An 8.8 Magnitude E.Q. Shook Offshore Maule, Chile on Feb 27, 2010An 8.8 Magnitude earthquake hit the offshore Maule, Chile on Feb. 27, 2010. The epicenter of the earthquake was located 95 kilometers from Chillan, the nearest major city of Chile. This earthquake took place at the boundary between the Nazca and South American tectonic plates at a depth of 35 kilometers [USGC fact sheet]. The two plates are converging at a rate of 70 mm per year. The death toll has exceeded 800 so far but the total fatality number is not clear yet. At least 1.5 million houses were damaged by the earthquake-tiggered tsunami in the Concepcion-Valparaiso area. Minor damage to boats and a dock in the San Diego area, California were caused by a Pacific-wide tsunami. The earthquake was felt in most parts of Chile, Argentina and some parts of Bolivia, southern Brazil, Paraguay, Peru and Uruguay. More than 90 aftershocks have been recorded, ranging from 4.9 to 6.9 in magnitude. A 6.2-magnitude aftershock was recorded near the earthquake's epicenter on Feb 28. The Feb 27, 2010 earthquake occurred 230 kilometers north of the 9.5 magnitude event that took place in May of 1960, the largest earthquake worldwide recorded by instrumental seismology. The Canadian Association for Earthquake Engineering is sending a reconnaissance team on March 8 and March 9, 2010 to investigate the effects of the earthquake on physical infrastructure. The initial report received from Professor Ruben Boroschek of University of Chile indicates that, at two locations measured in Santiago, the peak horizontal ground accelerations were 0.17g and 0.24g, with corresponding peak vertical ground accelerations of 0.14g and 0.13g, respectively. The peak spectral accelerations at these two locations are 0.56g and 0.66g, respectively. The soil conditions at these locations are unclear. Comparisons with Chilean Code requirements indicate that the recorded spectral accelerations were generally in agreement with code recommended design values, with lower values within the short period range, and exceeding design values slightly in the high period range (beyond T = 1.0 sec). Similar comparisons were made with the same two records by John Adams of the Geological Survey Canada against the Uniform Hazard Spectra for Victoria, B.C., using firm soil conditions and the National Building Code of Canada (NBCC-05). The comparisons indicates that the NBCC-2005 values provide a good envelop for the spectra of these two records, with slightly higher values at 0.2 sec. |
