Greetings from the Hurricane capitol of the goddamn universe!
As I contemplate falling trees I wonder if the shear forces of laterally moving ground snap big timber.
Any of you California dopers ever see a bunch of stumps after a nice tremor?
In general, no. There may be a few trees that get toppled, or branches fall off, but that’s fairly rare.
And actually in earthquakes, the shear forces that act on the tree are coming from the tree itself. So in order for a tree to snap, it would have to be really top-heavy, or the trunk would have to be weakened somehow. We get more toppled trees from windstorms, car crashes, and greedy developers than earthquakes.
Speaking from the experience of living through the biggest recorded earthquake to hit North America, I can tell you that I didn’t see any trees snapped off.
In the middle of the action, trees were whipping from side to side and actually touching tops to the ground, but keep in mind that the earth is moving in the opposite direction and tilting and doing all sorts of jitterbug moves. This occurred in late winter, so all the trees were frozen, but they still didn’t snap. Dead trees, of course, were toast.
Wood-frame buildings fared very well (at least the ones that weren’t dislodged from their foundations or didn’t slide down the embankment). Concrete buildings suffered heavy damage.