The earthquake risk at Scott Dam may be a key factor in PG&E’s decision to abandon the Potter Valley Project.

SAN FRANCISCO — A magnitude 7 earthquake rattled Northern California Thursday morning, triggering a tsunami warning for millions on the West Coast as coastal communities braced for the worst.

Its volatility is due to three tectonic plates meeting, an area known as the Mendocino Triple Junction. It is the movement of plates in relation to each other - whether above, below or alongside - ...