| Note: This is an old page, the best way to do this now is to use the USGS NEIC web site. I haven't deleted this page because the example shell script and awk command examples may be useful. |
Searching For Earthquake Locations
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The data format is described here.
Searching the PDE Files for Earthquake Locations
We have a simple program called "pde_srch" to search the PDE files. With this program you can search the PDE files one at a time, but using a shell script, you can automate a search of the entire data base.
Here is an example of a single execution of the program.The input from the user is in green.
mantle.eas.slu.edu:66% pde_srch What year (e.g. 1992)? 1989 Will search file: /geo/GeoData/PDEs/Data/p1989 What is the summary file name? summary.89 Search by box (1) or distance (2)? 1 Enter bounds: w,e,s,n? Units = degrees -124,-120,36,38 What are the minimum & maximum magnitude? 0,10 Use mb (1), Ms (2), or larger of the two (3)? 1 What are the minimum & maximum depths (km)? 0,10000
The output file, "summary.89" looks like this:
1989 01 15 00:07:13.199 37.417 -121.758 7 0.0 1989.038330078 1989 01 16 06:29:53.599 37.735 -121.983 4 0.0 1989.041870117 1989 01 16 07:07:03.799 37.737 -121.980 5 0.0 1989.041870117 1989 01 17 22:39:54.200 37.815 -122.598 12 0.0 1989.046386719 1989 01 20 20:48:53.799 36.150 -120.208 10 0.0 1989.054443359
. . .
Summary File Format
The output format is:
yyyy mm dd hh:mm:ss.ssss latitude longitude depth magnitude decimal_year
The individual values can be extracted using awk and then plotted using programs such as GMT, etc. For example, to make a file (let's call it the_locations.xy) that can be plotted using the GMT command psxy, use the command:
awk '{print $6, $5}' summary.89 > the_locations.xy
Note the switch to longitude latitude since that is the default in gmt. To scale the symbols in the GMT plot, make the diameter of the symbols in GMT proportional to the magnitude:
awk '{print $6, $5, $8 / 100 + 0.01}' summary.89 > the_locations.xy
The "+0.01" is used to insure that the earthquakes that have zero magnitude still show up int the GMT plot. Why are the zero magnitudes anyway? The PDE search we did was conducted using mb as the magnitude key. Not all the events in the catalog are large enough to have an estimate of mb. Small earthquakes are generally measured by ML or mb(Lg) or coda magnitude, but that information is not in the PDE files.
Using a Shell Script for a multi-year search
Suppose that you want to make a map of seismicity in a region and you don't want to type the same geographic search parameters into pde_srch over and over. Use a shell script to automate the process. Here's an example script that creates two files. A summary file called "my.events" and a file for plotting the locations with GMT called events.xy. In this example, the size of the symbol for each earthquake is scaled relative to the cube of the events' magnitude. The search depends on the file called "theList", which is a list of filenames located in the PDE directory.
#!/bin/csh # # script to search all the PDEs # makes two files, one with date and time, etc # the other just lat lon and mb (for gmt) # /bin/rm my.summary events.xy touch my.summary touch events.xy # foreach year ( `cat /geo/GeoData/PDEs/Data/theList` ) # echo '***********' $year '***********' # pde_srch << finished $year eve.tmp 1 -128,-115,40,55 0,10 1 0,2000 finished # # scale the magnitudes for plotting in GMT # cat eve.tmp >> my.summary awk '{print $5, $6, $8*$8*$8/1000 + 0.01}' eve.tmp >> events.xy # end # /bin/rm eve.tmp