Hayward Fault Zone - Probability of Future Activity

Probability of Future Activity

United States Geological Survey (USGS) scientists state that a major earthquake occurring on the zone is "increasingly likely". If a major earthquake were to occur on the fault, damage would be catastrophic. More than 1.5 trillion U.S. dollars in property exists in the affected area, and more than 165 billion US dollars in damage would likely result if the 1868 earthquake were to reoccur. Since the fault runs through heavily populated areas, more than 5 million would be affected directly. The Eastern Span of the Bay Bridge would probably be destroyed (unless its replacement span had been completed by that time), cutting off easy transportation between San Francisco and Oakland along with up to 1,100 other roads. Water could be cut off to 2.4 million people living in California's San Francisco Bay Area.

The probability of a major earthquake on the Hayward within the next thirty years was estimated at nearly 30 percent, compared to about 20 percent for the San Andreas Fault, which can have larger earthquakes but farther away from a significant portion of the urbanized parts of the Bay Area. Recent (January 2008) assessments suggest that the Hayward, Rodgers Creek, and Calaveras faults may be more likely to fail in the next few decades than previously thought.

The 140th anniversary of the 1868 event was in 2008, and the average time between the last five major events is also averaged at 140 years. Recent estimates of the damage potential of a major Hayward Fault earthquake by a professional risk management firm indicate the potential for huge economic losses, of which only a small percentage is insured against earth movement. (Earthquake insurance is not only quite expensive, it tends to be burdened with huge deductibles - at least 15 percent). Depending upon seasonal weather conditions at the time of a major event a seismic event could be followed by huge urban wildfires compounded by damage to water systems or massive landslides in saturated soils. In addition to direct damage the effects on commerce due to damaged infrastructure would also be substantial. Experience with large area urban destruction such as caused by earthquake, hurricane, and firestorms has shown that complete rebuilding can take up to a decade, owing to various factors including disputes with insurance companies, a lack of qualified local builders, shortages of supplies, and an influx of contractors from outside of the region of dubious qualifications with no incentive to maintain and enhance a local reputation.

The progressively more severe reports and estimates of event probability and consequences have awakened a broad interest in training people for emergency response. It is becoming widely understood that professional fire fighting, police, and medical services will be overwhelmed by a major event and that neighbors will have to assist each other as best they can. Appropriate area response organizations would likely be similar to the 1950s Civil Defense structure, but such civilian participation has yet to be organized.

In 2012, USGS scientists said the fault is due for another magnitude 6.8 to 7.0 earthquake, with the California Geological Survey concurring, stating they believe there is a 31 percent chance of a magnitude-6.7 earthquake or greater along the Rogers Creek-Hayward Fault in the next 30 years.