How did dense rock structures beneath South America affect shaking during the Chile earthquake of 2010?

Research indicates that two previously undetected, anomalously dense rock structures located beneath the South American Plate played a significant role in the Chile earthquake of 2010. These structures likely acted to slow the rupture as it progressed along the fault line between the Nazca Plate and the South American Plate. By impeding the rupture process, these dense formations effectively intensified the shaking experienced at the surface.1