The first weekend of summer vacation will be anything but summer-ish, but warmer conditions will be returning to the region next week. A cold low pressure center will move slowly though the Pacific Northwest this weekend, keeping winds high and temperatures low. Saturday’s high will drop to the upper 60s, and then on Sunday that will fall to the upper 50s, with a chance of valley rain and mountain snow continuing into Monday morning. Skies will clear out by Tuesday, and temperatures will warm back up to the 70s on Tuesday and then climb into the 80s for the rest of the week.

We had a small earthquake (3.9) hit the Topaz Lake area earlier this week. Bob wondered: “How far away will a 7.0 earthquake affect, versus a 6.0 and 5.0? Thanks for any input you have.”

It’s hard to put into real precise terms, because the distance felt depends on several factors, including direction of the fault movement and the rock it is passing through, as well as the depth of the hypocenter and the surrounding geology. And the magnitude of an earthquake isn’t a measure of how far away it will be felt.

It also depends on how you define “affected.” The Loma Prieta (a 6.9- 7.1 quake, depending on measurement type) in 1989 centered in the San Francisco area could be felt by some people over here in Reno, but we weren’t really affected. But a 7.0 quake can cause damage 100-150 miles away. The distance shrinks very rapidly as the magnitude drops.

But can an earthquake far away affect the tectonics (earthquake potential) in another area? That’s another tough question. There’s no way to say for sure if the 6.0 earthquake that hit the Wells area back in late February of 2008 had any effect on the earthquake swarm in NW Reno which started a week later. It’s not likely that it did, but there’s no way to say for sure.

But here’s another way to compare one earthquake to another of differing magnitudes: A 7.0 earthquake releases about 30 times the energy than a 6.0 quake, which in turn releases 30 times the energy of the 5.0 earthquake. So a 7.0 earthquake has nearly 1,000 times the energy release that a 5.0 quake has.