In Central America the forces of nature are unleashed. On land and sea the hurricanes rage, and deep in the earth it shakes.
The last time there was such an accumulation of hurricanes was seven years ago. In the hurricane season 2010 "Igor", "Julia" and "Karl" had raged within a very short time in the Caribbean. Irma", "Jose" and "Katia" are now making their rounds off the coasts of North and Central America – following in the footsteps of "Harvey", which hit Texas shortly beforehand. A record-breaking hurricane congestion in the Gulf of Mexico. "Irma" is shaping up to be the strongest hurricane ever recorded, according to meteorologists. Haiti, Cuba and Florida can expect wind speeds of 300 kilometers per hour. The latest hurricane "Katia", which is expected to reach the Mexican coast between Tuxpan and Veracruz on Saturday, can not yet keep up with that. Still, meteorologists predict meter-high waves, drastic rains, hurricane-force winds, landslides and mudslides for Mexico.
Storms from above, earthquakes from below
The storm will hit a battered country. On Friday night, 137 kilometers southwest of Tonala in Mexico’s Chiapas state, the seafloor shook with a magnitude of 8.2. The tremors even reached the capital, Mexico City, 700 kilometers away. Although the number of deaths so far has been 32, far below the 1985 figure. Back then, 9000 people died in an 8.0 quake. But the number may increase in light of numerous aftershocks.
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Earthquakes have nothing to do with hurricanes, which this time happen to occur in the same week. What the two phenomena have in common, however, is that gigantic amounts of energy are discharged.
In the case of hurricanes, it’s the energy of heat that sunlight uses to heat Caribbean surface water over the course of the summer. Warm, moist air rises, cold air from the surrounding area flows in, and winds and the earth’s rotation create the typical hurricane torque. The more the global climate heats up, the warmer the oceans become, and with them the likelihood of hurricanes. "Science has enough evidence that it has to do with climate change that storms are getting stronger," says Joachim Schellnhuber of the Potsdam Institute for Climate Impact Research.
The energy of the plate
While the destructive energy of the autumn storms originally comes from the sun, the power of the earthquakes comes from plate tectonics: off Mexico, the Pacific plate is pressing under the North American and Caribbean plates. "The Earth’s plates are moving toward each other at several centimeters per year," says Marco Bohnhoff of the German Geosciences Center in Potsdam. "In the contact zone, the plates are jammed, so the energy builds up year after year."As soon as this energy is greater than the strength of the subsoil, the energy accumulated over decades or centuries is discharged. "Within a few seconds, the plates slip past each other by several meters."
Even though Mexico City was hundreds of kilometers away from the site of the earthquake, the consequences could have been severe. Because the city of 8.8 million is built on a dry lake. "This loose subsurface causes ground motion to intensify," Bohnhoff says. The epicenter of the 1985 quake was hundreds of kilometers away.
86 seconds until the quake
This time the city got off lightly. The feared tsunami also failed to materialize. The movement of the seafloor caused by the quake only triggered elevated levels of 60 to 120 centimeters above normal and left no significant damage on the coasts, Bohnhoff says. And there is another positive aspect to the quake: "The tension in the ground has now been relieved."This applies at least to the area that triggered the quake, which is unlikely to trigger another quake in the next few decades. However, the risk is now increased in the neighboring areas. There, for example in Guatemala and El Salvador, the quake had increased the tension. The quakes that are expected there anyway could now – statistically – occur a little earlier.
The time until the next quake must now be used for precautionary measures. "Building earthquake-proof is the safest but also the most expensive option," says Bohnhoff. However, in many regions, people do not adhere to the relevant building regulations. "A more efficient method is an early warning system." This also exists in Mexico City, he said. Before the destructive earthquake waves arrive, harmless but very fast "P waves" race through the subsurface, which can be used to sound the alarm. Since Mexico City is quite far away from the earthquake regions, there is enough time. "In this case, it was 86 seconds." That’s a lot of time, says the researcher. "Traffic lights can be turned to red, gas lines closed and people warned to leave their homes."Protection from a tsunami would at best be provided by walls. "But who wants to build a ten-meter-high wall along an entire coastline?."
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There is one thing, however, that people in the region must keep in mind as they prepare for natural disasters in the future. What protects against one adversity can have a devastating effect in the face of other forces of nature: "To protect against big storms in Haiti, the ceilings were reinforced with concrete slabs so that the roofs wouldn’t be taken off," Bohnhoff recounts. "In the 2010 quake, this was the undoing of many."