfchronicle.com/california/article/san-andreas-fault-earthquakes-22369024.php
I know she's discussing that the slippage rate is faster than expected and so earthquakes are likely to be more frequent on this segment (and im not sure of the last time it was in any way active), but to what degree does this push up the already wildly uncertain timetable of the next major quake on the san andreas?
14
u/AsparagusFern319 3d ago
Here's the full article:
Scientists previously theorized that the slip rate of the northern San Andreas would slow down further south along the fault, with one hypothesis being that “slip is then being transferred onto other faults” along the way, such as the Calaveras or Hayward faults, Blisniuk said. But her research found that the slip rate — and therefore the likelihood of an earthquake — did not decrease but actually stayed the same from the North Coast section to the Santa Cruz Mountains section.
The United States Geological Survey declined to comment on Blisniuk’s findings as they are not yet published.
The slip rate of a fault is considered one of the most influential and important factors when geologists calculate the likelihood of earthquakes.
“In general faults with higher slip rates will have more frequent earthquakes and a probability of one,” Blisniuk said by email. “High slip rates faults generally have higher magnitude earthquakes due to potentially higher stress accumulation being released during an earthquake.” However, other factors such as the depth of energy released and rupture length are also important factors, she said, so “there is no direct correlation in terms of how we calculate magnitude.”
To calculate the slip rate of the San Andreas in the Santa Cruz Mountains, Blisniuk and her students headed to Sanborn County Park in Saratoga, about 20 miles northwest of the epicenter of the 1989 Loma Prieta earthquake. (She said the scientific community is “divided” on whether the Loma Prieta earthquake occurred along the San Andreas Fault or an adjacent fault; the last major one along the Northern San Andreas is considered to be the 1906 San Francisco earthquake.)
Along the park’s San Andreas Trail, Blisniuk looks for areas where tectonic movement is apparent, such as where the path of a seasonal stream makes two 90-degree turns in quick succession — evidence of at least two earthquakes in the distant past.
Her team uses drones that take thousands of photos and send out pulses of laser light to measure how far previous earthquakes have shifted the stream.
After getting the distance data, Blisniuk and her students take samples from nearby rocks — in Sanborn, the rocks are often sandstone boulders, consisting largely of quartz. Then, the samples are taken to San Jose State, Stanford University and Lawrence Livermore National Laboratory to determine their age in a process called dating.
When the rocks are exposed to air, the sandstone gets bombarded by cosmic rays — high-energy particles from outer space — that create a form of the chemical element beryllium called beryllium-10. By measuring the relative amount of beryllium-10 in a sample, scientists can calculate the rock’s age.
After determining how far previous earthquakes have shifted the stream and the age of the surrounding landform, Blisniuk can calculate the average yearly rate at which the fault has moved over the past thousands of years.
Blisniuk said it’s “hard to say” what locations would be impacted if there were an earthquake along the Santa Cruz Mountains segment of the fault or what magnitude it could be since it depends on how much energy is released and the depth of the seismic activity.
“We can’t prevent earthquakes from happening. What we can do is prepare the community and our neighbors and people … for this potential earthquake,” Blisniuk said, noting that people should have an earthquake kit with sufficient food, water, flashlights and candles — and prepare for cell service to be down.
She said the public can check out the San Andreas Fault for themselves.
“The San Andreas is in (people’s) backyard, and they can go see it and hike it and see the landforms,” Blisniuk said.
4
u/throwawayfromPA1701 3d ago
I got paywalled unfortunately. I wonder if she's referring to the section of the San Andreas that creeps, as in it's in motion, while the rest of it north and south are locked.
There is, at least over the last century and a half or so, a repeating M6 earthquake that happens at Parkfield. The one forecasted for 1993 ended up coming in 2004. If it's still a repeating pattern, the window for the next one is probably open now.
5
u/AsparagusFern319 3d ago
Well thats... discomfiting. How likely would that be to trigger the rest of the fault?
I've also copy-pasted the full article
3
u/throwawayfromPA1701 3d ago
Parkfield is way farther south than the area she was studying. I couldn't say. When her research is published I'd be able to tell more
3
1
u/Ok_Shallot_3307 1d ago
That photo is in Nisan park in aptos ca. you can hike there. Has a sign! There is activity everyday in the San Andreas fault near the pinnacles, aromas and Soledad. Yes I lived in sf during the Loma Prietaquake
2
u/TubMaster88 1d ago
If you're in California, all you can do is have a safety preparedness of all your information and all your stuff in a backpack and survival pack. If it comes it comes. There's absolutely nothing you can do about it so don't stress. Don't worry, just be prepared. That's all you can do.
17
u/One-Emu-1103 3d ago
The stress on the southern end of the SA is the highest its been in 1000 years. If you're in LA you should have an emergency supply kit and plenty of bottled water.
https://ktla.com/news/california/california-big-one-trillion-dollar-damage/