SDMT-based Analysis of the Liquefaction Phenomena Induced by the April 6, 2009 Earthquake at Ponte Rasarolo, L'Aquila (Italy) Paola Monaco University of L'Aquila, Italy. E-mail paola.monaco@univaq.it Gianfranco Totani University of L'Aquila, Italy. E-mail gianfranco.totani@univaq.it Sara Amoroso Istituto Nazionale di Geofisica e Vulcanologia, L'Aquila, Italy. E-mail sara.amoroso@ingv.it Keywords: liquefaction, seismic dilatometer, 2009 L'Aquila earthquake ABSTRACT: This paper analyzes the liquefaction phenomena induced by the April 6, 2009 L'Aquila earthquake (Italy) at the site of Ponte Rasarolo, L'Aquila, located in the epicentral area. The site was investigated by seismic dilatometer tests (SDMT). The SDMT results were used to perform liquefaction analyses by simplified methods which derive the cyclic resistance ratio CRR from the shear wave velocity V S (Andrus & Stokoe 2000, Kayen et al. 2013) and from the horizontal stress index K D (Monaco et al. 2005, Tsai et al. 2009, Robertson 2012). The cyclic stress ratio CSR was estimated based on data from strong motion recordings in the area. The results of the liquefaction analyses, both based on V S and on K D , confirmed the occurrence of liquefaction in a loose sand layer at about 3 to 4.5 m depth. 1 INTRODUCTION The April 6, 2009, magnitude M w = 6.3 L'Aquila earthquake (central Italy) caused 309 victims, about 1,600 injured, 40,000 homeless and huge economic losses. The earthquake produced a heavy damage in the city of L'Aquila (MCS Intensity I = VIII-IX) and in several near villages (maximum MCS Intensity I = IX-X at Onna and Castelnuovo). The main geotechnical aspects of the L'Aquila earthquake have been investigated by several researchers (see e.g. Monaco et al. 2012). A few cases of liquefaction triggered by the April 6, 2009 main shock have been reported. The most documented is the case of Vittorito, located about 45 km far from the epicentre, known as a nearly borderline "lower- bound" condition for the very low seismic stress which presumably triggered liquefaction. An analysis of the liquefaction phenomena at Vittorito based on the results of seismic dilatometer tests (SDMT) was presented by Monaco et al. (2011). Evidences of liquefaction and paleo-liquefaction near Fossa, about 10 km far from the epicentre, were reported by De Martini et al. (2012). The liquefaction phenomena analyzed in this paper occurred at the site of Ponte Rasarolo, L'Aquila, located only about 1.5 km far from the epicentre. 2 EVIDENCE OF LIQUEFACTION FROM FIELD RECONNAISSANCE Liquefaction and lateral spreading phenomena at the site of Ponte Rasarolo were first detected by Aydan et al. (2009). During post-earthquake field reconnaissance, from April 19 to 23, 2009, in this area (called "Martini district") they observed several sand boils, up to 15 cm thick, at various locations and many NE-SE trending fractures, parallel to the river banks, attributed to liquefaction (Fig. 1). The grain size distribution of soil samples taken from the sand boils (Fig. 2) was found to fall within the easily-liquefiable bounds according to the Japan Port and Harbour Research Institute classification (PHRI 1997). By use of empirical methods, Aydan et al. (2009) estimated a thickness of the liquefied sand layer between 1.5 and 2 m. 3 BASIC GEOLOGICAL SETTING The liquefaction site under study is located South of the hill on which the old city centre of L'Aquila was built, very close to the banks of the Aterno river, at an elevation of ≈ 614 m a.s.l.. This area is formed by Holocene gravelly-sandy alluvial deposits originated