The INTERPACIFIC project: a cooperative exercise for assessing reliability and accuracy of seismic methods

In recent years, the use of surface wave tests for seismic site characterization has expanded rapidly in the field of applied seismology and earthquake engineering. Indeed these methods are cost and time effective with respect to the invasive ones, which require the use of boreholes. For surface wave methods, difficult and onerous interpretation and inversion processes are needed to derive a reliable S-wave velocity (VS) profile. At the same time, the availability of affordable seismic equipment and “black-box” processing software has led to a wide diffusion of surface wave methods among inexperienced analysts. The combination of the aforementioned factors induces in the final user (i.e., the engineer or the seismologist who require the shear wave velocity model) a lack of confidence in results obtained from surface wave testing. On the other hand, borehole seismic methods are often considered a more reliable option since they provide a highly resolved VS profile with a simpler interpretation process. Nonetheless, some previous comparisons between repeated realizations of borehole methods have shown controversial results and an unexpected lack of repeatability. A systematic assessment of the performance of different seismic methods is thus crucial. Furthermore, it is also necessary to develop firm standards and guidelines for execution and interpretation of surface wave tests. Fixing a standard practice for surface-wave methods is a very challenging task because the measurements can be performed with a wide variety of experimental configurations and interpreted with an even larger spectrum of signal analysis and inversion techniques.