Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

We built a 3D seismic model of the Po Plain and neighboring regions of northern Italy, covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid. We started by collecting an extensive and diverse set of geological and geophysical data, including seismic reflection and refraction profiles, borehole logs, and available geological information. Major geological boundaries and discontinuities have thus been identified and mapped into the model. We used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness. Seismic-wave properties have been assigned to each unit using a rule-based system and, VP, VS, and. derived from other studies. Sedimentary strata, although with varying levels of compaction and hence material properties, may locally reach a thickness of 15 km and give rise to significant effects in seismic-wave propagation. We have used our new model to compute the seismic response for two recent earthquakes, to test its performance. Results show that the 3D model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments, whereas paths outside the basin may be well fit by more homogeneous (1D) hard rock structure. We conclude that the new model is suited for simulation of wave propagation, mostly for T > 3 s, and may serve well as a constraint for earthquake location and further improvements via body-or surface-wave inversion.