PREM In the 1960s and 1970s, Don Anderson (Caltech) and his collaborators investigated the relations between the behavior of mantle rock at high pressure and temperature, phase transformations of minerals in the mantle, and the generation of earthquakes. They contributed significantly to the understanding of tectonic plate motions by exploring convection currents in the Earth's mantle with seismological methods. These studies have led to the development of the Preliminary Reference Earth Model (PREM), in collaboration with Adam Dziewonski. PREM establishes a consistent radial model of the Earth for several important geophysical parameters, such as seismic velocities, attenuation, and density.
The seismic velocities from the PREM are related to the density inside the Earth. For example. the p-wave velocity is given by
where K and µ are elastic properties of the rock and ρ is the density. From those, the pressure gradient can be determined, because the pressure is related to density by
p = ρgh
A good rule of thumb is that a one-kilometer increase in depth results in a 30 MPa increase in pressure, or a 100 MPa increase in pressure results from an increase of 3 km in depth.
Definitions
Pressure is force per area. The SI unit of pressure is the pascal. 1 Pa = 1 N/m2. The unit of force is the newton; 1 N = 1 kg·m/s2.
