- Ground-motion model is:
where a is in g∕100, b0 = 0.04, bAN = 0.24, bAB = 0.23, bM = 0.41 and bd = -0.99 (σ not given).
- Use three site categories for Friuli records, although note that information is rather superficial:
- Alluvium with depth > 20m, 36 records.
- Rock-like: hard rock or stiff soil, 24
- Alluvium-like with depth ≤ 20m: includes sites for which thickness of deposit is reported to be very
small which accounts for a few metres of weathering of underlying bedrock, 60 records.
Alpide belt records divided into two categories: rock-like (25 records) and alluvium-like (40 records).
- Use data from free-field instruments or from instruments in basements of small structures and divide data
into three regions: those from 1976 Friuli shocks (120 records) ⇒ XAN = XAB = 0, those from 1972
Ancona swarm (40 records) ⇒ XAN = 1 & XAB = 0 and those from Alpide Belt (Azores to Pakistan
excluding those from Friuli and Ancona) (64 records) ⇒ XAN = 0 & XAB = 1. Exclude records with
PGA < 0.15m∕s2 to avoid possible bias at low acceleration values.
- Assume average focal depth of 6km.
- Note some PGA values derived from velocity records which are retained because compatible with other
data. No instrument corrections applied to Friuli records because correction does not substantially alter
- Use ML because determined at short distances and allows homogenous determination from lowest values
up to saturation at ML = 7.0 and it is determined at frequencies of nearly 1Hz, close to accelerographic
- Perform regression on PGAs from each of the three regions and each soil types considered within that
- Group rock-like (R) and thick alluvium (ThA) records together for Friuli. Find bd for Friuli equations
derived for thin alluvium-like and rock and thick alluvium not significantly different but bM is significantly
different, at 95% level. Repeat analysis using only Tolmezzo records because of large scatter in residuals
but decide it is in thA category.
- For Alpide belt equations find bM is almost the same for Rl and Al records and the difference in bd is less
than standard error, thus repeat analysis using a dummy variable XAl which equals 0 for Rl and 1 for Al