|Date 14 October 1997|
Depth 167 km (104 mi)
|Magnitude Mw 7.8|
The 1997 Fiji-Tonga earthquake occurred south of the Fiji Islands (about 190 km WSW of Nuku'alofa, Tonga, and 255 km SE of Ndoi Island) on 14 October at 09:53 UTC. This earthquake was located in the central part of the Fiji-Tonga subduction zone and it had a magnitude of Mw 7.8. The rupture area was about ~50 km × 25 km, and the average slip was estimated to be 6 m (20 ft). This earthquake could be felt in Wellington, New Zealand.
The Pacific Plate is subducting beneath the Australian Plate in the Fiji-Tonga subduction zone. The Tonga Trench is linear, fast converging, and seismically active. Mantle seismicity is active in this area. There is a belt of deep earthquakes in the west of the Tonga Trench. There are more earthquakes with focus depth h ≥ 300 km occurring in the Tonga-Kermadec region than in all other regions combined.
With a depth of 167 km (104 mi), this was an intermediate depth earthquake. Thermo-petrologic models suggest that water may have an important role in the generating process for earthquakes of intermediate depths, as hydrous minerals may exist where intermediate depth seismicity is abundant.