Location

St. Louis, Missouri

Session Start Date

4-26-1981

Session End Date

5-3-1981

Abstract

Long-Term measurements of earthquake ground motions offshore, using the Sandia National Laboratories' SEMS device which records only the strongest motions and transmits them upon command to a boat at the surface, have shown that offshore ground motions may in certain cases be substantially different from empirically predicted ground motions based on onshore data. In particular, the attenuation effects of soft and/or gassy soils, the wedging of offshore deposits as a function of direction to and distance from the source, and sharp velocity-depth profiles, are shown to be possible actors contributing to such differences. For the well constrained recording to date, the offshore ground motions are only 13 to 23 percent of those which would be calculated using empirical predictions based on onshore data. To address this situation, Sandia has installed a net of three long-lived (SEMS), two of them in the vicinity of instrumented platforms, in the Sandia Barbara Channel. The results are intended to evaluate the earthquake hazards of offshore energy developments and to provide firm data on the design parameters required for the harvesting of 0ffshore energy resources.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

First Conference

Publisher

University of Missouri--Rolla

Publication Date

4-26-1981

Document Version

Final Version

Rights

© 1981 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 26th, 12:00 AM May 3rd, 12:00 AM

Long-Term Measurements of Ground Motions Offshore

St. Louis, Missouri

Long-Term measurements of earthquake ground motions offshore, using the Sandia National Laboratories' SEMS device which records only the strongest motions and transmits them upon command to a boat at the surface, have shown that offshore ground motions may in certain cases be substantially different from empirically predicted ground motions based on onshore data. In particular, the attenuation effects of soft and/or gassy soils, the wedging of offshore deposits as a function of direction to and distance from the source, and sharp velocity-depth profiles, are shown to be possible actors contributing to such differences. For the well constrained recording to date, the offshore ground motions are only 13 to 23 percent of those which would be calculated using empirical predictions based on onshore data. To address this situation, Sandia has installed a net of three long-lived (SEMS), two of them in the vicinity of instrumented platforms, in the Sandia Barbara Channel. The results are intended to evaluate the earthquake hazards of offshore energy developments and to provide firm data on the design parameters required for the harvesting of 0ffshore energy resources.