The regional variation of the seismic velocity-ratio (γ) over a 200 km long traverse has been studied by means of microearthquake surveys. The Wadati-plot method is used with a minimum of four P and S arrivals for each of 49 earthquakes. The area as a whole is found to be characterized by a γ value of 1.74–1.76 for earthquakes of depth 12–40 km, except in a 50 km long section near Wellington, where γ is low at 1.60. This low γ has been attributed to the fault zones in the region. A small change of γ is observed between the upper crust (≤5 km) and lower crust (≥12 km), but there is no change of γ between the lower crust and uppermost mantle.
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Kayal, J.R. Seismic velocity-ratio in the crust and uppermost mantle in southeast Wellington province, New Zealand. PAGEOPH 120, 809–819 (1982). https://doi.org/10.1007/BF00876663
- Wadati plot
- Poisson's ratio