SAC Tutorial

8/17/2019 SAC Tutorial

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Overview

SAC, the acronym for Seismic Analysis Code, wasdeveloped at Lawrence Livermore National Laboratory,University of California, in the early 1980s!

"t is a command#driven pro$ram $enerallyimplemented on many types of UN"% operatin$ systemsand has become a standard data manip&lation tool in

seismolo$y!

"ts binary data format is one of the principle dataformats &sed today in storin$ and manip&latin$seismolo$ical time series data!

'ith SAC(

one can interactively read seismo$ram data andperform many standard data processin$ operations,s&ch as

filterin$time pic)samplit&de pic)s

correlation*o&rier transformsseismic instr&ment correctionsparticle motion rotationtrace envelopesspectral ratioslinear re$ressions

fre+&ency#waven&mber analysis


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and create a variety of plots of the data andres&ltin$ analysis

here are also &tility pro$rams that can be &sed toview plots or to convert SAC $raphics files into otherformats s&ch as -ostScript!

hese files can then be &sed with other $raphicspro$rams s&ch as Adobe "ll&strator to constr&ct morecomple. fi$&res!

/ne can also interact directly with the UN"% operatin$system while &sin$ SAC, callin$ system f&nctions orr&nnin$ secondary pro$rams as needed!

acros scripts of SAC commands2 can be combinedwith CShell scripts for a&tomatin$ seismic processin$!

SAC binary data files can be written and read fromfortran and C pro$rams &sin$ inp&t3o&tp&t ro&tinescontained in the SAC library, 4sac!a4!

last modified 3/05/01


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CERI Implementation

SAC is part of C56"s s&pported software!

/n lo$in, each &ser so&rces the 4ceri7common!cshrc4file which sets the followin$ UN"% environmentalvariables! hese variables are needed by the SACpro$ram to access internal databases!

he *ollowin$ are sac ariablessetenv SAC:"6 3ceri7common3s&pported3sac;0003sacset path < =path =SAC:"63bin2

setenv SACC*LA>S 4#w #:?S:@!; #:SUN/S@!04setenv SAC**LA>S 4#w #Nn;000 #N+004

setenv SAC-*LA>S 4#-4setenv SAC%'"N:/'S .11setenv SACAU% =SAC:"63a&.setenv SAC>6A-B"CS:5"C5 %

setenv L:7L"?6A67-AB=SAC:"63lib(=L:7L"?6A67-AB

Important Note:

At this time 30D3012 C56" does not have a $enerallyavailable copy of the SAC library, 4sac!a4 or 4sacio!a4,that can be &sed in compilin$ fortran or C pro$rams on

SUN Solaris systems! A copy is available at 3teteme)o3local3sac3lib3sac!a if yo& need to compile pro$ramswith SAC "3/ ro&tines!


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he SAC pro$ram is started by typin$, for e.ample(

system promptE sac;000

o& then see(

N5' S5"S"C ANALS"S C/:5 Farch ;8, 199G ersion 00!D12H

Copyri$ht 199D 6e$ents of the University of California

SACE

And SAC is ready to $oI



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SAC Commands

SAC commands are entered at the command prompt!>enerally data are constr&cted within SAC or readfrom a file before other operations are attempted!Alternatively, sometimes certain SAC commands areinvo)ed to prepare a certain )ind of data operation orto set &p parameters for a plot!

he definitive website on SAC commands is located athttp(33www!llnl!$ov3sac3 !

Bere is an alphabetical list of commands containedwithin SAC! Note, that a command may have a

shorthand form on the left of each word pair2!

absol&teval&eabsol&teval&e

abs absadd addaddf addf am )eepamap) ap)a.es a.esa.is a.es

fortrane.ternal7interfacefft fftdft fftfileid fileid

filterdesi$nfilterdesi$nfdfilterdesi$nfir firfloor floorf&nc$enf&nc$enf$ f&nc$en

lds ldslistdatasetsldsline linelinefitlinefitlinlin

linlinlinlo$linlo$listhdrlisthdrlhlisthdrloadloadloadctable

loadctable

+dp +dp+&antiJe+&antiJe

+&it +&itdone +&itend +&ite.it +&it+ +&it+&its&b+&its&b

vspacevspacevspvspace


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lctloadctablelo$ lo$lo$10lo$10lo$lablo$lablo$linlo$linlo$lo$lo$lo$lowpasslowpasslplowpass

bandpassbandpassbpbandpassbandreKbandreKbr bandreKbbf) bbf)beam beambeamform

beambe$indevicesbe$indevicesbdbe$indevicesbe$$be$indevicesb$be$indevicesbe$inframe

be$inframebe$frbe$inframebfbe$inframebe$inwindowbe$inwindowbwbe$inwindowbenioff benioff

binoperr

$etbb $etbb$map $map$rayscale$rayscale$s $rayscale$rid $rid$ro&p $ro&p$te.t $te.t$t $te.t

macromacrommacromapmapmar)ptpmar)ptpmar)pmar)ptp

mar)timesmar)timesmar)tmar)timesmar)val&emar)val&emar)vmar)val&emer$emer$e

messa$emessa$emesmessa$emtwmtwm&lm&lm&lfm&lf

m&lome$a

read readr readreadalphareadalpharareadalphareadbbfreadbbf rbbfreadbbf

readcssreadcssrcss readcssreaderrreaderrrerrreaderrreadhdrreadhdrrh

readhdrreadsddreadsddrsddreadsddreadspreadsprsp readsprenamerename

report

waitwaitwcsswritecsswhpfwhpf widthwidthwienerwiener

wnrwienerwildwildwindowwindowwritewritewwrite

writebbfwritebbf wbbfwritebbf writecsswritecsswcsswritecsswritehdrwritehdr

wh


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binoperrboecbinoperrborder border

m&lome$a

reportreversereverser$litchesr$litchesrmeanrmeanrms rmsrotate rotaterot rotater+ r+rtrendrtrendrtr rtrend

writehdrwritesdd

writesddwritespwritespwspwritesp

capf capf ccipf capf cds cdsc&rrentdatasetcdschnhdrchnhdrch chnhdrchpf chpf color color

col colorcomcorcomcorconto&rconto&rcont conto&rconvertconvertconv convertconvolve

convolveconvoconvolvecopy copycopyhdrcopyhdrcorrelatecorrelatecor correlatec&t c&t

c&terr c&terr

hannin$hannin$han hannin$help helph helphi$hpasshi$hpasshp hi$hpasshilbert hilbert

newsnewsnplotcnplotcn&lln&ll

scallop

scallopscp scallopsetbb setbbsetdevicesetdevicesetmacrosetmacros$f s$f hcd s$f smooth

smoothspe spespectro$ramspectro$ramsp$spectro$rams+r s+rs+rt s+rtsss sssstretch

stretchs&b s&bs&bf s&bf symbolsymbolsymsymbolsynchroniJesynchroniJesynch

synchroniJe

.div

.div

.f&d$e

.f&d$e

.f&ll

.f&ll

.$rid

.$rid

.label

.label

.labl

.label

.lim

.lim

.lin

.lin

.lo$

.lo$

.vport

.vport

.vp

.vport

.wind

.vport


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synta.synta.syn synta.systemcommandsystemcommandscsystemcommand

data$endata$end$ data$endecimatedecimatedelete deletedif dif div divdivf divf divome$adivome$a

ifft ifftidft ifftima$e ima$einicm inicminstallmacroinstallmacroint intinterpolateinterpolateinterpinterpolate

oapfoapf ocipfoapf ohpfohpf

taper tapertic)s tic)stitle titletrace tracetranscripttranscripttransfertransfertranstransfertransfertabletransfertabletsiJe tsiJe

ydivydivyf&d$eyf&d$eyf&llyf&lly$ridy$rid

ylabelylabelylablylabelylimylimylinylinylo$ylo$

yvportyvportyvpyvportywindyvport

echo echoenddevicesenddevicesed

enddevicese$enddevicesend$enddevicesendframeendframeef endframeendfrendframe

envelope

)eepam)eepam)hronhite)hronhite

pa&sepa&sepic)spic)s

plabelplabelplot plotp plotplot1plot1p1plot1plot;plot;

p;

&nsetbb&nsetbb&nwrap&nwrap

Jcolors

JcolorsJlabelsJlabelsJlevelsJlevelsJlinesJlinesJtic)sJtic)s


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envelopeerase eraseera eraseeval&ate

eval&ateeval eval&atee.p e.pe.p10 e.p10e.ternale.ternal7interfacee.te.ternal7interface

plot;plotalphaplotalphapaplotalphaplotcplotcpcplotcplotctableplotctableplotdyplotdyplotp)plotp)pp)plotp)plotp)tableplotp)tableplotpmplotpmppmplotpmplotspplotsp

pspplotspplot.yplot.yp.yplot.yprod&ctionprod&ctionprodprod&ction

A description of each command can be obtained whilein the SAC pro$ram by typin$

SACE help commandname

*or e.ample, here is what yo& wo&ld see for thecommand, abs(


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SACE help abs

SAC Command 6eference an&al A?S

SUA6(

a)es the absol&te val&e of each data point!

SNA%(

A?S

566/6 5SSA>5S( 101( No data files read in!

10( "lle$al operation on spectral file

B5A:56 CBAN>5S( :5-"N, :5-A%, :5-5N

LA5S 65"S"/N( Man&ary 8, 198 ersion 8!02SACE

SAC commands can be $ro&ped into several f&nctionalcate$ories(

5.ec&tive *&nction od&le, e!$!,manip&late blac)board variableshelpmacro

+&it:ata#Set od&le:ata *ile od&le, e!$!,

readc&tlisthdr

>raphics 5nvironment od&le, e!$!,.vport


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title>raphics Control od&le, e!$!,

be$indevicesenddevices

>raphics Action od&le, e!$!,plotplot1plotp)

Spectral Analysis od&le, e!$!,fftplotspbandpass

Unary /perations od&le, e!$!,addm&ls+rt

?inary /perations od&le, e!$!,

mer$eaddf divf

Si$nal Correction od&le, e!$!,rtrendrmeanrotate

decimate5vent Analysis od&le, e!$!,

ohpf oapf

Si$nal eas&rement od&le, e!$!,rmsmar)times

% :2 :ata od&le, e!$!,


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spectro$ramconto&r

"nstr&ment Correction od&letransfer

S&bprocess "nvo)in$ od&lespe Spectral 5stimation S&bprocess2sss Si$nal Stac)in$ S&bprocess2

Analysis oolsfilterdesi$n

*O Spectr&mbbf)beammap

As yo& can probably tell, there are many thin$s thatyo& can tell the SAC pro$ram to do! Us&ally, it pays to

4play4 with SAC, e.ec&tin$ commands to process a fewseismo$rams to &nderstand what yo& want to do withthe data! /nce yo& have yo&r processin$ clarified, thecommands can be written into a file and &sed as ascript # the SAC macro # to process more data, or to )eepa record of e.actly what yo& did to the data!



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SAC Data Formats

SAC can read data in a variety of formats(

SAC ?inary *ormat read2CSS format readcss2S:: format readsdd2ASC"" formats readalpha2

Use the 4help4 facility in SAC or refer to the onlineman&al for detailed descriptions of these formats!

SAC Binary Format

his is the standard format for most seismic data! ASAC binary file consists of a header of ascii data that

defines the followin$ binary seismic data! he datamay consist of e+&ally incremented or irre$&larlyspaced time series data, or comple. spectral data!

SAC header(

he header portion of the file is very important to thedatafile since it contains information on samplin$

interval, station location, event location, $ro&ndmotion components, and all other parametersimportant in earth+&a)e data processin$! heseparameters are &sed by the vario&s SAC commands tomanip&late the data!

*or e.ample, here is a listin$ of the header variables

for NS waveform data recorded at LN from the


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recent Shelby Co! microearth+&a)e(

Commands/Results Explanation

SACE r LN!5>N!N!1!sacSACE lh

*"L5( LN!5>N!N!1!sac #######################

N-S < 18100 ? < 0!0000000eP00 5 < 1!8098999eP0;

"*-5 < "5 S56"5S*"L5

L55N < 6U5 :5LA < 9!9999998e#0

:5-"N <#@!1800000eP0; :5-A% < G!G00000eP0; :5-5N < 1!08;9;8eP00 /A6O56 < 0

O:A5 < MAN 1 012,;001

O"5 < 01(;;(D9!0 "-5 < ?5>"N "5 O"NS < N OSN < LN C-A < 0!0000000eP00

C-"NC < 9!0000000eP01 SLA < !D@000eP01 SL/ < #8!98000;eP01

5LA < !D;;8001eP01'aitin$

5L/ < #8!9998001eP01

:"S < 1!9;8@D90eP01 A < D!;D81GeP01 ?A < ;!;@01eP0; >CA6C < 1!@;9GDe#01 L/6/O < 6U5

6ead the data filelist the header &sin$ 4lh4

file name

n&mber of points in the filebe$in timeendin$ time

type of fileevenly sampled time seriestime incrementminim&m amplit&de in filema.im&m amplit&de in filemean amplit&de of file

ori$in mar)er timedate M&lian day2U referencereference time e+&ivalence$eneric name of instr&ment

station namecomponent aJim&th relative to northcomponent 4incidence an$le4 reletive tothe vertical

station latit&destation lon$it&de

event latit&de

event lon$it&destation distance from event in )mstation aJim&th from event in de$rees

event bac) aJim&th from station inde$rees$reat circle arc len$th in de$reesparameter enablin$ the file to be modified

SACE


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Some of the information in the SAC header is comp&teda&tomatically once the appropriate header variableshave been defined! *or e.ample, 4:"S4, 4A4, 4?A4,and 4>CA6C4 are comp&ted once the station and eventlocations are defined by their $eo$raphicalcoordinates!

/ther information is essential for partic&lar SACcommands to wor)! *or e.ample 4C-A4 and4C-"NC4 m&st be defined to &se the 4rotate4 commandto rotate horiJontal seismic data into tan$ential andradial motions or to comp&te a particle motion plot&sin$ 4ppm4!

/nce data are man&ip&lated by SAC, the res&lt can bewritten to dis), in SAC binary format, &sin$ the 4write44w42 command!

SACE r file1SACE hp b& co 1 n ; p 1SACE w file;



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SAC Plotting

A partic&lar stren$th of SAC is in vis&aliJin$ the dataafter it is processed! SAC can be pro$rammed to $ive awide variety of plot types! Us&ally, a $raphics windowis initialiJed to view the plot and commands can be$iven to interactively chan$e plot characteristics! /ncethe plot has been constr&cted in s&itable form, it can be

saved to a SAC $raphics file in 4s$f4 format! hese s$f files are then &s&ally converted to another format, li)e-ostScript, for o&tp&t to a printer or as inp&t to another$raphics pro$ram!

his plot was made &sin$ the followin$ commandswhile wor)in$ on a acintosh at home(


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Commands/Results Explanation

SACE r mlnt!J mlnt!r mlnt!tSACE .vport 0!1 0!GSACE +dp off SACE .lim D8 0

SACE title on 46otated :ataat LN4SACE .label on 4ime, sec4SACE ylabel on 4:i$italCo&nts4SACE bd te)@01@

SACE p1SACE bd s$f

SACE p1SACE ed s$f SACE s$ftops f001!s$f plot1 1ySACE +

6ead the three data fileschan$e the . direction aspect ratio for theplot

t&rn of the 4+&ic) and dirt plot4 option

only plot time series data between D8 and0 secondsma)e a title

ma)e a label for the . a.isma)e a label for the y a.is

t&rn on the te)@01@ device to plot to te)window on my mac at homeplot all of this st&ff &sin$ 4plot14, view anddecide to save to a file

be$indevice s$f to save to a s$f file&se p1 a$ain, all other commands havebeen saved by SAC

enddevice s$f to finish the s$f plot file&se the s$ftops conversion &tility toconvert the s$f file to -ostScript+&it

At this point " ftpd the plot file to the ac and &sedAdobe "ll&strator to convert the -ostScript plot into a$if file for this webpa$e! Us&ally, " combine a n&mberof SAC plots with Adobe "ll&strator to prod&ce a fi$&re!

Common plottin$ commands incl&de(plot p2 # plot a sin$le seismo$ramplot1 p12 # plot almost any n&mber of seismo$ramsplotp) pp)2 # interactive windowin$ and phasepic)in$ ro&tineppm # plot particle motion for two components of motion &s&ally two horiJontal components2

plotsp # plot the amplit&de and phase spectra!



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Blackboard Variables

SAC also has the internal f&nctionality of a calc&lator!he 4?lac)board4 is simply a feat&re that saves &serdefined variables! hese variables can be manip&latedand &sed in calc&lations! 6es&lts can be fed into SACcommands for f&rther data processin$! h&s, SAC hasb&ilt into it a simple pro$rammin$ lan$&a$e!

he synta. for manip&latin$ blac)board variables isrelatively simple b&t sometimes obsc&re! 6efer to theSAC man&al for details!

ariables can be defined, eval&ated, and p&t intosimple e+&ations! here are also "*, 5LS5"*, 5LS5statements in addition to :/ loops! Sometimes it is a

real tradeoff whether to write a fancy SAC macro to&tiliJe blac)board variables or K&st &se yo&r favoritepro$rammin$ lan$&a$e to do the same thin$!

5.amples are $iven in the acros section of thesewebpa$es!



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acros

A SAC macro is a script of SAC commands! SAC macroscan ta)e several forms dependin$ on how yo& want toimplement them! hese incl&de(

A simple macro file containin$ SAC commandswitho&t )eywords or dependent ar$&mentsA macro with dependent ar$&ments

A macro with )eywords

5.ample 1 # A simple macro based on the plottin$e.ample

macro name = mlntplot How it is used

r mlnt!J mlnt!r mlnt!t.vport 0!1 0!G+dp off

.lim D8 0title on 46otated :ata at LN4

.label on 4ime, sec4ylabel on 4:i$ital Co&nts4

bd s$f p1ed s$f s$ftops f001!s$f plot1 1 y

SACE macro mlntplot

5.ample ; # he same macro driven by dependentar$&ments


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macro name = mlntplot2 How it is used

r =1 =; =.vport 0!1 0!G+dp off .lim D8 0title on 46otated :ata atLN4

.label on 4ime, sec4ylabel on 4:i$ital Co&nts4

bd s$f p1ed s$f s$ftops f001!s$f plot1 1 y

SACE macro mlntplot; mlnt!J mlnt!r

mlnt!t

5.ample # he same macro driven by )eywords

macro name =

mlntplot3How it is used

=)eys files val&es

r =files

.vport 0!1 0!G+dp off .lim =val&estitle on 46otated :ata at

LN4.label on 4ime, sec4ylabel on 4:i$ital Co&nts4

bd s$f p1

ed s$f s$ftops f001!s$f plot1 1 y

SACE macro mlntplot files mlnt!J mlnt!rmlnt!t val&es D8 0

acros can also call other macros! his is very &sef&lin applyin$ a $eneric operation to many specific datafiles!

Another &sef&l tric), partic&larly when &sin$ SAC with


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CShells, is to &se the UN"% directed inp&t! *or e.ample,&sin$ the first macro above, we co&ld prod&ce the plotby typin$ the followin$ at the UN"% system prompt(

syspromptE sac;000 Q mlntplot E sac!o&tp&t

4sac!o&tp&t4 is a file that catches all the sac i3o thatwo&ld normally be seen on the screen!

acro e.amples from the SAC files of C!A! Lan$ston #4he tr&th is o&t whereR42

mom7correlate # find the best scale factor betweentwo time series in the least#s+&ares sensedatasynplot!macro # plot data and syntheticseismo$rams to$ether

red&ce!macro # read in a file, red&ce the traveltimeand scale



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CS!ell Scripts

he UN"% CShell enables SAC macros to be b&ilt withina CShell script and then r&n! his is partic&larly &sef&lwhen r&nnin$ synthetic seismo$ram codes that o&tp&ttime series in SAC binary format! hese synthetic timeseries can then be processed with SAC with the samedata processin$ performed on real data!

Bere are fo&r CShell Scripts that incorporate SAC inthem to varyin$ de$rees

)intcalc; # prod&ce synthetic seismo$rams from awaven&mber inte$ration pro$ram!

data7model7plot # ma)e the SAC macros to prod&cedata3synthetic comparisons!

pic)set&p;, phasepic); # &se pp) interactively topic) amplit&de and times from seismo$rams! Savethe pic)s in file for more processin$!



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"se in Fortran Programs

ime series data can be $enerated in yo&r own fortranand C 2 pro$rams and o&tp&t in SAC binary format!any of my pro$rams &se this capability since it is&sef&l to compare data and synthetic seismo$rams inthe same format! "t also &sef&l to read SAC binary filesto perform more specialiJed f&nctions that SAC does

not incl&de!his is accomplished by called the followin$ "/ro&tines available in the SAC library, 4sac!a4!

rsac1 # reads an evenly spaced data file!rsac; # reads an &nevenly spaced data file!wsac1 # writes an evenly spaced data file!

wsac; # writes an &nevenly spaced data file!

"n addition to these ro&tines, there are a n&mber of s&bro&tines that access or define each SAC headervariable! See the SAC man&al for details!

An Example

Bere is an f pro$ram that constr&cts a $a&ssian timef&nction an o&tp&ts the res&lt in SAC binary format!

Source Code Explanation

c ###### $a&ss!f pro$ram to create $a&ssian timef&nction CBA6AC5690 ONA5

CBA6AC56 ANS


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dimension A66A819;2

CBA6AC5680 -ASNA5 Create the far field time f&nction#################### '6"5,1002

100 */6A"N-U time width and time shiftof $a&ssian p&lse(2 65A:,2 twidth,tshift

alpha>2C A66A"2>210 C/N"NU5C########## N/' C65A5 A B5A:56 "N SAC

*/6A!#####################C

C # Set all header fields to their defa&lt val&es!C CALL N5'B:6 CC # US56 AC"/N( Shown below are incomplete

statements &sedC to define each of the SAC header fields!C Usin$ yo&r own variables, complete thestatements

C which define the SAC header fields thatyo&C want to be in the file! :elete the

remainin$ lines!CC # he definitions for each of these variables canbe fo&nd in the

C appendi. to the SAC Command 6eferencean&al!

C

calc&late the $a&ssianf&nction

Set &p a new SACheader


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C # *ields which be$in with an 4L4 are lo$ical

fields and m&stC be either !6U5! or !*ALS5!C # *ields which be$in with an 4N4 are inte$erfields!

C # *ields which be$in with an 4"4 are alsointe$ers, b&t can onlyC be set to a limited n&mber of val&es, each

correspondin$C to a specific condition! See the abovementioned appendi.!C # *ields which be$in with a 4O4 are charactervariables of

C len$th 8 &nless otherwise noted!C # All other fields are real!CC # he followin$ fields are re+&ired(C N-S


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'6"51,;002 ONA5

;00 */6A1%,SAC *"L5 ,A;, BAS ?55N'6"5N / :"SO299 C/N"NU5 S/-

5N:

Bere is the ma)e file &sed to compile this pro$ram(

**LA>S < #$

?"N < 3yo&rdirectory3bin

L"? < =SAC:"623lib$a&ss( $a&ss!f f =**LA>S2 #o =?"N23$a&ss $a&ss!f =L"?23sac!a

Important Note:

At this time 30D3012 C56" does not have a $enerally

available copy of the SAC library, 4sac!a4 or 4sacio!a4,that can be &sed in compilin$ fortran or C pro$rams onSUN Solaris systems! A copy is available at 3teteme)o3local3sac3lib3sac!a if yo& need to compile pro$ramswith SAC "3/ ro&tines!


Documents

SAC Tutorial