Estimation of deep geological structures in urban areas from long-period microtremor data

ABSTRACT

Determination of geological structures more than several hundred meters deep is important for earthquake disaster prevention in urban areas where conventional seismic methods are difficult to apply. The frecuency-wavenumber spectrum method was applied to microtremor data with periods of 0.8 to 5 sec. in which phase velocities of surface waves were determined. Studies were carried out in 33 observation areas in the Tokachi Plain in Hokkaido, Japan. Results show that the Tokachi Basin has a V-shaped basement structure with an S-wave velocity of about 3 km/s and a depth of about 2 km at the bottom, extending from north to south. These results are supported by Bouger anomaly map. In order to estimate S-wave velocity structures in urban areas with thick sediments, the use of long-period microtremors is powerful alternative to coventional seismic techniques (AU)