dreamshovel

Updated: May 8 2008
Update 2: May 16 2008

Around early March the northwestern Reno neighborhoods of Mogul and Somersett began getting a lot of seismic activity, sometimes dozens of small M1-M2 quakes in a single day. There have also been a number of M3s and a few M4s, including a late-night M4.7 that shook up a lot of people. Because most of these quakes have been very shallow they are very noticeable, even M1 and M2 “micro-quakes” that usually  escape notice. And the M4s are way more violent and frightening than any M4 quake should be.

At the moment the rate of the quakes seems to have dropped off quite a bit and are no longer a kind of all-day background shimmer, but the sudden and often booming shakes continue. Just last night (about 4am) for instance a sudden loud M2.6 sounded like the ceiling cracking open.

The USGS web site has a lot of interesting data feeds so I thought I’d generate a bit of chart porn for the 2008 Reno Quake Swarm.

First-off, some disclosure: All graphs are prepared using USGS public data feeds (here and here) from 1970 to present. The region is restricted to a box marked by 39-40N latitude and 119-120W longitude (which includes the Mogul-Somersett area of Reno, NV) and only M1 or greater quakes are shown. And of course I am not a seismologist/geologist, have nothing at all to do with the USGS and these graphs are presented purely for curiosity and ‘entertainment’.

To start, here are the earthquake counts per year from 1970 to May 1 2008. Notice anything?

And the monthly breakdown for 2008 shows that April was shakin’.

The 26th was particularly active!

And just to round out the set:

So we’re getting lots of quakes this year, way more than in other years. And so far, April 2008 seems to have been the peak.

OK.

I’m about  a mile or so away from the epicenter of the swarm we are feeling lots of frequent shakes. How does the quake frequency of this current swarm compare with the historical record?

To take a look at quake historic quake frequency we’ll move away from the marketing-style charts and go olde-school:

The USGS provides timestamped data for quake events. By measuring the inter-quake time intervals for that data set, you can make a graph showing the number of hours between recorded quakes in the target area.

Note that on a count-based graph like this, the x-axis does not denote time, but rather a count of previous events, backwards in time from the present day. I have however, indicated a few dates just for reference.

The first graph includes the complete data set from 1970 to the present. You can see that the quake frequency really began to pick up on about Mar 8 2008, and that there have been quite a few quakes in this current swarm.

The second graph is scaled to show more detail for the current swarm. Wow, they were really coming fast and furious for a while there!

Well there you go. It would be interesting to see other likely regional swarms in the past and I’m sure the professional seismo people have long since published such work. But if I find a bit of free time I’ll do some auto-correlation analysis and post a few more graphs.

It sure seems that there has been an increase in the time between quakes over the last few days, but I’ll leave it to the experts to decide if this swarm is ending. I for one will be glad for this to be over and can certainly do without the sudden booms and crashes in the wee hours!

Update for May 8 2008:

Yep, still shaking.

Here’s an additional quake frequency graph that includes data for this last week. Note that the scale is changed to show more detail.

As you can see the quake rate has dropped off, although they continue to occur every few hours or so. And of course last night we got a M3.8 as a reminder that the ’swarm’ is still kicking.

Update for May 16 2008:

After working into the wee hours last night I awoke around 10am and a few minutes later the house got a pretty good rattle, enough to wiggle the bed and shake some books off a shelf. Easily an M3, I thought. Well that little quake must have been really shallow and right under me since the USGS site marked it as M1.6!

I’ll take that unwelcome wakeup call as an excuse for one last (?) inter-quake interval update. This update is based on data up to May 14.

I guess we’d all like those intervals to be growing a little faster, but considering the recent M7.9 tragedy in China I’ll gladly take hundreds of small rattles over a couple of larger catastrophic temblors.