Figure 4. Initial strength profiles of the model lithosphere. Flow stress is calculated from empirical steady-state creep relations at a constant strain rate of 10^-15 s^-1, with the maximum stress limited by Byerlee's (1978) frictional failure criterion. A. Profile of normal, unweakened lithosphere. B-D. Profiles through initial models MW, CW, and BS, respectively. The total strength (integrated stress) and relative strength of the lithosphere are indicated near the bottom of each curve.