M8.2 Iquique, Chile Earthquake and Tsunami: Preliminary Reconnaissance Observations

The EERI Learning from Earthquakes (LFE) Committee, led by chair Ken Elwood (M. EERI, 1994), reached out to colleagues in Chile to compile this article for the EERI membership that summarizes their initial observations from the April 1, 2014 M8.2 earthquake and tsunami. This article is compiled by Juan Carlos de la Llera Martin of Pontificia Universidad Católica de Chile external link icon with contributions from researchers at the National Research Center for Integrated Natural Disasters (CIGIDEN), Santiago, Chile; researchers from University of Concepción; and Rene Lagos Engineers.

Pounding and infill masonry damage to mid-rise structures. Photo source: Rene Lagos Engineers. (Chile, 2014)On April 1, 2014 at 20:46:50 local time (23:46:50 UTC), a Mw8.2 megathrust earthquake, with a depth of 20.1 km and epicenter 95 km NW from Iquique, ruptured an estimated surface of about 40 km (strike) by 30 km (dip) with a maximum slip of about 6.5 m (USGS). This earthquake occurred in a historic seismic quiescence zone in Northern Chile (previous significant Mw8.8, 1877). The seismic sequence started March 16 with an Mw6.7 earthquake, and foreshock activity that ended in a quiet period of 2.5 days. Following the main shock, a new aftershock (Mw7.6) occurred south of Iquique April 3 at 2:43:14 UTC (21:43:14 local time). Six people have been reported dead as a direct consequence of this earthquake.

More than a million people felt the ground shaking. The seismic intensity was strongest in Iquique (MMI VII), Arica (VII), and Tacna (VI). The earthquake also generated a tsunami with a maximum water run up measured of 4.4 meters above sea level and 3.15 meters above sea level at Patache and Iquique, respectively (CIGIDEN). The tsunami affected mostly fishermens’ activities and all coastal towns from Arica to Iquique. The maximum inland penetration of water was 315 m at the Ike-Ike beach.

Tall building with no visible structural or non-structural damage. Photo source: Rene Lagos Engineers. (Chile, 2014)The region is an industrial area (mining, fishing, commerce). Small towns and villages with non-engineered adobe and masonry houses were strongly affected by the main shock (Figure 1). Some concrete-block masonry houses and short buildings were severely damaged, but no collapse was observed. Heavy damage occurred in some locations in Iquique and Alto Hospicio, the latter showing a clear topographic amplification effect. Three-story building blocks founded on collapsible soils in Alto Hospicio were damaged due to seismically-induced settlement. Extensive diagonal shear cracks were observed in the first-story masonry walls of the 5-story complex Pablo Neruda (Iquique). The estimated total number of damaged houses in the affected region is over 13,000.

High-rise buildings (38 stories or less) showed no structural damage in Iquique beyond small pounding between structures (Figure 2), and localized moderate cracking and spalling in some columns. Large non-structural damage was observed in Zofri (Iquique’s free trade zone). Nonstructural failures contributed largely to the public’s perception of significant damage.

Damage to the north end of Iquique Port Pier 1. Photo source: Gonzalo A. Montalva and Fernando A. Cerda. (Chile, 2014)The port of Iquique had one of the two piers damaged due to liquefaction and lateral spreading in the eastward direction (Figure 3). The damaged pier dates from 1928, and the east wall of the damaged pier tilted outward leading to a settlement of about 1.4 m of the central platform measured next to the pier. The other pier, responsible for 85% of the cargo of the port, had been retrofitted in 2007, thus suffered only minor damage.

The electricity was shut down as a result of the earthquake, with 50% of the service recovered in Iquique in 24 hours. Water supply was recovered slower than electricity, taking a full week to recover at Cerro Dragon (Iquique).

Slope (20°) displacement on Route A16 is 40cm vertical and 10 cm horizontal. Photo source: Gabriel Candia A. (Chile, 2014)Traffic on route A16 was interrupted as a result of movement of several unstable slopes and rock falls. This route is strategic for the regional economy, and an 80 m long section dropped 40 cm (Figure 4). Slope stability failures occurred at various locations on the natural terrace along the coast; measured accumulated displacement reached over one meter. Rockfalls from the hillside caused major traffic delays, until the traffic flow was partially restored two days after the earthquake. Basement walls, bridge abutments, and retaining walls performed well at this level of ground accelerations (PGA ~ 0.3g). Some cantilever walls of Cerro Dragon (Iquique) sustained significant rotations (Δ/H~1%-8%).

More information can be found and continues to be added to the Clearinghouse website at http://www.eqclearinghouse.org/2014-04-01-chile/.