New approach predicts building collapse in quake aftershocks

Researchers have found a new approach to predicting which buildings might be most susceptible to potentially devastating collapse due to the ground-shaking aftershock tremors.
According to researchers from the Colorado State University and Michigan Technological University, it is relatively obvious that buildings that survive a main shock will be at varying degrees of risk of collapse as aftershocks travel through the earthquake zone.
In order to compute the risk of collapse, the probability, for building damaged by a main shock, the team has introduced a logical method based on two key earthquake variables: magnitude and site-to-source distance.
They have carried out tests using different site-to-source distances with an incremental dynamic analysis based on simulated ground motions caused by the main shock and aftershocks.

They then applied this to a computer modelled, two-storey, timber-frame building in a hypothetical town in California relatively close to a geological fault line, as a proof of principle.
Full-scale structural data was available from an actual building.

The team found that collapse probability increased if there were a sequence of aftershocks following a main shock just 10 kilometres distant from the building.
Stronger aftershocks mean greater risk that correlates with the actual magnitude of the shock.
As one might also expect if the site-to-source distance is greater, risk is lower, researchers said.
Overall, however, the analysis allows the team to quantify this risk based on the two variables, distance and aftershock magnitude.

Aftershocks are usually several orders of magnitude less intense than the primary earthquake, but can nevertheless have high ground motion intensity, last longer and occur at different vibration frequencies.