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The Poisson's Raio Surrounding the Subduction Megathrust

Description: 

Hydrologic and lithologic variations along the plate interface in subduction zones control the strength and slip behavior of megathrust faults. Many models of plate interface fault slip behavior invoke high pore-fluid pressure to explain the variability in rupture behavior. High pore-fluid pressure can explain apparently high Poisson’s ratio (> 0.33, Vp/Vs > 2) within a low-velocity zone (LVZ) along the plate interface, often inferred from studies of the scattered P-to-S seismic wavefield. We further investigate this region with array-based deconvolution which allows for identification of the receiver-side, surface-reflected and back-scattered P-to-P wavefield, and which has finer resolution than the upgoing P-to-S scattered wavefield. Using the timing of surface-reflected P-to-S and P-to-P scattered phases in both the Alaska and Cascadia subduction zones, inversions for LVZ properties result in Vp/Vs < 2. Using both array-based and time-domain deconvolved teleseismic waveforms, we show that Vp/Vs estimates that depend on the upgoing P-to-S scattered phases might be biased toward high Vp/Vs (> 2.2) owing to their lower volume resolution and the inherent frequency limitations in extracting these signals from P coda. These results indicate that anomalously high Vp/Vs found while including the upgoing (direct) P-to-S scattered mode may instead be an artifact of using band-limited signals or scattered-phase interference. These findings remove the observational requirement for a thick region of high pore-fluid pressure and allow for alternative hypotheses to explain the suite of fault slip behavior along the subduction zone plate interface.

Session: Earth’s Structure from the Crust to the Core - I

Type: Oral

Date: 5/1/2024

Presentation Time: 08:15 AM (local time)

Presenting Author: Michael

Student Presenter: No

Invited Presentation: Yes

Authors