Question: what type of earthquake caused the tsunami in japan
[{'answer': 'undersea megathrust earthquake', 'provenance': [{'wikipedia_id': '31150160', 'title': '2011 Tōhoku earthquake and tsunami', 'start_paragraph_id': 1, 'start_character': 32, 'end_paragraph_id': 1, 'end_character': 62, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]