Comment on the validity of the following argument: “The earthquake source may be thought of as a delta function that generates energy at all frequencies. However, Earth’s lowest normal mode has a...

Comment on the validity of the following argument: “The earthquake source may

be thought of as a delta function that generates energy at all frequencies. However,

Earth’s lowest normal mode has a period of 54 minutes. Thus, the normal mode

representation for seismic displacements is incomplete because it cannot represent

very long period energy generated by the source (i.e., periods longer than 54

minutes).’’