Spatiotemporal evolution of slow slip events in a nonplanar fault model for northern Cascadia subduction zone

<jats:title>Abstract</jats:title><jats:p>Slow slip events (SSEs) are identified as the quasi‐stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones. In the well‐instrumented Cascadia margin, a class of <jats:italic>M</jats:italic><jats:sub><jats:italic>w</jats:italic></jats:sub>6.0 slow slip events arise beneath Port Angeles every ∼14 months, as inferred from two decades of continuous geodetic monitoring. The along‐strike bending of the incoming oceanic plate beneath north Washington is a unique geometric feature whose influence on slow slip processes is still unknown. Here we incorporate a realistic fault geometry of northern Cascadia in the framework of rate‐ and state‐dependent friction law, to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault. The modeled SSEs capture the major characteristics revealed by GPS observations. The central 150 km long fault segment beneath Port Angeles acts as a repetitive slip patch, where SSEs appear every ∼1.5 years with a maximum slip of ∼2.5 cm. Two minor slip patches with smaller areas and cumulative slips straddle this central slip patch. The along‐strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone, suggesting strong geometrical control on the slow slip process. This correlation holds even after removing the effect of <jats:italic>W</jats:italic>/<jats:italic>h</jats:italic><jats:sup>∗</jats:sup>, ratio between velocity‐weakening SSE fault width and characteristic nucleation size. Besides the GPS‐detectable fast‐spreading phase, we find that each SSE cycle consists of deep pre‐SSE preparation and post‐SSE relaxation phases, which may be the driving mechanism for the deep tremor activity between major SSE episodes discovered in Cascadia.</jats:p>