Evaluation of Liquefaction Potential Through Geophysical Tests Case: Earthquake in Lagunas, Peru 2019

On May 26, 2019, at 02:41 h (Peruvian time), the Mw 8.0 Sismo Lagunas 2019 earthquake occurred. It had its epicenter at the coordinates: − 05.74°, − 75.55°, 60 km south of the town of Lagunas (Loreto), at a depth of 135 km with Mw 8.0. It caused a lot of damage, including the liquefaction phenomenon reported in the woody village of Tamarate. The maximum horizontal acceleration recorded was at the UNTRM Station (0.098 g) in Chachapoyas with an epicentral distance of 292.21 km. In December 2019, geophysical tests were conducted in the woody village center of Tamarate, the area where the soil liquefaction event was evidenced. The reasons for choosing to use multi-channel surface wave and ambient vibration tests are based on (i) the fact that the area is only accessible by river. And (ii) the used geophysical equipments are practical and easy to handle and transport compared to the usual equipment such as the Standard Penetration Test and Cone Penetration Test for liquefaction potential evaluation. Multi-channel surface wave and ambient vibration analysis tests were performed to determine the shear wave velocity profile and the fundamental period of the ground. Seismic profiles and average wave velocities were Vs30 (163–168 m/s). The predominant period values obtained in the study area were 0.5 and 0.7 s. The occurrence of soil liquefaction (FSL) was evaluated using the deterministic method as the ratio of the minimum strength normalized cyclic shear stress producing liquefaction or “Cyclic Resistance Ratio” (CRR) divided by the normalized cyclic shear stress induced by the earthquake or “Cyclic Stress Ratio” (CSR). The CRR parameter was determined at each depth up to 30 m. With this evaluation, the actual minimum acceleration value that occurred in Tamarate was found between 0.1 and 0.12 g. A soil liquefaction was generated up to a depth of 13.2 m.