Abstract

Two fault zones (La Cabrera and El Horno) have been detected by an acoustic reflection survey of the subsurface of Lake Valencia. These nearly parallel fault zones, which are about 15 km long, trend in an east-northeast direction and appear as normal faults in the reflection profiles. Movement along these faults occurred in late Pleistocene (El Horno fault zone) and late Pleistocene to Holocene time (La Cabrera fault zone). The amount of normal displacement is about 2.0 to 2.8 m for the late Holocene and 3.8 to 4.5 m for the entire Holocene, or calculated rates of normal separation of 0.2 to 0.3 mm/yr for late Holocene movement and 0.4 to 0.5 mm/yr movement during the entire Holocene. These fault zones are located within the La Victoria fault zone, a major structural boundary of the Caribbean Mountains. They pass through major population and industrial centers of the Lake Valencia basin. These data show that the La Victoria fault zone is an active feature, despite a low historical seismicity.

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