Earthquakes are not laughable affairs. The breadth of the destruction and depth of the human tragedy demand only a solemn response.
Yet, the science (or shall we call it an art?) of earthquake prediction is a different matter. Here -- while full chuckles are perhaps still inappropriate -- we may at least be allowed a brief quiver of the lips.
That is also the look on most visitors to Japan when they experience their first tremor. If not veterans of some other earthquake zone, these folks will hold fast to their grins until the bouncing is finally finished.