The ground motion recordings of several past earthquakes, e.g., the 1989 Loma Prieta M6.7 California earthquake, indicate that critical and post-critical reflections from the Moho boundary play important roles in creating larger than expected GMs at certain distances, typically 70 – 150 km, from the source. This is often referred to as the wide-angle reflection from Moho. The Moho, short for the Mohorovičić discontinuity, is the boundary between the Earth’s crust and the mantle. It is named after the Croatian seismologist Andrija Mohorovičić, who discovered it in 1909. The Moho is characterized by a distinct change in seismic wave velocities from the less dense silica-rich rocks of the crust to denser magnesium and iron-rich rocks of the mantle.