Ka cika wannan jumla: Gano da kuma sanin lokacin da tsunami ta faru yana da muhimmanci a kimiyyar binciken girgizar ƙasa. Girman wani takamaiman ajiya na iya taimakawa wajen yanke hukunci game da girman girgizar ƙasa da aka sani ko kuma yin aiki a matsayin hujja game da abin da ya faru a zamanin da. A game da girgizar kasa ta 869 Sanriku, gano wuraren tsunami sama da kilomita 4.5 a cikin ƙasa a kan Sendai Plain, wanda ya yi kusa da wani taron tsunami na tarihi, ya ba da damar kimanta girman wannan girgizar ƙasa da kuma yiwuwar yankin fashewa a cikin teku. An gano da kuma kwanan wata biyu da suka gabata tare da irin wannan hali. An yi amfani da ajiya uku don bayar da shawarar lokacin dawowa don manyan girgizar ƙasa na tsunamiigenic tare da gabar tekun Sendai na kimanin shekaru 1,000, yana ba da shawarar cewa maimaita wannan taron ya yi latti kuma cewa ambaliyar ruwa mai yawa mai yiwuwa ne. A shekara ta 2007, an ba da yiwuwar babban girgizar tsunami mai girgizar ƙasa da za ta buga wannan gabar teku a cikin shekaru 30 masu zuwa a matsayin 99%. Dangane da wannan bayanin TEPCO ya sake nazarin kimantawar tsayin tsunami mai yiwuwa a tashar wutar lantarki ta Fukushima Daiichi zuwa sama da mita 9, amma bai dauki mataki nan da nan ba. Tsunami ya haifar da
Girgizar kasa ta 2011 Tohoku tana da tsayin raƙuman ruwa a Fukushima na kimanin mita 15, sama da mita 5.7 wanda aka tsara tsaron tsire-tsire. Nisan ambaliyar tsunami ya kusan kama da wanda aka ruwaito don abubuwan uku na baya, kamar yadda girman gefe yake.