Seismic wave attenuation in the crust

Attenuation of seismic waves has been measured for many years. However, it is only recently that sufficient precision has been achieved and analytical techniques have been evolved which make possible the inversion of the experimental data [Anderson and Archambeau, 1964; Anderson and Kovach, 1964; Knopoff, 1964]. The resultant distribution of attenuation versus depth (usually expressed by the dimensionless quality factor Q) is a new and important source of information regarding the composition, state, pressure, and temperature in the earth's interior. As with all inversion problems, the more constraints on the solution in the way of direct measurements the fewer the solutions which satisfy the data. In this note we use seismic waves from nuclear explosions in Nevada as recorded by the long-range seismic measurements (LRSM) network of project Vela Uniform to obtain a direct measurement of Q for the upper continental crust. Profiles were constructed by selecting stations from the network in directions ESE, SE, and NE from the Nevada test site. The high standards of calibration of the stations, together with the large number of events, lead to a better precision than has heretofore been achieved with short-period seismic waves.