Coda

Observations and analysis of seismicsc attering in the heterogeneous earth have grown from the initial observations of Aki in the 1960s into a well-developed subfield of seismology. The area presents many challenging and interesting problems for seismologists today and there are many areas of fruitful research. We focus on a small subset of areas of research within the general area of, ‘‘coda study,’’ that can be most directly tied to Kei’s early work in this field: scattering coefficient, coda Q, coda normalization method, and the radiative transfer approach. These are the most useful tools in the interpretation of high-frequency seismograms. In each of these areas, Kei provided initial inspiration through insightful observation and well-thought out models for his observations. The results of ongoing work in these areas have provided insight into the complexity of wave propagation in the earth and have yielded new insights into the character of the earth’s lithosphere. They have also provided reliable means to obtain practical information like relative site amplification factors and relative source radiation as a function of frequency.