Build seismic cycle balance deformation with InSAR in Northen Chile

Lauriane Baylé (1), Romain Jolivet (2), Nadaya Cubas (1) and Laetitia Le

Pourhiet (1)

(1) Institut des Sciences de la Terre de Paris, UMR 7193, UPMC UniversitéParis 6, CNRS, Paris,

France

(2) Laboratoire de Géologie, Département de Géosciences, École Normale Supérieure, CNRS UMR 8538,

PSL ResearchUniversity, Paris, France

Recent studies have pointed out to a discrepancy between the short- and long-

term deformation of overriding plates in subduction zones. This led to debates

about when and how permanent deformation is acquired. This contradiction

has notably been observed along the Central Andes Subduction Zone, where

the coast subsides during and shortly after major earthquakes while a coastal

uplift with rates ranging between 0.1 and 0.3 mm/yr has been inferred the

last 4000 ky. For instance, during the 15th September 2015 Mw 8.3 Illapel

earthquake the geodetics (GPS and InSAR) data show a coastal subsidence

along the line-of-sight of 20 cm in InSAR.

To reconcile the seemingly contradictory observations, we here propose to

provide a seismic cycle uplift balance by constrainning inter-, co- and post-

seismic vertical velocities from InSAR time series. The study focuses on La

Serena peninsula (71.3°W, 30°S, Chile) along which the Illapel earthquake

occurred and for which long-term uplift rates have been provided by previous

geomorphological studies.

To build this seismic cycle balance, we use InSAR data (Sentinel-1) acqui-

red between the September 15, 2015 and January 19, 2019. The time series

for the ascendant orbite is calculated and the accumulated vertical displace-

ment extracted providing co- and post-seismic displacement. The co-seismic

displacement are similar to those previously obtain. To constrain the displa-

cement during the inter-seismic period, data on both sides of the peninsula

are used. In that respect, we aim determining when, during the seismic cycle,

and where, along the coast, the uplift occurs.

The deduced time series will then be confronted to numerical modelling

to provide the short- and long-term mechanics reproducing the short- and

long-term observations.