SCATTERED WAVE IMAGING OF THE CRUST AND UPPERMOST MANTLE ALONG STRIKE IN THE ALASKA AND CASCADIA SUBDUCTION ZONES

207 pagesThis dissertation details efforts to image the along-strike continuity of major seismic discontinuities in subduction zones using dense (~5) earthquake P waves. The time series of scattered phases are referred to as “receiver functions” (RFs) though they are slightly different from traditional RFs. Chapter 1 investigates the location and orientation of the subducting Juan de Fuca (JdF) Moho beneath Mount St. Helens (MSH) using RFs from a dense seismometer array that was deployed in a circular area around the volcano. Two-dimensional (2D) migration and three-dimensional (3D) common-conversion point (CCP) stacking imaging methods were used to reveal a continuous JdF slab at 68±2 km beneath MSH, which is the shallowest directly imaged subducting slab beneath an arc volcano in the world. Between 2016 and 2018, we deployed, serviced, and recovered 36 broadband seismometers in a dense array across the road system of southcentral Alaska, which provided the key data for Chapters 2 and 3. RFs from that array and two other dense seismometer deployments across southcentral Alaska were generated using an improved method that accounts for variations in surface geology. 2D migration of the RFs revealed the Yakutat terrane, an oceanic plateau, subducting down to at least 110-km depth on the eastern half of southcentral Alaska. 3D CCP stacking revealed a continuous LVZ atop the Yakutat terrane for over 450 km along strike, at depths