Geotechnical characterization of Viña del Mar for areas where buildings were affected by mega-earthquakes in Central Chile

Abstract

Over the course of little more than a century, several large-magnitude earthquakes have struck Central Chile. In the area within the Marga-Marga basin in the city of Viña del Mar, notable damage to buildings suggests the occurrence of local seismic site effects. While seismic microzonation studies have attempted to explain such effects, the geotechnical characteristics adopted are generally oversimplified. This article addresses this with a thorough geotechnical characterization of the areas in Viña del Mar that sustained outsized damage to structures. The article provides a robust and updated geotechnical and geophysical database of the area, with additional analysis from records of the city’s urban development, geomorphology, and geology features. The study builds on geotechnical data from previous seismic zonation studies following the 3 March 1985 earthquake; building design projects undertaken between 1977 and 2018, including 89 standard penetration test (SPT) boreholes, 58 dynamic cone penetration tests (DCPT), 18 refraction microtremor surveys (ReMI), and 16 Down-Hole tests; and rock depth estimates from 63 horizontal to vertical spectral ratio (HVSR) tests. These data were used in data spatialization techniques to model geotechnical units along one (1-D) and two-dimensional (2-D) profiles, for the foundations of buildings damaged after the 1906, 1985, and 2010 earthquakes. The results show the existence of deep the existence of deep soft soils, high impedance contrast between geotechnical units shape of rock, and the dynamic soil properties can explain the damage observed in the studied area damage in the studied area. The study provides significant background and experimental information for the area, where there is enough seismic potential available to produce a large earthquake in the coming decades of similar characteristics as the 1730 Valparaiso earthquake (9.1–9.3 Mw).