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M4.6 Earthquake – 2 km ESE of Berkeley, CA

earthquake.usgs.gov

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Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#61

Post by dredmorbius »

kijin wrote: post #26
roenxi wrote: post #18

Earlier quoted context omitted.

> The U.S. Geological Survey's most recent forecast, known as UCERF3 (Uniform California Earthquake Rupture Forecast 3), released in November 2013, estimated that an earthquake of magnitude 6.7 M or greater (i.e. equal to or greater than the 1994 Northridge earthquake) occurs about once every 6.7 years statewide. The same report also estimated there is a 7% probability that an earthquake of magnitude 8.0 or greater w…

There is an 80% probability that an earthquake of magnitude 8-9 will occur in the Nankai trough (massive subduction zone along the Pacific coast of Japan) in the next 30 years. Yes, you read that correctly. Eighty percent. It's almost a certainty. San Andreas sounds like nothing by comparison, especially since it doesn't pose as much of a tsunami risk.

It's also worth noting that a mag 8 is about the maximum expected from the San Andreas fault, a strike-slip fault, and most quakes come in well under that. The two largest quakes I'm aware of, the 1906 San Francisco and 1857 Fort Tejon quakes, were mag 7.8 and 7.9 respectively.

Significant damage can be experienced starting at about mag 6, though that tends to be pretty specific (individual structures, often pre-dating earthquake codes, and locations on poorly-suited terrain such as riverbottoms, reclaimed wetlands, or sand). Widespread general damage would only be experienced with larger quakes (mag 7--8).

Japan has a significantly higher risk of mag 8--9 quakes. The 2011 Tōhoku quake was a magnitude 9, which is 100 times more powerful than a mag 7, and over 100,000 times more powerful than this morning's temblor in Berkeley. Japanese faults include subduction zones and considerable tsunami risk.

Similar risks exist between the California-Oregon border through to British Columbia on the Cascadia Subduction Zone, and could similarly product a mag 9 event.

https://en.wikipedia.org/wiki/UCERF3>

https://en.wikipedia.org/wiki/Cascadia_subduction_zone>

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#63

Post by MontagFTB »

bombcar wrote: post #33
smcleod wrote: post #22

4.6 is really small, what's the actual news here? Was it strangely shallow or something?

Everyone is secretly (or openly) waiting for Teh Big One we’ve been promised for decades, when Western California will fall into the ocean and Las Vegas become a seaport.

This was the plot of a James Bond movie and when I was a teen I thought it was brilliant. Crack California off at the San Andreas- what could go wrong?

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#64

Post by kalleboo »

chrsig wrote: post #60
smcleod wrote: post #22

4.6 is really small, what's the actual news here? Was it strangely shallow or something?

From someone that grew up in New England, but experienced a 4.x in california: I assure you it does not feel small. The revelation that the ground does not stay where I left it was quite disturbing.

As someone who lives in Japan and has a lot of experience with earthquakes, the magnitude tells you not a lot, the depth and location/geology can easily change it from something you don't even feel to something quite big.

This is why I use every chance I can to espouse a scale like Japanese Shindo which actually measures the surface shaking (what matters to civilians) rather than the Magnitude scale that just measures the energy of the earthquake (more interesting to seismologists). Japanese news always focuses on the maximum observed Shindo which immediately tells you had bad it felt/affected people living nearby.

https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_se...

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#65

Post by jandrewrogers »

dredmorbius wrote: post #61
kijin wrote: post #26

Earlier quoted context omitted.

There is an 80% probability that an earthquake of magnitude 8-9 will occur in the Nankai trough (massive subduction zone along the Pacific coast of Japan) in the next 30 years. Yes, you read that correctly. Eighty percent. It's almost a certainty. San Andreas sounds like nothing by comparison, especially since it doesn't pose as much of a tsunami risk.

It's also worth noting that a mag 8 is about the maximum expected from the San Andreas fault, a strike-slip fault, and most quakes come in well under that. The two largest quakes I'm aware of, the 1906 San Francisco and 1857 Fort Tejon quakes, were mag 7.8 and 7.9 respectively. Significant damage can be experienced starting at about mag 6, though that tends to be pretty specific (individual structures, often pre-dati…

> a magnitude 9, which is 100 times more powerful than a mag 7

That is actually 1,000x more powerful. For historical reasons, the magnitude scale is 10^1.5 between whole numbers.

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#66

Post by fallinghawks »

sedatk wrote: post #2

This was the strongest earthquake I felt since I moved to Bay Area ten years ago. Luckily, it was quite short. Woke me and all my friends in the SF and vicinity up though.

I've lived in California all my life and was in San Mateo during Loma Prieta. How close you are to the epicenter has a strong effect on what you experience (it's undoubtedly more complicated than that but distance is a big factor). Last night's was 14.8 miles away from me and although I woke up, I didn't hear earthquaky sounds and shaking was moderate. Thought my partner had just flopped over in bed harder than usual. By contrast, a few years ago we had a 3.1 centered about 1.5 miles away that really made me fear it was a big one. The house jumped and stuff swayed, and I was just thinking I'd better get next to the bookcase when it stopped.

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#67

Post by dredmorbius »

smcleod wrote: post #22

4.6 is really small, what's the actual news here? Was it strangely shallow or something?

Mid-4s is where most people start feeling quakes, though the actual significance is pretty low. You'll tend to see/hear a lot of chatter online or in media.

At mag 5 there's localised damage, most characteristically of goods knocked off grocery store shelves, with glass-bottled liquids often producing a photogenic mess.

At mag 6, pre-code construction or at-risk areas (bay fill, river bottoms, sand) may see significant structural damage. The 2014 South Napa earthquake is the most recent of these, and downtown Napa was hit pretty hard, due to terrain (reclaimed river bottomlands, bay-fill, and some old masonry construction). See: https://en.wikipedia.org/wiki/2014_South_Napa_earthquake>.

Mag 7 is the scale of some of the largest quakes recorded in California, including the 1906 San Francisco quake. This would create widespread damage within 100+ miles of the epicentre. Marc Reisner's A Dangerous Place (2003) includes a detailed description of impacts of a mag 7 quake along the Hayward fault, which would extend well beyond the immediate region into Southern California due to reliance on delta and Central Valley water projects.

https://baynature.org/article/book-review-a-dangerous-place/>

Mag 8 is about the upper bound of expected seismic activity on the San Andreas and related fault systems.

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#68

Post by xkcd-sucks »

chrsig wrote: post #60
smcleod wrote: post #22

4.6 is really small, what's the actual news here? Was it strangely shallow or something?

From someone that grew up in New England, but experienced a 4.x in california: I assure you it does not feel small. The revelation that the ground does not stay where I left it was quite disturbing.

New England is seismically active :) If you're not aware of it, the tremors can feel like a large passing truck or something like that

https://earthquake.usgs.gov/earthquakes/map/?extent=40.31872...

Re: M4.6 Earthquake – 2 km ESE of Berkeley, CA

#69

Post by kijin »

dredmorbius wrote: post #61
kijin wrote: post #26

Earlier quoted context omitted.

There is an 80% probability that an earthquake of magnitude 8-9 will occur in the Nankai trough (massive subduction zone along the Pacific coast of Japan) in the next 30 years. Yes, you read that correctly. Eighty percent. It's almost a certainty. San Andreas sounds like nothing by comparison, especially since it doesn't pose as much of a tsunami risk.

It's also worth noting that a mag 8 is about the maximum expected from the San Andreas fault, a strike-slip fault, and most quakes come in well under that. The two largest quakes I'm aware of, the 1906 San Francisco and 1857 Fort Tejon quakes, were mag 7.8 and 7.9 respectively. Significant damage can be experienced starting at about mag 6, though that tends to be pretty specific (individual structures, often pre-dati…

The Cascadia earthquake in January 1700 produced a tsunami that traveled all the way across the ocean and hit Japan with 16-foot waves. That's what mag 9 looks like.
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