The Optimal Placement of Seafloor Geodetic Stations around Subducted Seamounts: A Case Study for Cascadia

We present design options for a seafloor geodetic network that is optimized for studying the role of subducted seamounts on megathrust locking. Subduction zones such as Costa Rica, Hikurangi, and Nankai are known for having prominent seamounts on the subducting plate. Due to their lack of prominence in bathymetric data because of thick sedimentary cover, seamounts in Cascadia have received less attention aside from studies related to seismic, magnetic, and gravitational data. Seamounts have been identified offshore Oregon approximately 30-70 km from the coast between 44° and 45° at about 10 km depth. As seamounts are subducted, they can alter the subduction mechanics by controlling the pathway for fluids and increasing fault roughness. The main question is whether these structures create increased locking on the subduction interface or promote aseismic fault slip, relieving a portion of the accumulated stress, by controlling the distribution of pore pressure or other fault conditions. Surface deformation created by aseismic slip and interseismic locking on the Cascadia Subduction Zone is simulated for a variety of scenarios. Synthetic data are created and inverted to test the performance of different seafloor geodetic network geometries and aid in developing the experiment design of future GNSS-Acoustic site deployments. We consider scenarios where aseismic slip is located directly over a subducted seamount or approximately updip of the seamount. The deformation models of Cascadia are constructed using Coulomb 3.3 which assumes a homogenous elastic half space. We assess the number and location of GNSS-Acoustic stations that are needed to observe a seamounts impact on subduction kinematics offshore Oregon. Utilizing GNSS-Acoustic observations could improve the knowledge of the effects of seamounts on subduction mechanics. GNSS-Acoustic data will give us more insight into the magnitude and distribution of the offshore locking state. The more we understand the impacts of plate roughness, the more we can understand megathrust earthquakes, especially in Cascadia, and improve our understanding of earthquake and tsunami hazards for the Pacific Northwest.