Study of seismic activization of the Chilean subduction zone at the beginning of the XXI century based on GPS data

Abstract

<p>The Chilean coast is one of the most seismically and tectonically active regions of the circum-Pacific belt. Over the previous decade, three strong tsunamigenic earthquakes occurred in central and northern Chile: the Maule earthquake on February 27, 2010 (Mw = 8.8), the Iquique earthquake on April 1, 2014 (Mw = 8.1), and the Illapel earthquake on September 16, 2015 (Mw = 8.3). We used GPS data from the Chilean coast in order to study the dynamics of seismic process in Chilean subduction zone.</p><p>The focal mechanisms of all the mentioned earthquakes represent a shallow thrust dipping towards the continent, which corresponds to the compressional regime typical for the convergent boundary of lithospheric plates. The recurrence periods of the large megathrust earthquakes occured within the fault zones of the considered earthquakes vary from 63 to 175 years according to historical data.</p><p>To assess the geometric parameters of the fault zones of the investigated earthquakes, we determined the corresponding spatial distributions of aftershocks using clustering algorithm by Molchan and Dmitrieva. Using obtained geometrical parameters, we constructed the models of slip distributions in the source zones of 2010 Maule, 2014 Iquique and 2015 Illapel earthquakes by solving inverse problem of minimizing the misfit between the GPS and simulated coseismic displacements. We used a radially inhomogeneous distribution of elastic moduli in the crust and upper mantle, specified by the PREM model, for numerical modeling of static coseismic displacements. Analysis of obtained models of fault zones of 2010 and 2015 earthquakes shows a bilateral development of seismic ruptures with a total length of 600 and 250 km, respectively. Distinctive features of the fault zone of 2014 earthquake are the predominantly one-directional propagation of the rupture and a rather small length, which is less than 200 km instead of the expected 600 km. The values of the maximum displacements in the fault zones in all three cases range from 6 to 12 m. The revealed features of the distribution of displacements in the source zones indicate possible inhomogeneities in the tectonic structure of the Chilean subduction zone.</p><p>To assess the pre-earthquake state of the interplate interface we have constructed the distributions of the coupling coefficient in the fault zones of the studied earthquakes using the same inverse method on the basis of pre-earthquake GPS data. We found good general agreement of the obtained parameters of the earthquake sources with the features of interpolate interface structure in the Chilean subduction zone.</p><p>We also constructed models of afterslip in the source zones of studied earthquakes using post-earthquake GPS data to assess the amount of energy released during the coseismic and postseismic stages of the seismic cycle in Chilean subduction zone.</p><p>The study provides new data about the irregular development of the seismic regime  within the Chilean subduction zone.</p><p>This study was supported by Russian Science Foundation (project 20–17-00140).</p>