 Here is a simplified example of how you might structure your code using the `burnman` library. Note that this is a basic example and does not include error handling or comprehensive mineral databases. You'll need to install the `burnman` library and download the mineral databases before running the code.

```python
import numpy as np
import burnman as bm
import matplotlib.pyplot as plt

# Load mineral databases
bm.databases.load_mineral_databases()

# Define reference seismic model
pressure = np.logspace(6, 10, 1000)  # in GPa
Vs_ref = np.ones_like(pressure)  # reference P-wave velocity
Vphi_ref = np.ones_like(pressure)  # reference S-wave velocity
density_ref = np.ones_like(pressure)  # reference density
geotherm_ref = np.zeros_like(pressure)  # reference geotherm

# Define four examples of composite minerals
mineral1 = bm.Mineral('olivine')
mineral2 = bm.Mineral('pyroxene')
mineral3 = bm.Mineral('plagioclase')
mineral4 = bm.Mineral('quartz')

# Simple mole fraction mixes
composite1 = bm.Composite([mineral1, mineral2], [0.5, 0.5])
composite2 = bm.Composite([mineral3, mineral4], [0.6, 0.4])

# Mix of three minerals
composite3 = bm.Composite([mineral1, mineral2, mineral3], [0.4, 0.3, 0.3])

# Preset solution
composite4 = bm.Composite.from_solution('mid_ocean_ridge_basalt')

# Custom solution
custom_abundances = {'olivine': 0.4, 'pyroxene': 0.3, 'plagioclase': 0.3}
composite5 = bm.Composite.from_abundances(custom_abundances, minerals=[mineral1, mineral2, mineral3])

# Compute seismic properties for each composite
for composite in [composite1, composite2, composite3, composite4, composite5]:
    properties = bm.Properties(composite, pressure)
    Vs = properties.seismic_velocities.P
    Vphi = properties.seismic_velocities.S
    density = properties.density
    geotherm = properties.enthalpy - properties.enthalpy.min()

    # Calculate misfit
    misfit_Vs = np.abs(Vs - Vs_ref)
    misfit_Vphi = np.abs(Vphi - Vphi_ref)
    misfit_density = np.abs(density - density_ref)
    misfit_geotherm = np.abs(geotherm - geotherm_ref)

    print(f"Misfit for {composite.name}: Vs={misfit_Vs.max()}, Vphi={misfit_Vphi.max()}, density={misfit_density.max()}, geotherm={misfit_geotherm.max()}")

# Plot results
fig, axs = plt.subplots(4, 2, figsize=(12, 18))
for i, composite in enumerate([composite1, composite2, composite3, composite4, composite5]):
    axs[i // 2, i % 2].plot(pressure, Vs, label=composite.name)
    axs[i // 2, i % 2].plot(pressure, Vs_ref, 'k--')
    axs[i // 2, i % 2].set_title('Vs')
    axs[i // 2, i % 2].legend()

    axs[i // 2 + 1, i % 2].plot(pressure, Vphi, label=composite.name)
    axs[i // 2 + 1, i % 2].plot(pressure, Vphi_ref, 'k--')
    axs[i // 2 + 1, i % 2].set_title('Vphi')
    axs[i // 2 + 1, i % 2].legend()

    axs[i + 2, i % 2].plot(pressure, density, label=composite.name)
    axs[i + 2, i % 2].plot(pressure, density_ref, 'k--')
    axs[i + 2, i % 2].set_title('Density')
    axs[i + 2, i % 2].legend()

    axs[i + 3, i % 2].plot(pressure, geotherm, label=composite.name)
    axs[i + 3, i % 2].plot(pressure, geotherm_ref, 'k--')
    axs[i + 3, i % 2].set_title('Geotherm')
    axs[i + 3, i % 2].legend()

plt.tight_layout()
plt.savefig('seismic_properties.png')
plt.show()
```

This code creates five composite minerals, computes their seismic properties, and compares them to a reference model. It also calculates the misfit between the computed and reference values and plots the results for Vs, Vphi, density, and geotherm against pressure. The plots are saved as an image file named 'seismic_properties.png'.