Earthquakes

 

Okay, so I got this photo from the internet because my attempt last year from the airplane did not turn out that well. To your left is the San Andreas Fault as it appears from the air heading into San Francisco. This is Silicon Valley ... the central place in the world for technology! In one of the James Bond movies "" the evil,power-hungry _____ is going to ignite a nuclear bomb underneath this area and release the tension built up in the fault. The resulting plate movement would be a disaster. The San Andreas Fault is perhaps the most famous fault in the world, and it is all the United States' fault!

Transform Faulting describes the interaction of plates that are sliding next to each other. This type of interaction is most familiar to us in general, and to Californians in particular, because these interactions are responsible for the earthquakes out west. When one plate is sliding alongside another, neighborhood relationships will slowly change over time.

Picture your house on the North American plate side of the San Andreas Fault. I, your neighbor, live along the same fault, but on the Pacific Ocean side, and hence my property is on the Pacific Plate. Yes ... it all looks like California, but in reality, Los Angeles is really on the Pacific Plate. Remember the three r's of realty ... Location, Location, Location. This plate is moving Northwest at a rate of 8-10 cm/yr, while North America is moving westward at only 2 cm/yr. Every evening, I might step outside and walk along the east side of my backyard white picket fence to visit with you, standing by your white picket fence at the back side of your west-facing yard. Within a year, my picket fence will have moved almost 10 cm north from yours. No longer will our fences be in alignment. In ten years, our yards will be one meter apart. If we continue to live as neighbors, by the time I am an old man (much older than now), my yard will have moved significantly north of yours. If we were both blessed with immortality, we would have new neighbors, and every several hundred years, get new ones. These motions are always happening, and therefore, the landscape is ever-changing.

 

 

 

 

 

 

We would all be happier if it were possible to grease the length of the San Andreas Fault, but the NAPA stores do not have enough for our purposes. Therefore, the plates get stuck. The forces underneath continue to apply pressure on the Pacific Plate to move north, but the plates get stuck along the fault and pressure builds up. The image below shows the areas of the fault that are presently stuck and the areas that are steadily moving forward as if they were greased. If the Pacific Plate moves north at a rate of 10 cm/yr and is stuck for 10 years, then a meter's distance of pressure remains to be released. When the plates do release at last, the Pacific Plate lunges forward that full meter to relieve the pressure, and the residents experience an earthquake.

Now, look at the photo below this paragraph and notice the San Francisco area. The San Andreas Fault runs right through San Francisco. Stanford University and the Golden Gate Bridge are on the Pacific Plate. Cal Berkeley and the Oakland Raiders are on the North American Plate, with the Bay Bridge spanning the gap. You can even see these bridges in the photo. Slowly, over time, Stanford is sliding north, away from archrival Berkeley. Eventually, the entire Stanford campus will slide up to the Aleutian Island Chain, and the palm trees will freeze ... some 65 millions years from now. Meanwhile, Los Angeleans complain about "falling into the ocean." This will not happen because LA is moving north as is hugs the coast. In 15 million years, LA will have slid all the way to Oakland. Picture life in that new community when the corner of Hollywood and Vine is now next to Haight and Ashbury!

The last major earthquake in the San Francisco took place in 1906. The quake that damaged Frisco and delayed the World Series in 1989 was not a major one, and did little to relieve the stress building up between the plates. Almost 100 years have passed, and a full 8-10 meters of movement needs to occur to release the built-up strain. There is not a multistory building constructed in such a manner to manage the sudden movement of such a potential earthquake, and it is only a matter of time before the next happens. This year marks the 100th anniversary of the famous San Francisco Earthquake of 1906. The April, 2006 National Geographic magazine ran a lead article on the possibility of a repeat event, citing the extreme damage that most certainly will occur. The USGS has a site devoted to the 100th anniversary of the 1906 quake that is really cool. Check it out at Quake Anniversary. Why people continue to build homes, offices, and other large stuctures continues to amaze me. This is a very dangerous neighborhood in which to live or even go to college, so I encourage my seniors at Hopkins to look into Canadian universities :)

Topographic Map of Minnesota

Okay, Dr. Franke ... why did you put this map of Minnesota in here, and the big map there? This is a page about tectonics. What is this map doing here? There's no hotspot under Minnesota. There is no subduction here. "So ... what gives?" you ask. You can travel to the North Shore of Minnesota and walk along the Gooseberry Falls trail to Lake Superior, and on the shore look down to find pillow lava formations. Pillow lava formations form when pahoehoe lava solidifies, such as along the shores of Hawaii. These formations along the North Shore are the result of a geologic rift which cracked open some 1.1 billion years ago when an ocean was forming. The rifting process halted, but not before a large deposit of basalt from the deep mantle welled up and gave rise to the depths of Lake Superior today. Lake Superior is deep because it is a crack in the continent whose spreading somehow stopped a long time ago. It is possible for spreading to begin anew, thus making Minnesota no safer a place to live than anywhere in the USA.

You might begin to think that there are no places in America to live where you can be free from the possibility of earthquakes, and perhaps you are correct. In the early 1811 and 1812, people living in New Madrid, Missouri awoke to some tremendous earthquakes which caused the Mississippi River to slide laterally almost 150 feet. The earthquake epicenter is depicted in the image below, and the effects of the shockwave shown.

This quake was frighteningly huge and damaging, but because few people were living there at the time, the death toll was minimized. An 11 on the Richter Scale is amazingly powerful. So ... what happened? The Earth's crust was splitting open, in the same manner as the spreading center in the mid-Atlantic is separating America from Europe. Our country is beginning a new continental divide ... and not along the Mason-Dixon Line either. The map alongside the earthquake image shows the location of earth tremors between 1975 and 1995. The line of splitting is rather obvious from the location of the tremors. Seismologists predict that a future major quake would destroy Memphis, and the death toll would be catastrophic.

Maybe we all should move north into central Canada where the original craton has survived undisturbed for billions of years :)

Within the past few years, quakes have rocked the Middle East, Afganistan, Pakistan, and Turkey. A major fault line run to the south of the Black Sea, and through the Bosporous Canal. The city of Istanbul, Turkey straddles this fault line. Geologists predict a major quake will strike this city of over 10 million people perhaps within the next 20-40 years, and the city of Istanbul advised to brace for major quake.

By Environmental News Network staff

April 28, 2000
Web posted at: 12:11 p.m. EDT (1611 GMT)

The probability is high that Istanbul, Turkey, will experience a major earthquake in the near future, an international team of scientists report in today's Science." In the next 30 years, the chance is roughly 60 percent," said Thomas Parsons, a geophysicist with the U.S. Geological Survey. Parsons and his colleagues urge a calm response to their report. Though an earthquake could occur tomorrow, they hope their finding will serve as advance warning to Turkish citizens to minimize hazards. Safety measures include fastening bookshelves and cabinets to walls, developing a safety plan in case of an earthquake and keeping a survival kit at the ready, said Parsons.

In arriving at a probability of 62 percent (with a 15 percent margin of error) for an episode of strong shaking in Istanbul, the researchers took into account the stress transfer from a magnitude 7.4 earthquake in Izmit, Turkey in August 1999. This map of Turkey traces the Izmit earthquake rupture and stresses to the Marmara Sea faults near Istanbul. Whenever an earthquake occurs at one point along a fault, it may create a higher stress level at another point. "Beginning in 1939, there were events well to the east of Istanbul that seems to have started a progressive sequence to the west. The question is, will the sequence continue further?" said Parsons. "Unfortunately, we think the answer is yes."

The researchers say that traditional models, based mainly on the average time between events, underestimate earthquake hazards on the North Anatolian fault system, where Istanbul lies, because they do not reflect the buildup of stress as earthquakes progress down the fault. The researchers assembled a catalog of major earthquakes occurring along the Yalova, Izmit, Prince's Islands and Marmara Sea faults — all faults in the North Anatolian system — since 1500. "The basic idea was to convert historical descriptions into an idea of where earthquakes happened and how big they were," said Ross Stein, Parsons' colleague at the U.S. Geological Survey. Two earthquakes occurred on the Izmit fault in 1719 and 1999, and three earthquakes ruptured the Yalova fault in 1509, 1719 and 1894, the researchers found. The central Marmara fault has been silent since 1509, and the Prince's Islands fault last broke in 1776. "Thus, at least two of the four faults are likely late in their earthquake cycles," the researchers report in Science.

Parsons and his colleagues are currently conducting a similar earthquake risk analysis for the San Francisco Bay Area in California.

MIT researchers monitoring earthquakes in Turkey say Istanbul could be next target
August 17, 1999

CAMBRIDGE, Mass. -- Yesterday's earthquake, which killed hundreds in northwestern Turkey, increased the likelihood of a future earthquake near the metropolis of Istanbul by increasing the forces on the fault just south of the city, say MIT researchers who have been studying earthquakes and tectonic deformation in Turkey since 1971. Turkey's North Anatolian fault runs east-west nearly 1,000 km and is very similar to the San Andreas fault in California. Since 1939 earthquakes have ruptured successive segments of the fault. The segment of fault ruptured yesterday is next to an unruptured segment extending westward under the Sea of Marmara. Istanbul is about 10 miles north of that area. As a result, if that particular segment ruptures in another earthquake, it could directly affect the metropolis of 12 million, said research team leader Nafi Toks?z, professor of geophysics and seismology at MIT and a native of Turkey. "[Yesterday's] earthquake increased the forces on the westward extension of the fault, increasing the likelihood of a future earthquake in this vulnerable area," he said. The last big earthquake on the North Anatolian fault occurred in 1967, just east of yesterday's temblor. The MIT team, in cooperation with universities and research centers in Turkey, is monitoring the ground deformation with great precision in and around the Sea of Marmara, using the Global Positioning System with accuracy better than 0.1 inch. These measurements showed the deformation along the fault segment that ruptured. A continuous network of monitoring stations is in the process of being established. The first of these was installed by MIT near the fault 18 months ago as part of a major research project monitoring seismicity and tectonic deformations in Turkey and surrounding areas, with a very intense effort around the Sea of Marmara, including the Izmit (site of yesterday's quake) and Istanbul areas.

The MIT research team includes Drs. Robert Reilinger, Robert King, Simon McClusky, and other members of the Department of Earth, Atmospheric, and Planetary Sciences.

DATA ON YESTERDAY'S EARTHQUAKE
A strong earthquake occurred in northwestern Turkey at the eastern extension of the Sea of Marmara at 3:01:48 local time (8:01:48 pm EDT) on August 17, 1999. The earthquake's epicenter was located 65 miles east of Istanbul, at 40.8?N latitude and 30.1?E longitude, near the town of Izmit on the North Anatolian fault. The earthquake measured 7.5 (moment magnitude) on the modified Richter scale. This was the largest earthquake in Turkey since 1976. The earthquake was followed by hundreds of aftershocks, which are still continuing. The earthquake did extensive damage to residential and industrial buildings in Izmit and surrounding areas. Preliminary reports from Turkey indicate heavy casualties, more than 1000 killed, several thousand injured, and more than a hundred thousand homeless. Property damage and some deaths occurred in Istanbul, 65 miles to the west, and in the city of Bursa, about 40 miles to the southwest of the epicenter. The most damage and casualties were in the towns on both shores of the Gulf of Izmit. This region is a highly industrialized area, and in addition to human casualties, the economic impact on the industrial facilities is likely to be in the billions of dollars. The largest earthquakes in Turkey have occurred on the North Anatolian fault. The latest episodes of earthquakes started in 1939 with a magnitude 8 earthquake near Erzincan. Earthquake activity migrated westward, rupturing the fault zone in a series of earthquakes with magnitudes 7 and greater, in 1942, 1943, 1944, 1955, and 1967.

A Triple Rift Zone in Africa

The final fault that is interesting to me is the African Rift Zone. At the southwest opening of the Gulf of Adea, three plates are separating from each other at what is called a Triple Junction of three rifts (RRR Junction). The Somalian Plate is moving to the East, the Nubian Plate is moving to the West, and the Arabian Plate is moving to the North. Click on the link to learn more about this fascinating triple rift area.

I wish that there was more time in the course to learn about Earthquakes, but right now, we must move ahead to other areas of Earth Science and keep our focus on Astronomical things :) IF THIS EARTHQUAKE STUFF REALLY EXCITES YOU ... CAUSING YOU TO TREMBLE, THEN CHECK OUT THE UNIVERSITY OF MICHIGAN GLOBAL CHANGE COURSE. Those of you who are interested in the Earth Science connection between earthquakes and people should check out the page ... Earthquakes and People.

You can move to Volcanoes , Recycling, or return to the Earth Introduction.


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