A fault zone deep beneath the eastern Pacific Ocean, about 1,000 miles off Ecuador, produces magnitude 6 earthquakes every five to six years in nearly identical locations and with consistent strength. This pattern, observed for at least three decades, stands out because most faults behave unpredictably. The Gofar transform fault, where the Pacific and Nazca plates slide past each other at roughly 140 millimeters per year, follows a more regular schedule. A study published in the journal Science explains the cause. Led by seismologist Jianhua Gong of Indiana University Bloomington, the research used data from ocean-bottom seismometers deployed in 2008 and again from 2019 to 2022. The instruments recorded tens of thousands of small earthquakes around two major events separated by twelve years. The findings show that specific barrier zones along the fault, characterized by complex geometry and fluid-filled rock, create a strengthening effect that stops ruptures and maintains the cycle. These barriers become highly active with small quakes before a large event and then quiet afterward. Although the Gofar fault poses no risk to coastal populations, similar barrier zones may exist on other oceanic transform faults worldwide. They could explain why many such earthquakes remain smaller than the available fault length would suggest, acting as natural limits on event size.
