Derivation of Acoustic and Physical Properties from High-Resolution Seismic Reflection Data


Pinson, Luke John William (2009) Derivation of Acoustic and Physical Properties from High-Resolution Seismic Reflection Data. University of Southampton, School of Ocean and Earth Science, Doctoral Thesis , 269pp.

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Description/Abstract

Acoustic measurements in sediments can remotely provide information about their physical
properties. This thesis develops methods using high-resolution marine seismic reflection
data to generate accurate, precise, and repeatable estimations of the in situ seismic
quality factor (Q) and velocity, within the uppermost 100 m of unconsolidated marine
sediments. This was achieved using a single channel Chirp sonar (1.5-13.0 kHz) and a
Boomer sonar (0.2-4.0 kHz) towed with a multi-channel streamer that provides offsets
up to 80 m. These methods were applied in the Solent (Southampton, U.K.) to test empirical
models that predict sediment physical properties from these acoustic properties,
and in lake Windermere (Cumbria, U.K.) where the new quantitative information helps
distinguish between, and identify, previously unknown glacial and lacustrine deposits.
The spectral-ratio technique was used to reliably estimate Q from seismic reflection data,
without assumptions on how attenuation varies with frequency. Based on empirical
observations, it is demonstrated here that Q can characterise the dominant fabric of the
sediment that is supporting wave-propagation - whether it is clay dominated and has a
Q over 75, or coarse-grain dominated and has a Q less than 75. The Chirp source is
the most effective single sonar to estimate Q, however, improved results were obtained
by combining Boomer and Chirp data to examine attenuation over four octaves (0.5-8.0
kHz). Frequency-independent Q (with 95% condence intervals) of 135 (+12; -10) was
obtained for silty-clay, 63 (+10; -7) for ne-sand, and 33 (+6; -4) for gyttja.
Boomer multi-channel seismic data were acquired in the Solent over a 30 m core and
a sampled sand deposit, and in lake Windermere where over 150 km of survey lines
were required to cover most of the lake. An optimal processing methodology was developed
for high-resolution seismic data using iterative Kirchhoff prestack depth migration,
Burg deconvolution and F-K ltering; velocities were derived using migration velocity
analysis. Additionally, a method was developed to obtain the streamer depth profile
from the surface ghost. The Solent study proved that measurements of velocity and
Q together can identify unconsolidated coarse-grain sediment and distinguish between
gravel, sand and silt, and differentiate between unconsolidated and over-consolidated
clay sediments. In Windermere, five seismic stratigraphic sequences were identified from
the depth migrated data: I - till (c. 2000-3000 m/s); II - glacio-uvial (c. 1750 m/s);
III - glacio-lacustrine/lacustrine (1500 m/s + 6 s-1); IV - disturbed/slumped (c. 1500
m/s); V - lacustrine (c. 1490 m/s). A new deglacial history for lake Windermere is proposed,
which has important implications on the overall character of the ice-sheet retreat
in Britain after the last glacial maximum.

Item Type: Thesis (Doctoral)
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Divisions: University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
ePrint ID: 168959
Date Deposited: 07 Dec 2010 16:43
Last Modified: 27 Mar 2014 19:19
URI: http://eprints.soton.ac.uk/id/eprint/168959

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