- Ground-motion model is: where Y is in cm∕s2 and Mref = 5.5 (to reduce trade-offs between attenuation and source parameters),
a = 3.0761, b1 = 0.1587, b2 = 0.0845, c1 = -1.0504, c2 = -0.0148, h = 7.3469, e1 = 0, e2 = 0.2541,
e3 = 0.1367, f1 = 0, f2 = -0.0059, f3 = 0.0168, σevent = 0.1482, σstation = 0.2083, σrecord = 0.1498
and σ = 0.2963 for larger horizontal component; a = 3.0191, b1 = 0.1643, b2 = 0.0674, c1 = -1.0284,
c2 = -0.0041, h = 6.8963, e1 = 0, e2 = 0.2275, e3 = 0.0774, f1 = 0, f2 = -0.0138, f3 = 0.0005,
σevent = 0.1465, σstation = 0.2184, σrecord = 0.1345 and σ = 0.2930 for geometric mean of horizontal
components; and a = 3.0421, b1 = 0.3762, b2 = 0.0925, c1 = -1.2350, c2 = -0.0891, h = 9.3012, e1 = 0,
e2 = 0.1787, e3 = 0.1146, f1 = 0, f2 = -0.0073, f3 = 0.0222, σevent = 0.1266, σstation = 0.2114,
σrecord = 0.1394 and σ = 0.2831 for vertical component.
- Use three site classes following Sabetta and Pugliese (1987, 1996):
- Rock: rock outcrops or deposits thinner than 5m.. 98 records. S1 = 1 and S2 = S3 = 0.
- Shallow alluvium: deposits thinner than or equal to 20m and thicker than 5m. V s of alluvium between
400 and 800m∕s. 62 records. S2 = 1 and S1 = S3 = 0.
- Deep alluvium: deposits thicker than 20m. 81 records. S3 = 1 and S1 = S2 = 0.
Site classification performed using verified geological, geophysical and geotechnical information, which
altered the previous categorization of some stations. Data from 146 different stations. Note that only 6%
of 600 Italian stations are associated with a V s profile.
- Focal depths between 2 and 29km.
- Use data from Italian Accelerometric Archive (ITACA) from between 1972 and 2004, which have
been carefully revised during a project funded by the Italian Department of Civil Protection. Records
individually processed using individually-selected filters. Analogue records corrected for linear trend and
instrument response and then band-pass filtered, selecting high-pass frequency from visual inspection of
Fourier spectra (generally between 0.3 and 0.5Hz) and low-pass frequency chosen close to instrument
frequency (generally between 20 and 25Hz). Digital records corrected for linear trend using entire trace
(because few records have usable pre-event portion) and then band-pass filtered in the same way as analogue
data (but with generally lower cut-offs, 0.1–0.3Hz and 25–30Hz). Use raised cosine filter for analogue
records, which often triggered on S-phase, and acausal fourth-order Butterworth for digital signals, which
were padded with zeros at both ends.
- Use three faulting mechanisms:
- F1 = 1 and F2 = F3 = 0.
- F2 = 1 and F1 = F3 = 0.
- F3 = 1 and F1 = F2 = 0.
Most earthquakes on normal faults in central and southern Apennines.
- Number of records per earthquake ranges from two (Ancona, 14/06/1972) to 25 (Umbria-Marche,
14/10/1997). Most earthquakes recorded by four stations or more.
- Near-source records are poorly represented: 11 records from 3 earthquakes have rjb < 5km (none with
Mw > 6.4 for which shortest rjb is 7km).
- Most data from 10 ≤ rjb ≤ 100km and 5 ≤ Mw ≤ 6.
- For Irpinia mainshock (23/11/1980), which is composed of three sub-events, used magnitude, location and
time-histories of first sub-event because it can be clearly recognized.
- Assess the standard error of each coefficient using bootstrap technique based on randomly resampling,
with replacement, the original dataset to obtain datasets of the same size as original (500 times). Note the
coefficients using this technique are very similar.
- Note that some coefficients are not significantly different than zero (e.g. c2 and fj) because of the
distribution of data w.r.t. Mw and mechanism.
- Examine residual plots w.r.t. Mw and rjb and find no significant bias or trends.
- Examine inter-event residuals and find them within range ±0.2 except for two earthquakes (2002 Molise
second mainshock and 1990 eastern Sicily), which note could be due to inaccuracies in magnitudes and
locations for these events. Find inter-event residuals for normal earthquakes show smallest dispersion, while
largest variability affects strike-slip events.
- Examine inter-station residuals. Note that most are within range ±0.3 with few with absolute values larger
than 0.4. Discuss the possible reasons for these large residuals in terms of local site profiles.
- Undertake other analyses to understand the source of observed variability in ground motions.
- Also derive model for larger horizontal component using hypocentral distance and no style-of-faulting
terms: log 10Y = 3.4192+0.4672(Mw-5.5)+0.1231(Mw-5.5)2+[-1.2221-0.1643(Mw-5.5)]log 10rhypo+
0.2474S2 + 0.1435S3.
- Note that unmodelled site effects are contributing a significant proportion of the observed variability and
that a more sophisticated classification scheme using depth of soil deposit, average V s of soil deposit and
resonance period could significantly reduce the inter-station variability component.