AIR Earthquake
Model for the
United States
If the 1906 M7.8 San Francisco earthquake were to recur
today, it would cost the insurance industry USD 117 billion.
And there are seismic sources throughout the United States
that could produce similar—or even larger—losses. The AIR
Earthquake Model produces a robust probabilistic view of
the risk, enabling companies to prepare for the next largescale event—wherever and whenever it occurs.
The robustness of an earthquake model
and its ability to produce reliable results
rests on the strength and scientific
rigor of each model component. The
Fully Consistent with the Most Recent USGS
Hazard Maps
In 2008, the USGS completed a major update to the U.S.
National Seismic Hazard Maps which, in the view of the
science and engineering community, are the most robust and
comprehensive to date. These maps cover all seismically active
hazard component requires the accurate
regions within the United States including California, the
depiction of regional and local seismicity
Cascadia Subduction Zone in the Pacific Northwest, the New
and reliable predictions of earthquake
Carolina, and the Northeast.
ground motion that account for local site
conditions. The vulnerability component
requires damage functions that
realistically capture individual building
response to those ground motions. The
AIR Earthquake Model for the United
States leverages the most current scientific
and engineering research in each of these
components, offering a comprehensive
approach to earthquake risk assessment
that redefines the state of the art.
Madrid Seismic Zone in the Central U.S., Charleston in South
AIR scientists actively participated in several regional
workshops held by the USGS in the course of developing
the maps. After conducting a thorough review of the
final version, AIR chose to incorporate all of the USGS
recommendations into the hazard component of the AIR
Earthquake Model for the United States.
A New Generation of Ground Motion
Prediction Equations
The understanding of earthquake hazard in the scientific
community has improved significantly in recent years, but the
single most important advance has been the development of
better ground motion prediction equations, or GMPEs, which
predict the level of ground shaking that a future earthquake
with given characteristics will generate at a specific site.
Taking advantage of a significantly improved data set of
strong motion records collected around the world during
the last two decades, scientists representing a consortium of
research groups—including the USGS, PEER, and SCEC—have
developed new sets of GMPEs for shallow crustal events like
those that occur in California and elsewhere on the West
Coast.
Recordings of M > 7
and Distance < 10 km
Total Number of Recordings
AIR’s smoothed seismicity rates (top) accurately reflect those from the USGS
(bottom)
4000
40
3500
35
3000
30
2500
25
2000
20
1500
15
1000
10
500
5
0
Pre 1997
NGA
0
Pre 1997
NGA
The NGA project incorporated more data, particularly at close proximity to
high magnitude earthquakes
2
The so-called Next Generation Attenuation (NGA) equations
1.0000
are based on a much larger database of recordings and
than previous equations. In particular, these equations
more accurately capture the effects of large magnitude
earthquakes at short distances. In addition, they better
PGA (g)
are considerably more reliable and scientifically defensible
0.1000
account for local soil conditions, site amplification, and fault
Observed
Previous Generation
NGA
rupture mechanism. The prediction equations applicable to
other parts of the country—in the East or along the Cascadia
Subduction Zone in the Pacific Northwest—have been
updated as well.
0.0100
0
1
10
Distance (km)
100
1000
NGA-based ground motion estimates are more consistent with observed
recordings than estimates obtained using older prediction equations
Several Steps Beyond
While the AIR Earthquake Model for the United States is fully consistent with the most recent USGS seismic hazard maps
and incorporates the latest findings on ground motion, faults, seismicity, and geodesy, the AIR model goes beyond the USGS
maps in several key areas.
High Resolution Soil Information
These basin effects are of particular importance for
The USGS hazard maps assume stiff soil conditions. Local
estimating the response of tall, flexible structures.
site conditions may in fact be quite different, which can
dramatically alter the intensity and the frequency content
of the ground motion at a site. The AIR Earthquake Model
for the United States employs three layers of soil maps, each
with a different resolution and areal coverage. The first layer
is the base soil map that covers the entire continental United
States. The second layer, with variable resolution ranging
from 100 to 500 meters, covers the most at-risk states. The
third layer, with resolution as high as 50 meters, covers urban
areas with concentrated exposure and significant seismic
Spatial Correlation
Earthquakes can produce patterns of spatially extended
pockets where the ground motion is consistently higher
or lower than predicted by attenuation equations. When
a higher-than-expected ground motion pocket occurs in
a densely populated area, the losses will be much larger
than expected within that area. This effect cannot be
captured from the use of GMPEs alone.
risk.
The USGS national seismic hazard maps are designed to
Basin Depth
correlation irrelevant. However, such correlation has
The USGS model uses a uniform soil depth that ignores the
potentially significant amplifying effects of deep alluvial
basins. AIR uses high resolution (0.2 km) depth information
for major basins in California, Washington, and Nevada to
take full advantage of the capabilities of the NGA equations.
capture the hazard at any given single site, making spatial
important implications for a probabilistic risk assessment
of a portfolio of properties. The AIR Earthquake Model
for the United States explicitly incorporates ground
motion correlation, which produces a wider distribution
of losses—a difference that is particularly important for
ensuring that the exceedance probability distribution has
a robust tail.
3
Damage Functions Derived Using Nonlinear
Dynamic Analysis
The model’s damage functions, which mathematically
describe the relationship between shaking intensity and
building damage ratio, are developed based on a synthesis
of engineering analysis, literature review, and analysis of
detailed damage, claims, and loss data. They also reflect
regional building practice and the evolution of seismic codes.
With the latest release of the AIR Earthquake Model for
FLOOR 8
10
the United States, AIR engineers have taken yet another
step in the advancement of objective, engineering-based
earthquake vulnerability assessment with the introduction
computer simulation using actual ground motion records,
which considerably reduces uncertainty and produces the
FLOOR 6
Peak Displacement
representations of buildings are shaken “virtually” in a 3-D
-10
0
10
20
30
40
50
60
0
10
20
30
40
50
60
0
10
20
30
40
50
60
0
10
20
30
40
50
60
10
FLOOR 3
of nonlinear dynamic analysis (NDA). Detailed structural
0
most robust estimation of building response available.
0
-10
5
0
-5
FLOOR 2
5
0
-5
TIME (SEC)
Independent Peer Review
AIR’s damage functions, as well as the methodology used
to develop them, have been peer-reviewed by leaders in
the field of earthquake engineering.
“The methodology used by AIR to develop
its damage functions is rigorous and well
conceived. AIR’s vulnerability assessment
framework is consistent with the objectives
of performance-based earthquake
engineering—the current state of the art.”
—Dr. Deierlein and Dr. Kircher
Recorded
Simulation
Using a detailed 3-D model of a seven-story reinforced concrete building
(top), nonlinear dynamic analysis reliably estimates the actual building
response recorded during the 1994 Northridge earthquake (bottom)
Estimating Losses to Buildings Under
Construction
The model supports the builder’s risk line of business for
residential and commercial construction. With builder’s risk,
both vulnerability and replacement cost vary significantly
during construction. The AIR model features time-dependent
cost functions, or ramp-up curves, and damage functions
developed based on extensive, component-level analysis
during each phase of construction.
Professor Greg Deierlein is the Director of Stanford
University’s John A. Blume Earthquake Engineering
The model estimates average annualized project losses and
Center, as well as the Deputy Director for Research at the
losses for each phase of construction. For projects already
Pacific Earthquake Engineering Research (PEER) center.
under way, users can enter percent completed to estimate risk
to just the remaining part of the project.
Dr. Charles Kircher, Structural Engineer and Principal at
Charles Kircher & Associates, is credited with being one
of the key developers of the HAZUS methodology and
damage functions.
Special Handling of Additional Coverages,
Lines, and Secondary Perils
Total losses caused by an earthquake are driven by more than
just building damage caused by ground shaking. The AIR
model features state-of-the-art treatment of the following
significant drivers of insured losses.
4
Minor
any significant BI. This assumption resulted in significant
Moderate
underestimation of BI losses. The AIR model uses an event-
Operation
tree approach to account not only for building damage—or
Relocation
Severe
Damage
No
Civil Authority
No
No
PGA = 0.05g
Utility
No
Utility
losses stemming from actions taken by civil authorities, loss
No
of business income from dependent properties, and utility
Destruction
Civil Authority
No Damage
No
direct BI—but also for BI from indirect sources, such as
service interruption.
Utility
No
Typical Event Path for Office
Utility
Typical Event Path for Hotel
No
Hypothetical event tree for business interruption loss estimation
Direct and Contingent Business Interruption
Historically, catastrophe models estimated business
interruption (BI) losses based primarily on repair time
estimates for different degrees of building damage and
the assumption that at low to moderate building damage
levels, most businesses remain in operation without incurring
Workers’ Compensation
When a workplace is damaged during an earthquake,
employees in or near the building can sustain a wide variety
of injuries—injuries that can result in significant workers’
compensation losses. AIR’s workers’ compensation module
incorporates the most likely types of injuries that are incurred
in buildings of different construction types with different
levels of damage. Average benefit levels for each injury type
are updated annually.
Component-Based Approach for Estimating Damage to Industrial Facilities
The evaluation of seismic risk to industrial facilities is a
functions for each of more than 400 components,
particularly complex task, stemming from the fact that they
including cooling towers, pipes and pipelines,
exhibit not only a large number, but also a wide variety of
transformers, tanks, and the like. The damage functions
distinct components (tanks, cooling towers, process towers,
for individual components vary by the region in which
flares, structures, machinery, equipment, transmission lines,
the facility is located, as both the seismic risk and design
transportation assets, and contents) and a high degree of
specifications vary across the United States.
interconnectivity between different parts of the facilities
(transportation, product chains, and electricity generation,
and other lifelines).
To assess the damage and loss to industrial facilities, AIR
employs a component-based approach in which primary
components are categorized into classes and subclasses
based on their function, as well as their vulnerability to
ground shaking. The damage functions for each component
class are evaluated using the same procedure adopted for
other types of assets. The model features separate damage
Industrial facilities contain a wide variety of components, each of which
has a unique response to ground motion
5
Fire Following Earthquake
and practices by region, and also recognizes differences
Fires are a common occurrence following earthquakes,
in vulnerability to water damage of various nonstructural
but can be especially significant in a dense metropolitan
building components and content types.
area with a preponderance of wood frame construction.
350
AIR’s fire-following module uses a dynamic fire simulation
capabilities. The stochastic fire ignition algorithm was
developed using historical data and captures how ground
motion intensity and fire class affect ignition rates. Fire
spread and fire suppression are modeled as a dynamic
300
USD billions
algorithm that accounts for ignition, spread, and suppression
250
200
150
100
process, taking into account such factors as wind speeds, fire
50
discovery and report speeds, fire engine speed and capability,
0
and water availability. These factors interact dynamically to
individual fire spreads and is eventually suppressed.
Liquefaction
Liquefaction occurs when, as a result of violent shaking,
water-saturated soils lose their strength and are unable
to support the buildings above them. The AIR model
incorporates data on over a million depth measurements
of water tables in areas of the U.S. at high risk from
liquefaction, including data on changes in the water depth
due to seasonal variation, water usage, and environmental
changes.
USD billions
determine how the fire simulation proceeds and how each
1906 San
1994
1989
Francisco Loma Prieta Northridge
7
6
5
4
3
2
1
0
1940 EL
Centro
1952 Kern
2001
2003 San
County
Nisqually Simeon
Estimated (with Range of Reported Damage)*
Modeled
Estimated vs. modeled ground-up damage for historical earthquakes
(*Estimated by various sources and trended to 2008 values)
Model Components Are Independently
Validated against Multiple Sources
AIR validates each component of the model to determine its
robustness and reliability. For example, AIR validates modeled
seismicity and ground motion using historical catalogs and
observed ground motion data in accordance with the USGS
Groundwater
Depth (meters)
0
<5
5 - 10
10 - 15
> 15
models. Damage functions for various construction types are
independently validated using claims data, post-earthquake
damage data, shake table tests, and published research. AIR’s
approach of validating model components against multiple
credible sources is far more robust than calibrating to a single
High resolution data on groundwater depths are employed for areas at risk from
liquefaction
Sprinkler Leakage
The AIR Earthquake Model for the United States features a
separate module to estimate losses caused by the breakage
and subsequent leakage of fire sprinkler pipes due to ground
shaking. The AIR approach is unique in that it takes into
account advances in technology, changes in building codes,
6
loss number.
As a final test, AIR loss estimates are validated against
company claims data and reported industry losses for
residential, commercial, and industrial assets. Modeled losses
include shake damage to building and contents and account
for the effects of demand surge.
Model at a Glance
Modeled Perils
Earthquake shake and resulting fire, liquefaction, and sprinkler leakage.
Model Domain
The 48 continental United States including the seismically active regions: California, New
Madrid, the Pacific Northwest, and Charleston, SC.
Supported Geographic
Resolution
Touchstone® users may input exposures at the following levels: county, ZIP Code, street
address, or latitude and longitude.
CATRADER® users may input exposures at the county or state level; losses are reported at
the county level.
Supported Construction
Classes and Occupancies
Touchstone supports 75 construction classes and more than 110 occupancy classes,
Supported Policy
Conditions
Separate industry loss file profiles are included with CATRADER that contain different
including general residential, temporary lodging, apartment/condo, and retail.
assumptions with respect to California residential earthquake policy conditions. These are
listed below:
–– Mini Policy—Assumes California Earthquake Authority (CEA) mini-policy conditions
for all California residential properties.
–– Non-Mini Policy—Assumes that all of the earthquake policies in California are nonmini-policies.
–– Hybrid—Assumes a California residential mix of 2/3 mini-policy and 1/3 non-minipolicy.
MODEL HIGHLIGHTS
–– The most comprehensive and up-to-date view of seismicity, based on the 2008 USGS National Seismic Hazard Maps
–– Newly developed sets of ground motion prediction equations, including the Next Generation Attenuation (NGA)
equations
–– Peer-reviewed damage functions reflect regional building practice and the evolution of seismic codes and were
developed based on a synthesis of state-of-the-art engineering analysis, literature review, and analysis of detailed
damage, claims, and loss data
–– Supports the builder’s risk line of business, with damage functions that reflect each phase of construction and timevariable replacement cost curves. Average project loss and loss during each phase can be calculated in Touchstone.
–– Modeling of industrial facilities using an engineering-based approach that combines individual component damage
functions into a facility-specific damage function
–– Direct and contingent business interruption (BI) losses estimated using an event-tree approach, based on published
research and detailed loss data
–– Fire-following module uses a dynamic fire simulation algorithm that accounts for ignition, spread, and suppression
capabilities
–– Workers’ compensation risk updated annually to reflect changes in the average benefit level for each injury type for each
state
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ABOUT AIR WORLDWIDE
AIR Worldwide (AIR) is the scientific leader and most respected provider of risk modeling software and
consulting services. AIR founded the catastrophe modeling industry in 1987 and today models the risk from
natural catastrophes and terrorism in more than 90 countries. More than 400 insurance, reinsurance, financial,
corporate, and government clients rely on AIR software and services for catastrophe risk management,
insurance-linked securities, detailed site-specific wind and seismic engineering analyses, and agricultural risk
management. AIR, a Verisk Analytics (Nasdaq:VRSK) business, is headquartered in Boston with additional offices
in North America, Europe, and Asia. For more information, please visit www.air-worldwide.com.
Cover image courtesy of Wikipedia
AIR Worldwide is a Verisk business.
AIR Worldwide, Touchstone, and CATRADER are registered trademarks of AIR Worldwide Corporation.
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