Abstract
We use numerical modeling and wavelet analysis to study slow slip events (SSEs) that occur along the shallow Hikurangi margin. The first part of this study is motivated by geophysical observations that suggest that temporal changes in pore fluid pressure correlate with shallow SSEs at Hikurangi. These fluctuations in pore fluid pressure are attributed to fluid migration before and during SSEs, which may modulate SSE occurrence. To examine the effect of pore fluid pressure changes on SSE generation, we develop numerical models in which periodic pore-pressure perturbations are applied to a stably sliding, rate-strengthening fault. By varying the physical characteristics of the pore-pressure perturbations (amplitude, characteristic length, and period), we find models that reproduce shallow Hikurangi SSE properties (duration, magnitude, slip, recurrence). Our results indicate that large permeability values of approximately 10 (super -14) to 10 (super -10) m (super 2) are needed to reproduce the observed SSE properties. Such high values could be due to transient and localized increases in fault zone permeability in the shear zone where SSEs occur. Our results suggest that SSEs may arise on faults in rate-strengthening frictional conditions subject to pore-pressure perturbations. In the second part of this work, we use wavelet methods, which are mathematical tools for analyzing time series, to analyze GNSS time series of shallow SSEs at Hikurangi. We apply a wavelet transform to GNSS data from Geonet and then stack the wavelet details over different GNSS stations to determine the timing of SSEs. Based on this detection method, we build a catalog of shallow Hikurangi SSEs, which we then compare with independent SSE catalogs. In addition to cataloging SSEs, we systematically study their occurrence pattern in time to better characterize their periodicity. Our results indicate that wavelet-based detection methods are a valuable tool to study SSE recurrence patterns.
Oral presentation.