Andrei Maksymowicz

Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake

The Mw 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find ~3–5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within ~6 km of the deformation front. After the Mw 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone.

Reestablishment of an accretionary prism after the subduction of a spreading ridge—constraints by a geometric model for the Golfo de Penas, Chile

Seismic studies offshore southern Chile have revealed the presence of a 70–80 km wide accretionary prism seaward of the Golfo de Penas (GPAP), where the Chile Ridge collided with the South American Plate between 3 and 6 Ma ago. Using the paleo-positions of the Chile Ridge relative to South America, the maximum age of this accretionary prism, which continues to be formed in the aftermath of the ridge–continent collision, has been estimated. Building on these earlier findings, this study presents a mass balance analysis based on a 2D model of accretionary wedge and trench geometry. This model can explain the relative importance of sedimentary fluxes and deformation front migration for the wedge restoration. The proposed model can also serve to evaluate the effects of fluctuations in (1) terrigenous sediment flux related to climate change, and (2) subduction channel thickness on the accretionary prism growth. Notably, the data reveal that the key parameters controlling the rebuilding of the GPAP are the terrigenous sediment flux (75 km2/106 years), the relative advance of the deformation front (39.6 km/106 years), and the thickness of the subduction channel (0.1 km). Moreover, the range of possible solutions for the observed size of the accretionary prism is narrowed by fitting the present-day thickness of sediments at the deformation front. Finally, climate-induced variations in sedimentary fluxes on the margin can affect the rate of growth of the accretionary prism during short periods of time (<100,000 years).

The Geometry of the Continental Wedge and Its Relation to the Rheology and Seismicity of the Chilean Interplate Boundary

A latitudinal tectonic segmentation along the Chilean subduction margin is defined by the modeling of the continental wedge geometry. The segments are characterized by different effective basal friction coefficients or Hubbert–Rubey fluid pressure ratio and are limited by the subduction of oceanic features and seaward continental prolongations. The analysis of the modeled parameters indicates that the process of tectonic erosion probably is associated with high levels of overpressure in the decollement and inside the continental wedge. The observed segmentation shows a spatial correlation with the distribution of large earthquake ruptures, which suggest a link between the long-term and short-term deformation process. Joint interpretation of the results with the b-value analysis and the density-depth models in the 2010 Maule Mw8.8 earthquake zone shows the importance of these studies to understand the geodynamics of the subduction zones.