- Ground-motion model is:
where PGA is in cm∕s2, c1 = 5.432, c2 = 1.035, c3 = -1.358, c4 = -0.0072 and σ = 0.397.
- Sites have different soil conditions, some medium and stiff sites and some very soft soil sites.
- Use some records from Moldova and Bulgaria.
- Focal depths, h, between 91 and 133km.
- Records from free-field or from basements of buildings.
- Originally include data from a shallower (focal depth 79km), smaller magnitude (ML = 6.1, Mw = 6.3)
earthquake with shorter return period than other three earthquakes, but exclude in final analysis.
- Originally do attenuation analysis for two orthogonal directions N45E (which is in direction of fault plane)
and N35E (which is normal to fault plane). From this define 3 90∘ circular sectors based roughly on tectonic
regions, and calculate attenuation relations for each of these sectors as well as for all data. Find azimuthal
- Remove 1 to 3 anomalous records per sector.
- Remove the only record from the 4/3/1977 earthquake, because it has a strong influence on results, and
repeat analysis using model lnPGA = b1 + b2M + b3 lnR, find lower predicted PGA.
- Find slower attenuation in direction of fault plane compared with normal to fault plane.
- Find faster attenuation and larger standard deviation (by finding attenuation equations for two different
earthquakes) for deeper focus and larger magnitude shocks.