#towers are too unstable in an earthquake zone

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The most horrific burn I've come across on this site so far.

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San Francisco’s Big Seismic Gamble

By Thomas Fuller, Anjali Singhvi and Josh Williams, NY Times, April 17, 2018

SAN FRANCISCO--Sailors arriving in San Francisco in the 19th century used two giant redwood trees perched on a hill to help guide their ships into the bay. The redwoods were felled for their lumber at around the time of the gold rush, but San Francisco now has a new beacon: Salesforce Tower, the tallest office building in the West.

Clustered around the 1,070-foot tower are a collection of high rises built on the soft soil and sand on the edge of the bay. They represent a bold symbol of a new San Francisco, but also a potential danger for a city that sits precariously on unstable, earthquake-prone ground.

San Francisco lives with the certainty that the Big One will come. But the city is also putting up taller and taller buildings clustered closer and closer together because of the state’s severe housing shortage. Now those competing pressures have prompted an anxious rethinking of building regulations. Experts are sending this message: The building code does not protect cities from earthquakes nearly as much as you might think.

It’s been over a century--Wednesday marks the 112th anniversary--since the last devastating earthquake and subsequent inferno razed San Francisco. Witnesses on the morning of April 18, 1906, described the city’s streets as rising and falling like a ribbon carried by the wind.

The violent shaking ignited a fire that lasted three days, destroying 500 city blocks and 28,000 buildings.

Half of the population of around 400,000 was made homeless. Many were forced to flee the city. With the city leveled, Los Angeles quickly grew to capture San Francisco’s place as the premier city of the West.

After decades of public hostility toward skyscrapers, the city has been advocating a more dense and more vertical downtown. San Francisco now has 160 buildings taller than 240 feet and a dozen more are planned or under construction.

California has strict building requirements to protect schools and hospitals from a major earthquake. But not skyscrapers. A five-story building has the same strength requirements as a 50-story building.

Yet skyscrapers cast a much broader shadow of risk across a city and their collapse or impairment could cause a cascade of consequences.

How safe are San Francisco’s skyscrapers? Even the engineers who design them can’t provide exact answers. Earthquakes are too unpredictable. And too few major cities have been tested by major temblors.

Previous earthquakes have revealed flaws with some skyscrapers. A widely used welding technique was found to rupture during the 1994 Northridge earthquake in Los Angeles. (Many buildings in San Francisco and Los Angeles have not been retrofitted.)

California has made significant strides in earthquake preparedness over the past century. Freeway overpasses, bridges and some municipal buildings have been strengthened. Many Californians live in single-family wood frame homes, which have been found to hold up relatively well during earthquakes.

But until recently, high-rise buildings were not a focus of San Francisco’s seismic safety.

This raises concerns among experts such as Thomas H. Heaton, the director of the Earthquake Engineering Research Laboratory at the California Institute of Technology and perhaps the most prominent skeptic of building high rises in earthquake zones.

“It’s kind of like getting in a new airplane that’s only been designed on paper but nobody has ever flown in it,” he said.

What shifted the debate on seismic safety was the sinking and tilting of the 58-floor Millennium Tower.

When it was completed in 2009, the building won numerous awards for ingenuity from engineering associations, including Outstanding Structural Engineering Project of the Year by the San Francisco office of the American Society of Civil Engineers.

The developer and city officials knew of the building’s flaws for years, but kept them confidential until 2016, when news leaked to the public. The latest measurements, taken in December, show that the building has sunk a foot and a half and is leaning 14 inches toward neighboring high rises. It is across the street from Salesforce Tower and right next to a transit hub for buses, trains and eventually high speed rail that is being touted as the Grand Central of the West.

With the Millennium Tower, San Francisco got a foretaste of what it means to have a structurally compromised skyscraper. If the city is hit by a severe earthquake, experts fear there could be many more.

The area around Millennium Tower is considered among the most hazardous for earthquakes. The United States Geological Survey rates the ground there--layers of mud and clay--as having a very high risk of acting like quicksand during an earthquake, a process known as liquefaction.

At least 100 buildings taller than 240 feet were built in areas that have a “very high” chance of liquefaction.

In light of the problems with the Millennium Tower, there are now increasing calls in California for a reassessment of earthquake risks, much of it focused on strengthening the building code.

Right now the code says a structure must be engineered to have a 90 percent chance of avoiding total collapse. But many experts believe that is not enough.

“Ten percent of buildings will collapse,” said Lucy Jones, the former leader of natural hazards research at the United States Geological Survey who is leading a campaign to make building codes in California stronger. “I don’t understand why that’s acceptable.”

The code also does not specify that a building be fit for occupancy after an earthquake. Many buildings might not collapse completely, but they could be damaged beyond repair. The interior walls, the plumbing, elevators--all could be wrecked or damaged.

“When I tell people what the current building code gives them most people are shocked,” Dr. Jones said. “Enough buildings will be so badly damaged that people are going to find it too hard to live in L.A. or San Francisco.”

“We’ve been sitting on our hands for decades about this problem,” said Keith Porter, a seismic engineer at the University of Colorado, who is hoping to spur greater public participation in a debate.

Dr. Porter’s research offers warnings on the economic consequences of a major earthquake in the San Francisco Bay Area. He has calculated that one out of every four buildings in the Bay Area might not be usable after a magnitude 7 earthquake, which although severe is not the worst the area could experience.

Charles Richter, the earthquake pioneer who invented the scale used to measure their power, had strong opinions about skyscrapers. Don’t build them in California, he said.

In the years since Mr. Richter’s death in 1985, construction materials have become stronger and engineering more precise.

Yet Hiroo Kanamori, an emeritus professor of seismology at the California Institute of Technology who developed the earthquake magnitude scale that replaced Dr. Richter’s, says the vast power and mysteries of earthquakes should continue to instill a deep humility.

In recent decades scientists have recorded violent ground motions that were previously thought impossible.

“People say, ‘Don’t worry about it, it’s an outlier,’” Dr. Kanamori said. “This is the problem with earthquakes. By nature of the process there are a lot of unpredictable elements.

“And a single event can be catastrophic,” he said.

[maia]

Mission District Walking Tour (San Francisco)

I love the Mission District. Climate reports say it is San Francisco’s warmest, sunniest neighborhood, but its vibrance extends far beyond the weather. Whenever I have friends visit from out of town, I take them on a walking tour of the Mission. I wrote the first version of the post in an email to a friend who needed something to do with an out-of-town guest. I fleshed it out to share publicly, in case anyone shares my love of history and standing in line for food. (Please leave questions, comments, suggestions!)

In red is the Mission tour, but you can easily see Bernal Heights and The Castro too by adding the blue parts.

#1. Dolores Park: 20th St. & Church St. Dolores Park has a crazy history. First, see one of the best views of downtown San Francisco from this top corner. Look over the park. In the late 1800′s, Dolores Park was a Jewish cemetery. Around 1900, land in SF was deemed too valuable for dead people and they DUG UP ALL THE GRAVES and moved them to COLMA. Then, in 1905 Barnum & Bailey graded the land for their circus, in 1906 it served as a refugee camp for earthquake victims, and now it's a pretty segmented park that becomes crowded with locals whenever the weather breaks 70°.

Wander through to park to 18th st. In the morning, you’ll find the controversial buses from Google, Facebook, etc. picking up tech workers from 18th & Dolores to truck them down to campuses in Silicon Valley.  If it’s warm out, stop at one of the best ice cream shops: Bi-Rite Ice Cream (you can skip the line if you’re buying a pint!). If it’s cold out, stop at #2. Tartine for a pastry and a coffee (sadly, I have no tips for skipping the line here). Tartine is famous for baking the best bread in America.

Meander down 18th St, admiring the Women’s Building on the way. Arrive at #3. Clarion Alley. The Mission District is famous for its murals and street art, mostly driven by the Latino movement. Clarion Alley is newer than Balmy Ave (which we’ll visit later) and is dedicated to using public art as a force for the marginalized. The featured artists are regularly rotated through, as managed by the Clarion Alley Mural Project. Clarion Alley is always a great way to view the current hot-button topics -- right now, it’s  around evictions and gentrification.

Cruise back to Valencia St. The lights on Valencia Street are timed in both directions so if you’re cycling 13mph, you’ll have green lights the whole stretch. It’s called the Green Wave.

Valencia has been described as a pinterest strip mall -- but I prefer to describe it as the longest shopping street in the US with no chain stores.  Between 18th & 19th streets you’ll find strings of expensive hipster storefronts. The highlights are Dandelion chocolate (single-origin chocolate! is that important?), Craftsman & Wolves (famous for their Rebel Within muffin which contains a softboiled egg), and Mission Bicycle (owned by my landlord!)

On to the next block, where there’s #4. three wonderful shops to explore: Paxton Gate, 826 Valencia, and City Art Cooperative Gallery.

Paxton Gate is a store for “natural curiosities”. Make sure to read the labels, and make it all the way to the garden in the back.

826 Valencia is Dave Egger's tutoring center. He bought an empty store front on Valencia to create a tutoring center for low-income kids. San Francisco was like "You can't do that; Valencia is zoned only for retail." So he was like "Fine, you need a retail store? I will make a retail store." So it's a half-joke pirate store that serves as a front for the tutoring center. Since then 826 has expanded to run many tutoring centers around the world, but their name pays homage to the address of their first one, here on Valencia St.

City Art Cooperative Gallery is a co-op that showcases wonderful local artists. For example, I adore the hyper-local work of Jessica Joy Jirsa - she paints so many scenes I walk past every day. The gallery is staffed by the artists, so go ahead and ask whoever’s around which art display is theirs!

Go back to Mission St. It’s obvious that both Mission and Valencia are major streets - despite being only one block apart. A brief history is in order. You’ll notice as you walk down Mission that there are many decrepit, old theaters. In the 1940′s, San Francisco had over 100 movie houses -- today, there are 5 theaters from this era on Mission street between 19th and 23rd.

Majestic theater turned Tower theater turned church turned semi-abandoned

Their demise was a combination of several forces. In the 1950′s, the home television set started reducing traffic to theaters. Then, in the 1960′s, construction started on BART, which tore up Mission Street. Entertainment seekers were diverted to Valencia street, instead of construction-filled Mission street, leading to the development of the shopping and restaurant area now. I think the theaters are easy to miss if you’re not looking for them so I make a point to notice their former glory. It’s so sad... some have been turned into parking garages!!

El Capitan - 2,500 seat theater + 85 room hotel turned into a parking garage in 1965

The good news, is that Alamo Drafthouse recently purchased and restored the New Mission theater.

Ok, next walk down to 24th St -- Calle 24. The whole Mission District has a reputation for being Latino, but there is some more nuance here: it’s a large neighborhood and constantly changing. The population first became predominately Mexican when California was a part of Mexico :) Ok but the next time was during the 1940′s-1960′s, as Mexicans were pushed out of their homes in the Rincon Hill neighborhood during the construction of the Bay Bridge. The west side of the Mission (the part we’ve seen so far) quickly changed in the 1960′s-1990′s to house a community of artists, LGBTQ, and punk musicians. Now, they’ve largely been displaced by severely Caucasian and very boring tech workers, like me!

Mission Street, Calle 24, and the eastern/southern parts of the Mission have a different history. They were predominately Mexican communities until the 1970′s-1980′s, when Central & South American started to fall apart. Many immigrants from politically unstable countries came to these microhoods, imbuing them with the Latino flavor that the Mission is now famous for. The 1970′s-1980′s also saw the rise of gangs in the Mission, and low-rider culture. It’s inconsequential, but as we walk South this is where we switch from Sureño gang territory to the Norteño gang’s territory.

Walk down 24th St. Everything here is great. My favorite part are the Lucha libra masks, but there are many wonderful shops, bakeries, community centers, and restaurants.

More murals down #6. Balmy Ave. These are more historic (and, I think, more famous) than the ones on Clarion Ave - they focus on the Latino history of the neighborhood, protests on US involvement in Central American, and the Chicano/Latino movement. All artists have origins from Mexico or Central America. Then, for a quick sharp contrast, visit hipster ice cream shop #7. Humphrey Slocumbe to try the Secret Breakfast ice cream.

That's the base tour - if you want more, start at the historic gay neighborhood of the Castro and 17th st and Market st before heading to Dolores Park. If you want even MORE, continue on to 8. Precita Park, #9. Bernal Heights (even better views of downtown) and #10. The Epicurean Trader in Bernal Heights neighborhood, SF’s historic lesbian neighborhood.

Have fun, and happy walking!