On recent seismic tomography for the western United States

In recent years, a number of relatively high resolution seismic tomography models for the uppermost mantle underneath the western United States have been published, and vigorous debate has ensued about their tectonic interpretation. I present a straightforward, yet quantitative, comparison between models in order to help establish a framework for geodynamic interpretation, and to help judge the role of tomographic theory vs. data selection. Mapped S and P wave anomalies are found to be remarkably consistent between models, which implies that seismologists are beginning to narrow down the structure underneath active continental margins to scales of ∼200 km. Large discrepancies between published anomaly amplitudes exist, however, and the models on the high end of the spectrum raise questions as to how they are to be interpreted in terms of temperature, composition, and melting.