Using Guralp's GCFInfo

The tool that makes SCREAM most useful as a replacement for the DOS-based QUAKES program is Guralp's GCFInfo. With GCFInfo, it is possible to combine files, cut files given specific time parameters, and convert gcf-format files into PEPP and other formats.

Putting Files into GCFinfo

Open GCFinfo. The main window will look like this (this picture is shown with an hour file already added):

Using Windows Explorer, locate and open the SCREAM file sets. SCREAM saves a file for every hour of the day. The file name denotes the time and date of the beginning of the data file.  For example, an hour file named 1990701_2300Z.GCF is read: year (1999), month (07), day (01), time (2300), component (Z) and format (GCF). The time is given in Universal (Greenwich Mean) time. So this file is for 11:00 PM to Midnight (in England) on July 1, 1999.  [Depending on your time zone here in the US, you might have to subtract 5 (or more) hours to convert to local time. Remember, though, that DRMs from Princeton and statements from USGS, SAC, and other sources are also in Universal time.]

Click onto a file. It will become highlighted.  If your time of interest spans two or more hours, you will need to select 2 or more files. To do this, hold down the Shift key and use the up and down arrows to highlight additional files, or use the mouse to select files. Click onto the highlighted area and drag the files to the GCFinfo window.  Release the mouse.

Combining Files

If you want to use the SCREAM Replay Mode to examine these hour files as a set, highlight all the files, again using the Shift key and arrows.  Right-click the mouse and a pull-down menu appears:

Select "Combine into single file". At this point, the combined file can be dragged into the Replay Control window of SCREAM.

Viewing a Combined File in GCFinfo

The quickest way to look at a combined file and/or cutting data is to Right-click onto the highlighted files and select View. If you are not going to use Replay Mode of SCREAM, you do not have to combine the files into a single file first. GCFinfo will open a new window like this:

This window is shown with the File pull-down menu already chosen. The + and ­ buttons are used to increase and decrease amplitude. The up and down bars simply move the display up and down on the screen. To expand an area of the display, click and drag across the section to be enlarged. To restore, just Right-click on the background.


Cutting a File to Send to Princeton

After receiving a DRM from Princeton, select the hour files which contain the times of the DRM quake (depending on the duration of the quake, it may require two individual hour files, never more than three). Drag the files into GCFInfo. Open the View pull-down menu.

Select Time Section. Another small window appears, showing the starting and ending times of the wave view window. Enter the desired starting and ending times for the event to be cut. Notice that the times in this window are in 12 hour (AM and PM), not 24 hour format.

The wave view window is adjusted, showing what the file will look like when sent to PEPP. If it appears to be OK, click onto the File selection and choose Save As. Another window will appear.

Give the file a name; type it in the space. Save as type PEPP in the pull-down menu [If you plan to reexamine the file with SCREAM or GCFInfo, you may save the file in GCF format.]. Indicate where to save the to: desktop, hard drive, floppy, etc. If you will send the data to Princeton and also want to be able to access the file in SWAP, WINquakes, or MATseis, it may be helpful to save to floppy. Insert a floppy into the computer and complete the save procedure.

Close out all the windows. To remove the list of hour files from the main GCFinfo window, Right-click on the highlighted files and select Remove.