The Hayward fault separates tidal marsh and coastal grassland at Point Pinole Regional Park just north of Richmond. Photos by Andrew Alden.

The Hayward fault threatens a lot of people and structures as it runs straight through the East Bay. But at its northern end, at Point Pinole Regional Shoreline, the fault can be walked and traced across open land with trees and grass. You can imagine the fault's biggest earthquake, a magnitude 7.5 event, doing little more than knocking you on your butt there.

Pinole Point is a gently rolling peninsula that points north-northwest into San Pablo Bay. It's underlain by 10-million-year-old gravelly sandstone of the Orinda Formation, but much more recent changes in sea level have left it draped in Pleistocene sediments, old soils and offshore peat beds. Still more recently the point was the home of an explosives manufacturer from 1881 to 1960. The East Bay Regional Park District bought the land in 1972, and today it's a nice place to stroll, run, ride, fish, picnic and geologize.

Much of the point is wooded, but the forest is exclusively eucalyptus, planted during the tree's heyday to help muffle the noise of explosives manufacturing and no doubt to provide shade. You can walk off the path easily when your curiosity beckons, and the light is beautiful.

You can see the green woods in this Google Earth view of the point, along with the mapped fault trace. Note that the park is named Point Pinole, but the point itself is Pinole Point.

Frame grab from the US Geological Survey's Hayward Fault Tour.

But let's peek under the trees with the lidar digital elevation model. (I showed you lidar imagery of the San Gregorio fault a couple months ago.)

Data from OpenTopography.

The fault crosses the railroad tracks at the south (right) edge, skirts the edge of the coastal marsh and traverses the west side of the point until it runs offshore into San Pablo Bay. (It's been traced most of the way across the bay, but it dies out as seismic motion steps eastward to the Rodgers Creek fault in the North Bay.) The maps at the park show a different line, which is incorrect.

The photo at the top of this post looks straight down the fault trace from the southern marshland toward the train tracks. The next photo below is looking north up the fault trace; on the lidar image it's where the fault trace, displaced west by a large landslide, returns to its straight track.

The grass was very tall here when I visited (goats will clean it up this winter), so the going was a bit hard. But it's quiet here off the trails, and I can recommend it as a place to meditate on the fault. The hollows along the break in slope all were much greener than the surrounding ground because faults tend to block the movement of groundwater. Very near here is where a trench was dug across the fault, one of several such scientific dissections made on the point in recent years. You can follow the fault north for a ways through the woods, but eventually it reaches the shore.

Landslides triggered by wave erosion have disturbed the western bluffs nearly everywhere on this part of the point, but where I was standing is as close as can be to where the fault meets the coast. As researcher Glenn Borchardt puts it, "the erosion produces seasonal changes in the exposure, so some lucky earth scientist or astute passerby may be the first to see the landward end of the fault." In the 1980s, a trench dug here in the surf zone revealed serpentinite on one side of the fault and mudstone on the other.

As you go farther north along the trail here, the bluffs grow quite high. The material they expose is coarse gravel, and the larger stones in the surf zone have an entertaining variety.

Near the point itself, the ground surface appears to be uplifted and tilted eastward. This is not unexpected around a major fault, but I have not seen anything documented about it. If you go out on the fishing pier at Pinole Point and look back, the tilt looks obvious.

Look all the way around while you're there; Pinole Point is uncommonly peaceful and remote while being in the center of a lot of North Bay landmarks.

None of the scenery at Point Pinole Park really shows the threat of the Hayward fault. But just south of the park is the Parchester Village neighborhood, a cookie-cutter of 1950-vintage suburbia planted right on the fault. There, just as clearly as in downtown Hayward, you can see the classic signs of aseismic creep slowly tearing apart the homes, lots and pavement.

Measurements show that the fault is moving around 5 millimeters a year there. Only our human encroachments reveal the ongoing action of the tectonic plates that brings the next big Hayward fault quake closer every day.

The gist of the 2008 TV story was that geologists are now able to use special paleoseismic techniques to analyze earthquake faults and determine their seismic history over several thousand years. By noticing patterns in earthquake activity over long periods of time, they can also make predictions about when major events are likely to happen in the future. They determined that a major event of 6.8 or higher happens every 140 years or so on the Hayward Fault. It's been 143 since the last one.

Engineer Khalid Mosalam

A 2003 report by the USGS found that there is a 62% probability of at least one magnitude 6.7 or greater earthquake in the 3-decade interval 2003-2032 within the San Francisco Bay region. With odds like this, I'm grateful that there are people like Khalid Mosalam and his colleagues at the Pacific Earthquake Engineering Research Center's Shaking Table Laboratory who dedicate their careers to learning how to make the built environment that we live in, work in and travel on more safe in an earthquake.

I'd included about a minute of video from the Shaking Table Lab in the 2008 piece but I always regretted that I wasn't able to show more of this facility. So when we started putting together an entire episode focused around the theme of earthquakes, I thought a short segment about the Shaking Table would be perfect for this show.

Substation equipment getting shaken up on the table

When we were there shooting in 2008, they were testing some electrical substation switches which were interesting but definitely not as dramatic as some of the other structures they build and shake in three axes, often until collapse. The generous engineers at PEER were able to provide us some videos of other structures they tested including a two story house, a masonry wall and a bridge pier support. The 20' x 20' table is one of the largest in the world to be able to move in three directions (translation and rotation) so, according to Mosalam, it's an extremely important piece of equipment at UC Berkeley and has contributed to important research that will result in people being safer when the next 'big one' hits.

^{Suburbia is warped in downtown Hayward, where fault creep is steadily distorting curbs, walls and pavement. All photos by Andrew Alden except where noted.}

In my first post on KQED Quest Science, I invited you to make friends with your local earthquake faults. The best place to do so, in my opinion, is in Hayward, where the Hayward fault runs right through downtown. You can start at the Hayward BART station and enjoy a good meal while you're in town.

What makes Hayward special is that the fault moves steadily there, even without earthquakes, in the process that geologists call aseismic slip, or fault creep. Very few faults are known to creep, but in the Bay Area we have three: the Hayward fault, the Calaveras fault in Hollister, and the San Andreas fault south of Gilroy.

I love my copy of U.S. Geological Survey Map MF-2196, "Recently Active Traces of the Hayward Fault," published in 1992 on a topographic map base. But the Survey's online database, updated twice since then, costs nothing and is projected on aerial photos. Here's how downtown Hayward looks in it; click the image for a larger version. North is to the left.

The BART station is at the bottom between A and D Streets. If you can, walk through the new City Hall on your way to Mission Boulevard; it's highly engineered for earthquake resistance, and the apron of stone around it hides a base-isolation system that lets the building shimmy like a surfer to ease the stress on it from a magnitude-7 event.

On Mission it's simply a matter of walking in either direction and going up each side street. The annotations have a simple code: C1 and C2 denote excellent and good creep evidence, respectively. Here are examples of the codes that follow them. First is "ec," for echelon cracks, like this set from Oakland's Lake Temescal where the fault has its own exhibit.

Before we go any farther I should point out that Hayward is not proud of its fault. Many homes and properties were built upon the fault trace before creep was first recognized in 1956. It's best not to stand and point. Geology teachers tell their classes the same thing.

The code "rc" stands for right-offset curb. These are easy to spot. I photographed this example a few years ago; since then the construction site has become a structure, but the curb still takes its rightward jog. The Hayward fault is classified as right-lateral, meaning that when you look across it, the other side moves to the right.

The curb on Sunset Street, near Prospect Street, is a clearer example.

The codes "rb" and "rw" mean offset buildings and walls, respectively. You'll see a lot of damaged brick buildings, or recent repairs, in line with the bent curbs. The code "jo" means open joints or cracks in concrete. This example shows a steadily opening gap that has been patched.

Localities marked "so" have had their offsets surveyed. The most commonly visited site is the corner of Rose and Prospect Streets, the yellow circle on the map. The corner curb has had a constant stream of visitors since it was built in 1971. This is how it looked in 2001.

_{Photo courtesy misspudding of Flickr under Creative Common license}

You can see from my photo taken in 2007 that it has moved further since then. The street here has a good set of echelon cracks too.

Prospect Street got its name because it runs along a low ridge with a nice view west. The ridge is a pressure ridge, thrown up during thousands of years of creep and earthquakes. That's one natural sign of fault activity. Another is offset streams, which are just like offset curbs only much larger. You'll see one on the map where a stream flows down from the top (east), turns sharply to its right, then jogs leftward on the other side of the fault. It's marked "G1, rs" meaning excellent geomorphic evidence consisting of a right-offset stream.

Another natural fault sign appears about 2 miles south on Mission at Holy Sepulchre Cemetery, where you can look up on the hillside just to the south and see another natural sign of the fault: a line of springs. It really stands out in the dry season.

This is just a beginning of what geologists learn to see, but you can follow in their footsteps as far as you care by visiting the USGS's Northern California earthquake home.

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^{Mineral springs, fresh air, and a cross-section of South Bay history—not to mention its rocks—are all on display at Alum Rock Park. All photos by Andrew Alden.}

Alum Rock Park occupies the small, steep valley of Penitencia Creek carved into the hills east of San Jose. The city has owned it since 1872, when it became California's first city park. For a generation it was a major regional attraction for its warm mineral springs and the entertainment complex surrounding them, of which only traces remain today.

Today it's a great place to get away from the city's hustle while pretending you're still at the office (except on Mondays, when it's closed). But if you put away the phone and pay attention to your surroundings, Alum Rock Park can show you some of San Jose's deep history and the Bay Area's rocks.

If nothing else, the park provides good views to the west over the Santa Clara Valley from its higher trails. You can choose from a warm south-facing slope and a cool north-facing one, too.

Have a look at the geologic map of the area (from USGS Open-File Map 98-795) below.

Penitencia Creek comes downhill from the right center and exits on the lower left. The park entrance is right at the edge of bedrock (Kbc, conglomerate of the Berryessa Formation), and the uppermost parking area is at the Tcc (Claremont Formation) mark. Hiking trails run along both sides of the creek giving you a good look at all the rock units from the park entrance to the Briones Formation (Tbr) on the right. Let's see some, starting with the conglomerate.

This very coarse grained rock and its related sandstone in the Berryessa Formation are part of the Great Valley Sequence, thick beds of sedimentary rock built up while the Sierra Nevada was intruding all that granite, back around 100 million years ago in Cretaceous time.

Behind the boulder is Eagle Rock, which corresponds to the pinkish blob surrounded by landslides to the right of the "Kbc" label. You can climb up there or stroll through the other outcrop labeled Jbk. The rock itself is well-traveled volcanic material that has been permeated and altered by hot mineralizing fluids. Here's a chunk of it.

The large outcrop along the creek gives the park its name. An early visitor mistook the whitish crust on these rocks as alum, which would have been a nice find at the time. It's actually sulfate minerals, but the name stuck.

Farther upstream, just past the visitor center, is where the mineral spring zone begins. On the geologic map, it corresponds to the exposure of Claremont Formation (Tcc), a belt of ribbon chert of Miocene age (about 10 million years) familiar in the East Bay Hills. Here the chert is dark with organic matter and its beds are upturned almost to vertical. That combination of chemistry and structure has given rise to warm upwellings of chemically interesting groundwater.

There are more than 20 different springs here, each with a nice stone housing. The ones I dipped my fingers into were bathtub-warm, and the water is sulfur-scented. A hundred years ago Alum Rock Park was a big health spa, with a rail line direct from downtown. That was when the stonework was done. You can see where seepage has built up cones of minerals on the lower wall. All of the springs issue from the Claremont chert—here's a closeup of the chert and the mineral crust.

After all that excitement you may want to continue upstream, into the structurally overlying and younger Briones Formation. This set of rocks is coarser grained than the Claremont, deposited nearer to shore. The other way to look at it is that the shoreline grew closer to this spot as geologic time progressed. This is a well-scrubbed outcrop in the stream bed that shows its bedding.

Parts of the Briones are so full of fossils that the rock is best described as shell hash. You'll see this same stone at Lime Ridge in Walnut Creek and other places in the East Bay.

This whole belt of rocks lies in the zone where the Hayward fault merges with the Calaveras fault. On the map above, the Calaveras runs down the right edge of the Briones Formation, between the Calaveras and Anderson Reservoirs. The Hayward fault formally ends a few miles northwest, but the many smaller faults marked as heavy lines are of the same ilk and reflect the same tectonics. Friction along the faults may account for the warmth of the springs, just one more way that the deep Earth affects us in our region.

You can also check out QUEST's Alum Rock Science Hike for more info.

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_{The Hayward fault crosses Oakland's Temescal Regional Park. Photo courtesy Andrew Alden}

Earthquakes will never be as predictable as the weather, I think it's safe to say, but if you get to know your nearest faults then earthquakes will be less of a surprise. When our local faults rupture, you will be less likely to panic and more likely to get through the event unscathed. So when I urge you to friend a fault, it's not to infect you with a scientific hobby but to bring you a lasting practical benefit.

A fault is a crack that has had movement along it. Geologists find them everywhere, and geologic maps are festooned with them. Almost all of them are inactive, though, and they're generally obscure even to practiced eyes. You can see what I mean on the U.S. Geological Survey's zoomable geologic map of the Bay Area.

_{US Geological Survey image}

Here's a part of it showing the area around Fremont. We can't be expected to worry about every heavy line, can we? Thankfully, no; and not the colors and symbols either. That's geology stuff: bedrock and contacts between stratigraphic units. But the two heaviest lines are important. On the left is the Hayward Fault and on the right is the Calaveras fault, both capable of major shocks.

_{US Geological Survey image}

Another USGS map called the Quaternary map focuses on just the active faults—well, the sort-of active ones that have moved during the Quaternary Period. You need to know only two things about the Quaternary: it's pronounced "qua-TERN-ary" and for our purposes it includes the last 1.8 million years of geologic time. Now a fault that hasn't moved in a million years, like a volcano that hasn't erupted in a million years, is not much of a threat. The color codes on the faults match the time of the latest fault movement, angry red being historic time (namely, 1868).

There are two good ways to visit our local faults. One is visiting them in parks (see the list below), and the other is the freelance approach of tracking them through the neighborhood. For that, the best tool is the State of California's Alquist-Priolo Earthquake Zone Maps, which have just been placed online by the California Geological Survey. Mandated by the Alquist-Priolo Act of 1972, these maps display the locations of faults that have ruptured during Holocene time, which is geologese for the last 11,000 years. Unlike Quaternary faults, activity on these Holocene faults is a pretty sure thing. And the maps display the detailed fault traces as mapped by geologists, superimposed on a high-quality topographic map.

With these, you can drive or stroll an area and assess the land for yourself. In places like downtown Hayward, the signs are plain and plentiful. In many others, you'll wonder what the heck those geologists were seeing. (The answer is that they were looking at historical aerial photos and data, finding subtle clues on the ground, and doing a lot of connecting dots.) You'll have a head-scratching good time, and you won't see your landscape the same way again.

Visit the San Andreas fault:
Fort Ross—Take Fort Ross Road east about 0.5 mile and spot the painted line across the road; an interpretive trail is nearby.
Olema—Take the Earthquake Trail near the Bear Valley Visitor Center in Point Reyes National Seashore.
Los Trancos Ridge—This ridgetop park above Palo Alto has an earthquake trail along the fault.
Sanborn County Park—South of Cupertino in the Santa Cruz Mountains is this park with the 2.5-mile San Andreas trail along the fault trace.
San Juan Bautista—The fault runs just yards east of the mission here.

Visit the Hayward fault:
Berkeley—Tour the fault in "Bear territory" including the infamous football stadium built across the fault in 1923.
Oakland—Lake Temescal park displays the fault in several places.
Hayward—The historic downtown and old City Hall straddle the fault, and signs of steady (aseismic) creep are abundant here.

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Bay Bridge and San Francisco / Flickr

The magnitude 7.0 earthquake that occurred a couple weeks ago near Christchurch, New Zealand is yet another reminder for those of us living in the Bay Area about the inevitable seismic danger we face. While many details of the New Zealand earthquake are different than what we face in the Bay Area, there are a few aspects that are comparable.

The fault that ruptured on the South Island of New Zealand was dominated by strike-slip motion, which is similar to the San Andreas, Hayward, and related faults in the Bay Area*. And, unlike the devastating earthquake that struck Haiti in January, the state of building construction in the Bay Area and Christchurch is, in general, much better.

But there are a lot of older structures in the Bay Area that could be quite dangerous in a powerful earthquake. Individuals need to be prepared. A few months ago, my wife and I declared a weekend ahead of time to be "seismic hazard preparedness weekend" (I even wrote that on the calendar). The USGS has incredible resources when it comes to Bay Area earthquake awareness, education, and preparedness. We downloaded their packet Putting Down Roots in Earthquake Country for putting together our kits.

We spent a good day and a half preparing kits with food, water, and other emergency supplies for our home, our car, and for both of our workplaces. I have to admit, it really felt good to get it done and feel like we could brave 3-4 days without power, water, and communications. We have plans for what to do if we are at work as well. Don't put it off. Declare next weekend or the one after that your own seismic hazard preparedness weekend. Put it on the calendar and make it real.

The last thing I'll mention about this has to do with mental preparedness. That is, you can buy all the supplies, have the plans all worked out, prepare your house, and so on — but you also need to be mentally prepared. A relatively large earthquake will happen, eventually. You can't stop it and deciding not to think about it won't decrease the chances. I'm not saying you need to worry every moment — worrying doesn't help either. It's good to come to terms with the high probability that you will be  affected by an earthquake and then take steps to reduce the risk to you and your family.

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* see this QUEST segment from 2008 about seismic hazards related to the Hayward Fault. You can search on our website for other related stories, including these:

Predicting the Next Big One
Earthquake Early Warning
Earthquakes: Breaking New Ground

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Updated: On March 11, 2011, a massive 8.8 magnitude earthquake hit the Pacific Ocean nearby Northeastern Japan. The quake, and a tsunami that followed, caused massive damage and loss of life. The news put quake prone California on alert. While many of us would rather not think about the possibility of another major quake, we are surrounded by active faults. One East Bay fault has scientists especially concerned.

It's been called the most dangerous fault in the U.S. The Hayward Fault runs 40 miles, from San Pablo Bay to Fremont, through some of the most densely populated areas in the country. Every 140 years for the past two thousand the Hayward Fault has jolted the East Bay. Geologists have figured out the regular history of these quakes by carbon dating trenches along the fault. A lesser known cousin of the San Andreas the Hayward fault is a creeper. Basically, it moves, slowly, along the surface but deep inside… it's locked until tension builds up and and it slips. It appears that it is time for the fault to slip again. The last major earthquake on the Hayward fault was 1868. Scientists believe that the temblor registered 7.0 in magnitude. Hayward and San Leandro were devastated. But if the quake were to happen today, it would be a much different story.

I met Mary Lou Zoback out at the Fremont Bart station, which sits right on top of the Hayward Fault. She pointed out cracks in the parking lot from the creeping fault. Zoback is a geophysicist who worked 28 years at the U.S. Geological Survey and who has done catastrophe modeling of risky residential buildings. Her company estimates that a 6.8 quake, or bigger, on the Hayward Fault could cause a disaster on par with Hurricane Katrina, causing 168 billion dollars in damage and leaving at least 200,000 homeless.

A number of public buildings in the east bay are undergoing retrofitting to make them more structurally sound. Area hospitals have until 2013 to meet seismic safety standards. There is a state inventory of public schools prone to collapse in a major quake, but no such list exists for private schools. And retrofitting standards for risky residences are confusing. I talked with Jim Cook, of Bay Area Retrofit. He says existing codes are unclear and there really is no specific licensing for seismic home retrofitters. Cook has been fighting local governments for years to improve seismic safety standards.

Homeowners can have their home evaluated but what if you are a renter? Many apartments and condos can collapse in earthquakes because they have parking or open commercial space on the first floor making this story weak or "soft." According to the Association of Bay Area Governments Earthquake and Hazards Program, soft-story apartment buildings were responsible for about two-thirds of the 46,000 uninhabitable housing units in the 1991 Northridge earthquake. In the Bay Area, unreinforced masonry (older buildings constructed of brick, stone or cement blocks) continues to be a threat.

The thought of a big earthquake is scary enough, never mind the chaos that can happen in the aftermath. But the damage from a large earthquake has repercussions that can last for a very long time. We can still see the scars from the 1989 Loma Prieta earthquake. Downtown Santa Cruz is not yet fully rebuilt and retrofitting continues on the Bay Bridge. We can prevent a lot of damage up front by shoring up our buildings and creating a family disaster plan and an earthquake kit. The Hayward Earthquake Alliance has put together some really helpful information on how to prepare for a major quake.

Listen to the Hayward Fault Radio Report and view the recent QUEST TV segment on the fault online.

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So we know – or should know – the seismic risks of living in one of the most vibrant, diverse places in the U.S. Short of leaving the region, what can we do?

Well, one of the most illuminating things about working on this story for me was learning a bit about retrofitting one’s home to make it withstand the lateral and vertical forces that accompany a strong earthquake. In short, you need to build shear walls – made of reinforced plywood and shear transfer ties – and bolt them to the walls in the foundation of your house. Suprisingly, there are no official codes as to what constitutes a proper seismic retrofit of a residential unit in California, nor is there a dearth of licensed contractors who will offer quotes and purport to retrofit your home but without any standards in place, homeowners are often at a loss to evaluate the quality of the retrofit which can easily exceed ten thousand dollars, depending on the size of the home and its location. Still, homeowners can avail themselves of a few retrofit resources online, such as Plan Set A, a guideline for retrofitting one's home that has been approved by building departments of several Bay Area municipalities such as Oakland and Hayward. Also on the Association of Bay Area Government's web site is a set of schematics illustrating shear wall construction. If you are interested in retrofitting your home, you should get quotes from several contractors, consult your city's building department to inquire about permits and possibly consult a structural engineer to perform a building analysis on your home.

If you're like me, though, and don’t own a home but want to prepare for "the big one," it's imperative to get an earthquake survival kit. The <red Cross sells earthquake survival kits but why not make your own, provided that it has water, first aid supplies, a flashlight, food rations and other essentials for you to survive 72 hours while waiting for emergency help. If you want to make your own kit, try the USGS, the city and county of San Francisco, or helpful suggestions from the San Francisco Chronicle and LA Times.

Living in earthquake country, it pays to be vigilant. I applaud the 1868 Hayward Earthquake Alliance, a consortium of agencies that are raising awareness of the risk posed by the Hayward fault with a series of events aimed at educating the public about the importance of preparedness, including a city-wide drill in San Francisco on October 21st, the 140th anniversary of the 1868 Hayward earthquake. We may not be able to predict when exactly the next earthquake on the Hayward fault may occur but we can start planning today to mitigate its effects.

For those who aren't familiar with the Hayward fault, check out our this link to the USGS Google Earth tour over the fault.

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