Measuring the sediment thickness in urban areas using revised H/V spectral ratio method

Abstract

For the sake of safety, it is crucial for civil engineers to determine the thickness of the sediment layers in the urban areas. However, the noisy detection environment in a city presents a significant challenge to the traditional artificial source geophysical methods which are used to estimate and monitor of sediment thickness. Given this otherwise challenging detection environment, the H/V spectral ratio method provides an effective and cheap means of detecting sediment thickness. It exploits microtremor signals to obtain the resonant frequency of the surface layer which is then used to determine site sediment thickness with an empirical equation using the data from a single observation station. In this study, we collected microtremor data at 109 locations in the Aoshan Bay area of the Shandong Peninsula and determined the resonant frequency and analysed the morphological features of the H/V spectral ratio curves. In order to calibrate the frequency-bedrock depth equation accurately to the local conditions, Vs profile estimation is used to fine tune the frequency-bedrock depth equation. By comparing the S-wave velocity structure obtained using the microtremor SPAC method with that found from borehole samples, we were able to verify the reliability and accuracy of application of the microtremor SPAC method. By using the H/V spectral ratio method and the modified equation that transforms resonance frequencies to sediment thickness, we generated a thickness map of the sedimentary layers in the Aoshan Bay area of the Shandong Peninsula. The map provides useful information for ensuring the safe construction of the city's infrastructure. We conclude that the use of microtremor signals can provide important geological information as a cheaper and quick way for the construction and development of urban infrastructure.