limited the time for satellite use by civilians. The window of opportunity for
having good satellite fixes was only about 6 h a day and it was most important to
calibrate the transponder network set on the seafloor in order for the submersible to
navigate. On the morning of the first dive, the transponders were in place, but the
person responsible for the submersible’s navigation did not have good fixes and he
had to rely on a classical system of navigation, which was less accurate, with a
distance discrepancy of up to 1 km on the sea floor.
In addition to the failure of the GPS, we were confronted with another technical
difficulty. The depth recorder, which was a single channel echo sounder system
called ‘‘EDO’’ that was supposed to record the depths, failed to work. This was an
old-fashioned type of depth recorder that I remembered using during my first
cruises back in 1964. This meant that for Dive 1 of the Garrett mission, we had to
give up the possibility of having our depth recorded during our approach to the
diving target. I asked the electronic engineer from IFREMER what was wrong
with the sounder and if he could fix it before making a final decision to launch the
submersible. His answer was that there was a piece that needed to be replaced,
however he did not have any spare-parts on board for such old equipment.
As we approached the diving site, I knew we badly needed to have precise
information about the depths, in order to follow the contour lines on a bathymetric
chart. I wanted to start the dive in the deepest area of the transform valley in order
to have the best chance of finding the exposed upper mantle peridotite. This was a
critical time, and I was eager to find a solution to help us choose the right spot.
The officer on the bridge was also desperate; he was trying very hard to give us
a precise estimate of the ship’s position. Time was running out, and the submersible group, the crew and the navigation team were all waiting for a decision.
Finally we managed to speculate on our location by positioning the ship using the
last depth recorded, which had been given 1 h earlier by our defective sounder, and
the last satellite fix. We just had to hope that in the meantime our vessel had not
drifted too far from this point. We did not want to lose any more diving time by
waiting for the calibration of the transponder network, so we decided to just go
ahead and dive. We were going to land in one of the deepest areas of the transform
fault’s active tectonic zone.
The Transform Fault’s Active Tectonic Zone
What characterizes a transform fault is the tectonic stress field that breaks the
lithosphere and dismantles the geological formations. The strike-slip motion of the
tectonic plates generates numerous fractures and fissures, while crushing the rocks
into fragments and causing numerous landslides.
Where the dislocation and fragmentation of the geological formation is most
intense is called the Active Tectonic Zone (ATZ). The ATZ is characterized by
steep fault scarps ([10 m relief) and by fractures within semi-consolidated pelagic
sediment. An abundance of fresh gullies and the presence of striations and fresh,
Garrett Transform Fault
261
having good satellite fixes was only about 6 h a day and it was most important to
calibrate the transponder network set on the seafloor in order for the submersible to
navigate. On the morning of the first dive, the transponders were in place, but the
person responsible for the submersible’s navigation did not have good fixes and he
had to rely on a classical system of navigation, which was less accurate, with a
distance discrepancy of up to 1 km on the sea floor.
In addition to the failure of the GPS, we were confronted with another technical
difficulty. The depth recorder, which was a single channel echo sounder system
called ‘‘EDO’’ that was supposed to record the depths, failed to work. This was an
old-fashioned type of depth recorder that I remembered using during my first
cruises back in 1964. This meant that for Dive 1 of the Garrett mission, we had to
give up the possibility of having our depth recorded during our approach to the
diving target. I asked the electronic engineer from IFREMER what was wrong
with the sounder and if he could fix it before making a final decision to launch the
submersible. His answer was that there was a piece that needed to be replaced,
however he did not have any spare-parts on board for such old equipment.
As we approached the diving site, I knew we badly needed to have precise
information about the depths, in order to follow the contour lines on a bathymetric
chart. I wanted to start the dive in the deepest area of the transform valley in order
to have the best chance of finding the exposed upper mantle peridotite. This was a
critical time, and I was eager to find a solution to help us choose the right spot.
The officer on the bridge was also desperate; he was trying very hard to give us
a precise estimate of the ship’s position. Time was running out, and the submersible group, the crew and the navigation team were all waiting for a decision.
Finally we managed to speculate on our location by positioning the ship using the
last depth recorded, which had been given 1 h earlier by our defective sounder, and
the last satellite fix. We just had to hope that in the meantime our vessel had not
drifted too far from this point. We did not want to lose any more diving time by
waiting for the calibration of the transponder network, so we decided to just go
ahead and dive. We were going to land in one of the deepest areas of the transform
fault’s active tectonic zone.
The Transform Fault’s Active Tectonic Zone
What characterizes a transform fault is the tectonic stress field that breaks the
lithosphere and dismantles the geological formations. The strike-slip motion of the
tectonic plates generates numerous fractures and fissures, while crushing the rocks
into fragments and causing numerous landslides.
Where the dislocation and fragmentation of the geological formation is most
intense is called the Active Tectonic Zone (ATZ). The ATZ is characterized by
steep fault scarps ([10 m relief) and by fractures within semi-consolidated pelagic
sediment. An abundance of fresh gullies and the presence of striations and fresh,
Garrett Transform Fault
261