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| UTC time | 1929-03-09 10:50:32 |
|---|---|
| ISC event | 907935 |
| USGS-ANSS | ComCat |
| Local date | 9 March 1929 (1929-03-09) |
| Local time | 22:50NZST |
| Magnitude | 7.1ML |
| Epicentre | 42°47′28″S171°55′41″E / 42.791°S 171.928°E /-42.791; 171.928 |
| Type | Oblique-slip |
| Areas affected | South Island New Zealand |
| Max. intensity | MMI VIII (Severe) |
| Casualties | None |
The1929 Arthur's Pass earthquake occurred at10:50 pm NZMT on 9 March. The sparsely settled region aroundArthur's Pass of theSouthern Alps shook for four minutes.[1] Tremors continued almost continuously until midnight and sporadic strong aftershocks were felt for several days.
The earthquake was measured at 7.1 on theRichter scale and the intensity of shaking in the epicentral region has been assessed from historical records as VIII (Severe) on theModified Mercalli Scale. Intensities of VI (Strong) were observed inChristchurch andWestport.[1] The earthquake occurred on the Poulter Fault, which was not identified and mapped until 2001.
New Zealand lies along the boundary between theAustralian andPacific plates. In theSouth Island most of the relative displacement between these plates is taken up along a single dextral (right lateral)strike-slip fault with a majorreverse component, theAlpine Fault. In theNorth Island the displacement is mainly taken up along theKermadec-Tonga subduction zone, although the remaining dextral strike-slip component is accommodated by theNorth Island Fault System.[2] The Poulter Fault runs for approximately 50 km east-northeast from near the confluence of the Bealey and Mingha rivers to the valley of the South Hurunui River. Between 16 km and 36 km of the fault ruptured, with dextral displacement of up to 4 metres and dip-slip displacement of 1–2 metres (North side up).[3]
Numerous landslides were triggered, damaging theMidland Railway and blocking roads. The highway connecting Canterbury and the West Coast via Arthur's Pass was closed for several months. Many water tanks and chimneys were damaged or toppled. Two years after the earthquake, trampers in the Otahake Valley discovered that a 900m high section of the side of amountain had collapsed, blocking the valley and sending debris 5 km downstream.[4]
Although (as of 2009[update]) this is one of the ten largest land-based earthquakes to strike New Zealand since European settlement, it was overshadowed by the more deadly1929 Murchison earthquake a few months later.[citation needed]