SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT 2.2.3 Valparaíso earthquake, 1985
On 3rd March 1985, in the central part of Chile occurred an earthquake of Mw = 8.0. Figure 9 presents selected acceleration records from the 1985 and 2010 seismic events, where it is possible
to observe the differences in terms of amplitudes and durations for the same stations.
Figure 9. Acceleration records of the Valparaíso (1985) and Maule (2010) earthquakes[4]
The seismic event of 1985 confirmed a quite systematic sequence of earthquakes that have occurred in this part of Chile. This sequence has been inferred from the large earthquakes which occurred in this area in 1575, 1647, 1730, 1822, 1906 and 1985. This sequence can be characterized by an average period of 82 years ± 6 years[6]. The aftershocks of the 1985 earthquake defined a rupture area of 170km by 110km. The main shock was the result of two shocks; the first motion began at 22:46:56 and then a larger event took place at 22:47:07 (Greenwich Mean Time). The maximum peak accelerations were recorded at the Llolleo seismic station, reaching a vertical component value of 0.85g, whereas the maximum peak horizontal component reached a value of 0.67g (N10E).
This situation of a larger vertical acceleration has deserved important studies regarding its effect on the stability of civil structures. However, in other stations such as Melipilla, the peak horizontal accelerations were larger than the vertical component: 0.67g in the north- south component and 0.59g in the vertical component[7].
Besides the enormous damage to buildings, industrial structures, ports, roads, and infrastructure in general, there was significant impact to some small earth dams and tailings dams, but only minor damages on large earth dams, as discussed in Chapters 3 to 6.
Vol XXXI Issue 3
DAM ENGINEERING
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