# 1917 Samoa earthquake

The 1917 Samoa earthquake affected the Samoan Islands, on June 26, 1917, at 18:49. The epicenter of the magnitude 8.0 was located in the southwest of the Samoan Islands. It was described as the worst earthquake in Samoa in 50 years. Though there were no casualties, residents on the island were frightened by the tsunami and sought refuge in higher ground. The earthquake damaged two churches and several homes. A tsunami also flooded the islands and washed away homes.

## Background

Before 1917, multiple changes underwent Samoa. Most notably a government takeover, which switched the government administration from Germany to New Zealand after a successful battle from which military units seized control from Germany. The territory was claimed to be the first enemy territory to fall to imperial forces.

## Geology

The Samoan Islands are composed of linear chains of volcanic islands placed on the top of the Pacific plate. The Pacific plate slightly moves west-northwest at a slow speed, causing old and active volcanoes under the surface. The youngest and most active volcano is named Vailuluʻu, with a volcanic cone just about 300 metres (330 yd) off the crater of Vailulu'u. Other than volcanos, there are multiple volcanic islands situated west of Vailulu'u. The geology of Samoa consists of mafic material, like basalt and gabbro because of volcanic hotspots.

## Earthquake

The earthquake measured M$_w$ 8.0 and struck at a depth of 15 kilometres (9.3 miles). The epicenter was located 120 km (75 mi) north-northeast of Hihifo, Tonga. Alongside the M$_w$  8.1 event in 2009, both earthquakes were among the largest to occur near the Samoan Islands. The earthquake occurred along the plate boundary between the Tonga and Pacific plates. Due to a lack of instrumental recordings, the earthquake's focal mechanism could not be determined.

## Impact

The earthquake was felt for two minutes and seven jolts were felt. In Apia, a customs building sustained a few cracks in its concrete and its verandah detached from the structure. Severe damage also occurred to homes and businesses. Rockslides and uprooted trees were observed in the hilly parts of the island. At Pago Pago, a Mormon temple was levelled, and another church was wrecked in Leone. The earthquake and tsunami did not cause any casualties.
The tsunami occurred during the low tide and its destructive effects were limited by the presence of coral reefs. It caused significant damage on coasts of the Aleipata Islands, Savaiʻi, Lotofaga and Pago Pago. Many native residents ran to the hills when the tsunami washed along the coast and crashed into homes. At Pago Pago Bay, the sea level fluctuated some 5–6 ft (1.5–1.8 m) higher or lower than the normal tide level. This observation by the native population sparked fear and they settled in higher grounds. A 3 ft (0.91 m) tsunami caused little damage along the southern parts of Bavail, Upola, and Tutuila. The water level at a lagoon on Keppel Island also rose. Half of the village of Lotofaga was flooded and destroyed.
The tsunami was described on Aleipata as a "white wall of foam fully 10 ft (3.0 m)" which washed over the beach and homes, carrying debris. The waves also washed coconut tree logs and dumped them several yards from their former position near the beach. On Lotofaga, the inundation extended through homes and into the island's plantations. Half a village was flooded, and a cement wall estimated to be a foot thick and three feet high was pushed some 30 ft (9.1 m) by the waves. A bridge at Palauli on Savaiʻi was carried away and several homes were demolished. All of the native homes at Satupaitea were smashed by the tsunami. On Tutuila, many homes were also lost. After the tsunami, many of the natives sought refuge in the mountains for the rest of the night. Dispatchers were deployed in Suva, Fiji to help relief efforts. A newspaper described the damage as only the "loan of several cutters and the dooding of several shops and dwellings."