April 12, 2008
Elaine Meinel Supkis
I have been too busy to post earth news lately but Mother Nature is now possibly going to have yet another underwater violent event that can trigger many other violent events. One of the greater dangers on this planet besides the entire coast of all of Indonesia and much of Japan is the entire West Coast of the USA. I have been watching a series of fairly big jolts happen at the very, very dangerous level of 10 kilometers under the earth, along the southern coast of Oregon. This is the infamous 'Triple Juncture' where three huge plates converge and these create not only earthquakes but huge tsunamis and spectacular volcanic eruptions. Tonight, the jolts are migrating south towards the San Andreas Fault. Also, many micro earthquakes are happening in this juncture. Time to discuss the geology of the most dangerous parts of the USA.
Scientists listening to underwater microphones have detected an unusual swarm of earthquakes off central Oregon, something that often happens before a volcanic eruption — except there are no volcanoes in the area.
Scientists don't know exactly what the earthquakes mean, but they could be the result of molten rock rumbling away from the recognized earthquake faults off Oregon, said Robert Dziak, a geophysicist for the National Oceanic and Atmospheric Administration and Oregon State University.
There have been more than 600 quakes over the past 10 days in a basin 150 miles southwest of Newport. The biggest was magnitude 5.4, and two others were more than magnitude 5.0, OSU reported.
On the hydrophones, the quakes sound like low thunder and are unlike anything scientists have heard in 17 years of listening, Dziak said. Some of the quakes have also been detected by earthquake instruments on land.
The Great Boxing Day earthquake started the same way. I noticed not only a series of 3-5 mag earthquakes, there was this huge cluster of much lower earthquakes. Then the whole thing blew out. The Sumatra earthquake happened when there was a solstice as well as a full moon. The full moon this month will be April 20th.
The Earth and moon are closest together—at perigee—once a month. The Earth and sun are closest together—at perihelion—once a year. Perihelion currently occurs in early January. Maximum gravitation force occurs when a syzygy and perigee occur on the same day as perihelion.
According to Berkland, seismometers left on the moon by Apollo astronauts show that moonquakes occur most frequently at perigee.
"So we know Earth's gravity triggers moonquakes. I don't think any scientist disputes that," Berkland said. "When I learned that, I went to my former [U.S. Geological Survey] colleagues in Menlo Park [California] and pointed out this really exists, so what's so difficult about turning it around?"
According to Berkland, the U.S. Geological Survey said such a theory is ridiculous—the Earth is 82 times more massive than the moon. Though the Earth can trigger quakes on the moon, they said, the moon is too small to trigger any earthquakes.
But the moon is mostly solid and lacks a liquid core like the Earth, Berkland said. The Earth "is an active, living planet, and so it is not at all surprising that minor gravitational stresses can trigger earthquakes," he said.
And Berkland is probably correct. Our planet is not a dead rock. It is very much 'alive'. Mars is not geologically alive. Venus is crushed by a vile atmosphere. But the earth is quite fluid. So fluid, even after a billion years, the land masses merrily float about the surface so easily, whole sections get run over by other sections. The earth also has layers. These vary greatly in thickness and materials.
One thing I have noticed over the years is that the Greater Quakes all come at the 10 kilometer level. This seems to be a vital separation point in the lithosphere. There is a great deal we don't know despite an army of fine geologists moving rapidly to write the geological history of this wonderful and dangerous planet. The main thing here is, these series of earthquakes are happening in a place and time as well as depth that leads me to issue of possible warning:
Tsunamis are always initially invisible. If the point of origin is far enough at sea, the earthquake launching it may be much milder on land than in the deep canyons where massive displacement of ocean bed can trigger a tsunami. It is nearly impossible to predict when these events will happen. But the fact that the plates next to Oregon and California are grinding their gears very badly at this most dangerous depth, and since these quakes are obviously moving down the major canyons in this area, the place most likely to give birth to tsunamis, this means to be on the alert for this possibility.
It has only been 4 years since the huge displacement/jump in the sea next to Sumatra happened. The new stresses at the opposite end of the Pacific Plate have yet to be released in an equally big quake. Let's look further into this history of tsunamis and quakes that rock alternately, the Asian rim and the North American West Coast:
Robert P. Dziak1 , Christopher G. Fox1, Andra M. Bobbitt2 and Chris Goldfinger3
Full-coverage multibeam bathymetric maps of the southern section of the Juan de Fuca Plate, also known as the Gorda Plate, are presented. The bathymetric maps represent the compilation of multibeam surveys conducted by the National Oceanic and Atmospheric Administration during the last 20 yrs, and illustrate the complex tectonic, volcanic, and geomorphologic features as well as the intense deformation occurring within this region. The bathymetric data have revealed several major, previously unmapped midplate faults. A series of gently curving faults are apparent in the Gorda Plate, with numerous faults offsetting the Gorda Plate seafloor. The multibeam surveys have also provided a detailed view of the intense deformation occurring within the Gorda Plate. A preliminary deformation model estimated from basement structure is discussed, where the southern part of the plate (south of ∼42°30′ N) seems to be deforming through a series of left-lateral strike-slip faults, while the northern section appears to be moving passively with the rest of the Juan de Fuca Plate. The bathymetry also demonstrates the Mendocino and Eel Canyons are prominent morphologic features in the northern California margin. These canyons are active depositional features with a large sediment fan present at the mouths of both the Mendocino and Eel canyons. The depositional lobes of these fan(s) are evident in the bathymetry, as are the turbidite channels that have deposited sediment along the fans over time. The Trinidad Canyon is readily evident in the margin morphology as well, with a large (∼10 km) plunge pool formed at the mouth of the canyon as it enters the Gorda Plate sediments.
Always, when there is severe deformations, these resolve themselves very explosively. We talk about 'snapping points' or 'stress points' when discussing any dynamic system. All systems can, if they are sufficiently dynamic, build up points where conflicts can't be resolved easily. These build up more and more energy and the parts frozen in place get increasingly crushed and warped. Then it explodes suddenly. The only way to not have this happen is for the forces at work to dissipate or vanish. Whether we are talking about economics, politics or nature, this process is the same.
So whenever I read that a geologically active region is either rising rapidly for collapsing rapidly, we can expect something dramatic. In the case of rising, these massive 9+ mag events cause sudden subsidence. This, in turn, can trigger landslides that rush in to fill the dropping space. Lisbon, Portugal, for example, had a very violent earthquake long ago and the lower parts of the city subsided and vanished into the ocean as well as the city being swept by a tsunami.
Kevin P. Furlong
Geodynamics Research Group, Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16801; email: email@example.com
Susan Y. Schwartz
Earth Sciences Department and IGPP, University of California, Santa Cruz, California 95064; email: firstname.lastname@example.org
Abstract The migration of the Mendocino triple junction through central and northern California over the past 25–30 million years has led to a profound change in plate interactions along coastal California. The tectonic consequences of the abrupt change from subduction plate interactions north of the triple junction to the development of the San Andreas transform system south of the triple junction can be seen in the geologic record and geophysical observations. The primary driver of this tectonism is a coupling among the subducting Juan de Fuca (Gorda), North American, and Pacific plates that migrates with the triple junction. This coupling leads to ephemeral thickening of the overlying North American crust, associated uplift and subsequent subsidence, and a distinctive sequence of fault development and volcanism.
The San Andreas has been fairly quiet. But as we can see from the map at the top, the line of earthquakes lead towards the San Andreas Fault system. This system is notorious for sudden, violent lurches. Usually, in sections. But these sections are quite capricious. Humans have chosen to build along this dangerous fault line. Many water, electrical and transportation systems run along this huge, totally unstable fault line system. Salton Sea, for example, didn't exist when my grandpa drove one of the first cars through that place back in 1900. But then, there was an earthquake and the canal system broke and flooded that depression and the lake was born. The whole length of Baja California used to be part of the landmass of Mexico but over the eons, has seen the central valley subside more and more until the ocean flooded in. Death Valley is well below sea level. And will eventually be flooded, too.
Indeed, over the next several million years, all of Central Valley of California will probably be flooded. Many people don't realize how low it is relative to the ocean because of the mountains on the coast protecting it from the fury of the sea.
Following the discovery of the first buried marsh sequences on land, Adams (1990) used existing cores to test the possibility that the Cascadia cores contained a record of Holocene great earthquakes of the Cascadia margin. Fortunately, Oregon and Washington cores all contain a unique datable event, the ash layer from the eruption of Mount Mazama, at 7627 ± 150 cal yr BP (Zdanowicz et al., 1999). The ash was distributed to the channel system via the drainage basins of major rivers, similar to the distribution of Mt St. Helens ash following the 1980 eruption (Nelson et al., 1968). Only channel cores contain the ash, indicating that airfall offshore was not significant.
Adams (1990) examined core logs for Cascadia Basin cores, and determined that nearly all of them had 13 turbidites overlying the Mazama ash. Following the discovery of the first buried marsh sequences on land Adams, (1990) assessed the possibility that turbidites in channels of Cascadia Basin contained a record of great earthquakes along the Cascadia margin. He found that cores along the length of Cascadia channel contain 13 turbidites and argued that these 13 turbidites correlate along the channel. Adams observed that cores from Juan de Fuca Canyon, and below the confluence of Willapa, Grays, and Quinault Canyons, contain 14-16 turbidites above the Mazama ash. The correlative turbidites in Cascadia channel lie downstream of the confluence of these channels. If these events had been independently triggered events with more than a few hours separation in time, the channels below the confluence should contain the sum of the tributaries, from 26-31 turbidites, not 13 as observed (Figure 1). The importance of this simple observation is that it demonstrates synchronous triggering of turbidite events in tributaries, the headwaters of which are separated by 50-150 km. Similar inferences about regionally triggered synchronous turbidites in separate channels are reported in Pilkey (1988). This elegant relative dating technique is used extensively in our Cascadia and SAF work.
Using 54 new cores in Cascadia, we have confirmed and extended the event record temporally and spatially. Thirteen post-Mazama and 18 Holocene events are found along~ 660 km of the margin in the Cascadia, Barclay, Willapa, Grays, and Rogue Canyon/Channel systems between latitudes 42N and 48N. The most recent event took place in 1700 AD (Satake et al., 1996; Nelson et al., 1995), and an additional 12 turbidite events have occurred during the preceeding 7200 years, yielding a mean recurrence time of ~575 years.
Let's keep this 500 year time frame in mind. The West Coast has a number of active volcanoes. The further up one goes, the more violent the earthquakes and numerous the active volcanoes. Alaska has the most active volcanoes and 9+mag earthquakes up there have had huge effects much further south. Yellowstone's caldera activities changes whenever there is a great quake up in Alaska, for example. Not to mention tsunamis triggered in Alaska have killed people in Washington State and Oregon.
The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demonstrated that the North America—Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the Cascadia region. The shock occurred just north of the Mendocino Triple Junction and caused strong ground motion and moderate damage in the immediate area. Rupture initiated onshore at a depth of 10.5 kilometers and propagated up-dip and seaward. Slip on steep faults in the Gorda plate generated two magnitude 6.6 aftershocks on 26 April. The main shock did not produce surface rupture on land but caused coastal uplift and a tsunami. The emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity.
This was north of this week's quake cluster. Note that it, too, was at the 10 kilometer depth. Also, a 7.1 is a large quake but not a great quake. Those are 8.5 and greater.
Recent research shows that at any time the Pacific Northwest can experience large earthquakes and accompanying tsunamis, and that tsunamis have affected the Oregon coast on a regular basis over time. Scientists have not yet had time to do local studies that will be able to tell you how high a tsunami may be in any one area and how far you must run inland or how high you must climb to escape. The best general advice available today is to (1) go up to 2 miles inland if you are in a low-lying area or at least 100 feet above sea level if you can; and (2) go on foot if at all possible because of traffic jams and earthquake damage.
A tsunami wave increases in height as it approaches shore. Typical wave heights from tsunamis occurring in the Pacific over the last 80 years have been between 21 to 45 feet at the shoreline. A few waves, however, have been much higher- as much as 100 feet or more because of local conditions. Also, tsunamis may affect local areas differently, causing great damage and loss of life in one area but little in another.
Anyone living in any part of the West Coast should review what one needs if these periodic and inevitable events happen. Living as if there is no need to prepare is not recommended. When I was a child, my grandparents warned me to NEVER turn my back to the ocean but to learn the danger signs of a tsunami. Even today, I have occasional dreams where I see the ocean suddenly withdraw and I try to run as fast as possible. Once, I was caught in a bad wave. As usual, as other people were trusting and ignoring the horizon, I noted a dark line that grew bigger as it approached us. I yelled to everyone to run as fast as possible inland. Two fishermen saw it too and we grabbed some children and ran. The wave struck us and lifted us and the children into the air and we swam to the piers and grabbed hold so we wouldn't be sucked back into the sea.
Luckily, it was a rouge wave and not a tsunami.
But Americans have moved endlessly towards the oceans. We love living on beaches. Most of the time, it is fun. But we have to remember the trade-offs. I had a girlfriend who had to be pulled from her disintegrating house in Coney Island during a fierce winter storm. Below is a story from 2004, when the people of this planet were horrified to see an extreme example of a tsunami:
Earthquake-caused tsunamis as severe as those that swept southeast Asia on Sunday have happened in the past off the Oregon coast, according to a University of Oregon geoscientist.
In fact, a tsunami caused by a magnitude 9.0 earthquake occurred on Jan. 26, 1700, wiping out Oregon tribal villages in low-lying coastal estuaries and causing damage as far away as Japan. Ray Weldon, who researches and teaches about of geologic hazards, says he hopes coastal residents will be motivated to learn about Oregon's tsunami potential in light of the devastation along the coasts of nine Asian nations on the Indian Ocean.
Weldon is leading a team of scientists studying uplift along the coast and how it informs the size of future earthquakes and tsunamis. He says a comparison of modern uplift rates in the Pacific Northwest to that predicted by models of past earthquakes--like that big one of 1700--reveals many similarities.
"This tells us that the subduction zone is accumulating strain for the next great earthquake," he says. Historically, such events tend to occur, on the average, every 300 to 500 years.
That was 300 years ago. And in the same area where these new quakes are now happening. Because of this fact, the state of Oregon should be issuing tsunami warnings. Ignoring this so tourists can relive the same horrors that hit the tourist resorts in Asia, is criminal. Even if there is no earthquake, giving people an alert and showing them, via maps, the outline of previous tsunamis would be merciful as well as a civic duty. Pretending this might never happen is as foolish as the Fed pretending they have no idea how a credit crisis develops.