FIRE and MUD Contents

Computer Visualization of Earthquake Hypocenters

By Richard P. Hoblitt,1 Jim Mori,1 and John A. Power1

1U.S. Geological Survey.


We present two computer programs--PINAPLOT and VolQuake--to simplify the task of analyzing the locations of earthquakes associated with volcanic activity. Both programs require an IBM-PC compatible computer. PINAPLOT runs under DOS; VolQuake requires Microsoft Windows, version 3.1. Earthquake locations are plotted in chronologic order, in both map and cross-sectional view, much like a movie. Consequently, the user can experience seismic data as they were received.


In many, perhaps most, scientific pursuits, data interpretation can be a leisurely affair. In contrast, data acquired for the purpose of hazard mitigation must be processed and interpreted quickly. When Mount Pinatubo reawakened, earthquake hypocenters were displayed by preparing a series of monochrome epicenter maps (plan view) and hypocenter plots (cross-sectional views). The size of plot symbols was keyed to earthquake magnitude, and the symbol type was keyed to hypocentral depth. Epicenter maps were examined in chronologic order to gain an appreciation of how activity was evolving through time. A program called ACROSPIN (Parker, 1990) allowed hypocenters to be rotated about three orthogonal axes and so provided a three-dimensional perspective. Although this approach was workable, it was rather cumbersome. The analyst had to prepare and examine a collection of graphs--essentially "snapshots" of activity through time. Earthquake data had to be reformatted before ACROSPIN would accept them. While none of these deficiencies is serious under normal circumstances, each is magnified in a crisis situation in which personnel are fatigued and time is at a premium.

Following the climactic eruption of Mount Pinatubo on June 15, 1991, Mori wrote an unadorned computer program (PINAPLOT) to display the earthquake hypocenters in a somewhat different manner. Epicenter maps and hypocenter plots were displayed as before, but the time between the plotting of two hypocenters was roughly proportional to the actual elapsed time between the two earthquakes. This simple change markedly improved an observer's sense of time. In addition, different colors were used to indicate depth intervals, and each new symbol was heralded by a brief flash of light and a beep. Rather than a series of static "snapshots," we essentially had a motion picture of earthquake locations. The value of this program soon became apparent, as it allowed us to quickly review and track continuing seismic activity. Furthermore, it was extremely easy to use: a brief explanation would prepare virtually anyone to run the program.

The reawakening of Mount Spurr in 1992 again presented the need to expeditiously interpret seismic data. PINAPLOT--hastily written specifically for Mount Pinatubo--was modified by Hoblitt to accept data from Mount Spurr. The modified program performed the same useful functions that it had during the Mount Pinatubo eruptions. Despite its usefulness, PINAPLOT had limitations. Opportunities for user input were limited, and code modifications were necessary before the program could be used for different volcanoes. Further, data still had to be reformatted before they could be examined in ACROSPIN. We needed a user-friendly version of the original program that could (1) be employed quickly at restless volcanoes without modification, (2) provide the functionality of ACROSPIN, and (3) permit data sets from previous eruptions to be compared easily. Following the Mount Pinatubo and Mount Spurr experiences, a new program, VolQuake, was written by Hoblitt, with the assistance of Mori and Power, to overcome the limitations of PINAPLOT while retaining its useful features.

PINAPLOT reads data in the HYPOELLIPSE format (Lahr, 1989); VolQuake reads data in the HYPOELLIPSE and the HYPO71 formats (Lee and Valdés, 1989). In addition to the original references, the formats are described within VolQuake's built-in Help system.

Both PINAPLOT and VolQuake are provided on the accompanying floppy disk, along with data files for Mount Pinatubo (1991), Mount St. Helens (1980-92) and Mount Spurr (1992). PINAPLOT will accept only the Pinatubo data; VOLQUAKE will accept all three data sets.


Hardware Requirements


PINAPLOT may be run from a floppy disk or a hard disk. The required files are provided in compressed form within PPSETUP.EXE, a self-extracting file in directory PINAPLOT. There is insufficient room on the distribution disk to contain the PINAPLOT files in an uncompressed form. You must therefore copy PPSETUP.EXE to a hard disk or floppy disk. From the DOS prompt, in the drive and directory to which to you have copied PPSETUP.EXE, type "PPSETUP", then press the Enter key; this will decompress the following files:






These decompressed files, plus the self-extracting file, occupy about 0.5 megabytes.


From the DOS prompt, in the drive and directory containing the PINAPLOT files, type "PINAPLOT", then press the Enter key. The program will request some information. Type an answer to each question; press the Enter key after each answer. Press only the Enter key to input the default value for a given question.


Hardware Requirements

Optional Hardware

Software Requirements


Insert the disk in drive A (or B). From Program Manager in Windows, choose Run from the File menu. Type A:\VQ\SETUP (or B:\VQ\SETUP) and press the Enter key. If you wish to install VolQuake in the default drive and directory (C:\VQ), then click the Continue button. Otherwise, type the drive and directory of your choice, then press the Enter key. Once they are decompressed, VolQuake files occupy about 2.1 megabytes.


Position the mouse pointer over the volcano icon and double-click the left mouse key; that is, depress the mouse key twice in rapid succession. Shortly after a brief introductory screen, a Menu will appear. In the present configuration, three topics are listed: Mount St. Helens (1976-92), Mount Pinatubo (1991), and Mount Spurr (1991-92) are listed. Each topic refers to an earthquake data set. To explore a given data set, select that set with the mouse pointer, then click the OK button. Alternatively, the desired topic may be selected by double-clicking. As soon as a topic is selected, two windows will appear. The window on the left shows earthquake locations around a volcano as seen in map view; this is called an epicenter map. The window on the right side of the screen shows earthquake locations as seen in cross section; this is called a hypocenter plot. Brief flashes of light and persistent symbols show earthquake locations. As an earthquake is plotted, its time of occurrence appears within a small box in the upper central part of the screen. A cartoonlike animation showing the volcano's outward behavior appears in this same box. Small boxes in the upper right and left corners of the screen explain the plot symbology. When the entire data set has been plotted, VolQuake will beep and display the number of earthquakes in the data set at the bottom of the screen. This is the standard presentation.

Numerous other presentations are available if you click the buttons along the bottom of the screen; you may click these buttons at any time. Probably the easiest way to learn how these buttons operate is to experiment with them.

Note that seismic data are unavailable for Mount Pinatubo between June 11 and June 29, 1991, due to eruption-related loss of seismometers. Within this time interval, VolQuake will display the eruption animation but will not plot any earthquake hypocenters.

Documentation of all aspects of VolQuake is contained within the built-in Help system. One way to enter the Help system is to click the Help buttons located on many of VolQuake's windows. This will produce a summary Help screen that pertains to the window that contains the Help button. An alternative way to enter the Help system is to press the F1 key on your keyboard. The Help system is context sensitive, which means Help topics are linked to VolQuake's various elements. When you press the F1 key, the topic that appears in the Help window depends on which VolQuake element is active when you press F1. The active button can be recognized by the small dots that surround the text on the button. You make a button active by repeatedly pressing the Tab key. Not all VolQuake elements can become active. If you want help on some part of VolQuake that you can't activate with the Tab key, press the F1 key, then use the browse keys (<<, >>) on the Help window until the desired topic appears. If this fails, click the Search key on the Help window, then follow the instructions to conduct a keyword search.

There are four ways to close a Help window.

1. On your keyboard, press the Alt key, followed by the F4 key.

2. Click the negative sign in the upper left-hand corner of the window, then click "Close."

3. Double-click the negative sign in the upper left-hand corner of the window.

4 Click "File" on the upper left of the window, then click "Exit."


PINAPLOT and VolQuake allow the user to experience seismic data as they were received. By using the Pause button in VolQuake, you can stop plotting at any time and ask yourself how you might have interpreted the data at that point or what advice you might have given to those at risk. Suggestions for future revisions are welcome.


We wish to thank Steven Malone for kindly providing the Mount St. Helens data set for inclusion with VolQuake.


Lahr, J.C., 1989, HYPOELLIPSE/Version 2.0: A computer program for determining local earthquake hypocentral parameters, magnitude, and first motion pattern: U.S. Geological Survey Open-File Report 89-116.

Lee, W.H.K., and Valdés, C.M., 1989, User manual for HYPO71PC, Chapter 9, in Lee, W.H.K., ed., IASPEI Software Library Volume 1, Toolbox for seismic data acquisition, processing, and analysis: El Cerrito, Calif., International Association of Seismology and Physics of the Earth's Interior in collaboration with Seismological Society of America, p. 203-236.

Parker, D.B., 1990, User manual for ACROSPIN, Chapter 6, in Lee, W.H.K., ed., IASPEI Software Library Volume 2, Toolbox for plotting and displaying seismic and other data: El Cerrito, Calif., International Association of Seismology and Physics of the Earth's Interior in collaboration with Seismological Society of America, p. 119-184.

FIRE and MUD Contents

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Last updated 09.23.98