The wording in Steve Winslow's answering machine message changes between scenes (when he leaves it from the airport and when other characters listen to it later).
Dan Milford goes into the shed without a jacket and inside he is wearing a jacket. When he leaves he is not wearing it.
South African Trade Minister David Motubu, a black man, could not have held any political office in South Africa during the apartheid era, which did not end until four years after the movie was made.
Daniel Motubu is introduced as a potential candidate for Prime Minister of South Africa. That position was abolished in 1984.
Houses in California do not have basements, at least not as large as the one in the Winslow's house.
Clare tells her boss Ray Goodrich that the major 5.7 foreshock that has preceded that "Big One, happened at the intersection of the Newport-Inglewood and Elysian Park Faults. In reality these fault lines run parallel to each other and at no point intersect.
When Claire opens her trunk after the quake, the "boulder" would have been too heavy for her to open it. However, she does open the trunk and when she closes the trunk, the "boulder" is still in the same position. It should have slid down when the trunk was open.
After the "Big One" hits, Clare Winslow is determined to get from Los Angeles City Hall to her daughter at her house in Pasadena. The distance between those two places is roughly ten miles. Under the best of circumstances that trip would take roughly 3 and 1/2 hours by foot. Clare begins her trip roughly before nightfall around 5 PM. At the end of the movie it's roughly 9:30 PM which is indicated by a character's wristwatch. It's highly unlikely in the heavily damaged and fire ravaged city that Clare could make the trip so fast.
The night before the "Big One" hits the city is rocked by 5.7 foreshock. The next morning Clare Winslow seems to believe that this is the major quake she's been predicting. Although Clare states that she would like to review incoming data she seems generally to believe that the worst is over. Only after studying global positioning satellite surveys sent to her does she realize the "Big One" is on its way. However, in an earlier scene Clare's associates Jerry Solaway and Dan Milford discuss the pattern of effects that occur according to her earthquake prediction theory. Solaway says that a day or so before the main quake hits there is 5.7 foreshock. Thus, Clare and company should had been extremely worried the minute that quake hits.