Your answers are correct.
The sentence has something missing however, perhaps "and":
Most cities in the world have large populations crowded with bad housing and often far from effective emergency services.
Sometimes you will see adjectival phrases with hyphens, which can make it easier to read: "often far-from-effective government/emergency/coastal/whatever services"
To use necessary: "... and often lacking necessary services."
This particular event 11 March 2011 was the largest earthquake recorded in Japan, with very many people killed. Wikipedia describes it like this:
The tsunami warning issued by the Japan Meteorological Agency was the most serious on its warning scale; it was rated as a "major tsunami", being at least 3 metres high"
Be clear that wave is not incorrect, except that as it was so powerful it is almost universally referred to as tsunami. The wikipedia article explains the characteristics: at sea tsunamis are metres high but hundreds of kilometres wide.