Researchers have found a new approach to predicting which buildings might be most susceptible to collapse due to the ground-shaking aftershock tremors.
According to researchers from the Colorado State University and Michigan Technological University, 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 and the probability of collapse of buildings damaged by a main shock, the team introduced a logical method based on two key earthquake variables: magnitude and site-to-source distance.
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 the risk to be lower if the site-to-source distance is greater, researchers said.
They 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.
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.
