Planners Tool Up for the Next Big One

By Laurie A. Johnson, FAICP, and Anne Wein

Thousands of earthquakes of varying sizes occur annually in the U.S. Most are hardly felt and even fewer cause damage. Large earthquakes like the magnitude 6.4 and 7.1 events that hit near Ridgecrest, California, this July, are rare. Fortunately, these earthquakes occurred in a remote area, causing no deaths and only localized damage and impacts. However, had they struck just 50 miles south, closer to the Los Angeles region, the consequences would have been far more extensive.

The infrequency of major earthquake events like these when compared with floods, hurricanes, and other hazards can lead planners and policy makers to treat them as unforeseeable "black swan" events. But that doesn't have to be the case. Thanks to decades of data collection and increasingly sophisticated seismic hazard mapping, risk analyses, and disaster scenario tools, at-risk communities are better equipped than ever to prepare for the next big one.

And these tools are important. Over the next 50 years, nearly half of the U.S. population and approximately $59 trillion in buildings and contents in the 48 contiguous states could experience potentially strong ground shaking. That says nothing of the other direct and indirect costs.

The latest earthquake scenario development effort is under way right now in California. When completed, it will reveal priorities for resilience policy and investments to reduce the risks of the next major earthquake in the San Francisco Bay region. The "HayWired" scenario, a multiyear development by the U.S. Geological Survey and more than 60 researchers and partner organizations, is a hypothetical yet scientifically plausible scenario of a magnitude 7 earthquake occurring on the Hayward Fault. The name speaks to not just the fault itself, but the vulnerabilities and strengths posed by the inter-connectedness of the region's people, utilities, roads, and economy — including the digital economy.

Some examples:

• Shock waves from the HayWired scenario earthquake race at speeds of 7,000 miles per hour, rupturing a 52-mile-long section of the Hayward Fault.
• At least 30 seconds of strong ground shaking is felt by many of the San Francisco Bay Area's seven million residents.
• More than 400,000 people — or 150,000 households — could be displaced from their homes and communities due to building damage and extended infrastructure outages.

The HayWired earthquake scenario study models impacts on the San Francisco Bay region from a magnitude 7 quake on the Hayward Fault (black line). Here, a USGS map shows the intensity of shaking at the epicenter in Oakland and beyond. Courtesy USGS.

Assessing risk

Under the National Earthquake Hazards Reduction Program, the USGS is charged with reviewing and compiling all known earthquake sources and other seismological and geological information into a national seismic hazards model. The model was last updated in 2014 and was used as the basis of USGS's current set of National Seismic Hazard Maps.

The pattern of high-hazard areas depicted on the National Seismic Hazard Maps corresponds to a great extent with the locations of past damaging earthquakes. Those events also provide data for earthquake scenarios that depict the possible physical, social, and economic impacts that could result from a reoccurrence of such an earthquake given today's population, building, and infrastructure exposures.

This probabilistic view of the nation's seismic hazards has several practical uses, most notably for updates to the International Building Code and other seismic-design regulations for buildings and infrastructure.

For planners and allied hazards professionals, the value lies in combining the seismic hazard information with the vulnerability of the built environment, which allows for the consideration of potential damages and costs over time.

The 2017 study of annualized earthquake losses in the U.S., led by the Federal Emergency Management Agency, used the 2014 National Seismic Hazard Maps and Hazus 3.0 — a GIS-based earthquake loss estimation tool — to quantify future potential earthquake losses. According to the findings, the long-term earthquake risk to the nation's general building stock in any single year is $6.1 billion, not including the value of projected loss of life and casualties. While this kind of risk information is commonly used in insurance underwriting, it can be invaluable in informing federal, state, and local decision making on hazard mitigation policies, priorities, strategies, and funding levels.

Drilling down to a regional level, using publicly available software like Hazus, MAEViz, and Open-Quake, earthquake risk modeling has shown that a single major earthquake in California, the Pacific Northwest, or central U.S. could cause unprecedented life loss and catastrophic damages in excess of $100 to $150 billion.

Simulating disaster

Earthquake scenarios are an important planning tool for emergency managers, lifeline utility operators, and the growing number of hazard mitigation and resilience planners because they provide a single "deterministic" view of potential seismic hazard events and vulnerabilities, which can complement probabilistic, multievent risk analyses with a much more in-depth, focused look at how a major disaster can impact a specific community or region.

Some scenarios are based directly on historic seismic events. In 2009, the University of Illinois and Virginia Tech modeled an earthquake sequence impacting the central U.S. based on three major earthquakes in 1811 and 1812 along the New Madrid Fault; it served as the basis for the Shaken Fury 2019 national response and recovery exercise led by FEMA in June. A scenario for a magnitude 9 earthquake on the Cascadia subduction zone uses research on a 1700 earthquake impacting the Pacific Northwest, and a scenario for a magnitude 7.8 earthquake on the northern San Andreas fault is based on knowledge of the massive earthquake that struck the San Francisco Bay region in 1906.

Other seismic scenarios have been developed for hypothetical earthquakes. The magnitude 7.8 "ShakeOut" scenario models the impacts of a 200-mile rupture of the San Andreas fault in southern California. Since 2008, when the USGS released the study, annual Great ShakeOut Earthquake Drills have been conducted, and have since grown into a major international movement; last year, more than 63 million people participated around the world.

HayWired is the latest of these scenarios. It illustrates the rippling and complex impacts a magnitude 7 earthquake along the Hayward Fault from an epicenter in Oakland could have to the Bay Area region's people, utilities, roads, and economy.

The last major earthquake to strike the region was the magnitude 6.9 Loma Prieta of October 1989. In the three decades since, as much as $80 billion in seismic investments have substantially strengthened critical infrastructure and greatly reduced the region's future risk. However, as the HayWired scenario has shown, much more work remains to be done to ensure that the region is ready for the next big one.

HayWired is innovative for a number of reasons, but particularly for what it reveals and emphasizes that other scenarios haven't, including several key factors that can help communities in the Bay Area region better prepare.

An earthquake sequence of a magnitude 7 main shock followed by thousands of aftershocks, including 17 magnitude 5 or 6 aftershocks, each large enough to cause further significant damage to the built environment, will occur within a two-year period.

Likelihood of ground failure or movement where the fault ruptures the ground surface and in areas of development on artificial fill and along streams, as well as landslides in the hills, will damage building and utility pole foundations and buried infrastructure such as water pipelines and telecommunication cables. Geologic hazard investigations can ensure proper siting and design of structures and infrastructure.

Post-earthquake fires will consume the equivalent of 52,000 single-family homes, with a property value loss approaching $30 billion.

An integrated building damage assessment will amount to $101 billion in building repair and replacement costs. Stronger building codes could reduce damages and increase the potential immediate post-earthquake occupancy of many more buildings.

Human impact estimates include 800 deaths, 22,000 people trapped in elevators due to a widespread power outage, and 2,500 people trapped in areas of building collapse.

Water supply disruption will span from seven days to seven months in the most heavily impacted areas. Replacing brittle pipe or equivalent water service protections can reduce the total days of water service loss to customers and help ensure supplies are available for critical response activities like firefighting.

Tall buildings will be unusable for up to 10 months, primarily due to nonstructural damages to elevators, stairways, water and wastewater systems, HVAC, fire sprinklers, and unanchored equipment. Ensuring nonstructural systems are resilient to earthquake shaking can improve the post-earthquake functionality and habitability of buildings.

Several of these findings are explored in volumes 1 and 2 of the HayWired scenario analysis. Work on a third volume of the HayWired scenario study is currently under way. It will explore the scenario's impacts on information and communications technology and the social and economic consequences, including spatial analyses of damages to business districts and residential neighborhoods and the potential risk of displacement of vulnerable and mobile populations such as renters; the vulnerability of middle-income industry jobs and potential shifts in economic activities during the region's recovery; and the types of areas that are likely to require substantial government intervention and planning as part of community recovery.

On the ground

Local, regional, and state agencies in California are already using information from HayWired to better understand earthquake hazards and risk in their communities.

The state of California and the city of Berkeley have both used the HayWired scenario in recent hazard mitigation plan updates. The state, USGS, and partners also launched a new public awareness campaign, called Outsmart Disaster, to build on the momentum of HayWired's findings and energize residents and businesses to prepare the region for future earthquake events.

In the San Francisco region, the Association of Bay Area Governments and Metropolitan Transportation Commission have incorporated HayWired into their latest cycle of long-range planning, which projects how a magnitude 7 earthquake striking in 2035 could affect the region's long-term land-use and economic outlooks as well as the potential effectiveness of different regional resilience investments. The interim report for the initiative, called Horizon, was released in March 2019.

In June, to recognize the positive impacts of the HayWired scenario on the region's future resilience, ABAG and MTC named it one of the recipients of their inaugural Bay Area Metro Award. According to the organizations' resilience planner, Michael Germeraad, "HayWired represents the best available research today on what an earthquake could mean for the [Bay Area] region."

Laurie A. Johnson is an urban planner based in San Rafael, California, and lead author of the Communities-at-Risk analyses in the forthcoming volume of the HayWired scenario. Anne Wein is a principal investigator with the U.S. Geological Survey in Menlo Park, California, and a research coordinator and lead author for HayWired's aftershock, economic, and telecommunication analyses.