My answers are: emergency- wave

  • Earthquakes, storms, floods and droughts are hazards for everybody. Most cities in the world have large populations crowded with bad housing often far from effective (emergency / necessary) services. Between 1990 and 1999, 82 natural catastrophes took place. Thousands of people were killed and economic losses rose to 535 billion dollars.
  • A strong earthquake hit Japan on 11 March 2011; it triggered a powerful (tsunami / wave)
  • A tsunami is an extremely large wave, so both are correct, but usually you'd want to say tsunami. – Gort the Robot May 29 '19 at 19:53

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.

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