Overview

SAC2000 was designed as an aid to research seismologists in the study of seismic events. As such, it is used for quick preliminary analyses, for routine processing, for testing new techniques, for detailed research, and for creating publication quality graphics. It is used by both computer novices and experts. In order to make SAC2000 quick to learn and easy to use, default values for all operational parameters were carefully chosen. At the same time, almost all of these parameters are under direct user control. This design combines ease of use with significant flexibility.

User Interface

SAC2000 is an interactive command driven program. Commands may be typed at the terminal or placed in a macro file. SAC commands fall into three main categories: parameter-setting, action-producing and data-set manipulation. The parameter-setting commands change values of internal SAC parameters. Action-producing commands perform some operation on the signals currently in selected memory based upon the values of these parameters. Data-set commands determine which files are in active (selected) memory and therefore will be acted upon (data-set commands are not currently operational). The effect of a parameter-setting command remains in effect until it is reset. The effect of an action-producing command is immediate and transitory. Action-producing commands also have options which normally remain in effect until reset. These options, however, apply only to that particular command. The underlying assumption is that you are more likely than not to want to use the same values the next time you execute the same command. When you start up SAC2000, default values are defined for all of these parameters. SAC2000 can be reinitialized to this default state at any time by executing the INICM command.

Mode of Operation

Each signal is stored in a separate data file. Each data file contains a header that describes the contents of that file. See the section on Data File Format for details. Signals are read from disk into memory using the READ command. CSS 3.0 formated flat files can be read using the READCSS command. SAC2000 can process up to 200 signals of arbitrary size at a time. Once data is in memory other commands are typed at the terminal (or read from a macro file) to perform operations on these signals. All operations work concurrently on all signals in memory. You can look at the results at any time using the plot commands. There are several plot formats to choose from. You have control over titles and labels, plot limits, file identifications, axes and tick mark locations, etc. You can also save the results of these operations at any time using the WRITE command. All of the commands are described briefly in the sections on Analysis Capabilities and Graphics Capabilities of this manual and documented in detail in the Commands Reference Manual.

How SAC Handles Time

The SAC header contains a reference or zero time, stored as six integers (NZYEAR, NZJDAY, NZHOUR, NZMIN, NZSEC, NZMSEC), but normally printed in an equivalent alphanumeric format (KZDATE and KZTIME). This can be set to any reference time you wish. It is often the time of the first data point, but can also be the origin time of the event, midnight, your birthday, etc. It does not even have to be a time encompassed by the data itself. All other times are offsets in seconds from this reference time and are stored as floating point values in the header:

Many SAC commands work with these header variables. They are discussed in the two sections on Analysis and Graphics Capabilities. The CUT command is one of the most important of these commands. It lets you select portions of data files using the offset time header fields to be read in by subsequent READ commands. Examples of the use of CUT and READ are shown in the Tutorial Guide and also in the Command Reference Manual.

Getting Started

The second best way to get started (after you have finished reading this section) is to sit down at a terminal or workstation with a copy of the Tutorial Guide For New Users, and try the examples as you read the manual. (The best way is corner an experienced and patient user and make him or her show you how things work!) The examples in the tutorial cover the basic commands you need to know in order to proceed further. The next step is to browse through the lists (one alphabetical and the other functional) of SAC commands in the Command Reference Manual, find a few that sound interesting, and try them. SAC2000 is fairly careful in checking for errors so you can't do much harm in experimenting. After you have become somewhat comfortable using SAC2000, you might want to return to this manual to get a better overview of the program. Be sure and read the section on SAC macros. They will definitely save you time when you get ready to do fairly complicated or repetitive analysis on large data sets. Eventually you will probably want to sit down and wade through the complete Command Reference Manual to get a complete picture of what you can do with SAC2000. It's better to defer that step until you have used the code for awhile.

This page maintained by:

LLNL Disclaimer
8/12/98
UCRL-MA-112836