Using data from the USArray Transportable array, I make two-station phase measurements on
surface waves recorded in the western US. These data are inverted for models of the
phase-velocity structure at periods from 25-100 seconds, roughly corresponding to depths of about
40-200 km. After publication, these models will be available on this website.
Phase-velocity map for 50 s Rayleigh waves
Phase-velocity map for 50 s Love waves
While studying the structure of the earth in the project described above, we became interested
in the way waves from an earthquake propagate. Because the USArray data covers such a large area,
we can use these data to get a snapshot of how the wavefield behaves. Here, we look at the
direction from which energy arrives. This information can be used to improve the two-station
measurements from above, and tells us something about the gradients of velocity changes.
At left is an example of arrival angle measurements for an earthquake
in the southwest Pacific, for 50 s Rayleigh waves.
It has been known for awhile that it can be difficult to separate out the
fundamental-mode surface-wave signals from overtone signals. In this project,
we examine the effect this has on several types of phase measurements.