This new multidisciplinary research program will develop a comprehensive database of ground motions recorded in subduction earthquakes worldwide and a set of resulting next-generation attenuation relationships, also called ground motion prediction equations (GMPEs), for regions with subduction zone earthquakes.
Recent successful PEER research projects including NGA-West and NGA-West2 have developed and updated GMPEs for regions of shallow crustal seismicity. PEER’s NGA-East project currently underway is developing a database of processed ground motion records and a set of resulting GMPEs for regions with stable continental seismicity. With the creation of NGA-Sub, researchers will now address the outstanding type of seismic source – subduction zones. Examples of subduction zones include the Pacific Northwest in the US, Japan, Chile, among others.
Most of the current subduction attenuation models were developed before the recent major subduction earthquakes in Chile (2010) and Japan (2011), thus the ground motion databases used to develop these models did not include the extensive number of recordings from these recent events. There is a pressing need to develop a comprehensive well-documented, peer-reviewed and publicly available database of ground motions from subduction earthquakes, and a set of GMPEs that can be used by both the academic and professional communities to estimate the seismic hazard from subduction zone earthquakes.
The NGA-Sub project will begin by collecting empirical data from subduction earthquakes around the world including the 2011 Tohoku Earthquake in Japan and the 2010 Chile Earthquake, as well as earthquake ground motion recordings from many other historic subduction earthquakes. With this data and the associated meta-data, researchers will develop GMPEs that apply to regions with subduction seismicity.
NGA-Sub is scheduled to continue through 2016 when the new set of GMPEs will be released. A website and other updates will become available as the project progresses.
What are GMPEs?
Ground Motion Prediction Equations (GMPEs), or “attenuation” relationships, provide a means of predicting the level of ground shaking and its associated uncertainty at any given site or location, based on an earthquake magnitude, source-to-site distance, local soil conditions, fault mechanism, and other parameters. GMPEs are used to estimate ground motions for use in both deterministic and probabilistic seismic hazard analyses.
The results of such hazard analyses are used for a wide range of applications such as: (1) site-specific seismic analysis and design of structures and facilities; (2) development of regional seismic hazard maps for use in building codes, financial estimation, etc.; and (3) social and financial loss estimation. Today, the most common Intensity Measures (IMs) used in GMPEs are peak ground motion values (e.g., peak ground acceleration, PGA; and peak ground velocity, PGV), and elastic response for various spectral ordinates.