The Seismic Analysis Code (SAC) is one of the most widely used analysis packages for regional and teleseismic seismic data. For the first time, this book provides users at introductory and advanced levels with a complete guide to SAC. It leads new users of SAC through the steps of learning basic commands, describes the SAC processing philosophy, and presents its macro language in full, supported throughout with example inputs and outputs from SAC. For more experienced practitioners, the book describes SAC's many hidden features, including advanced graphics aspects, its file structure, how to write independent programs to access and create files, and much more. Tutorial exercises engage users with newly acquired skills, providing data and code to implement the standard methods of teleseismic shear-wave splitting and receiver function analysis. Methodical and authoritative, this is a key resource for researchers and graduate students in global seismology, earthquake seismology and geophysics.

Preface page ix

Acknowledgements xi

1 Introduction 1

1.1 What is SAC? 1

1.2 History and development 2

1.3 Alternatives to SAC 2

1.4 SAC variants 3

1.5 Requirements and installation 4

1.6 Scope of this book 4

2 The SAC data format 5

2.1 Philosophy and structure 5

      SAC file format 5

      Alphanumeric and binary forms 5

      Interconversion of formats 6

2.2 Conversion from other data formats 6

      GSE files 6

      SEG Y, MSEED, GCF and CSS formats 7

2.3 Byte-order issues 8

2.4 SAC file layout 1 0

3 The SAC processing philosophy 1 1

3.1 Phases of a typical analysis task 1 1

      Organize 1 1

      Interact 1 3

      Process 1 4

      Display 1 4

3.2 Command summary for each phase 1 4

3.3 Further information about SAC commands 1 5

4 Basic SAC commands 1 7

4.1 Command style 1 7

4.2 Command history 1 7

4.3 Reading and writing data 1 8

      Reading examples 1 8

      Writing data 1 9

4.4 Plotting and cutting 1 9

      Devices 1 9

      Windows and window placement 20

      Plotting data 21

      Cutting data 24

      Permanent plots 24

4.5 Picking 25

4.6 The file header 25

      Time representation 27

      Listing 27

      Changing 28

      Writing 29

4.7 Trace preparation and resampling 29

      De-glitching 29

      Mean and trend removal 30

      Resampling 30

4.8 Rotation 31

4.9 Frequency-domain operations and filtering 32

      Filtering 34

      Designing filtering strategies 35

4.11 SAC utility programs 37

5 SAC macros 38

5.1 Macros and invoking them 38

5.2 Writing a simple macro 39

5.3 Tracing macro operations 39

5.4 Searching for macros 40

5.5 Decision making in macros 40

5.6 Variables in macros 41

      Types and scope 41

      Setting 41

5.7 Expressions 42

      Syntax 43

      Built-in functions 43

      Escape character 48

      Evaluation order 48

      Conditions 49

5.8 Suspension, resumption and escape from macros 50

5.9 Operating system interaction 51

5.1 0 Looping commands 52

      WHILE 53

      WHILE READ 54

      Escaping from loops 54

      DO 55

5.1 1 Macro parameters 57

      Positional 57

      Keyword 59

      Recursion 60

      5.12 Advanced operating system interaction 61

6 Accessing SAC functionality and data from external programs 64

6.1 Automating SAC execution 64

      Running SAC from the shell 64

      Automation of SAC execution in the shell using scripting 65

6.2 Accessing SAC data in external programs 68

      Accessing SAC data from Fortran using the sacio library 68

      sacio90: object-oriented SAC data interaction in Fortran 70

      Other languages 71

6.3 Accessing SAC functionality in Fortran programs 72

7 Graphical data annotation 74

7.1 Plot annotation 74

      Seismograms 74

      Composite plots 77

7.2 Annotating plots with graphical elements 79

      Graphical elements 80

      Assembling graphical elements 80

      Parameters controlling graphical elements 83

7.3 Using PLOTC 83

8 Array data handling 86

8.1 SAC subprocesses 86

8.2 The signal stacking subprocess 87

      Trace collections 87

      Adding, deleting and changing traces 88

      Plotting record sections 89

      Stacking 90

      Saving stack data and uncertainties 95

      Picking data in stacks 95

8.3 Array maps 101

8.4 Beamforming 102

8.5 Travel-time analysis 106

9 Spectral estimation in SAC 109

9.1 Spectral estimation 109

9.2 The spectral estimation subprocess 110

      Correlation 110

      Spectrum 112

      Saving the correlation and the spectrum 113

10 Three-dimensional data in SAC 115

10.1 The concept of 3D data 115

10.2 Spectrograms 115

10.3 Contour plots 117

10.4 Composite 3D data plots 119

10.5 Properties of 3D data 120

10.6 Writing 3D data files 121

11 Implementation of common processing methodologies using SAC 123

11.1 Seismic anisotropy and shear wave splitting 123

      Overview 123

11.2 Shear wave splitting analysis 123

      Parameter estimation methodologies 124

      Macro and auxiliary program design 125

      SAC implementation 127

11.3 Receiver function analysis 127

      Overview 127

      Estimation methodologies 129

      Macro and auxiliary program design 30

      SAC implementation 130

Appendix A Alphabetical list of SAC commands 135

Appendix B Keyword in context for SAC command descriptions 142

References 167

Index 170

Color plate section is found between pp. 116 and 117.

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