What New Seismic Updates in California and Beyond Mean for Your Building and Construction Projects

If you’re working on building projects in California, you’re probably aware of the new California Building Code 2025. Effective January 1 of this year, the changes are part of an update the state performs every six years. Similar changes are being adopted by many other states during their code update schedules.

Part of these updates includes how structures are designed. If you’re a civil engineer, you know several of these updates are impacting or will soon impact your projects. In this blog, I’ll dive deeper into several of the more notable changes to building design and what they mean to you.

First, a little background. The building standard defining what building load structures must be designed for is ASCE 7 from the American Society of Civil Engineers. This standard includes seismic loads (the forces acting on a structure when the ground shakes during an earthquake) for buildings. It is adopted by the International Building Code, which is in turn adopted by many states.

These standards are regularly updated to make the building code safer and more cost effective, which includes the adoption of ASCE 7-22 in the 2025 California Building Code. Many practicing engineers, researchers, and building officials volunteer their time to write ASCE 7. Disclaimer: I have been one of those involved in developing ASCE 7 for the last decade.

Let’s take a quick look at the most significant ASCE 7-22 updates, affecting building and construction efforts across the United States.

Multi-period response spectra

This is one of the most significant changes because previously structures were designed using two-period spectra, a tool which sometimes produces an artificial box-shaped design that can lead to significantly inaccurate metrics related to the actual seismic demand of the site.

These issues were alleviated by the adoption of a smooth, multi-period spectra, which is more accurate. Design ground motions are now conveniently available from a website rather than contours from a map.

Seismic site changes

Another positive change is the adoption of several new seismic site classes. In simple terms, the code now uses more “fine-tuned” ground categories so the design reflects the site’s soil and rock conditions more closely. That means the required seismic design loads are less likely to swing noticeably just because the site is close to the cutoff between two categories. As a result, designs are more consistent and predictable.

Additional new requirements encourage a more accurate measurement of shear wave velocity onsite. Shear wave velocity is the speed at which shear waves travel through the ground. While this change replaces the old but familiar Standard Penetration Test tables, the new provisions offer more accurate ground motion estimates for the design of structures.

The neutral plane method

One of the changes I personally led is a significant change for deep foundation design. Although not widely known, ASCE 7-16 did not allow the use of the neutral plane method to design deep foundations against seismically induced ground settlement.

The neutral plane method is widely regarded as the most accurate way of designing piles when the ground around the pile settles, such as in an earthquake. A simpler, more traditional way of designing deep foundations is to calculate the “dragload” from the settling soil. The dragload is the extra downward force on a pile caused by the pull of the soil as the soil settles. Engineers add the dragload to the load from the structure and design the pile to have great enough geotechnical capacity below the settling soil to accommodate both loads. This often results in conservative pile designs.

Although the neutral plane method is a difficult concept to understand fully, it is actually not necessary to design a pile to resist the dragload in such a manner. That’s because pile groups respond to downdrag by settling. Determining how much settlement will occur before the pile load and pile resistance become balanced is accomplished with the “neutral plane” method. This is necessary to determine if the settlement is acceptable.

Now, the seismic update (ASCE 7-22) allows deep foundations to be designed with the neutral plane method when subject to seismically induced ground settlement and provides criteria for the allowable settlement. For more information on using the neutral plane method, refer to the commentary in ASCE 7-22 and literature by Bengt Fellenius, retired professor at the University of Ottawa.

Seismically induced settlement requirements

Another change I led expands the allowable earthquake induced settlement structures can tolerate to address additional causes of ground movement beyond only liquefaction-induced settlement and lateral spreading. An earlier seismic update made an important improvement by which these criteria were provided for these two situations; however, these phenomena are only two of many reasons the ground moves in an earthquake.

The settlement tolerances of structures have now been expanded to address additional causes of ground movement, such as the settlement of unsaturated soils, strains in clayey soils, slope movement, and other earthquake-induced ground movements. Many types of ground movement can be estimated using procedures developed by Professor Jonathan Bray at UC Berkeley.

Additionally, the first building code provision addressing landslides is now in ASCE 7-22. I personally witnessed the deadly effect of earthquake-induced landslides with the Geotechnical Extreme Events Reconnaissance (GEER) Association after the 2016 Kumamoto earthquake, and ASCE 7-22 now directly addresses construction of structures at sites prone to seismically induced landslides.

Importantly, these seismically induced ground movement provisions are not meant to apply to surface fault rupture. However, for those interested in the requirements for designing structures in areas where surface fault rupture could occur, I have led a team more recently to develop the first provisions addressing this issue. These provisions have been adopted into the forthcoming 2026 NEHRP Recommended Seismic Provisions and provide rationale requirements for designing structures that could be subjected to ground movement caused by surface fault rupture displacement. These guidelines will complement the excellent work done recently by many academic researchers in predicting surface fault rupture displacements, most notably those associated with the Fault Displacement Hazard Initiative.

Topographic amplification in seismic hazard assessments

Topographic amplification is a phenomenon where structures on the top of topographic highs (e.g., hills) are often subject to increased ground shaking as the result of an earthquake. The flip side of this is that structures at the foot of topographic highs (e.g., the foot of a hill) could be subject to lower ground motions potentially. While this phenomenon has been widely known, accounting for it has been difficult. Academic researchers including Dominik Asimaki of Caltech and GEI’s own Jake Dafni, have been making significant advances in this area.

I felt it was time that topographic amplification was officially addressed in ASCE 7, so I led an effort to include guidelines for topographic amplification. This change recognizes the higher ground motions that can occur at topographic highs.

These new guidelines describe how to incorporate this phenomenon where needed.

Closure

The road to changes in the building code is a long one, filled with countless committee meetings, votes, responses to comments, votes on the responses to comments, and seemingly endless proposal iterations. But ultimately these changes will have a positive impact to communities, businesses, and the U.S.

If you’re leading building projects under ASCE 7-22 and want to know more about what these updates mean to you, contact me.