M 7.0 Gisborne, Wed Mar 26 1947

There were two severe earthquakes off the coast of Gisborne in March and May 1947, each generating large tsunamis in the surrounding area. The March tsunami was one of the largest tsunami in New Zealand's historical record.



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Origin


PublicID 1542993
UTC Time 1947-03-25T20:32:07Z
Latitude -38.85 (± 0.1 km)
Longitude 178.80 (± 0.1 km)
Depth 12 km (± 0 km)
Depth Type operator assigned
Earth Model nz1dr
Used Phase Count 6
Used Station Count 5
Standard Error 0.54 (s)
Azimuthal Gap 305.00 (degrees)
Minimum Distance 1.29 (degrees)

Magnitudes


Type Magnitude Station Count
Preferred (Mw) 7.0  
ML 5.9 (± 0.3) 4
MS 7.2 0
Mw 7.0 0

GeoNet combines magnitudes into a summary magnitude, M, which consists of a weighted average of the individual magnitudes and attempts to be a best possible compromise between all magnitudes for a range of earthquake sizes. Summary magnitude for GeoNet is then defined as:

M = (2 * MLv + (0.4 * number_of stations(Mw(mB)) - 1) * Mw(mB)) / (2 + (0.4 * number_of_stations(Mw(mB)) - 1))

Where MLv is local magnitude calculated on the vertical component and Mw(mB) is a Mw estimation based of mB by Bormann and Saul (2008).

Origin Map


Map of New Zealand.

Map showing stations with picks used to locate the earthquake. Stations with picks that have a zero weight in the solution are shown as small grey circles. Those with a higher weight are shown as larger circles. The quake is shown by the largest circle.

Pick Residuals


-1.00.01.0residual (s)0123Distance (degrees)Pick Residuals