Professor Dean Whitman, of the Department of Earth and Environment, studies earthquakes. He answered questions about the geophysics of the destructive event.
Most earthquakes occur on or near a plate boundary between two tectonic plates. This did occur very near the plate boundary between the Caribbean Plate to the north and the South American Plate to the south. The Caribbean Plate is moving to the east relative to the South American Plate at about two centimeters, or about an inch per year.
Over time, the stress caused by that motion along the plate boundary builds up in the Earth's crust. Eventually, that stress becomes so great that it overcomes friction holding the two sides of the fault together, and it slips. That rapid slip is what an earthquake is.
Q: Why were these earthquakes considered unusual?
These earthquakes are somewhat unusual because they're what is being called a doublet. In some cases, earthquakes will occur in clusters where you will have two or more large earthquakes occurring in a short period of time. But this was a little bit unusual in that the period of time between the shocks was very short, less than a minute. Perhaps we are going to need to look at this as just one very complex event.
One feature of this pair of earthquakes is that it's likely that the first event damaged some buildings, which then, when the second shock came in, completely collapsed. The first event often will create damage to the building, but the building will not fail. Then the second set of shaking will come through, which will cause a complete collapse.
Q: Are earthquakes happening around the world connected?
People often ask about the linkage between earthquakes. Both yes and no. If the earthquakes are near each other, certainly one earthquake can trigger another, and that certainly appears to be the case here, where we had a smaller magnitude 7.2 earthquake triggering a larger magnitude 7.5 earthquake about a minute later.
When earthquakes are very far away from each other, this usually isn't the case. For example, there was an almost magnitude 6.9 earthquake in Japan and a magnitude 5.5 earthquake in Northern California. These are so far away that the influence of those earthquakes is largely not going to affect something halfway across the globe. It just physically can't really happen.
Q: Are earthquakes becoming more frequent?
A lot of times people ask, "Are the numbers of earthquakes increasing because we hear about them all the time?" There's really no evidence for that. What has changed is that we now have so many means of communication where people are informed of things instantly.
Earthquakes are occurring at the same rate globally as they always have. In fact, small earthquakes are occurring all the time—hundreds, thousands every day across the world. It's just when you get to the larger events, they occur less frequently.
Q: Why was this earthquake so destructive?
This earthquake was especially destructive for a few reasons. For one thing, its size—over magnitude 7—was certainly capable of creating damage. The other thing was that it occurred on land and at a relatively shallow depth in the Earth's crust, so it was close to the Earth's surface.
In many parts of the Americas, much of the construction is masonry construction. In some places, that masonry is unreinforced by steel. This type of construction is particularly susceptible to earthquakes because these structures will break rather than bend. Much better types of structures are those built out of steel frame or wood frame, which can bend but not break.
Q: Can scientists predict when the next big earthquake will strike?
While we cannot predict exactly when earthquakes will occur, there is ongoing research. At this time, we can't predict when earthquakes will occur like we can for predicting hurricane landfalls.
There's some very interesting research going on here at FIU led by Shimon Wdowinski, who's using techniques known as space geodesy to measure how the Earth's crust is deforming over time. They utilize data taken from satellites in orbit that beam radar waves down to the Earth's surface, and they can measure how the Earth's crust moves over time. By analyzing this, they can determine whether or not a particular section of fault is ready or susceptible to slipping. We just can't tell when exactly it will break.
Q: Will there be more earthquakes in Venezuela?
There is an aftershock sequence occurring from these events. Just yesterday there were two magnitude 4-plus earthquakes near Caracas. These aftershocks will continue over the next several months. In general, they will become smaller over time, and they will also occur less frequently. But the sequence will continue for a year or so.
