HR: 17:50h
AN: S24A-07    [Abstracts]
TI: Methodology for the Caracas Seismic Microzonation Study
AU: Hernández, J J
EM: julher@cantv.net
AF: Consultant, Venezuelan Foundation for Seismological Research (FUNVISIS), Caracas, Venezuela
AU: * Schmitz, M
EM: mschmitz@funvisis.gob.ve
AF: FUNVISIS, Venezuelan Foundation for Seismological Research, Caracas, Venezuela
AB: Currently, the Venezuelan Foundation for Seismological Research (FUNVISIS) is executing the Caracas Seismic Microzonation Study. Fundamental objectives are the selection of microzones of similar response and the determination of landslide susceptibility. Both result from a guided combination of damage data of 1967 Caracas earthquake, landslides inventory, geophysical investigations, seismic hazard analysis, geological information, geotechnical database, and earthquake engineering estimations of soil response and probable hillside behavior. Geophysical investigations include refraction seismic, microtremor and gravimeter measurements, for modeling the valley basin; sediment thickness to bedrock reaches 350 m. The model was calibrated with three deep drillings, in which accelerometers will be placed for future comparisons between surface and bedrock seismic motions. Probabilistic seismic hazard analysis was performed, leading to uniform hazard spectra for 475-year mean return period and deaggregation of magnitude-distance pairs, differentiated within the Caracas bedrock. A parametric one-dimensional dynamic soil response study was performed with varying sediment thickness (0-350 m), average shear wave velocity in the upper 30 m (150-500 m/s), and nonlinear soil properties; 144 representative soil profiles were analyzed. The mean amplification of spectral response values of ther surface regarding to the bedrock is obtained, in order to determine probable surface spectra using the bedrock PSHA spectra as input. The seismic effects of the basin are incorporated in an approximate way, from numerical simulations of the 2D and 3D seismic response and statistical data around the world. Finally, a set of microzones with similar average response spectrum is selected, by means of correlating their geological, geophysical and geotechnical properties with those of the parametric study. Hillside pre-seismic hazard is established from lithological properties, slope gradients and seasonal and rainfall wet indexes, estimating the static factor of safety. Newmark displacements and probability of failures are estimated using PSHA results and statistical correlations, leading to the qualification of the earthquake-induced landslide susceptibility. The results will allow updating the municipality ordinances, in order to improve the design and safety construction of new buildings and establish reinforcement priorities of the existing ones. Contribution to projects FONACIT 200400738 (with funds from IDB) and FONACIT-ECOS Nord 2004000347.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 9360 South America
SC: Seismology [S]
MN: 2007 Joint Assembly