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What Controls the Along-Strike Segmentations of Shallow Slow Slip Events? Insights From 3D Numerical Modeling of Slow Slip Events Along the Hikurangi Margin, New Zealand

Session: Overdue?

Type: Oral

Date: 4/21/2021

Presentation Time: 10:00 AM Pacific

Description: 

Over the last two decades, geodetic and seismic observations have revealed a spectrum of slow earthquakes along the Hikurangi margin in New Zealand. Of those, shallow slow slip events (SSEs) that occur at depths of less than 15 km show a strong along-strike segmentation in the location of slip patches and recurrence intervals, which vary from ~1 to 5 years from offshore Tolaga Bay in the northeast to Cape Turnagain ~300 km to the southeast, respectively. To understand the factors that control this segmentation, we conduct numerical simulations of SSEs incorporating laboratory-derived rate-and-state friction laws and either a planar or a non-planar fault geometry. Among a wide range of parameters considered here, we find that a relatively simple model assuming non-planar fault geometry, derived from a recent model of the plate interface, can reproduce the observed segmentation of shallow SSEs. Our preferred model shows a spatial pattern of magnitudes and durations of SSEs that is consistent with observations, and captures the northward decrease of their recurrence interval. We also find that modeled SSEs release at least 60 % of the slip accrued due to plate convergence, which suggests that SSEs are the main mechanism of strain release along the Hikurangi margin. Our results indicate that the segmentation of SSEs’ recurrence intervals is favored by along-strike changes in both the plate dip angle and the plate convergence rate, in that modeled SSEs with longer recurrence times concentrate in the southern part of the fault (offshore Cape Turnagain) where the plate has a shallower dip angle and the plate convergence rate is lowest. Notably, the observed segmentation of shallow SSEs could not be reproduced as closely with a planar fault model, which indicates that a realistic plate interface is an important factor to account for in the modeling of SSEs. These results may help explain the segmentation of SSEs observed in other subduction zones as well, such as Nankai and Mexico.

Presenting Author: Andrea Perez

Student Presenter: Yes

Authors