Slip Pulses and PSHA

Thomas H. Heaton

Submitted September 7, 2025, SCEC Contribution #14468, 2025 SCEC Annual Meeting Poster #TBD

21st Century multistory US buildings are typically designed using Performance Based Earthquake Engineering (PBEE). The goal is to design such that building collapse is very improbable; typically, buildings are designed to survive the largest shaking expected over a 2,500-year duration. Probabilistic seismic hazard analysis (PSHA) is used to select a suite of ground motions to validate PBEE structural designs. The 2023 M 7.8 Türkiye-Syria earthquake is the first meaningful test of PBEE. More than 60,000 people perished because 21st-Century concrete frame buildings were too flexible to survive the large near-source ground displacements. Most of the collapsed buildings were designed with PBEE. The Turkish ground motions and building collapses are similar to a simulation of a 1906-like earthquake on the San Andreas fault (Olsen and others, 2008). Olsen and others (2015) concluded that motion with peak ground velocities (pgv) exceeding 60 cm/s, combined with peak ground displacement (pgd) exceeding 60 cm, is the best predictor of collapse of flexible frame buildings designed to California building codes (see Chapter 6 of Heaton’s online textbook, Physics of Earthquakes and Buildings).

PBEE’s 2,500-year design motions for the Anatolian fault were seriously underestimated. One key mistake is the use of 5% damped response spectral acceleration as a measure of shaking intensity; pgv and pgd are better predictors of collapse. Since pgd is about 2/3 of the slip on nearby rupture, PBEE is achievable only if it’s possible to estimate the probability of slip on nearby fault segments. Slip-pulse rupture implies that rupture physics is chaotic. Slip-pulse dynamics implies that the spatial statistics of slip is described by power laws (log-uniform?). Power laws can be converted into a probability distribution function only if the power law is truncated as a function of slip.

California cities are destined to see collapse of modern tall flexible buildings designed to current standards. We urgently need to develop a new strategy to design multi-story buildings and to communicate the risk associated with existing buildings. Earthquake engineers must collaborate with geophysicists to solve this critical problem. It seems likely that effective solutions will require architectural changes that are necessary to increase the stiffness and strength of multi-story building.

Citation
Heaton, T. H. (2025, 09). Slip Pulses and PSHA. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Applied Science Implementation (ASI)