3 Criteria needed for all Earthquakes
- Fault Parameters
- Rupture length
- Rupture width
- Dip Angle
- Fault type
Definition of Magnitude
- Measure of earthquake strength in terms of:
- Maximum ground motion
- Energy released
- Other measures of amplitude of seismic wave of earthquake
- AIR uses Moment Magnitude to classify magnitude
Definition of Intensity
Earthquake's potential for damaging property at the specific location of the property.
Determined by reported effects on human beings and structures. Measured using MMI (Modified Mercalli Index).
Most seismically active area of the world?
Pacific Ring of Fire
3 Sources of Earthquake Activity
- Subduction Zone
- Crustal Faults
- Intraplate (Northridge)
Seismic Sources within a Country
- Background Seismicity (small quakes on known faults, or unknown faults)
- Known/Special Seismic Zones (not well studied faults)
- Known Faults (well studied, usually big, geodetic and/or paleoseismic data often used too)
Fracture along which there is displacement of the sides relative to one another, parallel to the fracture.
3 Types of Faults
- Strike-Slip (2 sides crash into each other and they move in opposite directions laterally)
- Thrust/Reverse (2 sides crash into each other, one goes over the other)
- Normal (2 sides go away from each other)
Blind Thrust Fault
Little to no surface expression except for a hill. Hidden faults. This category can include subduction zones.
Can one fault impact another?
Yes. Rupture of one fault can trigger rupture of nearby faults.
Earthquake Catalog controls:
- Location based risk
- EP Curve
- - Frequency of events in catalog will drive return period of losses
- - Largest events in the catalog will control the shape of the tail
What factors are used to construct the earthquake catalog?
- Historical data
- Fault information
- Geodetic Data
What is Gutenberg-Richter distribution?
Relationship between magnitude and frequency.
As the magniture goes up, the cumulative frequency goes down. (i.e. big earthquakes are less frequent than lots of little ones)
Cumulative Annual Frequency driven by
Magnitude driven by
- Catalog data
- Fault slip rates
- GPS data
4 Features that Earthquake Catalog Data provides info on:
- Spatial Distribution
- Magnitude Distribution
Carbon Dating and Paleoseismic data
Reveals offsets in rock and soil layers.
Provides info on recurrence rates.
For well studied faults, they use logic trees to calculate recurrence probabilities with the following 4 parameters:
- Tectonic loading
- Fault friction
- Regional distribution of deformation
- Rupture length and multi-segment rupture
Stress on faults indicates
greater seismic risk.
They use GPS data to measure stress accumulation.
Spacially smoothed background seismicity
fills in the gaps on historical data, ensuring full spatial coverage in the catalog
AIR Earthquake Model Stochastic Catalog contains how many years?
Time Independent earthquakes
The probability of an earthquake happening on a particular fault is independent of similar faults that have happened in the past on this fault. Like the lottery. Past events don't impact future ones.
Used everywhere EXCEPT CA.
Time Dependent Earthquakes
Annual probability of an earthquake along a fault increases with the amount of time elapsed since the last earthquake there. i.e. We wouldn't have 2 1906 earthquakes back to back.
Used in CA.
(GMPE) Ground Motion Predictive Equations
mathematically describe the rate of decay in ground motion with distance. (image with source, path effects, site effects).
Sensitive to fault mechanisms and site locations relative to the fault rupture plane.
In strong earthquakes, sandy soil can experience this and produce these:
Earthquake Damage Types
- Shake Damage (most common)
- Liquefaction Damage
- Tsunami Damage
Exposure Classification Criteria
- Construction material
- Resisting Mechanisms (UnR/R/C Masonry, Moment Resisting Frame (MRF), Shear Walls, Braced)
- Height (Low 1-3 stories, Mid 4-7 stories, High 8+ stories)
AIR Building Classes:
Building behavior in an earthquake is determined by:
- Mass (1:1)
- Stiffness (1:1/K - inverse)
(SDOF) Single Degree of Freedom Oscillator
Structure where mass is connected to the ground via column of stiffness K
Building Damage Estimation is calculated by what 2 things:
- Ground Motion Intensity
- Building Capacity
Mean Damage Ratio is:
- Ratio of
- Repair Cost/Replacement Value
(PGA) Peak Ground Acceleration
- Maximum horizontal acceleration measured on the ground.
- Used as a measure of input ground motion.
- Only one measurement though and doesn't account for shaking frequency, duration, or how a building will respond to ground motion.
Represents the behavior of all possible structures to a specific ground motion
What variable correlates to damage?
Drift (relative displacement)
Our Vulnerability Module includes 2 major components:
- Predicting Structural Responses
- Estimating Damage
To calculate Building Respond, we use
Capacity Spectrum Method
Capacity Curve represents a building's:
Formula for Roof Drift Displacement:
Three geometrical factors that are specifically addressed in the EQ model:
- Building Pounding
- Varied height/Tapered profiles
- Angled wings
Causes of Tsunami damage:
- Velocity Impact
Causes of Liquefaction:
- Underlying soil is loose and saturated
- Strong Shaking
Liquefaction damage is estimated from:
Expected Ground Settlement
Fire Following Earthquake
- Secondary peril. Contributing factors are:
- ground motion intensity
- building density
- local building practices
AIR's EQ models consider these vulnerability factors:
- Structural vulnerability at portfolio level
- Building code relative effect in certain age bands within each country
- Construction practice between countries
EQ model considers:
- Soft-story behavior
- Angled wings
- Tapered profiles
- Corner buildings, etc.