Lovin Love Waves

July 19th, 2010

Since my last blog I have flown through a TON of data processing. As I stated earlier I've been keeping a research journal. Here's a selection from this past week (not all figures not included):

The first step in data analysis involved measuring the relative phase of both Rayleigh and Love waves against a reference station for the land, SIO and WHOI data. The program Intdisp enabled me to align the phase of the transfer functions from each event per station and isolate it for further processing. After completing all the measurements I found that less than ~5% of the OBS data (SIO and WHOI) could be recovered for the next step due to noise. As such I decided to focus on the measurements from the land stations which were less noisy and provided more accurate measurements. Figures 18a-c juxtapose Love wave measurements from a land station, SIO and WHOI data from an event on day 219 in 2006.

From the phase measurements I then used the program unwrapn to convert to phase velocity perturbation. Through unwrapn I corrected each event for 2π problems that could affect the accuracy of the dispersion curves.

In the final stage of data preparation I used several programs to create dispersion curves for both Love and Rayleigh waves between all possible station path combinations. The program run.newlleg first calls an fcell with all the events and sorts which events are within 10º of the specified station path (ex. 75-76). Then the program run.events calculates all of the dispersion curves and provides the azimuth, distance from the great circle and the correction factor for each event per station path. The correction factor is particularly important because it shows the correction for off-great circle propogation, meaning that all earthquakes do not actually approach the station along the two station great circle. The final program, run.avepha, averages all of the dispersion curves for each path and plots 2 new curves: a simple and weighted average dispersion curve (Figure 19).

Figure 18a. A Love wave phase measurement using Intdisp from the land station POHA. The wave in the middle window is from the reference station BIG2.

I am currently working on the Love wave processing which has proven far more difficult than the Rayleigh waves. This will likely take me another day to complete and then I will start mapping. I also will be taking a tour of the Scripps OBS lab later today so more to come tomorrow...