The hidden fault

Between December 16, 1811 and February 7, 1812, a series of four earthquakes -- each estimated to be above magnitude 7 -- hit what you might think is one of the most unlikely places on Earth; southeastern Missouri.

The fault (named the New Madrid Seismic Zone for the county right in the center of it) is located in the middle of the North American craton, an enormous block of what should be old, stable, geologically inactive rock.  But even so, the biggest (and final) earthquake of the four was powerful enough that it was felt thousands of kilometers away, and allegedly rang church bells in Charleston, South Carolina.  The shift in terrain changed the course of the Mississippi River, cutting off a meander and creating horseshoe-shaped Reelfoot Lake.

It's well known that most of the world's earthquakes take place along the "Ring of Fire" and other junctions between tectonic plates, but it's not always so.  The New Madrid Fault is thought to be either a failed rift zone -- when a convection current in the mantle tried, but failed, to split the continent, but created a weakness in the middle of the plate -- or else the rebound of the crust from the passage of the Bermuda Hotspot, which is also one possible explanation for the process that created the Ozark Mountains.

The point is, earthquakes don't always occur where you might expect, and sometimes fault lines can stay hidden until suddenly they slip and catch everyone off-guard.  This is the situation much closer to where I live; the Saint Lawrence Rift System, aligned (as you'd expect) with the Saint Lawrence River, is an active seismic zone in northern New York and southern Canada, and like New Madrid, is very far away from any plate margins.  Here, the weakness is very old -- geologists believe the fault actually dates to the early Paleozoic, and may be related to the Charlevoix Asteroid Impact 450 million years ago -- and has been reactivated by something that is causing super slow convergence on opposite sides of the fault (on the order of 0.5 millimeters a year).

What that something might be, no one is certain.

The reason the topic comes up is a paper in the journal Tectonics this week that I found out about because of my friend, the wonderful author Andrew Butters, who is an avid science buff and a frequent contributor of topics for Skeptophilia.  It describes a newly-discovered 72-kilometer-long fault that runs right down the middle of Vancouver Island -- passing just northeast of the city of Victoria.

To be fair, British Columbia isn't exactly seismically inactive; as I described last month, it's in the bullseye (along with the rest of the coastal Pacific Northwest) of the horrifyingly huge Cascadia Subduction Zone.  But even so, the discovery of a hitherto-unknown fault right near a major city is a little alarming, especially since the southeast corner of Vancouver Island is actually pretty far away from Cascadia.  The authors write:

Subduction forearcs are subject to seismic hazard from upper plate faults that are often invisible to instrumental monitoring networks.  Identifying active faults in forearcs therefore requires integration of geomorphic, geologic, and paleoseismic data.  We demonstrate the utility of a combined approach in a densely populated region of Vancouver Island, Canada, by combining remote sensing, historical imagery, field investigations, and shallow geophysical surveys to identify a previously unrecognized active fault, the XEOLXELEK-Elk Lake fault, in the northern Cascadia forearc, ∼10 km north of the city of Victoria...  Fault scaling relations suggest a M 6.1–7.6 earthquake with a 13 to 73-km-long surface rupture and 2.3–3.2 m of dip slip may be responsible for the deformation observed in the paleoseismic trench.  An earthquake near this magnitude in Greater Victoria could result in major damage, and our results highlight the importance of augmenting instrumental monitoring networks with remote sensing and field studies to identify and characterize active faults in similarly challenging environments.

So that's a little alarming.  Another thing to file under "You Think You're Safe, But..."  I've frequently given thanks for the fact that I live in a relatively calm part of the world.  Upstate New York gets snowstorms sometimes, but nothing like the howling blizzards of the upper Midwest; and we're very far away from the target areas for hurricanes, mudslides, wildfires, and volcanoes.

But the scary truth is that nowhere is natural-disaster-proof.  As New Madrid, the Saint Lawrence Rift System, and -- now -- Victoria, British Columbia show, we live on an active, turbulent planet that is constantly in motion.  And sometimes that motion makes it a little dangerous for us fragile humans.

The Earth is awe-inspiring and beautiful, but also has little regard for our day-to-day affairs.  You can do what is possible to minimize your risk; forewarned is forearmed, as the old saying goes.  But the reality is that the natural world is full of surprises -- and some of those surprises can be downright dangerous.

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Birds down under

I've been an avid birdwatcher for many years, and have been fortunate enough to travel to some amazingly cool places in search of avifauna.  Besides exploring my own country, I've been to Canada (several times), Belize (twice), Ecuador (twice), Iceland (twice), England (twice), Scotland, Sweden, Finland, Denmark, Russia, Spain, Portugal, and Malaysia.

One place I've never been, though, is Australia, which is a shame because it's got some incredible animals.  And despite a pretty well-deserved reputation for having far more than their fair share of wildlife that's actively trying to kill you, most tourists come back from trips to Australia alive and with all their limbs still attached in the right places.

The main reason for Australia's unique ecosystems is that it's been isolated for a very long time.  During the breakup of Pangaea, the northern part (Laurasia, made up of what is now Europe, North America, and most of Asia) separated from the southern part (Gondwanaland, made up of what is now Africa, South America, Antarctica, Australia, and India), something on the order of 180 million years ago.  The other pieces gradually pulled apart as rifting occured, but Australia remained attached to Antarctica until around thirty million years ago.  At that point, the whole thing had a fairly temperate climate, but when the Tasman Gateway opened up during the Oligocene Period, it allowed the formation of the Antarctic Circumpolar Current, isolating and cooling Antarctica and resulting in the extinction of nearly all of its native species.  Australia, now separate, began to drift northward, gradually warming as it went, and carrying with it a completely unique suite of animals and plants.

The reason all this comes up is a sharp-eyed Australian loyal reader of Skeptophilia, who sent me a link to a news story about a recent discovery by a dedicated amateur fossil hunter and birdwatcher, Melissa Lowery, who was looking for fossils on the Bass Coast of Victoria and stumbled upon something extraordinary -- some 125 million year old bird footprints.

Lowery's bird footprints [Image by photographer Rob French, Museums Victoria]

At that point, the separation of Australia and Antarctica was some 65 million years in the future, the sauropod dinosaurs were still the dominant animal group, and Victoria itself was somewhere near the South Pole.  Lowery's find led to a full-scale scientific investigation of the area, and uncovered a great many more bird tracks, including some with ten-centimeter-long toes.  Also in the area were the footprints of dozens of kinds of non-avian dinosaurs.

"Most of the bird tracks and body fossils dating back to the Early Cretaceous are from the Northern Hemisphere, particularly from Asia," said Anthony Martin, of Emory University, who led the study.  "Our discovery shows that there were many birds, and a variety of them, near the South Pole about 125 million years ago."

Of course, being a birdwatcher, I'm intensely curious as to what these birds looked like, but there's only so much you can tell from a footprint, or even fossilized bones.  It's simultaneously intriguing and frustrating to think about the fact that these animals -- and all the other animals and plants that lived alongside them -- had every bit of the diversity, all the curious and wonderful and beautiful adaptations and behaviors, that our modern wildlife does.

Imagine what it would be like to transport yourself back to Australia in the early Cretaceous, and witness all of that with your own eyes and ears.  (With, of course, a guarantee of coming back alive and with all your limbs still attached in the right places.  Back then, Australia was a rougher place than it is now.)

So thanks to the reader who sent me the link -- it's renewed my desire to visit Australia.  If I can't see the amazing birds they had 125 million years ago, at least I can have a look through my binoculars at some of the ones they have today.

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