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\begin{document}

\title{Analysis of the 2017 Valparaiso Earthquake Sequence}



\author[1]{Luc Moutote}%
\author[1]{Olivier Lengliné}%
\author[2]{Zacharie Duputel}%
\affil[1]{Institut Terre et Environnement de Strasbourg, UMR7063, Université de Strasbourg/EOST, CNRS}%
\affil[2]{Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Université de Paris, CNRS}%


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  \date{June 14, 2024}


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\begin{abstract}
One of the key questions in fault mechanics is how do earthquakes begin
? This is central to our understanding of earthquakes, including the
long controversial issue of their predictability. Earthquakes preceding
large events are commonly referred to as foreshocks. They are often
considered as precursory phenomena reflecting a nucleation process of
the main rupture potentially driven by an underlying slow pre-slip. On
the other hand, some studies suggest that foreshock sequences may only
be explained by cascades of triggered events. In this work, we choose to
test the cascading hypothesis against the foreshock seismicity observed
during a previously reported slow slip event preceding the 2017 Mw=6.9
Valparaiso earthquake. We build a very complete 5 years long earthquake
catalog of the sequence using refine detection and location algorithms.
We test the detected seismicity against the Epidemic Type Aftershock
Sequences model. We identify time windows with anomalously high seismic
activity compared to what is expected by the typical earthquake
interactions. We analyze statistically these anomalies over 5 years to
understand if the Mw=6.9 foreshock sequence presents a specific
anomalous activity. In addition, using a hierarchical clustering method,
we identify earthquakes with similar waveforms to evidence any repeating
ruptures. We analyze the time distribution of these clusters over 5
years to understand if unusual rates of repeating events emerge during
foreshock time ranges. The conjoint analysis of seismicity rate
anomalies and repeating events along with the results of previous
pre-slip studies allows to accurately describe the nucleation process
and evolution of the 2017 Valparaiso earthquake sequence.%
\end{abstract}%



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