A major magnitude-8.1 earthquake struck roughly 600 miles northeast of New Zealand on Thursday afternoon, triggering concerns of a potentially damaging tsunami across large portions of the Pacific.

The risk spanned from New Zealand and Australia to as far east as Central and South America.

The 8.1 tremor was the third major earthquake in less than eight hours on the Kermadec Fault, which passes east of New Zealand. A magnitude 7.3 hit near New Zealand early on Thursday, followed by a 7.4 about 560 miles to the north a few hours later.

The National Weather Service Pacific Tsunami Warning Center issued tsunami alerts for Australia and New Zealand, numerous islands in the South Pacific, and along the western coasts of South America and Central America, for projected tsunami waves of up to 1 to 3 feet. Ecuador, Costa Rica, Nicaragua, Mexico, Chile, Colombia, and Peru in Central and South America were under these alerts, where tsunami waves were expected to arrive between midnight and the early morning hours on Friday.

The Pacific Tsunami Center projected the largest tsunami waves, of up to 10 feet (3 meters) or more in the Kermadec Islands, about 500 to 600 miles northeast of New Zealand, with waves of 3 to 10 feet (1 to 3 meters) in New Caledonia and Vanuatu.

The National Tsunami Warning Center concluded that there was no tsunami risk for places like California, Oregon, Washington, British Columbia and Alaska. A tsunami watch had been issued for Hawaii, but it has been discontinued.

Seismologists on Twitter stressed the expected tsunami is not anticipated to be comparable to the 2011 tsunami disaster in Japan.

A tsunami warning was issued for large stretches of New Zealand’s northeast coastline on March 5 after a magnitude 8.1 earthquake struck the Kermadec Islands. (Flaxworx NZ via Storyful)

New Zealand and Australia predictions

A tsunami warning, which had previously been in effect for New Zealand, was downgraded to an advisory as the largest waves had passed. New Zealand’s National Emergency Management Agency continued to caution about the risk of “strong and unusual currents and unpredictable surges at the shore.”

Earlier in the day, the country’s National Emergency Management Agency tweeted “TSUNAMI WARNING issued following Kermadecs earthquake.”

“People near coast from the BAY OF ISLANDS to WHANGAREI, from MATATA to TOLAGA BAY, and GREAT BARRIER ISLAND must MOVE IMMEDIATELY to nearest high ground, out of all tsunami evacuation zones, or as far inland as possible,” it wrote.

Action messages were dispatched via smartphone alerts and, in some areas, tsunami sirens sounded.

At a news conference, Bill Fry, seismologist for GNS Science, a leading earth science consultancy in New Zealand, projected tsunami waves up to 1 to 3 meters above sea level.

Officials in New Zealand urged residents “walk, run or cycle” to higher ground to avoid the chance of becoming stuck in traffic.

The first tsunami waves were forecast to arrive around 9:49 a.m. Friday local time in areas around Lottin Point, the easternmost point on New Zealand’s northern island.

Officials in New Zealand and Australia had cautioned that tsunami activity could persist for several hours, and that it was too early to relax precautions. With tsunamis, the first wave is not necessarily the largest.

Before the largest waves passed, reports of water departing the coastline, and muddy waters sighted in other areas, legitimized the concern of an offshore tsunami approaching the coast. Tsunamis, which have wavelengths of several hundred miles, often draw water away from shore before it returns abruptly when the tsunami strikes.

One buoy located over the open Pacific recorded a 3 to 5 inch spike in water levels. The height of a tsunami wave is minimal until the tsunami reaches the coastline and enters shallow water.

The Australian Bureau of Meteorology tweeted that a tsunami wave exceeding two feet had impacted the coastline.

Hawaii and Guam predictions

A tsunami watch was initially issued by the Pacific Tsunami Warning Center for Hawaii, but later dropped. First impacts could occur beginning at 4:35 p.m. Hawaii Standard Time. Impacts should be minimal, with only a slight increase in water levels. Tsunamis travel at roughly the pace of a passenger jet.

It was initially unclear what threat exists in Guam, Micronesia and the Northern Mariana Islands.

Context for earthquakes and the tsunami threat

It is extremely unusual for three severe earthquakes to occur within a 300 mile radius of a point in less than eight hours.

The first two earthquakes occurred far enough apart that they likely were not related. It is probable that the second quake was a foreshock to the third, the stress it released triggering another larger slip nearby. A quake is a foreshock to a larger event less than 5 percent of the time.

The first quake, nearest to New Zealand, released some of its stress horizontally, rather than being a fully “thrust” quake. That minimized the initial tsunami threat. The second quake, much farther north, was a shallow thrust quake, meaning part of one tectonic plate — the Pacific Plate — slid beneath the other, or the Indo-Australian Plate. That’s a recipe for a tsunami, but a serious one did not occur. Much of the stress appears to have been released deeper in the Earth than originally thought.

The third quake, a severe magnitude 8.1, also appears to have been a thrust quake, and is much stronger. That appeared to boost the odds of a damaging tsunami.

Fortunately, there were emerging indications that the greatest slip, or release of stress, may have occurred deeper in the Earth’s crust than where the slip initially began closer to the sea floor. That decreases the risk of a damaging tsunami. Initial estimates suggest that a slip of up to 30 feet occurred.

In some “megathrust” quakes, slips on the order of 50 to 100 feet — or more — are possible. That was the case with the infamous 2004 Indian Ocean tsunami, which struck west of Sumatra in Indonesia. It killed roughly a quarter-million people.

New Zealanders were forced to rush to high ground twice within six hours.

A magnitude-8.1 quake releases about 30 times more energy than a magnitude-7.0 quake. It’s the strongest quake to strike worldwide since May 26, 2019, when a magnitude 8.0 hit Peru.

The magnitude of an earthquake is a product of the extent of the slip, as well as the area affected. A greater slip area releases more pent-up stress. Each slip can also induce a domino effect that causes additional quakes.

Already, several aftershocks of magnitude 5 or greater had followed the main earthquake sequence, with a 6.5 quake also observed. Aftershocks should not get too much stronger than that; seismologists use Bath’s Law, which posits that the largest aftershock should be about 1.1 to 1.2 in magnitude less intense than main quake.

Earthquake waves recorded globally

Just minutes after the earthquakes first occurred, the ground began moving on the opposite side of the world — not enough that it could be felt, but enough that the highly sensitive seismometers that comprise the Global Seismic Network detected subtle motions. How sensitive are those seismometers? If it was possible to lift North America and place a dime beneath Los Angeles, a seismometer in New York would feel it.

A record section, or compilation of seismic data from all around the world, showed P and S waves — or body waves — which travel directly through the Earth. Some even skimmed the Earth’s molten core. Surface waves, which travel slower, crawled along the Earth’s surface.

Surface waves, which are strongest near the quake’s epicenter, are what cause the damage. P and S waves arrive earlier; that’s what allows officials in Japan, Mexico and Chile to occasionally issue earthquake early warnings seconds or minutes before the ground starts shaking.

Jason Samenow and Andrew Freedman contributed to this report. This report will continue to be updated as more information becomes available.