Strong Motion File Formats

Accelerogram Data Filenames and Formats

File Names


The file extensions for accelerograms are V1A (uncorrected) and V2A (corrected).

The file name can take three forms:

1 A, E, S - MO1 or MO2, D - DCA, G - GSR, I - IDS, K - MO2, O - EARSS (derived from velocity readings), Q - QDR

Data fields in the V1A and V2A files are in a block format dating from the days when Fortran was the programming language of choice. Programs for converting them to a single-column format suitable for spreadsheets are provided in file csvconversionprograms.zip.

File Formats


Each accelerogram data file contains heading data and accelerations for three orthogonal component directions. Corrected accelerograms also contain velocity and displacement signals calculated from the digitised acceleration record.

Horizontal components normally correspond to the longitudinal and transverse accelerometer axes, although for some cases other directions may be selected.

For each of the three components, the file structure is as follows:

A. Alphanumeric heading.

16 lines, maximum of 80 characters/line

B. 40 integer heading values.

``` 4 lines, 10 integers/line (Fortran input format: 10I8)

 1   event origin (UTC) .. year,
 2   .. month,
 3   .. day,
 4   .. hour,
 5   .. minute, and
 6   .. seconds x 10
 7   NZ seism obs log number (obsolete)
 8   aftershock number (obsolete)
 9   buffer start time (UTC) .. year,
10   .. month,

11   epicentral latitude S, .. degrees,
12   .. minutes, and
13   .. seconds
14   epicentral longitude E, .. degrees,
15   .. minutes, and
16   .. seconds
17   hypocentral depth (km)
18   centroid depth (km)
19   buffer start time (UTC) .. day,
20   .. hour,

21   site latitude S, .. degrees,
22   .. minutes, and
23   .. seconds
24   site longitude E, .. degrees,
25   .. minutes, and
26   .. seconds
27   longitudinal axis bearing (degrees E of N)
28   component direction (degrees E of N)
29   site-epicentral bearing (degrees E of N)
30   epicentral distance (km)

31   number of .. digitised samples,
32   .. prepended samples,
33   .. appended samples,
34   .. acceleration samples,
35   .. velocity samples, and
36   .. displacement samples
37   unused
38   unused
39   buffer start time (UTC) .. minute,
40   .. seconds x 1000 

```

C. 60 floating-point heading values.

``` 6 lines, 10 real numbers/line (Fortran input format: 10F8.0)

 1   instrument frequency (hz)
 2   ratio of critical damping
 3   film speed (mm/s) (MO film recorder)
 4   scale factor to mm on film (MO film recorder)
 5   inverse sensitivity (g/mm) (MO accelerometer)
 6   deviation angle 1 (radians) (MO accelerometer)
 7   deviation angle 2 (radians) (MO accelerometer)
 8   factor to give unit of mm/s/s
 9   timing lamp offset (never implemented)
10   time of common timemark (s) (never implemented)

11   site latitude, degrees S
12   site longitude, degrees E
13   epicentral latitude, degrees S
14   epicentral longitude, degrees E
15   local magnitude (Ml)
16   surface-wave magnitude (Ms)
17   moment magnitude (Mw)
18   body-wave magnitude (Mb)
19   unused
20   unused

21   digitised duration (s)
22   prepended duration (s)
23   appended duration (s)
24   record duration (s)
25   orig sampling interval (s)
26   sampling interval (s)
37   unused
28   unused
29   unused
30   local g (mm/s/s)

31   peak unfiltered acceleration (mm/s/s)
32   time of above (s)
33   rms unfiltered acceleration (mm/s/s)
34   unused
35   unused
36   peak filtered acceleration (mm/s/s)
37   time of above (s)
38   rms filtered acceleration (mm/s/s)
39   peak horizontal acceleration (mm/s/s)
40   dominant filtered accel freq (hz)

41   peak velocity (mm/s)
42   time of above (s)
43   rms velocity (mm/s)
44   peak horizontal velocity (mm/s)
45   dominant velocity frequency (hz)
46   peak displacement (mm)
47   time of above (s)
48   rms displacement (mm)
49   peak horizontal displacement (mm)
50   dominant displacement frequency (hz)

51   high-pass cutoff frequency (hz)
52   high-pass transition frequency (hz)
53   high-pass rolloff frequency (hz)
54   unused
55   unused
56   low-pass rolloff frequency (hz)
57   low-pass transition frequency (hz)
58   low-pass cutoff frequency (hz)
59   unused
60   unused

```

D. NPTA acceleration values, mm/s/s, 10 values per line

FORTRAN input format: 10F8.0

E. NPTV velocity values, mm/s, 10 values per line

FORTRAN input format: 10F8.0 (Not present in unfiltered accelerogram files.)

F. NPTD displacement values, mm, 10 values per line

FORTRAN input format: 10F8.0 (Not present in unfiltered accelerogram files.)

Response Spectra

File Name


The file extension for a response spectra file is V3A.

The file name can take three forms:

1 A, E, S - MO1 or MO2, D - DCA, G - GSR, I - IDS, K - MO2, O - EARSS (derived from velocity readings), Q - QDR

Data fields in the V3A file are in a block format dating from the days when Fortran was the programming language of choice. Programs for converting them to a single-column format suitable for spreadsheets are provided in file csvconversionprograms.zip.

File Format


Each file contains header data, and acceleration, velocity and displacement response spectra for three orthogonal component directions.

Horizontal components normally correspond to the longitudinal and transverse accelerometer axes, although for some cases other directions may be selected.

For each of the three components, the file structure is as follows:

A. Alphanumeric heading.

16 lines, maximum of 80 characters/line

B. 44 integer heading values.

``` 4 lines, 10 integers/line, then 1 line of 4 integers (Fortran input format 10I8)

 1   event origin (UTC) .. year,
 2   .. month,
 3   .. day,
 4   .. hour,
 5   .. minute, and
 6   .. seconds x 10
 7   NZ seism obs log number (obsolete)
 8   aftershock number (obsolete)
 9   buffer start time (UT) .. year,
10   .. month,

11   epicentral latitude S, .. degrees,
12   .. minutes, and
13   .. seconds
14   epicentral longitude E, .. degrees,
15   .. minutes, and
16   .. seconds
17   hypocentral depth (km)
18   centroid depth (km)
19   buffer start time (UTC) .. day,
20   .. hour,

21   site latitude S, .. degrees,
22   .. minutes, and
23   .. seconds
24   site longitude E, .. degrees,
25   .. minutes, and
26   .. seconds
27   longitudinal axis bearing (degrees E of N)
28   component direction (degrees E of N)
29   site-epicentral bearing (degrees E of N)
30   epicentral distance (km)

31   number of .. digitised samples,
32   .. prepended samples,
33   .. appended samples,
34   .. acceleration samples,
35   .. velocity samples, and
36   .. displacement samples
37   unused
38   unused
39   buffer start time (UTC) .. minute,
40   .. seconds x 1000

41   number of viscous damping ratios (NDR) (usually 5)
42   number of natural vibration periods (NVP) (usually 100)
43   algorithm key  (0 => Duhamel Integral)
44   total number of (interpolated) data samples used in response spectrum calculations

```

C. 60 floating-point heading values.

``` 6 lines, 10 real numbers/line (Fortran input format: 10F8.0)

 1   instrument frequency (hz)
 2   ratio of critical damping
 3   film speed (mm/s) (MO film recorder)
 4   scale factor to mm on film (MO film recorder)
 5   inverse sensitivity (g/mm) (MO accelerometer)
 6   deviation angle 1 (radians) (MO accelerometer)
 7   deviation angle 2 (radians) (MO accelerometer)
 8   factor to give unit of mm/s/s
 9   timing lamp offset (never implemented)
10   time of common timemark (s) (never implemented)

11   site latitude, degrees S
12   site longitude, degrees E
13   epicentral latitude, degrees S
14   epicentral longitude, degrees E
15   local magnitude (Ml)
16   surface-wave magnitude (Ms)
17   moment magnitude (Mw)
18   body-wave magnitude (Mb)
19   unused
20   unused

21   digitised duration (s)
22   prepended duration (s)
23   appended duration (s)
24   record duration (s)
25   orig sampling interval (s)
26   sampling interval (s)
37   unused
28   unused
29   unused
30   local g (mm/s/s)

31   peak unfiltered acceleration (mm/s/s)
32   time of above (s)
33   rms unfiltered acceleration (mm/s/s)
34   unused
35   unused
36   peak filtered acceleration (mm/s/s)
37   time of above (s)
38   rms filtered acceleration (mm/s/s)
39   peak horizontal acceleration (mm/s/s)
40   dominant filtered accel freq (hz)

41   peak velocity (mm/s)
42   time of above (s)
43   rms velocity (mm/s)
44   peak horizontal velocity (mm/s)
45   dominant velocity frequency (hz)
46   peak displacement (mm)
47   time of above (s)
48   rms displacement (mm)
49   peak horizontal displacement (mm)
50   dominant displacement frequency (hz)

51   high-pass cutoff frequency (hz)
52   high-pass transition frequency (hz)
53   high-pass rolloff frequency (hz)
54   unused
55   unused
56   low-pass rolloff frequency (hz)
57   low-pass transition frequency (hz)
58   low-pass cutoff frequency (hz)
59   unused
60   unused 

```

D. NDR (usually 5) viscous damping ratios.

Fortran input format: 10F8.0

E. NVP (usually 100) natural vibration periods, s

Fortran input format: 10F8.0

F. Spectral acceleration heading

G. NVP spectral acceleration values, mm/s/s

Repeat for each of the NDR viscous damping ratios.

H. Spectral velocity heading

I. NVP spectral velocity values, mm/s

Repeat for each of the NDR viscous damping ratios.

J. Spectral displacement heading

K. NVP spectral displacement values, mm

Repeat for each of the NDR viscous damping ratios.

L. Fourier Spectral heading

M. NVP Fourier spectral values, mm/s