How Homes Fail in an Earthquake and How to Stop It

In the video shared by our owner here at Seattle Seismic, we break down one of the most important questions homeowners in the Pacific Northwest can ask: what actually causes homes to fail during an earthquake?

It turns out, there are two main ways. The first is when a house slides off its foundation. The second is what’s called a cripple wall failure. Neither of these sound great, and they’re not. But both can be prevented with the right retrofit.

Let’s take a closer look at what’s going on underneath your home, how these failures happen, and what we do at Seattle Seismic to stop them before they start.

What Causes Homes to Fail in an Earthquake

When the ground shakes, a house doesn’t just bounce up and down. It sways and shifts side to side. If it isn’t properly anchored, that movement can break it apart.

The first kind of failure is probably the most straightforward. Some homes, especially older ones, aren’t bolted down to their foundations. During an earthquake, these homes can literally slide right off the concrete. It sounds extreme, but it’s actually one of the most common types of earthquake damage in wood-framed houses.

The second kind is a little more complicated. A lot of homes, especially those with basements or crawl spaces, are built with a short wall between the foundation and the first floor. This is called a cripple wall. It’s usually just a few feet tall, and it’s made of wood studs.

When an earthquake hits, that short wall can’t always handle the side-to-side shaking. It can rack back and forth, or collapse entirely, causing the house to tilt or even fall down on itself. In the video, we look at photos where the first floor just drops several feet because the cripple wall gave out. That’s what we call a cripple wall failure. Both of these scenarios are dangerous, and both are completely avoidable with the right kind of retrofit.

What a Seismic Retrofit Actually Does

Our job at Seattle Seismic is to make sure your house stays where it belongs during an earthquake. We focus on three main things: anchoring the house to the foundation, bracing the cripple walls, and connecting the upper structure to the braced walls below.

The first step is installing anchor bolts. These bolts secure the sill plate of your house directly to the concrete foundation. Think of it like adding seat belts for your home. Without them, the whole structure can slide sideways as the ground moves. With them, the foundation and the house act as one solid unit.

Next, we reinforce cripple walls. If your home has that three- or four-foot wall between the foundation and the first floor, we strengthen it with structural plywood. This sheathing gets nailed directly into the studs, turning the flimsy wall into something solid that can resist sideways forces. In engineering terms, we’re turning it into a shear wall. In regular terms, we’re making sure it doesn’t fold over during a quake.

The final piece of the puzzle is connecting everything together. We install framing clips, also called shear transfer ties, that secure the floor of your house to the braced cripple walls. This creates a continuous path from the roof to the foundation so the force of the earthquake can move through the whole structure without breaking it apart.

While no retrofit can guarantee your home won’t be damaged in a major earthquake, it significantly increases the chances that your house will stay standing and structurally sound. It’s about improving resilience and giving your home the best possible chance to ride out the shaking.

What Makes Retrofitting Tricky

Every home is a little different. Some homes don’t have cripple walls. Some have irregular crawl spaces or lots of openings like garage doors and windows that limit where we can add reinforcements.

As our owner explains in the video, we pay special attention to these openings. If we can’t brace around a garage door, for example, we’ll make the areas we can access extra strong to balance it out.

Retrofitting isn’t just about following a checklist. It’s about understanding how forces move through a structure and knowing how to strengthen the weak points. Our team is trained to identify those points and make smart, customized choices for every home.

Why Retrofitting Matters in Seattle

If you live in Seattle or anywhere in the Pacific Northwest, the threat of a major earthquake isn’t a matter of if, it’s a matter of when. The region sits on top of several fault lines, including the Seattle Fault and the massive Cascadia Subduction Zone. Seismologists believe a major quake is overdue.

In 2001, the Nisqually earthquake shook the region with a magnitude of 6.8. While it caused damage, it was relatively deep underground and not nearly as destructive as what scientists predict could come next. The next large quake could bring much stronger shaking, especially near the surface.

That’s why the City of Seattle created a permit system that makes it easier for homeowners to get retrofits done. In many cases, you don’t even need custom engineering drawings. The city has a prescriptive plan set that allows contractors like us to follow pre-approved methods, which saves time and money.

What the Process Looks Like

Every retrofit starts with a thorough assessment. We’ll take a look at your crawl space or basement, check for existing anchors, and evaluate the condition of your foundation. From there, we’ll figure out the best approach for reinforcing your home.

If your home meets the criteria for the city’s standard retrofit plan, we can usually move forward without needing custom engineering. This helps streamline the permitting process and keeps things simple for homeowners.

Once we have the plan and permit in place, we’ll schedule your installation. Our crew takes care of everything with a focus on quality and safety. We also coordinate with city inspectors to ensure the work meets all requirements and is fully up to code.

Final Thoughts

If your home was built before the 1980s, and especially if it has a raised foundation or cripple walls, you’re likely a good candidate for retrofitting. It’s not a flashy upgrade, but it’s one of the smartest investments you can make for your safety and your property value.

Earthquakes don’t give warnings, but retrofitting gives you peace of mind.

And that’s something we think every homeowner deserves.

Ready to take the next step? Reach out to us at Seattle Seismic to schedule a free evaluation. We’ll help you understand what your home needs and how we can help.