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\journal{International Review of Financial Analysis}

\begin{document}

\begin{frontmatter}

\title{Faster, Wider, More Fragile? The Evolution of Intraday Shock
Propagation in U.S. Equity Markets, 1992--2026}

\author{[Author identity withheld for review]}

\begin{abstract}
We study how intraday shocks travel across U.S.\ equities using
\DataRowsBn{} billion one-minute bars covering the full listed and delisted
cross-section from 1992 to 2026. Three findings emerge. First, isolated
idiosyncratic shocks barely spread: across \NEventsRealMM{} million
$\pm6\sigma$ one-minute events, the abnormal share of other securities with
an extreme standardized return, measured against matched within-stock
placebos, lies between zero and about \StratShareOfBase\% of its base rate at
horizons of 1 to 120 minutes, in every decade. Second, transmission is
concentrated and has intensified: the shocked stock's twenty closest
lagged-correlation neighbors respond (+\NetDiffFive$\times10^{-4}$ in the
probability of an extreme move at five minutes), and this network channel
roughly tripled between the 1990s and the 2020s while market-wide spillover
stayed bounded near zero---a rise that partly reflects sharper identification
of the network as the Epps effect receded. Third, common information is
impounded far faster (one-minute pairwise correlation \EppsNinetySixOne{} in
1996 versus \EppsFifteenOne{} in 2015), ordinary extreme minutes became an
order of magnitude rarer after decimalization, and severe co-jump
minutes---more than a tenth of the universe moving together---are roughly
ten times more frequent in 2008 and 2020 than in calm years. Modern markets
absorb the idiosyncratic, transmit it narrowly along statistical linkages,
and synchronize on the systemic.
\end{abstract}

\begin{keyword}
Intraday shock propagation \sep market fragility \sep high-frequency data \sep
contagion \sep co-jumps \sep Epps effect \sep market microstructure
\JEL G10 \sep G12 \sep G14
\end{keyword}

\end{frontmatter}

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\input{sections/08_robustness}
\input{sections/09_conclusion}
\clearpage

\section*{Declaration of competing interest}
The author declares no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this
paper.

\section*{Data availability}
The underlying market data were originally sourced from Finnhub.io
(\url{https://finnhub.io}). The aggregated monthly archive used in this study
is publicly accessible but carries no explicit licence; the minute data are
therefore not redistributed. The exact pinned snapshot identifier and
checksums, the full replication code, the event-level estimates, and all
machine-readable results accompany the paper.

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