HYPODD Version 2.1 beta  - June, 2016
==========================================

by: Felix Waldhauser, felixw@ldeo.columbia.edu
    Lamont-Doherty Earth Observatory, Columbia University

   
			PURPOSE	

HypoDD is a Fortran77 computer program package for relocating earthquakes
with the double-difference algorithm of Waldhauser and Ellsworth (2000). 
It incorporates phase-pick and/or cross-correlation P- and/or S-wave
relative travel-time measurements. Residuals between observed and theoretical 
travel time differences (or double-differences = DD) are minimized for pairs
of earthquakes at each station while linking together all observed
event/station pairs. A weighted least squares solution (SVD or LSQR) is found
by iteratively adjusting the vector difference between hypocentral pairs.
Layered 1D or 3D velocity models are used to solve the forward problem.

A User Guide to installing and running hypoDD is included in the 
package (hypoDD2_UserGuide.pdf; Waldhauser, 2001). 
When referencing the program please indicate version number (hypoDD2.1). 

Main changes/additions in hypoDD 2.1b:
   - use of station elevation for travel time prediction
   - accepts variable vp/vs ratios in layered velocity models (imod=1)
   - use station specific velocity models possbile (imod=4)
   - accepts source-station configurations where stations can be below source
     (forward solution computed along straight rays)  (imod=5)
   - acceptes 3D velocity models using the simul2000 ray tracer (originally 
        implemented by Andreas Rietbrock) (imod=9)
   - improved weighting scheme 
   - backwards compatible with hypoDD 1.0 input files

This software benefited from numerous user feedbacks and contributions over 
the years, which are greatly appreciated!


			VERSION HISTORY:

Version 1.0 - 03/2001   (written while at USGS, Menlo Park)
Version 1.1 - 10/2004
Version 1.2 - 07/2010 
Version 1.3 - 08/2010   (same as v1.2, but compiles with gfortran in addition
			 to gcc/g77 and f77)
Version 2.0b- 05/2011    
Version 2.1b- 08/2011,09/2012/02/2012,06/2012,08/2012,01/2013,11/2015,
	      06/2016 (this version)


			DISCLAIMERS, WARRANTIES

The program has been extensively tested, but is made available
without warranty.  Users of the program are free to make modifications
to the programs to meet their particular needs, but are asked not to
distribute modified code to others. Tell me about your improvements
and bug fixes, and I will add them to the code for everyone's benefit.
Please use appropriate references and acknowledments when this software 
is useful to you (see below).


			REFERENCES

Waldhauser, Felix, and William L. Ellsworth, A double-difference
earthquake location algorithm: Method and application to the northern
Hayward fault, California, Bull. Seism. Soc. Am. 90, 1353-1368, 2000.

Waldhauser, Felix, hypoDD -- A program to compute double-difference
hypocenter locations, U.S. Geological Survey Open-File Report 01-113, 2001.


			DOWNLOADS

The complete program package can be downloaded from 
   http://www.ldeo.columbia.edu/~felixw/hypoDD.html

Alternatively, these files can be downloaded via anonymous ftp from 
ftp.ldeo.columbia.edu.  After login, cd archive/felix/HYPODD and get the
(binary) gzip-compressed tar files
   HYPODD_2.1.tar.gz   (source codes and user guide; 168Kb)
   HYPODD_examples.tar.gz   (small and medium size example data sets; 1Mb)
   HYPODD_moreExamples.tar.gz   (1 large example data sets; 9Mb)
   README  (how to get started...)
   BUGLIST_2.1  (continously updated bug list for HYPODD version 2.1)

The files can be unpacked with the command
   gunzip -c HYPODD_2.1.tar.gz | tar xf -


			ORGANIZATION OF THE SOURCE CODES

The file HYPODD_2.1.tar.gz contains a directory subtree containing source
code and associated files implementing the "double-difference" earthquake-
location method. This README file resides in the top-level directory.

CONTENTS OF THE TOP-LEVEL DIRECTORY

    README - This file.
    doc - Directory containing tutorial documentation.
    include - Directory containing source-code header files.
    src - Directory containing source code for commands, in separate
	subdirectories. 
    utils - Various utility programs/scripts.

Each directory contains its own README file explaining its contents
and usage.  For installation of hypoDD see the README files in the
src subtree.


			TEST CASES AND EXAMPLES

Example cases are included in the files HYPODD_examples.tar.gz (small 
and medium size example data sets; 3MB) and HYPODD_moreExamples.tar.gz  (1 
large example data sets; 20MB). These files are unpacked in the same manner 
as the source-code file, described above.  Each directory contains a Readme 
file.


			IMPORTANT NOTE

If the programs abort with 'Killed' when executed, then there is most
likely not enough memory available on the computer on which the
programs are started.  Switch to a larger computer or edit hypoDD.inc
and/or ph2dt.inc in the directory include/ to adjust array dimensions
according to the size of the problem to be solved or available computer
memory.


		    	BUG REPORTS, QUESTIONS, ENHANCEMENTS, ETC.

Please send questions, bug reports, news about how you have improved
the programs, etc. to felixw@ldeo.columbia.edu.


			UPDATES ALERT

Send email to felixw@ldeo.columbia.edu with 'HYPODD UPDATE' included in the
subject line.