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Use of DCP and SASW Tests to EvaluateLiquefaction Potential: Predictions vs.Observations during the Recent New ZealandEarthquakesRussell A. Green, Clint Wood, Brady Cox, Misko Cubrinovski, Liam Wotherspoon, Brendon Bradley, Thomas Algie, John Allen, Aaron Bradshaw, and Glenn RixRussell A. Green, 1 Clint Wood, 2 Brady Cox, 2 Misko Cubrinovski, 3Liam Wotherspoon, 4 Brendon Bradley, 3 Thomas Algie, 5 John Allen, 6Aaron Bradshaw, 7 and Glenn Rix 8INTRODUCTIONFollowing both the 4 September 2010 M w 7.1 Darfield and22 February 2011 M w 6.2 Christchurch, New Zealand, earthquakes,Geotechnical Extreme Events Reconnaissance (GEER)team members from the United States and New Zealand visitedthe affected areas to assess geotechnical related damage(e.g., Allen et al. 2010a, b). As shown in Figure 1, liquefactionwas pervasive in large portions of the region after both earthquakes.The widespread liquefaction caused extensive damageto residential properties, water and wastewater networks,high-rise buildings, and bridges. For example, nearly 15,000residential houses and properties were severely damaged fromliquefaction and lateral spreading. More than 50% of thesehouses were damaged beyond economic repair. Also, portionsof the central business district (CBD) were severely damagedby liquefaction during the Christchurch earthquake. It is estimatedthat approximately 30% of the buildings in the CBDwere damaged beyond repair, although not all of the damageresulted from liquefaction.Among the field tests performed by the GEER teamwere the dynamic cone penetrometer (DCP) test (Sowers andHedges 1966) and spectral analysis of surface waves (SASW)test (Stokoe et al. 1994). Both of these tests can provide informationabout the liquefaction susceptibility of soil and are relativelyportable, making them suitable for rapid post-earthquakereconnaissance field studies. The objective of this paper is to1. Department of Civil and Environmental Engineering, VirginiaTech, Blacksburg, Virginia U.S.A.2. University of Arkansas, Fayetteville, Arkansas U.S.A.3. University of Canterbury, Christchurch, New Zealand4. University of Auckland, Auckland, New Zealand5. Partners in Performance, Sydney, Australia6. TRI Environmental, Inc., Duluth Minnesota, U.S.A.7. University of Rhode Island, Kingston, Rhode Island, U.S.A.8. Georgia Tech, Atlanta, Georgia, U.S.A.provide an overview of DCP and SASW tests performed acrossthe Christchurch region and to summarize the comparison ofthe observed versus predicted liquefaction occurrence duringboth the Darfield and Christchurch earthquakes.BACKGROUNDAt 4:35 a.m. on 4 September 2010 NZ Standard Time, thepreviously unmapped Greendale fault ruptured, producing theM w 7.1 Darfield earthquake. The epicenter for this event wasapproximately 40 km west of the center of Christchurch, butthe closest distance from the fault rupture to the western suburbsof Christchurch (e.g., Hornby) was only about 10 km (e.g.,Allen et al. 2010a). As shown in Figure 2, representative geometricmeans of the recorded horizontal peak ground accelerations(PGAs) were 0.71 g in the epicentral region, 0.20 g in theCBD, 0.32 g in Kaiapoi (north of Christchurch), and 0.27 gin Lyttelton (south of Christchurch) (e.g., Allen et al. 2010b).The M w 6.2 Christchurch earthquake occurred at 12:51p.m. on 22 February 2011 NZ Standard Time. As with theDarfield earthquake, the Christchurch earthquake occurred ona previously unmapped fault, the Port Hills fault, located in thePort Hills south of Christchurch. The distance from the epicenterto the center of Christchurch was about 8 km, but the ruptureplane was directly beneath some of the southern neighborhoodsof Christchurch (e.g., Heathcote Valley) and Lyttelton.As shown in Figure 2, representative geometric means of therecorded PGAs were 1.31 g in the epicentral region, 0.42 g inthe CBD, 0.20 in Kaiapoi (north of Christchurch), and 0.11 gin Templeton (west of Christchurch).Much of Christchurch and its environs were originallyswampland, beach dune sand, estuaries, and lagoons that weredrained as part of European settlement (Brown et al. 1995).Consequently, in large areas the near-surface soil stratigraphyis characterized by inter-bedded, loose Holocene aged silt,sand, and gravel that are highly susceptible to liquefactiondoi: 10.1785/gssrl.82.6.927Seismological Research Letters Volume 82, Number 6 November/December 2011 927