Monte Carlo inversion of body-wave observations

An efficient Monte Carlo scheme has been implemented to generate families of velocity models, all of which are consistent with observations of dT/dΔ versus Δ and T versus Δ. Uncertainties in the observations are translated into uncertainties in the velocity structure when we examine the envelope of the family of models passed. As an example of the application of the Monte Carlo technique, we have inverted a set of dT/dΔ observations of P-wave arrivals measured at Tonto Forest Seismological Observatory in Arizona. These observations require that the resulting compressional velocity models exhibit two major discontinuities. The uncertainty of the depth to these discontinuities is 30–40 km. Contrary to other interpretations of these data, however, we have found models either with or without a low-velocity layer below the M discontinuity. In addition, some models contained low-velocity zones immediately above the two major discontinuities. The width of the envelope of models varies from 0.46 km/sec at 100 km to 0.06 km/sec at 1000-km depth.