Observations of Aseismic Slip Driven by Fluid Pressure Following the 2016 Kaikōura, New Zealand, Earthquake

Abstract

In this paper we examine a short-lived aseismic slip episode which began immediately following the 2016 Kaikōura earthquake in the South Island of New Zealand. Using synthetic aperture radar data, we form an interferometric synthetic aperture radar time series over the epicentral region of the Kaikōura mainshock. Immediately following the earthquake, we observe 150 mm of localized uplift over an ∼25-km2 region which is best explained by an increase in pore pressure within a shallow fluid trap as a result of a coseismic permeability change. After the initial uplift stops, deformation becomes focused along a NE-SW trending discontinuity which cuts through the uplifted region. The fault lies within a large (∼−4 MPa) stress shadow induced by the coseismic stress change suggesting that failure should be inhibited. However, a reduction in the effective normal stress caused by the local pore pressure increase was sufficient to induce a short-lived aseismic slip episode.