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03/31/2021

What Causes Earthquakes (Complications & Impact on Foundations)

If you live on the left coast, particularly if you reside in sunny SoCal, odds are high you’ve experienced an earthquake.

Most recently, California was seriously rocked by the  Ridgecrest earthquake on the 4th of July 2019 and by the Borrego Springs Earthquake of June 10th, 2016.

The second Ridgecrest earthquake had a massive magnitude of 7.1, lasting just over 12 seconds. It was felt all the way from San Diego up to Sacramento by 30 million people and over 6000 homes were without power.  

Both of these earthquakes wreaked havoc on roads, public structures, and private homes.

However, it is important to note that while earthquakes can cause millions of dollars of damage, expansive soil is the numero uno perpetrator when it comes to property damage across the USA as expansive soil can instigate foundation settlement and/or foundation heave.

The number one question about earthquakes is not if another one is going to happen, but when. And because earthquakes are inevitable, they are important to learn about and learn how to properly secure your home’s foundation.    

In this article, we are going to cover:

  1. What causes earthquakes
  2. Problems/Complications Stemming from earthquakes
  3. How Earthquakes affect your foundation
  4. How to prepare your home’s foundation for an earthquake

What Causes Earthquakes?

Earthquakes are generated by abrupt slips across faults. The earth is comprised of tectonic plates (sections of the earth’s crust/uppermost mantle) that are in perpetual motion. Occasionally, due to friction, these plates get caught and stick against each other. Stress compounds on both sides of the fault, creating static energy as both sides refuse to budge. Eventually, there is a slip (one side gives way) and a burst of pent-up energy is released sending waves of energy through miles and miles of the earth’s crust. This incredibly fast, powerful release of energy is the shaking that we feel.

The fault we have to worry about most in Southern California is the San Andreas Fault. The San Andreas Fault is a magnificent 650 miles long and can reach depths of up to 10 miles

Faults that stem from the San Andreas are the San Jacinto Fault (SoCal) and the Hayward Fault (NorthCal).  

The two plates that comprise the San Andreas fault are the North American Plate and Pacific Plate. Yeah – they sound like meals at a surf and turf joint in Huntington Beach.   

The North American Plate takes up the majority of the North American continent and reaches out into sections of the Atlantic Ocean Floor. 

The Pacific Plate is comprised of the majority of the Pacific Ocean floor and the California Coastline

The Pacific Plate steamrolls forward with tremendous force to the northwest, pushing past the North American Plate at a break-neck speed of two inches per year.

Sections of the San Andreas Fault line have conformed to this perpetual movement by a constant creep, culminating in small shockwaves and a few mild to moderate earth tremors.  

In sections of the fault where this creep/slippage movement is not constant, energy BUILDS

This pressure can build for hundreds of years and suddenly snap – generating a true earth-shattering experience.

The Pacific Plate and North American Plate creating the San Andreas Fault is an example of a lateral/transform fault – the plates push past one another in a parallel fashion.  

The vast majority of seismic activity revolves around 3 Plate Boundaries:

·   Divergent – the tectonic plates are moving away from each other

·   Convergent – the tectonic plates are moving towards each other

·   Lateral/Transform – the tectonic plates are moving past each other

Convergent fault lines are responsible for 80% of all earthquakes!   

Fun Facts with BrianThe Pacific Rim (often referred to as the Ring of Fire) has over 452 volcanoes (that’s 75% of all of the world’s dormant and active volcanoes) and is responsible for 80% of the world’s seismic activity.  

Earthquake Damage Dalinghaus (Photo Credit_ Jonathan Cooper)

 Problems/Complications Stemming from Earthquakes

Earthquakes are the result of a sudden release of power – like a taut rubber band finally being let go to hit your little brother’s shoulder (sorry, Brad). 

Obviously, this explosive release of power can cause a lot of damage from toppled homes to landslides to tsunamis to bruises.    

Structural Failure

The incredible vibration (waves of energy) zipping through the earth’s crust can cause serious damage to the world above. 

This shake, shake, shaking can instigate mudslides, landslides, and liquefaction (vibrating earth creating a type of quicksand).

 Remember from Physics 101 - energy is transferred. 

The majority of damage results from seismic waves zipping beneath roads, buildings, and other structures – these structures are not able to withstand the load of the transfer of energy.  

Ground Displacement & Surface Rupture

The numero uno earthquake hazard is surface rupture (instigated by horizontal or vertical movement from either side of the fault).

This ground displacement can incur severe damage to railways, roads, pipelines, and other structures.  

Landslides/Mudslides  

Earthquakes are notorious for triggering landslides and mudslides, particularly in areas with already drenched expansive soils that rest on a precarious slip plane

Debris (such as rocks, trees, swaths of loose soil) can sweep up, bury, or just straight up collide against people, vegetation, buildings, vehicles, and animals. Landslides have buried entire villages.

They often obstruct roads and rupture utility lines, cutting off entryways of assistance and communication.

Liquefaction/Soil Milkshake

So there’s really no such thing as a soil milkshake…or is there?!

Okay, not really, but when earthquakes shake, shake, shake, they can joggle soil into liquid (like the quicksand I mentioned above). 

Obviously, liquid has less load-bearing capacity than soil, damaging bridges, pipelines, roads, and foundations. These structures can collapse or sink or simply dissolve.    

Tsunamis

Tsunamis are colossal, cyclopean waves that are generated on the ocean floor when triggered by an earthquake. 

Large tsunamis can incur a tremendous amount of property damage and loss of life. The deadliest tsunami in recorded history was the 2004 Indian Ocean Earthquake which claimed 230,000 lives and cost 15 billion in damages.

Fires

Turns out, fires are the second most common hazard incurred by earthquakes. Broken gas and powerlines often spark and ignite loose debris around the flame. 

And, as we know, fires are particularly dangerous here in the Pacific Northwest – not to mention Southern California alone with 2020 being the worst recorded fire season yet.

Over 5 million acres were burned in Washington, Oregon, and California in the summer of 2020.  

Now, while an earthquake wasn’t responsible for these forest fires, an earthquake sure could be in the future.

And, final note for this section, all scientists believe “the big one” is inevitable.  

 How Earthquakes Affect your Foundation

Earthquakes pose a direct negative threat to your foundation due to the violent movement – the earth throwing your home around like a Raggedy Anne Doll in the grip of a malicious little boy.

Even small earthquakes can damage your home’s foundation due to the extreme force exerted and transferred up through your foundation, into the wooden bones of your home, and outward into sheetrock from there. 

Again. Energy. Is. Transferred.  

Fun Facts with Brain – Shallow earthquakes tend to be more dangerous than deeper earthquakes. This is because the seismic waves from the deeper quakes have to travel farther to hit the surface, shedding more energy along the way.

Truth be told, raised foundations are inherently the most susceptible to earthquake damage, but all types of foundations can be affected by seismic activity.

Signs your foundation might have earthquake damage are:

  •   Exterior cracks on your foundation blocks/footing. Any crack wider than ¼ of an inch poses a potential hazard.
  •   Exterior cracks with exposed rebar/steel reinforcement (this can point to serious foundation damage)  
  •   You have cracks in your sheetrock, most notably above your window and doorframes, where the quake transferred a significant amount of energy/pressure.
  •   Your house slid off of your raised foundation (the problem here is obvious)

All these symptoms, except for the last one, could be either attributed to foundation settlement or foundation heave, both caused by expansive soil.

To differentiate between what exactly is affecting your foundation, get in touch with a professional.   

Seismic Retrofitting (Dalinghaus)

How to Prepare Your Home’s Foundation for an Earthquake

Slab foundations and basement foundations inherently manage fairly well against earthquakes. However, foundations that may require some additional support against seismic activity include:  

The first three foundations listed can be seismically retrofitted to provide extra support reinforcement against earthquakes.

Seismic Retrofitting  

Seismic retrofitting is achieved by securing the foundation to the walls of the home via anchors, bolts, and sill plate connectors, and hold-downs.

Essentially, these brackets (comprised of bad-ash galvanized steel) connect your stem/cripple walls directly to your home.

So, when mother nature hits the dance floor, your home is secure.    

Metal straps or tie-downs are also utilized to secure the subfloor. In addition, the beams and joists are joined together by metal connectors so that the roof is secured to the walls of the structure.

And, finally, any minor cracks are addressed via epoxy.  

Seismic Retrofitting generally costs anywhere between $3000 to $7000.

*Note – Not sure you can afford Seismic Retrofitting? The California Residential Mitigation Program (CRMP) gives qualifying homeowners $3000 to go towards retrofitting California homes to prevent future earthquake damage. The homes that qualify have:

  •   Raised foundations
  •   Are built on a low or level slope
  •   Were built prior to 1979
  •   Are made of Wood    

It’s better to be safe than to be sorry for when the big one hits. 

We here at Dalinghaus recommend seismic retrofitting because when geological push comes to shove, it can keep you safe, ensure you have a place to live, and keep your biggest financial investment secure.  

Fun Facts with Brian – If you ever do happen to find yourself in an earthquake stop, drop, and take cover under sturdy furniture (a desk or table). 

If you’re on the coast, wait until it is safe to move, then get as far away from the ocean and as high as you can on the chance there’s a tsunami.   

Get Ready for the Big One

Geologists are kind of like Jedi – they are always in tune with the force of mother nature and prophesying about the chosen one- big one, I mean big one.  

Experts agree the Big One will be at least 7.8 in magnitude along the San Andreas Fault.

This earthquake will be 44 times stronger than SoCal’s Northridge earthquake of 1994 which resulted in 9000 injuries, 72 deaths, and around 25 billion in damages.  

For our geologists & mathematicians out there, check out this article Earthquake Magnitude, Energy Release, and Shaking Intensity.     

For those of you who don’t reside in Sunny Southern California or red-rocked Arizona. For you push pier enthusiasts and helical tieback junkies – keep reading our blog! 

We see you. We appreciate you. We dig it.

If you have a specific question about foundation repair you think would make a great article, drop us a line!  

Whatever your foundation repair needs, Dalinghaus is here to provide peace of mind, especially with our new lifelong warranty on our Steel Pier Systems. If you live in Southern California and would like your raised foundation seismically retrofitted or:

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