I hope all of our CA members are OK and have not had extensive damage to their homes & businesses!

Damage From California Quake Could Top $1 Billion


What is particularly disturbing is that some buildings that had been retrofitted to withstand earthquakes still failed in this M 6 event. This is not encouraging for when an even stronger event occurs, which will happen sooner or later. As most ETS readers are aware, the earthquake Magnitude Scale is logarithmic with respect to deflection on a seismograph. Thus an M 7 event has 10 times bigger amplitude. However, in terms of energy release, an M 7 event releases almost 32 times as much energy as an M 6! See the USGS earthquake calculator.

More technical info:
M6.0 - 6km NW of American Canyon, California

Im in L.A. ... did not feel it. But they are right.
This is a relatively small quake by our standards.
Much bigger ones coming soon :-)

Pete

Magnitude 6 is not small when it's under your feet. That having been said, a 6.0 is not the big one, not even close.

500 times stronger...wow. And the Japanese one in 2011 was about 9.0 on the Richter scale, wasn't it? I don't know how you coastal folk handle it. (although we're at risk in the Rockies, as well.)

--M

Pete & Russ,

Yes, M 6.0 is not "the big one", however with earthquakes there are several other factors that can make even a moderately strong quake very dangerous. The depth at which the quake occurs is important, as well as the local geology.

This M 6.0 quake under the Napa area was at a depth of about 11.3km (7.0mi). By way of comparison, the 2011 M 6.3 under Christchurch New Zealand was at a depth of only about 5km (3 mi). Apparently Christchurch is also underlain by relatively soft sediments. There were 185 deaths in Christchurch, at least 220 major trauma cases, and about 6000 people were treated for various less severe injuries.

In many situations, even a "relatively small by our standards" quake can be quite deadly.

" I don't know how you coastal folk handle it."

Let's just say that mirrors on the ceiling is not a very good idea...The threat of earthquakes tends to make one think preparedness.

Just don't sit below old brick walls to sip your latte or glass of wine! Or else it might be the last time you "seize the day"!

Even buildings with seismic retrofits damaged in Napa earthquake

During this quake and the 1989 quake, I was near the epicenter each time. Both quakes shook me hard enough to make me think "this is the end". By the way, I have consciously felt at least 40 quakes in my lifetime.

As far as I'm concerned, any earthquake that kills people is "The Big One". A quake that kills you or a family member will certainly be the The Big One to you. It doesn't get any bigger than death.

Years ago the National Park Service was in the process of purchasing a portion of Santa Cruz Island and I was on the island, spending the night in one of the historic buildings that graces the island. The last thought that went through my drowsy brain was "I hope there is no earthquake - there must be at least forty feet of unreinforced masonry above me. I wonder if that will affect the sale"

Bringing the subject up later at a meeting, I learned that indeed it did, and great was the wailing and gnashing of teeth thereof. A similar building has been reinforced and retrofitted at significant expense and now serves as an island visitor center, but this building, at Smuggler's Cove, is still off limits to Park personnel for sleeping overnight.

On a more positive note, I and many others have watched the construction of a significant addition to our local hospital. The first step was significant excavation of an immense hole and the pouring of a very large concrete plug - I believe to serve as a sub-foundation. The most prominent feature of the multi=story framing now rising is beefy steel X-bracing. We've learned a lot in the last century.

Retrofitting is expensive, a real hassle, and it won't necessarily ensure the survival of the building, but the occupants are more likely to live. In that sense, the Napa quake retrofit was successful.

Big +1. We noticed the one up near D.C. here in E. TN. No damage but it felt like a large truck going by rattling the office trailer. IIRC they said the underlying geology is such that it transmitted the quake like a rung bell.

Here's an example of what role the plate can play. Red is strong shaking, yellow moderate.

Hikermor has a good point about what the point of most seismic retrofitting is. I think the popular understanding is that it makes an old (sometimes VERY old) brick building with old, crumbly mortar impervious to earthquake damage, but that is generally not the case. Most retrofitting jobs seem to be intended to prevent the structure from collapsing onto occupants during the quake itself. Beyond that, such as whether the structure is still functional/habitable, is a whole different matter.

So, I think the news I see is doing a disservice when it reports that retrofitting "failed" when it may have actually done exactly what it was intended to do. Just because a structure is damaged (sometimes severely) and becomes red tagged does not mean the retrofitting failed, unless the job was specifically designed do just that.

On a related note, I was reading that even for the folks with earthquake insurance, most probably will not benefit from it because real estate prices are so high in the area and that the cost of most damage will not exceed the 5-10% deductible that exists on most policies.

Bit late to the party--I was awake at 3:20am, at the time of the quake, in San Francisco. My house is on solid ground and not on sand or landfill like many other parts of San Francisco. To me, I felt a moderate bump, and then the house seemed to feel "squirrely" for 5-10 seconds. My coworker in the East Bay said it feel like a giant was violently jerking his condo back and forth, and another coworker in the East Bay slept right through it, so people definitely felt different things in the Bay Area.

I tuned to the news and radio right away, but didn't see anything at all, so I shrugged and finally went to bed. When I woke up around 10:30am, I was shocked that all the stations were showing non-stop news coverage and how badly Napa City had been hit. I guess it takes time to ramp up the newsroom, call in anchors and such in the middle of the night.

Yes and no. You are correct that many (most?) retrofits of old buildings are meant to protect life & limb, not necessarily keep the building useable after the quake. However, protecting life and limb also includes people outside the building injured by falling debris. As the article I linked noted, had the quake happened at other times of day there easily could have been dozens killed and injured in the wine bar on the sidewalk below the building. But then again, as the article also notes, there is simply no economically feasible way to reinforce the brick facade on many of those old buildings. We can only try to do the best we can with old buildings, and accept some risk.

Along the same lines, here is an article about the boy who was badly injured by a collapsing fireplace. Most people who are injured in earthquakes (at least in 1st world countries) are not hurt by the whole building collapsing, but rather by falling stuff inside the building. There is a reason that the experts recommend Drop, Cover, and Hold!

For quick information (within minutes of the event), it is hard to beat the USGS - http://earthquake.usgs.gov/earthquakes/map/

In some cases, a brick wall/façade can be reinforced by applying a polymer backing layer that actually bonds to each brick, but it's generally not feasible for every square foot of a structure. Techniques that rely on reinforcing bars bolted to a wall won't anchor every brick in place.

This Napa quake does reinforce the idea that the most dangerous place (assuming you're not sleeping next to a brick (unreinforced?) fireplace at a slumber party, like the one seriously injured teen) is to stay away from the interface between inside/outside of a building. In general, if you're inside, stay inside during the shaking. If you're outside, stay outside. Falling bricks could have killed people. In a Third World country with little to no building codes, I'd want to get out of any building ASAP during a quake, but not someplace like California.

I saw at least a couple interviews with people at the mobile home park who were injured because their homes had shifted off the foundations and they fell because the stairs were no longer lined up with the front door. Another guy had a small apiary next to his mobile home and he dislocated his hip when he went to check on his birds and stepped into a hole after his unit had shifted over from it used to be. I'm not sure if they had flashlights or not and whether they would have made a difference, particularly when you've just woken up at 3:20am.

Lasting 4 minutes and 38 seconds, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph. It had a moment magnitude of 9.2, making it the second strongest earthquake in recorded history — the strongest being the 1960 Valdivia earthquake in Chile.

1964 Alaskan Earthquake ( Good Friday Earthquake ) - http://en.wikipedia.org/wiki/1964_Alaska_earthquake

Everyone on Reddit kept saying "Wow, that was long" for the Napa earthquake. It was only 20 seconds long. I guess most are only about 5-10 seconds. I cannot imagine constant shaking for nearly 5 minutes.

I saw at least a couple interviews with people at the mobile home park who were injured because their homes had shifted off the foundations and they fell because the stairs were no longer lined up with the front door. Another guy had a small apiary next to his mobile home and he dislocated his hip when he went to check on his birds and stepped into a hole after his unit had shifted over from it used to be. I'm not sure if they had flashlights or not and whether they would have made a difference, particularly when you've just woken up at 3:20am.

Above is a good reason to keep a headlamp available at the bedside, rather than a flashlight. When wishing to exit your structure, after doing the Drop, Duck, and Cover, using a headlamp gives you 2 free hands to steady yourself or break a fall if an aftershock hits

Front page article in the LA Times re unreinforced brick buildings - http://www.latimes.com/local/lanow/la-me...ory.html#page=1

Basically, they are bad juju.