Instruments and methodology:
The primary instrument is a Guralp Seismometer package which contains the sensors on leveling gymbals, a small cpu that drives a self-leveling program, and a rechargeable battery. The aluminum housing includes handles for ROV manipulation and the male side of an 8-pin Nautilus connector. The selected site is on Smooth Ridge, to the west of the Clam Flats cold seep area. This site was prepared by sinking a PVC caisson and removing the sediment from inside the caisson; this was accomplished ten days prior to the deployment of the seismometer package. Following site preparation, a magnetometer package provided by UBO and CNRS was deployed in the vicinity of the seismometer site. Three days after deployment of the magnetometer, the seismometer package was subsequently lowered to the seafloor by elevator with the sensors and gymbals in a locked position.
After deployment, the ROV Ventana connected the Guralp seismometer toan L-Cheapo datalogger; the datalogger was connected, in turn, to the ROV and to the ship computer, which sent commands to unlock and level the sensors. While the ROV was connected, we observed the data as they were recorded in the flash memory onboard the L-Cheapo to confirm proper operation of the system. The ROV disconnected at that point and left the instrument to collect data. The digitized data are being acquired via an RS232 connection onto a 4.2 GB disk. After allowing a week for additional settling of the sensor package, the ROV returned to reconnect via a second RS232 connection to retrieve samples of noise data and one teleseismic event which occurred on the second day of recording. At the same time, the ROV connected a second Benthos sphere with adequate lithium batteries to power the instrument for a total deployment period of up to 100 days. A second visit to the site is planned one month later (July 22) to download additional data samples and cover the seismometer with a conical cover (already on the ocean floor), to shield it from noise due to ocean currents.
At the end of the 3 month deployment period, the software will automatically instruct the instrument to shut down and to lock the gymbals. The ROV will attempt to reconnect and confirm that the instrument is prepared for recovery. The battery sphere and the logger will be disconnected and all the components will be recovered in the same manner as they were deployed. The schedule for development, testing, and deployment of this system is critical and has been agreed upon by all participants. The scheduling for the other components is less critical and can be adjusted to take advantage of unused contingency days.
Collaborators from UBO and CNRS are also providing a magnetometer to monitor the the covariation of the magnetic field and seismic events. The seismometer and magnetometer are the basis of an envisioned submarine geomagnetic-seismic observatory. Some studies have suggested that there are electromagnetic signals associated with seismic activities due perhaps to the movement of water through the basement rocks; however, contemporaneous measurements have been rare. To address the question of tidal effects, a CTD/pressure gauge has been deployed. This instrument is on loan from Curt Collins. It has an onboard datalogger but we have constructed a support frame and anchor for the system. An S4 current meter is mounted on the frame with the CTD/pressure gauge to measure local tidal current directions and velocities.
An S4 current meter will be deployed on a short mooring to measure local tidal current directions and velocities. The tidal effects are anticipated to be the most profound marine noise present in the seismometer record. The CTD/pressure gauge, magnetometer and current meter are all stand-alone instruments and were placed in position by the ROV. However, we plan to recover these instruments using an elevator. In addition, the magnetometer required the ROV to extend the arms for proper deployment.
The broadband seismometer and the magnetometer can record both local and global events. There are three other instruments that will focus more on local events. These instruments will provide data of direct value to the primary goals of Project 8 but may be considered secondary to the MOISE experiment. These instruments include standard OBS and a single channel hydrophone. These instruments are self-contained and can be deployed from the R/V John Martin.
We plan to deploy these instruments to provide as much contemporaneous data with MOISE as possible. Another seismometer may be available from Spahr Webb at SIO. This (the STS-2) is a 1-hz three axis seismometer modified to record broadband signals. If will provide a complementary data set to the other instruments. The instrument is self contained and can be deployed from a surface ship or via an elevator. The additional value of these types of instruments is that they will be recovered by 1 August to permit an initial analysis of tides and mass wasting events by summer intern John DeLaughter.
Deployment methods for other instruments:
ROV |
R/V John Martin |
Elevator |
Some of the vessels used by MOISE
- ROV Ventana
- The Point Lobos
- Installing the seismometer housing: The Movie364 kbytes
- Inserting the seismometer package: The Movie287 kbytes
Other MOISE Links
More about the Monterey Bay Region