Research on splay faults in the Cascadia Subduction Zone (CSZ) from the Cascadia CoPes Hub was recently published in a special issue of Seismica. In the article titled “Late Quaternary Surface Displacements on Accretionary Wedge Splay Faults in the Cascadia Subduction Zone: Implications for Megathrust Rupture”, graduate student researchers Anna Ledeczi and Madeleine Lucas along with investigators Harold Tobin and Janet Watt took a closer look at splay faults along the CSZ.

Ruptures along splay faults in the CSZ can cause larger tsunamis compared to main fault ruptures due to their steep angle. Sediment from the Juan de Fuca plate gets scraped off as it subducts under the North American plate, creating piles of sediments known as accretionary wedges at the plate boundaries. When large earthquakes occur, multiple faults within the accretionary wedge can slip, affecting tsunami size and impact. Because the last big earthquake in Cascadia was in 1700, the likelihood of splay fault activity is uncertain. This new research analyzed high-frequency seismic data and crustal-scale multi-channel seismic data to examine the most recently active offshore faults. 

The data gathered spanned from Washington to northern Oregon, which will support tsunami and earthquake models to refine predictions and preparations for coastal impacts during future Cascadia earthquakes. The researchers determined there is a higher likelihood of megathrust earthquakes on multiple splay faults, which should be accounted for in future tsunami hazard modeling scenarios. Read more here.

a. Map of the Cascadia subduction zone with deformation front in yellow. The region where landward-vergent thrusting dominates (LVZ) is shaded pink. Black and pink tracklines are for low-frequency CASIE21 MCS reflection data collected on the R/V Marcus G. Langseth and for the high-frequency sparker and chirp taken in 2019 on the R/V Rachel Carson, respectively. Incoming plate boundaries shown in white. Relative plate motion between the Juan de Fuca plate and the North American plate indicated by white arrows at rates varying between 42 mm/yr in the north and 34 mm/yr in the south (DeMets et al., 2010). b. CASIE21 Line PD08 showing the megathrust fault, splay faults, and the location of the inner and outer accretionary wedge.

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