hypoDD Tutorial
written by Zhigang Peng and Chunquan Wu
This website contains a brief tutorial on how to use the wellknown hypoDD program
(Waldhauser and Ellsworth, BSSA, 2000) to compute DoubleDifference 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 .
 HypoDD is a Fortran computer program package for relocating earthquakes with the doubledifference
(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 eventstation
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 doubledifference 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 Sphase data into input files for hypoDD.
 "hypoDD" is the computer program that performs the doubledifference relocations based on either inputs
from catalog travel times (output of ph2dt) and/or crosscorrelation differential travel times.
 Other
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 crosscorrelations
Programs to compute the waveform crosscorrelation and time delays
