San Andreas Fault: 93% Chance of M7.0+ Quake in California by 2045 — Is State Ready for Big One?

A major seismic forecast has renewed concern over earthquake risk in California, with scientists estimating a 93% probability that at least one magnitude 7.0 or higher earthquake will strike the state by 2045.

The projection, based on long-term rupture models across multiple fault systems including the San Andreas Fault, raises urgent questions about whether infrastructure and emergency planning are sufficient to withstand a major event affecting millions of residents.

Seismic Forecast Points to High Long-Term Risk

The 93% probability figure comes from statewide earthquake rupture forecasting models that assess the likelihood of significant seismic events over time.

Researchers emphasise that the estimate refers to at least one magnitude 7.0+ earthquake occurring somewhere in California before 2045, rather than a single fault rupture or specific location.

While the figure does not predict timing or exact epicentres, it reflects the accumulated risk from multiple fault systems across the state. Scientists stress that earthquake probability increases over longer time windows, even though individual events remain impossible to schedule or precisely forecast.

San Andreas Fault Ongoing Risk Concerns

The San Andreas Fault remains one of the most closely monitored seismic features in North America due to its length, history of major earthquakes, and location near densely populated areas. It forms a transform boundary between the Pacific and North American tectonic plates, which move past each other at several centimetres per year.

Sections of the fault are known to become locked for extended periods, allowing stress to build over decades or centuries before being released in sudden ruptures. This process has produced some of California's most significant historical earthquakes, including the 1906 San Francisco event and the 1857 Fort Tejon earthquake.

Although the San Andreas Fault is often associated with the so-called 'Big One', scientists note that the statewide risk also includes other fault systems, meaning multiple regions contribute to the overall probability estimate.

How Scientists Measure Earthquake Likelihood

Earthquake forecasting relies on geological and geophysical data, including fault slip rates, GPS measurements of crustal movement, and trenching studies that reveal past rupture patterns. These methods help researchers estimate how much stress is accumulating along fault lines over time.

A key concept in earthquake science is elastic rebound theory, which explains that tectonic plates gradually build stress until rocks fracture and slip suddenly, releasing energy in the form of seismic waves. Once released, the cycle begins again as stress slowly accumulates.

Recent geological studies of the San Andreas Fault system have also suggested that some sections may have experienced larger or more frequent earthquakes in the past than previously assumed, adding complexity to long-term hazard assessments.

Potential Impact of a Major Rupture

A magnitude 7.0 or higher earthquake in California could cause widespread disruption, particularly in urban regions. Scientists warn that strong shaking may damage older buildings, trigger gas line failures, and lead to fires that spread rapidly in densely built areas.

Emergency planning scenarios suggest that tens of millions of people could be affected across Southern California in a major rupture event, with significant strain placed on transport networks, hospitals, and emergency services.

As reported by MSN, a major rupture scenario along California's fault systems could affect up to 20 million people across the state, particularly in densely populated southern regions. Economic losses could reach hundreds of billions of dollars depending on the location and severity of the quake.

Preparedness and Remaining Uncertainty

California has implemented stricter building codes in recent decades, improving the resilience of newer structures to seismic shaking. The state also operates early warning systems that can provide seconds of alert before strong shaking arrives, allowing limited time for protective actions.

However, scientists continue to stress that earthquake prediction remains impossible in terms of exact timing and location. While long-term probability models such as the 93% estimate help guide preparedness planning, they do not indicate when the next major earthquake will occur, leaving ongoing uncertainty for communities living along major fault zones including the San Andreas system.