Characterizing Long-Period Ground Motions Using Bayesian Model Class Selection

National (or regional) seismic hazard maps, determined from probabilistic seismic hazard analysis, quantify the expected intensity of shaking in a region(s) over the course of one or more desired time interval(s). Building codes use these maps to define the lateral force levels for the design of new and the retrofit of existing structures. In the past, the maps depicted the shaking intensity measure of peak ground acceleration (PGA). In recent times, they have switched to depicting short period (0.2 s) and long period (1.0 s) spectral accelerations as these values may be directly used to fully define the code design response spectrum. Two hazard levels are typically of interest to the engineering community, the shaking intensity with a 10% probability of being exceeded in 50 years and the shaking intensity with a 2% probability of being exceeded in 50 years. These two levels of shaking define the Design Basis Earthquake (DBE, an earthquake with a recurrence interval of 475 years) and the Maximum Considered Earthquake (MCE, an earthquake with a recurrence interval of 2475 years) spectra. Typically, the codes’ design intent is to avoid loss of life under the DBE and collapse under the MCE.