Investigating asperity activity during multiple earthquake cycles

点击翻译按钮获取中文摘要

The West coast of South America is one of the most seismically active regions worldwide. The nucleation and rupture propagation associated with giant earthquakes has been conceptualized with the model of seismic asperities; these represent irregularities on the subducting plate interface that accumulate elastic strain and subsequently rupture generating an earthquake. However, it is still matter of debate whether asperities represent persistent geologic features that control the spatial extent of ruptures and the seismotectonic segmentation of forearcs or if they represent dynamic features related to the release of elastic strain accumulated in seismic gaps. Since the total magnitude of subduction earthquakes depends on the amount of slip and the total area over which it occurs, it is crucial to determine the location, extent, and temporal evolution of seismic asperities in forearcs. The focus of this project is the study of seismic asperities at the Northern Chile margin at different temporal scales; the project will combine observations from uplifted Pleistocene marine terraces with geodetic observations of surface displacements during and between earthquakes at decadal time scales. As seismic asperities are usually located offshore and hidden from direct inspection, I propose an innovative method combining high-resolution bathymetry, morphometry, and numerical modeling to estimate deformation rates from drowned marine terraces. These estimates will be complemented with dedicated mapping and dating of emerged marine terraces using the U/Th and optically stimulated luminescence methods. In contrast, short-term deformation patterns and rates will be determined from the analysis of GPS time series and published models of interseismic and coseismic deformation. This innovative approach will allow for a direct comparison of displacement and deformation rates at different time scales and to determine the underlying processes controlling the accumulation of permanent deformation and the role of asperities shaping the morphology of forearc regions. Considering the importance of assessing the activity patterns of asperities and their potential as seismogenic sources in light of existing infrastructure and human settlements, the results of this project will be relevant to evaluate the mechanisms, recurrence, and possible earthquake scenarios along the coast of the Valparaiso, Illapel and Atacama seismotectonic segments of Northern Chile.