The Earth’s Surface Floats On A Sea of
Molten Rock
The Earth’s surface plates are in constant motion very slow constant motion.
 The lines created by the collision of the immense plates are called faults .
 The surface plates are held in place by friction until the buildup of pressure causes sudden movement an earthquake.
Diagram Courtesy of J.H. Wiggins Co.

How Does This Work?
 Earthquakes move surface plates in any direction or any combination of directions. Each such movement causes unique damage.
Diagram
Courtesy of J.H.
Wiggins Co.

In Addition to Movement...
 The earth can radiate waves that will shake structures without actually moving them .
 Shaking is a major source of earthquake damage to structures.
 The graphic illustrates a P-Wave - a form of compression and release.
Similar to a slinky motion.

S-Wave
 S-Waves travel by vibrating up and down.
 S-Waves can cause vertical cracks and change the elevation of parts of buildings.
 The hammer in the illustration represents the point where energy is released.

The Fault Plane
 This thin line represents the fault line . Earth movement occurs along this line.

Fault Movement
Two Types of Fault Movement :
 Strike-Slip
A sideways movement.
 Dip-Slip
An up and down movement.

Strike-Slip Fault Movement
 Little change in elevation on either side of the fault plane. A very common type of earth movement.
Lateral
Movement

Dip Slip Fault Movement
Graben
Horst
 Graben the fault-bounded valley.
 Horst the fault-bounded ridge.
Vertical and
Upward
Movement

Normal Fault Movement
 The earth on the right side of the fault plane line drops.

Thrust Fault Movement
Normal Reverse
 Thrust Fault Movement [Reverse]
The earth on one side of the fault plane rides up and over the earth on the other side of the fault plane.

Thrust Fault
Thrust Fault
 Thrust Fault
A reverse fault with gently dipping fault surface.

Left Lateral Strike Slip
 The earth moves laterally along the fault line with primary movement along the left side of the fault.
Diagram Courtesy of J.H. Wiggins Co.

Other EQ-Related Earth Movement
Landslides and
“Poor Ground”
 This type of movement is the result of earthshaking versus actual direct faultrelated movement.

Typical Landslide Remediation
Soil Nailing - Used to stabilize hillsides.

Rockfall Landslide
 Rock masses that fall through the air.

Slump Landslide
 Intact masses move with other large masses to cause instability and soil erosion.

Debris Slide
 Typified by broken masses of rock and earth, a debris slide moves on the underlying surface.

Earthflow or Liquefaction
 Soil moves like thick fluid, seeking its own level, generally caused by the vibrations
(waves) that accompany earthquakes.

Soil Types Prone to Liquefaction
 Sand
 Gravel
 Soft soils
 Dried lakebeds
 High water table areas
 River flood planes with high deposits of silt

Evidence of Liquefaction
 Sand Boils
Sub-surface sand is liquefied by the vibration waves of the earthquake. The discharge to the surface resembles boiling water.

Typical Liquefaction Damage
 Note how foundation shows signs of sinking into the earth.
 Following liquefaction, the soil around a building must be stabilized before commencing repairs.

Soil Densification
Soil Densification is the :
 Compaction of unstable soil caused by earthquake vibration and shaking.
 Creation of minor depressions in the earth’s surface.
 Cause of serious damage to foundations and superstructures when beneath buildings.

Voids
Diagram Courtesy of J.H. Wiggins Co.
Voids are created by:
 Improper drain fields,
 Erosion,
 Improperly channeled roof runoff,
 Leaking plumbing such as exterior faucets, evaporation, and surface water.

Subsidence
Land subsidence
 Occurs when large amounts of ground water have been withdrawn from certain types of rocks, such as finegrained sediments.
 Common to areas with underground mines, subsidence can occur when mines experience cave-ins (see diagram).

Subsidence
 Location of maximum subsidence in U.S. as identified by researcher
Joseph Poland. Signs show position of land surface in
1925, 1955, and 1977.
 Subsequent use of surface water greatly reduced the rate of subsidence, but renewed ground-water pumping during the drought (1987-92) resulted in additional subsidence.

Subsidence (continued)
 Rocks and water are responsible for holding the ground up.
When the water is withdrawn, the rock falls in on itself, resulting in subsidence.

What Causes Land Subsidence:
 Underground mining.
 Natural compaction of soils.
 Loss of water in organic soils.
 Dissolving of subsurface limestone rock.
 Withdrawal of ground water and petroleum.
 First-time wetting of formerly dry, low-density soils.

Sinkholes
Common when ground water circulates through rock below the surface, then naturally dissolves it. Rocks such as:
 Limestone,
 Carbonate and
 Salt beds.

Areas Prone to Subsidence and Sink
Holes

Mining
Diagram Courtesy of J.H. Wiggins Co.
Not limited to these areas.
However, the most notable instances of mining-related soil problems are shown here.

Underground Fluid Withdrawal
Diagram Courtesy of J.H. Wiggins Co.

Hydrocompaction
Diagram Courtesy of J.H. Wiggins Co.

Sinkholes
Diagram Courtesy of J.H. Wiggins Co.

Natural Compaction
This area is a collection point for organic soils precipitating from the Mississippi
River. As the soils continue to decompose and condense, the ground settles.
Diagram Courtesy of J.H. Wiggins Co.

Drainage of Organic Soils
Also referred to as Erosion .
Diagram Courtesy of J.H. Wiggins Co.

Typical Damage from Frost
 Note that attached structure does not have the same foundation as the main structure, resulting in frost heave movement .

Soil Soaking and Drying
 Soil can shrink and swell according to its level of moisture content.
 Moisture extremes can cause damaging stress to foundations and concrete slabs.
Diagram Courtesy of J.H. Wiggins Co.

Soil Bearing Failure
 Caused by improper support installation and related excavation.
 Common to buildings with additions.

Soil Stabilization
A process used:
 After an earthqauke to stabilize liquefied or liquefaction-prone soil, but
 Prior to the actual repairing of a damaged structure.

Stabilizing Methods
 Soil nailing
 Slush grouting
 Ground Anchoring
 Dynamic Compaction
 Chemical additive stabilization
 Introduction of superlight materials
 Vibro-compaction and vibro-displacement
 Installation of vertical drains, retaining walls, or subterrainian perimeter containment walls around a building’s foundation

Slush Grouting
 Involves pouring cement grout into cracks, fissures, or other earthquakedisturbed soil to fill surface fractures.
 Includes pumping grout materials under pressure into subsurface unstable soils.

Deep Dynamic Compaction
 Pounds the ground into a compact density by dropping a heavy compactor onto the surface.
 Not used close to buildings.
 Not an economical method of soil stabilization for small areas such as yards and drives.

Soil Nailing
Diagram Courtesy of J.H. Wiggins Co.
 Used to hold soil of the unstable ground in place.
 Long rods are drilled into metal or concrete surface plates.

Soil Mixing
 Stabilizing additives are mechanically mixed into the soil to improve viscosity and soil stability.

Tie-Back Retaining Walls
 To hold the wall in place, long metal rods are drilled into the hillside through the concrete or gunnitecoated wall.

Soil Stabilization Involves Many
Approaches
 Be aware that all soil stabilization processes are not effective under specific circumstances.
 Warning!
Experience has shown that any soil stabilization effort must be closely examined by a qualified expert prior to implementation to avoid costly problems such as future failure or contamination.

Every Earthquake Is Different
 Soil conditions vary. They each cause different earth movement and building damage.
 Proximity to epicenter affects local intensity.
 How a building responds to an earthquake depends on its specific type of construction.
 The type of earthquake affects damage, such as slip-fault versus strike-fault.

Earthquake Losses Are Different From
Most CAT Losses.
 Damage starts at the foundation and works out, often causing loss that can’t be seen from the exterior of the building .
Diagram Courtesy of J.H. Wiggins Co.

An Example of Foundation-Up Damage
 Change in elevation under a building’s foundation can result in walls shearing and substantial damage to the superstructure.
Diagram Courtesy of J.H. Wiggins Co.

Types of Damage Common to Landslides
Diagram Courtesy of
J.H. Wiggins Co.
 In this case, a landslide causes the ground to spread, splitting the foundation.

Summary
Earthquakes:
 Can physically move the earth beneath structures.
 Are caused by the sudden movement of massive plates along fault lines.
 Can cause shaking from a various types of shock waves.

Summary (continued)
Soil conditions around a building have a major effect on the amount of EQ-related damage.
 Soft, sandy loam or gravel-type soils experience liquefaction.
 Structures built on unstable fill are susceptible to foundation damage and shaking.

Summary (continued)
Different types of earthquakes cause different types of damage.
 Direct land movement
 Subsidence
 Liquefaction
 Landslide
 Shock waves.
Earthquake damage starts with the foundation and moves up and outward. Other catastrophes damage the exteriors first.

Summary (continued)
Not all soil movement is earthquake-related.
 Soil densification can be caused by heavy traffic nearby.
 Subsidence can be caused by collapsing underground mines and overuse of naturally occurring ground water.
 Frost, soaking, and drying can also cause earth movement around foundations.

Summary (continued)
Soil Stabilization
Used to correct or mitigate earth movement-related losses.
 Soil nailing - installing retaining walls or anchoring unstable hillsides with long metal rods and slush grouting.
 Soil mixing - adding stabilizers to existing soil.
 Deep dynamic compaction - mechanically compacting the soil by dropping a heavy weight onto the ground.

Summary (continued)
Soil stabilization is regulated in most states and may not be an available option.
 Consult an expert to when considering this an option.