You know Mount Diablo. But do you know what kind of rock it's made of? Photo by Andrew Alden

If you're like me, one highlight of your Christmas celebration is the consternating quiz that columnist Jon Carroll publishes in the San Francisco Chronicle every year. Acknowledging the greatness as well as the priority of the Carroll quiz, I am humbly pleased to bring a geological version to the pages of KQED Quest Science Blogs. The quiz is centered on the Bay Area, which in addition to its other virtues is a premier destination for Earth scientists.

There are 20 questions, each with one correct answer. Some answers may be found in my posts from this year. Some answers can be found on Google and others cannot, but you're coolest if you don't need to search. There is one big hint on this page.

And now the fine print: No prizes are awarded; answers will be added to this post on Boxing Day; until then please post questions, not answers, in the comments. All right? OK!

1. What is California's state rock: gold, mariposite, quartz, serpentine?

2. How big was the 1906 San Francisco earthquake: 7.8, 8.0, 8.2, 9.0?

3. Which of these places is on the North American plate: Aptos, Bolinas, Colma, Davenport?

4. Which of these places is on the Pacific plate: San Francisco, San Jose, Santa Clara, Santa Cruz?

5. What is the highest magnitude earthquake that the Hayward fault is capable of: 6.7, 7.0, 7.5, 8.0?

6. Mount Tamalpais is primarily what rock type: blueschist, chert, marble, melange?

7. What mineral resource has NOT been produced in the Bay Area: coal, mercury, petroleum, uranium?

8. What fossils are NOT found in the Bay Area: ammonites, dinosaurs, hypsodonts, mammoths?

9. What fault continues north where the Hayward fault ends: Calaveras, Rodgers Creek, San Andreas, Zayante?

10. Mount Hamilton is primarily what rock type: gneiss, granite, graywacke, greenstone?

11. What fault continues north where the Concord fault ends: Flint Hills, Green Valley, Greenville, Maacama?

12. Which Spanish word tells you there was once a lime kiln here: calabaza, calavera, calera, calesitas?

13. The San Gregorio fault occurs onshore in what county?

14. Franciscan rocks are mapped in 14 different entities called what: belts, formations, melanges, terranes?

15. What rock type is at the top of Mount Diablo: basalt, harzburgite, rhyolite, schist?

16. Which entity allows personal fossil collecting: BLM, Caltrans, Coastal Commission, state parks?

17. Which North Bay mountain is an actual (former) volcano: Burdell, Konocti, St. Helena, Tamalpais?

18. Mount St. Helena is primarily what rock type: diatomite, serpentinite, slate, tuff?

19. What kind of ore was mined south of Livermore during World War II: iron, magnesium, uranium, vanadium?

20. Where is the Bay Area's only geyser: Calistoga, The Geysers, Great America Park, Mount Diablo?

And here are the answers:

1. California's state rock is serpentine, better known as serpentinite.

2. The 1906 San Francisco earthquake was magnitude 7.8.

3. Colma is east of the San Andreas fault and therefore on the North American plate.

4. Santa Cruz, conversely, is on the Pacific plate.

5. The Hayward fault is considered capable of a magnitude 7.5 earthquake.

6. Mount Tamalpais is primarily melange, an intimate mixture of metamorphic rocks.

7. To my knowledge, uranium has never been produced in the Bay Area.

8. No dinosaur fossils are known from the Bay Area.

9. The Rodgers Creek fault continues north where the Hayward fault ends.

10. Mount Hamilton is primarily graywacke, a variety of sandstone.

11. The Green Valley fault continues north where the Concord fault ends.

12. "Calera" is the Spanish term for a limekiln, where limestone is roasted into lime. You may now look up the other three words.

13. The San Gregorio fault occurs onshore only in San Mateo County, just missing San Francisco and Santa Cruz counties.

14. Franciscan rocks are mapped in 14 different entities called terranes.

15. The top of Mount Diablo consists mostly of basalt.

16. The Bureau of Land Management allows personal fossil collecting on the public lands it administers.

17. Mount Konocti, overlooking Clear Lake, is a former volcano, although the others contain volcanic rocks.

18. Mount St. Helena is primarily tuff, or volcanic sediments.

19. Magnesium ore, the mineral magnesite, was mined in the ultramafic rocks south of Livermore during World War II.

20. The Bay Area's only geyser is in Calistoga, but it's an artificial one that erupts in a drilled hole.

The Bay Bridge upgrade is part of the Bay Area's response to future earthquakes. Preparedness in your home is just as essential, and not half as complicated. Photo courtesy Todd Lappin under Creative Commons license

I've talked about some of the science related to earthquakes here on KQED, things like shake-table studies and triggered creep and long earthquake cycles. And I've introduced some of the Bay Area's earthquake-producing faults like the San Andreas fault (here), the Hayward fault (here and here), the San Gregorio fault (here and here) and the Green Valley fault (here). I've showed you some ways to friend your local fault on your own, too.

But talking about all this cool fun science is circling around something that's more urgent: earthquakes are on their way, wherever you live in the Bay Area. And by preparing in advance for these earthquakes, you can save a whole lot of trouble for yourself, your family and your neighborhood.

I know all this; I've known it and written about it for years. But I shy away from the implications, like a lot of people, and as a result I haven't done much serious preparation. Truth be told, I'm kind of paralyzed at the prospect.

There are people out there who understand this resistance to action. They are being as creative as they know how in a sincere effort to draw us into doing the right things. What works?

Before I go there, I can tell you what has and hasn't worked for me:

1. The authorities tell us that a big, damaging earthquake is a certainty (over 99 percent) in the next 30 years in California. (My instinctive, self-justifying response is, "Fine, the Big One will be down south.")

2. They tell us that a big, damaging earthquake has 2-to-1 odds of happening in the Bay Area in the next 30 years. (Yeah, the epicenter will most likely be somewhere else and not this year either.)

3. They tell us that damaging shaking from that big quake will affect my area. The scenarios show that problems from the quake will affect my area's infrastructure, its traffic, its economy. (Well . . . that's hard to ignore.)

4. Recent, realistic simulations show that the experience will be scary and challenging under the best of circumstances. (Imagining this keeps me awake sometimes.)

5. You insure yourself against sudden death, illness and car crashes, don't you, so why not treat earthquakes the same way? (Um, O.K.)

Nevertheless, all that feels more like being harangued than being helped. Can earthquake preparation be easy instead? Or failing that, can it be simple?

Would you settle for orderly? That is definitely doable. Some things come before other things, and those sincere, creative people have sorted them out in a program called Seven Steps to Earthquake Safety. That turns the daunting mountain of earthquake preparedness into a path, with one step at a time. For instance, step 1 is "Secure it now!" That sounds like something with a beginning and an end; like something I could incorporate into my routine, one errand at a time, a small new item in the family-meeting agenda and the household budget. That sounds like something I can actually manage. And once it's done, step 2——but let's not get ahead of ourselves; that's how the paralysis started.

There is coaching available, too. At least I think of it that way. A creative team at TotallyUnprepared.com has a growing set of stories and demonstrations of the small, ordinary things that make up "securing it now." There's a lovely set of videos answering the simple question, Will it shake? The newest one tests a snowglobe collection. Of course it will shake; you know that; but it still helps to see it shake. The how-to section covers lots of specific problems, from securing refrigerators to getting earthquake insurance. You can even sign up for a regular email message from the Totally Unprepared team with tips and encouragement. Links from Totally Unprepared go to lots of good background info. It seems like just the place to bookmark and, dare I say it, make part of a New Year's resolution.

All photos by Andrew Alden

Pillar Point, topped by its military base, is the bulwark of Half Moon Bay on the San Mateo County coast. You may be familiar with it as the nearest place to the great Mavericks surf break. Its abrupt appearance along the shoreline, and the linear hill extending from it to the north, are geomorphic oddities that gain significance when the geologist checks them out in detail. Here's what the area looks like on the Geologic Map of San Mateo County:

The pink area is granite and related rocks of the Montara Mountain block, which I showed you in August. Those rocks are something like 80 million years old. The ridge between Pillar Point and the town of Moss Beach is made of something else, though: the much younger Purisima Formation, shown in beige. Between them is a thick black line denoting a good exposure of the San Gregorio fault, which we saw a few months ago at its other end, at Point Año Nuevo. The units labeled "Q" are geologically recent sediments and not rocks at all—Qmt represents marine terraces like those at Point Año Nuevo and elsewhere.

The coastline here and parts of the ridge are part of the Fitzgerald Marine Reserve, a county park with a dedicated group of supporters at fitzgeraldreserve.org. When you visit, leave your rock hammer at home. Oh, and check the tides first, too.

At the reserve's south end is a trail leading over the ridge to the beach. Here we get our first look at the extensive wave-cut platform, exposed at low tides, that makes Fitzgerald such a destination for tidepoolers as well as surfing fans.

The cliffs here are a good place to become acquainted with the Purisima Formation, a mixture of shale and mudstone with occasional large concretions along certain bedding planes. You can find a few fossils here if you look carefully, but there are better places farther along.

The middle portion of the Fitzgerald Reserve is on the east side of the ridge facing the Half Moon Bay airport. From Airport Road you can see where the San Gregorio fault runs along its base.

The north end of the reserve is where the tidepoolers all go. The fault comes out here, pointing straight at Stinson Beach in Marin County where it merges with the San Andreas fault.

Before you go out on the rocks, turn around and look at the east side of the entrance, which is typical marine terrace sand.

Then go to the west side and see the contrast presented by the Purisima Formation.

The Purisima in the tidepools is sanded by the surf to bring out its tilted bedding layers, which are punctuated by layers of dropstones and shell hash.

Shell hash is pretty much what it sounds like, a layer rich in shell fragments.

Farther along the north side of the beach, the rocks turn rapidly into coarse granite conglomerate, some layers containing outright boulders. It was an extremely vigorous environment that produced rocks like this—perhaps a high sea level and large landslides produced by major earthquakes. Perhaps something like Devils Slide today.

But at some point, be sure and climb to a higher vantage point to see why every geology class in the Bay Area comes here to practice mapping.

It is a magnificant syncline, or folded trough, where fault motion has bent the rock layers and the sea has planed them off into this dramatic arc.

Long overdue for an upgrade, much of the Hetch Hetchy water delivery system was built in the 1920s and 1930s, with large swathes of pipelines made of riveted steel that don't perform well during big earthquakes. At a cost of $4.6 billion, paid for by 2.5 million residents in Alameda, Santa Clara, San Mateo and San Francisco counties who rely on a blend of Hetch Hetchy and local reservoir water, the San Francisco Public Utilities Commission has been installing new pipes and employing state-of-the-art engineering elements designed to withstand, for example, a magnitude 7.1 earthquake on the Hayward fault. Water storage capacity is also being expanded under the Hetch Hetchy Water System Improvement Program. When the program is completed in 2016, a new tunnel built 100 feet below the San Francisco Bay will carry a steel water pipeline 5 miles from the peninsula to the East Bay. The nearly 90 year-old, earthen Calaveras dam in southern Alameda county will also be replaced, allowing the adjacent reservoir to finally be filled to its original storage capacity of 31 billion gallons.

Cameraman Josiah Hooper and Producer Sheraz Sadiq inside a concrete vault containing two Hetch Hetchy water pipelines.

When I was assigned this story, I knew that it would be a challenge to describe key features of the Hetch Hetchy Water System Improvement Program while also explaining the controversial history of the creation of the Hetch Hetchy aqueduct after San Francisco officials received federal permission in 1913 to flood and dam Hetch Hetchy valley in Yosemite National Park. Fortunately, my job was made much easier thanks to the assistance provided by the San Francisco Public Utilities Commission to film the construction activities on several key projects and to interview members of their staff, including General Manager Ed Harrington and the director of the Hetch Hetchy Water System Improvement Program, Julie Labonte.

It also helped to find an eloquent historian, Gray Brechin at UC Berkeley, to share with me the colorful history of Hetch Hetchy. He used to work as a TV Producer at KQED in the '80s, so he knew the importance of delivering concise and engaging soundbites.

The earliest and most vocal champion for Hetch Hetchy water was San Francisco Mayor James Phelan, who served from 1897 to 1902. Mayor Phelan hired an official at the USGS who was willing to moonlight on Phelan's behalf and file water rights to stretches of the Tuolumne River which flows through the Hetch Hetchy valley. Other water sources such as the American River, Sacramento River and even Lake Tahoe were also considered, and while they would have been cheaper to divert for the bustling metropolis of San Francisco, they wouldn't provide the quality of drinking water passing through the Hetch Hetchy valley in Yosemite National Park. Even President Theodore Roosevelt, a pragmatic conservationist who had camped with John Muir in Yosemite and established five national parks during his presidency, sympathized with San Francisco's request for the Sierra water flowing through Hetch Hetchy.

John Muir, a Scottish-born naturalist and founder of the Sierra Club, led the fight to save Hetch Hetchy. After the 1906 San Francisco earthquake, local publications like The Call pilloried Muir for refusing to go along with the city's plans to dam the valley. But Muir stood firm, writing passionately about the "cathedral" of Hetch Hetchy in national publications and trying to rally wealthy East Coast contacts and friends to his cause.

After Phelan left office in 1902, a corruption scandal involving his successor and a series of ineffectual, caretaker mayors didn't help the city's grasp for the waters of Hetch Hetchy. But the tide began to turn with the election of James Rolph Jr. in 1911 and President Woodrow Wilson's appointment of Phelan business associate and attorney, Franklin K. Lane, as Secretary of the Interior.

In 1913, Congress passed and President Wilson signed into law the Raker Act which allowed the city to move forward with the construction of the Hetch Hetchy water system. Muir died just a year later, embittered by the loss of his David vs. Goliath struggle to protect the valley.

Although we didn't have the resources to visit the reservoir created by the dam at Hetch Hetchy, we were granted rare access inside a new tunnel being adjacent to the Irvington Tunnel. This tunnel transports 95% of the system's water from Sunol to Fremont and it has not been taken out of service for maintenance and repair since 1966. When it's completed in 2014, the nearly 9-foot in diameter new Irvington Tunnel will offer an important level of redundancy to back-up a critical piece of Hetch Hetchy infrastructure.

A roadheader inside the New Irvington Tunnel which is being built alongside the old Irvington Tunnel to convey Hetch Hetchy and local reservoir water from Sunol Valley to Fremont.

"Redundancy" is a word that came up quite often during my research into the Hetch Hetchy Water System Improvement Program which, in addition to the New Irvington Tunnel, is building other infrastructure to ensure the continued delivery of 265 million gallons of water a day within 24 hours of a major earthquake. Take for example the new Bay Division Pipeline, a fifth regional pipeline that will extend for 21 miles, including a five mile-section bored under the San Francisco Bay that will connect to a seven mile-section of pipe extending from Newark to the New Irvington Tunnel in Fremont. The new 6-foot diameter, welded steel water pipeline will also extend nine miles from Menlo Park across the peninsula in San Mateo county. The last time a regional water pipeline was added to the Hetch Hetchy water system was Bay Division Pipeline #4, built in 1973 to carry water south of the San Francisco Bay alongside another regional pipeline completed 17 years earlier.

Two sections of trailing gear located next to the new Bay Tunnel construction site in Menlo Park.

So the overhaul of the Hetch Hetchy system will improve earthquake reliability, in part through redundant, back-up structures like the New Irvington Tunnel and the new Bay Division Pipeline #5. The upgrades to the water system will also boost storage capacity and, according to Julie Labonte and Ed Harrington, will also enable more efficient use of water through enhanced delivery of recycled water or groundwater. Given the likely increase in the Bay Area's population, and the effects of climate change on rainfall and Sierra snowpack levels, making sure the taps continue to flow with Hetch Hetchy water for future generations is a daunting task.

It's also a race against time. A stretch of Hetch Hetchy water pipelines cross the Hayward fault, an active fault which last ruptured in 1868. The past five earthquakes on that fault had intervals of roughly 140 years, so the fault could slip at any time, triggering a massive earthquake in a dense urban corridor. Having water on hand to drink and fight fires will be essential to minimizing the repercussions of a massive, magnitude 7.1 earthquake on the Hayward fault.

Since ancient Rome, water has been essential to the growth of cities and the expansion of empires. To paraphrase William Mulholland, the visionary engineer behind the 230-mile Owens Valley aqueduct that serves Los Angeles, "if we don't get it, we won't need it." Indeed, empires may come and go but the need for water will persist. The challenge today, it would seem, is how to continue to meet this need while upgrading these marvels of 20th-century engineering to adapt to a 21st-century landscape of seismic hazards, urban growth and stretches of hot, dry days.

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 20-foot shake table at the Pacific Earthquake Engineering Research Center in Richmond. Photo by Andrew Alden.

Earthquake engineering is a discipline that uses a wide range of techniques: There's forensics, for diagnosing collapsed structures. There's 3D dynamic computer simulations, to test building designs in silico. And there's the mechanical joy of giving things a good hard shake. The last part, clearly, is the sugar that draws the news flies. It certainly brings out the little boy in me.

There are all kinds of ways to subject things to seismic-style shaking. At a scientific meeting not long ago I watched a contest that took student-designed model buildings and put them on a shake table the size of a large microwave oven. A shake table is outfitted with actuators—pistons pushing in all directions—that "play" a seismogram, the record of an actual earthquake. The students and judges were serious, but somehow gleeful too, as the models began to shed pieces onto the floor.

Photo by Andrew Alden

At the same meeting we could ride in a much larger apparatus as it played the 1989 Loma Prieta earthquake for us. As a veteran of that quake, I found this an uncanny experience but still couldn't keep a smile off my face.

Photo by Andrew Alden

The Pacific Earthquake Engineering Research Center, in Richmond, is a leading institute for this stuff. (If you can get a tour, don't miss PEER's 4 Million Pound Universal Testing Machine, a steel behemoth built in 1932, and the boneyard of broken stuff out back.) It has the biggest shake table in the Bay Area, 20 feet square. That's big enough to subject a full-sized cottage or model house to a realistic earthquake experience.

The University of Buffalo used two of these at once to test a full-sized two-story townhouse in 2006 at its Structural Engineering and Earthquake Simulation Lab. (Both PEER and SEESL share resources as part of the nationwide George Brown Network for Earthquake Engineering Simulation or NEES.) In that experiment, the building danced to the tune of the 1994 Northridge earthquake. . . a break dance, you might say. Videos from the project are uncanny, period.

But when something is too big to put on a shake table—like the Earth itself—we have to use a different approach. There's the equivalent of a submarine's sonar or the doctor's tap on your chest (a technique called auscultation, you should know) called active-source seismology. This has a long history and is best developed by oil companies and geotechnical consultants. The actuator that sends out the seismic signal can be as small as a sledgehammer blow or as large as blowing up a ton of dynamite, but I think that a fleet of Vibroseis trucks, pushing their thick steel baseplates against the ground in unison, may be the most impressive.

Courtesy Wikimedia Commons under CC-BY-SA license

This week a California research project went to the Sacramento Delta, a water source for some 23 million people among other things, and did some shaking experiments to help get a handle on what a Big One might do there. The news people made a point of getting out to Sherman Island, because what could be cooler? There was a big shiny machine with whirling weights, used to shake nuclear plants, mounted on a segment of simulated levee on top of pure Delta peat. It was easy to visualize mayhem.

The test was not a realistic one: the actuator didn't play a seismogram, just a straight eyeball-rattling vibration. The model levee wasn't twice as tall, a hundred years old, or holding back 20 feet of water like the real levees. The point was to do a basic test of the underlying peat soil—something simple, fundamental and not too dangerous. It was just the start of the thorough science we need, but the experiment made great video. Three newspapers gave it coverage and included footage; links below. In its own way it was as cool as Burning Man.

• San Jose Mercury News, "Earthquake simulator gives model levee a big shake"
• Sacramento Bee, "UCLA researchers shake model levee, for peat's sake"
• Stockton Record, "Ground rumbles for sake of research"

Point Año Nuevo from the air, with Año Nuevo Island to its left. When Sebastian Vizcaino sighted this point on New Year's Day 1603, the island was part of the mainland.

Point Año Nuevo gets a crush of visitors during the mating season of elephant seals, a spectacle well worth the trip down the San Mateo coast. The rest of the year, especially at low tide, is good for enjoying the Point's geology. For instance, nowhere else on the California coast is a major fault zone so well exposed.

But first let's notice something about the Point: it's all a big flat space. In fact, looking at it from the edge, down on the beach, you'll see that it's a classic marine terrace, just like ones I've described previously at Pebble Beach a few miles to the north and at Shell Beach in Sonoma County.

Photos by Andrew Alden

The top layer of this geologic cake is a thin frosting of brown soil, some orangish stream deposits just beneath it and lighter-colored beach sands. The bottom layer is solid rock all the way down to the beach. The contact between the two layers is a strip of vegetation, where groundwater collects. That contact represents an ancient wave-cut platform, from a time about 105,000 years ago (105 ka) when the sea level was higher than today (because the glaciers had melted even more than they have today).

Here's a closer look at that wave-cut surface. It appears just like the modern seafloor, complete with the borings of pholad clams.

The reason I could photograph this without having to climb the cliffs is that the ground in places has been faulted since 105 ka.

Field trip leader Gerald Weber of UC Santa Cruz lectures at a downdropped wave-cut terrace. Behind him, this surface is several meters higher.

Time to look at the geologic map, which shows several faults crossing Point Año Nuevo. The photo above is from the beach cliff above the word "Bay."

Extracted from USGS Geologic Map of San Mateo County (http://pubs.usgs.gov/of/1998/of98-137). Click image to see a larger version. Qmt, marine terrace; Qs, dune sand; Tsc, Santa Cruz Mudstone; Tp, Purisima Formation; Qyf, active alluvial fan; gold color, older alluvial fan deposits. Año Nuevo Island is Monterey Formation.

All of these faults are part of the San Gregorio fault zone, an obscure part of the San Andreas family that runs mostly offshore. It is thought capable of a very large magnitude 7.5 earthquake. The two most prominent strands at Point Año Nuevo are on the right-hand side of the map; they're informally named the Coastways fault (on the east) and the Frijoles fault. The Frijoles is at the center of this view:

This closeup shows where Año Nuevo Creek, long ago, took advantage of the downdrop on the fault and cut into the underlying Purisima Formation (which is about 5 million years old).

Point Año Nuevo is a very active place today, even though no large earthquakes have been documented here for about a thousand years. When first logged by European explorers in 1603, there was no island here. By the end of the 1700s there was one. Researcher Gerald Weber, who has tramped the Point since 1973, has evidence that this change created a huge washout of sand that protected the southern seacliffs of the Point until just recently. In a field trip recently, he paced off the amount he has seen the cliffs retreat since about 1980. The hat sits where renewed erosion uncovered an old pier post dating from the 1850s, when the pier served lumbering operations in the nearby hills.

Weber thinks that this sand has moved down the coast and is now affecting Santa Cruz Harbor. Eventually it will spill into Monterey Canyon and wash out to the deep sea.

The San Gregorio fault zone is an important mystery. This image from an old map shows its extent in this part of the San Mateo coast.

Recent mapping has improved this picture, but the work is very difficult. Lidar technology promises big advances, though. This light-based form of radar mapping allows us to strip buildings and vegetation off the underlying ground surface, making even subtle fault features stand out. Lidar imagery now covers this region:

Courtesy www.opentopography.org

. . . and the Frijoles fault trace on Point Año Nuevo stands out beautifully in it.

Learn more about Point Año Nuevo's geology from the park's 2009 docent training materials.

Lidar data from many Northern California fault traces is freely viewable in Google Earth.

^{The carbonate crust called tufa coats a high boulder over the Salton Sea, testifying that the Colorado River fed mighty Lake Cahuilla there in the geologically recent past. Photo by Andrew Alden.}

Geologic research is a remote and dusty undertaking that can look tedious to most people. But if it bears on subjects we fear, like earthquakes, even painstaking background projects can be blown out of proportion. A recent example from Southern California went from an intriguing journal article to "we're all gonna die" TV stories in the space of a day. Maybe it will help you spot the next time this happens in the Bay Area.

The article, published in the prestigious Nature Geoscience on June 26, presented the fruits of years of heat and tedium on the foul waters of the Salton Sea, in southernmost California. The Salton Sea occupies a sinking basin, the Salton Trough, that would rather be part of the Sea of Cortez except that the Colorado River has built a delta that dams it dry. As the river wanders over its delta, draining sometimes south and sometimes north, it periodically creates a geologically temporary lake in the Salton basin that has filled and dried out many times in the last few million years. (A short video by the University of Redlands illustrates the process.)

The repeating lake is known as Lake Cahuilla, and the Salton Sea is today's version of it. The Salton Sea is actually a terrible blunder, formed in 1905 when an irrigation canal tapping the Colorado River burst its banks and flooded a huge area of farmland in the dry bed of Lake Cahuilla. The breach was eventually fixed before the reborn lake could drown everything from Mexicali to Indio, but floods continued to be a problem until Hoover Dam was built upstream 30 years later.

The Salton Sea covers up the southern end of the San Andreas fault, and that's where our science story begins. A research team from Scripps Institution of Oceanography crisscrossed the drowned land in a small boat with a state-of-the-art CHIRP sonar system. They mapped a swarm of short faults running from the end of the San Andreas toward the end of the Imperial fault lying to the south—a tectonic configuration called a stepover. Here's the figure showing how it all fits together.

_{Tectonic setting of the Salton Trough and Salton Sea. SJF is San Jacinto fault, SSAF is southern San Andreas fault and IF is Imperial fault. Green grid is ship tracks in the dashed box; awz (acoustic wipeout zone) marks disturbed sediments. (Scripps)}

From their sonar database the researchers extracted a decent record of recent ruptures on some of these stepover faults. My figure below shows, schematically, how the sediment record is built as downdrops on the fault combine with sediment being deposited on top.

The researchers ran this process backward to reconstruct the history of faulting for a few thousand years into the past.

What made things interesting was how this record of stepover quakes meshed with records of lake floods and San Andreas mega-quakes. The correlation is imperfect, but intriguing: every time the lake was reborn in a flood, the stepover faults gave way, and half of the recent mega-quakes coincided with stepover quakes. To connect the dots further, the researchers said that "at least one of the last three dry-basin floods coincides with an earthquake on the SSAF (southern San Andreas fault)." In their cautious words, "We propose that loading by (Lake Cahuilla) may have induced failure on faults beneath the Salton Sea that, in turn, has the potential to trigger an earthquake rupture on the SSAF."

That's all ingenious science (seismic oceanography, in the desert!), but not news. To get news takes a press officer with a nose for a hook, and the hook is that the SSAF hasn't broken in some 300 years when we might (given the recent record) expect it to happen more often. Has our failure to let Lake Cahuilla be reborn held off triggering the next Big One? Well, has it??

That question is something for geologists to wave their arms about at meetings and parties, not hold out to the world as a sure thing. But between the paper, whose abstract is world-readable, and the press release from Scripps we can see the story begin to morph. It's a scattershot press release, meant to serve any news angle, that immediately confuses today's managed Salton Sea with wild prehistoric Lake Cahuilla. It includes a great hook, a quote about the "overdue" SSAF likening it to "a woman who is 15 months pregnant." The quote is only part of the background to the science, just a tangential part of the paper itself, but irresistible to the troutlike mind of the news reporter.

First out the chute on June 26 was the San Diego Union-Tribune's website, where Gary Robbins immediately removed all scientific uncertainty in his first sentence: "The Salton Sea east of San Diego is a deceptively dangerous backwater, hiding faults that repeatedly produce powerful earthquakes that jolt all of Southern California, says a new study by the Scripps Institution of Oceanography."

Later that day a Los Angeles TV station rewrote Robbins's story under the headline "Mega Quake Around the Corner?" with the lead sentence, "Man's interference with Colorado River floods that used to regularly flow to the Salton Sea may have 'stopped the clock' on a regular series of big earthquakes, setting the stage for a mega quake that could wreck Southern California, scientists said Sunday." The accidental flood of 1905 has become "interference" with regular flows to the Salton Sea, and the reasoning has turned upside-down: If we had let the Imperial Valley drown, Southern California's "Big One" might already have happened and been a few tenths of a magnitude unit smaller. How anyone wins under that scenario is not explained.

After a few days, more and better journalists weighed in. Some of them had actually studied the Nature paper (as I have). Many, including Discovery News's Tim Wall, apparently did not. USA Today's Dan Vergano did well. So did Chris Clarke on KCET's website. Charles Q. Choi did fresh reporting, as usual, for OurAmazingPlanet.com. Science News's Devin Powell wins my prize for his succinct, factual and well-written account. As you peruse the items collected by Google News under a search on "salton earthquake," look for those items that get the details right—specifically the fact that the Salton Sea arose by mismanagement, not on purpose.

The Bay Area has excellent media when it comes to our own earthquakes, with seasoned staff and good support from academic and government experts. But still—if scary news comes up, look around the science mediasphere and wait a few days before deciding what you think. Even better, track down the news at its source whenever you can. Learn who to trust.

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^{The Cordelia fault, west of Fairfield, provides the best exposure of the San Andreas fault zone in the Bay Area. Photos by Andrew Alden.}

The San Andreas fault is called the boundary between the North American and Pacific plates. It gets a lot of attention, but the plate-tectonic action actually is spread over a wide band of active faults on both sides, west and east, of the San Andreas proper. The easternmost strand of the San Andreas fault zone lies in Napa and Solano counties. This simple road trip will get you acquainted with it.

The textbooks say that the thin bright line of the San Andreas fault is the plate boundary, but in real life the North American plate is deeply splintered halfway to the Rockies. North America and the Pacific have about 2 inches a year of motion between them. The San Andreas proper accounts for the majority of that, but lesser faults in the Coast Range like the Hayward, Calaveras, Rodgers Creek and Maacama take up a large share too. Even the crustal cracks east of the Sierra Nevada move a few millimeters a year. Basically, the whole Bay Area sits within the plate boundary.

Around here, the easternmost part of that boundary consists of the Greenville/Concord fault in the East Bay and the Green Valley fault in the North Bay. The two faults are considered to be connected, although they are offset a few kilometers from each other beneath Suisun Bay. Both are worth a day trip, but let's go north this time. Here's a look at the geology of the area between Fairfield and Napa.

_{From the USGS Napa County geologic map and Solano County geologic map in Google Earth—click for 750-pixel version}

The purple area is young lavas and related rocks of the Sonoma Volcanics. The green area is much older sedimentary rocks of the Great Valley Sequence; we won't see those. The gold in between is widespread landslide deposits.

We'll start west of Fairfield at the Green Valley Road exit from I-80 eastbound, which is just before the intersection with I-680. From 680 take exit 70 and take three right turns to reach Lopes Road, which becomes Green Valley Road. Now the fun part begins as you make your leisurely way into Green Valley. The valley is bounded along its west side by the Green Valley fault, which runs north into private land in the rugged hills. The Green Valley fault seems to rupture every thousand years or so (and last ruptured between 1600 and 1800), but there isn't much data. There is some creep motion measured on it.

The Green Valley fault is not easily visited, but its smaller sibling is—the Cordelia fault. It runs through the lava hills on the east side of Green Valley. About 3.5 miles up Green Valley Road, Rockville Road exits to the right. Take it over the hills for about a mile and a half until you reach a dramatic roadcut. This is it looking west from the far side. On the geologic map above, it's at the north end of the Cordelia fault.

Pull over and find the distinct trace of the fault, made obvious where the finely ground rock, or gouge, in the fault zone has crumbled out.

The west side of the Cordelia fault is moving north, but no movement has been recorded in historic time. This is an easygoing fault, at the edge of the busy zone on the plate boundary. It's about as user-friendly as a fault can be, and its appearance here is the best fault exposure in the Bay Area.

Take the time to inspect the rocks, too. Take a sample if you like. These are volcanic rocks—not lava flows, but tuff: hot-welded bodies of ash and other volcano stuff laid down in huge burning avalanches back when this region was an eruptive center. (Today Clear Lake and The Geysers is the center of activity.)

In a few places you'll find welded tuff, an assemblage of an intriguing variety of material that has cooked together into a sturdy stone. (Here's a closeup.)

If you have the time, just a little farther there's an entrance to Fairfield's Rockville Hills Regional Park and an EarthCache connected to the Cordelia fault.

From here, continue on Rockville Road and turn left on Suisun Valley Road. This leads into the hills and becomes Wooden Valley Road. After about a 10-mile drive you'll enter the charming Wooden Valley, at the top center of the geologic map. From there you can look west to the Green Valley fault again as it emerges from the hills and runs along a high scarp. The fault ends just north of here.

Wooden Valley Road ends at state route 121, Monticello Road. Turn left on it and drive along the Green Valley fault. Notice the landslide scar from 2006 in the picture above and watch for it as you drive past; the whole hillside is unstable. Where the road turns sharply right and heads into the woods, there's a small turnout where you can admire the view east over Wooden Valley to the highest spot in this part of the Coast Range, Blue Ridge topped by Mount Vaca.

From here it's a nice drive through the volcanic hills down to Napa and the heart of the wine country.

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^{The tiny ranching town of Parkfield is California's seismic playground for scientists. This instrument package sits in Turkey Flat. Photos by Andrew Alden.}

Besides earthquakes, there is a whole spectrum of energetic activity in the solid Earth. Thankfully, most of it doesn't disturb anyone's sleep. After a century of focus on jolts and jiggles, earthquake scientists have begun turning their attention to these more subtle signals. And California is one of the prime laboratories for this research.

Most big earthquakes happen in the mid-crust in a zone between 10 and 20 kilometers deep, where rocks are strongest. Above this zone, rocks are cold and brittle and tend to crack; below, they are hot and ductile and tend to stretch. Menlo Park seismologists looking at the deeper, ductile crust have put a new piece of the great puzzle into place this week.

Earthquakes of the classic type—cracks in the ground, alarums and mayhem in the human sphere—are only the best known type of seismic activity. They center around the brittle–ductile transition zone, but can be found from very near the surface down to almost 100 kilometers deep, if tectonic forces have put cold, brittle rock down there. (Deep earthquakes, which occur down to almost 700 kilometers, are a separate species.)

The new types of seismic events are small and slow murmurings within the deep crust. They involve motions that are gentler and at much lower frequencies than typical earthquakes. Think of them as less like the crisp cracking of a baguette crust and more like the quiet ripping of the bread inside.

Different varieties of these slow events have been discovered by different people in the last two decades. Their names include tremor, slow earthquakes, episodic slip events, transient creep and so on. They are hard to detect and difficult for seismologists to model. But that's what they used to say about ordinary earthquakes, and I'm sure that we will tame these creatures too. I suspect that they will eventually align in a kind of spectrum with names akin to the colors we designate in the blurry bands of the rainbow.

This week's news centers on the lively research topic of triggering: Do distant earthquakes set off local events as their seismic waves roll through? It seems obvious that they would, but science looks for proof before accepting even what seems obvious. Triggering was first accepted when the 1992 Landers earthquake in Southern California was shown to set off small quakes all the way out to Yellowstone, in Wyoming. The effects are subtle and of scientific rather than engineering interest.

The San Andreas fault is a laboratory for slow-event research; the area around Parkfield, east of Paso Robles, has been intensively instrumented since the 1970s. Recently, persistent clusters of tremor have been mapped there at depths below the earthquake zone. A paper by U.S. Geological Survey seismologist David Shelly and others published this week in Nature Geoscience notes that these ticklish spots of "ambient tremor" are sensitive to large, distant earthquakes in the right circumstances.

_{Frame from Supplementary Movie 3, Shelly et al., Nature Geoscience doi:10.1038/ngeo1141. North-south profile of San Andreas fault; shaded zone and star represent slip in and hypocenter of the 28 Sept 2008 Parkfield earthquake; blue dots are earthquake events, crosses are ambient tremor locations; depth grid is 10-km intervals.}

Here's an example grabbed from a Quicktime movie file showing these ambient tremor spots "lighting up" after passage of the surface waves from the February 27 2010 Chile earthquake (magnitude 8.8). Surface waves are the strongest, most damaging and slowest-moving vibrations of an earthquake; they are what makes the entire planet reverberate as long as weeks afterward. What interested the researchers about this triggered tremor is that it lasted long after the triggering waves had passed. Something was moving very slowly after the trigger left, something that continued to set off tremor until the stresses finally dissipated.

What moves slowest of all the new seismic slow events? It is creep, which I described in last week's post. Creep is known to be variable—some parts of a fault have it while others don't; its speed also varies in different locations. It's known to change speed, too. In fact, you might think of it as just an extremely slow earthquake with a frequency of years instead of seconds.

Shelly and his coauthors therefore suggest a new kind of triggered event to go along with triggered earthquakes and triggered tremor: triggered creep.

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