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(A)(B)▲▲Figure 4. DCP test being performed adjacent to a house inBexley after the 4 September 2010 M w 7.1 Darfield earthquake.Photo by R. Green on 15 September 2010.PN 1,60−SPTequiv ≈ N SPTequiv ( N DCPT )⋅⎛ a⎝ ′σ vo⎞0.5 ER⎠ 60% , (1)where N SPT equiv (N DCPT ) is the functional relationship betweenN SPT and N DCPT shown in Figure 5A, P a is atmospheric pressure(i.e., 101.3 kPa), σ′ vo is initial vertical effective stress (in thesame units as P a ), and ER is energy ratio. This relationship usesthe effective stress and hammer energy normalization schemesoutlined in Youd et al. (2001).Although the energy ratio for the system was not measured,the DCP hammer is similar to the donut hammer usedfor the SPT. Skempton (1986) and Seed et al. (1984) suggestedthat the energy ratio for an SPT donut hammer system rangesfrom about 30 to 60%. However, because the DCP system does▲▲Figure 5. A) Relationship between DCP test and SPT N-valuesfor an energy ratio of 60%, and B) comparison of N DCPT and theequivalent N 1,60cs (N 1,60cs-SPTequiv ) for a site in an eastern neighborhoodof Bexley.not have pulleys, a cathead, etc., we anticipate that the energyratio for the DCP is likely to be near the upper end of this range.Therefore, we assumed an ER = 60% for our calculations. Inaddition to the effective stress and hammer energy corrections,the N SPT equiv values were also corrected for fines content followingthe procedure proposed in Youd et al. (2001). Figure5B shows a plot of N DCPT and N 1,60cs–SPTequiv for a test sitein the eastern Christchurch neighborhood of Bexley, whichSeismological Research Letters Volume 82, Number 6 November/December 2011 931