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The 2007 M8.0 Pisco, Peru Earthquake

 

Approximate area of a massive lateral displacement of the marine terrace in Canchamaná. The boundary of the mobilized area on the north is uncertain and could possibly extend further (background image from Google Earth).

The Mw8.0 Pisco, Peru Earthquake of August 15, 2007 struck the coastal and inland mountainous regions of central Peru (epicenter approximately 150 km south of Lima), causing severe damage to the cities of Pisco, Ica, Cañete, Chincha, and Tambo de Mora, killing more than 500 people (INDECI 2007).  INDECI also reports that the earthquake destroyed 55,000 buildings and damaged an additional 21,000. Most of the fatalities occurred in the city of Pisco, where about 80% of the buildings either collapsed or were seriously damaged. The earthquake was a result of the subduction process between the Nazca plate and the South American continental plate, and was recorded at 16 stations within 150 km of the fault. The figure to the right illustrates the approximate area of a massive lateral displacement of the marine terrace in Canchamaná. 

The Massive Canchamaná Lateral Spread

During the earthquake a massive liquefaction-induced lateral spread occurred on a marine terrace in Canchamaná, 2 km north of Tambo de Mora, Peru. Several of the researches involved with the project documented this lateral spread in the field immediately after the earthquake, estimating it to be at least 3-km long by 1-km wide (see figure). At approximately the midpoint of this feature, the cumulative lateral displacement (obtained from adding up the widths of tension cracks) totaled more than 5 m (Meneses et al. 2009).  

A review of the literature indicates that the Canchamaná lateral spread is likely the largest documented in historical times. However, owing to its enormity the team members could not conclusively establish its boundaries and quantify its displacement in the field. Therefore, upon returning from Peru, pre- and post-earthquake satellite images of the area were acquired and analyzed by personnel from the Center for Advanced Pisco, Peru Earthquake map of displacement vectors. Map produced during preliminary study. Center for Advanced Spatial Technologies CAST, University of Arkansas. Spatial Technology (CAST, at the University of Arkansas) as a means to determine the magnitude and spatial variability of the lateral displacement (shown on map to the left). Due to a limited budget of this preliminary study, the satellite images could not be purchased as desired for optimum processing (both in terms of the raw data format and their areal extent). Despite this shortcoming, results from preliminary analyses confirmed significant lateral movement along the marine terrace and indicated that the lateral spread may have extended at least another 3 km further to the north (resulting in a total length of approximately 6 km). These preliminary results spatially link a 400-m long, liquefaction-induced slope failure that damaged the Pan American Highway at Jahuay (north of Point D) to the Canchamaná lateral spread (two events that were initially believed to be separate).

Further Satellite Image Processing of the Canchamaná Lateral Spread

Pre- and post-earthquake satellite images with rigorous sensor orientation models have been shown to produce orthoimage accuracies in the 2-3 meter range when combined with DTED Level 2 elevation models (Toutin 2001, Fraser 2003) and even sub-meter accuracy when combined with better elevation models. Therefore, “basic” product pre- and post-earthquake images were purchased for the study area and well distributed ground control was collected with carrier-based differential GPS to complement the existing control.  New points were collected across the entire area and distributed in a way designed to yield the highest possible bundle adjustment accuracies of the satellite images (Grodecki 2003, Cothren 2005a, Holland et. al. 2007, Noguchi, et. al. 2004). Redundant points were also collected and used as check points to better assess the accuracy of the resulting orthoimages and DEM's.

      After processing the new imagery, approximately 400 identifiable points were measured on the new orthoimages to look again for horizontal displacements of the extended (6-km) stretch of the marine terrace relative to the Canete formation.  Similar to the preliminary results, significant lateral displacement was measured along the marine terrace and further analysis is ongoing.

This project is a joint effort between members of the University of Arkansas, Drexel University, Washington State University, and the Center for Advanced Spatial Technologies. Members include Dr. Brady Cox (University of Arkansas College of Engineering), Dr. Joseph Wartman (Drexel University College of Engineering), Dr. Adrian Rodriguez-Marek (Washington State University Department of Civil & Environmental Engineering), Dr. Jack Cothren and Dr. Jason Tullis (University of Arkansas Department of Geosciences and CAST), and Adam Barnes (CAST).