Some said because of natural factors; others said because they have much indecency, adultery and fornication on these shores and cities.
The true cause of disasters and afflictions is because of the wrong-doing : people are wrong doers: they wrong each other and wrong themselves --> and God then misguides them and they fall in the idolatry: they worship the sun, the idols and their religious leaders associating them with God Almighty --> so God punishes them.
This is explained in the Quran 31: 41
ظَهَرَ الْفَسَادُ فِي الْبَرِّ وَالْبَحْرِ بِمَا كَسَبَتْ أَيْدِي النَّاسِ لِيُذِيقَهُم بَعْضَ الَّذِي عَمِلُوا لَعَلَّهُمْ يَرْجِعُونَ
( Corruption has appeared in the land [like earthquakes, hurricanes, volcanoes ...etc] and sea [like floods, tsunamies ...etc],
because of [the works] that the hands of people have earned;
so that He may let them taste [the punishment of] some of their deeds;
that they may desist [from their wickedness.])
Now, what will people do? Are they immune against other catastrophes like this and may be more?
The Japanes people have to resort to God Almighty alone without associate and leave their association according to their enthusiasm about the religious leaders,
and the most correct way is to resort to the Quran and the Islam , or else such quakes and tsunamies may come on them again and again, when neither their scientific progress nor their alleys will save them.
Japanese people should take the lesson and resort to God alone, and they should not listen to the words of atheists and their misguided religious patrons.
The patron saint
The earthquake and cleavage