Seismic and Aseismic Fault Slip During the Initiation Phase of the 2017 MW=6.9 Valparaiso Earthquake

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 Valparaiso 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.

Automated summary

Transient deformation associated with foreshock activity can indicate detectable preseismic slow slip before large earthquakes. Research on the Valparaiso earthquake sequence suggests a significant contribution of aseismic pre-slip during the initiation phase preceding the mainshock. Comparisons between observed and predicted displacements show that only half of the total displacement can be explained by the contribution of foreshocks.