6. Scale that is based on observable earthquake damage.*1 pointFujita ScaleSeismoscaleMercalli ScaleRichter Scale

The correct answer to the question about a scale that is based on observable earthquake damage is the Mercalli Scale.

Explanation:

1. Fujita Scale: This scale measures tornado damage, not earthquakes.
2. Seismoscale: This term is not commonly recognized in the context of measuring earthquakes.
3. Mercalli Scale: This scale rates the intensity of an earthquake based on observed effects and damage in populated areas, which makes it the right choice.
4. Richter Scale: This scale measures the magnitude of an earthquake based on seismic waves, rather than the damage caused.

In conclusion, the Mercalli Scale is the appropriate choice as it effectively assesses the observable impact of earthquakes on people, structures, and the Earth's surface.