Historical clue formulations

• Quivers — 2025-09-25
• Some seismic activity — 2024-06-29
• Mercury poisoning symptoms — 2015-09-05
• No great shakes — 2012-10-06
• Seismological activity — 2004-11-10
• Small quakes — 2001-07-03
• Earth movers? — 1999-05-22
• Aftershocks — 1997-09-12