Passive seismic exploration in an urban environment along the projected route of an underground railway

We utilised the Refraction Microtremors (ReMi) seismic technique to conduct a survey in the city of Malaga in Spain to support a project for the construction of a new subway line in the vicinity of the coast. The ReMi technique was chosen to carry out the survey because of the expected difficulties of conventional seismic operations in a densely populated urban area with its logistical and administrative restrictions and with a very high level of background noise. A total of about 1400 m of profiles were collected in two days of field work. The correlation of shear wave maps with the available borehole stratigraphy was generally good. In a few areas, probably because of structural complexity, ReMi interpretation of the data was not definitive. Poor ReMi performance was seen as an indicator of zones of geological complexity requiring either further geophysical investigation or special attention during tunnel excavation. The ReMi technique proved to be adequate for characterising the shallow subsurface in the study site in terms of geometry and shear wave velocity down to a depth of 5070 meters. The bandwidth andamplitude of the spectrum of the traffic and urban noise were sufficient to generate usable surface waves