Once you know the cause of the vibration that comes from the earthquake. Some companies even add spin black by default. Because it is sure to be another shake or not.
When you know the cause of the shaking from the earthquake. Some companies with a pretty black PI order because they are not sure whether there will be another shake?
When you know the cause of vibration that comes from some companies to order an earthquake off the sampan by default as they are not sure there will be a flicker or not.