Monday, June 29, 2015

SCIENCE OF FICTION OR BOTH?

Okay, we live in Hollywood and everyone’s a film critic. Including me. SO, I would to write a few words about the movie that just hit the theaters "San Andreas". Many of you know that I'm a "young" (ha-ha-ha...) father again with two little creatures (one 3 years old and the other 4 months old) to take care of, which leaves me no time at all to go to the movies. In fact I have not been to the movies over the past 3 years, but this was a movie I had to see for obvious reasons. I design structures for earthquakes and I wanted to see what will happen to my buildings when the dreaded San Andreas hits.

So I went to see the movie. Well, I got far more than I was asking for and I’m now considering a move to Riggins, Idaho.I knew that a disaster movie has to have improbable scenes, breathtaking visual effects to keep people on the edge of their seats. I remember similar movies from the 70’s like the "Poseidon Adventure", "The Towering Inferno" and many others. But I think this was a little bit over the top.

Why? For several reasons.

Can a large, devastating earthquake happen at any time along the San Andreas Fault? Yes of course it can and it will as I’ve warned many times before. It is not the "if" but the "when" we have to ponder. Can it be a 9.3 or 9.5 as it is in this movie? No. By seismologist experts the San Andreas is capable of producing an earthquake in the magnitude of 8.3 to 8.5 max.

Can the San Andreas produce a canyon like the one in the movie, almost as big as the Grand Canyon? Not really. The San Andreas is a fault line where tectonic plates, like the Pacific plate and the North American plate, are moving side by side, parallel to each other not perpendicular to each other. Trenches may be created by earth collapsing on the surface, but very insignificant in size.

Can the San Andreas produce a tsunami at all? Very unlikely. The San Andreas is mostly on land and earthquakes created on land do not produce tsunamis. Tsunamis are created when an earthquake happens under the ocean floor and the ocean floor is moving up and down. This is not the case with the San Andreas, because this is a vertical fault moving only horizontally, roughly north and south, not vertically, up and down. Of course it can have some vertical component, seismologists do not know everything about the San Andreas, but a tsunami is very unlikely. The tsunami in the movie made the parting of the Red Sea from the Bible look like a kid's wading pool.

Can a tsunami, by the San Andreas or any other earthquake, create waves that crash onto the Golden Gate Bridge’s roadway, which is roughly 250 feet above the water level? The answer is a resounding no, because a really big tsunami is "only" about 30-50 feet high. Also in the movie this tsunami comes in like a big cresting, surfing wave which would not happen. Tsunamis come in like a rising sea wall of water. Remember the gruesome video footage of the Indonesian earthquake-created tsunami about 10 years ago, or the more recent devastating Fukushima earthquake-created tsunami.

Can a large earthquake created by the San Andreas cause this type of devastation with so many skyscrapers collapsing? Not at all. The movie exaggerates the scale of destruction, especially for tall buildings. Recently designed modern high rises are less likely to collapse. They will sway, some of them 10-15 feet at the top, but not collapse. We are going to have pockets of destruction, pockets of collapse and causalities, but it's not going to be an Armageddon. The toppling of buildings is very rare.

So what is the moral of the story? The movie is a good reminder that we live in earthquake country and we have to live our normal happy life, but we have to be prepared for the "Big One" (and for the smaller ones too). Earthquake retrofitting of vulnerable buildings is a must and earthquake preparedness should be taken very seriously. And when the San Andreas is awakened, then structural engineers will have a lot of work to do. As in the parting scene in the movie, the wife, Carla Gugino asks: "What do we do now?" Our hero of the movie Dwayne Johnson answers: "We start rebuilding our life" ... and we will need a lot of structural engineers... Dwayne, call me.