Instrument Response Removal with SAC Pole Zero Files

The Homework Assignment

Download the broadband three--component (BH?) seismograms from the 08 April (098), 1999 13:10:34.100 deep, $M_W$ 7.1, Priamurye-Northeastern China border region earthquake recorded at station IU-YSS. Start the seismograms about five minutes before the earthquake and continue until about 15 minutes after the earthquake. You can use Wilber to acquire the data.

Remove the instrument response using SAC. As you do so, eliminate any long-period instability and keep track of the frequency range for which the signals are unaffected by filtering (the corners of the transfer command). Create a three component (P1-style) plot using SAC and hand-label all the seismic phases that you can confidently identify. Describe the resulting signals. Do you see any evidence for near-field motions in the seismograms?

The Screencasts

These screen casts should help you complete the "data" part of the second homework assignment. You should watch them in order.

Part 1 - A Very Simple Intsrument Response Correction

If you find that you are not getting the same result as I do, the difference may arise because you may have selected a different time "window" (range). The mean amplitude in my seismogram is very close to zero, which is what you want when you are doing a standard instrument response removal. Try removing the mean (sac command: rmean) and removing the trend (sac command: rtr) before you apply the instrument correction.

Part 2 - Computing Impulse Responses

To introduce the problems that can arise with instrument deconvolutions, it's helpful to be able to compute and instrument response. That's what we do here.

Part 3 - Dealing with Low-Frequency Noise

Using SAC's transfer command to stabilize the low-frequencies with filtering.