IODP-MSP
drilling and logging contractor: ESO
Hole: M0029A
Expedition: 313
Location: New Jersey (NW
Atlantic)
Latitude: 39° 31.1605 N
Longitude: 73° 24.7925 W
Logging
date: July 11 - 16,
2009
Sea
floor depth (driller's): 53.41 m DRF
Sea floor
depth (logger's): 53.26 m WRF
Total
penetration: 754.55
m DSF
Total
core recovered:
454.31 m (74.55 % of cored section)
Oldest
sediment recovered: Early Miocene
Lithologies: Clays to gravels
|
Date |
Top
depth (m WSF)
|
Bottom depth (m WSF)
|
Spacing (m)
|
Open hole survey (m WSF)
|
Through
pipe survey (m WSF)
|
|
11-Jul-09 |
753.42 |
207.83 |
3.05 |
n/a |
0-753 |
|
14-Jul-09 |
226.12 |
12.76 |
3.05 |
n/a |
0-226 |
VSP survey data was acquired in two stages in
M0029A due to a lightning storm halting operations on the first run around 200
m from the top of the borehole. All data was acquired through pipe in this
hole. For M0029A it was necessary to apply F-K and bandpass
filters prior to picking seismic arrivals through the sediment for survey
“a”. An F-K
filter and AGC (automatic gain control) was applied prior to picking sediment
arrival times on survey “b”. The F-K filters were designed to
remove all upgoing waves and downgoing
waves traveling with velocities over ~3000 m/s. These filters were not saved in order to
preserve the information within the data for further research. Interference from seismic arrivals
through steel meant that despite processing, the only consistent first break
from survey “a” was a peak, while in survey “b”, where
this interference did not exist, the first break picked was a trough.
For M0029A the suspended hydrophone and its
known distance from the airgun source was used to determine the firing time of
the airgun, and from this the stacked data was shifted to reflect the airgun
firing at time zero. The peaks
observed on the hydrophone records were picked for this purpose. First breaks (peaks) were also picked
for the seafloor geophone and used to determine the traveltime
through the water column. The ROV
was dispatched for both surveys on this hole to assess the location of the
seafloor hydro/geophone. In both
cases there was estimated to be a maximum 5 m horizontal offset between the top
of the cable where it came onto the ship and the bottom of the cable where it
connects to the seafloor hydro/geophone.
The layout of the VSP survey can be seen at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/iodp-eso-313-vsp-layout.pdf, http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/M0029A/documents/313-M0029A_vsp-survey-layout1.pdf, and http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/M0029A/documents/313-M0029A_vsp-survey-layout2.pdf . Each VSP shot was recorded and stored digitally. The signal received by the geophone was digitized in a Geometrics geode and recorded using the Geometrics Seismodule Controller software. Each VSP shot was recorded on 7 channels (Table 1) to measure the vertical component on the downhole geophone, the vertical and two horizontal components on a seafloor geophone, a seafloor hydrophone (within the housing of the seafloor geophone), a suspended hydrophone, and the electrical signal caused by the movement of the airgun shuttle. Of the two airguns (20 and 40 cubic inches), only one was fired during each shot. The record lengths were 2.5 s long covering the time period from -0.5 to 2 seconds. The sampling rate
Data flow was monitored for quality in real
time and data quality was recorded on paper to be entered into an Excel
spreadsheet post survey, along with shot and receiver coordinates (datum
WGS84). Where available, borehole
tilt and azimuth measured by borehole logging is used to calculate horizontal
location of the downhole receiver. Where this information is not available, the borehole is assumed to be
vertical. The Excel quality and
coordinate measurements were entered into the VSP data files using MATLAB and
Processing involved removing poor quality
shots and stacking the remaining shots at a given depth to improve the signal
to noise. 3-D offset information
was calculated and entered. Where
possible, first break arrival times were picked for the downhole data, the
vertical seafloor geophone, the suspended hydrophone, and the airgun shuttle
signal. Based on a combination of
data from the vertical seafloor geophone, suspended hydrophone and airgun
shuttle signal, static correction were calculated and applied to account for
any time shift caused by the airgun firing past time zero. The wave form and arrival times of these
data were assessed for each survey to determine the best technique of
calculating static corrections.
The unstacked raw seismic data were organized into a SEG-Y revision 1 format file that included the necessary shot and receiver positions. A smaller corresponding file that contained the stacked data at each depth is 313-M0029A_vsp-stacked.segy. This file is available online and should be accessible by any program that is able to read the SEG-Y format data.
Additional information about the drilling and logging operations can be found in the Operations section of the Site Chapter in IODP Proceedings of Expedition 313. For further questions about the data, please contact:
Jennifer
Inwood
University
of Leicester
Phone:
011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail:
IODP-UK
Johanna Lofi
University
of Montpellier 2
Phone: 033-
467-149- 309
Fax: 033- 467-
143- 244
E-mail:
IODP-UK
For any web
site-related problem please contact:
E-mail:
Database Manager