Research

Surface-wave tomography

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. This research is published in Geophysical Journal International (Foster et al., 2013), and the models and data can be accessed below.

Phase-velocity map for 50 s Rayleigh waves

Phase-velocity map for 50 s Love waves

Models:
Click the links below to download models for Rayleigh and Love waves. Each zip file contains 11 text files, one for each of the following periods: 25, 27, 30, 32, 35, 40, 45, 50, 60, 75, 100 s. Each text file contains the latitude and longitude of the center of the pixel, pixel size, and phase velocity.
Rayleigh wave phase-velocity models
Love wave phase-velocity models

Data:
Click the links below to download two-station phase measurements for Rayleigh and Love waves. Each zip file contains 11 text files, one for each of the following periods: 25, 27, 30, 32, 35, 40, 45, 50, 60, 75, 100 s. The Rayleigh wave text files contain station location information and inter-station phase and phase-velocity measurements corrected for arrival angles; the Love wave text files contain station location information and inter-station phase and phase-velocity measurements, without arrival-angle corrections.
Rayleigh wave two-station phase measurements
Love wave two-station phase measurements

Arrival angles

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.

Overtone interference

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.