Coseismic Contortion and Coupled Nocturnal Ionospheric Perturbations During 2016 Kaikoura, Mw 7.8 New Zealand Earthquake

Abstract

The oblique-thrust Kaikoura earthquake of Mw 7.8 that struck New Zealand on 13 November 2016 at 11:02:56 UTC (local time at 00:02:56 a.m. on 14 November 2016) was one of the most geometrically and tectonically complex earthquakes recorded onshore in modern seismology. The event ruptured in the region of multisegmented faults and propagated unilaterally northeastward for more than 170 km from the epicenter. The GPS derived coseismic surface displacements reveal a larger widespread horizontal and vertical coseismic surface offsets of ~6m and ~2 m, respectively, with two distinct tectonic thrust zones. We study the characteristics of coseismic ionospheric perturbations based on tectonic and nontectonic forcing mechanisms and demonstrate that these perturbations are linked to two distinct surface thrust zones with rotating horizontal reinforcement trending the rupture, rather than merely to the displacements oriented along the rupture propagation direction. Plain Language Summary In general, the Earth crust uplift during any earthquake produces compressional waves in the overlying atmosphere. These waves propagate upward in the region of exponentially decreasing atmospheric neutral density, and thus, its amplitudes increase with atmospheric heights. On arrival at ionospheric heights, the waves redistribute ionospheric electron density and produce electron density perturbations known as coseismic ionospheric perturbations. The thrust earthquakes induce significant crustal uplift, while the strike-slip event mostly deforms the crust horizontally. The massive Mw 7.8 Kaikoura earthquake occurred in the complex multisegmented fault system between the Australia-Pacific plate boundary with a combination of vertical and differently oriented horizontal crust movements. This study reports that the two distinct thrust zones over the rupture area resulted from the uplift with reinforcement of rotating horizontal motion from the epicenter act as key tectonic sources for the peculiar distribution of coseismic ionospheric perturbations around the epicenter.