It was a moderate one - 4.2, according to initial reports. Quite a good jolt, and I propelled myself right out of the sofa in a panic until it was apparent that it was over.
Here’s USGS on the topic: M 4.0 - 8 km E of Gilroy, CA.
There were also two prompt aftershocks at roughly 2 minute intervals:
M 2.7 - 9 km E of Gilroy, CA.
M 3.9 - 5 km SE of Gilroy, CA.
Gilroy, Hollister, and San Juan Bautista are places where you can readily see earthquake fault displacements. I went there in July and took these pictures.
I would have thought that a 4.2 would be routine, for Californians.
Indeed.
Didn’t feel it in Fremont. I woke up about that time, but I usually do.
They had a nice exhibit in Central Park in Fremont where they dug down a bit to where you could see the Hayward fault. You can also see where a parking berm which was right on the fault has been split.
Why do I smell garlic, now?
[Hope all living beings and property are intact and well. Signed … former San Diegan]
It is hard to miss one like that if you happen to be right on top of it. You only hear about one below five on a slow news day.
4.2 is on the high end of routine. If you’re just a couple of miles away from it, like we are, it’s a real bouncer.
I was right on top of one a few months back. USGS had it at 3.6 and about 3 miles away. It was unmistakable.
We had another one the next day, almost as big. This one was on the San Andreas fault, a few miles south of San Juan Bautista. There’ve been several small aftershocks since then. Since we’re pretty near that fault, I hope that all these little jolts are relieving pressure, but I think I’ve read that that’s a fallacy. Well, we’re up to date on earthquake insurance.
Surely aftershocks and little jolts allow the built-up pressure to release? I always thought they did. But you’re saying that’s a fallacy?
Here’s some relevant text from the California Governor’s Office of Emergency Services:
“While small earthquakes can indeed relieve some stress along a fault, they typically DO NOT significantly affect the likelihood of larger earthquakes. In fact, a sequence of smaller quakes can SOMETIMES indicate that a larger one is on the horizon, but not always.”
Yikes.
Thanks. Yes I do believe that small quakes do relieve some stress, in the short term, but plate tectonics being what they are, the plates are nevertheless always moving and so eventually there will be major quakes.
I have a problem with this line,
The most important earthquake safety tip we can share is to simply “Drop, Cover, and Hold On” during an earthquake.
and that’s because, what if you’re in a bad place to begin with? What if there’s a better place that you can get to quickly? For example, what if you’re near a wall that has several heavy items on shelves? Aren’t you better off getting away from the wall first, then drop, cover, and hold on? What if you’re in an aisle in a warehouse store with high shelves full of heavy items? Aren’t you better off getting out of that aisle first? Or maybe you’d be better off getting under one of the stronger shelves first?
An earthquake can strike at any time. When it strikes, I believe you have to very quickly assess where you are and act accordingly. You might have less than one second to do so, or you might have up to 2-3 seconds.
There has been a bit of a seismic swarm in Alaska of late. The latest jolt was 6.0, centered not far from Anchorage.
Even if small earthquakes relieved the built-up stress that causes large earthquakes in a simple linear manner, consider the sizes involved. The recent Gilroy quake was magnitude 4.2. The 1906 San Francisco earthquake was about magnitude 7.9. That’s over 5000 times larger. It would require a Gilroy-size earthquake every day for 14 years to equal the size of the 1906 quake. There just aren’t anywhere near enough small earthquakes to significantly relieve the stress.
Wow! That’s really sayin’ something! (Not Really)
The small quakes could be relieving pressure but they could also be clearing the way for the imminent big one.
I agree with your sentiment. But …
Messaging like this is designed to steer the least smart, least aware 50% of the population away from doing the dumbest most obvious thing. It’s not designed to steer the most smart, most aware 10% of the population towards doing the optimal thing. Those latter folks have to figure it out on their own or do their own (legit, not BS) research.
In your e.g. 3 seconds you can spend 1 second thinking and 2 seconds covering about 5, maaaaybe 10 feet. Time’s up. No matter where you are, good or bad, there aren’t that many places that much better within 5-10 feet. At least not most of the time. Occasionally yes, and that’s where routine situational awareness helps.
And all that’s assuming the surface isn’t bucking so bad all you can do is fall down.
Standing in the middle of an e.g. Home Depot aisle, you better hope there’s a nearly empty bottommost shelf bay within about arms’ reach. If the shaking gets bad enough to drop stuff off the upper shelves, you’re gonna be screwed otherwise.
The “cover” part of the standard advice amounts to “find a rigid object big enough and open-framed enough to get underneath.” A heavy 4-poster dining table being the canonical example. Or the footwell of a heavy desk.
I don’t now live in earthquake country, but looking around my residence, I have exactly zero rigid open-framed items to get under. I suspect that’d be true for a lot of people in a lot of homes and commercial places. Where in a grocery store or Target are such things? Where in the main halls of an indoor mall? Where in a modern cube-farm open-plan office?
Because of the power law distribution of quakes, most people who live a lifetime in earthquake country will experience a lot of non-damaging non-hazardous quakes, one or two scary ones where a few unlucky souls have something big and injurious or fatal fall on them but most don’t. Nearly nobody is going to experience the full horror of can’t even crawl because the ground / floor is shaking so much, Home Depot shelves domino-ing down en masse, instant crevasses in streets swallowing cars, etc. And if that worst case scenario does happen to you, I’m really doubting that the survival difference between optimal play versus crumple up in your smallest ball and hope for the best is going to make much difference for most people.
There’s always the marginal situation where bad play is fatal and superb play saves the day. We sure know that from our military days. But I’m not sure there’s much great advice you or I could internalize and walk around all our days with one eye on our earthquake response instant hiding place.
I don’t know about the stores, but I imagine most residences and most offices have a table, desk, or something similar.