One Big Earthquake or Many? Fault Segmentation in the Eastern Precordillera, western Argentina

Why do some earthquakes repeatedly rupture discrete fault segments, while others rupture entirefaults? Answering this remains fundamental to improving seismic hazard analysis and, in turn, tohazard preparedness and mitigation efforts. Over the past two decades, several mechanisms forrupture termination and propagation have been proposed, including variation in geometric,structural, and geologic characteristics of faults (Aki, 1979; King and Nabelek, 1985). In this studywe investigated the Eastern Precordillera (EPC) of the Andes Mountain in Argentina which isclassified into three segments: Villicum, Las Tapias, and Zonda–Pedernal (Siame et al., 2002) todetermine whether the historical surface ruptures associated with major earthquakes crossed thesegment boundaries, or whether rupture propagation was arrested by structural asperitiesindicating an asperity-controlled behavior. To address this, we conducted a new paleoseismicinvestigation at this site to complement and integrated with the preexisting dataset to evaluate theextent of past surface ruptures in relation to fault geometry and structural segmentation. We havecomplied earthquake timing of six earthquakes. Preliminary results suggest that, of the sixidentified events, only one earthquake appears to have ruptured across an ~18 km-long segmentgap, including a ~4 km stepover and notable lithologic variation evidence consistent with a multi-segment rupture event.