The 9.0 earthquake off the coast of Japan that sent cable news networks’ ratings skyrocketing — and tossed CNN back in that ratings race at least temporarily — also served as a potent reminder of the power of broadcast television.

ABC, for instance, reported Thursday that 6 million people watched “Good Morning America” last Friday — the day Japan was hit with the worst earthquake in its history, followed by the devastating tsunami.

That was “GMA’s” biggest Friday audience in eight years. That’s also more people than watched prime-time CNN and Fox News Channel combined that night, as the networks updated their disaster news.

Fridays tend to be the least-watched day for the broadcast networks’ morning infotainment programs, but last Friday’s “GMA” was not only its most-watched edition of the week — it also spiked the show’s week-long ratings to its highest level in four years.

“GMA” played second fiddle to NBC’s “Today,” which clocked 6.6 million viewers that morning — the program’s biggest single-day audience since February 2010.

In average audience, “GMA” (5.2 million people) finished the week a close second to “Today” (5.94 million).

Late Friday night, ABC News’s “Nightline,” which also covered the catastrophe in Japan, attracted its largest Friday audience in 61/2 years — more than 5 million viewers.

On Friday in prime time, Fox News Channel maintained its lead over CNN, but it was a close race: FNC averaged 2.7 million viewers to CNN’s 2.6 million.

That day, CNN had pulled off the now rare feat of edging out FNC for the total day’s ratings lead.

CNN, which has taken a battering in the ratings (and in perception) of late, averaged 2.3 million viewers for the day last Friday — its biggest audience since the presidential inauguration in January 2009.

Since last Friday, CNN has been a competitive second to FNC, leading in prime-time ratings Saturday and Sunday nights with coverage of the disaster. CNN’s Saturday audience was nearly 270 percent greater than its average for the night this year.

By Wednesday — the most recent day for which numbers are available — FNC was firmly back on top in the ratings, with an average of 2.5 million prime-time viewers to CNN’s 1.6 million. MSNBC was well behind, attracting 873,000 viewers.

Friday through Wednesday, CNN had averaged 1.9 million viewers and FNC 2.2 million. MSNBC averaged 807,000.

Given the American public’s ongoing interest in the tragedy in Japan, industry pundits are forecasting that CNN will beat MSNBC in prime time and in total day ratings for the month of March.

It would be the first time that CNN has accomplished such a ratings feat since Michael Jackson’s death in the summer of 2009.

NBC renews comedies

NBC has renewed the soon-to-be-Steve Carell-less “The Office,” as well as “Parks and Recreation” and “Community” for next season.

Thursday’s news leaves only “Outsourced” and “Perfect Couples” among NBC’s Thursday sitcoms that are still awaiting word of their fate. And it looks as though those poor shows are going to have to wait until closer to May — when the network unveils its new prime-time plans to advertisers — to find out whether they will get the thumbs-up for another season. (NBC announced ages ago that it was picking up “30 Rock” for next season.)

Carell, the lead of NBC’s remake of Brit hit “The Office,” has said he’s leaving the show at season’s end, sending fans into an ecstasy of speculative recasting.

NBC’s new programming chairman, Bob Greenblatt, carefully complimented the three reordered sitcoms for being at the top of their game creatively, saying that “they represent the best of what the NBC comedy brand stands for in terms of originality, wit and sophistication.”

Although “The Office” is a solid demographic hit, the other two have small-ish, though rabid, fan bases. Many of those rabid fans are professional TV critics, who insisted Thursday that both “Parks and Rec” and “Community” have the potential to grow (that’s “can only get better” to you and I).

Some of the TV critics noted that “Parks” tends to attract about 2.8 percent of the country’s 18- to 49-year-olds, and “Community” about 2 percent. Some said the addition of Rob Lowe to the cast could do much for the ratings of “Park and Rec.” The little dears.