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Header Variables


This table lists the header variables, their types, and descriptions. They are grouped by category: required fields, time fields, phase picks, instrument parameters, station parameters, event parameters, misc. The header types are defined in the second table.


Name Type Description
NPTS N Number of points per data component. [required]
NVHDR N

Header version number. Current value is the integer 6. Older version data (NVHDR < 6) are automatically updated when read into sac. [required]

B F Beginning value of the independent variable. [required]
E F Ending value of the independent variable. [required]
IFTYPE I Type of file [required]:
= ITIME {Time series file}
= IRLIM {Spectral file---real and imaginary}
= IAMPH {Spectral file---amplitude and phase}
= IXY {General x versus y data}
= IXYZ {General XYZ (3-D) file}
LEVEN L TRUE if data is evenly spaced. [required]
DELTA F Increment between evenly spaced samples (nominal value). [required]
ODELTA F Observed increment if different from nominal value.
IDEP I Type of dependent variable:
= IUNKN (Unknown)
= IDISP (Displacement in nm)
= IVEL (Velocity in nm/sec)
= IVOLTS (Velocity in volts)
= IACC (Acceleration in nm/sec/sec)
SCALE F Multiplying scale factor for dependent variable [not currently used]
DEPMIN F Minimum value of dependent variable.
DEPMAX F Maximum value of dependent variable.
DEPMEN F Mean value of dependent variable.
NZYEAR N GMT year corresponding to reference (zero) time in file.
NZJDAY N GMT julian day.
NZHOUR N GMT hour.
NZMIN N GMT minute.
NZSEC N GMT second.
NZMSEC N GMT millisecond.
NZDTTM N GMT date-time array. Six element array equivalenced to NZYEAR, NZJDAY, NZHOUR, NZMIN, NZSEC, and NZMSEC.
KZDATE A Alphanumeric form of GMT reference date. Derived from NZYEAR and NZJDAY.
KZTIME A Alphanumeric form of GMT reference time. Derived from NZHOUR, NZMIN, NZSEC, and NZMSEC.
IZTYPE I Reference time equivalence:
= IUNKN (Unknown)
= IB (Begin time)
= IDAY (Midnight of refernece GMT day)
= IO (Event origin time)
= IA (First arrival time)
= ITn (User defined time pick n, n=0,9)
O F Event origin time (seconds relative to reference time.)
KO A Event origin time identification.

Phase Picks
A F First arrival time (seconds relative to reference time.)
KA K First arrival time identification.
F F Fini or end of event time (seconds relative to reference time.)
KF A Fini identification.
Tn F User defined time picks or markers, {\ai n}=0,9 (seconds relative to reference time).
KT{\ai n} K A User defined time pick identifications, {\ai n}=0,9.

Instrument Fields
KINST K Generic name of recording instrument.
IINST I Type of recording instrument. [not currently used]
RESPn F Instrument response parameters, n=0,9. [not currently used]

Station Fields
KNETWK K Name of seismic network.
KSTNM K Station name.
ISTREG I Station geographic region. [not currently used]
STLA F Station latitude (degrees, north positive)
STLO F Station longitude (degrees, east positive).
STEL F Station elevation (meters). [not currently used]
STDP F Station depth below surface (meters). [not currently used]
CMPAZ F Component azimuth (degrees clockwise from north).
CMPINC F Component incident angle (degrees from vertical).
KCMPNM K Component name.
KSTCMP A Station component. Derived from KSTNM, CMPAZ, and CMPINC.
LPSPOL L TRUE if station components have a positive polarity (left-hand rule).

Event Fields
KEVNM K Event name.
IEVREG I Event geographic region. [not currently used]
EVLA F Event latitude (degrees, north positive).
EVLO F Event longitude (degrees, east positive).
EVEL F Event elevation (meters). [not currently used]
EVDP F Event depth below surface (meters). [not currently used]
MAG F Event magnitude.
IMAGTYP I Magnitude type:
= IMB (Bodywave Magnitude)
= IMS (Surfacewave Magnitude)
= IML (Local Magnitude)
= IMW (Moment Magnitude)
= IMD (Duration Magnitude)
= IMX (User Defined Magnitude)
IMAGSRC I Source of magnitude information:
= INEIC (National Earthquake Information Center)
= IPDE (Preliminary Determination of Epicenter)
= IISC (Internation Seismological Centre)
= IREB (Reviewed Event Bulletin)
= IUSGS (US Geological Survey)
= IBRK (UC Berkeley)
= ICALTECH (California Institute of Technology)
= ILLNL (Lawrence Livermore National Laboratory)
= IEVLOC (Event Location (computer program) )
= IJSOP (Joint Seismic Observation Program)
= IUSER (The individual using SAC2000)
= IUNKNOWN (unknown)
IEVTYP I Type of event:
= IUNKN (Unknown)
= INUCL (Nuclear event)
= IPREN (Nuclear pre-shot event)
= IPOSTN (Nuclear post-shot event)
= IQUAKE (Earthquake)
= IPREQ (Foreshock)
= IPOSTQ (Aftershock)
= ICHEM (Chemical explosion)
= IQB (Quarry or mine blast confirmed by quarry)
= IQB1 (Quarry/mine blast with designed shot info-ripple fired)
= IQB2 (Quarry/mine blast with observed shot info-ripple fired)
= IQBX (Quarry or mine blast - single shot)
= IQMT (Quarry/mining-induced events: tremors and rockbursts)
= IEQ (Earthquake)
= IEQ1 (Earthquakes in a swarm or aftershock sequence)
= IEQ2 (Felt earthquake)
= IME (Marine explosion)
= IEX (Other explosion)
= INU (Nuclear explosion)
= INC (Nuclear cavity collapse)
= IO_ (Other source of known origin)
= IL (Local event of unknown origin)
= IR (Regional event of unknown origin)
= IT (Teleseismic event of unknown origin)
= IU (Undetermined or conflicting information)
= IOTHER (Other)
NEVID N Event ID (CSS 3.0)
NORID N Origin ID (CSS 3.0)
NWFID N Waveform ID (CSS 3.0)
KHOLE k Hole identification if nuclear event.
DIST F Station to event distance (km).
AZ F Event to station azimuth (degrees).
BAZ F Station to event azimuth (degrees).
GCARC F Station to event great circle arc length (degrees).

Miscellaneous Fields
LCALDA L TRUE if DIST, AZ, BAZ, and GCARC are to be calculated from station and event coordinates.
IQUAL I Quality of data [not currently used]:
= IGOOD (Good data)
= IGLCH (Glitches)
= IDROP (Dropouts)
= ILOWSN (Low signal to noise ratio)
= IOTHER (Other)
ISYNTH I Synthetic data flag [not currently used]:
= IRLDTA (Real data)
= ????? (Flags for various synthetic seismogram codes)
KDATRD K Date data was read onto computer.
USER{\ai n} F User defined variable storage area, {\ai n}=0,9.
KUSER{\ai n} K User defined variable storage area, {\ai n}=0,2.
LOVROK L TRUE if it is okay to overwrite this file on disk.
NXSIZE N Spectral Length (Spectral files only)
NYSIZE N Spectral Width (Spectral files only)
XMINIMUM F Minimum value of X (Spectral files only)
XMAXIMUM F Maximum value of X (Spectral files only)
YMINIMUM F Minimum value of Y (Spectral files only)
YMAXIMUM F Maximum value of Y (Spectral files only)


Header Data Types


This table lists the header types and their definitions. The third column lists the special value used to signify that a particular header variable is undefined in a particular file.

Type Definition Undefined Description
F Floating -12345.0 Single precision.
N Integer -12345 Name begins with an ``N''.
I Enumerated -12345 Name begins with an ``I''. Has a limited set of integer values. Each value is given a specific name. Each value represents a specific condition. Subroutines use the equivalent alphanumeric name.
L Logical FALSE Name begins with an ``L''. Value is either TRUE or FALSE.
K Alphanumeric ``-12345'' Name begins with a ``K''. Either 8 or 16 characters long.
A Auxilary Not really in the header. Derived from other header fields.


Enumerated Header

Enumerated Header Field Values

The enumerated header field values are stored in the header as integers. Their names and values are given in the table below.

Name Value Name Value
itime 01 irlim 02
iamph 03 ixy 04
iunkn 05 idisp 06
ivel 07 iacc 08
ib 09 iday 10
io 11 ia 12
it0 13 it1 14
it2 15 it3 16
it4 17 it5 18
it6 19 it7 20
it8 21 it9 22
iradnv 23 itannv 24
iradev 25 itanev 26
inorth 27 ieast 28
ihorza 29 idown 30
iup 31 illlbb 32
iwwsn1 33 iwwsn2 34
ihglp 35 isro 36
inucl 37 ipren 38
ipostn 39 iquake 40
ipreq 41 ipostq 42
ichem 43 iother 44
igood 45 iglch 46
idrop 47 ilowsn 48
irldta 49 ivolts 50
ixyz 51 imb 52
ims 53 iml 54
imw 55 imd 56
imx 57 ineic 58
ipde 59 iisc 60
ireb 61 iusgs 62
ibrk 63 icaltech 64
illnl 65 ievloc 66
ijsop 67 iuser 68
iunknown 69 iqb 70
iqb1 71 iqb2 72
iqbx 73 iqmt 74
ieq 75 ieq1 76
ieq2 77 ime 78
iex 79 inu 80
inc 81 io_ 82
il 83 ir 84
it 85 iu 86


If you have technical questions about this page, contact:
peterg@llnl.gov -- Peter Goldstein


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peterg@llnl.gov -- Peter Goldstein

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