Although news media first reported the earthquake as an aftershock of the February earthquake, the initial geological summary given by the United States Geological Survey said it was a different earthquake. Though unchained by the regional stress caused by the February 27 earthquake, the March event was not a fast adjustment to February's thrust fault rupture between the Nazca and South American plates, but it was caused by normal faulting inside one of those plates. However, it has not been positively decided in which plate the earthquake occurred.