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Nanaimo 25.0 km Bowen Island 26.84 km Port Renfrew 96.6 km Map showing the Port

ID: 304755 • Letter: N

Question

Nanaimo

25.0 km

Bowen Island

26.84 km

Port Renfrew

96.6 km

Map showing the Port Renfrew, Nanaimo, and Bowen Island seismic stations.

The locations of the three seismic stations are shown on the map, Based on the distances estimated above, describe in words, the approximate epicentre of the earthquake.

Comment on what you think accounts for the significant difference in amplitude of the S waves at Port Renfrew compared with the S waves at Nanaimo and Bowen Island.

Nanaimo

25.0 km

Bowen Island

26.84 km

Port Renfrew

96.6 km

Strait owen Island of Vancouver Nanaimo Georgia Island 0km krii 50 Port Renfrew

Explanation / Answer

Based on the distances given above, we can clearly see that the distances the seismic waves travelled to reach the stations at Nanamio and Bowen Island are nearly same. At the same time it travelled about 4 times more distance to reach Renfrew. So we can say without any confusion that the approximate epicentre of the earthquake is somewhere between Nanaimo and Bowen Island, almost at the middle of the strait of Georgia.

The waves reached Nanaimo and Bowen Island travelled most of the distances through the Strait of Georgia. We know that water supports no shear and thus it is impossible for the S waves to travel through water. While the waves that reached Port Renfrew has travelled a significant portion through hard land. Therefore the amplitude of S waves at Port Renfrew will be significantly larger than that at Nanaimo or Bowen Island.

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