Updated GK17 Ground Motion Prediction Equation for Shallow Crustal Continental Earthquakes and Use of Proper Terminology

Date: 4/24/2019

Time: 11:15 AM

Room: Pike

The Pacific Earthquake Engineering Research Center's Next Generation Attenuation Phase 2 ground motion database developed from shallow crustal earthquakes in active tectonic regions was used to develop a ground motion prediction equation (GMPE) for the median horizontal components of peak ground acceleration, and 5% damped elastic pseudo-absolute acceleration response spectral ordinates. The GK17 (Graizer, 2018) model has a number of significant improvements relative to the previous GK15 (Graizer and Kalkan, 2016) model including improved magnitude scaling for M≤5.5, a bilinear attenuation slope reflecting attenuation of shear and surface waves, a refined shallow site response V_S30, a sediment thickness correction through the Z_2.5 term, style-of-fault corrections and a different approach in the estimation of apparent anelastic attenuation of response spectral accelerations (SA). The new GMPE is applicable for earthquakes with 4.0≤M≤8.5, at rupture distances of 0≤R_rup≤400 km, at sites having V_S30 in the range of 150 to 1500 m∕s, for spectral periods of 0.01–10 s, and sediment thickness Z_2.5≤10 km.

Using appropriate terminology and clarifying the meanings of such terms is critical in the GMPE development. For seismologists the term “spectra” means the Fourier, and for engineers – it refers to the response spectra (RS). Another example of confusion may be the definition of anelastic attenuation. In seismology, it refers to intrinsic and scattering attenuation of seismic energy, while in engineering seismology, when applied to GMPEs it is the apparent anelastic attenuation of the RS. The estimates of apparent attenuation factor demonstrate a difference between classical seismological Q(f) and the SA Q_SA(f) quality factors. Yet, another example is the basin effect. In seismology, it refers to trapped seismic waves in a basin which tends to significantly amplify ground motions. In GMPE development, however, this effect is not as pronounced, because it is usually interpreted to be a sediment thickness adjustment not yet covered by an average V_S30 correction.

Presenting Author: Vladimir Graizer

Authors