Results from seismic studies during 1978 for coal exploration in Central Otago

By: Broadbent, M. (DSIR, Geophysics Division. Wellington).
Contributor(s): DSIR, Geophysics Division. Wellington.
Material type: materialTypeLabelBookSeries: Report / Geophysics Division ; 194.Publisher: 1983 MayDescription: 24 p.Report number: GEOP--194Subject(s): SEISMOLOGY | REFRACTION | REFLECTION | CENTRAL OTAGO | VELOCITY | COAL | EXPLORATION | SEDIMENTS | SCHISTS | SEISMIC SURVEYS
Incomplete contents:
Seismic refraction and reflection measurements made at 20 sites in the Manuherikia, Ida, and Maniototo Basins of Central Otago in 1968, 1978, and 1981 are reported and assessed. The measurements yielded estimates of the thickness of Cenozoic sediments unconformably overlying the basement rocks, which are Mesozoic sediments in the most northern part of the basins and schist elsewhere. Seismic reflectors within or at the base of the Cenozoic sediments were defined at some locations. Compressional wave velocities in Cenozoic sediments, which were not saturated with water, were between 0.8 and 1.3 km/s, while velocities were between 1.6 and 2.5 km/s where the sediments were saturated. Velocities between 3.0 and 4.2 km/s were measured for Mesozoic sediments, and velocities from 3.6 to 5.6 km/s were recorded for schist. The velocity in schist tended to increase with depth of burial. Maximum thickness of Cenozoic sediments in the Manuherikia, Ida, and Maniototo Basins exceed 440, 660, and 600 meters, respectively. The inferred sediment thickness are in quite good agreement with those determined earlier from gravity measurements by Woodward and Whitla (1978)
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1 Available 36101-1001

9 refs; 9 figs; 4 tables

Seismic refraction and reflection measurements made at 20 sites in the Manuherikia, Ida, and Maniototo Basins of Central Otago in 1968, 1978, and 1981 are reported and assessed. The measurements yielded estimates of the thickness of Cenozoic sediments unconformably overlying the basement rocks, which are Mesozoic sediments in the most northern part of the basins and schist elsewhere. Seismic reflectors within or at the base of the Cenozoic sediments were defined at some locations. Compressional wave velocities in Cenozoic sediments, which were not saturated with water, were between 0.8 and 1.3 km/s, while velocities were between 1.6 and 2.5 km/s where the sediments were saturated. Velocities between 3.0 and 4.2 km/s were measured for Mesozoic sediments, and velocities from 3.6 to 5.6 km/s were recorded for schist. The velocity in schist tended to increase with depth of burial. Maximum thickness of Cenozoic sediments in the Manuherikia, Ida, and Maniototo Basins exceed 440, 660, and 600 meters, respectively. The inferred sediment thickness are in quite good agreement with those determined earlier from gravity measurements by Woodward and Whitla (1978)

GP

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