hypoDD Tutorial
by Zhigang Peng
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.
This is part of the lecture course
titled "Seismology II" offered to the Geophysics graduate students at GT
in Spring 2008 by Professor Zhigang Peng .
- 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 (Fréchet, 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).
- "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
hypoDD is already installed at "/usr/local/geophysics/src/HYPODD".
To run it, simply type the command: hypoDD, ph2dt.
Part 2: Examples in the hypoDD program
- 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
Last updated by Zhigang Peng
Sun Mar 9 10:19:22 EDT 2008
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