Read all All stone houses have been damaged, wrote a contemporary chronicler of the earthquake of 1356 in Basel, the most devastating in central Europe since time immemorial. Within a radius of 200 kilometers houses, churches and castles collapsed. Researchers from France and Switzerland have now discovered the fault zone south of Basel. The break was still very active, the geologists warn at a press conference in Basel. Now is the time to take the necessary precautions. In their investigations of the rock strata at Bruch, the researchers found that Basel was shaken by a severe earthquake every 1, 500 to 2, 500 years. In addition to the 1356 earthquake, the earth in the area of ​​Basel between 890 n. Chr. And 850 v. Chr. BC and between 850 BC BC and 6480 BC Violently trembling, the geologists report in the journal Science.

Thus Basel will probably not experience a massive earthquake in this century, says Peter Huggenberger from the University of Basel. The Director of the Swiss Seismological Service, Domenico Giardini, makes it clear that cycles of more than 1, 000 years are only supposedly long: "If we assume that Basel will be shaken by a violent earthquake sometime in the next 1, 000 years, there is a risk Born today at nearly ten percent. "And the building codes are not designed for an earthquake of the magnitude of the 1356 earthquake. According to estimates, four percent of the buildings would collapse. According to Giardini, insurance and public offices suffer losses of between 60 and 100 billion marks.

The first indications of the location of the fracture zone were found by geologists in historical testimonies. For example, a priest from Avignon mentioned cracks in the earth, says Mustapha Meghraoui of the University of Strasbourg and principal author of the study. In addition, the well-documented damage to castles had paved the way for breakage. With ground-penetrating radar, reflection seismics, electrical resistance measurements and several exploratory excavations, the researchers finally discovered the fracture zone that extends at least from the Jura mountains over eight kilometers to near Basel. Probably, however, the break even hit the heart of the city, says Meghraoui.
In the dredged trench, the break is clearly visible. A straight line separates the gray squeezed sand from the dark brown stone-infilled earth. The sand is part of the one earth block, explains Bertrand Delouis from the Swiss Federal Institute of Technology in Zurich. The earth, on the other hand, had been piled up during earthquakes, through river deposits and other processes, and lay on the other earth block, which is about fifty meters deep. However, the crack between the two earth blocks penetrates to a depth of 10 to 15 kilometers, says Delouis. The 50-meter-high fault has piled up in several hundred thousand years in an earthquake. The three quakes over the past 8, 500 years had moved the blocks almost two meters apart, the researchers found. In Basel, an estimation of the seismic hazard of individual quarters or even houses is possible within a few years. The researchers are currently working on a unique microzonation for Switzerland, which provides information about the underground beneath Basel's houses. The destruction of the last major earthquakes in Los Angeles or Turkey has shown that the local subsoil heavily influences the burdens on buildings, says Huggenberger. For example, buildings on soft ground - as if they were standing on pudding - would have to withstand far greater horizontal deflections than houses built on rock. Many of today's buildings would be damaged by about twenty centimeters even at the average earthquake of the 1356 earthquake.

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