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Ground-motion Directionality in Chile From CSN Strong-motion Data

Chile's National Seismological Center (CSN) provides open-access strong-motion recordings from networks spanning a wide range of Chilean site conditions. Using this resource, we examine whether earthquake ground motions in Chile exhibit systematic directionality (polarization) and what controls it. We select stations with robust sampling (>100 accelerograms per station). For each record, we rotate the two horizontal components and compute orientation-dependent intensity measures: PGA, PGV, 5%-damped pseudo-spectral acceleration (PSA) for periods 0.05-10 s, and significant duration (D_5-95). Directionality is quantified using IMRotD100 (maximum rotated intensity), the ratio IMRotD100/RotD50 (ratio of the maximum rotated intensity to the orientation-independent median, RotD50), and the azimuth of maximum intensity. We then relate these metrics to source, path, and site parameters, including moment magnitude, focal mechanism, source-to-site distance, and dynamic soil properties. Preliminary results indicate that some stations exhibit persistent preferred orientations of maximum intensity across many events and multiple intensity measures, suggesting a systematic contribution from site effects at specific locations, even when accounting for source and path variability. These preliminary outcomes provide empirical constraints for directionality models in subduction environments and help identify when orientation-specific intensity measures could be considered in site-specific hazard and risk assessments in Chile

Session: Recent Research on Ground Motion Directionality [Poster]

Type: Poster

Room: Exhibit Hall A+B

Date: 4/17/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Victor Contreras

Student Presenter: No

Invited Presentation: 

Poster Number: 27

Additional Authors