Miguel Ángel Rodríguez Pascua
By Sid Perkins
The Incan citadel of Machu Picchu in Peru is known for its marvelous stonework. But several structures at the site suffered through at least two earthquakes as they were being built, a new study suggests. Those temblors not only damaged walls, but also triggered a sudden change in construction techniques.
The study—an archaeological survey of three of Machu Picchu’s most significant temples—reveals more than 140 examples of damage. These include large blocks of stone that have shifted or whose corners have been chipped. Some of this damage can be attributed to slumping rocks or soil beneath the temples. But the movement of many damaged blocks, including substantial gaps between some formerly interlocking blocks of stone, was likely driven by seismic shaking from at least two major quakes, the team concludes. That’s because the type of damage seen on the corners of blocks embedded in the stone walls only occurs as they rhythmically clatter against each other during an earthquake, researchers report this month in the Journal of Seismology.
The quakes that rattled Machu Picchu likely occurred between 1438 and 1491 C.E., the period when the main parts of the city were developed and well before Europeans arrived in the area. A lack of written records or oral tradition make it difficult to narrow that window of time. Regardless of when those quakes occurred, construction thereafter shifted to a cheaper and easier scheme of merely stacking smaller blocks of rock (upper layer of stones, above right), not carving them so that they interlocked.
The Andes are no stranger to strong quakes. Besides a major subduction zone offshore, which can spawn megaquakes with magnitudes of 8 or greater, there are active faults inland as well as some that lie directly beneath Machu Picchu itself.
Source: Science Mag