hypoDD Tutorial

This website contains a brief tutorial on how to use the well-known hypoDD program (Waldhauser and Ellsworth, BSSA, 2000) to compute Double-Difference hypocenter relocation (originally written by Professor Zhigang Peng, and then modified by his student Chunquan Wu ). This is part of the lecture course titled "Observation Seismology" offered to the Geophysics graduate students at GT in Spring 2011 by Professor Zhigang Peng .

Part I: Introduction to hypoDD

• Overview of hypoDD package
• Source code, user guides and relevant publications
• Programs included in the hypoDD package
• How to run it at GT geophysics laboratory

  Part 2: Examples in the hypoDD program

• Extract the hypoDD examples
• Play with the first two examples

  Part 3: How to obtain differential travel times for hypoDD from waveform cross-correlations

• Programs to compute the waveform cross-correlation and time delays
• Examples to to computed differential travel times from waveform cross correlation

Overview of hypoDD package (Taken from the hypoDD manual)

• HypoDD is a Fortran computer program package for relocating earthquakes with the double-difference (DD) algorithm of Waldhauser and Ellsworth (2000).
• The DD technique (described in detail in Waldhauser and Ellsworth, 2000) takes advantage of the fact that if the hypocentral separation between two earthquakes is small compared to the event-station distance and the scale length of velocity heterogeneity, then the ray paths between the source region and a common station are similar along almost the entire ray path (Frechet, 1985; Got et al., 1994). In this case, the difference in travel times for two events observed at one station can be attributed to the spatial offset between the events with high accuracy.
• HypoDD calculates travel times in a layered velocity model (where velocity depends only on depth) for the current hypocenters at the station where the phase was recorded. The double-difference residuals for pairs of earthquakes at each station are minimized by weighted least squares using the method of singular value decomposition (SVD) or the conjugate gradients method (LSQR, Paige and Saunders, 1982). Solutions are found by iteratively adjusting the vector difference between nearby hypocentral pairs, with the locations and partial derivatives being updated after each iteration. Details about the algorithm can be found in Waldhauser and Ellsworth (2000).

Source code, user guides and relevant publications

• The latest version, hypoDD v1.1 can be downloaded at http://www.ldeo.columbia.edu/~felixw/HYPODD/HYPODD_1.1.tar.gz .
• The user guide can be viewed at http://www.ldeo.columbia.edu/~felixw/papers/Waldhauser_OFR2001.pdf .
• For more information on the DD method, please see Dr. Felix Wauldauser's website at http://www.ldeo.columbia.edu/~felixw/DD.html .

Programs included in the hypoDD package

• "ph2dt" is a computer program that transforms catalog P- and S-phase data into input files for hypoDD.
• "hypoDD" is the computer program that performs the double-difference relocations based on either inputs from catalog travel times (output of ph2dt) and/or cross-correlation differential travel times.
• Other

How to run it at GT geophysics laboratory

• hypoDD is already installed at "/usr/local/geophysics/bin/".
• To enable it for your account, add the following line to your ~/.bashrc

  export PATH=/usr/local/geophysics/bin/:$PATH
  

• To run it, simply type the command: hypoDD, ph2dt.

Part 2: Examples in the hypoDD program

Extract the hypoDD examples

• Let's start with the first example in the hypoDD program. Please use the following command to extract those examples

  tar zxvf /usr/local/geophysics/src/HYPODD/HYPODD_examples.tar.gz 
  

Play with the first two examples

• Please go to HYPODD_examples/example1 directory follow the Readme to reproduce their results. Then use Matlab script eqplot to plot the results.
• Please go to HYPODD_examples/example2 directory follow the Readme to reproduce their results. Then use Matlab script eqplot to plot the results.

Part 3: How to obtain differential travel times for hypoDD from waveform cross-correlations

Programs to compute the waveform cross-correlation and time delays

• Please use the following example to learn how to use "sac_wfcc" program to compute waveform cross-correlation coefficients and time delays.

  tar zxvf /data/teaching/EAS8803_S08/hypoDD/CAD_wfcc.tar.gz
  cd CAD
  vi Readme	
  

• Then follow each steps in Readme to learn how to use the program.

Examples to computed differential travel times from waveform cross correlation

• Please use the following example to learn how to compute differential travel times from waveform cross-correlation and use it to generate dt.cc in hypoDD program.

  tar zxvf /data/teaching/EAS8803_S08/hypoDD/hypoDD_example1_wfcc.tar.gz
  vi Readme
  

• Then follow each steps in Readme to learn how to use the program.