Another underwater quake recorded

  • Jan. 11, 2008 6:00 a.m.

An unsettling cluster of earthquakes during the last few weeks is reminding islanders how active the Queen Charlotte Fault is, says seismologist John Cassidy of Natural Resources Canada. Haida Gwaii is the most seismically active area in Canada, but he said the recent quakes are not an indicator “The Big One” that earthquake experts are predicting for the Cascadia subduction zone is imminent. The most recent earthquake occurred at 6:40 am PST on Wednesday (Jan. 9) and measured 6.1 on the Richter scale. Its epicenter was off the southwestern tip of the islands, Mr. Cassidy said, but the earthquake centre received no reports from anyone who felt the shake. Three other earthquakes were measured in quick succession in the early morning hours of Jan. 5 in the Queen Charlotte Sound area. The first measured 5.3, then 6.7 and finally a 6.5. These were felt in Bella Bella. On Dec. 12, people all over the north and central coast and the islands felt a 5.7 quake. These earthquakes are taking place in a very complicated region, Mr. Cassidy said. Plates are either sliding past one another in the fault zone which runs along the west coast of the islands or pushing beneath each other in the subduction zone, which runs south of the Queen Charlotte Islands to California. Mr. Cassidy said the biggest earthquake in Canada took place in the Queen Charlotte Fault zone in 1949. The quake measured 8.1 and was bigger than the 1906 earthquake which helped destroy San Francisco. Mr. Cassidy said the recent quakes were horizontal slip/slide earthquakes and were not the type to cause tsunamis. Tsunamis are caused by vertical movement of the sea floor and the magnitude must be at least 7.5 to create a wave, he said. “But it’s a good reminder of how active the area is,” he said. He also said any earthquake could cause landslides, which may in turn cause waves. So the general rule of, “If you feel shaking, get away from the water and move to higher ground,” still holds, he said. Anyone interested in looking at maps showing just how active the region is should go to earthquakescanada.nrcan.gc.ca.