填空题.Heavy Rain Can Trigger Earthquakes暴雨会引发地震 Huge downpours of rain can trigger earthquakes in landscapes riddled with 1 and channels by increasing pressure within underlying rock, 2 a new study. It was already known that rainfall could cause tremors, but the 3 of water needed is much more than previously thought, says Steve Miller, a geologist 4 the University of Bonn, Germany. In recent years, 5 have documented small earthquakes that occurred after heavy rainfall in Germany, Switzerland and France. All 6 low in magnitude-meaning they could 7 detected by seismographs, but not felt by humans. Some experts have 8 that although the rainfall was heavy, the fact that rain could 9 an earthquake at all suggests that it takes extremely little to 10 a tremor. They concluded that the Earth's crust in a delicate 11 , teetering on the edge of a slight shake-up at any moment. 12 , in the new study, Miller disagrees, pointing out that 13 the three documented events happened in a specific type of landscape 14 as karst. Other geologists studying rain-triggered earthquakes did note that they 15 in karst geology, but they did not delve into the possible 16 . Karst landscape features a distinctive topography of soft carbonate rock riddled 17 deep fissures, underground channels and cave systems. These characteristic features are carved out 18 carbonate bedrock-typically limestone or dolomite-is 19 slowly by the action of slightly acidic rainwater over thousands of 20 . And these structures, says Miller, are key.