IRIS Wilber Seismogram Acquisition and Picking Arrival Times with SAC

The Homework Assignment

Download the broadband vertical-component (BHZ) seismograms from the 2015-01-28 MWP 6.1 Fiji Islands Region earthquake. You are going to use these data to construct  a P-wave traveltime-curve for the distance  range from 0 to 100 degrees. You want to include about 50 travel times in your curve. You can access Wilber 3 at: Explore the Wilber 3 site, it can help you select the data carefully to minimize your work.

I have a web-tutorial on Wilber 3 on the class web site.  The basic procedure is to select the event (use the magnitude slider and it will be easy to find), click on the event link and select the data. To minimize you work, you can use only data the GSN network, but there are many more data available than just those from that network. Measure the P-wave arrival time using the SAC ppk command.  

Picking the arrival time will be easier if you filter the signals using a WWSSN seismogram response using the SAC transfer  command (I have a web-tutorial on that on the class site as well).

  • Comment on the general pattern of the times and anything that you find interesting in the observations.
  • Do you see any stations with what may be notable timing errors?
  • What is the approximate value of the curve's intercept (value at zero distance)? What does this time represent physically?
  • Submit a plot of the travel times versus distance with your brief comments.

The Screencasts

These three screen casts should help you complete the "data" part of the second homework assignment. Each segment is about 9-10 minutes long and you should watch them in order.

Part 1 - Unpacking the data and using SAC's PPK command

Part 2 - Using AWK to make a SAC macro to automate processing

Part 3 - Accessing the SAC file header using the SAC utility: saclst