M 6.7 Gisborne Thu, Dec 20 2007

A magnitude 6.7 earthquake struck at 8:55 pm on Thursday 20 December. Located offshore, it caused damage to chimneys and buildings at several places along the East Coast, particularly in the Gisborne CBD.

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PublicID 2839343
UTC Time 2007-12-20T07:55:16Z
Latitude -38.89 (± 0.0 km)
Longitude 178.54 (± 0.0 km)
Depth 33 km (± 0 km)
Depth Type operator assigned
Earth Model nz1dr
Used Phase Count 48
Used Station Count 43
Standard Error 0.21 (s)
Azimuthal Gap 236.00 (degrees)
Minimum Distance 0.46 (degrees)


Type Magnitude Station Count
Preferred (Mw) 6.7  
ML 6.7 (± 0.2) 74
Mw 6.7 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

-2.0- (s)01Distance (degrees)Pick Residuals

Station Magnitudes (ML) (degrees)Station Magnitudes (ML)

Magnitude Residuals (ML)

- (degrees)Magnitude Residuals (ML)