Publication Date:
2019-02-01
Description:
To investigate the seismic velocity structure of the shallow
sediments in the Bohai Sea of China, we conducted a shearwave
velocity inversion of the surface-wave dispersion data
from a survey of 12 ocean-bottom seismometers (OBSs)
and 377 shots of a 9000 in3 air gun. With OBS station spacing
of approximately 5 km and air-gun shot spacing of approximately
190 m, high-quality Scholte-wave data were recorded
by the OBSs within 0.4–5 km offset. We retrieved the Scholtewave
phase-velocity dispersion for the fundamental mode and
first overtone in the frequency band of 0.9–3.0 Hz with the
phase-shift method and inverted for the shear-wave velocity
structure of the shallow sediments with a damped iterative
least-squares algorithm. Pseudo-2D shear-wave velocity profiles
with a depth of approximately 400 m revealed coherent
features of relatively weak lateral velocity variation. We also
estimated the uncertainty in shear-wave velocity structure
based on the pseudo-2D profiles from six trial inversions with
different initial models, which suggested a velocity uncertainty
less than 30 m∕s for most parts of the 2D profiles. The layered
structure with little lateral variation may be attributable to the
continuous sedimentary environment in the Cenozoic sedimentary
basin of the Bohai Bay basin. The shear-wave velocity
of 200–300 m∕s in the top 100 m of the Bohai seafloor may
provide important information for offshore site response studies
in earthquake engineering. Furthermore, the very low
shear-wave velocity structure (150–600 m∕s) down to
400 m depth could produce a significant traveltime delay of
approximately 1 s in the shear-wave arrivals, which needs
to be considered to avoid serious bias in shear-wave traveltime
tomographic models.
Type:
Article
,
PeerReviewed
Format:
text
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