The US Geological Survey [USGS] took advantage of the anniversary of the 1906 San Francisco earthquake this week to update its working scenario on what may happen when the Big One hits the Bay Area again, focused not on the San Andreas fault but on its potentially more hazardous Hayward Fault neighbor to the east.
Dubbed the “HayWired scenario” (unfortunately), a USGS press release stresses that the study is a possible projection but not a prediction:
The HayWired Scenario is a scientifically realistic, highly detailed depiction of what may happen during and after a7.0 earthquake on the Hayward Fault with an epicenter in Oakland, CA.
But it is not a prediction, and a real earthquake on the Hayward Fault could occur at any time and with a different pattern of shaking causing damage to be concentrated in different spots.
The fact that nobody can predict an earthquake or its outcome is, ironically, the entire point.
But the hypothetical posed by the USGS study is meant to be a plausible one based on our best current scientific understanding of the region and past disasters. Here’s some of what we might expect the near future:
- A major Hayward Fault quake is pending: “Scientists have documented a series of major prehistoric earthquakes on the Hayward Fault. [...] On average, for the past 12 major earthquakes on the fault, the interval between events has been about 150 years plus or minus 60 years. The last major earthquake on the Hayward Fault was a magnitude-6.8 earthquake in 1868—150 years ago.” It bears repeating: Earthquakes do not keep schedules, averages can vary wildly, and nobody can predict when a quake will happen. But one will definitely happen sooner or later.
- The direct seismic effects of a quake can last years: “Slow offset (afterslip) along the fault will continue for several months. Strong shaking is felt throughout the San Francisco Bay region. [...] Many aftershocks occur in the minutes to years following the mainshock, with the largest ( M 6.4) occurring in Santa Clara County, near San Jose. [...] Eighty percent of shaking damage is caused by the M 7.0 mainshock, and the rest is due to aftershocks over a two year period.”
- Building codes account for earthquake safety, but they only do so much: “Even if all buildings in the bay region met current building code, 0.4 percent could collapse, 5 percent could be unsafe to occupy, and 19 percent could have restricted use. [...] Property damage and direct business disruption losses are estimated to be more than $82 billion (in 2016 dollars). Most of the losses are attributable to shaking damage, liquefaction, and landslides (in that order).”
- Even in the best case scenario, casualties are as inevitable as the quake itself: “Estimates of casualties in the San Francisco Bay region include 800 deaths and 18,000 nonfatal injuries from building and structural damage.”
- And just as in 1906, the threat from fire may outstrip the quake itself: “During and soon after the mainshock, more than 400 gas- and electric-related fires could ignite. These fires could form conflagrations that might be as destructive as the powerful ground shaking of the mainshock. [...] Building space equivalent to more than 52,000 single-family homes could burn as a result of more fires than can be fought by available firefighters and fire trucks. “East Bay residents could lose water service for 6 weeks, some for as long as 6 months.”
Although nobody likes to think about these things, the inevitability of such an event within most of our lifetimes makes preparation a necessity.