Tuesday, May 17, 2011

UNH now has a seismometer!

On Friday, April 29th, Mike Hagerty, from the New England Seismic Network came up to UNH to help us install our very own seismometer. It is installed in the basement of James Hall in a vault that has been dug out beneath the building:

The seismic vault in the basement of James Hall

Our location in New Hampshire means we don't have to dig very deep to hit bedrock, and so the vault is only a couple feet deep. The seismometer sits in the vault, coupled to the bedrock, while the data cables are kept safe and secure in the PVC pipe running from the vault to the cabinet. The seismometer is a Trillium 120 P with a RefTek 130 broadband seismic recorder.

Reftek 130 seismic recorder
Trillium 120P seismometer

We still have to properly align the seismometer so that its north axis is actually pointing north, but in the meantime we can have some fun looking at the data. James Hall is located rather close to the train tracks; fortunate for those wishing to take the train, but unfortunate for seismometers (unless you wish to study seismograms of passing trains). Below is a high-frequency seismogram from our station, the big spike in blue is a passing freight train:

click to see full-size

You can also see when the building's HVAC system kicks in. This means that eventually we'll probably try to find the UNH seismometer a new home, so that we don't have to worry about local small earthquakes getting lost in the noise of trains and building maintenance.

The nice thing is that building noise and passing trains get filtered out when you just look at the long-period signal. This is excellent for looking at teleseisms (a tremor cause by an earthquake more than 1000 km from the station). Below we can see two teleseisms in the seismic recordings from 5/15/2011:

click to see full size

The spike in red is a teleseism from a Mw 6.0 earthquake (event time = 13:08 UTC) located on the St. Paul transform fault system in the mid-Atlantic. The much larger teleseism in green -- if you look you can see that it actually starts in blue around 18:57 and continues on through the black wave until about 20:55 or so -- is from a Mw 6.5 quake off Papua New Guinea. The Papua New Guinea quake occurred at 18:37 UTC, but it took about 20 minutes for the first p-waves to hit our stations. The s-waves appear kick in around 18 minutes after the p-waves, and the surface waves start to hit at 19:37, a full hour after the event time. This may seem like a long time, but remember that seismic waves can take a while to travel through the earth, particularly as they reflect and refract through different layers in the earth's mantle. Surface waves take the longest to arrive, as they alternatively speed up and slow down through different surface materials such as rock, sand, soil, etc. The chart below gives an estimate of travel time for various seismic waves versus angular distance from the earthquake:

source: http://geophysics.eas.gatech.edu/classes/Geophysics/misc/Seismology.html

If you wish to check out the seismograms that are being generated by the UNH seismometer, or any of the New England Seismic Network (NESN) stations, check them out here. You can select DUNH from the station drop-down list and check out the seismograms for any day since the seismometer was successfully installed. If you click on station list, you can see all the stations in the NESN. If you want to hunt for teleseisms, check the period to long-period. If you think you've found one, you can go to the USGS Earthquake page (http://earthquake.usgs.gov/earthquakes/recenteqsww/) and see if you can find a matching event. Large earthquakes greater than Mw 5.5 usually generate teleseisms that most modern seismometers anywhere in the world can see. You can also use the above chart to figure out how long after the event you should see seismic waves arriving at the station.

UPDATE:  Kurt Schwehr just blogged about the UNH seismometer as well. He talks about network setup and how we initially configure the seismometer with a Palm Pilot. He also shows the results of a jump test.

Tuesday, January 4, 2011

How to fix PostBox email client preferences

I use Postbox 2.1 for my email client on the Mac. It is efficient, has advanced searching, and let's you view photo thumbnails, attachments, and todos from any folder and directly export them to another program. This makes finding that lost attachment somewhere on the server very easy.

I recently encountered a problem, however, where despite having set the account-specific preferences to not quote the original email in a reply, it was doing it anyway. No matter what I did or tweaked, Postbox would automatically included the quoted message. It was pretty annoying, as I had to delete everything manually, and for emails that include a lot of HTML that can be a pain. So if you have issues with your Postbox preferences too, you can do what I did ($ refers to command link prompt in the terminal)

  1. Make sure preferences are set to how you want them to behave (e.g. quote message  on reply box in unchecked) and the close Postbox.
  2. Navigate to the Postbox preference file location:  $ cd /Users/username/Library/Application\ Support/Postbox/Profiles/random_characters.default/
  3. save a backup: $ cp prefs.js prefs.js.backup
  4. open prefs.js (I just did $ open prefs.js to open it in xcode)
  5. if your problem is quoting on reply, find the: user_pref("mail.identity.id4.reply_quoting_style", 2)  and set it to user_pref("mail.identity.id4.reply_quoting_style"0)
  6. save the file and reopen Postbox and it should be fixed

You can scroll through and pretty easily figure out what the different preferences are from there name, just be sure that you have a backup in case you mess something up. Worst case scenario you just rename your prefs.js.backup back to prefs.js and you're good to go

Jabref export to HTML Table is awesome!

So I just discovered that Jabref, the free, open-source, cross-platform citation manager that I use has a very kick-ass feature thanks to Mark Schenk. Mark wrote a very nifty export tool for Jabref that exports selected entries to an interactive HTML table that is searchable and lets you view abstracts and the raw bibtex entry. Here is an example provided by Mark.

Here are the features as listed in the exported HTML source code:
  • optionally searches Abstracts and reviews
  • allows Regular Expression searches
  • e.g. to search for entries between 1980 and 1989, type: 198[0-9]
  • e.g. for any entry ending with 'symmetry', type: symmetry$
  • e.g. for all reftypes that are books: ^book$, or ^article$
  • e.g. for entries by either John or Doe, type john|doe

UPDATE: Browsing around Mark's page, I found that he has added even more features to this HTML table export, including the ability to sort columns by clicking on the header, and filtering list entries by entry type, year, author, etc. Here is an example from Mark.

Jabref comes with the first version of the export tool I described as well as a more simplified table (no abstracts or bibtex) already. To get more enhanced versions, visit Mark Schenk's Jabref tools webpage.