The appropriate expert group to review this material is Senior Structural Engineers and Historic Preservation Specialists.
Abstract:
This document details the $2 billion seismic retrofit and modernization of the 130-year-old Salt Lake City Temple of The Church of Jesus Christ of Latter-day Saints. Driven by high seismic risk from the nearby Wasatch Fault (57% probability of a magnitude 6.0+ earthquake in the next 50 years), the project utilizes advanced base isolation techniques to decouple the massive granite structure from ground motion. The structural intervention requires extensive underpinning and deep excavation (10.6 meters) to install 98 eight-ton base isolators beneath a newly constructed, reinforced concrete foundation network secured by over 423 kilometers of post-tensioned cables. The project’s necessity is contextualized by the building’s historical role as the architectural and urban anchor of Salt Lake City, which was established on the unique "Plat of Zion" planning template. Originally expected in 2025, project completion is now anticipated in 2026, with the temple reopening in 2027.
Seismic Retrofit of the Salt Lake City Temple
1:04 Project Scope and Risk: The Salt Lake City Temple, a 130-year-old granite and quartz monzonite structure featuring walls up to nine feet thick, was not originally designed to withstand earthquakes.
1:44 Seismic Imperative: The Wasatch Fault, which runs through the Salt Lake Valley, presents a significant risk, with a 57% probability of a magnitude 6 or greater earthquake occurring within the next 50 years. A major quake could cause catastrophic damage, referencing the 2011 Christchurch Cathedral collapse as a precedent for potential outcomes (2:51).
5:21 Base Isolation Strategy: The central technical solution is base isolation, or "decoupling," the structure from ground motion. The system is engineered to allow up to 1.5 meters of horizontal movement in any direction during a strong seismic event (5:37).
5:55 Excavation and Underpinning: Construction required excavation around the existing foundations down to 10.6 meters to create space for the isolators. Extensive underpinning techniques, including micropiles, secant piles, tie-back anchors, and consolidation grouting, were deployed to prevent the heavy stone walls from shifting or settling during footing removal (6:04).
6:26 New Foundation System: A new, seismically designed concrete foundation was constructed, incorporating transfer beams and girders. Over 423 kilometers of post-tensioned cables were installed to structurally tie the temple into this new foundation (6:41).
7:08 Isolator Installation: Ninety-eight massive base isolators, each weighing approximately 8,000 kilograms, are being installed. These isolators function as bearings between the original footings and the new foundation, providing vertical stiffness while allowing horizontal flexibility (7:48). Soil is subsequently removed directly under the isolators to facilitate the required range of motion (7:41).
8:14 Project Timeline and Cost: The complex retrofitting effort requires extreme caution to protect the historic stonework. The project budget is estimated at $2 billion (0:27). The completion timeline has been extended from the original 2025 estimate to 2026, with the temple opening to the public in 2027.
8:20 Additional Reinforcements: Beyond base isolation, the scope includes reinforcing walls, spires, and other architectural elements, along with creating new spaces for rituals and a north addition for sealing (marriage) ceremonies.
11:44 Historical Context and Urban Planning: The temple serves as the architectural and planning centerpiece of Salt Lake City. The city's unique, deliberately engineered urban layout, the "Plat of Zion," features exceptionally large blocks (200 x 200 meters) and wide streets (over 40 meters) centered around the 11-acre Temple block (12:48).