Apulia–Microplate Motion Change Following the MW 6.4, 26 November 2019 Durrës, Albania Earthquake

Abstract

Plate motion steadiness during the earthquake cycle is a central tenet of the plate tectonic theory. The advent of geodesy in geosciences allows measuring plate motions over periods much shorter than such cycle, and thus permits testing the tenet above against observations. Here I focus on the Apulia microplate, a tectonic unit that buffers the Nubia/Eurasia convergence. On 26 November 2019, a $M_W$ 6.4 earthquake occurred along the Apulia eastern margin, near the city of Durrës, Albania. I utilize publicly–available position time–series measured at sites within Apulia via the Global Navigation Satellite Systems to infer a temporal change of the whole–Apulia motion from before to after the earthquake. I calculate Euler vectors for the motion of Apulia relative to fixed Eurasia via the classical minimization of the sum of squared misfits. A comparison of Euler vectors and associated surface motions from before to after the earthquake illustrates a 20% speedup that is beyond the impact of data noise and uncertainties at the 95% confidence level virtually anywhere within Apulia, and seems compatible with the direction of coseismic stress drop upon Apulia implied by focal mechanism solutions. I use quantitative models to show that the torque–variation required upon Apulia to generate the observed speedup appears to be consistent with the torque–variation imparted to Apulia by the coseismic stress drop over the Durrës rupture area.