On Friday, after the massive earthquake and subsequent tsunami had hit Japan, Gretchen Weber of KQED’s Climate Watch spoke with Tom Brocher, Director of the Earthquake Science Center at the U.S. Geological Survey in Menlo Park. Pretty interesting conversation for those of us who live in quake territory. After cautioning to be mindful of the tsunami’s effects for 12 hours after the first waves struck (the tsunami advisory has now been canceled), he got into the subject of giant earthquakes.
Some things that Mr. Brocher pointed out:
- The type of giant quake that hit Japan Thursday is not expected to menace the Bay Area, where the 7.9 quake of 1906 is thought to be at the upper limit of quakes in the area. The Japan quake was 30 times larger than the 1906 quake, and 900 times the size of the Loma Prieta temblor in 1989.
- North of California, however is another story. A magnitude 9.0 or above quake in the Pacific Northwest is expected. Those quakes, which are the product of vast and deep faults, are characterized by their severity and the duration of shaking when they strike. Brocher said strong shaking lasted for 3-5 minutes during Thursday’s tembler.
- A quake in the 9.0 range occurs in the Pacific Northwest region every 300 – 500 years. The last one was in 1700, which scientists know because of a tsunami that was recorded in Japan at the time.