Glob Warm Earthquakes Landslides

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GLOBAL WARMINGThe "Hockey Stick" diagram is a graphicillustration of how the atmospheric temperatureof our planet has increased dramatically overthe past 1000 years.

Global warming is attributed to a rise in carbondioxide (and other greenhouse gases) in ouratmosphere. However, the Earth has alsoexperienced natural periods of global coolingduring periodic "ice ages" and global warmingduring the inter-glacial periods. These glacialcycles are shown below. We have had foursuch cycles in the last 400,000 years. TheEarth is currently experiencing a natural periodof global warming due to the inter-glacial cyclethat we are currently in. As the plot belowshows, this warming has been associated withincreasing CO2. However, superimposed on this

natural period of warming is additional warming caused by even greater amounts of CO2 generated bythe burning of fossil fuels since the beginning of the industrial revolution.

EARTHQUAKE SCIENCEFAULTS

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TEST YOURSELF:

(1) Find the fault.(2) Find the hanging wall and the footwall.(3) Determine the relative movement of each.(4) What type of fault is this?(5) What type of stress generated this fault?

THERE WILL ALWAYS BE A LOCALIZED AREA OF TENSION OR COMPRESSION IN THE BEND OF A STRIKE-SLIP FAULT.

Test yourself: In the figures below determine whether these faults are left-lateral or right-lateral, and then determine whether the bends are charaterized by tensional stress or compressionalstress.

SEISMIC WAVES:

HYPOCENTER = the source of the earthquake

EPICENTER = area on surface, above hypocenter

Slip at the hypocenter releases energy, resultingin the development of seismic waves that traveloutward in all directions. Some travel throughthe body of the Earth (body waves), whereasothers will travel along the Earth's surface(surface waves).

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BEHAVIOR OF GROUND MATERIALS AND BUILDINGS:

Seismic waves will slowdown as they travelthrough looser andlooser ground materials.Notice that the amplitude(height) of the waves alsoincreases in the loosestmaterials, thus generatinggreater degrees of groundshaking.

LIQUEFACTION - Loose ground material(cubic packing, left) will become morecompacted during severe earthquakevibrations (hexagonal packing, right). Wateris then forced out of the small volume ofpore space in the more compacted materials,thus rising upward to liquifiy the uppersurface. Liquefaction results in sinking ofbuildings, lateral flow of the ground, and thedevelopment of sand blows (or blow holes).

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FAULTS IN AND AROUND SAN DIEGO:

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HISTORICAL EARTHQUAKE EVENTS:

San Francisco (1906) -- The April 18, 1906 earthquake was one of the largest to occur in North Americain historic times (M8.3). The earthquake was centered near SF. Despite the severity of the groundvibrations, the greatest amount of damage (80%) was caused by the ensuing fires. The city was not builtto withstand earthquakes. Not only did buildings collapse, but both water and gas pipes were ruptured.The gas leaks caught fire and there was no water to stop the flames. One of the most devastating fires(known as the "ham and eggs fire") was started by a housewife making ham and eggs without realizingthat her chimney had fallen away. The fire ravaged the city for three days and burned an area of 520 cityblocks. About 700 people died directly from the earthquake, and up to 5000 deaths occurred in theensuing months due to epidemics of hideous diseases. An outbreak of bubonic plague was reported inover 150 cases.

New Madrid (1811-1812) -- Although the vast majority of earthquakes occur along plate tectonicboundaries, there are occasional earthquakes that occur within tectonic plates, and these are thereforecalled intraplate earthquakes. The U.S. has experienced two such earthquakes, both in the last century:(1) New Madrid, MO (1811-1812), and Charleston, SC (1886; seismic moment = 7.4). There is very littlewe know about the cause of these earthquakes. However, we do know that (1) they are often of largemagnitude, (2) they probably occur along zones of weakened crust, and (3) fortunately, their recurrenceintervals are large (probably around 500-800 years).

The small town of New Madrid is located in southeast Missouri along the banks of the Mississippi River.The town was near the epicenter of three great earthquakes that occurred over 53 days in late 1811 andearly 1812 (Dec 26, Jan 23, and Feb 7). The Modified Mercalli projections suggest that they were at leastas large as the 1906 San Francisco earthquake, and probably greater at about 8.5. There were over 1500powerful aftershocks.

These earthquakes may have been felt over a larger area than any known historic earthquake. Extensivedamage occurred over an area covering 7 states, and it was strong enough to knock down chimneys inCincinnati (400 mi away), rattle doors and chimneys in Washington D.C. (800 mi), and ring a church bellin Boston (1200 mi). Luckily this region of the Mississippi River valley was sparsely populated. It had onlyrecently been purchased by the US in 1803 in the Louisiana Purchase. If such earthquakes would occurtoday, the damage and loss of life would be enormous (12 million people now live within a radius of 100km).

Near the epicenter, entire forests were flattened. Thousands of square kilometers of prairie landsubsided, and geysers of sand and sulfurous gas erupted (we don't know why). The earthquake produceda new lake and two waterfalls on the Mississippi River (each with a drop of about 6 feet), and it causedthe Mississippi River to locally reverse its course.

One eyewitness described the scene at New Madrid in this account:

"The earth observed to roll in waves a few feet high with visible depressions between. By and by theseswells burst throwing up large volumes of water, sand, and coal (liquefaction and 'sand blows')."

". . . the shocks were clearly distinguishable into two classes, those in which the motion was horizontal(Love wave) and those in which it was perpendicular (vertical? -- Rayleigh wave). The latter wereattended with explosions and a terrible mixture of noises, but they were by no means as destructive asthe former (i.e., side-to-side Love waves were more destructive)."

Lisbon (1755) -- As powerful as the New Madrid quakes were, they were small in comparison to thethree earthquakes that struck Lisbon, Portugal in 1755. These earthquakes were also in an intraplatesetting. The epicenter was located outside the harbor of Lisbon. The three quakes struck in rapidsuccession over a two-hour period in the morning of November 1. The first was the greatest, estimated tohave had a magnitude of 9.0. It lasted for an incredible 6 to 7 minutes. This earthquake is considered bymost seismologists to be the greatest earthquake in recorded history.At the time of the earthquake, Lisbon was a very wealthy capital city, and a center for European culture.

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The earthquakes essentially demolished the entire city, including all of its finest buildings, churches, andpalaces. What wasn't destroyed by the ground vibrations was destroyed by the resulting fires. In all,about 60,000 people were killed, and damage was recorded throughout adjacent Spain and across theMediterranean in North Africa. The shocks were felt as far north as Sweden.In addition to the quake destruction, a giant tsunami struck the town. The water first emptied from theharbor, then swept back engulfing much of the city with waves up to 50 feet high. The same Tsunamitraveled clear across the Atlantic Ocean to produce 12-foot waves that crashed against the shores of theCaribbean Islands, 3500 miles away. Nothing of this magnitude has ever been recorded before or since.

Alaska (1964) -- The most violent earthquake recorded inNorth America, however, was near Anchorage, Alaska onGood Friday, March 27, 1964. The epicenter was located offthe coast in Prince Edward Sound (midway betweenAnchorage to the west and the port of Valdez to the east),within the eastern Aleutian subduction zone (a convergentplate boundary).

The earthquake had a magnitude of 9.2, which is 900 timesthe energy of the Northridge CA earthquake. It lasted 3-4

minutes, killed 131, and generated 24 aftershocks, 10 of which were >6. The earth vibrations generated2-m height (6 feet) oscillations waves (known as seiches) in the Gulf of Mexico which destroyed smallboats in Texas. The damage would have been much worse if it weren't for the low population.

The amount of crustal deformation for this earthquake was the most extensive ever recorded. Many areaswere uplifted and many others were downdropped. Several low-lying settlements and many miles of thecoastal railroad were dropped below the level of high-tide. Landslides were ubiquitous, with numerousrock and snow avalanches, and slope failures. Soil liquefaction played a major role in most landslides.

A major tsunami was created by the crustal deformation, and smaller submarine landslides produced localtsunamis Most of the deaths (121) were from these tsunami, with the local, slump-generated tsunamiaccounting for 71 of the deaths. The major tsunami caused extensive damage along the British Columbiacoast and took 16 lives in coastal Oregon and California.

RECENT SOUTHERN CALIFORNIA EARTHQUAKES -- We've had 5 strong earthquakes hit southernand central California in the last 20 years. Four of these are described here: the Loma Prieta earthquakein 1989, the Landers and Big Bear earthquakes in 1992, and the Northridge earthquake (1994).

Loma Prieta (1989) -- On October 17, 1989 a 7.1 magnitude earthquakeoccurred in the Santa Cruz Mountains, about 80 km south of San Francisco.This was the Loma Prieta earthquake. Movement occurred along a 40-km longsegment of the San Andreas fault. This same segment was designated by theUSGS in 1988 as the most likely section of the northern San Andreas fault torupture in the next 30 years!

Despite its distance from San Francisco and Oakland, the earthquake did atremendous amount of structural damage in the Bay area ($7 billion in propertydamage). There were 12,000 people displaced from their homes, over 3500injuries, and 67 deaths.

There were three sites that were particularly damaged:

Nimitz Freeway -- Most of the deaths (41) occurred in Oakland when the upper deck of Interstate880 (the Nimitz Freeway) collapsed onto the lower deck.

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San Francisco-Oakland Bay Bridge -- Like the Nimitz freeway, this is a two-deck bridge. Youmight remember the home video of a car driving into an open breach between a collapsed spanon the upper deck. The bridge was fixed in less than a month, but to this day many residents arestill afraid to use it.

Marina District -- Liquefaction played a significant role in structural damage. This was most evidentin the San Francisco Marina District, just east of the Golden State Bridge. The Marina District wasan expensive real-estate development built on land-fill. This same area was a lagoon at the timeof the 1906 San Francisco earthquake, but it was latter filled with sand and rubble from the earlierearthquake. There were 35 buildings in the Marina District torn down, and 150 others that werestructurally damaged. There were two reasons for the damage: (1) liquefaction, and (2) poorstructural design.

Landers / Big Bear (1992) -- The Landers earthquake was the most powerful shock in the contiguous 48states in 40 years. It was a 7.5 magnitude quake that occurred on the morning of June 28, 1992 in aremote area east of San Bernadino and north of Palm Springs. Its epicenter was near a small town calledLanders (110 mi east of LA). Three hours later, a 6.5 magnitude aftershock occurred 30 km west of themain shock near the mountain resort of Big Bear. More than 3000 aftershocks were recorded in fourdays.

Surprisingly, neither of these large shocks were on the San Andreas fault. Field and seismic studiesindicated that the main shock occurred along three faults trending NNW (nearly N-S): the Camp Rock,Emerson, and Johnson Valley faults. These three faults had ruptured over a linear distance more than 70km, with a maximum displacement of 6.7 m, almost as much as that of the 1906 earthquake. A number ofaftershocks occurred along this same NNW trend.

Other aftershocks, including the large Big Bear quake, occurred along a separate NE-trending fault. Thetwo fault trends intersect to form a lambda shape. At the base of the lambda is the San Andreas fault,which connects the two legs of the lambda to form a triangle. Landers movement was R-lateral, and BigBear was L-lateral, so that the triangle moved northward by about 18 feet (6.7 m, max.). Because of thelarge number of aftershocks along the NNW fault, some seismologists have predicted that this fault willreplace the San Andreas over time and evolve into the main fault accommodating R-lateral movementbetween the Pacific and North American plates.

Both earthquakes caused buildings to collapse, ignited fires, damaged water mains, and producednumerous rock slides in the San Bernadino Mountains. Most of the damage occurred in the Big Bearregion. The earthquake caused two fatal heart attacks, more than 400 injuries, and left 750 peoplehomeless, but amazingly, only one death, a small child who died when a fireplace collapsed.. For thesize of the earthquakes, the damage was relatively minor because of the sparse population of the area.

Northridge (1994) -- Whereas the Landers and Big Bear epicenters were in sparsely populated areas,the 1994 Northridge earthquake occurred in the densely populated San Fernando Valley, immediatelynorth of downtown LA. The earthquake occurred in the early morning hours of January 17, 1994. It had aRichter magnitude of 6.7. In the weeks following the main shock, there were several large aftershocks,many of them >M4.The earth shook violently for more than 40 seconds. When the initial shock was over, 61 people hadbeen killed, thousands injured, 9 freeways and thousands of homes and buildings were destroyed orseverely damaged. The damage was $20 to $30 billion.The effort placed on finding and mapping active faults in California is greater than anywhere else in theworld. Although most active faults are known, the fault that caused the Northridge earthquake wasunknown. Geologists know that most of the large California earthquakes occur on the San Andreas, or itsnumerous subsidiary faults. We have only recently come to realize that there is a network of possiblyinterconnected faults that are hidden beneath the Los Angeles basin and may cause the greatest amountof earthquake activity there. These faults show no evidence of their existence because their fault planesdo not reach the surface.

Haicheng (1975) -- In 1966, after two devastating earthquakes near Beijing, the Chinese Premier ChouEn Lai made a declaration to understand and predict future earthquakes. He called it the "People's Waron Earthquakes." To gather data, he recruited 10,000 seismologists, 100,000 citizens, and set up 250

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regional seismic stations.

The effort paid off. In late 1974 and early 1975, some unusual events occurred in southern Manchuria(Liaoning province). Among them: (1) water being drawn from wells bubbled with high levels of radon gas,and (2) thousands of snakes crept out of winter hibernation only to freeze to death on icy roads. This wasa warning to Chou En Lai's earthquake army, and they focused their attention on the region's populationcenter, Haicheng (90,000 residents). -- On the morning of February 1 (1975), a number of earth tremorsoccurred in the Haicheng area (the largest was 4.8). That afternoon, the seismologists issued anearthquake advisory and ordered the residents to extinguish their cooking fires, leave their dwellings, andevacuate to the city's parks and fields. That evening, at 7:36 p.m., a powerful earthquake (7.6) destroyedalmost 90% of the city's dwellings, so that a disaster of enormous proportions was averted. This was thefirst earthquake to be accurately predicted over the short term.

The euphoria of this spectacular prediction was short-lived, because one year the region near Tangshen,China experienced a 7.8 magnitude earthquake that killed an estimated 250,000 people. There were noprecursor events associated with this tragic event.

MASS WASTING AND LANDSLIDESMAJOR LANDSLIDE TYPES:

LANDSLIDE DISASTERS:

Gros Ventre, Wyoming (1925-1927) -- On May 18, 1927, the entire village of Kelly, Wyoming (35 kmsouth of Yellowstone NP) was wiped out by a giant flood that was indirectly related to a landslide thatoccurred two years earlier.

The Gros Ventre landslide of 1925 was a rock glide involving many of the classical conditions for a majordisaster: (1) sedimentary layers inclined towards a valley, (2) permeable sandstone above impermeableclay layers (the slide plane), and (3) the Gros Ventre River was being undercut at the base of the slope,exposing the potential slide plane. In addition, the rock mass had been saturated by Spring rains andsnowmelt, so that the entire mass suddenly and violently slid on the clay layers into the river valley. Thelandslide dammed the river, and a lake formed behind it.

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The lake rose continuously over a two year period, until the dam was breached by the rising waters. At11:00 a.m. on May 18 a wave of water 15-feet high came rushing down the river gorge and sweptthrough the floodplain where Kelly had stood. Luckily, the people of Kelly did get some advanced noticeso that only 7 of its 70 inhabitants drowned. Most of the deaths were from people trying to retrieve theirpossessions. -- The disaster could have been prevented by building a spillway through the slide mass toprevent the lake from overtopping the dam.

Vaiont Dam Disaster (1963) -- On October 9, 1963 a terrible disaster occurred in the Alps of northernItaly, near the Austrian border. A massive debris slide (2 km long and well over 200 m high) movedrapidly downslope into a reservoir behind the Vaiont Dam. The impact created a wave of water thatoverflowed the dam by 100 m and was still 70 m high about 1.5 km downstream (amazingly the dam wasnot destroyed)! The resulting flood killed nearly 3000 people downstream. The shock wave was felt byseismograph stations all over Europe. The following contributed to the slide:

(1) The rocks were dipping in the same direction as the glacial valley.

(2) The rocks were composed of highly fractured limestone with numerousinterbedded clay beds. Groundwater could easily dissolve the limestonethrough cracks and fissures, whereas the clay bed were highly susceptibleto slippage.

(3) Heavy rains occurred two weeks before the slide. This added extraweight as well as lubrication. Also -- water from the reservoir infiltrated therocks further reducing their strength.

Weeks before the slide, the entire block began to creep downslope (associated with minor landslides).This was monitored at 1 cm/day in mid-September, but was measured at 40-80 cm/day the day beforethe major slide.

Several investigators argued that the dam should never have been built, based on (1) the fact thatancient landslide scars were present on the valley walls, and (2) the poor geologic conditions.

Yungay, Peru (1970) -- On May 31, 1970, a devastating earthquake occurred in the high PeruvianAndes north of Lima. The earthquake tore loose a huge block of snow, ice. and rock from the north peakof Nevado Huascarin (6,654 m), setting in motion one of this century's worst landslides. This landslidediffers somewhat from the two just described, in that it involved a 1000-m free-fall of this huge block of

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snow, ice, and rock that then smashed to the ground and displaced thousands of additional tons of rockand generated a gigantic debris avalanche. The avalanche hurtled down the mountain's steep glacialvalley at speeds up to 320 km per hour and obliterating everything in its path.About 3 km east of the town of Yungay, part of the debris flow overrode the valley walls and withinseconds buried Yungay, instantly killing more than 20,000 of its residents. The main mass of the flowcontinued down the valley, overwhelming the other towns burying about 5,000 more people. 25,000people died in a span of roughly 4 minutes. -- Ironically, the only part of Yungay that was not buried wasCemetery Hill, where 92 people survived by running to its top.

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