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1%% International Review of Financial Analysis — submission manuscript2%% Elsevier elsarticle class, author-year (harvard) references.3\documentclass[preprint,12pt,authoryear]{elsarticle}45\usepackage{amsmath,amssymb}6\usepackage{booktabs}7\usepackage{threeparttable}8\usepackage{adjustbox}9\usepackage{caption}10\captionsetup{font=small,labelfont=bf}11\usepackage[hidelinks]{hyperref}12\graphicspath{{figures/}}13\biboptions{round}1415\IfFileExists{results_macros.tex}{\input{results_macros.tex}}{}1617\journal{International Review of Financial Analysis}1819\begin{document}2021\begin{frontmatter}2223\title{Faster, Wider, More Fragile? The Evolution of Intraday Shock24Propagation in U.S. Equity Markets, 1992--2026}2526\author[uqo]{Simon-Pierre Boucher\corref{cor1}}27\ead{simon-pierre.boucher@uqo.ca}28\cortext[cor1]{Corresponding author.}29\affiliation[uqo]{organization={D\'epartement des sciences administratives,30 Universit\'e du Qu\'ebec en Outaouais},31 addressline={Pavillon Alexandre-Tach\'e, 283 boulevard Alexandre-Tach\'e},32 city={Gatineau},33 postcode={J9A 1L8},34 state={Qu\'ebec},35 country={Canada}}3637\begin{abstract}38We study how intraday shocks travel across U.S.\ equities using39\DataRowsBn{} billion one-minute bars covering the full listed and delisted40cross-section from 1992 to 2026. Three facts emerge. First, markets absorb41idiosyncratic shocks: across \NEventsRealMM{} million isolated $\pm6\sigma$42one-minute events, abnormal market-wide propagation---measured against matched43within-stock placebos---is economically zero at horizons of 1 to 120 minutes,44in every decade. Second, transmission is concentrated and has intensified:45the shocked stock's twenty closest lagged-correlation neighbors respond46strongly (+\NetDiffFive$\times10^{-4}$ abnormal jump probability at five47minutes), and this network channel tripled between the 1990s and the 2020s48while market-wide spillover stayed at zero. Third, tail synchronization49migrated to the market-wide minute: ordinary extreme minute returns became50roughly \ExtremeDropFactor{} times less frequent than in the 1990s, the Epps51curve flattened (one-minute pairwise correlation \EppsNinetySixOne{} in 199652versus \EppsFifteenOne{} in 2015), and severe co-jump minutes spike by orders53of magnitude in 2008 and 2020. Modern markets absorb the idiosyncratic and54transmit the systemic.55\end{abstract}5657\begin{keyword}58Intraday shock propagation \sep market fragility \sep high-frequency data \sep59contagion \sep co-jumps \sep Epps effect \sep market microstructure60\JEL G10 \sep G12 \sep G1461\end{keyword}6263\end{frontmatter}6465\input{sections/01_introduction}66\input{sections/02_literature}67\input{sections/03_data}68\input{sections/04_measurement}69\input{sections/05_empirical_design}70\input{sections/06_results}71\input{sections/07_mechanisms}72\input{sections/08_robustness}73\input{sections/09_conclusion}7475\section*{CRediT authorship contribution statement}76\textbf{Simon-Pierre Boucher:} Conceptualization, Methodology, Software,77Validation, Formal analysis, Investigation, Data curation, Writing -- original78draft, Writing -- review \& editing, Visualization.7980\section*{Declaration of competing interest}81The author declares no known competing financial interests or personal82relationships that could have appeared to influence the work reported in this83paper.8485\section*{Data availability}86The underlying market data were originally sourced from Finnhub.io87(\url{https://finnhub.io}). The aggregated monthly archive used in this study is publicly accessible;88the exact pinned snapshot, full replication code, manifests, checksums, and89machine-readable results accompany the paper.9091\section*{Acknowledgments}92[To be completed.]9394\bibliographystyle{elsarticle-harv}95\bibliography{bibliography/references}9697\end{document}98