Monday, January 12, 2015

Shakin' It in New England

We had an earthquake this morning. A 3.3 on the Richter Scale. Sure, my friends in California and Japan might chuckle at this, but for here in New England it is a novelty.
Here there be movin' rocks!
Boom! Yeah.
The epicenter was in the southwest corner of Sterling, CT and shook a number of homes in the area for several seconds. A friend of mine who lives fairly close to the epicenter commented that her fish definitely do not like earthquakes because there was water splashed all over her living room floor. (Her fishtank is almost 500 gallons and her fish are huge.)
There was another, smaller, earthquake on Friday. I suspect they are probably related, in that the smaller one may have released some stress that in turn, increased stress on the other part of the fault that released this morning.
While rare, earthquakes do happen here. Most of the time, they go unnoticed. More often than not, when an earthquake is felt most people around here think it was just a truck rumbling by the house until it occurs to them they didn’t hear an engine. And then there are the ones like this morning’s earthquake that actually are able to shake the house.
I was far enough away from the epicenter of this morning’s quake that I didn’t feel a thing. I only learned about it when I checked the weather and the weather map showed the epicenter, indicating the earthquake had occurred less than an hour before.
What makes it more interesting is I know very well right where the epicenter happened, as I go past this spot frequently when I'm out riding. It's a beautiful road, following along the top of a ridge and passing through farm land—it's one of Connecticut's scenic byways.
To date, I cannot definitively say that I have experienced an earthquake. It is possible that I have and simply have not recognized the situation. Over the years, every once in a while I would hear a boom or two and my house would shudder. One in particular that happened while I was a teenager I remember very specifically that the house shuddered a moment and the load springs on the garage doors vibrated enough to make some noise. However, I live a couple miles from a rock quarry, and sometimes when they were blasting the vibrations could be felt. So, it is more likely I was experiencing that and not an actual seismic event.
Other situations, I remember older friends and neighbors commenting that they could hear the sonic booms from the Concord leaving New York City and that the booms would shake their houses. The problem with that assumption is that the Concord would be going supersonic after it was clear of US soil, which means the sonic boom would be going away from us, not at us. However, when that I  stop and think about it, I wonder if these were small, local earthquakes they were describing.
It's always been a private interest of mine to watch for stone walls in New England woods. Over 150 years ago, most of New England was cleared of trees, and farmers pulled the rocks out of the ground and built walls to delineate their farm fields. When farming faded away from New England, the forests grew back, leaving iconic stone walls mysteriously hidden in the woods. The walls were built in straight lines. So any wall that has an odd shift in it, could actually be crossing a fault line that has slipped over the years. One of these days, I'm going to find one. Then I'll be able to say, I found a seismic fault.
In 1989 after the Loma Prieta earthquake, I wrote an article about earthquakes in New England for the Brockton Enterprise. I like to think that my article may have inspired one New England resident to consider her insurance options.
After learning that a fault line ran up along the Taunton River from Narraganset Sound, a woman who lived near Fall River, MA decided she wanted to get earthquake insurance for her home. After arguing with her husband about it, she called her insurance agent and added earthquake coverage to their home insurance for a tiny increase to their premium.
A while later, in 1996 there was a small earthquake in the Fall River area. The insurance agent, recalling his client adding the earthquake insurance, decided to give her a call, just for some laughs.
Did you know we just had an earthquake, he asked.
No, she replied,
While he had her on the phone, he had her walk around the house to see if anything had been damaged—no there wasn’t. 
Then he suggested she go outside.
While they were having a good laugh, she stepped outside and looked around and didn’t see any—oh, wait. There was an odd crack in the driveway.
The crack didn’t go across the driveway, it went right up the middle.
The insurance agent suggested she follow it.
It went right up into the garage. And through the garage floor. Through the foundation of the house. And right on through the in-ground swimming pool which was in the process of draining out.
So, for an insurance rider that cost no more than maybe $5 per month, it turned out their house had suffered over $70,000 worth of damage from the earthquake!
“The Faithful shall be rewarded…”
What makes New England earthquakes fun is that scientists cannot fully explain them with the current seismological model. Does that mean that science is wrong, that the earth is actually flat, only 6,000 years old, and humans danced with dinosaurs? No, it simply means that while we generally know what causes earthquakes and why they happen, we don’t know all the things that can cause an earthquake. We don’t know fully all the mechanisms behind earthquakes and what finally triggers one or another. If we did, then the daily weather report would include an alert that there would be an earthquake in Sterling, CT at 6:38AM and residents should take the family crystal off the shelves and put towels around the family fishtanks.
New England is geologically interesting.
It was formed as part of Gondwana, the southern half of the Pangea supercontinent. When the African plate slammed into the North America plate, the Appalachian Mountains were thrust into the air. Eventually, tectonic forces reversed and Pangea began to pull apart.
The land that would eventually become New England was right in the middle of this rifting process. The Connecticut River missed being the Atlantic Ocean by just 70 miles. The rift that created the Atlantic Ocean still exists today as the Mid-Oceanic Ridge. The tectonic forces that are spreading the Atlantic Ocean wider are pushing North America against the Pacific plate, the edge of which is along the California coast and is why there are so many strong earthquakes along the west coast.
New England was in the middle of a lot of pushing and pulling over the eons. Now, it lies almost at the halfway point between the Mid-Oceanic Ridge and the Pacific coast subduction zone. Expanding this to a wider field of view, the whole Appalachian Mountain chain marks this border, with New England at the northern end.
New England is part of the snowplow pushing North America over the Pacific plate (and a few more smaller plates).
There’s more to it.
We also just got out of an ice age just over 10,000 years ago. As the extended ice cap receded, all that weight from the ice was removed. The continental rock around here is still rebounding from the weight and rising, bit by bit. That introduces stresses, too.
At some point or another, something has to give.
Not the most sophisticated geological dissertation, but it gets the point across. Every now and then, New England shakes, rocks, rattles, and rolls. And splashes water out of fish tanks.