比萨斜塔经历地震为何还能屹立不倒
New research has revealed how the iconic Leaning Tower of Pisa has managed to stay standing - and intact - in the face of four strong earthquakes and a precarious lean of five degrees.
意大利的标志性建筑比萨斜塔有5度的倾斜度，而且还历经4次大地震，却依然屹立不倒，完好无损，最新的研究揭开了这个谜底。
The vulnerability of the Unesco World Heritage Site has mystified engineers and scientists for millennia. Moderate seismic activity was expected to significantly damage the 58m tall Tower, or even result in collapse but, incredibly, this has not happened.
A research group of 16 engineers at the University of Bristol has now discovered that the considerable height and stiffness of the Tower, combined with the softness of the foundation soil, ensure it doesn't resonate with earthquake ground motion.
This phenomenon is known as dynamic soil-structure interaction (DSSI) and the Tower now holds the auspicious title of world record holder in DSSI effects.
"Ironically, the very same soil that caused the leaning instability and brought the Tower to the verge of collapse, can be credited for helping it survive these seismic events," said Professor Mylonakis, head of the Earthquake and Geotechnical Engineering Research Group at the University of Bristol.