Fig.2 shows the attenuation relation of
the recorded peak ground acceleration (PGA) and the fault
distance. The fault distance is referred to in NIED’s definition.
In the figure, the empirical attenuation relation by Si and
Midorikawa (2000), with amoment magnitude of 6.8, is also illustrated. The empirical relation goes through the center of
the recorded values. This means that the earthquake produced
average groundmotion. However, in a very short range, the
discrepancy between the recorded value sand the empirical
ones is very large. Several PGA values exceed the gravity unit
(e.g., 980cm/s2) in the short range. The largest PGA is
obtained at Ichinoseki-Nishi Station (IWTH25), which is the
closest station to the hypocenter (Fig. 3). APGA value of
3866 cm/s2 was obtained for the vertical component, which is
a world record of PGA. This ground motion will be discussed
later in the chapter. The largest horizontal PGA value of
2449cm/s2 was obtained at AKTH04.