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 entire

faults? Answering this remains fundamental to improving seismic hazard analysis and, in turn, to

hazard preparedness and mitigation efforts. Over the past two decades, several mechanisms for

rupture termination and propagation have been proposed, including variation in geometric,

structural, and geologic characteristics of faults (Aki, 1979; King and Nabelek, 1985). In this study

we investigated the Eastern Precordillera (EPC) of the Andes Mountain in Argentina which is

classified into three segments: Villicum, Las Tapias, and Zonda–Pedernal (Siame et al., 2002) to

determine whether the historical surface ruptures associated with major earthquakes crossed the

segment boundaries, or whether rupture propagation was arrested by structural asperities

indicating an asperity-controlled behavior. To address this, we conducted a new paleoseismic

investigation at this site to complement and integrated with the preexisting dataset to evaluate the

extent of past surface ruptures in relation to fault geometry and structural segmentation. We have

complied earthquake timing of six earthquakes. Preliminary results suggest that, of the six

identified events, only one earthquake appears to have ruptured across an ~18 km-long segment

gap, including a ~4 km stepover and notable lithologic variation evidence consistent with a multi-

segment rupture event.