Constraining the relationship between orogenesis and seismogenesis along the southern Cascadia forearc

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Mountain building in the Pacific Northwest region of the United States of America shows significant variation along its length (northern California to the US-Canada border). In particular, the region between the coastline and the active volcanic system has the highest elevations over the broadest region in northernmost California (between 40 – 42 degrees latitude) compared to the same locations in Oregon and Washington State. This likely arises from the complex interactions between the northern portion of the San Andreas Fault System that can generate magnitude 7 earthquakes and the Cascadia Subduction Zone in the Pacific Northwest, thought to be able to generate magnitude 9 earthquakes. In addition, relatively newly-discovered phenomena (episodic tremor and slow slipping earthquakes) are prevalent in this portion of the margin, and may contribute to mountain building, and therefore earthquake potential. The purpose of this project is to better understand how deformation in this portion of the Cascadia forearc relates to mountain building and earthquake style and genesis by analyzing a recently acquired dataset created from subsurface images of the upper 40 miles of Earth. Understanding the interrelationships between these different geological characteristics in northern California and comparing them to what is observed further to the north in Oregon and Washington State, may also provide insights into the hazard and mountain building processes in those regions. The team will also engage with the local community in northern California to communicate the basic geologic and tectonic context of the region; develop a Wikipedia page to make the experiment, project goals, and major results accessible to the general public; and contribute to the training of graduate and undergraduate students.The structural and rheological properties of a subduction margin directly influence seismogenesis and overriding plate deformation, but several aspects remain poorly understood. The research team will investigate how the composition, structure, and seismic character of the southern Cascadia margin (northern California) contributes to broad uplift, topographic evolution, and high rates of episodic tremor-and-slip by analyzing newly-collected data from 60 nodal seismic stations with pre-existing and currently operating seismic stations. To constrain the characteristics of the forearc, the team will apply both robust and novel seismic methodologies, including: 1) teleseismic receiver function imaging, 2) body and surface wave ambient noise interferometry, 3) a joint inversion of receiver functions and surface wave dispersion measurements to obtain a new 3D shear-wave velocity model of the region, and 4) focal mechanism analysis. Insight into how these characteristics relate to the expression of subduction in southern Cascadia will then be used to better understand what controls variability in the manifestation of subduction elsewhere along the Cascadia margin. In addition, these high-resolution images of forearc crustal structure will allow for the better understanding of the possible physical, compositional, and rheological controls on the processes of episodic tremor-and-slip.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.