- Ground-motion model is:
where y is in g, a1 = 1.330095 ± 0.068, a2 = 0.640047 ± 0.066, b = -1.65663 ± 0.055, c = 0.14963 ± 0.098,
σ1 = 0.196 (intra-event), σ2 = 0.191 (inter-event) and σ = = 0.274.
- Initially use four site classes:
- Rock. 6 stations, 20 records.
- Stiff soil. 11 stations, 57 records.
- Soil. 11 stations, 32 records.
- Deep soil. 9 stations, 59 records.
Sites classified using horizontal/vertical spectral ratios of the S-wave window of records grouped by station
(details not given). Only use data with S/N ratio > 3 and smooth spectra using a nine-point moving
average. Since data insufficient to obtain coefficients for all classes, combine classes 1 and 2 and classes 3
and 4 to produce categories A (S = 0) and B (S = 1) based on 77 and 91 records, respectively. Display
average H/V spectral ratios for each category.
- Focal depths between 4.3 and 31.8km.
- Note that ideally would account for faulting mechanism but for many earthquakes this parameter is
unknown and also dataset is not large enough to assess its impact.
- Use data from the Turkish National Strong Motion Network of the Earthquake Research Department
of the General Directorate of Disaster Affairs and the temporary Western Anatolia Seismic Recording
- Use rhypo because fault geometries unknown for most earthquakes.
- Initially use 2123 records from all regions of Turkey. Discard records with unknown and poor estimates
of magnitude, distance and/or site conditions and those outside western Anatolia. Select data with:
rhypo < 200km, Mw ≥ 4.0 and PGA > 0.0015g.
- Check low- and high-frequency noise for all records. Find that much data from SMA-1s have significant
long-period noise (especially records of small earthquakes at large distances). Do not filter data but
eliminate suspect records. Apply correction for instrument response. Numerically differentiate data from
velociometers of WASRE network. Baseline correct all data.
- Most data from 4.5 ≤ Mw ≤ 5.5 and 25 ≤ rhypo ≤ 125km.
- Note that due to lack of records from < 10km cannot include fictitious depth in functional form.
- Initially include a quadratic magnitude term but this term does not improve match so drop this term.
- Test significance of site coefficients and find that they are generally significant at more than 90% confidence
- Plot residuals w.r.t. distance, magnitude and predicted log PGA. Find systematic trends, especially for
site B residuals versus Mw. Derive linear site coefficient correction terms to remove these trends (not clear
how they are applied), which relate to nonlinear site response.
- Compare predictions and observations for selected earthquakes.
- Discuss reasons for differences in site effects in western Anatolia and in other regions.
- Based on results, suggest that number of stations on rock should be increase and site classifications should