Matlab Function socal_sed.m to generate bottom properties for the South
California Bight Region
This program generates sediment parameters for the South California Bight region which
was chosen as the test site in the last ESME workshop. The location lies between
latitudes 32 N and 34.5 N and 117 W and 120 W. The program is written in such a way
that given the location and the frequency of interest, the sediment properties are estimated
using all the available data. The sediment information available include core data,
sediment maps, sediment type information etc. For this location we were able to find
some historical data which is listed below.
1. Bathymetry: Bathymetry is directly interpolated from the Navy Database (DBDBV1).
2. Core data: Deep Sea Drilling Program core data. Sites include : 467, 468, 469 (Leg
63) and 1012,1013,1014,1015 and 1017 (Leg 167).
3. Sediment type information: Emery2 gives a description of the type of sediments in the
continental shelf.
4. SWellEx data: Musil et. al3 . and Bachman et. al.4 gives sediment information (type
of sediment and layer thickness) at the SWellEx-96 site.
5. Sediment and geoacoustic models:
 Bachman5: Used for predicting the properties in the Catalina Basin.
 Hamilton model6: Used for predicting the compressional and shear wave
speeds as well as attenuation as function of frequency for different sediment
types.
 Bowles7: Used for predicting attenuation as a function of frequency and shear
speeds for known sediment types .
6. Sediment layer thickness maps8: Used for predicting the sediment thickness.
The program uses these data to arrive at the sediment parameters at a given location.
The sediment compressional speed is estimated using the core data, sediment type
information and the Hamilton’s values for these sediment types. Sediment thickness
is estimated based on the core data and sediment thickness map. Shear speed, and
Compressional and shear attenuation are determined mainly using the sediment type
information and predictions by Hamilton and Stoll. The bottom properties are
specified for a simple two layer model.
Sediment
Basement
Compr. Speed, Shear Speed
Attenuation, Density
Compr. Speed, Shear Speed
Attenuation, Density
Some of the properties (compressional and shear speeds in the basement) are
assumed constant throughout the area. The output parameters are also written in a text
file sediment_par. They are written in the order as shown in the Appendix 1.
References
1) DBDB-V : Digital Bathymetric Database – Variable resolution, http://
128.160.23.42/dbdbv/database-doc.html.
2) Emery. K. O, “Continental shelf sediments of Southern California,” Bull. Geol. Soc.
Am. Vol. 63, (1962).
3) Musil, M, Chapman, N. R and Wilmut M. J, “Range dependent matched field
inversion of SWellEX-96 data using the downhill simplex algorithm,” J. Acoust. Soc.
Am. 106 (6), (1999).
4) Bachman R. T, Schey P. W, Booth N. O and Ryan F. J, “Geoacoustic databases for
matched field processing: Preliminary results in shallow water off San Diego,
California, J. Acoust. Soc. Am., 99(4), (1996).
5) Bachman R. T, “A Three-dimensional geoacoustic model for Catalina Basin,”
Version 1.0, NraD Technical Report 1669,
www.nosc.mil/sti/publications/pubs/tr/1669/
6) Hamilton E. L, “Geoacoustic modeling of the sea floor,” J. Acoust. Soc. Am. 68(5),
(1980).
7) Bowles F. A, “Observation on attenuation and shear-wave velocity in fine grained
marine sediments,” J. Acoust. Soc. Am. 101 (6), (1997)
8) Winterer E. L, “Sediment thickness map of the Northeast Pacific,” The geology of
North America, Vol. N, The eastern Pacific Ocean and Hawaii, The Geological
Society of America, 1989.
Appendix 1. Inputs to socal_sed.m are as follows:
1. location : location specifies the location where the sediment properties are desired.
It is specified as [latitude, longitude] using the latitude and longitude of the location.
Currently the program can only handle only one location at a time.
2. freq
: Frequency (Hz) at which the attenuation values are desired.
The outputs of this function are listed as follows:
The outputs of this function is written into a file sediment_par as a text file in the
following order.
1. Bathymetry at the location (m)
2. Compressional wave speed in the sediment layer (m/s).
3. Thickness of the sediment layer (m).
4. Compressional speed in the basement layer (m/s).
5. Compressional wave attenuation (db/m)
6. Shear wave speed in the sediment (m/s)
7. Shear wave speed in the basement (m/s)
8. Shear wave attenuation (db/m)
9. Density in the sediment layer (g/cc)
10. Density in the basement (g/cc)
Example: Let location=[33 –119] and freq=3000.
Then socal_sed(location,sed) will output
Sediment Properties:
At location (lat,long) 33 -119
bathymetry at the location (m)
1800
Sediment Compr. Speed (m/s)
1546.7587
Depth of sediment (m)
34.86197
Compr. speed - basement (m/s)
1750
Compr. wave attenuation (dB/m) 0.1897541
Shear speed - sediment (m/s)
206.8277
Shear speed - basement (m/s)
400
Shear wave attenuation (dB/m)
45.6
Density - sediment (g/cc)
1.65
Density - basement (g/cc)
1.8