Largest Hayward Fault earthquake since 1981 raises questions about what could happen next

By David Jacobson and Ross Stein, Ph.D, Temblor

Last night’s M=4.4 earthquake beneath Berkeley was felt by approximately 10 million people across the entire Bay Area. The quake struck along the Hayward Fault, which has a 29% of rupturing in a large magnitude earthquake in the next 30 years.
Last night’s M=4.4 earthquake beneath Berkeley was felt by approximately 10 million people across the entire Bay Area. The quake struck along the Hayward Fault, which has a 29% chance of rupturing in a large magnitude earthquake in the next 30 years.

 

The entire Bay Area was awakened

Last night, at 2:39 a.m. local time, a M=4.4 earthquake struck along the Hayward Fault underneath the city of Berkeley. The quake was felt throughout the entire Bay Area, and by noon today, over 35,000 people had filled out felt reports on the USGS website. Based on the distribution of shaking, nearly 10 million people would have been exposed to some level of shaking. Close to the epicenter shaking was moderate, and no damage is expected. Based on its magnitude, the quake was felt across a much greater area than expected.

The last M=4.4 shock on or close to the Hayward Fault struck near Fremont in 1981, some 36 years ago. A M=4.5 shock struck on the Rodgers Creek Fault in 2006 near Santa Rosa. The Rodgers Creek Fault is effectively the same Fault with a different name.

This Temblor map shows the location of last night’s M=4.4 earthquake beneath Berkeley. Despite its moderate magnitude, shaking was felt over the entire Bay Area.
This Temblor map shows the location of last night’s M=4.4 earthquake beneath Berkeley. Despite its moderate magnitude, shaking was felt over the entire Bay Area. Although the USGS has moved the earthquake 3 km (2 mi) west of the fault, precise relocations by Felix Waldhauser of Lamont Doherty Earth Observatory of Columbia University show that it is actually on the fault.

 

The Hayward Fault—149 years and counting since the last large event

Based on the location, depth (13 km or 8 mi), and mechanism (right-lateral strike-slip), this earthquake very likely occurred on the Hayward Fault itself, and not a secondary strand. The Hayward Fault extends from San Pablo Bay where it joins up with the Rodgers Creek Fault, to south of San Jose, where it merges with the Calaveras Fault, a length of 140 mi (230 km). It makes up one of the larger faults within the San Andreas Fault System, and has a history of large, damaging earthquakes. In 1868, a M~6.8 earthquake destroyed downtown Hayward, and did significant damage in San Francisco. In fact, the 1868 earthquake was known as the “Great Earthquake” until 1906.

This figure shows LiDAR topographic imagery of the Hayward Fault, as well as the location of this morning’s earthquake. This quake struck in an area where fault creep observed. However, at the depth at which this quake occurred (13 km or 8 mi), the fault is believed to be locked.
This figure shows LiDAR topographic imagery of the Hayward Fault, as well as the location of this morning’s earthquake. This quake struck in an area where fault creep observed. However, at the depth at which this quake occurred (13 km or 8 mi), the fault is believed to be locked.

 

The Hayward Fault creeps, as does a 100-mi (170-km) long section of the San Andreas, and only a handful of other California faults. This means that the Hayward Fault is not frictionally locked and can slip without large earthquakes. While some creeping faults are completely unlocked and do not build up the significant stress needed to generate large earthquakes, the Hayward Fault is only partially locked. So while there is creep at the ground surface, large (M~7) earthquakes tend to occur on average every 161±65 years. For those keeping track, it has been 149 years since the last major event.

This picture from the New Yorker shows evidence of creep along the Hayward Fault. Because the fault is not completely locked, there is movement in the absence of earthquakes. Evidence such as this is visible throughout the East Bay in sidewalks, buildings, and roads.
This picture from the New Yorker shows evidence of creep along the Hayward Fault. Because the fault is not completely locked, there is movement in the absence of earthquakes. Evidence such as this is visible throughout the East Bay in sidewalks, buildings, and roads.

 

Today’s quake struck on the edge of a large stuck patch of the Hayward Fault

In the area around this morning’s earthquake, there is significant evidence of creep. The figure below, from Shirzaei and Burgmann, 2013, shows creep along the Hayward Fault, with the approximate location of today’s earthquake shown. What becomes evident from this figure is that the area in which this morning’s earthquake nucleated is a locked portion of the fault, and that locked patch extends for 20-30 km (12-20 mi) to the southeast.

Prof. Manoochehr Shirzaei at Arizona State University told Temblor that today’s event “occurred in an area that is stressed due to creep on the surrounding segments, and so was encouraged.” USGS geologist David Schwartz added that, “the M=4.4 occurred along a ‘hotspot’ on the Hayward fault. This is an approximately 8 km (5 mi) long section of the fault that has hosted 15 M 3.0-4.0 shocks in the past 10 years. [Today’s earthquake is] the largest and deepest event in this grouping but its location not unusual.” Because of all of this, this earthquake should not be considered surprising.

 

This figure, courtesy of Professor Manoochehr Shirzaei at Arizona State University shows the amount of creep along the Hayward Fault in addition to the location of notable earthquakes. This highlights how the area is a “hotspot” and that this morning’s event should not be considered surprising. As Prof. Shirzaei also points out, aseismic slip surrounding the location of this morning’s quake could contribute to the activity.
This figure, courtesy of Professor Manoochehr Shirzaei at Arizona State University shows the amount of creep along the Hayward Fault in addition to the location of notable earthquakes. This highlights how the area is a “hotspot” and that this morning’s event should not be considered surprising. As Prof. Shirzaei also points out, aseismic slip surrounding the location of this morning’s quake could contribute to the activity.

 

What next?

Based on the lack of creep in the location of today’s event, as well as the large locked patch to the south toward Fremont and Hayward, if a large earthquake were to start here, we believe it would rupture to the south. This area also has a slip deficit of more than a meter (3.3 ft) since 1868, as shown in the figure below, suggesting it could be more susceptible to a large earthquake.

 

This Figure from Shirzaei and Burgmann, 2013 shows the slip deficit along the Hayward Fault since the last major earthquake in 1868. This highlights how the area in which today’s earthquake occurred is within a section of fault where there is a significant slip deficit, suggesting that if a major quake were to occur it would likely rupture to the south (to the right in the figure).
This Figure from Shirzaei and Burgmann, 2013 shows the slip deficit along the Hayward Fault since the last major earthquake in 1868. This highlights how the area in which today’s earthquake occurred is within a section of fault where there is a significant slip deficit, suggesting that if a major quake were to occur it would likely rupture to the south (to the right in the figure).

 

Nevertheless, the statistical likelihood of this morning’s earthquake being a foreshock to a M=6+ event in the next week is low, about 1 chance in 250, according to the USGS. However, the USGS does also estimate that there is a 10% chance that this could be a foreshock to an earthquake of equal or greater magnitude. Therefore, people should renew and reconsider their seismic readiness.

One of the reasons why the Hayward Fault is of great importance is because James Lienkaemper and Patrick Williams, 2010 calculated from the record they unearthed of prehistoric earthquakes that there is a 29% chance of a large quake along this portion of the Hayward Fault in the next 30 years. The USGS has multiple earthquake scenarios for this section of fault, some of which reach M=7.4. Such an event would have a significant impact on the entire Bay Area, stressing the importance of preparation. The USGS is developing a scenario of such an event (HayWired)

 

We are behaving like cigarette smokers

David Oppenheimer, the former director of the USGS Northern California Seismic Network, had this to say to Temblor: “The scientific and engineering communities have led us to the solution to seismic resilience, but the public behaves like a cigarette smoker. They know that quakes are bad for them, but they are not willing to do what they should.”

He continues, “The solution is to follow the leads of San Francisco, Santa Monica and Los Angeles that require substandard residential structures to be identified and seismically retrofit in a timely fashion. Unfortunately, none of these programs apply to homes; they only address apartment and larger buildings. Mortgage lenders should require property owners to carry earthquake insurance. Elected officials must do their part to implement ordinances and laws that require the public to upgrade at-risk private property. A small investment in mitigation will have large payoffs to property owners, inhabitants, and resiliency of our metropolitan area.”

 

References

Manoochehr Shirzaei, Roland Bürgmann, Taka’aki Taira (2013), Implications of recent asperity failures and aseismic creep for time-dependent earthquake hazard on the Hayward fault, Earth and Planetary Science Letters 371–372 (2013) 59–66, doi.org/10.1016/j.epsl.2013.04.024

Shirzaei, M., and R. Burgmann (2013), Time-dependent model of creep on the Hayward fault from joint
inversion of 18 years of InSAR and surface creep data, J. Geophys. Res. Solid Earth, 118, doi:10.1002/jgrb.50149.

James J. Lienkaemper, Patrick L. Williams, and Thomas P. Guilderson, Evidence for a Twelfth Large Earthquake on the Southern Hayward Fault in the Past 1900 Years, Bulletin of the Seismological Society of America, Vol. 100, No. 5A, pp. 2024–2034, October 2010, doi: 10.1785/0120090129

Detweiler, S.T., and Wein, A.M., eds., 2017, The HayWired earthquake scenario—Earthquake hazards: U.S. GeologicalSurvey Scientific Investigations Report 2017–5013–A–H, 126 p., https://doi.org/10.3133/sir20175013v1.

Berkeley Seismology Lab – Link

USGS – Event page

Felix Waldhauser’s Lamont-Doherty Earth Observatory double-difference real-time earthquake catalog –
Event page

  • Patrick McClellan

    To somewhat allay the lament of David Oppenheimer that “none of these programs apply to homes” (referring to the required retrofit programs in San Francisco, Santa Monica and Los Angeles) – it ain’t for lack of tryin’. A few months after the Loma Prieta earthquake, I left the USGS to briefly serve as the first Disaster Preparedness Manager for the City of San Leandro, astride the Hayward fault on Oakland’s southern border. I developed and led the city’s novel “Earthquake Home Strengthening Program”, which still thrives today (details here: https://www.sanleandro.org/depts/cd/bldg/retrofit/default.asp ). The program won the highest awards and recognition from the Association of Bay Area Governments, California’s Emergency Services Association and Seismic Safety Commission, the National League of Cities, US Conference of Mayors, and FEMA. It was replicated by Los Angeles, Oakland, and Seattle, and other cities along the West Coast. Unfortunately, as David noted, in every instance private property rights have trumped any home retrofit requirement. Without a mandate, a community can only incent the willing to act in their own best interest. In San Leandro, we waived permit fees, provided a prescriptive retrofit plan set at no charge, offered DIY homeowners retrofit training and lent them tools from a public library, trained and registered contractors on the city’s retrofit standards, and even subsidized the cost of retrofit materials with CDBG funds. The homeowner training classes were overflowing back then (and I hope they have continued to be), but progress is slow when only voluntary.

    So, here’s the value proposition for property owners in today’s pricy metro areas. Strengthening older homes against earthquake damage ultimately helps to preserve what taxpayers say they prize most about their hometown: its community services – law enforcement, fire protection, paramedics, libraries, clean well-lighted streets, and so on. In California, where municipal revenues flow from local taxes, a city’s building stock and its community services are mortally connected – injure the first, the other bleeds. (Bear with me on this.) When a house falls in an earthquake so does its property value. When thousands of houses are damaged, the real estate “comps” suddenly plummet in neighborhoods all over town. The community’s homeowners, still paying pre-earthquake tax rates on quake-damaged or devalued properties, appeal their high assessed values, which are adjusted downward wholesale and now generate far less property taxes. Damage to commercial buildings means businesses suffer. Some fail completely causing unemployment and lost industrial output, retail input, and rental income. These residential and commercial losses rob the city of property-tax and sales-tax revenues – which pay for OVER HALF of the operating budget of many cities. And these cuts in operating budget mean cuts in community services: police, fire, ambulance, library, street maintenance, etc.

    So, if we allow our houses and other buildings to be damaged, our prized community services will be victims of the next earthquake, too. To preserve the services we need most in our community we have no choice but to strengthen our cities’ legacy of old and vulnerable buildings. Sorry to ramble.

  • Tracey McTague

    Hi there Patrick, could we connect on LinkedIn? I’m really interested in what you think about the Old City Hall in Hayward….

  • Carrie

    After the 1989 quake, everyone I know retrofitted their homes. It was the best wake-up call! But we don’t buy earthquake insurance because it is prohibitively expensive and provides little coverage. All policies have a 15% deductible before it pays one cent. In the Bay Area since homes are worth $600K plus, that means that the homeowner must spend $90,000 on earthquake repairs. The standard policy, which costs double the typical homeowner policy premium, provides only $5,000 of property coverage for contents, whereas it would cost ten times that much to replace the home’s contents. I’m not blaming the insurers since earthquake losses would be catastrophic for them, so they probably do need to charge high amounts. Please don’t say that government must force people to buy earthquake policies !! People anticipate, and thus gamble, that where they live, earthquake damage would most likely be less than their 15% deductible.

  • I can testify to San Leandro’s retrofit course. As an earthquake preparedness consultant, I took their homeowner’s retrofit class to check it out. (We had already done our home’s retrofit). The instructors knew their stuff, taught us how to use the tools and they even provided nails in addition to full-size planning sheets for their plan sets. The class my husband had taken in Berkeley prior to our retrofit in 2009 was great but it is currently defunct. San Leandro is lucky to have this inexpensive program.

  • Eva Zembera

    I live in Rossmoor Walnut Creek. Is it any requirement in this city to retrofit apartments and larger buildings. I know that this community was build in the ’60’s , I know that they are not bolted to the foundation. What can you tell me about this specific area?? I would appreciate an answer if possible . Thank you, Eva

  • Ross Stein

    Carrie, While a 15% deductible is still the most common for quake policies, most carriers now permit a range of deductibles from 5%-25%, and some go down as low as 2.5%. The premiums increase as the deductible decreases, but one’s chance of receiving a payout greatly increases. The ‘Find a Pro’ tab in Temblor takes you to our recommended providers, including quake prep consultants, retrofit contractors and products, structural engineers, and insurance agents.

  • Ross Stein

    Not as far as we know, Eva. You can check your hazard in Temblor; at 87, it is quite high because there are major faults on all sides. Any building not bolted to its foundation is extremely vulnerable, and getting it bolted and braced is generally inexpensive given its enormous value. The ‘Find a Pro’ tab in Temblor takes you to our recommended providers, including quake prep consultants, retrofit contractors and products, structural engineers, and insurance agents.

  • Ross Stein

    Sarah’s company, Quake Readiness, LLC, is a provider of on-site consulting to homeowners and businesses that is recommended by Temblor. She helps you assess your vulnerability, and evaluates your options to make yourself safer and reduce your quake costs and down-time. At Temblor, we view quake prep consulting as a highly cost-effective way to get smart about your needs.

  • Ross Stein

    Tracey McTague led Schlumberger’s quake risk program, first in Japan, and then in the S.F. Bay area. We need more people like Tracey, looking out for their company’s needs and encouraging cost-effective preparation an training.

  • Kate Stillwell

    “…there is a 29% chance of a large quake along this portion of the Hayward Fault” … over what timeframe? 30 years?

  • David Oppenheimer

    I too used to reject purchasing earthquake insurance for the reasons given by Carrie. I now view the product differently than betting that my damage will be less than my deductible. If there is substantial equity in a property, as would be the case if a property owner has owned the house for many years and benefitted from appreciation or has paid off the mortgage, then a **complete** loss of the structure due to an earthquake would likely be a financial calamity. Construction costs in the SFBay area are quite high, and as Carrie notes, it is not unusual for the insured value of the structure to significantly exceed $600K. Without earthquake insurance, a homeowner would be on the hook for all of the costs of the replacement construction, which for many people would be impossible to afford. With insurance, a catastrophic loss is limited to the deductible, which presumably is a more affordable proposition for rebuilding.

    For recently purchased properties with a mortgage, the financial benefit from earthquake insurance becomes less clear, especially if the down payment is less than the earthquake insurance deductible. In this case, it might be less expensive to default on the mortgage (i.e., to lose the down payment) and give the damaged property to the lender. However, the loss doesn’t go away. It is transferred to the lenders and the community, as described below.

    Patrick McClellan (above) makes a good argument for mandatory insurance. Moreover, in New Zealand where private homeowner insurance includes loss from earthquake damage (https://www.eqc.govt.nz/what-we-do/eqc-insurance), the payout after their recent damaging earthquakes stoked the local economy and hastened the recovery process. The alternative was demonstrated in New Orleans which was damaged by hurricane Katrina. Damaged properties lacking flood insurance were abandoned, and property values declined. People moved away, businesses suffered, and the recovery process continues to drag on. This lack of “resiliency” can be expected in the San Francisco Bay area after a major quake due to the low (15%?) levels of earthquake insurance coverage. Perhaps someone can explain why lenders insist on fire insurance coverage, but ignore a similar risk due to earthquake damage. Presumably, this risk is baked into the cost of their mortgages, so everyone is paying for it, regardless of where the property is located.

    I encourage the local media to write about this issue, especially after an earthquake when readers are tuned in. The public should be educated to the financial risk they face so they can make informed decisions on the benefits of purchasing earthquake insurance. Government officials, lenders, and the CEA should be asked to account for why the current status quo is acceptable.

  • Patrick McClellan

    No opinion about that, Tracey, since I’m not an engineer (“I only play one on TV”). (Joking, of course.) The engineer’s first question to you would be, “which Old City Hall in Hayward?”, as there are three of them: (1) the historic one on Mission Blvd (in which the Hayward fault is rupturing through the lobby), abandoned by the city in 1969; (2) the soft-story high-rise on Foothill Blvd (about a quarter-mile NE of the fault), abandoned after the 1989 Loma Prieta earthquake; or (3) the temporary city hall on Clawiter Rd (in a state-designated liquefaction zone near the Bay), vacated in 1998 when the current city hall opened on B Street (a block W of the fault, a modern building on a seismic-isolation system in the basement)? (Sorry. I abandoned LinkedIn a decade ago.)

  • Temblor

    Yes, 30 years