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Earthquake in Bay Area/San Jose not an Earthquake? 1

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I never heard or felt that yesterday and I was in a quiet place doing mostly paperwork and computer stuff. (Santa Cruz)

Most likely a bolide no one saw.

Keith Cress
kcress -
 
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We live in a rural part of North Yorkshire, England. Three years ago we had an earthquake - well the symptoms, rattling doors, crockery rattling. About 14:00 hours. Reported it to the British Geological Survey earthquake response.

Non of their sensors picked it up, they said some of these events are very local and sometimes do not fit in with usual event symptoms.
 
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Maybe it is a sensor problem. I believe most earthquake sensors have a limit of a plain in which they can operate in.

I noticed something like this years ago while working on pinball machines, which is why those devices had several sensors, and of different types for different types of machine movement.

And maybe the sensors ignored it, as they should be setup to ignore a large truck driving by.
 
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I've been in several "earthquakes" where the effect was no more than a slight dizzy sensation from the computer screen sway. Took me a minute to realize that it wasn't my eyes.
 
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Ah yes BigInch. We get all types here in California. We get ones that cause one single 'tuned' item in the house to rattle sort of violently, you feel nothing.

The completely/only circular motion types that make you dizzy and you think you're having a vertigo attack initially.

Then the 'single jerk' P-wave only style, where everything just creaks one time like the whole place just had a "thermal adjustment".

Then the rolling sea-wave style where you get up/down with an accent of left and right tilting just like sitting in a row boat in 6 inch swells.

And finally the really ugly ones that make you stop and wonder what that loud noise is that's approaching: "Is that a train coming - wait there are no fast trains arou@n#d&&#^@%!)_!)#!)!!!!" They hit like having a rug pulled out from under you followed by large circular motion on the order of a foot or two of diameter with a serious 12 inch rolling swell overlaid.



Don56; You could have something there. There is major angst around here. It could've been the head beating reaching some sort of resonance briefly.

Keith Cress
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If you've been in California long enough (we've been here 36+ years) one of the things that everyone does when they first feel an earthquake is to immediately look at your watch, particularly if it's one of those "rolling sea-wave style" quakes that itsmoked described, and you start to count off the seconds. If things stop moving within five seconds or so, you can relax as it was a 'small one', but if it gets to 10 seconds you start looking around to where you're at and start to contemplate whether there might be some place close by where it might be safer to be, like standing in a door frame or under something more than substantial than just the ceiling of your house or office. The 'big one' is going feel like a 'small one' for the first five seconds or so but from there the 'curve' moves-up logarithmic-ally.

The strongest quake that I've experienced personally was the Northridge quake in 1994. Now we were about 45 miles from the epicenter but it was still a pretty good shake. Our two oldest sons had an apartment about another 10 miles closer and they had actual damage like kitchen cabinets breaking loose from the ceiling and bigger things falling over. We only had maybe one picture fall over and no real damage except a few cracks in the ceiling that got a bit more noticeable.

As for the frequency of quakes here in SoCal, it's a daily event, just that you don't feel most of them. Note that I also have a 'quake' app on my iPhone that keeps me up-to-date in almost real time (I get a 'message' type notice for any event over 3.0 that hits anywhere in California).

As of this moment, here's what's been happening locally for the last few days:

Screen_Shot_2016-11-19_at_8.18.27_AM_xejp2v.png


Note that Yellow squares are within the last week and the Blue ones in the last 24 hours. There were no Red ones, which would have been in the last hour. Also, the size of the squares indicate the magnitude. Everything you see on that map was less than a 2.0 (for the record, we live just above the first 'a' in 'Santa Ana' on that map). The 'red lines' on that map are the KNOWN faults.


John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without
 
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Been in 2 strong ones in Colombia, one rolled me out of bed. Thought a train hit the hotel. 1 really good one in Venezuela, killed 50 in the next town. 2 in Turkey, one mild one on the 13th floor in Ankara and another, fortunately small, at 2am during a very critical moment in the bathroom in my container-accommodation out in Erzincan and two, one a 4.5, one 6.2, in the UAE while at work. My wife was on the swaying 29th floor of our apt. Like I'm going to wait and count 6 seconds before I take off? NOT! Even if I was in the bathroom. Zip up outside!
 
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I remember one relatively small quake in Eureka, CA in the early '90's that really illustrated the P- and S- waves... (i was driving elsewhere in CA during the 'big' one in 1994, so didn't notice it at all when it happened).

I was doing the dishes in my apartment, and suddenly felt woosy (it was actually the ground moving laterally under my feet - the P waves). I looked over at my ex, and was about to say "did you feel that?" Just then, the S- waves came on, and rattled everything up and down for a bit.

From growing up in San Jose and all the earthquake drills, we made a bee-line right outside once I understood what was happening, but my first thought was that I was just weak-kneed from just standing up too long!

It was really neat to experience the text-book P- and S- waves first hand (and safely :) )
 
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Apparently the P-waves move faster and if you're any distance from the epicent will definitely feel them early.

In the Loma Prieta Quake, which was nowhere near Loma Prieta, but actually over in the middle of The Forest of Nisene Marks, every thing facing in one direction was launched sideways and nothing perpendicular was bothered. You could go thru the house and see it plainly. Pretty fascinating.

Keith Cress
kcress -
 
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My wife tends to lose her balance and often falls down at the least bit of ground movement as she has a compromised sense of equilibrium.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without
 
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That sucks. I'd have to admit mine sure isn't what it used to be either. I used to ride around on a bike hands free without even thinking about it but now it's a big pucker-factor to remove my hands keeping them about... 1/16th of an inch from the grips.

Keith Cress
kcress -
 
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I'm sure part of that is a loss of confidence driving loss of competence thing.

I don't do a lot of riding around hands-off these days either, but I remember that when I did, I got best control by sitting as upright as possible as soon after letting go of the bars as possible. Time spent still bent over, with the potential to knock things accidentally, was always a bit wobbly.

Could never bring myself to ride hands-off on a tandem - mine never had quite enough natural damping and on the one I borrowed to take a girlfriend for a week's touring round the Cotswolds, you really did need to ride with both elbows locked the whole time.

but I digress......

A.
 
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My office is very close to where the Space Shuttle would go sub-sonic when it landed in California, so we'd get the sonic boom. Even after a bunch of them, most people here thought "earthquake!" first.

One time I had heard on my morning commute that it was still up in the air whether the Shuttle would land in Florida or California because of uncertain weather at the Cape. When we heard the sonic boom, I said to my visitors, "I guess it's still raining in Florida!" and got the strangest looks!
 
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" I used to ride around on a bike hands free without even thinking about it but now it's a big pucker-factor to remove my hands keeping them about... 1/16th of an inch from the grips."

Be aware that's a function of bicycle geometry, too, and unless you're using the same exact bicycle you did years ago, you may be mistaking a difference in bike geometry for a change in ability.
 
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Thanks JS; for pointing that out. It IS a very different (weird) full suspension mountain bike that I switched to fairly recently.

Funny aside: It had a cracked rear strut that I took to a guy to TIG weld. When the guy struck his first arc it welded every single slide cable into their housings.

Keith Cress
kcress -
 
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And probably pitted every bearing in the bottom bracket and headset...

JS is definitely right. Head tube angles and trail/rake values have a big impact on hands-off stability. I have a triathlon bike (super long trail) which can be ridden hands off around corners and obstacles without batting an eyelash, while my track bike with very low trail is scary under full power with only one hand on the bars.
 
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