def calc_stress_drop(magnitude):
    """Stress drop using Atkinson & Boore (2011, :cite:`atkinson11`) model.

    Parameters
    ----------
    magnitude : float
         Moment magnitude of the stress drop.

    Returns
    -------
    stress_drop : float
        Stress drop (bars).

    """
    return 10 ** (3.45 - 0.2 * max(magnitude, 5.0))
