North Idaho hasn’t exactly demonstrated an active fault for a number of decades. Although seismic faults have been mapped under the city of Coeur d’Alene. Just as there have been geological studies made, that a percentage of the Idaho panhandle was actually created out of vulcanism, many thousands of years before the last known Ice Age. Well the evidence certainly does exist, that Idaho is among the Inland Northwest states that can be called seismically active. Just that our earthquakes are infrequent, and the last time there was factual volcanic activity in the region, was 10s of thousands of years ago.
So you can imagine to everyone’s surprise when North Idaho experienced a series of temblors; epicenter: fifteen miles south of Sandpoint, Idaho. That was last night 23 April 2015, that measured 4.1 on the Richter scale for the first one, at 7:35 pm. Suffice it to say that I was on Facebook at the time the first jolt hit. What I first heard sounded like a pop, then some definite rattling that lasted for seconds. I actually got up from my laptop computer, and went around to where the electric furnace is located. I placed my hand briefly on the main door, wondering if I had a major problem here. Nothing further seemed to be going on, so I went back to dinging away on Facebook. But a matter of an hour later, news had reached the local Facebook feeds about an earthquake hitting Coeur d’Alene. What made me think that the book shelves were rattling? That would have been the only other explanation, since there was ultimately nothing wrong with the furnace. Oh and incidentally, stuff sitting on top of the bookshelves were slightly askew this morning. It wasn’t enough of a jolt to knock stuff flying, but it was enough of a temblor to where you could definitely hear things rattling.
Some three hours later, a stronger jolt was reported to rattle the same region. I am still dinging away on Facebook, when the next news feed was a 4.6 magnitude aftershock(?) came rolling along the same fault line, that the first shock had activated. Interestingly enough, I didn’t pick up on anything actually getting rattled by 10:45 pm as was the case earlier in the evening. But depending on where people were living, either they did feel both jolts, or they felt one or the other. And finally there were reports that a third aftershock had also struck the region. Not that I was aware of such an aftershock,after the first jolt at 7:35 pm. I will not doubt however, that other people did feel up to two or more aftershocks.
So on Facebook friend gets a conversation going about who felt the successive temblors, and where we were at the time of the incident(s) in question. All kidding aside, some people definitely heard a noise that came with the earthquake, and some of us just experienced a slight shaking. Also a friend of this Facebook friend brought up a link that detailed some of North Idaho’s seismic history. Such as a devastating earthquake back in the 1930s. Plus near volcanic upthrusts that made mining in North Idaho mountains particularly treacherous. To say the least, wow! So now I am going to add here, that Idaho has a long period of volcanic activity. This inserted photo of Lake Coeur d’Alene is one of three glacial lakes that were the result of the Ice Age great melt off and flooding. Lake Pend O’Reille which is a massive lake and during World War 2, was deemed sufficiently deep enough for inland submarine training. Hayden Lake which is much smaller, but definitely located in a picturesque setting. And finally Lake Coeur d’Alene. The mountains that serve as a backdrop, not all of those would have been created by shifts in the tectonic plates. It is possible that many of them were volcanic in origin. But of particular interest is Tubbs Hill. Walk along its many trails, and you will notice the angular upthrust in Basalt and other rocks, that would definitely suggest the hill was formed in part from seismic activity. I noticed that one year, when I went to take photographs along one of our most scenic landmarks, that Coeur d’Alene can actually boast of. What made Tubbs Hill possible? Hard to say. But with newly activated seismic faults in the region, North Idaho is going to be in for some interesting times.
There were two earthquakes that came rolling northward from South Idaho. One I know of back in the mid 1980s. It registered a 7.3 on the Richter scale closest to its epicenter. By the time it rolled across the entire state of Idaho; it was felt in parts of Washington and also at the Canadian border. That earthquake was likely in the 4.something range. Its effective force had decreased significantly, the further from the epicenter the temblor traveled. The second one, was recorded recently in the last few years. I don’t think that we felt the jolt from it. Comparing the former to the Sandpoint epicenter of last night, and Kootenai County would have been less than two hours away. So we would have gotten nearly the same measurable jolt, as the residents of Sandpoint and Cocalala would have felt. A hell of a noise. Out of this, do we again experience volcanic activity?