资源环境科技发展态势分析平台

In this paper we examine a short-lived aseismic slip episode which began immediately following the 2016 Kaikoura 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 Kaikoura mainshock. Immediately following the earthquake, we observe 150 mm of localized uplift over an similar to 25-km(2) 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 (similar to -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.

Plain Language Summary Pore fluid pressure plays a critical role in fault behavior. As the pressure increases, the stresses which help prevent the fault from breaking are reduced making it easier for the fault to move. In this study, we use interferometric synthetic aperture radar data to measure an aseismic slip (no earthquakes) episode within the epicentral region of the 2016 Kaikoura earthquake in New Zealand. Localized uplift observed immediately after the earthquake was likely caused by a pore pressure increase within a shallow fluid trap as a result of a coseismic permeability change. The observed uplift rapidly dissipates with displacements becoming focused along a NE-SW trending fault. Because of the position and orientation of the fault relative to the Kaikoura rupture, slip along the fault would have been inhibited by the Kaikoura stress change. However, because of the local increase in pore pressure, the fault was able to move over a period of a few weeks without generating detectable seismic energy until the pore pressure dissipated and the fault relocked. Based on these observations and scaled to larger displacement episodes, along-strike variations in fluid budget could explain the changes in fault behavior observed along larger fault systems.