Lab-Inversion using Surface Wave Dispersion and Receiver Function Waveform

Prepared by Zheng Tang (Davey) KAUST, for Ambient Noise Seismology Class

Oct 20^th, 2014

Goal

The goal of this exercise is to practice the surface wave inversion, the inversion of receiver function waveform and the inversion of both receiver function and surface wave dispersion curves utilizing the linearized scheme of Julia et al. (2000). The raw seismic data and the surface wave dispersion group velocities for 2 stations (ARSS & BTHS) are provided. Also, a number of scripts that will facilitate the completion of the lab are included.

STEP-BY-STEP INSTRUCTIONS

1. Before starting

Before the lab, the software “Virtualbox” has to be downloaded and installed in your Laptop. The link is as following: https://www.virtualbox.org/wiki/Downloads.

You can choose the right version based on the operation system. After installation, copy the “.vdi” file and import it to virtualbox. Login in the virtual Linux (ubuntu) system (password: asi123asi) and open a terminal window. Find the major folder by inputting

“cd Ambient_noise_Seismology/RF_Surf”.

Here, we have 2 stations (ARSS & BTHS) with the raw earthquake data and surface wave dispersion curves. We can check the earthquake data under ARSS/raw_data, as well as the dispersion data (urayl.ARSS, ulove.ARSS) by SAC.

2. Surface wave inversion

The key program developed by Julia et al. (2000) is to jointly invert the shear wave velocity structure using both receiver functions and dispersions.

We can obtain a simple surface wave inversion by choosing the weight parameter p to be 1.

Procedure:

a. Make a folder “Surf_INV” under the station folder, and copy the necessary files including obs.d obs.r obs.j, the starting model model.0, the dispersion curves urayl.ARSS ulove.ARSS, and the staff for plotting the inversion result disp.ARSS plot.gmt.

b. Check and set some parameters in three files (obs.j, obs.r, obs.d)

obs.j

6 #Iteration number

1 #Weight parameter, 1 means no receiver function but only dispersion

0.2 #Smooth parameter

-1.0

58 #Total layers of model

0.0

obs.d

1 #The number of dispersion curves

urayl.ARSS #The file name of surface wave dispersion

2.0 5.0 0.05 0.0001 10 #cmin, cmax, dc, tol, itr

obs.r (not useful for surface wave inversion)

1 #The number of receiver functions

'rftn_hf01.ARSS' #The receiver function file

0.5 #Ray parameter

2.5 #Gaussian width

5 #Time delay (s)

c. Input “jointsmth” to run the program.

d. Input “sh plot.gmt ARSS 01” to plot the inversion result, and display that by “evince ARSS.eps”.

We also can change the inputted dispersion curve to be the Love wave dispersion “ulove.ARSS”, and rerun the inversion and check the result. Furthermore, we can utilize both Rayleigh wave and Love wave dispersion to run the inversion and see the result. What are the differences of the results? Why?

3. Receiver function calculation (optional)

Procedure:

a. Make a folder “wvfm” under the major directory. Copy all the necessary scripts including “rename.sh, prep_p.sh, cut_p.sh, check_inc.sh, rotate.sh and iter.sh” to wvfm. Also, copy all the raw seismic data to the folder “wvfm”.

b. Run these scripts one by one

sh rename.sh

sh prep_p.sh

sh cut_p.sh

sh check_inc.sh

sh rotate.sh

sh iter.sh

The script “rename.sh” is trying to change the name of the earthquake data.

· “prep_p.sh” is trying to do rmean, rtrend, low-pass filter (<8Hz, avoid aliasing), highpass filter (>0.05Hz, remove low-frequency noise) and down-sample the data to be 10 samples per second.

· “cut_p.sh” is cutting the seismograms to be 10 sec before first P wave arriving and 110 sec after P arriving.

· “check_inc.sh” is checking and changing the incident angle and azimuth to be right values.

· “rotate.sh” is to rotate the horizontal seismograms (E-W & N-S) to be tangential and radial components.

· “iter.sh” is doing deconvolution to estimate receiver functions.

c. After the deconvolution, copy the output (*.eqr, *.eqt, radial and tangential receiver functions) to the folder “rftn”.

· Run “sh selec.sh” to finish data quality control automatically.

· Run “sh markrayp.sh” to input ray parameter to each receiver function.

· Run “sh stack.sh” to stack and average these radial component receiver functions. The output file is “rftn_hf01.ARSS”.

4. Receiver function inversion (optional)

Choosing the weight parameter to be 0

5. Joint inversion (optional)

Choosing the weight parameter to be 0.5