In the theatrical cut of the film (not the "television version," where this shot is excised), "cartoon-like" animated blood is "sprayed" on the camera lens when the elevator hits the bottom of the shaft. The effect is poorly executed, and ruins an otherwise nerve-wracking scene.
There are two main theories as to why the animated blood sequence was created, but first the facts must be addressed: After reviewing call sheets and production reports from director Mark Robson's personal archives, the fan web site "earthquakemovie.com" has uncovered the fact that the elevator sequence was shot three times, on three separate days (March 26, March 27 and April 4, 1974). Whether this indicates that certain shots of the elevator sequence were simply spread out over three shooting days, or whether it was the result of the sequence being problematic (and thus, shot and reshot again) is unclear. What is telling, is the production report lists several stunt artist's injuries from the final day of shooting the elevator crash on April 4, 1974 (including Gary Epper and Stephanie Epper). The end result of the "animated blood" sequence in the final film is telling, since one of the theories hinges on the fact that shooting the sequence was problematic.
The elevator set itself was a three wall set built out of polystyrene plastic, which was suspended three feet off the stage floor (Universal Stage 27). The rig was held in place by water driven pumps, which were designed to drive the suspended set down at a faster rate than the 13 stunt artists inside would fall (thus, providing a "free fall" effect). As the set hit the stage floor, the polystyrene walls would collapse on the stunt artists. Also visible in the sequence are several areas of the set and of the stunt artists clothes, which have forming blotches of blood that last a few frames, revealing the fact that the stunt artists and / or the set itself was rigged with bladders of "stage blood" which would deploy on impact. This is visible for three or four frames prior to the infamous "animated blood" shot.
Which brings us to the two theories:
THEORY ONE: Based on the problematic nature of the shooting, and the probablility that director Mark Robson never got what he wanted from the shot, he opted to "fix it in post production." Since the crash was shot three times over two weeks, the break in shooting between the second and third attempts suggest this was time for the special effects department to continue working to get the effect right. After three attempts, the plug was pulled on the scene (and possibly due to the injuries sustained by the stunt artists on the final day), and an optical effect was added in post. This theory is further supported by the fact that the optical effect of the animated blood was superimposed over a still frame of the elevator crash, with the stunt artists splayed about on the elevator set, and not a moving shot (the moving shot may not have worked).
THEORY TWO: This theory holds that Robson finally got the effect he was after from the sequence on the third try. Crashing elevator, falling stunt artists, and splattering blood, which would have been a very effective (and gory) sequence. However; the MPAA rated "Earthquake" some time around October, 1974 (for a November 15, 1974 release date), and the violence and gore of the scene may have been a red flag for the MPAA to slap an "R" rating on the film (remember, this was 1974). An "R" rating on "Earthquake" would have doomed the picture, cutting out the huge teenage market, so the scene may have had to be cut. With little time to reshoot the scene (and likely, no money), Robson opted to cut the scene and add the animated blood optical effect in post production, rather than cut the scene earlier or some other option.
Regardless of the motivation for Robson and Universal opting for the animated blood option, the scene made it into the final print of the film.