Unless you live in California or another earthquake-prone area of the United States, you probably don't worry much about seismic loads on the decks you build. And that's okay; a recent study has shown that even in a high-risk seismic zone, a deck ledger connection that conforms to the IRC is more than capable of resisting the lateral loads produced in a seismic event.
Washington State University engineering professor Don Bender and his team used the equivalent lateral force procedure contained in Minimum Design Loads for Buildings and Other Structures (ANSI/ASCE 7-10), the standard reference for general structural design, to calculate possible seismic loads on residential decks. The math for this procedure is complicated (let's just say it involves kips and slugs), at least for a non-engineer like me, but the results are fairly straightforward and compelling: The largest allowable stress design (ASD) seismic load on a 12-foot by 12-foot deck that is 10 feet above the ground was 517 pounds, with a reaction hold-down force of 259 pounds. According to the report, lateral load anchors with a design capacity of 625 pounds—not 1,500 pounds, as currently specified in the IRC—would be more than sufficient to resist even the most severe seismic lateral load.
To read the actual study and see for yourself exactly how to use the equivalent lateral force procedure to determine seismic loads on a residential deck.