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Keck Strong-Motion OBS

The Keck strong-motion OBS is used for regional and local earthquake monitoring.
It is equipped with a Kinemetrics Episensor strong-motion accelerometer with a clip level of ±2 g.

Design and Specifications



Physical AttributesThree 17” Nautilus glass ball pressure housings holding: (i) data-logger, storage device, controllers; (ii) acoustic-release board, WHOI recovery board, and lithium batteries; (iii) lithium batteries. One 17” Nautilus/Benthos balls for floatation. A 12” I.D. Al sphere holds the strong-motion accelerometer. Leveling is via a gravity-driven, 2-axis gimbal system. Sensor is suspended in a high-viscosity oil to improve coupling. Descent rate: ~43 m/min. Ascent rate: ~ 43 m/min.
Data LoggerQuanterra Q330 6-channel data engine with 24-bit A/Ds.
Simultaneous sample rates of 200, 100, 50, 40, 20, 10, and 1 Hz.
Quanterra Packet Baler storage device with 20 GByte rotary disk-drive.
ClockSeascan low-power, digitally-temperature-compensated (DTCXO), clock with drift rate, before end-point correction, of < 5 ms/day.
SensorsKinemetrics Episensor strong-motion 3-axis accelerometer mounted on a gravity-driven, 2-axis gimbal system. Clip level is +/- 2 g. Differential Pressure Gauge (DPG) long-period pressure sensor.
Recording DurationLithium battery pack for ~15 months recording at 100 Hz.
Separate keep-alive battery for clock.
OperationOperated in closed-ball mode i.e. programming of acquisition parameters, offloading of data, clock setting, etc, all done through penetrators. Glass spheres carry an electronic vacuum gauge to ensure spheres are well sealed prior to deployment.