Continuous Seismic Monitoring of a Colonial Church in Cusco, Peru: Unveiling Remarkable Soil-Structure Interaction and Nonlinear Dynamics

Abstract

The dynamic response of historical masonry structures involves multiple sources of nonlinearity, arising from the materials used, the ageing, the complex geometries and boundary conditions involved. As a result, modelling the seismic response of these buildings requires detailed instrumentation beforehand. Crossed by active faults and frequently shaken by moderate earthquakes (Mw3–4), the Cusco region (Peru) has many stone and earth masonry buildings that turn out to be particularly vulnerable to the seismic hazard. We therefore conducted an ambient vibration-based survey in the 17th-century church of San Cristobal in Cusco, seriously damaged by the 1950 earthquake. By combining an Operational Modal Analysis, single-sensor monitoring for over a year and free-field microtremor measurements, our work highlights the existence of strong soil-structure interaction and topographic effects resulting in the excitation of a rigid-body-like mode. Continuous instrumentation also made it possible to study the structure’s response to earthquakes, revealing an unexpected frequency drop during a Mw4.2 earthquake, followed by a slow recovery process that lasted more than two months. These results shed new light on the seismic vulnerability of the church, and call for further investigation into the processes behind the site effects and nonlinear dynamics that characterise the response of Andean built heritage.