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Posts Tagged ‘Earthquake’

MendoCoastCurrent, March 11, 2011

Awakened this morning to a tsunami warning phone call on the landline from Sargent Barney warning of an impending tsunami to occur in just over half an hour at 7:23 a.m. He continued that it was due to a 9.0 earthquake in Japan hours earlier. Our coastal community is urgently called to prepare for a tsunami. At risk situations are at land elevations of 150 ft and below, especially low lying areas at & near river mouths here on the coast of northern California. The reverse-911 tsunami warning phone call suggested everyone go to higher ground immediately and it was 6:55am.

First action was to call a close neighbor without a land line suggesting we meet at our highest ground probably between 250-300 feet. Packing stuff I needed, making a pot of coffee, I am writing this post right now and it’s 9:17am.

I packed my car, went to highest ground here as suggested. Around 9am, a friend called to say the tsunami had been downgraded. The tsunami has passed (or so I believe right now). It was an excellent exercise.

Realized long after the early morning reverse-911 warning that the tsunami sirens were not sounded here on the coast.

A friend mentioned that a tsunami drill had been scheduled for March 11, not sure of the time.

Redheaded Blackbelt also has tsunami updates for Humboldt county ~ http://bit.ly/hspXcz

10:20 am: Here’s the NOAA Tsunami report ~

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE EUREKA CA
1020 AM PST FRI MAR 11 2011
REDWOOD COAST-MENDOCINO COAST-
1020 AM PST FRI MAR 11 2011

...A TSUNAMI WARNING REMAINS IN EFFECT FOR DEL NORTE...HUMBOLDT
AND MENDOCINO COUNTIES COASTAL AREAS...

EARTHQUAKE DATA...
 PRELIMINARY MAGNITUDE 8.9.
 LOCATION 38.2 NORTH 142.5 EAST.
 NEAR EAST COAST OF HONSHU JAPAN.
 TIME 2146 PST MAR 10 2011.

A TSUNAMI WAS GENERATED AND HAS CAUSE DAMAGED ALONG THE DEL NORTE
COUNTY AND DAMAGE ALONG THE HUMBOLDT AND MENDOCINO COASTS IS
STILL EXPECTED. PERSONS AT THE COAST SHOULD BE ALERT TO
INSTRUCTIONS FROM LOCAL EMERGENCY OFFICIALS.

DAMAGING WAVES HAVE BEEN OBSERVED ACROSS HAWAIIAN ISLANDS.
DAMAGING WAVES HAVE ARRIVED AT CRESCENT CITY HARBOR WHERE ALL
DOCKS HAVE BEEN DESTROYED. WAVES HAVE BROKEN OVER THE SPIT AT
STONE LAGOON. A 3 FOOT WAVE HAS BEEN REPORTED IN HUMBOLDT BAY. A
2-4 FOOT FLOOD WAVE WAS REPORTED MOVING UP THE MAD RIVER AT 8:45
AM PST. DAMAGING WAVES WILL CONTINUE FOR THE NEXT SEVERAL HOURS.

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY
GAUGE LOCATION        TIME      AMPLITUDE
CRESCENT CITY CA     844 AM       8.1FT
NORTH SPIT HUMBOLDT  830 AM       3.1FT
ARENA COVE           917 AM       5.3FT

REMEMBER...DONT BE FOOLED...TSUNAMI WAVES CAN SEEM STOP FOR LONG
PERIODS AND THEN BEGIN AGAIN. WAIT FOR THE OFFICIAL ALL CLEAR TO
RETURN TO THREATENED AREAS.

IN DEL NORTE COUNTY...PEOPLE ARE ORDERED TO EVACUATE TO ABOVE 9TH
STREET. SHELTER LOCATIONS INCLUDE SMITH RIVER ELEMENTARY...DEL NORTE
HIGH SCHOOL AND YUROK TRIBAL OFFICE IN KLAMATH.

IN HUMBOLDT AND MENDOCINO COUNTIES...PEOPLE ARE ADVISED TO STAY
OFF BEACHES...NOT TRAVEL BY WATERCRAFT AND EVACUATE LOW LYING
COASTAL AREAS IMMEDIATELY UNTIL ADVISED THAT IT IS SAFE TO RETURN.

PEOPLE SHOULD STAY CLEAR OF LOW LYING AREAS ALONG COASTAL RIVERS AS
TSUNAMI WAVES CAN TRAVEL UP FROM THE MOUTH OF COASTAL RIVERS.

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT
TO KEEP YOU INFORMED OF THE PROGRESS OF THIS EVENT. IF AVAILABLE...
REFER TO THE INTERNET SITE HTTP://TSUNAMI.GOV FOR MORE INFORMATION.

DUE TO RAPIDLY CHANGING CONDITIONS ASSOCIATED WITH TSUNAMI WAVE
ACTIVITY...LISTENERS ARE URGED TO TUNE TO LOCAL EMERGENCY ALERT
SYSTEM MEDIA FOR THE LATEST INFORMATION ISSUED BY LOCAL DISASTER
PREPAREDNESS AUTHORITIES. THEY WILL PROVIDE DETAILS ON THE
EVACUATION OF LOW-LYING AREAS...IF NECESSARY...AND WHEN IT IS SAFE
TO RETURN AFTER THE TSUNAMI HAS PASSED.
****************************************

It’s 4:44 pm March 11, 2011: Receive the reverse-911 phone call ‘canceling the tsunami warning’ on the coast.

****************************************

4:50pm March 11, 2011: Governor Brown “has ordered San Mateo, Del Norte, Humboldt and Santa Cruz counties to utilize state aid in handling local emergencies, and repairing “damage to ports, harbors and infrastructure” caused by the tsunami. ~ http://bit.ly/fQxMIl

March 15, 2011: Mendocino Town Seeks Aid for $4M Tsunami Damage ~ http://bit.ly/gWy090

Videos of today’s Japanese tsunami and the 8.9 earthquake ~

Video taken near Crescent City, CA morning of March 11, 2011 ~

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msnbc.com, January 27, 2010

Lots has been said about warming temperatures and rising sea levels, but a new study puts the spotlight on a more imminent threat to coastal communities: extreme waves that are growing taller in some parts of the world.

Data from buoys off the Pacific Northwest coast found that since the mid-1970s the height of the biggest waves has increased on average by nearly four inches a year. That’s about 10 feet over that period.

“The waves are getting larger,” said lead author Peter Ruggiero, an assistant geosciences professor at Oregon State University.

And that, he said, means “the rates of erosion and frequency of coastal flooding have increased over the last couple of decades and will almost certainly increase in the future.”

In the study published in the journal Coastal Engineering, Ruggiero and his colleagues report that the reasons are not completely certain.

“Possible causes might be changes in storm tracks, higher winds, more intense winter storms, or other factors,” Ruggiero said. “These probably are related to global warming, but could also be involved with periodic climate fluctuations such as the Pacific Decadal Oscillation, and our wave records are sufficiently short that we can’t be certain yet.”

The team also looked at how high a “100-year event” might be, given that planners use those scenarios in approving development projects. Using the new data set, the researchers  estimated that the biggest waves could get up to 46 feet tall — a 40 percent increase from 1970s estimates of 33 feet.

Ruggiero said that the study reinforces earlier ones showing similar trends off some other coasts, among them the U.S. Southeast Atlantic, the Northeast Pacific and southwest England. On the other hand, areas like the North Sea and the Mediterranean have shown little to no increase.

Double Whammy

Ruggiero said he’s working on a publishing another study that shows the increase in Pacific Northwest wave heights over the last 30 years “has been significantly more important than sea level rise” in terms of flooding and erosion threats to the coast.

“The bottom line,” Ruggiero said, “is that water levels have already increased in the Pacific Northwest due to wave heights and as sea level rise accelerates the region will experience a ‘double whammy’. So it is critical for engineers and planners to consider both processes.”

Both “winners and losers” are expected in terms of beach stability, with some areas gaining sand, but already some negative effects are visible in coastal towns like Neskowin, Ore.

“Neskowin is already having problems with high water levels and coastal erosion,” Ruggiero said.

“Communities are going to have to plan for heavier wave impacts and erosion, and decide what amounts of risk they are willing to take, how coastal growth should be managed and what criteria to use for structures,” he added.

Ruggiero emphasized that another factor for the Pacific Northwest is that a large earthquake could drop the shoreline by several feet, worsening the impact of extreme waves.

That proved to be the case in Sumatra, Indonesia, during the 2004 quake and tsumani, he said, and some of the shoreline there dropped by up to five feet.

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DAVID PERLMAN, San Francisco Chronicle, January 11, 2010

The powerful earthquake that rocked the seabed off the Northern California coast near Eureka on Saturday underscores the complexity of seismic dangers within the Earth’s crust, and is likely to be followed by a large aftershock this week – but it is not expected to exceed the 6.5 magnitude of the temblor that was felt as far away as Reno, scientists said Sunday.

A “probability report” from the U.S. Geological Survey said there is a 65% chance for a “strong and possibly damaging aftershock” from the temblor in the next seven days. As many as 90 weaker aftershocks are expected to be felt in local communities, the report said, but it’s not probable any will be larger than Saturday’s mainshock.

More than 20 smaller aftershocks – some with magnitudes larger than 4 – churned the seabed throughout the day Sunday.

Although Californians are most conscious of the quakes that constantly hit the San Andreas Fault Zone, where its many offshoots include the dangerous Rodgers Creek and Hayward faults, offshore quakes are extremely common.

Saturday’s quake was unrelated to the San Andreas, but struck within the southern end of an offshore geological feature of the Earth’s crust called the Gorda Plate, according to David Oppenheimer, a seismologist with the Geological Survey’s main research center in Menlo Park.

Scientists have long known that the entire crust of the Earth is composed of vast crustal plates that are constantly in slow movement. The familiar San Andreas Zone, for example, marks the boundary between the huge Pacific Plate and the North American Plate, and when these two plates suddenly slip after building up pressure grinding past each other, potentially deadly quakes are the result.

The Gorda Plate, with its eastern edge along the coasts of California and Oregon, is a much smaller slab of the crust, and above it lies a far larger segment of the crust called the Juan de Fuca Plate that extends along the coast well north of Seattle and Vancouver Island.

The San Andreas Fault’s northern end veers sharply west at Point Arena in Mendocino County, and there the fault is known as the Mendocino Fracture Zone. That area – the most seismically active in the continental United States – marks the southern edge of the Gorda Plate and the boundary between the Gorda and Pacific plates.

“It’s a highly complex region,” Oppenheimer said, “and the convergence of all these plates has generated earthquakes of many types.

Saturday’s powerful temblor was known as a “strike-slip” quake, where the convergence of the Pacific and Gorda plates caused one side to slip past the other.

The Gorda and Juan de Fuca plates, however, form part of an offshore crustal segment called the Cascadia Subduction Zone where the huge slabs dip deep beneath the North American Plate and can cause truly giant quakes every few hundred years. Those quakes actually are the tectonic forces that have raised the volcanic Cascade Mountains, including – in California – Mounts Shasta and Lassen.

Saturday’s offshore quake struck 18 miles deep within the Gorda Plate, in an area very close to the epicenters of two large aftershocks that followed a magnitude 7.1 earthquake on land near Petrolia and Cape Mendocino on April 25, 1992.

Those two aftershocks, centered 16 miles offshore and within the Gorda Plate’s southern edge, registered magnitudes of 6.6 and 6.7. They were very similar, Oppenheimer said, to Saturday’s 6.5 magnitude mainshock – which struck at 39 seconds past 4:27 p.m., 23 miles northwest of Ferndale and 29 miles southwest of Eureka.

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