It's high time for a mega earthquake in the South American country of Chile, scientists say, where tension's been mounting along a high-risk fault line since the late 1800s and recent shaking eased the stress only a little.

Two studies published in the journal Nature suggest the 8.1-8.2 magnitude quake in April that shook the city of Iquique in North Chile, killing six people and forcing a million flee their homes, was not the anticipated large-impact "Big One" event geologists believe will occur soon, according to a report by AFP.

Scientists have been keenly observing the north Chilean subduction zone, where a chunk of the earth's crust is pushing under the South American continent at an average rate of about 7 centimeters, or 2.75 inches, per year.

In 1877, the AFP story explains, a tremor with an estimated 8.6-8.8 magnitude fractured nearly 500 kilometers, or 311 miles, of the northern fault.

But researchers concluded the April 1 quake, which was followed by a notable aftershock, failed to relieve enough of the region's growing tension stress.

"Our results ... indicate that this [Iquique event] was not the earthquake that had been anticipated," wrote the authors of one of the studies, which was led by Gavin Hayes of the United States Geological Survey. "Significant sections of the northern Chile subduction zone have not ruptured in almost 150 years, so it is likely that future mega-thrust earthquakes will occur to the south and potentially to the north of the 2014 Iquique sequence."

Mega-thrust earthquakes are often followed by killer tsunamis.

"Observations suggest that enough strain has accumulated along this plate boundary segment to host an earthquake close to M9 [magnitude 9]," the team asserted.

The authors of the second study as well agreed "the remaining locked segments [along the fault zone] now pose a significant increased seismic hazard."

The second study predicted a future quake of magnitude 8.5 or more.

"The Big One may still be to come," said University of California geologist Roland Burgmann, who wrote a comment on the studies that was also published by Nature.