Monday, March 17, 2014

Wake Up Call

6:25 AM wake-up call this morning.

The shaking went on for a very long time for an earthquake. The shaking was mild at our house and we wondered if it was a very big earthquake far away, or a moderate one closer to home.  The SCEC map shows we live about 50 km from the epicenter.

Check out the waveforms.  Notice how, the further from the source, the longer (and weaker) the shaking?

I guesstimated, in my half asleep state, that the shaking went on for 15 seconds.  The waveform plots show 120 seconds, so each major tick represents 12 seconds.  The shaking at the stations ~50 km from the epicenter showed pronounced shaking for ~15 seconds.

The earthquake was widely felt.  Notice that ground motion does not go down monotonically with distance.  Factors like bedrock versus alluvial soils also determine how much shaking an area experiences.


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8 comments:

  1. I'm glad you're safe.

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  2. I'm glad you're safe. It intrigues me, how the terrors beyond our actual experience frighten us more than those we have a direct relationship with. Never having been in an earthquake, it is beyond my understanding, yet I grew up with tornados and hurricanes. The idea of an earthquake frightens me more.

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    1. I've lived in Kansas and California. Tornados frighten me more than earthquakes. I think I was traumatized by spending summer afternoons in the basement, only to be allowed up in time to see flattened nearby towns on the evening news.

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    2. I should clarify.

      At least, with an earthquake, I feel like I have some control. I don't live on a fault or in a ground liquifaction zone. (I checked the USGS maps before buying). My house meets or exceeds the post 1984 building codes. I strapped down tall and/or heavy things...

      Tornados are semi-random within tornado-alley--which covers a huge swath of the US.

      Then there is the dread factor of having an early warning.

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    3. your points make sense. And I agree with all of them. But still, much as I know it is nonsense, the unknown scares me more. Interesting thing that, and it explains so much of human behavior, irrational as it is.

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  3. As someone who moved here from other regions, I think the biggest surprise for me is how quick a *small* earthquake is--it's usually over before you realize what it was. (This morning's did rumble on for a little longer than most.) And then you continue whatever you were doing, the kids went to school as usual, it was a beautiful day, nothing was cancelled. I grew up with blizzards and floods, which can rearrange your life for weeks; even a tornado warning can bring hours or days of disruption. Small earthquakes aren't like that at all.

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  4. I'm glad everyone is ok. Living in an earthquake zone must be a constant worry.

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    1. It's not as worrisome to me as other risks.

      Modern CA building codes, and our infrastructure, is designed to withstand 7.0+ earthquakes. Northridge was higher than that and many of the older buildings pancaked. However, modern buildings only failed if they were right on top of the fault. Since I don't live on a fault, in a liquefaction zone, tsunami basin or wildfire interface, my home is lower risk than in most other places around the world.

      It would have been nice to have a view of something other than the apartment building next door. But, I looked at risks, convenience, amenities (schools, public services) and affordability. So my neighborhood may be meh, but it is generally safe from avoidable risks. In fact, my car and home insurance rates went .down. when I moved from Boulder to here.

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