HR: 1400h
AN: S33B-07    [Abstracts]
TI: Dynamic Soil Modeling of Caracas Valley for the Simulation of the 1967 Caracas Earthquake
AU: Tanaka, I
EM: ichiro@oyointer.com
AF: OYO International Corporation, 6 Rokubancho, Chiyoda-ku, Tokyo, 1020085, Japan
AU: Yamazaki, Y
EM: yamazaki@oyointer.com
AF: OYO International Corporation, 6 Rokubancho, Chiyoda-ku, Tokyo, 1020085, Japan
AU: Orihuela, N
EM: norihuela@funvisis.gob.ve
AF: FUNVISIS, Venezuelan Foundation for Seismological Research, Apartado Postal 76.880, Caracas, 1070, Venezuela
AU: Hernandez, J
EM: julher@cantv.net
AF: FUNVISIS, Venezuelan Foundation for Seismological Research, Apartado Postal 76.880, Caracas, 1070, Venezuela
AU: * Schmitz, M
EM: mschmitz@funvisis.gob.ve
AF: FUNVISIS, Venezuelan Foundation for Seismological Research, Apartado Postal 76.880, Caracas, 1070, Venezuela
AU: Feliziani, P
EM: geologia.2000@cantv.net
AF: Geologia 2000, Caracas, Caracas, Venezuela
AB: We developed a ground model in Caracas metropolitan area in Venezuela, to evaluate seismic amplification of the site and to develop earthquake scenarios. This is a part of the results obtained from a study on "Disaster Prevention Basic Plan in the Metropolitan District of Caracas in the Bolivarian Republic of Venezuela", executed by Japan International Cooperation Agency. Geotechnical borings database development in Caracas was underway that contains description of geological texture, ground water level, and SPT-N value. The maximum depth of boreholes database with geotechnical information is about 30m, whereas the deepest depth of the basin may reach more than 300 m. Wells and seismic refraction surveys results were available for estimation of the soil characteristics of deeper deposit and thickness distribution of the alluvial deposit. Micro-tremor measurements in large plain area in Caracas valley were carried out in 500m mesh by FUNVISIS and researchers from Japanese universities with the total number of 329 points. The depth of bedrock was estimated from deep wells and seismic refraction surveys results. The average shear wave velocity of the deposit above the bedrock was estimated from micro-tremor measurement. Shear wave velocity of geological layers in top 30 m or less were estimated from average SPT-N values of each layer using empirical relationship between soil types, N-value and shear wave velocity developed in Japan, For the non-linear properties of soils, such as damping and rigidity versus shear strain, appropriate curves according to soil types developed in Japan were used. The ground model in each mesh was calibrated by comparing the predominant period of H/V (Horizontal/Vertical) spectrum ratio of micro-tremor with the predominant period of theoretical amplification curve computed from the ground model. The selected 287 borehole data were applied to each nearer mesh for the modelling of shallow subsurface soils. To verify the reasonableness of the methodology and the ground model, the possibility of the reproduction of the 1967 Caracas earthquake was firstly tested. Scenario fault was located between two major sub-events, separated by 42 km, with a mechanism of strike slip with Mw= 6.6. An empirical attenuation formula that involves near-field source mechanism and different ground conditions, and which is applicable to earthquakes with large magnitudes, was used to estimate the ground motion on bedrock. The input wave was selected from worldwide strong motion database, generated from an earthquake with the same mechanism and compatible magnitude, recorded on bedrock at a distance compatible to the distance between the fault and the study area. Higher seismic intensities were observed in Palos Grandes and San Bernardino area during the 1967 Caracas earthquake. This was attributed to the thick deposit in those areas. The seismic intensity calculated using an empirical relation between spectrum intensity (SI) and seismic intensity (MMI) was able to reproduce the higher intensities in the two areas with application of the developed one dimensional dynamic ground model. This methodology was applied to simulate other earthquake scenarios as well.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 9360 South America
SC: Seismology [S]
MN: 2007 Joint Assembly