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Chile Project: Forearc Segmentation and the Earthquake Cycle in South-Central Chile

Funding: Deutsche Forschungsgemeinschaft (Leibniz Award to M. Strecker), German Ministry of Science and Technology (BMBF; TIPTEQ grant); DFG investigator grant by D. Melnick (pending)

Starting date: March, 2004

Manfred R. Strecker (PI), Daniel Melnick, Katrin Rehak (PhD student)

Collaborating researchers (PI’s only)

K. Bataille (U de Concepcíon), B. Bookhagen (UC Santa Barbara) http://www.geog.ucsb.edu/~bodo/, M. Cisternas (U de Valparaiso), T. Dunai (Edinburgh), H. Echtler (GFZ Potsdam) http://www.gfz-potsdam.de/portal/, G. Khazaradze (U de Barcelona), J. Klotz (GFZ Potsdam), Y. Lagabrielle (Montpellier), M. Moreno (GFZ Potsdam), C. Mpodozis (ENAP, Santiago), F. Preusser (U Bern), M. Summerfield (Edinburgh), A. Tassara ( U de Chile)


Description

Forearc regions are among the most tectonically active settings worldwide, often subject to pronounced tectonic uplift and subsidence. Surface uplift, subsidence history, and the composite landscapes that evolve in such regions may thus provide important insight into the factors that govern the geodynamic and structural evolution of these dynamic environments. An ideal setting to investigate the relation between forearc segmentation, surface uplift, and changing subduction processes is the forearc of south-central Chile. This sector of the margin has experienced a change from subduction erosion to subduction accretion in late Miocene to early Pliocene time. Furthermore, this forearc is characterized by different seismotectonic and geomorphic segments, documenting a distinct spatiotemporal tectonic evolution that may encapsulate important information concerning crustal behavior during the seismic cycle.

DEM Isla St Maria

DEM of the Chile forearc region. The gently inclined surface west of the region with high topography (brown) constitutes the uplifted marine terraces of the Arauco Peninsula.
The location of Isla Santa Maria is denoted by a black frame. Blue box in South America denotes area shown in the DEM.

Understanding the processes that govern the seismic cycle of subduction margins has been a major research focus during the past decades. Indeed, improving our ability to recognize and correctly interprete tectonic signals contained in coastal landscapes is paramount to efficient hazard evaluation and mitigation of immediate and secondary seismic hazards, such as landslides, natural and artificial dam bursts, etc. The necessity of obtaining more expert knowledge concerning the evolution of structures and landforms in coastal environments is underscored by the fact that approximately two thirds of our coasts are in areas of active tectonism and major population centers, important infrastructure, and pronounced economic development. A premier research topic in these environments is therefore understanding repeated, major earthquake ruptures and the seismotectonic behavior of coastal segments during the seismic cycle and beyond. Thus, the identification of similar patterns in seismotectonic segments that have, and probably will continue to generate giant-magnitude earthquakes, is key to unraveling the overall deformation and seismic history and possible future behavior of seismically active coasts.

Sustained tectonic activity during the Cenozoic, a relatively well dated change in kinematic regime, elevated erosion surfaces formerly located at or near sea level forming a formidable staircase morphology, coseismically uplifted beach berms, and surface rupture during large earthquakes make the south-central Chile an ideal target to evaluate forearc processes at various time scales.

beach berms

  1. Linear relationship between the distance from the active beach berm at the shoreline and beach-berm crest elevations. Mean elevation gain corresponding to individual earthquakes is 0.4 m. From Bookhagen et al., 2006

  2. Asymmetrically uplifted Isla Santa Maria with beach berms (1-21) on E side of island


Our principal goals in this study are:

  1. Defining the long-term style and chronology of tectonic processes in the forearc region.
  2. Estimating deformation rates over the seismic cycle and the Quaternary Period in the southern sector of the Valdivia 1960 earthquake segment.
  3. Obtaining a paleoseismic record of subduction earthquakes in this region.
  4. Integrating deformation rates and paleoseismic records to obtain a strain partitioning budget and explore its influence on modulating earthquake recurrence and magnitude.

In order to reach these goals we use measurements of cosmogenic 10Be and 26Al in in-situ quartz clasts obtained from geomorphic surfaces, OSL and 14C dating of fluvial and marine terrace deposits, and GPS measurements. In addition, we analyze the fluvial network and determine clast provenance to assess the flow reversals, stream piracy and channel development as indicators of active tectonic processes.


SELECTED PUBLICATIONS

Bookhagen, B., Echtler, H.P., Melnick, D., Strecker, M.R., and Spencer, J.Q.G., 2006, Using uplifted Holocene beach berms for paleoseismic analysis on the Santa María Island, south-central Chile: Geophysical Research Letters, v. 33, p. L15302.

Melnick, D., Bookhagen, B., Echtler, H., and Strecker, M., 2006a, Coastal deformation and great subduction earthquakes, Isla Santa María, Chile (37°S): Geological Society of America Bulletin, v. 118, p. 1463-1480.

Melnick, D., Charlet, F., Echtler, H.P., and De Batist, M., 2006b, Incipient axial collapse of the Main Cordillera and strain partitioning gradient between the Central and Patagonian Andes, Lago Laja, Chile: Tectonics, v. 25, p. TC5004.

Melnick, D., and Echtler, H.P., 2006a, Inversion of forearc basins in south-central Chile caused by rapid glacial age trench fill: Geology, v. 34, p. 709-712.

Melnick, D., Folguera, A., and Ramos, V.A., 2006c, Structural control on arc volcanism: The Caviahue-Copahue complex, Central to Patagonian Andes transition (38°S): Journal of South American Earth Sciences, v. 22, p. 66-88.

Rehak, K., Strecker, M.R., Echtler, H.P. (2008) Morphotectonic segmentation of an active forearc, 37°-41°S, Chile. Geomorphology 94 (1-2). 98-116.

Rehak, K., Strecker, M.R., Echtler, H.P., Binnie, S., Summerfield, M. A., Dunai, T., Freeman, S.P.H.T. (submitted): Reconstructing surface uplift using cosmogenic nuclides - the Coastal Cordillera in south-central Chile. Earth and Planetary Science Letters.

Rehak, K., Bookhagen, B., Strecker, M.R., Echtler, H.P. (in preparation): Climatic controls on drainage-basin morphology - the western Andean flank between 15.5° and 41.5°S.

Rehak, K., Niedermann, S., Preusser, F., Strecker, M.R., Echtler, H.P. (in preparation): Late Pleistocene landscape evolution in south-central Chile constrained by OSL and stable cosmogenic isotopes.

 

Arauco

Uplifted marine terraces on the Arauco Peninsula of south-central Chile

 

Isla Santa Maria

Uplifted Holocene beach berms on Isla Santa María West of the Arauco Peninsula of south-central Chile

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