MEE20704

Mónica Beatriz Olivar Amaya

Supervisor: Toshiaki YOKOI, Takumi HAYASHIDA

Country: El Salvador

Abstractfulltext

We obtained the site effects from two strong motion observation sites around the City of Tsukuba, with strong ground motion and microtremor records. We estimated the Horizontal-to-Horizontal Spectral Ratio (HHSR), which is a direct estimation of the site amplification, and the Horizontal-to-Vertical Spectral Ratio (HVSR) from 13 earthquakes recorded at a KiK-NET station. We also calculated the HVSR for microtremor records from measurements of a broadband seismometer and a strong motion accelerometer, and the dispersion curves of Rayleigh waves from array measurements performed with broadband seismometers, and short period sensors. With these products we performed the joint inversion analysis and obtained the S-wave velocity structure for three groups of data: the reference group, when we perform a single point measurement and array measurements with broadband sensors; the group called Case-1, when we perform a single point measurement with a broadband sensor, but do not have enough broadband seismometers to perform an array, so we use short period seismometers; and the group called Case-2, when we do not have any broadband sensor to perform single point and array measurements. This way we highlighted the necessity of a broadband sensor to perform this type of analysis. Additionally, we estimated the theoretical site amplification factor, with the velocity structure obtained from the joint inversion of the reference data. We concluded that we can obtain a reliable inverted velocity structure with at least, one broadband sensor. The theoretical amplification factor based on the reference inverted velocity structure can give a good and reliable estimation of the amplification factor of the site. The HVSR of earthquakes and microtremor records cannot be regarded as site amplification factor, however, they are useful to determine the resonant frequencies.