Seismic Detection and Discrimination Using Ocean-Bottom Seismographs
Abstract
We have developed a model for generating seismic noise at the sea floor which will enable us to extrapolate measurements made at seafloor with ocean bottom seismographs to depths within the underlying sediment and basement. This physical model is consistent with seafloor noise measurements made during the past decade and largely discounts the hypothesis that noise is generated at the seafloor by current motion inducing instrument 'rocking' through mechanisms such as vortex shedding. Although we have never been able to demonstrate a correlation between bottom currents and seismic noise on the seafloor, there is a definite correlation between seafloor noise and the general weather in the vicinity of the seismographs using data from a DARPA-sponsored experiment using Marine Seismic System (MSS), a vertical-component, digitally-recording, short- period seismograph system which was part of the borehole instrumentation of Deep Sea Drilling Project 78B. The instrument package rested unclamped in Hole 395 A, 517 meters within basement rock. Reliable estimates of microseismic noise levels were obtained between 0.16 and 2.2 Hz. The observed microseismic noise was quasi-stationary on the time scale of one hour, but not ten. If the relationship observed between noise at and below the seafloor during Leg 78B is a general one, the range of ocean bottom levels implies that borehole noise levels could approach those at quiet continental sites.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1983
- Accession Number
- ADA154136
Entities
People
- J. A. Oecutt
- T. H. Jordan
Organizations
- Scripps Institution of Oceanography