- See Section 2.147
- Ground-motion model (horizontal component) is:
- Ground-motion model (vertical component) is:
- Response parameter is pseudo-acceleration for 5% damping.
- Notes importance of depth to basement rock, D, for modelling long period site response. For shallow
sediments defines D as depth to top of Cretaceous or older deposits, for deep sediments determine D from
crustal velocity profiles where define basement as crystalline basement rock or sedimentary deposits having
a P-wave velocity ≥ 5km∕s or shear-wave velocity ≥ 3km∕s (called ‘seismic basement’ by geophysicists).
- Uses different data than for PGA equations hence: reverse (3), thrust (H:9, V:6), reverse-oblique (2)
and thrust-oblique (0), total (H:14, V:11) (H:140 records, V:85 records), strike-slip (H:124 records, V:88
records). Only two normal faulting earthquakes in horizontal set of records (contributing 2 records) so a
difference in not modelled although F = 0.5 is given as first approximation (later revised to F = 0) to use
as for PGA case.
- Only excludes records from toe and base of dams, included those from buildings and bridge columns which
were excluded from PGA study, because of lack of data.
- Uses weighted regression analysis. Assigns recordings from a given earthquake that fell within the same
distance interval (ten logarithmical spaced) same weight as those recordings from other earthquakes that
fell within the same distance interval. Gives recordings from a given earthquake that occurred at the same
site location the same cumulative weight as a single recording at that distance, thus reducing the bias.
- Performs analysis on spectral ratio ln(PSA∕PGA) because of unacceptably large period-to-period
variability in regression coefficients when direct regression is applied and strongly correlated coefficients.
Notes that are too many regression coefficients so it was necessary to perform analysis in many steps, at
each step different coefficients are determined and detrended and residuals examined to find appropriate
functional forms for trends present. Yields more stable results.
- No consideration of nontriggering instruments made, unlike PGA study.