Rotation of objects during the 2009 L’Aquila earthquake analyzed with 3D Laserscans and discrete element models

Abstract

Earthquake-rotated objects (EROs) have been observed and described for centuries (e.g., Hoffmann, 1838; Mallet, 1862; Reid, 1910). Several theories about the rotating mechanisms have been developed. Kozák (2006) classified rotating effects as those caused by a deviation between the projection of the center of gravity into the contact plane and the point of strongest adhesion (Rot1) and those due to subsequent arrival of ground-motion phases from different directions (Rot2). The EROs found in the literature include parts of buildings, such as chimneys, monuments, tombstones, and columns, often described with great care and in detail by early earthquake reports (Mallet, 1862) or still accessible (Boschi et al., 1995). However, in most cases rotational effects are observed on vertically oriented objects such as gravestones, tall monuments, and single columns (Kozák, 2009). Although earthquake- toppled objects (ETOs) allow the determination of minimum ground-motion thresholds which caused the toppling (Kamai and Hatzor 2008; Hinzen, 2010, 2012), EROs and earthquake-deformed objects (EDOs) present the chance to make a more detailed back calculation of the causative ground motion (Yegian et al., 1994; Lee et al., 2009; Hinzen et al., 2010; Hough et al., 2012). Numerous EROs were observed and documented during the 2009 L’Aquila earthquake in central Italy. Cucci and Tertulliani (2011) and Castellano et al. (2012) showed a correlation between the occurrence of EROs in the mesoseismal zone, the fault orientation, and the site conditions. Some of the simply structured and vertically oriented objects mapped by Cucci et al. (2011) and Cucci and Tertulliani (2011) offer the opportunity to use local strong-motion records to test different hypotheses about the mechanisms that caused the rotation. A main question in this context is whether near-field rotational components of ground motion are necessary to rotate the studied objects or whether 3D purely translational ground motions are sufficient to explain the observations. In this study, we use discrete-element models of EROs that are based on laser scans to study the dynamic behavior of the EROs and rotations induced by translation ground motions and uneven foundations.