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Strong Ground Motions and Damage ConditionsAssociated with Seismic Stations in theFebruary 2011 Christchurch, New Zealand,EarthquakeHiroaki Iizuka, Yuki Sakai, and Kazuki KoketsuHiroaki Iizuka, 1 Yuki Sakai, 1 and Kazuki Koketsu 2INTRODUCTIONThe February 2011 Christchurch, New Zealand, earthquakewas highly destructive, causing a number of buildings to collapseand killing many people. We examined the properties ofstrong ground motions in this earthquake using the recordsreleased by GeoNet (http://www.geonet.org.nz/). We alsoinvestigated the damage around the seismic stations to determinethe relationship between structural damage and strongground motions.SEISMIC GROUND MOTION INTENSITIES ANDELASTIC RESPONSE SPECTRUMThe locations of the seismic stations in our study are shown inFigure 1. Accelerograms and the elastic acceleration responsespectra, with a damping factor of 0.05 in the maximum horizontaldirection, are shown in Figures 2 and 3, respectively. Peakground accelerations (PGA) and peak ground velocities (PGV)are shown in Table 1. I j and I 1–2 are also shown in Table 1. I j isJMA (Japan Meteorological Agency) seismic intensity (Tables2, 3 and 4). It is publicly used to describe the damaging powerof seismic shaking in Japan. I 1–2 is also an index like I j . It wasdefined by Sakai, Kanno, and Koketsu (2002, 2004) based onelastic responses between 1 and 2 seconds period that wereclosely related with heavy structural damage (the subscript 1–2means between 1 and 2 seconds) and represents the damagingpower of an earthquake much better than I j .As shown in Figures 2 and 3, the records of stationsREHS, CCCC, and PRPC display pulse waves with a periodof 1–2 seconds and have high response in the region of 1–2seconds, whereas stations HVSC and LPCC with large PGAare dominated by short periods below 1 second, and theirresponses between 1 and 2 seconds are low. We comparedREHS’s spectrum, which shows the highest response in the1. Graduate School of Systems and Information Engineering,University of Tsukuba, Japan2. Earthquake Research Institute, University of Tokyo, Japan▲▲Figure 1. Locations of the seismic stations.1–2-second period, with those at Takatori, Fukiai, and JMAKobe recorded in the 1995 Kobe earthquake, which devastatedthe city of Kobe and the surrounding region (Figure4). REHS’s response in the 1–2-second period is similar tothat of JMA Kobe, but it is lower than that of Takatori andFukiai.NONLINEAR SEISMIC RESPONSE ANALYSISWe performed a nonlinear seismic response analysis with asingle-degree-of-freedom system, accounting for Japanesereinforced concrete (RC) buildings (Kumamoto and Sakai2007) and wooden houses (Sakai and Iizuka 2009) and comparedthat data with REHS’s record, which shows the highestelastic response in the period of 1–2 seconds. We adopted theTakeda Model (Figure 5A; Takeda et al. 1970) for RC build-doi: 10.1785/gssrl.82.6.875Seismological Research Letters Volume 82, Number 6 November/December 2011 875