California Earthquake: Is the Big One Coming Soon?

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Experts agree…

The “Big One” is coming.

Sooner or later, a major earthquake in California will strike.

But when and how bad will it be?

Read on to find out the latest.

Why is California Prone to Earthquakes?

The Earth’s surface isn’t one solid piece…

Instead, it’s more like a jigsaw puzzle made up of oceanic or continental tectonic plates — or a mix of both.

For example:

Pacific Plate (mostly oceanic)
North American Plate (oceanic/continental)
Eurasian Plate (oceanic/continental)
African Plate (oceanic/continental)

California sits above the boundary between the Pacific and North American tectonic plates — better known as the San Andreas Fault.

The plate boundaries where the edges meet are where most geological activity takes place, including:

Earthquakes
Volcanoes
Mountain building
Ocean formation

It takes thousands of years for a mountain or an ocean to form, but earthquakes and volcanic eruptions can happen any minute without warning.

There are three main types of boundaries where tectonic plates meet…

Convergent boundaries where plates collide, often creating volcanoes, mountain ranges, and deep ocean trenches.
Divergent boundaries where plates move apart, enabling molten rock (magma) to escape from beneath the Earth’s crust, and creating geographical features like the Mid-Atlantic and East African Rifts.
Transform boundaries where the plates slide past each other. Transform boundaries, like the San Andreas Fault, are typically responsible for the most significant seismic events, including devastating earthquakes.

California is unusually prone to major earthquakes because it sits above the transform boundary of the San Andreas Fault, which is constantly subject to friction and stress buildup.

To make things even more precarious, it’s also within striking distance of the Cascadia Subduction Zone, a convergent boundary in the Pacific Northwest, that could potentially trigger seismic events.

What are the Chances of a Major Earthquake in California?

Expert consensus is that “The Big One” is coming…

It’s not a matter of if, it’s a matter of when.

Christine Goulet, director of the U.S. Geological Survey (USGS) Earthquake Science Center, recently told US Today, "It's gonna happen. An earthquake could be in a matter of minutes, the next hour, tomorrow, or in a week from now, we can't predict that precisely at this time. We don't know. But… we need to prepare for them.”

San Francisco and Los Angeles are among the locations most at risk.

Los Angeles County and the Bay Area are the two biggest population centers in California.

Let’s explore the earthquake risk profile for each.

Los Angeles Region

The most comprehensive earthquake forecast for California in recent years was published in 2015.

However, USGS representatives say little has changed since.

According to the USGS forecast, the probability of a major earthquake in the next 30 years is:

60% chance of an earthquake measuring magnitude 6.7
46% chance of an earthquake measuring magnitude 7.0
31% chance of an earthquake measuring magnitude 7.5

will occur in the Los Angeles region.

San Francisco and the Bay Area

Within the next 30 years, the USGS forecasts the probability of a major earthquake as:

72% chance of an earthquake measuring magnitude 6.7
51% chance of an earthquake measuring magnitude 7
20% chance of an earthquake measuring magnitude 7.5

will occur in the San Francisco region.

What Would a Major Earthquake in California Look Like?

A major inland earthquake in a heavily populated area like Los Angeles, San Diego, or the Bay Area is projected to have devastating effects, including extensive damage to critical infrastructure and thousands of deaths.

Long-term California residents have likely experienced several relatively minor seismic events, such as the Julian earthquake in April 2025, which garnered over 40,000 reports to the USGS Did You Feel It webpage, despite being only a 5.2 magnitude quake.

Here are two potential scenarios that could unfold when the Big One strikes.

Los Angeles and Surrounding Areas

The Shakeout Scenario, published by the USGS in 2008, is a detailed projection of what is likely to happen if a magnitude 7.8 earthquake occurs along the southernmost 200 miles of the San Andreas Fault, stretching from Lake Hughes to the Salton Sea.

Los Angeles has the highest population density in close proximity to the event, but the effects would also be felt in neighboring cities and counties like San Diego and San Bernardino, as well as Riverside and Orange Counties.

The dollar and population figures haven’t been adjusted since 2008, so the projections would be significantly higher today.

Significant Casualties: The report models approximately 1,800 deaths and 50,000 injuries requiring emergency care.
Economic Losses: $213 billion (2008 dollars)
Widespread Building Collapses and Property Damage
Infrastructure Breakdown: Significant disruption is expected to utilities such as power, gas, communications, and transportation. The water supply is expected to be severely impacted. Some areas may be without running water for six months or longer.
Widespread Fires: Casualty projections are split almost evenly between those dying as a direct result of seismic activity and from the expected widespread fires. Approximately $50 billion (2008 dollars) in fire damage is projected to the $213 billion mentioned above.

San Francisco and the Bay Area

Over 7,000,000 people in the Bay Area live above or within striking distance of the Hayward Fault, a smaller fault within the San Andreas Fault System that runs along the Eastern Side of the San Francisco Bay.

The Hayward Fault has a history of major earthquakes, with studies suggesting an average interval of 100-220 years between significant seismic events.

However, these are averages, and the exact timing of future earthquakes is uncertain.

Geologists believe that significant seismic events happened in or around the following years (AD):

397
651
769
940
1032
1265
1425
1587
1695
1868

The last Hayward Earthquake occurred in 1868 — 157 years ago — meaning another one is likely due.

Until the devastating 1906 San Francisco Earthquake and Fire, which occurred along the San Andreas Fault, the 1868 Hayward Earthquake was known as the Great San Francisco Earthquake.

The HayWired Scenario, published by the USGS in 2017, forecasts the impact of a 7.0-magnitude earthquake originating below Oakland, resulting in a 52-mile rupture along the Hayward Fault.

Projected impacts include:

Casualties:
- Estimated 800 deaths and 18,000 nonfatal injuries.
- Over 2,500 people needing rescue from collapsed buildings, and 22,000 needing rescue from stalled elevators.
Economic Losses: $30 billion in total losses (2016 dollars)
Fires: More than 400 gas and electric-related fires could ignite, potentially burning building space equivalent to 52,000 single-family homes. Over half of the total projected losses could come from fires: $16 billion (2016 dollars)
Infrastructure Damage: The Hayward Fault runs beneath or near critical infrastructure, including buildings, utilities, transportation networks, and communication lines.
Water Supply Disruptions: East Bay residents could lose water service for 6 weeks or longer.

The seismic events precipitating the ShakeOut and HayWired projections are considered likely, not worst-case scenarios.

Experts consider “The Big One” inevitable, but that doesn’t mean you can’t prepare for it.

How to Prepare for an Earthquake: A Step-by-Step Guide

Know the Risks: Understand your local earthquake hazards
Create a Plan: Develop a family emergency plan, including a communication strategy, meeting place, and evacuation routes.
Assemble a Disaster Kit with essential supplies, including:
- Water (1 gallon/person/day for several days)
- Food
- First-aid kit
- Flashlight
- Radio
- Medications

Secure Your Home

Practice "Drop, Cover, and Hold On"
Consider Earthquake Insurance
Enable ShakeAlert Notifications on Your Phone
Stay Informed: Monitor official sources for alerts and updates during an earthquake.