Tuesday, August 5, 2008

Last Tuesday's 5.4

Wow, this is something I should've written about exactly a week ago! It may not suffice to say that I was so giddily excited about the earthquake that I couldn't sit down at my computer to spew text onto a single site for more than a few minutes, but yeah. I'm a week late - but I'm still excited about it! This was the largest earthquake I've felt thus far, and that was made more amusing by the fact that, six days earlier, I felt my smallest quake, a 2.6 on the San Jacinto Fault.

I was in the car for this one. I'd just finished buying some food and toys for the faultcats at Petsmart, and was going about 25 mph down the street. I saw that the light was red, so I went for the brake. As soon as my foot hit the pedal, the car wobbled from side to side. Since the wobbling was not yet continuous, I worried something was wrong with the brakes, so I started to push the button that brings up the display that supposedly tells me when something is wrong with the car. (I love how my car tells me when it needs work. Not that it has needed work yet. But!) As I was pushing the button, though, the side to side motion returned in an intensified state. A look around confirmed that street signs and trees were also all wobbly, and that was all the confirmation I needed for the cause of my car's wiggle. The light turned green at this point, so I turned the corner and went on my way, anxious to get home and check the USGS site for a magnitude and location. I figured it had to be at least in the mid 4s, since a car's shocks absorb smaller vibrations. I certainly did not expect 5.6, as the USGS text message said, though! By the time I got to the Did You Feel It page on the website, it was saying 5.8, and my jaw was further unhinging. Except by the time I finished filling out the form, it was down to 5.4. I admittedly felt a bit gipped out of that extra 0.4, but still was excited to the point of being giddy about the whole thing.

Now that I think about the feeling of it in the car, I'm sure I felt two separate wave arrivals. My initial thought was that these were P and S arrivals, but after talking about it with people in the lab at school, it doesn't make sense that the smaller vertical P-wave would be noticeable in a car with good shocks, at least not in a quake that wasn't epically huge. More likely, these were the arrivals of the S wave and the surface waves. Friends of mine who were stationary and in buildings at the time said they felt three separate pulses.

My computer, so it seems, also got a really good ride out of this earthquake. This was the first event of any significance since the Quake Catcher Network alpha test went online in the winter, and thus the first really solid test. According to the event-specific site, there were a bunch of laptops triggered, but three of them had clean and clear records. This says, of course, that more computers involved will mean more clean records on the whole, but it's also good for determining what might make noise on the record, and how to clean it up further.

That QCN worked so well is exciting in and of itself, and I was already giddy from the quake without the QCN factor, so imagine my excitement when I received an email on 30 July from the person heading the Stanford branch of QCN, stating that one of those three spotless clear records came from my own little laptop! That I got a decent recording makes sense - the computer was closed in a room where the cats could not get to it, and thus was only moved by the earthquake. But I have to say I am probably inordinately proud of my computer, since it is a machine and all, for making the top three.
The middle four seismograms came from my computer!

Since last Tuesday, there have been a bunch of little aftershocks that I did not feel. There was, however, a 3.0 on that part of the San Jacinto closest to my building. People outside of the building were definitely talking about it, but it seems like none of them reported it to the USGS, since there's no Did You Feel It map. I know I'm not the only one who felt it! Bah!


Alessia Maggi said...

Hi Julian,

thanks for the great description of last Tuesday's Californian earthquake. I spent over a year in California without ever feeling one - I was so annoyed!!

Congratulations also on your QCN success!


Silver Fox said...

Great report - thanks! I'm glad to hear your laptop worked successfully. I wonder if placement of laptops on certain types of substrate (desks, floors, laps, rickety tables, whatever) has anything to do with how they work, or if it's a software thing.

Julian said...

I may be twelve days late in saying this, but I'm glad you both liked the post! I'm also glad you're excited about the laptop thing, because the more people who are interested enough to try it, the bigger and better the network gets.

Alessia: A whole year? Which part of California? I only had to wait three months for my first one, though it was a really tiny one. Maybe I notice the little ones since they're on my mind to begin with, or maybe I just live in an unstable building...Yikes!
I would've definitely been annoyed if I'd gone a year without so much as a shake.