Where does a person put their hands when the floor suddenly moves?
This question again brought the living rooms and parking lots of the Coachella Valley into consideration with the 5:56 p.m. PT magnitude 4.9 earthquake that struck about 12 miles northeast of Indio on Jan. 19, according to the U.S. Geological Survey. This earthquake brought the special shock of looking up from dinner to check the lighting fixtures and take mental stock of whatever is on the top shelf. It also brought something that Californians know is part of the package deal: aftershocks. By early evening, at least 17 earthquakes had been attributed to the sequence.
For most people, the most important thing that can be learned from a moderate earthquake is not the number itself, but the fact that the body reacts faster than the mind. The most important thing that is always being stressed in earthquake preparedness is that there are only a few things that can be done to avoid injuries. In a building, the most important thing is to DROP, COVER, and HOLD ON until the shaking stops, and then be cautious, taking into consideration the broken glass and loose objects. This is also the most important thing that people always seem to forget when an earthquake occurs.
And then there are the ones that seem so normal until they become something else. If you are in your bed, the thing to do is to just hunker down and protect your head with a pillow, unless something heavy is on top of you that might fall. Outside, the thing to do is to get as far away from buildings, streetlights, and power lines as you can. And when driving, the need to “get out of the way” has to be translated into something less panicked: pull over to safety and stay in the car, avoiding stopping under overpasses or power lines. But beneath all that very practical advice is a truth that never changes: Earthquakes are not a weather pattern with a countdown clock. They begin when the friction gives way and a fault moves, and the energy is released in the form of waves through the rock.
California is a state that sits on top of a very complex fault system that is a result of two giant plates, and according to the UC Berkeley Seismology Lab, the Pacific Plate moves northwest past the North American Plate at two inches a year, with the San Andreas Fault as the main boundary and a series of smaller faults throughout the state. This is exactly why the sudden motion is so unfair. Magnitude, on the other hand, can be very deceiving to those who felt the earthquake as “barely anything” or “the whole house jumped.” Magnitude is a number that measures the earthquake, while what the residents felt is distance-dependent, depth-dependent, soil-dependent, and construction-dependent.
As for measuring the actual experience, there is also intensity, and according to the UC Berkeley Seismology Lab, the Modified Mercalli Intensity Scale is a measure of shaking based on its effects, such as people waking up, furniture shaking, and chimneys cracking, rather than a calculation. One legend seems to get around with a definite shake: the idea of California falling off and sinking into the ocean. The Berkeley Seismology Lab has directly addressed this legend: “Earthquakes in California are horizontal, not giant sinkholes or land dropping into the sea,” and “No part of California is sitting on an ‘edge’ that can suddenly break off.”
The coastline is moving on a geological timescale, but not like it does in the movies that immediately come to mind. The 4.9 is not the biggest problem facing the state, but it is a good reminder. The best time to use earthquake knowledge is in the quiet moment because the loud one does not schedule itself.
