In late May, 2013, PEER’s NGA-West2 project, the second and final phase of the Next Generation Attenuation relationships for shallow crustal earthquakes in active tectonic regions (Western U.S.A.), released a series of reports of its work in developing Ground Motion Prediction Equations (GMPE). Updated and expanded GMPE procedures (from the original 2008 models) are available, data files used in various research components of NGA-West2 are documented (See: Timothy D. Ancheta et al, PEER-2013/03), and the earthquake ground motion data have been made public as the NGA-West2 database “flat files”.
|The NGA-West2 project database expands on the current PEER NGA ground-motion database to include worldwide ground-motion data recorded from shallow crustal earthquakes in active tectonic regions, post-2003. Events are considered shallow crustal if they occur within the continental lithosphere. The region used to collect shallow events is considered “tectonically active” if the earthquake is not located in a stable continental region (SCR), within a subducting slab or on the interface between the slab and the continental lithosphere; typically these events are near a plate boundary. Additionally, events were not excluded if they occurred in close proximity (time and space) with a previous event.|
The new data set comprised 21,539 recordings obtained during earthquakes with magnitudes ranging from 3 to 7.9, recorded at distances ranging from 0.2 km to over 300 km, and for recording stations with Vs30 (time-averaged shear-wave velocity in the top 30 m at the recording sites) ranging from 100 to 2000 m/sec. These data spanned the larger magnitude range (M = 4.5 to 7.9) and the small magnitude range. Thousands of ground motions recorded from small-to-moderate magnitude (with M = 3 to 5.5) events in California were also added. The new database includes uniformly processed time series as well as response spectral ordinates for 111 periods ranging from 0.01 to 20 sec and with 11 different damping ratios.
The quality of the strong motion database and of the subsets selected for closer study by each GMPE model team are critical for wider application of the NGA-West2 GMPE. (See: Iztok Peruš and Peter Fajfar. How Reliable are the Ground Motion Prediction Equations? SMiRT 20 – August 2009; for discussion of some other key issues for wider application). The recent history of earthquake ground motion prediction models has been well documented by John Douglas (See: ESEE 01-1 A comprehensive worldwide summary of strong-motion attenuation relationships for peak ground acceleration and spectral ordinates (1969 to 2000); BRGM/RP-56187-FR Further errata of and additions to ‘Ground motion estimation equations 1964 – 2003′ – final report and PEER-2011/102/Ground-motion prediction equations 1964 – 2010.