Seismic and Aseismic Fault Slip During the Initiation Phase of the 2017 MW = 6.9 Valparaíso Earthquake. Issue 6 (22nd March 2021)

• Record Type: Journal Article
• Authors: Caballero, Emmanuel; Chounet, Agnès; Duputel, Zacharie; Jara, Jorge; Twardzik, Cedric; Jolivet, Romain
• Is Part Of: Geophysical research letters. Volume 48:Issue 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-22
• Subjects: earthquake -- foreshocks -- initiation phase -- slow slip -- Valparaiso; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL091916
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Transient deformation associated with foreshocks activity has been observed before large earthquakes, suggesting the occurrence of a detectable preseismic slow slip during the initiation phase. A critical issue consists in discriminating the relative contributions from seismic and aseismic fault slip during the preparation phase of large earthquakes. We focus on the April–May 2017 Valparaíso earthquake sequence, which involved a M W = 6.9 earthquake preceded by intense foreshock activity. To assess the relative contribution of seismic and aseismic slip, we compare surface displacement predicted from foreshocks source models with transient motion measured prior to the mainshock. The comparison between observed and predicted displacements shows that only half of the total displacement can be explained by the contribution of foreshocks. This result suggests the presence of aseismic pre‐slip during an initiation phase preceding the mainshock. Plain Language Summary: Several studies suggest that some large earthquakes are preceded by aseismic fault slip. Such pre‐slip could explain foreshock activity and transient displacements observed before some large earthquakes. However, a large portion of observed preseismic deformations could be associated with the displacement field caused by each individual foreshock earthquakes. This study focuses on the 2017 M W = 6.9 Valparaíso (Chile) earthquake that was preceded by a noticeable Global Positioning System displacement and numerous foreshocks. By combining geodetic and seismic observations, our results show that only half of preseismic displacement can actually be explained by the contribution of foreshocks. This confirms that the Valparaíso earthquake was preceded by detectable aseismic fault slip accelerating into the main dynamic rupture. Key Points: The 2017 Valparaíso M W = 6.9 earthquake presents a preseismic transient displacement We evaluate the contribution of foreshock‐induced displacement to the preseismic Global Positioning System observations Results suggest that 50% ± 11% of the preseismic displacement is caused by aseismic slip