Answers:
1. Focus is a point at some depth in the earth from where radiation of seismic waves starts. Earthquakes are caused by the strain in the earth's crust which in turn is a result of a number of factors. The point directly above the focus on the surface is called epicentre.
2. While epicenter is the place on the Earth's surface under which they start. The effects of the earthquake may not be most severe in the vicinity of the epicentre.
3. Magnitude is different from intensity because magnitude is a measure of the “size,” or amplitude, of the seismic waves generated by an earthquake source and recorded by seismographs. (The types and nature of these waves are described in the section Seismic waves.)
4. While intensity is describes the degree of shaking caused by an earthquake at a given place and decreases with distance from the earthquake epicentre. It is a number (written as a Roman numeral) describing the severity of an earthquake in terms of its effects on the earth's surface.
5. Active fault is one that is likely to cause another earthquake in the near future. If there has been movement or evidence of seismic activity within the last 10,000 years, geologists generally consider faults to be active. Active faulting is a geologic hazard associated with earthquakes.
6. While inactive faults are do not show signs of ever having generated an earthquake for the last 10,000, but may possibly still generate another in the future.
Hope it helps!