- Ground-motion model is: where Y is in g, C1 = -1.8559, C2 = 0.2549, C3 = 0.0111, C4 = -0.0013, C5 = 0.3061, C6 = 0.0734,
C7 = 0.3552, C8 = 1.5149, C9 = -0.103 and σ = 0.2137.
- Use two site classes because of limited number of records:
- V s,30 ≥ 900m∕s, Rock Quality Designation ≥ 50% or compressive strength qu ≥ 10MPa. 25 records. Z = 0
- Otherwise. 92 records. Z = 1 following the Chilean seismic code.
- Focal depths (H) from 18 to 53km.
- Use data from 1985 to 2010 obtained from public databases and records from National Accelerograph
- Most records from SMA-1s or similar analogue instruments.
- Most instruments on ground floor of 1-storey buildings (79 different stations).
- Only use data from large interface earthquakes (9 mainshocks and 4 aftershocks). 8 events in north
(including two in Peru) and 5 in central area of Chile.
- Locations from Chilean Seismological Service and magnitudes from Global CMT.
- Data well-distributed w.r.t. Mw and rrup.
- Two events: 3/3/1985 and 27/2/2010 contribute 27 and 31 records, respectively; about half the data.
- Estimate rrup using CMT solutions and aftershock distributions assuming that rupture area generally
smaller than aftershock area.
- Filter (using acausal 4th-order Butterworth) based on visual inspection of Fourier amplitude spectra in
log-log space. Generally use fmax of 90Hz for Nyquist of 100Hz and 40Hz for Nyquist of 50Hz. Use iterative
process to find fmin based on examination of displacements and displacement response spectra. Seek lowest
fmin that preserves natural appearance in time domain and without obvious drift.
- Coefficients C6, C7, C8 and C9 derived using algorithm to minimize mean residual for PGA from
rrup ≤ 80km (47 records). Fix these coefficients for other periods.
- Compare predictions and observations for 8.3 ≤ Mw ≤ 9.3 and find good fit.
- Plot total residuals w.r.t. distance and find no trends.