Back to full interseismic plate locking decades after the giant 1960 Chile earthquake

Abstract

Great megathrust earthquakes arise from the sudden release of energy accumulated during centuries of interseismic plate convergence. The moment deficit (energy available for future earthquakes) is commonly inferred by integrating the rate of interseismic plate locking over the time since the previous great earthquake. But accurate integration requires knowledge of how interseismic plate locking changes decades after earthquakes, measurements not available for most great earthquakes. Here we reconstruct the post-earthquake history of plate locking at Guafo Island, above the seismogenic zone of the giant 1960 (Mw = 9.5) Chile earthquake, through forward modeling of land-level changes inferred from aerial imagery (since 1974) and measured by GPS (since 1994). We find that interseismic locking increased to ~70% in the decade following the 1960 earthquake and then gradually to 100% by 2005. Our findings illustrate the transient evolution of plate locking in Chile, and suggest a similarly complex evolution elsewhere, with implications for the time- and magnitude-dependent probability of future events.

Holocene relative sea-level change along the tectonically active Chilean coast

“…This pattern, apparent from two sites separated by~40 km, was previously recognised by Garrett et al (2015) and tentatively attributed to incomplete interseismic uplift following coseismic subsidence during the 1960 earthquake. Interseismic uplift rates have been slowly increasing over the past few decades (Melnick et al, 2018), a trend that would raise the dated sediments back towards present sea level. In addition, effects at a local scale such as sediment compaction, or at a larger scale such as neoglacial forebulge collapse, might influence RSL in this region over the last millennium.…”

Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles

“…However, the slip models of the earthquake itself derived from rare offshore geodetic data suggested a coseismic trench‐breaching rupture (Ozawa et al., 2011; Simons et al., 2011; Sun et al., 2017). Besides short‐term (geodetic) elastic surface deformation information, it is considered worthwhile to explore long‐term (geologic) permanent deformation signals for potential diagnostic patterns linked to megathrust behavior (Geersen et al., 2018; Jara‐Muñoz et al., 2015; Madella & Ehlers, 2021; Malatesta et al., 2021; Melnick et al., 2018; Molina et al., 2021; Normand et al., 2019; Ott et al., 2019; Saillard et al., 2017). Hence, for the sake of completeness of seismotectonic insights, long‐term geological information should be referred to.…”

Unexpected coseismic surface uplift at Tirúa-Mocha Island area of south Chile before and during the Mw 8.8 Maule 2010 earthquake: a possible upper plate splay fault

“…This contrasts with the normal interseismic subsidence observed at other near trench islands such as Santa María Island after the Concepción 1835 earthquake (Wesson et al, 2015) and Guafo Island (43.6° S) after the Valdivia 1960 earthquake (Melnick et al, 2018); and also in the western border of Arauco Peninsula (Fig. 4).…”

“…However, during the interseismic period between Valdivia 1960 and Maule 2010 earthquakes, an unexpected behaviour occurred, the 1960 coseismic uplift at Mocha Island remained, or even should be increased (Nelson and Manley, 1992) and the theoretically expected interseismic subsidence did not occur. This contrast with the normal interseismic subsidence observed at other near trench islands such as Santa María Island after the Concepción 1835 earthquake (Wesson et al, 2015) and Guafo Island (43.6° S) after the Valdivia 1960 earthquake (Melnick et al, 2018); and also in the western border of Arauco Peninsula and Santa María Island (Fig. 4).…”