Preliminary Observations by Montalva and Cerda at Universidad de Concepción

Although the 8.2 Mw that struck Iquique this past April 1st was less energetic than the 2010 Maule EQ, the available records show the same surface intensity demand for similar site conditions. The geotechnical and structural damage is much less than the one registered in 2010, the reason will probably be attributed to better site conditions. Since distance to the rupture are about the same and preliminary finite fault solutions (by USGS) show that the major slip occurred very close to the city of Iquique (Figure 1) these variables would not explain the relatively minor damage observed.

From a geotechnical perspective, the port of Iquique is a major feature where an entire pier liquefied and spread eastward, this was a 1928 structure that had not pass any major earthquake. Some field measurements where already performed and more are likely to be done to further study this case. Due to the stiff site conditions, it was difficult to observed evidence of site effects on structural damage distribution (as it is so clear for the 2010 event). Perhaps the only case where topographic amplification was observed was in Alto Hospicio, where a building located at a topographic disruption had some structural damage on the compression reinforcement (figure 3). Also in Alto Hospicio three story building blocks, located on saline collapsible soils, were damaged due to seismically induced settlements of this very stiff soil material. Retaining wall failures were observed at different locations, all of them were on the steep zones of Cerro Dragón (southern aeolian dune) and built with confined masonry, RC retaining walls showed excellent behavior. Slope stability failures occurred at various locations on the natural terrace along the coast, measured accumulated displacement reached over a meter.

Nonstructural failures contributed largely to the public’s perception of significant damages. This is an issue that the engineering community should address.

Figure 1. Finite fault solution with major slip near the city of Iquique.

Figure 2. Northern end of pier 1 at port of Iquique.	Figure 3. Buckled reinforcement at Villa La Tortuga, Alto Hospicio.