- Ground-motion model is (for in-slab): where Y is in cm∕s2, H is the Heaviside function, h0 = 100km, c31 = -1.7 (fixed, see below), Rref = 1km,
c1 = 4.229, c2 = 0.877, c32 = -0.00206, c41 = -0.481, c42 = -0.152, c51 = 0.425, c61 = 0.267, c62 = 0.491,
σ = 0.351 (intra-event), τ = 0.112 (inter-event) and ϵ = 0.369 (total).
- Ground-motion model is (for interface):
where Y is in cm∕s2, c31 = -1.7 (fixed, see below), Rref = 1km, c1 = 3.945, c2 = 0.974, c41 = -0.00172,
c42 = -0.00099, c51 = 0.189, c52 = 0.707, σ = 0.330 (intra-event), τ = 0.257 (inter-event) and ϵ = 0.418
- Use 3 site classes:
S = 1, SS = 0
- NEHRP class C site (stiff soil)
SS = 0, S = 1
- NEHRP class D site (soft soil)
S = 0, SS = 0
- NEHRP class B site (rock)
- Use 2 earthquake classes:
- Often oblique-thrust mechanism with down-dip extension and arc-parallel compression. Focal depths
(h) between 67 and 163km. 4.4 ≤ Mw ≤ 6.7. Generally on inner Hellenic arc. 14 earthquakes.
- Often thrust mechanism. 47 ≤ h ≤ 66km. 4.6 ≤ Mw ≤ 6.4. Generally on outer Hellenic arc. 7
Separation made based on Atkinson and Boore (2003) and source location relative to subducting slab.
- Consider 2 locations w.r.t. arc:
ARC = 0
ARC = 1
For h < 100km, define record as back-arc or along-arc based on whether the travel path from source to
site predominantly passes through back-arc or along-arc area (complex classification). For h ≥ 100km
classification is based on location of station, independently of rhyp.
- Locations and magnitudes selected by comparing values from several national and international institutes.
- Use data from accelerometers and broadband instruments (both permanent and temporary) from various
networks from 1994 to 2008.
- Check converted Mw to measured Mw for those earthquakes with both and find good fit (mean difference
of 0.04) with low scatter (standard deviation of 0.16).
- Kythera earthquake (8/1/2006, Mw6.7, h = 67km) contributes large portion of data.
- Note lack of data for h > 100km and Mw > 5.5.
- Study effects of back-arc low-velocity/low-Q mantle wedge. Note challenge in expressing in functional
forms the conceptual geotectonic and wave-propagation model.
- To determine final form of model firstly fit a simple functional form: log Y = c1 + c2(M - 5.5) + c3 log R +
c4R + c51S + c52SS. Classify data by focal depth: 60 ≤ g < 80km, 80 ≤ h < 100km and h ≥ 100km. Also
classify records into back-arc and along-arc. Use c2, c51 and c52 to adjust motions to Mw5.5 and rock and
compute running averages for the different classes. Find large difference in back-arc along-arc motions for
h ≥ 100km for short periods but not for long periods. For shallower depths the difference between back-arc
and along-arc motions is noticeable at long rhyp. These observations motivate the final functional form.
Provide a schematic presentation of the different wave propagation paths depending on depth and location
- For in-slab events, the limited range of rhyp does not allow reliable estimation of geometrical spreading due
to trade-off with anelastic-attenuation coefficient. Hence regress to find geometric coefficient after fixing
anelastic attenuation and using data from two magnitude bins (to examine magnitude dependency). Use
average value of -1.7 as a fixed coefficient in all regressions. Try similar technique for interface events but
did not find reasonable value so use the same coefficient as for in-slab events.
- Examine event terms as function of Mw and h and intra-event residuals w.r.t. rhyp and find no trends.
- Compare observed (adjusted to Mw5.5 and rock) and predicted motions for earthquakes with 60 ≤ h <
100km. Find sufficient fit.
- Note that the large difference between back-arc and along-arc motions may not be usual for other