Unraveling the history of Quaternary faults in an active orogen: Paleoseismology and neotectonics of the Subandean foreland fold-and-thrust belt in southern Bolivia

• Applicant: Magda Patyniak, Ph.D.
• Subject Area: Geology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528296045

Actively deforming orogens are regions of significant seismic hazard, especially in areas with seismogenic structures, steadily growing populations, and infrastructure. An essential, yet often inadequately understood attribute for a coherent hazard and risk assessment is whether the responsible tectonic fault systems are subject to permanent, creeping deformation or episodic, seismogenic rupture processes. Recent regional geodetic surface velocity measurements in the southern Bolivian Subandes indicate that the décollement beneath the eastern orogen is the primary contributor to its lateral and vertical growth. The surface manifestation of the décollement is the Mandeyapecua fault system - the focus of this study - at the leading edge of the Subandean thrust belt that records Quaternary surface offsets. Here, fault scarps that are several tens of meters high document repeated surface ruptures as well as long-wavelength deformation of landforms, yet neither instrumental nor historical archives record large-magnitude earthquakes in this region. Furthermore, the GPS-derived rate of present-day contraction in this region is low and studies of the deformation rate are mainly based on the tectonic evolution on geologic (10^6-year) timescales. This creates a major gap in knowledge regarding the relationship between faulting processes acting over timescales of several hundreds to thousands of years and large-scale offsets in the recent geological past. To obtain a holistic assessment of faulting despite the lack of pronounced seismicity and rupture processes in recent times, the key focus of this project is to decipher the faulting history and seismogenic behavior of the Mandeyapecua fault system. In this multi-method and multi-scale study spaceborne-lidar and high-resolution topographic assessment will be combined with near-surface geophysics, paleoseismologic trenching and exposure-surface dating to obtain a 4-D view of the tectonic forcing processes impacting the Subandean thrust belt. Through cooperation with local authorities the expected results will ultimately lead to a better evaluation of regional seismic hazards, an increased awareness of seismic hazards, and new insights into the recent tectonic evolution of the Subandean frontal thrust system. In a global context, it is expected that the study will contribute to unraveling the history of seismotectonic segmentation of thrust fronts in active, non-collisional mountain belts and its imprint in the landscape.

• DFG Programme: Research Grants
• International Connection: Argentina, Bolivia, USA
• Co-Investigators: Professor Bodo Bookhagen, Ph.D.; Professor Manfred Strecker, Ph.D.
• Cooperation Partners: Dr. Ahmad Arnous; Professor Ramon Arrowsmith, Ph.D.; Professor Michael Bevis, Ph.D.; Professor Dr. Fernando Hongn; Professor Osvaldo Aquiles Rosales Sadud; Jonathan Weiss, Ph.D.