27 May 2024
 | 27 May 2024
Status: this preprint is open for discussion.

On the role of trans-lithospheric faults in the long-term seismotectonic segmentation of active margins: a case study in the Andes

Gonzalo Yanez, Jose Piquer, and Orlando Rivera

Abstract. Plate coupling play a fundamental role in the way in which seismic energy is released during the seismic cycle. This process includes quasi-instantaneous release during megathrust earthquakes and long-term creep. Both mechanisms can coexist in a given subducting margin, defining a seismotectonic segmentation in which seismically active segments are separated by zones in which ruptures stop, classified for simplicity as asperities and barrier, respectively. The spatiotemporal stability of this segmentation has been a matter of debate in the seismological community for decades. At this regard, we explore in this paper the potential role of the interaction between geological heterogeneities in the overriding plate and fluids released from the subducting slab towards the subduction channel. As a case study, we take the convergence between the Nazca and South American plates between 18°–40° S, given its relatively simple convergence style and the availability of a high-quality instrumental and historical record. We postulate that trans-lithospheric faults striking at a high angle with respect to the trench behave as large fluid sinks that create the appropriate conditions for the development of barriers and promote the growth of highly coupled asperity domains in their periphery. We tested this hypothesis against key short- and long-term observations in the study area, obtaining consistent results. If the spatial distribution of asperities is controlled by the geology of the overriding plate, seismic risk assessment could be established with better confidence.

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Gonzalo Yanez, Jose Piquer, and Orlando Rivera

Status: open (until 18 Jul 2024)

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Gonzalo Yanez, Jose Piquer, and Orlando Rivera
Gonzalo Yanez, Jose Piquer, and Orlando Rivera


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Short summary
We postulate that the observed spatial distribution of large earthquakes in active convergence zones, organized in segments where large events are repeated every 100–300 years, depends on large scale continental faults and fluid release from the subducting slab. In order to support this model, we use proxies at different spatial and temporal scales (historic seismicity, megathrust slip solutions, inter-seismic cumulative seismicity, GPS/viscous plate coupling, and coast line morphology).