hypo71 Tutorial

by Chunquan Wu

This website contains a brief tutorial on how to use the hypo71PC program (Lee and Valdes, USGS open report, 1985) for determining hypocenter, magnitude, and first motion pattern of local earthquakes. 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 .

Overview of hypo71 package (Infered from the hypo71 manual)

  • HYPO71 is a computer program for determining hypocenter, magnitude and first motion pattern of local earthquakes written by Lee and Lahr (1972) using a stepwise statistical regression procedure outlined in Draper and Smith (1966)
  • The HYPO71 program takes the station locations, crustal seismic velocity model, and the phase information in the input file. It assumes a trial origin time and hypocentral location for the earthquake, and improve the origin time and hypocentral location by iteratively minimizing the least square error of the travel time computed from the input station, velocity model and phase information.
  • Duration, amplitude and period for each station are used to give a magnitude value for each station. These values are averaged to give the event magnitudes. The P and S phases are used to estimate the first motion pattern of the earthquake.

Source code, user guides and relevant publications

Programs files included in the hypo71PC package

  • "HYPO71PC.EXE" is the executable PC version of the hypo71 program. It can be run under the "Command Prompt" on a PC running under the Windows XP operating system.
  • "HYPO71PC.FOR" is the Fortran source code for HYPO71PC.EXE. You can compile it with any standard Fortran compiler.
  • "HYPO71.FOR" is the Fortran source code for the original hypo71 program (SUN based).
  • "HYPO71.INP" is an example input file for HYPO71PC.EXE program.
  • "HYPO71.OUT" is the output file for HYPO71PC.EXE program.

How to run it on your computer

  • Download the PC version of hypo71 at http://jclahr.com/science/software/hypo71/hypo71.zip .
  • Extract the zip package, you will see an executable file "HYPO71PC.EXE" and an example input file "HYPO71.INP".
  • Double click "HYPO71PC.EXE" or run it in the "Command Prompt" window
    Select "Start"
    Select "All programs"
    Select "Accessories"
    Select "Command Prompt"
    Go to the directory of HYPO71PC.EXE
    Type "hypo71pc" in the command window
    Follow the directions of the hypo71PC program

Part 2: Example in the hypo71 program

Understanding the hypo71 input file format

  • Let's start with the input file of the hypo71PC "HYPO71PC.INP"
    station information:
    SR013842.55 12259.17      -0.15     0.40   0.25 8
    SR01 is the station name
    3842.55 is the latitute
    12259.17 is the longitude
    -0.15 is the station delay
    0.4 is the station correction for FMAG
    0.25 is the station correction for XMAG
    8 is the system number.
    velcity model:
    3.30   0.0
    5.00   1.0
    5.70   4.0
    6.70   15.0
    8.00   25.0
    The first column is the p wave velocity (in km/s)
    The second column is the depth of the top of that layer (in km).
    phase parameters:
       5.  50. 100. 1.78    2        18    1    1         1   11
    5 is the trial forcal depth
    50 is the distance in km from epicenter where the distance weighting is 1
    100 is the distance in km from epicenter where the distance weighting is 0
    1.78 is the Vp/Vs ratio
    2 is the quality class
    18 is the minimum first motion records required
    the following five "1"s are indicator for punched cards
    mathod for selecting magnitude, indicator for printed output, 
    and indicators for the using auxiliary RMS value and azimuthal weighting.
    phase information:
    SR04IPU0 691005111258.05       62.45ISU0   29. .20        0.78
    SRO4 is the station name
    IPU0 means P-arrival phase (U means the first motion is up, D means down)
    6910051112 is the date and time of the event in yr-mt-dy-hr-mi format
    58.05 is the seconds for P-arrival
    62.45 is the seconds for S-arrival
    ISU0 means the S-arrival phase
    29. is the maximum peak-to-peak amplitude in mm
    .20 is the period of maximum amplitude in second
    0.78 is the weight assigned to this station.

Understanding the hypo71 output file format

  • Next let's look into what we got from the hypo71 program "HYPO71PC.PUN"
    691005 1112 52.83 38-28.59 122-41.94   8.41   1.81 19  59  1.2  .16   .5  1.1 B1
    691005 12 6 44.56 38-28.53 122-42.09   3.85   2.05 17  59  1.4  .03   .1   .1 A1
    691005  612  4.22 38-28.40 122-40.88   7.82   2.55 14  67   .4  .07   .3   .5 A1
  • Please refer to the HYPO71 manual for a detailed explanation of the complete output file "HYPO71PC.OUT" with the first motion patterns, and etc.

Play with the example

  • Please follow the directions in "How to run it on your computer" to run the HYPO71PC program and see if you can get the earthquake locations from the example input file.

Last updated by Chunquan Wu Thu Mar 10 15:49:35 EST 2011