Imaging the 3D basin structure of the Santa Clara Valley by ambient noise tomography

Abstract The seismic velocity structure of sedimentary basins in urban areas is important for seismic hazard assessment. Ambient noise tomography (ANT) was applied to generate a velocity model of the Santa Clara Valley (SCV), one of the major urban sedimentary basins in the USA. A three-dimensional shear-wave velocity model was constructed, including depths of up to 4 km using 5-month and 1-year short-period data recorded by temporary and permanent arrays. Despite the difficulty in using ANT to analyze short-period data, our results allowed us to distinguish two small basins located in the southwestern and northeastern parts of the SCV, which correspond to the Cupertino and Evergreen basins, respectively. The basins cover approximately 25–100 km 2 area and have 2.5–3 km of basement depth by assuming shear wave velocity at the basement as 2.5 km/s based on rapid velocity changes of the model. This implies that although only short-term short-period data are available, the ANT can be an appropriate option for constructing velocity models of regional areas with complex structures. Thus, we expect that our data will support the active use of ANT in conjunction with other imaging methods for seismic hazard assessment of urban sedimentary basin areas.