Long period ground motion simulations at the Bogota basin, Colombia, based on a 3D velocity model of the basin from dense microtremors arrays measurements, gravity and …

Abstract:

Bogotá, a megacity with almost 8 million inhabitants is prone to a significant earthquake hazard due to nearby active faults as well as subduction megathrust earthquakes. The city has been severely affected by many historical earthquakes in the last 500 years, reaching MM intensities of 8 or more in Bogotá. The city is located at a large lacustrine basin extending approximately 40 km from North to South and East to West. The sediment infill of the basin is composed of very thick and soft clay deposits (up to 300 m in thickness) in wide areas of the basin, as well as alluvial deposits from rivers towards the South of the basin. We constructed the first 3D velocity model of the basin based on dense microtremors arrays measurements (radius from 60 cm to 1700 m) at 300 sites within the basin as well as single microtremors measurements at 800 points, which allowed us to estimate in detail the velocity model of the basin from the shallow deposits up to the seismic bedrock. Our dense single microtremors measurements in Bogota indicate that horizontal to vertical ratios of microtremors are characterized by large predominant peaks for periods as large as 4 seconds, near the center of the basin. To constraint the geometry of the basin we used available gravity data at approximately 400 points, as well as available geological information from boreholes within the basin. Our results show that the deepest point of the Neogene-Quaternary deposits reach a depth of 800 m with a bottom S wave velocity of 700 m/s. The seismic bedrock (Cretaceous sandstones, Vs= 3000 m/s) reach a depth of 3800 m at the deepest point of the basin. We simulated three …

Año de publicación:

2020

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Fuente:

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