Peak ground acceleration underestimates narrow-band seismic amplification on mountain slopes
Year: 2026
Type: article
Abstract: Topographic amplification is widely invoked to explain strong shaking and slope failure in mountainous terrain, yet direct field observations remain limited. Here we analyze 24 regional earthquakes recorded by a four-station strong-motion array spanning a ridge crest, a valley bottom, and two contrasting slope facets on a single ridge in central Japan. Peak ground acceleration (PGA) and frequency-dependent measures reveal markedly different representations of local seismic response. PGA ratios vary among events and are positively associated with epicentral distance; however, earthquake magnitude also increases with distance, so source-size and propagation-distance effects cannot be separated in this catalog. In contrast, the NS slope exhibits a persistent narrow-band station-to-valley Fourier spectral-ratio peak at 3.5–4.0 Hz that remains stable across events and processing choices. Absolute spectra confirm enhanced energy at the slope in this band, while also showing that a relative spectral depression at the valley reference contributes to the large ratio magnitude. Most importantly, the geometric-mean 5%-damped response-spectral ratio reaches 6.67 at 0.277 s (3.61 Hz), compared with a corresponding full-record geometric-mean horizontal PGA ratio of 1.13. These observations show that PGA can substantially under-represent frequency-specific elastic response on mountain slopes, while the responsible mechanism cannot be uniquely attributed to topography or near-surface structure alone.
Source: Scientific Reports
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,690
OpenAlex ID: W7215944458
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