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Does the direction of rupture influence the size of the impact in different places?

Seismic energy gets focused in the same direction as the direction of rupture – a kind of Doppler shift. So if you are unlucky enough to be in the line of fire, a magnitude 6.5 earthquake may hit you with the force of a much bigger quake. This phenomenon has been observed many times in New Zealand and overseas. Other factors such as topography and rock type can also focus seismic energy in different ways.

Many New Zealand faults trend northeast/southwest. This dictates the likely direction of rupture for these faults. Predicting the likely impact of a given magnitude quake at a particular site involves extremely complex three-dimensional mathematics.

Tree stumps protrude above the surface of the Rangitaiki River following the 1987 Edgecumbe earthquake. The stumps, the remains of a forest destroyed by fallout from the c. AD 233 Taupo eruption, were revealed after the river bed was down-faulted and then scoured back upstream, thus providing dramatic evidence of active tectonism at work in upper central North lsland. The crumpled land in the foreground results from local ground shaking.

Tree stumps protrude above the surface of the Rangitaiki River following the 1987 Edgecumbe earthquake. The stumps, the remains of a forest destroyed by fallout from the c. AD 233 Taupo eruption, were revealed after the river bed was down-faulted and then scoured back upstream, thus providing dramatic evidence of active tectonism at work in upper central North lsland. The crumpled land in the foreground results from local ground shaking.