Alaska is one of the most tectonically active areas in North America. A series of tectonic processes have shaped the unique and complex geological structures. Although geological surveys conducted on the Earth’s surface play an important role in understanding these processes and structures, mapping the subsurface structures can provide additional constraints on the tectonic history of this region.

Seismic imaging, utilizing the information provided by the seismic waves that travel through the Earth’s interior, is one of the most important method to map the subsurface structures. Traditionally, ray theory is used to model the seismic waves, which often results in inaccuracy and low resolution in the imaging result, because the ray theory is a high-frequency approximation and is only valid when the scale of heterogeneity is larger than the wavelength. Taking advantage of the high-performance computing facility, the adjoint tomography method, or sometimes also referred to as the full-waveform tomography method, has been developed during the past two decades to address the limit of the ray-based method and improve the accuracy and resolution of seismic imaging.

Conducting tomographic studies in Alaska was challenging in the past because the area lacked seismic stations, especially in the northern and western parts, due to the harsh environment for station deployment. Recently, the coverage of seismic stations has been significantly improved due to the deployment of USArray after 2016. Utilizing this groundbreaking dataset, we map the shear velocity and anisotropy in the entire Alaskan crust and uppermost mantle with the adjoint tomography method.

In this presentation, I will first introduce the geologic setting and the tectonic history of Alaska. Then, I will talk about the technique of seismic imaging in general, and the adjoint tomography method. Finally, I will go through the procedure of our study, and briefly show our result.