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 .
- 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.
- "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.
Part 2: Example in the hypo71 program
- Let's start with the input file of the hypo71PC "HYPO71PC.INP"
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.
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).
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.
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.
- 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.