Tectonics and culture make for interesting, and uncomfortable, bedfellows. Especially earthquakes when the happen in places not used to them like, oh, Germany, or Austria, or the Mississippi River embayment. Most of my work focuses on more gradual things, like river erosion and aggradation (building up the bed), with a few volcanic tweaks tens of thousands to hundreds of thousands of years ago. When the earth moves in my work, it is because a river carried it away. But some places are more dramatic.
The ground does not just move of its own accord. Subsurface forces, generally channeled along weak places in the crust called faults, impart a twisting, or rising and falling, or sliding motion to the seemingly solid ground. They may go for hundreds or thousands of years without anything happening on the surface, until one day, snap, shake, rattle, roll. People have just discovered a new fault, the hard way. Because many faults are not visible at the surface, or are of a kind that is not blatantly obvious to the untrained eye. Like the New Madrid fault, which in theory is smack in the middle of the earthquake-proof “stable interior craton” as John McPhee put it. Or the Humbolt Fault, running through Nebraska and Kansas.
Even people living in places where one would expect earthquakes can be taken aback when a truly strong one hits, or a new fault makes itself known. Christchurch, NZ is one that caught people by surprise because of its location and intensity. New Zealand is exceedingly tectonically active, but Christchurch was thought to be in less danger than other areas. As it turned out, the pattern of quakes and aftershocks raised serious speculation that the submerged caldera-like feature nearby had become active. I’ve not seen much about that recently, but parts of the suburbs around Christchurch have been declared too high-risk for rebuilding.
What is a fault? A weak place in the Earth’s crust that allows tectonic strain to turn into motion, a place where rock-layers don’t match across the fault. They range from microscopic lines inside otherwise solid-seeming sediment to things like the San Andreas and Heyward, New Madrid, and the Rhine Valley Rift Zone (actually a bunch of faults, old volcanoes, and other cool stuff you would not expect in Germany. And then there’s the Puy de Dome volcanic region within the Massif Central in France . . .) The ones you can have your picture taken beside are usually the exception.
http://www.ldeo.columbia.edu/research/blogs/malawi-earthquakes-assessing-danger-east-african-rift Has a lot of fascinating material. The image above comes from this site.
Ecuador, Japan, Peru, Nepal, Tibet, and a few other places are at the edges of moving tectonic plates, places where large chunks of rock are sliding under each other, or are grinding past. But the motion is not steady. The rocks stick, or the fault locks. Pressure builds up, and then things move, causing earthquakes. When a large fault has been locked for many years, tension and strain build up. Ideally, the fault will release that a little bit at a time. If not, then it makes international news and gets books written about it.
There are all kinds of faults. A normal fault is one where one side rises (the horst) and the other drops (a graben). When the usual up side drops, then you have a reverse fault. When they slide past, it is strike slip. When they do all that at the same time, it is a mess (or a dissertation).
When you add vulcanism into the mix, it gets more complicated. In places like the Afar Triangle and the Great Rift Valley in Africa, you get volcanoes because of faults. In other cases, the volcanoes cause local faulting, or interrupt older faults.
Most people associate earthquakes with California, Japan, and maybe South America, New Zealand, and Alaska. Missouri and Tennessee are probably very far down the list of “places that shake,” but the strongest documented quake in North America happened on the New Madrid in 1811-1812. Europe is also not quake free. Africa is pushing into Europe, and lifting the Alps. The Carpathians are also active, and the Rhine Rift and French volcanics are closer to dormant than extinct. A severe earthquake series in the 1300s shook down a lot of churches and castles in what is now southern Austria, and ended the use of a Roman bath on the Rhine in modern Germany. Iran is still plagued with quakes because it is a collision zone, while at some point quakes will finish tearing the Dead Sea open and letting in the Red Sea, which will break into the Great Rift Valley in Africa, creating a mess for whoever is living there in a few tens of thousands of years or millions of years.
I’ve felt one small earthquake, when I was in LA many years ago. It was sort of, “Oh. That’s interesting. Earthquake.” Why bother getting excited if no one else is?
Those who have read Peaks of Grace may recall Marta de Sarm looking at a map with black lines on it, and her confusion as to why someone would spoil an otherwise nice picture with the marks. She was studying a tectonic and mineral map of the Sarm Valley. The black lines show the faults. It is that faulting that makes the hot springs and mineral concentrations possible that allow the de Sarm (von Sarmas) family to protect itself and to survive in such a harsh area. Rada Ni Drako, too, deals with geology, since “her” estates sit on the edge of an active volcanic area (a bit like the San Juan Mountains in the US). It is an earthquake that leads to her long facial scar and eventually becoming ruling regent of Drakon IV.
Yes, geology slides into my fiction. It’s one of my many faults.