Very Early Postseismic Deformation Following the 2015 Mw 8.3 Illapel Earthquake, Chile Revealed From Kinematic GPS

• Published in: Geophysical research letters 2022-06, Vol.49 (11), p.n/a
• Main Authors: Liu, Kai, Geng, Jianghui, Wen, Yangmao, Ortega‐Culaciati, Francisco, Comte, Diana
• Format: Article
• Language: English
• Subjects: Aftershocks; afterslip; Chile subduction zone; Deformation; Displacement; Distribution; early postseismic deformation; Earthquakes; Evolution; Global positioning systems; GPS; Ground motion; Interferometric synthetic aperture radar; Kinematics; Plate boundaries; Plates; Plates (tectonics); Positioning systems; SAR (radar); satellite geodesy; Satellite navigation systems; Seismic activity; Slip; Spatial distribution; Synthetic aperture radar
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL098526

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. Plain Language Summary A large Mw 8.3 megathrust earthquake ruptured on the plate boundary between the Nazca Plate and South American Plates along Chile on 16 September 2015. Global Positioning System (GPS) stations in this area clearly recorded significant ground displacements. This work reveals the rapid ground displacements in the first few hours since completion of the rupture. From kinematic GPS, we find that the postseismic deformation in the first 2 hr accounts for about 50% of the total amount accumulated in the first 12 hr, and the deformation in the first half of the day accounts for about 60% of the total during the first 3 days following the mainshock. The very early rapid ground displacements do not strictly follow the logarithmic or exponential decay, but can be well described by the power function model. Besides, the distribution of coseismic slip and the early afterslip are spatially complementary. We also find that the spatial distribution of the early aftershocks is highly consistent with the spatiotemporal evolution of the early afterslip in the first few hours since the mainshock, showing that early aftershocks may be dominated by early afterslip. Key Points We map the very early afterslip (first 12 hr) of the 2015 Mw 8.3 Illapel earthquake using kinematic Global Positioning System Early postseismic displacements are significant and decay very rapidly in the first few hours, and can be better described by power function The spatial distributi