Seismic velocity-ratio in the crust and uppermost mantle in southeast Wellington province,New Zealand

The regional variation of the seismic velocity-ratio () 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 value of 1.74–1.76 for earthquakes of depth 12–40 km, except in a 50 km long section near Wellington, where is low at 1.60. This low has been attributed to the fault zones in the region. A small change of is observed between the upper crust (5 km) and lower crust (12 km), but there is no change of between the lower crust and uppermost mantle.