LUIS VALENZUELA P, RAMON VERDUGO A, JOSE CAMPANA Z & CARMEN G OPAZO A


Considering the large extension of the rupture zone the concept of a hypocenter associated with a single point has to be replaced by the actual physics of the phenomenon, consisting of an approximately planar area from where the seismic energy has emanated according to the evolution of the rupture itself. In the context of earthquakes of large magnitude, the hypocenter has to be identified as the place of initiation of the rupture, or the starting point of the earthquake.


The horizontal peak ground accelerations (PGA) recorded on rock outcrop and soil deposits are presented in Figure 5. It is interesting to observe that horizontal PGAs recorded on rock outcrops are surprisingly moderate; in fact, according to the available data the maximum recorded value is 0.32g in Santa Lucia Hill, Santiago. However, it is important to recognize that there was a lack of accelerometers in the most affected area toward the south of the rupture zone.


Figure 5. Recorded PGA on rock outcrop and soil deposits of the Maule earthquake (2010)[5]


Another important characteristic of this mega-earthquake is its duration. The available records show two general patterns; to the south of the rupture zone the duration of the ground motion tends to exceed 2 minutes (i.e. San Pedro, Figure 6a), but to the north of the rupture the duration is systematically shorter (i.e. Melipilla, Figure 6b). In any case, the long duration of the ground motions is a characteristic of earthquakes of large magnitude, which certainly increases their destructiveness.


190 DAM ENGINEERING


Vol XXXI Issue 3


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