Board Thread:Questions and Answers/@comment-174.114.213.173-20131030150611/@comment-205.170.118.162-20131030151305

1. Because that's where Terumi and Izanagi aim it.

2. Continuum Shift, son. Since the Master Unit and the Takamagahara where still active when it went down, multiple timelines were able to continue existing, the ending of CT more or less being the divergence point (Kinda like the School Dance in Back to the Future parts I & II.)

3. Calamity Trigger is a mere title, describing the events "triggered" of all the "calamity" that ensues. The Continuum Shift is the answer to your second question