Abstract

The very early phase of postseismic deformation spanning the first few hours is difficult to capture using daily Global Positioning System (GPS) and interferometric synthetic aperture radar. Using kinematic GPS instead, we analyzed the surface deformation that occurred during the first 3 days immediately after the 2015 Mw 8.3 Illapel earthquake. Particularly, the displacements at station PFRJ reached 2-3 cm during the first 2 hr, and grew to 6.1 cm after 12 hr from the origin time. We hence imaged the afterslip evolution by inverting kinematic GPS and found that the very early afterslip was mainly concentrated around the hypocenter. The early afterslip evolved to be distributed along three main slip zones along the strike, which was complementary to the coseismic slip zones in space. The location of aftershocks was highly consistent with the spatiotemporal evolution of early afterslip, suggesting that the occurrence of aftershocks may be influenced by afterslip in the very early postseismic period.