An empirical relationship between seismic attenuation and velocity anomalies in the upper mantle

Abstract

We use recent P wave attenuation (Q(a) -1) and velocity (V(p)) tomographic models of the Tonga/Fiji region to obtain an empirical relation between attenuation and velocity for the upper mantle. The attenuation and velocity anomalies show a strong inverse correlation, allowing the determination of an empirical relationship. The relationship is similar to a predicted relation derived from laboratory experiments on peridotite and dunite, assuming the observed anomalies result from temperature variations. The results here suggest that the observed anomalies are generally consistent with the effect of temperature, and demonstrate that the combination of velocity and attenuation data provides powerful constraints on the physical state of upper mantle materials. We find that the chosen geotherm and activation energy has a strong effect on the position of the solidus within the seismic data.