A wave of attention has swung my way in the wake of this YouTube video (which looks more like a film), taken in China shortly before the Sichuan earthquake of 12 May. It's three and a half minutes of a static shot showing three iridescent clouds along the horizon. Everybody says it must be earthquake lights, but the clouds don't match any of the characteristics of earthquake lights, which are more like auroras. Instead they look like haloes related to the high sun (at about 1:30 local time), such as the uncommon circumhorizontal arc (see a spectacular example here). Spotting haloes is a wonderful hobby, because nobody pays much attention to the sky and there's a lot going on up there. Just don't mistake them for earthquake lights.
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I agree it is an iridescent could. However, do you think an escape of steam/gas from the fault line, preceding the earthquake, may have caused the sudden simultaneous condensation of the clouds; they look linear, along the fault (need to know where the camera and the fault rupture was). From the Atmospheric Optics website:
“Iridescence is seen mostly when part of a cloud is forming because then all the droplets have a similar history.”
The droplet diameter has a restricted size range, as the droplets form at the same time in response to a sudden event, release of steam/gas perhaps. There is enough here for further exploration.
It is possible from the sun & clouds position, to precisely calculated droplet diameter. Also, the cloud is not cirrus, its too blowy, looks like cumulus. Lastly, if you carefully fast forward and rewind the video, you will find the clouds are rising and seem to be dissipating.