MULTI-CHANNEL ANALYSIS OF PASSIVE SURFACE WAVES (MAPS) A POWERFUL WEAPON IN URBANGEOPHYSICAL ARSENAL

摘要

Urbanization is an inevitable trend in modernization of human society. In the next 10 years, China's urbanization process will run at the highest speed in the urbanization history of China, Environmentally friendly, non-destructive and non-invasive geophysical assessment method has played an important role in the urbanization process in China. Claerbout demonstrated that the autocorrelation of a seismic record at the free surface transmitted from the bottom of a horizontal layered medium is equivalent to the zero-offset seismic record. This idea is known as Claerbouts hypothesis: by calculating the cross-correlation of noise records at two surface points can reconstruct wavefileds that are received at one point with excitation at the other point. Based on this idea and the virtual source method, we proposed Multi-channel Analysis of Passive Surface Waves (MAPS). This method acquires cultural noise in town, extracts effective surface wave signals by cross-correlation, and analyzes virtual source surface wave signals using Multi-channel Analysis of Surface Waves (MASW) with a source azimuth correction. Modeling and real-world examples along riversides, roads and railways show that MAPS can be used for accurate and fast imaging of the surface wave energy, and some examples also show that high quality imaging similar to those with active sources can be generated only by the use of a few minutes of noise, which is achieved by quality control of noise recording in real time. Acquisition and processing of active source and passive source data can be completed simultaneously in the same flow of MAPS. The use of cultural noise in town, MAPS can effectively image S-wave velocity structure from the ground surface to hundreds of meters depth; due to the combined use of active source data, MAPS increases an investigation depth but also to maintain the model resolution of a shallow part of the earth.