Hello, everyone. My presentation focuses on
a recently published study – the Analysis of Communities at Risk
in the HayWired Scenario – which is part of Volume 3,
The Societal Consequences of the HayWired Earthquake Scenario
and now available on the USGS website.
I want to take this moment to acknowledge my amazing co-authors,
Jamie Jones, Anne Wein, and Jeff Peters, all with the USGS.
Understanding disparate hazard and risk is the main purpose and interest of our
study, and I’m excited to be part of this important panel and to share our work.
Having studied or helped manage community recovery following
many major disasters, I was interested in understanding what the risk
of large-scale population displacement and other long-term community
recovery challenges might be in the San Francisco Bay region.
Three disasters in particular are the subject of case studies in our analysis –
the 1994 Northridge earthquake that caused extensive damage to older
multi-family housing and led to a major federal local multi-year,
multi-million-dollar effort to address the resulting blight and repair
damaged buildings in 17 ghost town neighborhoods of Los Angeles.
Flooding from Hurricane Katrina that displaced 90% of New Orleans’
455,000 residents, with severely damaged areas having profoundly
lower rates of population return than less-damaged areas.
Socially and economically vulnerable populations also had lower return rates
than other cohorts. By 2015 and 10 years on, the city had recovered
about 80% of its pre-Katrina population, but nearly half of its
72 neighborhoods still had less than 75% of their pre-Katrina population.
The 2010-2011 Canterbury earthquake sequence in New Zealand resulted in
as many as 10 distinct episodes of liquefaction, rockfalls, and other
ground failure hazards and a government buy-out offer to
more than 7,000 properties in red zone areas that caused
regional housing shortages and cost inflation as well as homelessness.
Replanning of the red zone areas continues today, over 10 years later.
Specifically, our work looked at three things – where concentrated
damage would occur from a magnitude 7 earthquake
on the Hayward Fault centered in southeast Oakland.
To do this, we first developed a methodology to combine the Hazus
estimates of building damage resulting from earthquake shaking, landslide,
and liquefaction by Seligson and others with the fire following
earthquake damage calculated by Scawthorn and others.
We then used a threshold of 20% of total building square footage in
an extensive or complete damage state and thus deemed uninhabitable
until necessary repairs or rebuilding are completed to identify census tracts
with areas of concentrated damage.
Who – we then applied a number of methods to consider the potential size
and composition of the region’s population that could be displaced
as a result of key physical impacts of the HayWired scenario.
We considered a series of socioeconomic vulnerabilities
as well as federal, state, and local emergency response policies and
plans related to emergency shelter and temporary housing that may impact
displacement and population return. And finally what – we then explored
three key issues that our case studies and other past disasters have shown to
impede long-term community recovery, assembling funding for recovery,
repairing and replacing damaged housing, and areas requiring
substantial governmental intervention and replanning.
Now I will share a bit more on each.
Combining the Hazus estimates of building damage caused by earthquake
ground shaking, landslides, and liquefaction with the fire
following building damage, results in nearly 1 million residential buildings,
1.4 million housing units, and nearly 40,000 non-residential buildings
sustaining damage in the HayWired scenario.
That means that almost a third of the Bay Area’s
housing stock would be damaged. Of this, 100,000 residential buildings
sustained extensive or complete damage and thus are potentially uninhabitable.
Over half of the property losses for building content and replacement cost
are concentrated in Alameda County, as you can see in the graph on the right.
Contra Costa and Santa Clara Counties also sustain heavy losses.
Areas of concentrated damage cover only 8% of all census tracts
in the nine-county region but contain nearly 50% of all the housing
that is likely to be uninhabitable or completely destroyed.
These areas also contain about 600,000 employees.
This map shows the footprint of these areas of concentrated damage that
are located within seven economic sub-areas used in the HayWired
economic analyses. These sub-areas are located in Alameda, Contra Costa,
and Marin Counties, and each has more than 25% of the total building
square footage in an extensive or complete damage state.
Field work conducted in areas of concentrated damage found that most
are densely developed neighborhoods with older seismically vulnerable
single-family and multi-family wood-frame buildings that sustain
higher levels of shaking damage and are also quite vulnerable to
post-earthquake fires. These maps show the areas of
concentrated damage for all occupancies combined on the left and
multi-family occupancies on the right. We analyzed eight key occupancy
groupings separately. All of the footprints show similar
patterns of concentrated building damage along the entire East Bay
corridor in the Santa Clara, San Ramon, and Livermore Valleys,
and in the flatlands surrounding San Francisco and San Pablo Bays.
They also show the expanded and intensified levels of concentrated
damage that result from fire following earthquake hazards.
In the next stage of the analysis, we looked at a number of
socioeconomic factors affecting immediate post-disaster displacement
as well as subsequent waves of displacement.
The table shows a range of estimates that we made of potential populations
at risk of displacement from the magnitude 7 main shock of the
Hayward scenario earthquake. The 152,000 displaced households
used in the April 2018 release of the Hayward scenario was based upon
the Hazus analysis of shaking, landslide, and liquefaction and
roughly equals about 6% of the nine-county region’s households
and population. Integrating in post-earthquake fires and lifeline
outages yields potential displacement estimates of up to 10% of the region’s
households and population. Up to 20% of the region’s households
and population live within the areas of concentrated damage.
While it is not likely that all households or people in areas of concentrated
damage would be displaced, neighborhoods serving infrastructure
and services and – the disruption of those and heavy levels of
surrounding building damage could lead to higher rates of
displacement in these areas than in less damaged areas.
We used a set of 10 community vulnerability indicators, or CVIs,
developed by ABAG and the Bay Conservation and Development
Commission to evaluate the social and economic vulnerabilities of
residents in areas of concentrated damages for
all building occupancies combined. In these areas, around 350,000 people
reside in block groups with CVI scores of 5 or more.
Of those, most reside in Alameda and Contra Costa Counties.
These graphs also show how the prevalence of different vulnerability
indicators vary by CVI score. For example, in areas with CVI scores
of 5 or more, there is a greater prevalence of housing
and income-related indicators and literacy indicators.
We supplemented the CVIs with population analyses of other
socioeconomic factors causing displacement – school-aged children,
households with disabilities, and homeless populations.
Those estimates are shown in the top right.
We also created an indicator set to account for the potential voluntary
displacement of young mobile populations, which we know
contributed to high vacancies and ghost town neighborhoods following
the Northridge earthquake. Young mobile populations have
also been leaving the region now as a result of the pandemic.
Jones and others’ study of lifeline infrastructure systems and
interdependencies for the HayWired scenario show that damage levels and
downtime potential for some systems could affect both immediate population
evacuations, especially in areas with post-earthquake fires,
as well as long-term displacements.
Utility restoration curves for Alameda County show long delays
in water and BART services. Jones’ mapping of the co-location
of three or more lifeline assets and the exposure to multiple hazards
shows a strong correlation with areas of concentrated building damage
in parts of western Contra Costa County and much of Alameda County.
Regional earthquake response plans do not consider the possibility
of widespread fires and extensive lifeline utility disruptions,
and their estimates are for far fewer individuals requiring shelter
after a Bay Area earthquake than some of ours.
Available shelters in the central nine-county region may quickly
reach capacity, especially in heavily impacted areas
of Alameda and Contra Costa County. Regional response plans identify
potential host communities in surrounding communities,
but if the immediate sheltering needs exceed the 16-county regional
sheltering capacity, plans then call for relocating residents to other parts of
California and adjoining states. An already constrained regional
housing market, combined with the limited supply of interim housing
options, may impact the timing and ability of people to return to
their home communities. Renters, particularly low-income renters
and people with access and functional needs,
may have more difficulty finding alternative housing.
It will be difficult for residents, businesses, governmental,
and non-governmental agencies to assemble the substantial funds
necessary for repairs and rebuilding after such a scenario.
Hazus and Corelogic building-related loss estimates demonstrate the
considerable scale of losses estimated for the Hayward scenario.
Corelogic’s 2018 study estimates that insured losses would cover
about 23% of commercial losses and 12% of residential losses
for the HayWired earthquake sequence and fire.
Such a major earthquake would also certainly trigger state and federal
disaster assistance programs that would help provide valuable resources,
however, studies from past disasters have shown that the accessibility
and distribution of formal disaster assistance, especially from
governmental sources, is not equitable. As we’ve seen, some of the hardest-hit
communities also have high levels of socioeconomic vulnerability and thus
may have difficulty obtaining formal disaster assistance.
Of the nearly 1 million residential buildings and 1.4 million housing units
that are damaged, those with fire damage are more likely to
have insurance coverage. Otherwise, federal disaster loans
and grants, conventional loans, individual savings, or assistance from
nonprofit funders would be needed. Several large government housing
repair programs have been created to address financing gaps after Hurricanes
Katrina and Sandy in the U.S., to name a few, and might be needed here as well.
A major earthquake could damage some communities so extensively that market
forces alone will not facilitate recovery. Determining which areas can
successfully recover according to existing plans and policies,
and which need to be re-planned, is a difficult task that largely falls to
local governments to address. This analysis defines a typology
of potential areas that may require governmental interventions
and re-planning for earthquake disasters.
These images are close-up views of the region-wide maps
that we created for each type. Substantial land and building damage
caused by liquefaction or landslides, potential surface fault rupture,
including afterslip, concentrated building damage caused by
ground shaking and fire, and areas with substantial transportation
and infrastructure damage – all these areas could face additional
damage from aftershocks and an increased vulnerability to other
hazards like flooding and slope failures. Uncertainty about the feasibility
and affordability of repairs could lead to mortgage defaults,
occupant displacement, property blight, and declining property values.
An array of governmental interventions and re-planning actions may be
necessary to address these conditions, all of which would require money,
community engagement, and time. These demands will likely come
at a point when populations are still displaced and local governments
are facing reduced tax revenues and repair costs for publicly owned
facilities and infrastructure.
A 2018 analysis by Tom Brocher and others estimates that,
since the 1989 Loma Prieta earthquake, as much as $80 billion of investment
across the region has been directed to critical infrastructure upgrades
as well as extensive retrofitting of seismically vulnerable residential,
commercial, and public buildings. Nonetheless, as this analysis
has revealed, substantial vulnerabilities remain.
Furthermore, some of these vulnerabilities are only likely to
continue to grow unless there are some fundamental shifts in the scale
of attention and investment given to reducing the region’s seismic risk.
Seven policy implications for improving community seismic
resilience in the San Francisco Bay region stem directly from insights
gained through our analysis. The first three policy topics direct
more investment and focus in local and regional land use, development,
and capital planning to upgrade the seismic resilience of existing
communities, particularly older homes and infrastructure, while future,
more resilient communities are being planned and built.
Four additional policy topics place greater emphasis on the risk of
population displacement in government, individual, and business disaster plans,
exercises, and preparedness campaigns and planning to manage long-term
recovery and recovery financing ahead of time at all levels of government.
The Communities at Risk analysis for the HayWired scenario adds
a social dimension and long-term perspective to the rich details of the
hazard and immediate impacts covered in Volume 1 and 2 of the scenario.
It shows communities at risk are the places where disparate hazards,
vulnerabilities, and risks converge, not only immediately after
a major disaster, but over time, as disaster effects continue to
compound and unfold. While the HayWired scenario is
just one of many potential disaster scenarios the San Francisco Bay region
could face, it reveals the places where normal community functions are likely
to be severely impaired or cease to exist for months, even years,
after a major East Bay earthquake and where residents may be forcibly
or voluntarily displaced because of direct damage to their homes
and neighborhoods. This methodology can be applied
to other scenarios to identify other patterns of disparate hazard and risk.
These are the places that need our priority attention for hazard mitigation
and community resilience-building efforts and investments before
a major disaster strikes. Thank you.
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