Earthquake Tomography

By recording local earthquakes, we can generate seismic velocity images (maps of the rate at which earthquake waves travel through the Earth's crust) of the Bay Area. The seismic velocity correlates with rock composition, and allows us to identify fault structures at depth where two different types of rock contact one another. Such contrasts are visable across the San Andreas and Hayward faults on the map below. Additionally, these velocity models are applied to strong-ground-motion simulations to assess where the strongest and weakest shaking is expected if a large earthquake should occur in the Bay Area. This information is useful to engineers as they design safer structures.

From: Parsons, T., and Zoback, M. L., Three-dimensional upper crustal velocity structure beneath San Francisco Peninsula, California, J. Geophys. Res. v. 102, p. 5473-5490.