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  • richardmitnick 4:06 pm on November 16, 2015 Permalink | Reply
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    From UCSD: “From the Field: Chilean Tsunami Rocks Antarctica’s Ross Ice Shelf” 

    UC San Diego bloc

    UC San Diego

    Scripps Institution of Oceanography UCSD
    Scripps Institution of Oceanography

    Chance timing leads to first seismic observations of tsunami impacts on an ice shelf

    Nov 13, 2015
    Peter Bromirski

    1
    Servicing a seismic station in subzero temperatures and high winds. Photo courtesy of Spencer Niebuhr

    The magnitude 8.3 earthquake on Sept.16, 2015 off the coast of Chile generated a tsunami that was felt throughout the Pacific. Serendipitously, a Scripps Institution of Oceanography, UC San Diego-led project has a broadband seismic array deployed on the Ross Ice Shelf (RIS) in Antarctica.

    These seismic stations made the first large-scale broadband seismic array observations of the response of an ice shelf to tsunami arrivals. A team of Scripps researchers now in Antarctica is recovering seismic data from 34 seismic stations spanning the ice shelf. Strong signals generated by the tsunami impacting the shelf were detected at all stations from which data has been recovered, with the expectation that the entire ice shelf was rocked.

    Because the shortest direct path for the tsunami to the RIS goes through West Antarctica, refraction and scattering by seafloor ridges and seamounts must have diverted the tsunami energy that impacted the RIS.

    Ice shelves are slabs of ice that extend from land over the ocean like a half-cover on a jacuzzi. Ice shelves provide a buttressing effect, restraining the flow of grounded ice sheets to the sea. When this restraint is removed, the flow of land ice into the ocean accelerates, raising sea level. The Ross Ice Shelf is the largest ice shelf in Antarctica that covers an area of the Ross Sea roughly the size of Texas, and restrains West Antarctic grounded ice sheet that could contribute as much as three meters of sea-level rise.

    The seismic survey studying the vibrations of the Ross Ice Shelf (RIS) in response to ocean wave impacts will provide information on the structure and strength of the RIS, giving baseline “state-of-health” ice shelf measurements that will be used to identify the magnitude of changes in its integrity over time.

    The servicing of the stations installed in November 2015 involves flying by Twin Otter aircraft to the stations and uncovering the instrument recording boxes buried by about 3-4 feet of snow. The Scripps team, led by Peter Bromirski with Anja Diez, Zhao Chen, and Jerry Wanetick, swap out the disc drives that contain the full year of data. Temperatures at the stations during data recovery have ranged from about -15 to -26° C (5 to -15° F), with winds as high as 40 knots.

    The National Science Foundation Division of Polar Programs-funded project will continue collecting seismic and GPS data for another full year, including through the austral winter.

    The triggers that initiated the collapse of the Larsen B Ice Shelf in 2002 and the Wilkens Ice Shelf in 2008 have not been identified. While tsunamis were not factors in those events, West Antarctic ice shelves are exposed to circum-Pacific-generated tsunamis that could provide the trigger for the collapse of weakened ice shelves, removing their restraining influence.

    Institutions participating in the study include Woods Hole Oceanographic Institution, Washington University in St. Louis, Colorado State University, and Penn State University.

    See the full article here .

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    UC San Diego Campus

    The University of California, San Diego (also referred to as UC San Diego or UCSD), is a public research university located in the La Jolla area of San Diego, California, in the United States.[12] The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha).[13] Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. UC San Diego is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. UC San Diego was ranked 8th among public universities and 37th among all universities in the United States, and rated the 18th Top World University by U.S. News & World Report ‘s 2015 rankings.

     
  • richardmitnick 3:34 pm on October 2, 2015 Permalink | Reply
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    From CBS: “Is ancient 800-ft megatsunami wave a sign of things to come?” 

    CBS News

    CBS News

    October 2, 2015
    Michael Casey

    Temp 1
    The tsunami generated by Fogo’s collapse apparently swept boulders like this one from the shoreline up into the highlands of Santiago Island. Here, a researcher chisels out a sample. RICARDO RAMALHO

    Off the west coast of Africa, scientists have found evidence that tens of thousands of years ago a collapsing volcano sparked a megatsunami producing waves up to 800 feet high.

    The tsunami, which engulfed an island 30 miles away, raises questions over whether such a collapse poses a threat to people living on volcanic islands today. By comparison, waves from biggest tsunami in modern times – the 2004 Indian Ocean tsunami – were only 100-feet tall.

    The apparent collapse occurred some 73,000 years ago at the Fogo volcano, one of the world’s largest and most active island volcanoes. These days, it towers 2,829 meters (9,300 feet) above sea level, and erupts about every 20 years.

    2
    Pico do Fogo

    “(Collapses) probably don’t happen very often,” said Ricardo Ramalho, who did the research as a postdoctoral associate at Columbia University’s Lamont-Doherty Earth Observatory and is the lead author of a new study in Science Advances. “But we need to take this into account when we think about the hazard potential of these kinds of volcanic features.”

    Ramalho and his colleagues found the evidence of the ancient megatsunami on Santiago Island, about 55 kilometers (34 miles) from Fogo. Today the island is home to some 250,000 people.

    The researchers spotted unusual boulders – some as big as delivery vans – lying as far as 2,000 feet inland and nearly 650 feet above sea level. The only realistic explanation the scientists could come up with for how they got there: A gigantic wave must have ripped them from the shoreline and lofted them up.

    To date the event, Ramalho and Lamont-Doherty geochemist Gisela Winckler measured isotopes of the element helium embedded near the boulders’ surfaces. Such isotopes change depending on how long a rock has been lying in the open, exposed to cosmic rays. The analyses centered around 73,000 years – well within an earlier estimate of a smaller event.

    The analysis “provides the link between the collapse and impact, which you can make only if you have both dates,” said Winckler.

    Tsunami expert Bill McGuire, a professor emeritus at University College London who was not involved in the research, said the study “provides robust evidence of megatsunami formation [and] confirms that when volcanoes collapse, they can do so extremely rapidly.”

    “Our point is that flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis,” said Ramalho.

    Though some scientists question whether a volcano of this size really would collapse, the new study is the latest evidence to support concerns about the threats posed by volcanic flanks. Several have collapsed over the past several hundred years, including eight smaller ones in Alaska and Japan.

    A handful of previous other studies have proposed much larger prehistoric collapses and resulting megatsunamis, in the Hawaiian islands, at Italy’s Mt. Etna, and the Indian Ocean’s Reunion Island. But critics have said these examples are too few and the evidence too thin.

    Based on his own work, McGuire said that such megatsunamis probably come only once every 10,000 years.

    “Nonetheless,” he said in a statement, “the scale of such events, as the Fogo study testifies, and their potentially devastating impact, makes them a clear and serious hazard in ocean basins that host active volcanoes.”

    Ramalho cautions that the study should not be taken as a red flag that another big collapse is imminent here or elsewhere. “It doesn’t mean every collapse happens catastrophically,” he said. “But it’s maybe not as rare as we thought.”

    Still, he said the Fogo eruption last year produced lava flows that displaced some 1,200 people, and destroyed buildings including a new volcano visitors’ center. “Right now, people in Cape Verde have a lot more to worry about, like rebuilding their livelihoods after the last eruption,” said Ramalho. “But Fogo may collapse again one day, so we need to be vigilant.”

    See the full article here .

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  • richardmitnick 4:32 pm on September 8, 2015 Permalink | Reply
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    From NBC: “Study Finds Greater Tsunami Risk From Southern California Quake” 

    NBC News

    NBC News

    Sep 8 2015
    Charles Q. Choi, LiveScience

    Californians may be used to hearing about the threat of potentially deadly earthquakes, but a new study finds that quake-triggered tsunamis pose a greater risk to Southern California than previously thought.

    Tsunamis are monster waves that can reach more than 100 feet (30 meters) high. They are often caused by earthquakes; the 2004 Banda Aceh earthquake and tsunami killed about 250,000 people, while the 2011 Tohoku earthquake and tsunami that struck offshore of Japan killed about 20,000 people and triggered a nuclear disaster.

    Tsunamis increase in size as the depth of water in which they occur decreases. Since water depth is usually shallow near coastlines, tsunamis can grow as they approach land, becoming particularly dangerous along heavily populated coastlines, such as those in Southern California, the researchers said.

    1
    Map of regional peak tsunami amplitude in meters resulting from an earthquake on the Pitas Point and Lower Red Mountain fault system. The thin solid black line indicates the coastline and the thick black line indicates the Pitas Point fault trace. Kenny Ryan, UC Riverside

    Scientists focused on the Ventura Basin in Southern California, which has offshore faults that can probably generate earthquakes of magnitude 7 or greater. The researchers created 3D models of ruptures on the 31-mile-long (45 kilometers) Pitas Point and 22-mile-long (35 km) Lower Red Mountain undersea faults.

    Although homes and buildings on the coastlines directly opposite these faults would naturally be vulnerable to any tsunamis, until now, additional low-lying areas farther to the east were not necessarily expected to be in harm’s way. The new study suggests the cities of Ventura and Oxnard might be under greater threat of tsunami flooding than was previously thought.

    In the computer simulation, a tsunami generated by a magnitude-7.7 earthquake on the Pitas Point and Lower Red Mountain faults divided in two. One wave moved north toward Santa Barbara, reaching the city about 5 minutes after the quake. The other wave moved south toward Santa Cruz Island, but the shape of the coastline and seafloor then unexpectedly caused the southward wave to change direction toward the cities of Ventura and Oxnard.

    The simulation showed the tsunami could reach up to 23 feet (7 m) high at Ventura and Oxnard and flood up to 1.2 miles (2 km) inland less than 30 minutes after the quake, penetrating twice as far inland at some locations as California’s official tsunami-inundation line.

    “This is a severe, but plausible, scenario,” study lead author Kenny Ryan, a geophysicist at the University of California, Riverside, told Live Science.

    The scientists detailed their findings in the Aug. 18 issue of the journal Geophysical Research Letters.

    See the full article here .

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  • richardmitnick 4:41 pm on August 19, 2015 Permalink | Reply
    Tags: , Tsunami,   

    From UCR: “Computer Models Show Significant Tsunami Strength for Ventura and Oxnard” 

    UC Riverside bloc

    UC Riverside

    August 19, 2015
    Iqbal Pittalwala

    Study led by UC Riverside seismologists shows modeled tsunami resulting from simulated earthquake in Ventura basin first propagates south but then turns unexpectedly toward Ventura/Oxnard

    1
    Topographic/bathymetric map of onshore/offshore Southern California, with height and depth in meters. The Red Mountain and Pitas Point faults are considered in this study. Triangles indicate direction of dip; faults without triangles are considered strike-slip. Letters show approximate (central) city locations: SB = Santa Barbara; V = Ventura; O = Oxnard. Inset shows the map boundary in black. Image credit: Kenny Ryan, UC Riverside.

    Few can forget the photos and videos of apocalyptic destruction a tsunami caused in 2011 in Sendai, Japan. Could Ventura and Oxnard in California be vulnerable to the effects of a local earthquake-generated tsunami? Yes, albeit on a much smaller scale than the 2011 Japan earthquake and tsunami, according to computer models used by a team of researchers, led by seismologists at the University of California, Riverside.

    According to their numerical 3D models of an earthquake and resultant tsunami on the Pitas Point and Red Mountain faults – faults located offshore Ventura, Calif. – a magnitude 7.7 earthquake would result in many parts of the regional coastline being inundated a few kilometers inland by a tsunami wave, with inundation in places greater than that indicated by the state of California’s current reference inundation line.

    Study results appear in Geophysical Research Letters.

    “The hazard from earthquake-generated tsunamis in the Ventura/Oxnard area has received relatively little attention,” said Kenny J. Ryan, a graduate student in the Department of Earth Sciences at UC Riverside and the first author of the research paper. “For our study, the shape of the coastline and seafloor produce the most interesting effects on the tsunami, causing a southward moving tsunami to refract – and therefore rotate – and focus on the Ventura/Oxnard area. Unfortunately, the Ventura/Oxnard area has relatively flat topography along the coast, so a tsunami can inundate that area quite effectively.”

    Tsunamis are mainly generated by earthquakes. Sustained by gravity, they are long ocean waves that increase in amplitude (the tsunamis become larger) as water depth decreases. Since water depth is generally shallow near coastlines, the tsunami can grow in size as it approaches land, becoming particularly hazardous along heavily populated coastlines such as the Southern California coastline. Capable of achieving propagation speeds of about 435 miles per hour in deep water, tsunamis can get reflected and refracted due to changes in topography/bathymetry along shorelines.

    3
    Map of regional peak tsunami amplitude in meters resulting from an earthquake on the Pitas Point and Lower Red Mountain fault system. The thin solid black line indicates the coastline and the thick black line indicates the Pitas Point fault trace. The fault trace is where the fault surface intersects the seafloor; it is seen as a straight line in the east-west direction. Note that significant regional tsunami inundation occurs. Image credit: Kenny Ryan, UC Riverside.

    In their study, the researchers used two different modeling codes: one for the earthquake and one for the tsunami. The vertical seafloor deformation from the earthquake model was used as input into the tsunami model to generate the tsunami. The tsunami code then calculated tsunami propagation and inundation.

    “Our study is different in that we use a dynamic earthquake model to calculate seafloor displacement from the earthquake,” said coauthor David D. Oglesby, a professor of geophysics in whose lab Ryan works. “Dynamic models such as these calculate movement in time by looking at the forces on and around the fault in time. They are physics-based, and fault slip distribution and ground motion are calculated results of the models.”

    A magnitude 7.7 earthquake generated by the researchers’ models along the Pitas Point and Red Mountain faults results in the following scenario:

    The earthquake occurs much more rapidly than the tsunami. First, the fault slips (within the first 20 seconds of the model) and seismic waves propagate outward in all directions. The seafloor is permanently deformed from the earthquake. This happens in less than a minute.
    The tsunami is generated by the permanent vertical displacement of the seafloor, and begins to propagate outward through the ocean.
    Part of the tsunami propagates north and arrives at the northward coastline, where Santa Barbara is located, in approximately five minutes. Also, part of the tsunami propagates south toward the deeper water in the Santa Barbara Channel. Because of deeper water here and the local bathymetry, this southward propagating tsunami begins to refract after five to ten minutes, rotating counterclockwise in the direction of Ventura and Oxnard. Meanwhile, some of the tsunami waves are being reflected off the regional coastline. These refracted and reflected waves focus toward Ventura and Oxnard in 15-20 minutes and begin to inundate that area in less than 30 minutes.
    The entire regional coastline sees a tsunami wave train that inundates many parts of the coastline in the region. The tsunami inundation in Ventura/Oxnard is significant in the model owing to a combination of factors: large slip and seafloor displacement from the modeled earthquake scenario, refraction, focusing, and Ventura/Oxnard’s flat topography that facilitates water flowing inland.

    “The models result in large tsunami amplitudes northward and eastward of the fault due to the shape of the coastline and seafloor,” Ryan explained. “The probability of such an event in a given time frame is low compared to smaller earthquake events. Nonetheless, it is crucial to investigate the possible effects from such rare but plausible earthquake and tsunami scenarios so that a full hazard assessment can be made. Results from such modeling efforts can help reveal potential regions of high tsunami hazard.”

    Research has shown that the faults in the Ventura basin in Southern California are capable of generating earthquakes of magnitude 7 or greater as well as significant local tsunamis. Research has also shown that tsunamis generated locally by faulting and landslides offshore California can impact the California coastline in a matter of minutes.

    4
    David Oglesby and Kenny Ryan (seated). Photo credit: I. Pittalwala, UC Riverside.

    “Our study describes one potential earthquake and tsunami scenario along the Pitas Point and Red Mountain faults, and is designed to illustrate the usefulness of rupture modeling in determining tsunami inundation,” Ryan cautioned. “It is not intended to give an overall distribution of all possible earthquakes and tsunami hazards in this region. Our models simply give an indication of what may be possible in this region.”

    Ryan and Oglesby were joined in the research by Eric L. Geist at the U.S. Geological Survey and Michael Barall at Invisible Software, San Jose, Calif. Geist applied the tsunami models and serves as Ryan’s tsunami mentor. Barall wrote the earthquake software and guided Ryan through the use of the software.

    The research was supported by the Southern California Earthquake Center, which is funded by the National Science Foundation and the U.S. Geological Survey.

    5
    Map of localized peak tsunami amplitude, in meters (around Ventura, CA), resulting from slip on the Pitas Point and Lower Red Mountain fault system. The solid black line indicates the coastline. The solid red line is the statewide tsunami inundation map coordinated by the California Emergency Management Agency. Letters indicate example locations (approximate): SB = Santa Barbara; VH = Ventura Harbor; SCRM = Santa Clara River Mouth; MSB = McGrath State Beach; CIHE = Channel Islands Harbor Entrance. Inset shows the map boundary in black. Note that inundation from the model is significantly greater in many places than the statewide estimate. Image credit: Kenny Ryan, UC Riverside.

    See the full article here.

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    The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

    Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

    We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

     
  • richardmitnick 8:24 am on August 18, 2015 Permalink | Reply
    Tags: , Tsunami,   

    From U Washington: “UW researchers model tsunami hazards on the Northwest coast” 

    U Washington

    University of Washington

    August 17, 2015
    James Urton

    1
    The coast of the Pacific Northwest from space.SeaWiFS Project, NASA/Goddard Space Flight Center, ORBIMAGE

    2
    Wave height of the tsunami from the 2011 Tohoku earthquake off the east coast of Japan.NOAA

    Recent press and social media coverage have reminded residents of the Pacific Northwest that they live in a seismically active region. Stretching offshore from northern California to British Columbia, the Cascadia subduction zone could slip at any time, causing a powerful earthquake and triggering a tsunami that would impact communities along the coast.

    4
    The area of the Cascadia subduction zone.

    Scientists from multiple disciplines at the University of Washington and other institutions are learning more about this hazard. Dozens of UW scientists are part of the M9 Project, a research endeavor funded by the National Science Foundation to study the Cascadia subduction zone and communicate information about potential hazards to government officials and the public. Key goals of the M9 Project include mathematical modeling of tsunami waves, which tries to predict where and how an earthquake-triggered wave will affect the coast.

    Two University of Washington scientists — applied mathematics professor Randy LeVeque and affiliate professor of Earth and space sciences Frank Gonzalez — recently talked about how they model tsunami hazards along the Northwest coast.

    How did you become involved in the field of tsunami modeling?
    Randy LeVeque: In 2003 or 2004, my former doctoral student Dave George started applying Clawpack — a software we developed here to model wave propagation — for tsunamis just before the Indian Ocean tsunami happened. I started working with Frank Gonzalez, who at the time was the director of NOAA’s Center for Tsunami Research here in Seattle. Frank had all of these contacts in the tsunami community and the hazard community because he had already been working on this for 30 years.

    How do you model tsunami danger on a stretch of coastline?
    LeVeque: We use GeoClaw, the tools we adapted from Clawpack to be used specifically for geophysical modeling. We originally geared GeoClaw for tsunamis, but it’s also been used for storm surge modeling and there’s a version now for landslides and debris flows.

    What information do you put into your models?
    LeVeque: The software is set up so you can easily put in a new region just by having a fine-scale topographic digital elevation model for that particular region. The U.S. is pretty good about doing fine-scale mapping down to a resolution of about 33 feet along the coast. We also need some representation of what the earthquake will be and how the seafloor is moving, because the motion of the seafloor is what’s driving the tsunami.

    Have recent earthquakes and tsunamis helped improve your models?
    Frank Gonzalez: Very much so. For example, after the 2011 Tohoku earthquake and tsunami in Japan, geologists and seismologists learned that splay faulting may be more common than was believed before.

    What is splay faulting?
    Gonzalez: Ordinarily in an earthquake, there’s a lot of slippage far below the ocean floor and it simply raises up the ocean bottom. But in the case of Tohoku, the rupture extended all the way up to the ocean floor — these are splay faults, which are angled to the main fault, and where the seafloor itself can rupture. And it’s believed that that’s a very efficient mechanism for generating large tsunamis. We’re now including splay faulting as an option for models.

    What areas along the Washington coast have you modeled?
    LeVeque: Pretty much up and down the coast. We did some modeling of La Push and Neah Bay to develop tsunami inundation maps, for example. We’re just now starting models for some communities in the Strait of Juan de Fuca — like Port Townsend and Port Angeles.

    6
    La Push

    7
    Neah Bay

    8
    The Strait of Juan de Fuca is the wide waterway stretching from the Pacific Ocean on the west to the San Juan Islands on the east, with Vancouver Island to the north and the Olympic Peninsula to the south. The Strait of Georgia lies north of the San Juans. Puget Sound is the narrower waters south of the Strait of Juan de Fuca.

    How would a tsunami from a large offshore earthquake affect Puget Sound?
    LeVeque: The tsunami would be coming from the open ocean, so it would come in through the Strait of Juan de Fuca and come down to Puget Sound. We’re just starting to look down there. But by the time the tsunami gets down into Puget Sound it will be smaller than on the coast.
    Gonzalez: But in the case of a big magnitude-9 offshore earthquake, that will create shaking severe enough in Puget Sound to trigger small to moderate landslides, and they’ll create tsunamis as well.

    So, is the tsunami danger in Puget Sound not as bad as the open coast?
    LeVeque: Not nearly as much danger during an earthquake along the Cascadia subduction zone. But there’s also the Seattle Fault, which runs right across the Sound, and others like the Tacoma Fault and the South Whidbey Island Fault. These faults are actually under Puget Sound and can have big earthquakes and cause tsunamis.
    Gonzalez: That Seattle Fault tsunami has been modeled by others. That wave is quite severe, quite high. And the magnitude used to generate that wave is only about 7.5, as opposed to a magnitude-9 earthquake off the coast. And since those models for the Seattle Fault were published, there’ve actually been many more Puget Sound faults discovered.

    9
    Seattle Fault map

    3
    Geology of the Cascadia subduction zone.USGS

    How useful can your models be for communities in tsunami hazard areas?
    Gonzalez: People take the kind of information Randy and I provide about tsunami hazard and assess the vulnerability of communities, and emergency management officials assess preparedness efforts.
    LeVeque: In Westport they just had their groundbreaking in January to build a new vertical evacuation structure for tsunamis at Ocosta Elementary. It happens to sit on a relatively high part of that peninsula. From the modeling that we did, it looks like under a worst-case scenario that the area right around the school would have only a couple of feet inundation.

    What would you like to improve or change about your approach to tsunami modeling?
    LeVeque: Well, they’re based on particular models of possible earthquakes, but we could always get one that’s different or even worse. So, we’re also looking at doing probabilistic hazard assessments of the coast. That’s where we don’t just look at the worst case. We look at many scenarios.
    Gonzalez: That approach gets us results to say that one area has a much higher probability of flooding than another area. Eventually I think emergency managers will want those kinds of maps. It provides a more sophisticated view of the hazard. Not just worst-case, but what the probability is of each scenario and if there is a more likely case we should prepare for instead.
    LeVeque: That’s useful information to know if you’re deciding where to put a hospital or road.

    What do you think the public most misunderstands about tsunami modeling?
    LeVeque: Most people probably don’t understand how little is known about what the next earthquake might look like — all the sources of uncertainty that you have to deal with to come up with any model of what a tsunami will do. That’s why one big goal of the M9 Project is to develop better probabilistic techniques for both tsunamis and earthquakes, and to figure out how to communicate those probabilities to the public and emergency managers.
    Gonzalez: There is a big educational effort that is ongoing. Randy and I go to community meetings and handle questions on the science of tsunami risks and give short presentations. You have to be really, really careful and specific in sending a message to the public.

    What do you like best about your work on tsunami modeling?
    LeVeque: It’s a discovery topic, with people learning things all the time. That makes it interesting.
    Gonzalez: What’s really fun about this is you’re on the cutting edge, and you’re collaborating outside of your field. It’s very interdisciplinary. You’re talking to geophysicists, civil engineers, emergency managers. So there’s a lot of variety, and you’re developing projects that are meaningful — they’ll save lives and property.

    See the full article here.

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  • richardmitnick 1:12 pm on August 8, 2015 Permalink | Reply
    Tags: , KQED, , Tsunami   

    From KQED via UC Santa Cruz: “What Would Really Happen If a Tsunami Hit San Francisco?” 

    UC Santa Cruz

    UC Santa Cruz

    KQED bloc

    August 5, 2015
    Johanna Varner, KQED Science

    1

    As part of our series Bay Curious, we’re answering questions from KQED listeners and readers. This question comes from Steven Horowitz, who wanted to know:

    If a tsunami were to hit the Golden Gate, what would be its real effect on communities facing the San Francisco Bay?

    Steven’s question came from watching the summer’s action flick, “San Andreas.”

    “I was sitting there watching the giant tsunami course through the Golden Gate and into the bay,” he says. “I looked at that and thought: Wouldn’t there be some kind of dissipation coming through the Golden Gate?”

    It’s All About Our Faults

    Despite the terrifying image of a 500-foot wave about to wash over the Golden Gate Bridge, tsunamis do not actually pose a considerable threat to the Bay Area.

    It all has to do with the kinds of geologic faults that we have (and don’t have).

    Tsunamis are caused when a tectonic plate under the ocean smashes into and slides underneath a continent.

    6
    The tectonic plates of the world were mapped in the second half of the 20th century.

    That process, known as subduction, never happens smoothly or quietly. It shakes up the seabed, displacing a huge volume of ocean water that races across the ocean, and eventually floods the shore.

    But the San Andreas Fault is different.

    7
    Map of the San Andreas Fault, showing relative motion

    It’s called a slip-strike fault because the two plates slide past each other horizontally. Of course, any time plates move, the ground shakes. But here, there is no subduction and no displaced ocean.

    Meaning no killer tsunamis. Even San Francisco’s infamous 1906 earthquake generated only a 4-inch wave at the Presidio gauge station.

    Small Waves Still Pack a Punch

    Although they aren’t generated here, tsunamis do occasionally hit our shores. Since 1850, more than 50 tsunamis have been recorded in San Francisco Bay. Most were generated by earthquakes in subduction zones near Russia, Japan or Alaska.

    Eric Geist, a geophysicist at the U.S. Geological Survey in Menlo Park, says that size is the most important factor in evaluating risk.

    “We can look at anything, from huge waves to micro-tsunamis, that you’d never see with your eyes but our instruments can detect,” he says.

    The worst tsunami to hit the Bay Area was triggered in 1964 by a magnitude 9.4 earthquake in Alaska, Geist says. That wave rolled in at just under 4 feet and damaged marinas and private boats in Marin County.

    The infamous 2011 tsunami that devastated parts of Japan also arrived in the East Bay 10 ten hours later at just over a foot in height, and caused millions of dollars of damage in Crescent City.

    2
    The 2011 Japanese tsunami, photographed as it arrived in Emeryville.

    The Cascadia subduction zone, which runs roughly from Mendocino County to Vancouver Island, could also produce a massive earthquake and tsunami.

    8
    The area of the Cascadia subduction zone.

    But Geist says it’s unclear how a tsunami from “The Really Big One” would affect the Bay Area.

    “Oregon, Washington and California north of Eureka would really bear the brunt of that tsunami,” he explains.

    But What If a Big One Arrived?

    Although it’s unlikely, Steven Ward, a professor of Earth & Planetary Sciences at UC Santa Cruz, has created a series of animations to show how a big tsunami might spread through San Francisco Bay.

    In Ward’s simulations, the incoming wave stands just over 16 feet tall. This is much larger than historical tsunamis, but Geist agrees that a wave this size is theoretically possible.

    Approaching the Golden Gate at 55 mph, the wave would first hit the outlying areas of Point Reyes National Seashore and Montara. It would then start to flood low-lying areas like Half Moon Bay.

    “It’s not like splash and dash,” explains Ward. “When the water comes in, it’s going to flood.”

    It would feel like a 12-hour tidal cycle was packed into an hour.

    “And it will do as much damage when it goes back out and drags along cars and debris,” he adds.

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    A 30-foot-high tsunami would barely reach the top of the pylon on the Golden Gate Bridge. (Salim Virji/Flickr)

    The original wave and splashbacks from shore would then start to pile up as they squeeze through the 1-mile-wide Golden Gate Strait. In Ward’s simulations, the wave reaches a maximum height of about 30 feet.

    “That’s barely to the top the pylon,” says Ward, who is confident that the bridge would have no trouble withstanding the wave energy. “It probably wouldn’t even touch the steel.”

    Finally, the wave would fan out into San Francisco Bay. Parts of Mission Bay and the Marina could see significant flooding, but by the time it reached Treasure Island or the East Bay, the wave would be less than 3 feet tall. It would probably not even make it to the South Bay.

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    Red regions of San Francisco may be vulnerable to inundation by a tsunami.

    Verdict: San Francisco Is Relatively Safe

    Steven Horowitz, who asked Bay Curious the question, was glad to hear that the tsunami would be nothing like the movie.

    “By the time it gets to Berkeley, which is where I’m sitting right now, I think I’m pretty safe,” he says. “Sounds like it’s not going to come rushing up University Avenue.”

    Bay Area residents can also rest assured that there have been no recorded deaths from tsunami-related events in San Francisco. And even a worst-case-scenario Cascadia tsunami would take several hours to reach the city, providing ample time to mobilize a response.

    And just in case, the City and County of San Francisco has a tsunami plan in place. It includes a strategy for evacuating people from vulnerable areas like Ocean Beach, coordinating basic services (like shelter, water, food, and medical attention) and performing search and rescue.

    Still, “if you get a warning and are in a tsunami zone, follow the evacuation instructions,” says Ward. “What do you have to lose, a couple hours of your time?”

    See the full article here, and you can view the animations referred to above.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

     
  • richardmitnick 4:31 pm on December 27, 2014 Permalink | Reply
    Tags: , , Tsunami   

    From NASA Earth Observatory: “Coastal Recovery in Aceh Province, Sumatra” 

    NASA Earth Observatory

    NASA Earth Observatory

    On December 26, 2004, one of the largest earthquakes in recorded history reshaped the floor of the Indian Ocean. The magnitude 9.1 Sumatra-Andaman temblor generated tsunami waves that caused widespread damage to nations around the Indian Ocean, with most of the damage affecting Indonesia. One decade later, recovery is apparent in areas such as this stretch of coastline along the island of Sumatra in western Indonesia.

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    The series of natural-color images above shows a small area along the Sumatran coast in Aceh province, north of Meulaboah. In this region, the wave cut a swath of near-total destruction 1.5 kilometers (roughly one mile) in most places, but penetrating farther in many others.

    The first two images, acquired with Landsat 7’s Enhanced Thematic Mapper Plus (ETM+) on December 13, 2004 (top) and December 29, 2004 (middle), show the area before and after the tsunami crashed ashore. The third image, acquired by the Operational Land Imager (OLI) on Landsat 8, shows the same scene almost ten years later on November 15, 2014 (bottom).

    According to research published in 2010, coastline along the Aceh coast eroded back about 500 meters (1,600 feet) during the tsunami. Along straight coastline north of Meulaboah, beach ridges running parallel to the shoreline eroded and streams became connected directly to the ocean. Within weeks, however, observations showed a new coastline beginning to emerge that closely resembled the old one. Within a few years, beach ridges were recovering and vegetation was returning.

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    Tsunami wave field in the Bay of Bengal one hour after the M=9.1 Sumatra-Andaman Earthquake. View to the northwest.

    With a magnitude of 9.1–9.3 this is the third largest earthquake in the world. It caused the entire planet to vibrate as much as 1 centimetre and triggered other earthquakes as far away as Alaska. The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters high. [Wikipedia]

    The great Sumatra–Andaman tsunami has been observed in 14 countries in South Asia and East Africa. The tsunami caused more casualties than any other in recorded history and was recorded nearly world-wide on tide gauges in the Indian, Pacific and Atlantic Oceans. Seiches were observed in India and the United States. Subsidence and landslides were observed in Sumatra. According to our SWE results, the tsunami wave reveals the propagation through the whole Indian Ocean and shows the wave hitting the adjacent coast- line areas. Wave continues to propagate through the open ocean reaching the coastline of Africa. On its arrival on shore, the height of the tsunami varied greatly, depending on its distance and direction from the epicentre and other factors such as the local bathymetry. Reports have the height ranging form 2-3 m at the African coast near Kenya. Simulation revealed the height of tsunami waves reaching the Kenyan coastline of ap- proximately the same height. The tsunami was observed also in Struisbaai, South Africa, where a 1.5 m high tide surged on shore. Similar results were observed in the simulation.

    Imagery produced by VAPOR (www.vapor.ucar.edu), a product of the Computational Information Systems Laboratory at the National Center for Atmospheric Research

    Liew, Soo Chin et al., (2010, February 1) Recovery from a large tsunami mapped over time: The Aceh coast, Sumatra. Geomorphology 114 (4), 520-529.
    NASA Earth Observatory:Natural Hazards Earthquake Spawns Tsunamis. Accessed December 25, 2014.
    National Academy of Engineering (2007) Engineering for the Threat of Natural Disasters. Accessed December 25, 2014.
    U.S. Geological Survey FAQ – Everything Else You Want to Know About this Earthquake & Tsunami. Accessed December 26, 2014.

    NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey and the Landsat Project Science Office. Caption by Kathryn Hansen.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Earth Observatory’s mission is to share with the public the images, stories, and discoveries about climate and the environment that emerge from NASA research, including its satellite missions, in-the-field research, and climate models. The Earth Observatory staff is supported by the Climate and Radiation Laboratory, and the Hydrospheric and Biospheric Sciences Laboratory located at NASA Goddard Space Flight Center.

     
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