[J03-1] Deformation of the lithosphere: Integrating seismology and geodesy through modelling I

[J03-1-04] Hidden Earthquake Potential in Plate Boundary Transition Zones

^○Kevin Furlong, Matthew Herman (Penn State University, University Park PA)

Plate boundaries can exhibit abrupt changes in their tectonic deformation at triple junctions and other plate boundary transitions. At such locations, the superposition of two crustal deformational regimes may combine to generate displacement signals that do not reflect the actual earthquake cycle strain accumulation in the region. Two examples of this effect are in the vicinity of the Mendocino triple junction (MTJ) along the west coast of North America, and at the southern end of the Hikurangi subduction zone, New Zealand. In the region immediately north of the MTJ, the observed signal (GPS) of crustal displacements is intermediate between Pacific and Juan de Fuca (JdF) motions. With distance north, the signal rotates to become more aligned with JdF - NAm displacements - the motions expected along a coupled subduction interface. The deviation of that subduction interface signal near the MTJ has been previously interpreted to reflect clock-wise rotation of a coastal, crustal block and/or reduced coupling at the southern Cascadia margin. The geologic record is consistent with the signal reflecting the combined effects of northward crustal shortening (on geologic time scales) associated with the MTJ Crustal Conveyor overprinted onto the subduction earthquake cycle signal. At the Hikurangi to Alpine Fault transition in New Zealand plate interactions switch from subduction to oblique translation along the Alpine fault system. Here the signal recorded by GPS shows a reduction in plate motion-directed displacements, which has been interpreted to reflect reduced coupling. This signal records both the subduction interface coupling related to the megathrust earthquake cycle, and the shear deformation produced by the extensive right-lateral shear of the Marlborough Fault system. The relevance of this effect is seen in the recent (November 2016) Kaikoura earthquake, which ruptured the megathrust interface and produced strike slip displacements on upper-plate crustal faults.