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The other 'Big One'

The other 'Big One' would be a nightmare for the Bay Area

Dr. Mario Picazo
Meteorologist, PhD

Tuesday, May 1, 2018, 9:12 - A new report published by the U.S. Geological Survey backed by key academic, local and industry partners, reveals the type of scenario the Bay Area could live if a 7.0 magnitude earthquake fractured the Hayward Fault under the Oakland area.

The Hayward fault which runs southeast to northwest along the eastern side of the San Francisco Bay, is one of the most feared faults of the complex system that threatens many areas of the state of California. This one in particular passes through an area of dense construction with more than 7 million in population. In the past 1,900 years, earthquakes have occurred along this fault about every 150 years, plus minus 60 years depending on the period. The last major earthquake on the Hayward Fault was a magnitude 6.8 back in 1868. 

Hypothetical mainshock and aftershock sequence of the HayWird earthquake scenario on the Hayward Fault. In the scenario, aftershocks are modeled for 2 years after the mainshock—an innovation unique to HayWired. Early in the sequence, most aftershocks are concentrated near the Hayward Fault. Courtesy: USGS.

RELATED STUDY: 'The Big One' puts California at risk of significant sinking

What is now known as the "HayWired Scenario" is not a prediction, but rather a model, or hypothetical depiction. If it really happened, close to 800 people would die, 18,000 would be injured, 400 fires would claim more lives and reshape the Bay Area landscape and the cost of structural damage would be somewhere close to $82 billion.

Hayward Quake factsheet. Courtesy: USGS.

Where the fault fracture actually occurs is hard to pinpoint down, but the shaking, the casualties and the major damage would still be large. The idea of the study is not to scare people, but rather have them better prepared in the event a major quake hits the region. The HayWired Scenario was developed to guide residents and policymakers in earthquake-risk reduction and resilience-building actions. With all the information provided, the USGS hopes to reduce injuries, damage and losses to buildings and infrastructure, and human migration.

Aerial image of Hayward fault line.

Oblique aerial image showing how the main active traces of the Hayward Fault (red lines) cut through the urban landscape of the East Bay part of the San Francisco Bay area. The main football stadium at Univ. of California, Berkeley (oval in center of image), is nearly bisected by the fault, and it has been extensively retrofitted to withstand fault offset and shaking. USGS

Many cities in the Bay Area, especially along Silicon Valley, have been investing and preparing for a potential major earthquake like this one. In the past 30 years, anywhere from 25 to $50 billion have been put into strengthening buildings, roads, rails, water conducts, electrical and phone wiring and other vital structures. 

Map of geological faults in Bay Area

Map of known active geologic faults in the San Francisco Bay region, California, including the Hayward Fault.  The 72 percent probability of a magnitude (M) 6.7 or greater earthquake in the region includes well-known major plate-boundary faults, lesser-known faults, and unknown faults.  The percentage shown within each colored circle is the probability that a M 6.7 or greater earthquake will occur somewhere on that fault system by the year 2043.  The dark, thick lines outlined in various colors represent major plate boundary faults; the thinner, yellow lines mark lesser-know, smaller faults.

The HayWired Scenario also contemplates a possible 6.4 magnitude aftershock in the Silicon Valley area following the major 7.0 quake. The chances of this happening is close to 20%, but it has to be considered as part of the situation the Bay Area could experience. 

Earthquakes are a day to day threat for many California residents but also for other people living in seismic regions around the country. According to USGS, earthquakes pose a threat to the safety of 143 million in the United States, while estimated long-term annualized earthquake losses are more than $6.1 billion a year. 

As population continues to increase, so will development in hazard-prone regions of the country and thus earthquake risk. The more the population knows about earthquake hazards, the more we can reduce social and economic impacts in earthquake country.

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