Investigating asperity activity during multiple earthquake cycles

• Applicant: Professor Manfred Strecker, Ph.D.
• Subject Area: Palaeontology ; Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 439670567

• Final Report Year: 2025

Final Report Abstract

Multiple flights of uplifted marine terraces in the forearc of Chile reflect the accumulation of permanent forearc strain, but the mechanisms for current/decadal deformation patterns viewed at millennial timescales are not understood. We developed a database of last interglacial terrace elevations and uplift rates along the South American coast to decipher mechanisms causing permanent coastal uplift. Interglacial terrace elevations reveal an almost continuous signal of background-uplift rates along the South American coast at ~0.22 mm/yr, modified by short- to long-wavelength changes associated with crustal faults and subducted bathymetric ridges on long timescales. Comparisons between the terrace-uplift rate signal with different tectonic parameters reveal short-wavelength deformation to result from crustal faulting. Intermediate- to long-wavelength deformation indicates various extents of long-term seismotectonic segments on the megathrust, which are partially controlled by bathymetric anomalies. The observed signal of backgrounduplift rate is likely accumulated by moderate earthquakes near the Moho, suggesting multiple, spatiotemporally distinct phases of uplift that form a continuous uplift signal over millennial timescales. Various levels of late Pleistocene marine terraces in the 2015 M8.3 Illapel-earthquake rupture zone uplift rates of 0.1-0.6 mm/yr and indicate decreasing uplift rates since ~400 ka. These glacial-cycle uplift rates do not correlate with current or decadal estimates of coastal deformation, suggesting that seismic asperities are not persistent features on the megathrust that control the accumulation of permanent forearc deformation on 105yr timescales. In addition, trench-parallel, normal faults modulate permanent forearc-deformation, likely a second-order phenomenon resulting from underplating, which leads to tectonic uplift and local gravitational collapse.

Publications

• Marine terraces of the last interglacial period along the Pacific coast of South America (1° N–40° S). Earth System Science Data, 13(6), 2487-2513.
  Freisleben, Roland; Jara-Muñoz, Julius; Melnick, Daniel; Martínez, José Miguel & Strecker, Manfred R.
  
• Deciphering Permanent Uplift Along the Pacific Coast of South America Through Signal Analysis of Various Tectonic Processes. Tectonics, 42(10).
  Freisleben, Roland; Jara‐Muñoz, Julius; Melnick, Daniel; Molina, Diego; Tassara, Andrés; van der Beek, Peter & Strecker, Manfred R.
  
• Deciphering the mechanisms of permanent forearc deformation based on marine terraces. Dissertation, Universität Potsdam, Potsdam, Germany, 153 p.
  Freisleben, R.