- Ground-motion model is: Do not report coefficients, only display predicted ground motions. H is the depth to top of coseismic
rupture in km, PGAr is the reference value of PGA on rock with V s30 = 1100m∕s, D is depth to 2.5km∕s
shear-wave velocity horizon (so-called sediment or basin depth) in km.
- Use V s30 (average shear-wave velocity in top 30m in m∕s) to characterise site conditions.
- Model developed as part of PEER Next Generation Attenuation (NGA) project.
- State that model is not final and articles should be considered as progress reports.
- NGA database only includes records that represent free-field conditions (i.e. records from large buildings
- Include earthquake if: 1) it occurred within the shallow continental lithosphere, 2) it was in a region
considered to be tectonically active, 3) it had enough records to establish a reasonable source term and 4)
it had generally reliable source parameters.
- Exclude records from earthquakes classified as poorly recorded defined by: M < 5.0 and N < 5,
5.0 ≤ M < 6.0 and N < 3 and 6.0 ≤ M < 7.0, rrup > 60km and N < 2 where N is number of records.
Include singly-recorded earthquakes with M ≥ 7.0 and rrup ≤ 60km because of importance in constraining
- Include records if: 1) it was from or near ground level, 2) it had negligible structural interaction effects
and 3) it had generally reliable site parameters.
- Find two-step regression technique was much more stable than one-step method and allows the independent
evaluation and modelling of ground-motion scaling effects at large magnitudes. Find random effects
regression analysis gives very similar results to two-step method.
- Use classical data exploration techniques including analysis of residuals to develop functional forms.
Develop forms using numerous iterations to capture observed trends. Select final forms based on: 1) their
simplicity, although not an overriding factor, 2) their seismological bases, 3) their unbiased residuals and
4) their ability to be extrapolated to parameter values important for engineering applications (especially
probabilistic seismic hazard analysis). Find that data did not always allow fully empirical development of
functional form therefore apply theoretical constraints [coefficients n and c (period-independent) and ki
- Use three faulting mechanisms:
FRV = 1, FN = 0
- Reverse and reverse-oblique faulting,30∘ < λ < 150∘, where λ is the average rake angle.
FN = 1, FRV = 1
- Normal and normal-oblique faulting, -150∘ < λ < -30∘.
FRV = 0, FRV = 0
- Strike-slip, other λs.
- Find slight tendency for over-saturation of short-period ground motions at large magnitudes and short
distances. Find other functional forms for magnitude dependence too difficult to constrain empirically or
could not be reliably extrapolated to large magnitudes.
- Note transition depth for buried rupture (1km) is somewhat arbitrary.
- Find weak but significant trend of increasing ground motion with dip for both reverse and strike-slip faults.
Do not believe that seismological justified therefore do not include such a term.
- Nonlinear site model constrained by theoretical studies since empirical data insufficient to constrain
complex nonlinear behaviour.
- Use depth to 2.5km∕s horizon because it showed strongest correlation with shallow and deep
- Believe that aspect ratio (ratio of rupture length to rupture width) has promise as a source parameter
since it shows high correlation with residuals and could model change in ground-motion scaling at large
- Do not find standard deviations are magnitude-dependent. Believe difference with earlier conclusions due
to larger number of high-quality intra-event recordings for both small and large earthquakes.
- Find standard deviation is dependent on level of ground shaking at soft sites.