The third and final broadband seismometer installation of this summer's cruise was completed on 17 September. It joins the two we installed at Barkley Slope and ODP 1027 to form a small networked array of seafloor seismometers. If all works out next year, we will install another broadband seismometer and four short-period seismometers at our Endeavour location.
Original plans called for this seismometer to be deployed together with a battery pack, differential pressure gauge and acoustic current meter, but these additional components were not deployed. This decision came after a ground fault in an identical set of instruments at ODP 1027 forced us to recover them. It's hoped we will be able to augment the seismometers with back-up batteries and additional instruments during a future installation cruise.
We had to make another quick adjustment during deployment. The ROPOS tool basket was rigged to hold the caisson, seismometer and 14 bags of glass beads. Then the tool basket was strapped beneath ROPOS and the two lifted by crane over the water. Only when the basket was lowered to the sea surface did we discover the weight distribution was uneven. When hit by a wave, the basket slopped to one side and three bags of glass beads fell from it into the sea. We had to abort the deployment, bring it back on deck and add three more improvised bead bags.
The new bags lacked the built-in spouts on our custom-made blue bead bags so ROPOS was sent down with a kitchen knife, with which to cut the bag open and spill the beads.
Except for the above variations, our deployment followed the now familiar script. We:
- set the deployment package down on the seafloor
- found the instrument platform and extended the seismometer connection hose
- plugged the connector into one side of a connection plate
- plugged the seismometer cable connector into the other side of the connection plate
- stowed the connection plate in a 'parking position' on the seafloor
- chose a spot for the seismometer
- set the caisson on the spot and jumped up and down on it with ROPOS to push it down into the sediment
- used the ROPOS zip pump to excavate the caisson
- poured glass beads into the base of the caisson
- put the seismometer into the caisson
- buried it and the caisson in glass beads
- tidied up
Everything went relatively smoothly except step 10 above. When ROPOS was ready to place the seismometer into the caisson, it suddenly slipped from the manipulator hand and fell a short distance from just above the caisson into it. We're crossing our fingers that the seismometer will survive that jolt. So far, we have not had a chance to power it up and test it, but we hope an opportunity will open up shortly.