Modeling social interest dynamics after earthquake disasters: A time-series analysis of newspaper coverage using STL decomposition and two-phase decay models

Great earthquakes attract intense media coverage and public attention, but their decay dynamics—and their variation across newspaper sections—remain underexplored. This study quantitatively examines long-term social interest following two major Japanese earthquakes: the 1995 Great Hanshin-Awaji Earthquake and the 2011 Great East Japan Earthquake. Using a 26-year newspaper corpus, we classify articles by section (e.g., local news, social news, opinion) and analyze monthly counts. We apply Seasonal-Trend decomposition using Loess (STL) to separate sustained interest from spikes (e.g., anniversaries), followed by a two-phase decay model combining an initial exponential drop-off with long-term power-law attenuation. Our results reveal clear contrasts: coverage of the Great East Japan Earthquake was broader, more sustained, and decayed more slowly—likely due to its nuclear-accident dimension. In contrast, coverage of the Hanshin-Awaji Earthquake was irregular and less persistent, largely influenced by competing news events. Local and social news sections provided enduring coverage in both cases, underscoring their role in sustaining collective memory. We also identify a switching point occurring at around 40 months for the Great East Japan Earthquake—marking a shift from communicative to cultural memory—while for the Hanshin-Awaji Earthquake, the transition was slightly later and more irregular. This study offers a novel quantitative framework that integrates agenda-setting, the issue-attention cycle, and journalism–memory studies, clarifying how media attention forms, consolidates memory, and resets agendas. It demonstrates the media's dynamic role in constructing and preserving collective memory. • Twenty-six year corpus analysis reveals post-disaster news attention dynamics. • Local and social news show sustained attention after initial decay. • Complex disasters reactivate media coverage via re-agenda setting. • Media plays strong role in constructing long-term social memory.