The seismic cycle in subduction zones: quantification of deformation rates and strain partitioning in the 1960 Chile earthquake segment

点击翻译按钮获取中文摘要

Subduction zones have generated the largest earthquakes on Earth; there, it has been thought that the longer the time since the last earthquake, the larger the next earthquake s slip, and consequently magnitude will be. However, historical and paleoseismic data has shown variable recurrence times and magnitude of large subduction earthquakes, which not necessarily follow this logical predictor. Gaining insight into this poorly understood problem is of utmost importance. All historical events that exceeded moment magnitude (Mw) 9 occurred in subduction zones where plate convergence is oblique. However, seismic and geodetic data show that coseismic slip occurred nearly normal to the megathrust s strike, implying that oblique convergence is somehow partitioned across the margin. The role of strain partitioning in the seismic cycle and the mechanism as to how transient variations in the degree of partitioning could modulate recurrence times and magnitudes of great subduction earthquakes, has not been fully explored. The Valdivia earthquake segment in south-central Chile, which in 1960 generated the largest, instrumentally recorded earthquake with Mw 9.5, is a suitable testing ground to study the seismic cycle and strain partitioning processes. This project attempts gaining insight into this problematic by determining: (1) deformation rates over the seismic cycle in the southern sector of the Valdivia segment; (2) deciphering the recurrence interval of large subduction earthquakes; and (3) characterizing the strainpartitioning budget over the seismic cycle. These objectives are best achieved through combined geomorphic and structural mapping, isotopic dating of deformed Quaternary landforms in the foreand intra-arc regions, measuring present-day deformation rates using continuous and campaign GPS, and by integrative tectonic modeling.