Local earthquake noisy, but light

This evening’s magnitude 4.5 earthquake near Porirua at a depth of 30 km was noisy, but light. The earthquake had a noticeable P component, the initial jolt that is felt when the faster P-wave passes through, followed about 5 seconds later by a noisy S-wave which had a distinct vertical component that made roofing iron rattle and could be felt through the floor as the rumble was heard.

The absence of goods rattling in cupboards has been remarked upon here in Tawa, owing to the absence of horizontal shaking on firmer ground. Lights and other suspended objects hardly moved.

As the Pacific Plate slides under the Australian Plate, it has to be expected that these events will occur under our feet. Tonight’s earthquake follows a magnitude 5.0 earthquake at 25 km depth further east (to the south-west of Weber) near the subduction interface at 2:55 this morning.

On a pleasant still evening in early summer, many people would have noticed this quake, as it was rumbly and the vertical movement would have made house components emit noises, rather than contents like crockery, glassware and cutlery rattle.

Further north, on the soft soils of the Kapiti Coast, a more pronounced swaying may have been evident.

Here at Tawa the birds, who were packing up for the evening and heading off to their nests, sang throughout the event, and seemed unconcerned.

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