Earthquake Occurrence and Effects in Ocean Areas.
Abstract
Present-day concepts of the major seismic zones round the world are discussed in relation to observed features of earthquake occurrence. There is mounting evidence that vertical cellular convection of earth's mantle material is responsible for sea floor spreading about the mid-ocean ridges and for under-thrusting of oceanic crustal blocks beneath adjacent continental crusts. Earthquake activity is largely confined to the boundaries of these crustal blocks where thrust faulting along island arcs and shear along transform or transcurrent faults are proceeding. Seismicities of different oceanic regions are presented in terms of available statistics on earthquake occurrence relative to earthquake magnitude. Characteristic features of terrestrial earthquakes are reviewed, as well as known features of large submarine earthquakes, both as to tectonic movements and sea disturbances. From measurements of accelerographs and general statistical information, accelerations and velocities of ground motion are assessed in relation to earthquake magnitude. Other parameters such as fault length, duration time of shaking, maximum tectonic displacement are related statistically to earthquake magnitude. Tsunami generation is also reviewed and approximate statistical relationships given for wave height, period and source dimensions in terms of earthquake magnitude. The vulnerability of ocean bottom structures to effects from earthquakes is then dealt with from the viewpoints of seismic risk, foundation failure, structure dynamics and tsunamis. A number of suggestions are made for needed research in areas of deficient knowledge. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1969
- Accession Number
- AD0859931