By Aron Mirwald, M.Sc., Ross S. Stein, Ph.D., and Volkan Sevilgen, M.Sc., Temblor

Citation: Mirwald, A., Stein, R.S., Sevilgen, V. (2019), The 5 worst (and 5 best) places to live in the S.F. Bay Area if the great 1906 earthquake recurred today, Temblor, http://doi.org/10.32858/temblor.019

The 1906 San Francisco earthquake was one of the worst natural disasters in U.S. history. Despite more than a century of improvement in structural design and construction, if the same earthquake were to strike again, the shaking damage likely would be even greater. That is largely because of the 20-fold increase in population, a significant portion of which occupies homes and offices built on Gold Rush and other artificial fill. While exact repeats of earthquakes are rare, large shocks loom in the Bay area’s future and so knowing your risk will enable you to take action now to reduce it.

Few people know what happens after an earthquake strikes a city, and even less are prepared for it. I witnessed this in Mexico City, one and a half years ago, when the 2017 M=7.1 Puebla earthquake killed over 369 people and threw 57 buildings down. There was a severe shortage of first aid kits to treat the injured. Thousands of people were wounded, and the pharmacies were short of supply of the much-needed disinfectant and bandages.

The S.F. Bay Area shares elements of Mexico City. Everyone knows—or should know—that there is the risk of an earthquake lurking, but it seems too far away to be worried about. So, let’s use the anniversary of the Great 1906 San Francisco earthquake as a way to remind ourselves of the disastrous consequences of such an event, so that it does not befall our families.

Destruction in San Francisco by the earthquake and subsequent fire. Source: USGS (https://pubs.usgs.gov/fs/1996/fs094-96/)

The Great San Francisco Earthquake

Due to the chaos and confusion that emerged after the disaster, it is not possible to precisely know how many people died, but estimates range from 700 to 3,000 fatalities (Aagaard and Beroza, 2008). Additionally, the earthquake caused a property loss of over $10 Billion dollars and left ~220,000 homeless (using the present value of the dollar; Ager et. al., 2019). An investigation published this month argues that the Great 1906 San Francisco earthquake affected the economy of cities in the S.F. Bay Area for four decades after the shock (Ager et. al., 2019).

Jack London, the famed author of ‘The Call of the Wild,’ lived in Oakland, and wrote about the earthquake in the 5 May 1906 issue of ‘Collier’s Weekly’: “San Francisco is gone. Nothing remains of it but memories and a fringe of dwelling-houses on its outskirts. Its industrial section is wiped out. Its business section is wiped out. Its social and residential section is wiped out. The factories and warehouses, the great stores and newspaper buildings, the hotels and the palaces of the nabobs, are all gone. Remains only the fringe of dwelling houses on the outskirts of what was once San Francisco. On Wednesday morning at a quarter past five came the earthquake. A minute later the flames were leaping upward. In a dozen different quarters south of Market Street, in the working-class ghetto, and in the factories, fires started. There was no opposing the flames. There was no organization, no communication. All the cunning adjustments of a twentieth-century city had been smashed by the earthquake.

This train was overturned at Point Reyes by the 1906 earthquake, which requires at least 0.4 g of acceleration, evidence of very severe shaking. Source: Veeraraghavan et. al. (2019)

Worst places to live in the Bay area if the 1906 quake were to recur

Since 1906, the population in the S.F. Bay Area has increased from 400,000 to 7.7 million people, and property values have risen drastically. The good news—or at least more hopeful news—is that the fire that consumed most of San Francisco is less likely to erupt unchecked today, thanks to greater fire-fighting capacity, technology, and cisterns. But, the damage still can be expected to surpass the one of 1906: Using the intensities reported in 1906, the economic damage would be of the order of $90 Billion with 400,000 people at least temporarily losing their homes, affecting about 160,000 households (Kircher et. al., 2006).

Estimated intensities of the 1906 earthquake. The scale is a Modified Mercalli Intensity (MMI) scale, in which ‘X’ corresponds to extreme destruction, and ‘I’ to not felt. Source: Aagaard et. al. (2008)

In order to make it easier to visualize where this would happen, we used the data shown in the map from Aagaard et. al. (2008)above to compute which cities with a population greater than 100,000 in the Bay area would be most (and least) affected. We used the Peak Ground Velocity, which is closely related to the Modified Mercalli Intensity (MMI) scale depicted, and is considered a good predictor of the damage to homes and medium-rise buildings.

Our Top 5 List

5 Worst Cities in a 1906 quake 5 Best Cities in a 1906 quake Peak Ground Velocity (m/s) Peak Ground Velocity (m/s) Daly City 1.22 Fairfield 0.00 San Francisco 0.47 Antioch 0.00 Santa Rosa 0.43 Hayward 0.13 Sunnyvale 0.42 Fremont 0.18 San Jose 0.37 Oakland 0.24

To give a sense of the magnitude of these numbers: 0.5 m/s is strong enough to turn over a train (Veeraraghavan et. al., 2019). While it’s no surprise that San Francisco is on the list of the worst cities, few people realize that Daly City, which straddles the fault in a landslide-ridden area west of the City, towers above S.F. in its vulnerability. In addition, San Francisco is almost in a dead heat with Santa Rosa and Sunnyvale, with San José not far behind.

The best cities to live in were the 1906 quake to repeat lie in the East Bay, farther from the San Andreas Fault, on which the 1906 earthquake struck. However, these East Bay cities are vulnerable to earthquakes on the Hayward Fault, which is considered to have the highest probability of suffering a Magnitude ~7 shock in the next 30 or so years (Field et. al., 2019). Topping that list are Fairfield, Antioch and Hayward.

Continually Grinding Plates: No end of Earthquakes in Sight

This last observation is important: The San Andreas Fault is not the only fault that can render produce deadly earthquakes. At California’s coast, the Pacific Plate is grinding past the North American Plate. The movement between the two plates is accommodated through a set of faults, including the San Andreas. The rate of deformation between the plates is around 5 cm (2 in) per year (Aagaard and Beroza, 2008). Unfortunately, this is bad news for the habitants of the S.F. Bay Area.

At the present, scientists estimate that the S.F. Bay Region has a deficit of 4 meters (13’) in slip (Schwartz et. al., 2014), which is about the mean displacement that occurred on the San Andreas Fault 1906. In other words, a quake with 13’ of slip would catch it up. The most recent Uniform California Earthquake Rupture Forecast (UCERF3) estimates that there is a 33% chance that a M>6.7 earthquake will strike on the northern part of the San Andreas Fault, and 53% on the southern part (Field et. al., 2015).

A recent investigation of earthquakes in the last millennium found that California is currently in an unusually long period of ‘seismic sleep’ (Biasi et. al., 2019). The scientists point out that the absence of large earthquakes in the last century is exceptional compared to the mean rates observed in the pre-historic record. At best, this shows us that we still have a lot to learn. At worst, it means that the slip deficit is both large and growing, and so we should prepare for large earthquakes now.

A fence displaced in a right-lateral sense during the 1906 earthquake (whichever side you are on, the other has been shifted to the right). Source: Aagaard and Beroza (2008)

Better Safe than Sorry

How should we prepare for an earthquake? Here are four actions you can take today to be safer:

Make your house earthquake resilient. If you are a homeowner, consider retrofitting. Luckily, seismic retrofit generally roughly halves the likely damage for most older wood frame homes (Retrofitters). Make sure that there is nothing in your house that can fall and injure you. Are the shelves fixed to the wall? Could anything in your house fall and injure somebody in case of strong shaking? You can engage quake prep consultant to visit your home and help you make these improvements for a modest cost. (Quake Prep providers). Insure your home. Even if your house remains standing, it may be too damaged to live in. Dealing with the chaos and losses after an earthquake will be hard. But you can at least remove the worry of being homeless. (Insurance agents, Jumpstart insurance) Prepare for the time after the earthquake. Be sure to have enough disinfectant and bandages. Prepare for a possible food shortage (canned food) and a period of no power supply.

In the case of the earthquake that struck Mexico City, many lives could have been saved this way. In the case of the S.F. Bay Area, hopefully these measures will be useless for a long time. But, we can’t be sure of that, and leaving this important issue to fate would be reckless.

References

Aagaard, B. T., & Beroza, G. C. (2008). The 1906 San Francisco Earthquake a Century Later: Introduction to the Special Section. Bulletin of the Seismological Society of America, 98(2), 817-822

Aagaard, B. T., Brocher, T. M., Dolenc, D., Dreger, D., Graves, R. W., Harmsen, S., … & Petersson, N. A. (2008). Ground-motion modeling of the 1906 San Francisco earthquake, part II: Ground-motion estimates for the 1906 earthquake and scenario events. Bulletin of the Seismological Society of America, 98(2), 1012-1046.

Ager, P., Eriksson, K., Hansen, C. W., & Lønstrup, L. (2019). How the 1906 San Francisco Earthquake Shaped Economic Activity in the American West (No. w25727). National Bureau of Economic Research.

Biasi, G. P., & Scharer, K. M. (2019). The Current Unlikely Earthquake Hiatus at California’s Transform Boundary Paleoseismic Sites. Seismological Research Letters.

Field, E. H., Biasi, G. P., Bird, P., Dawson, T. E., Felzer, K. R., Jackson, D. D., … & Milner, K. R. (2015). Long‐term time‐dependent probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Bulletin of the Seismological Society of America, 105(2A), 511-543.

Kircher, C. A., Seligson, H. A., Bouabid, J., & Morrow, G. C. (2006). When the big one strikes again—Estimated losses due to a repeat of the 1906 San Francisco earthquake. Earthquake Spectra, 22(S2), 297-339.

Schwartz, D. P., Lienkaemper, J. J., Hecker, S., Kelson, K. I., Fumal, T. E., Baldwin, J. N., … & Niemi, T. M. (2014). The earthquake cycle in the San Francisco Bay region: AD 1600–2012. Bulletin of the Seismological Society of America, 104(3), 1299-1328.

Veeraraghavan, S., Heaton, T. H., & Krishnan, S. (2019). Lower Bounds on Ground Motion at Point Reyes during the 1906 San Francisco Earthquake from Train Toppling Analysis. Seismological Research Letters, 90(2A), 683-691.

http://temblor.net/earthquake-insights/the-lesson-to-be-learned-from-mexico-citys-building-collapses-5405/

http://temblor.net/earthquake-insights/mexico-city-building-collapses-experts-on-drop-cover-and-hold-on-or-run-5340/

https://pubs.usgs.gov/fs/1996/fs094-96/