SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


Figure 1. Reservoir capacity in millions of m3, MOP[3]


2. Tectonic and Seismic Chilean Environment 2.1 Subduction seismic environment


The seismic activity of Chile is mainly the result of the subductive seismic environment generated by the collision between the Nazca and South American tectonic plates, which are converging at an estimated rate of 65-80mm per year. The Nazca plate is subducting under the South American plate, moving down and landward. Accordingly, four types of seismic mechanisms in the Chilean subductive seismic environment can be identified: outer rise (outside trench, in the bending zone of the Nazca Plate), interplate or thrust-faulting type that occurred on the interface between the plates, intraplate that takes place inside the Nazca Plate, and cortical (faults on the South American Plate).


From an engineering point-of-view, the most important earthquakes are the interplates of large magnitude. Then, the intraplates and corticals are important too, but their severe effect is restricted to a rather limited zone close to the epicentre. Typical acceleration records of both intraplate and interplate Chilean earthquakes are shown in Figure 2 and Figure 3, respectively. The records obtained at Pica are associated with an intraplate earthquake


(Tarapacá earthquake, Mw = 7.8, 13th June 2005), and the recorded accelerations at Talca are associated with an interplate earthquake (Maule earthquake, Mw = 8.8, 27th February 2010). The main features of intraplate earthquakes are the high value of the peak vertical


acceleration (PGA), the high frequencies (low period), and the rather short duration. On the other hand, the interplate earthquakes have high peak accelerations (in general, horizontal components are greater than vertical), a broad frequency band, and a long duration.


Vol XXXI Issue 3


DAM ENGINEERING


187


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