[1] As a civil engineering term, it defines the percent of a cycle of oscillation that is absorbed (converted to heat by friction) for the structure or sub-structure under analysis.
[2] Usually it is assumed that the equivalent dumping coefficient is linear, which is to say invariant compare to oscillatory amplitude.
Modern seismic studies have shown this not to be a satisfactory assumption for larger civic structures, and have developed sophisticated amplitude and frequency based functions for equivalent dumping coefficient.
When a building moves, the materials it is made from absorb a fraction of the kinetic energy (this is especially true of concrete) due primarily to friction and to viscous or elastomeric resistance which convert motion or kinetic energy to heat.
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