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All About Quakes

5 Things to Do When The Shaking Starts

- Duck, cover, hold: Duck or drop down on the floor, take cover under a sturdy desk or table and hold on. Be prepared to move with it.

- If indoors, stay there: At least, until the shaking stops. If you’re outside, find a clear spot away from buildings, trees and power lines and drop to the ground. If you’re in a car, slow down and drive to a clear place.

- After the shaking stops: Get to a safe place outdoors if you think the structure you’re in is in danger of collapsing. Provide first aid for anyone slightly injured and seek medical attention for anyone seriously injured.

- Assume there will be aftershocks: Secure anything heavy that could fall, and eliminate fire hazards.

- Gas and water: Listen to the radio for instructions regarding turning off gas and water. If you smell gas, or think it is leaking, shut it off. Only a professional should turn it back on.

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6 Things To Now To Prepare For A Disaster

- Contacting loved ones: Create a plan for how you will contact one another after the quake, such as establishing an out-of-area contact who can help coordinate the locations of family members and other information should you become separated. Make sure children learn these phone numbers and addresses and know the emergency plans.

- Important papers: Keep copies of important documents at the house of your out-of-area contact or keep important documents and valuables in a fireproof storage box or safe deposit box.

- Disaster supplies kit: Keep a smaller version in your vehicle. Families with children should have each child create their own personal pack.

- Know evacuation routes: Establish several different routes in case certain roads are blocked or closed.

- Plan for pets: Animals are typically not allowed in places where food is served, so you will need to have a place to take your pets if you have to go to a shelter.

- Don’t run out of gas: Always run on the top half of the tank, not on the bottom half.

Things To Remember

Water may be in short supply.

Natural gas and electric power may be out for days or weeks.

Garbage and sewage services may be interrupted.

Telephone, Internet, cell phone, and wireless communications may be overloaded or unavailable.

Mail service may be disrupted or delayed.

Gasoline may be in short supply, and rationing may be necessary.

Bank operations may be disrupted, limiting access to cash, ATMs, or online banking.

Grocery, drug, and other retail stores may be closed or unable to restock shelves. Businesses may sustain damage and disruption—many small businesses require a long time to reopen or do not survive disasters.

Your income may be affected — payroll checks or direct deposits may be delayed.

For more information, go here

Source: County of Sonoma

Just after the first light of dawn, his house was slammed by a sudden, gigantic shock. Then, as he ran out onto Tupper Street near downtown Santa Rosa, J.W. Brown noticed a “great noise” approaching from the west. He could see the tops of trees waving in that direction, and as he watched, the motion and roaring sound came racing towards him. He grabbed a small tree for support, but the shaking tore it from his grasp. As the ground swayed in waves “about 2 feet high and 15 feet long”, he watched the tall dome of the nearby courthouse sway west, then east, and back, and with the third swing, collapse.

Brown’s first-hand account of that April morning in 1906 offers a glimpse of what residents today might experience when the next big quake hits Sonoma County. His testimony appeared in the official 1908 Lawson report on the San Francisco Earthquake, which included interviews on the violent shaking’s disastrous effects in Santa Rosa.

Scientists at the US Geological Service, who constantly analyze and monitor California earthquakes, confirm the North Bay may now be due, and perhaps even overdue, for one as powerful as 7.2 in magnitude, or possibly greater.

So, what can we expect it to be like when it happens? Many of today’s county residents may not have experienced a large earthquake, authorities say, and so may not fully appreciate what’s in store.

To understand what’s coming, scientists have to peer beneath the earth’s surface, and back in time.

To the casual observer, the ground and landscape seem permanently fixed and firm. But to Suzanne Hecker, a research geologist with the USGS in Menlo Park, it looks quite different. Northern California is riding atop a giant slab of earth’s crust, which is grinding past another plate beneath the Pacific Ocean. The titanic slow motion collision between the two has fractured the state from Baja to Mendocino County, and is steadily driving the western slice of California northward at about the speed that fingernails grow.

The intense force of this ongoing continental grinding has broken the upper crust into large crack-like features we call faults. As most Californians know, the broken crust slides along these faults, driven by the motion of the great plates. Unfortunately, because the sliding is uneven, the faults can lag or lock. Then, when enough stress accumulates, they will suddenly lurch past each other, releasing tremendous energy, in earthquakes.

Sonoma County is bracketed by two such active faults, the San Andreas on the west, and the Rodgers Creek on the east. Hecker studies the Rodgers Creek fault. She was a key member of a team who recently confirmed for the first time that Rodgers runs beneath the center of Santa Rosa, using advanced laser ground mapping techniques.

While the county has other active faults, these two are the most worrisome for a particular reason. How intensely an earthquake shakes depends on how much of the fault has ruptured. Longer ruptures generate earthquakes with increasingly higher magnitude. Which means that longer faults can produce larger quakes.

Janet Watt, a research geophysicist with the USGS in Santa Cruz, also studies the Rodgers Creek fault, and last year made an important discovery: the Rodgers Creek is almost certainly connected under San Pablo Bay to the Hayward fault, which runs along the East Bay hills. The Hayward fault, which has been steadily accumulating stress since it last erupted with an estimated magnitude 6.8 quake, in 1868, is considered by some to be one of the most dangerous in the state.

Scientists have long suspected the Hayward/Rodgers Creek faults might interact in some way. But the new finding introduces the possibility that both segments could rupture at the same time, along their entire 120 mile length, with incredible force.

Hecker, who investigates the history of quakes along the Rodgers Creek fault, has found evidence to suggest that might have happened once before, in the early 1700s.

Hecker and Watt also note that the rate of creep along the Hayward segment and the Rodgers Creek segment to the north are not the same, despite being under the same level of pressure. The Hayward creep has averaged about 5.4 millimeters a year, while movement on the Rodgers is 0 to 1.5 millimeters. That means parts of the fault in the Sonoma County section are locked, and steadily accumulating more energy, which can only be released by a major earthquake.

Historically, very large earthquakes occur on the Hayward fault about every 160 years, give or take 65 years. The last major quake on the Hayward fault happened 150 years ago. And, Hecker notes, smaller quakes really don’t do much to relieve the pressure that generates the big ones.

What would a 7.2 earthquake be like? Local residents may recall the earthquake that struck Napa in 2014: for scale, that one was 6.0. Scientistst say that a 7.2 quake on the Rodgers fault would be fifteen times larger in magnitude, and release 60 times more energy.

What level of shaking that will produce on the surface depends somewhat on the type of ground one’s standing on.

The rupture front can travel at a speed of 3,000 mph down the fault as it unzips, producing the first sharp, intense shock when it passes.

If a greater than magnitude 7 quake occurs on the combined Hayward-Rodgers Creek faults it could produce an earthquake lasting nearly 100 seconds. This prolonged shaking is what has such a devastating effect on buildings and other structures. The Loma Prieta “World Series” earthquake in 1989, for comparison, lasted 20 seconds.

Hecker notes that the city of Santa Rosa suffered unexpectedly intense shaking in the 1906 quake because it sits on an underground basin filled with deposits washed down from the mountains. The basin amplifies the shaking, like a bowl of jello.

A major quake can also cause opposite sides of the fault to jump in opposite directions by several feet. This can be a significant problem for buildings, pipelines, power cables and other structures that happen to run across the fault. Hecker’s recent mapping of the fault beneath Santa Rosa found that it was also wider than previously expected, meaning the area of surface breaks could be more extensive.

While the highest concern is focused on the Hayward / Rodgers Creek fault zone, the San Andreas, which passes beneath Bodega Bay, is also considered due for a major earthquake. In both cases, scientists know they’re going to happen — just not when.

So, what should residents expect? On a human scale, major earthquakes release tremendous amounts of energy as the spring-loaded fault ruptures, and this energy radiates through the ground. If the quake epicenter is nearby, the first effect is usually a hard, sharp thump, much like a powerful sonic boom, which rattles doors, windows, furnishings and entire buildings. Within seconds, loud, deep rumbling can often be heard approaching, which some have compared to giant dump trucks roaring down the street. That rumbling accompanies secondary earthquake waves, which arrive with intense, sometimes violent shaking, up and down and side to side. These waves can be so strong it can be impossible to stand or walk, and may last seconds or minutes in the most extreme case. Drivers may feel they’ve had tires blow out.

Following the major quake, there are usually aftershocks, which can vary in intensity.

Intense, prolonged shaking can damage buildings, roads and bridges and underground components like water, electrical and communication systems. Extensive efforts have been invested by the city, county, state and emergency services to strengthen and retrofit vulnerable structures in recent years.

But authorities throughout the county and state also warn the community to individually prepare now for what’s coming: once the earthquake hits, it will be too late.

As scientists continue to explore and reveal the mysteries and history of our seismic region, Hecker notes, we’re getting a more detailed picture of how and where they’re most likely to occur. But, she points out, none of the research suggests we’re likely to wait too long before the next big one. The most recent official assessment advises it can happen any time, with a 93 percent probability that a 7 magnitude earthquake will occur in California by 2045.

Stephen Nett is a Bodega Bay-based Certified California Naturalist, writer and speaker.

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