Earthquake

Definitions

Earthquake
A trembling or shaking of the earth that is volcanic or tectonic (seismic) in origin, often resulting in severe damage.

Earthquake insurance
Coverage for property damage caused by the perils of earthquake or volcanic eruption. The coverage is limited to direct damage caused by an earthquake and excludes a loss resulting from another peril even if it is triggered by the earthquake, such as a fire, explosion, flood or tidal wave. Any earth tremors or aftershocks following an initial occurrence within a 168-hour period is considered the same event for claims purposes. Most forms provide earthquake coverage as earth movement coverage.

In some jurisdictions fire following earthquake is not allowed to be excluded by law.

In some jurisdictions volcanic eruption is not a part of the earthquake coverage nor is it excluded in a standard form.

In some polices Avalanche, landslide or volcanic eruption, explosion or effusion are covered perils unless they are caused by an excluded earth movement.

Earthquake exclusion
An exclusion in some property insurance policies for any loss resulting from an earthquake or volcanic action.  Most policies contain a broader earth movement exclusion, which includes earthquake.

Earth movement coverage
A form of earthquake coverage that is extended to include landslide, mudflow, earth sinking, earth rising or shifting, and volcanic eruption.

Blind thrust fault
A geological thrust fault that does not break the earth’s surface, making it difficult to identify. Thrust and strike-slip are the other two types of geological faults.

Epicenter
In an earthquake, the point on the earth’s surfacedirectly above the subsurface focus (or the point where slippage begins).

Focus
As respects an earthquake, the point in the earth along afault line where the slippage begins to occur. As energy is released from this point, it radiates outward in seismic waves.

Liquefaction
In an earthquake, the percolation of subsurface water through unconsolidated soils such as sand, gravel, or silt, or the changing of unconsolidated soils into an unstable form to the point where it acts as a liquid and causes ground failure.

Mercalli scale
A numeric scale with Roman numerals that describes the effects of an earthquake, reflecting local seismic destruction, as opposed to the Richter and moment-magnitude scales, which more scientifically estimate a quake’s release of energy. The Mercalli scale is based on observations at the site and therefore reflects the effects of soil conditions, distance from the epicenter, etc.

Moment-magnitude scale

A measure of total energy released by an earthquake that scientists generally prefer to the Richter scale because it is more precise. It is calculated in part by multiplying the area of the fault’s rupture surface by the distance the earth moves along the fault. A few well-known U.S. earthquakes show different readings between the Richter (R) and the moment-magnitude (M) scales: earthquake R M New Madrid, MO, 1812 8.7 8.1 San Francisco, 1906 8.3 7.7 Alaska, 1964 8.4 9.2 Northridge, CA, 1994 6.4 6.7

Off-set ground motion
As respects an earthquake, the shaking of the ground caused by movement along a geological fault line in opposite directions, which can create a vibration effect on structures, causing them to collapse.

Richter scale
The Richter scale measures the amount of energy released by an earthquake. It is a logarithmic scale, so each whole number on the scale indicates an earthquake ten times more powerful than the preceding number. An earthquake reading 1.5 is the smallest tremor that people can feel, though most tremors that small are not felt.

Seismograph
An instrument to measure and record vibrations andtremors within the earth.

Strike-slip fault
A geological fault where each side slips past the other without significant vertical motion. This is the most predominant type of fault in the United States. It is one of three types of fault, along with blind thrust and thrust faults.

Thrust fault
One of three type of geological faults (with blind thrust and strike-slip). One side of the fault rides up over the other. This vertical motion can cause especially violent shaking.

Volcanic action
A violent explosion in a vent in the earth’s crust (eruption), which results in the flow of lava, discharge of ash and dust, volcanic blast or shock waves. The term does not include loss from any form of earth movement. Coverage for loss by volcanic action is provided in most property insurance forms. Coverage does not extend to the cost of removing ash, dust, or particulate matter that does not cause direct physical loss or damage to the insured property.

Volcanic eruption
The earth movement associated with a volcanic action including the eruption, explosion or effusion. Coverage for this peril is specifically excluded from property insurance forms but is included with earth movement and earthquake coverage.

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