Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 255

(c)
Figure 7.31 Vertical component: (a) Effect of last ball; (b) Influence of P waves
(Gioncu and Mazzolani, 2002); (c) Vertical-to-horizontal ratios, the Northridge
earthquakes (Gioncu and Mazzolani, 2002, after Hudson et al, 1996)
Peak ground velocity. Looking to Figures 7.27 and 7.29, one can note that the
velocity records are the most significant for characterizing the ground motions in
the near-source areas. It is a damage potential indicator, due to the high influence
on the material properties (strain rate) (Gioncu and Mazzolani, 2002). Near-source
records obtained during the 1979 Imperial Valley strike-slip earthquake contain
severe velocities. Figure 7.33a shows the location of the recording stations, while
Figures 7.33b-e present the recorded velocities of the fault-normal components in
the four stations: two can be considered as influenced by forward directivity, one is
in a neutral position and one is situated in backward directivity conditions. One can
see that the maximum-recorded velocity in the forward directivity is about 120
m/sec, while it is about 40 cm/sec only in the backward directivity (Mollaioli et al,
2006). During the 1989 Loma Prieta strike-slip earthquake (M 6.9), the recorded
velocity was about 179 cm/sec (Lexington Dam station); for the 1994 Northridge
thrust earthquake (M 6.7), the maximum recorded velocity was 174 cm/sec
(Rinaldi station) and for the 1995 Kobe strike-slip earthquake (M 6.9), a velocity
of 174 cm/sec (Takatori station) was recorded (Fu and Menun, 2004).