[1] The movie opens with a small tremor occurring in the hills outside Los Angeles near a United States Geological Survey (USGS) research post, cutting to a scene of a teenage girl on a date with her boyfriend at the Earthquake Ride at Universal Studios Hollywood.

Steve works closely with high-powered and wealthy real estate developer Wendell Cates (Robert Ginty) who faces losing money and his socio-political reputation from public fear of the possibility of the earthquake.

Not long after preparations and evacuations begin, the long-feared earthquake strikes, reaching 8.0 in magnitude and quickly followed by a 7.2 aftershock, causing massive damage and killing thousands; among the victims is Anita, who had been trapped in a high-rise condominium elevator with Laurie during the quake.

A more redeeming storyline is that of Kevin Conrad, who is transformed from a cut-throat reporter looking for a hot story into a more sensitive and humanitarian character deeply affected by the tragedy and devastation.

According to an interview in The Los Angeles Times, the film's theme was inspired by the bombing of Pan Am Flight 103, based on the idea of someone raising the alarm with no action being taken.

They feel sheepish about all the money they make from mediocre entertainment and are haunted by the fear that there's biblical-scale retribution in the works.”[4] Michael Hill of The Baltimore Sun praised the special effects and compared it to the poignancy of The Day After.

He also described it as “a throwback to TV films of more than a decade ago, "The Big One" is a well-made mess of a melodrama, hitting every one of its predictable notes with force and clarity, adding the bombastic percussion of nearly-spectacular special effects to an appropriately responsible cautionary message.