Earthquakes

Workers position support beams to steady titling homes in San Francisco's Marina District after a disastrous earthquake hit the city in 1989. The 7.1-magnitude earthquake buckled highways and bridges, crushed cars, and toppled homes and buildings throughout the city. (Nichols, 2009)

A Widespread Danger• Earthquakes are one of the most costly natural

hazards faced by the United States, posing a significant risk to 75 million Americans in 39 States.

• The risks that earthquakes pose to society, including death, injury, and economic loss, can be greatly reduced by – (1) Better planning, construction, and mitigation

practices before earthquakes happen – (2) Providing critical and timely information to

improve response after they occur.USDI, 2006

USGS Earthquake Facts• The largest recorded earthquake in the United States was a

magnitude 9.2 earthquake in Prince William Sound, Alaska, on March 28, 1964.

• In 1985, a swimming pool at the University of Arizona in Tucson lost water from sloshing, or a “seiche,” caused by a magnitude 8.1 earthquake in Michoacan (pronounced Me-sho-acan), Mexico, 1,240 miles away.

• Alaska is the most earthquake-prone State and one of the most seismically active regions in the world, experiencing a magnitude 7 earthquake almost every year and a magnitude 8 or greater earthquake every 14 years (on average).

• In the United States, there are an average of 6 magnitude 6 or greater and 57 magnitude 5 or greater earthquakes each year.

• 26 major urban areas in the United States are at risk of significant seismic activity, including New York City.

USDI, 2006

What is an Earthquake?• An earthquake is any vibrating, shaking, or rapid motion of Earth’s

crust. • Most earthquakes occur when stress builds along a zone of

weakness or a break in the rock known as a fault. • The focus (or hypocenter) is the place underground where the

earthquake occurs.• The epicenter is the location at Earth’s surface just above the focus. • Faults typically allow the earth to move next to itself.• Pressures build up in the rocks on the fault to a point where stress

is so great that rocks fracture and shift along one another. • The shockwaves sent off as the rock ruptures and moves are what

we experience as an earthquake.

Karnath

Earthquake Wave Propagation

Karnath

3 Types of Basic Faults

A normal fault is caused by at least 2 sections of rock pulling apart.A reverse fault is caused by at least 2 sections of rock pushing together.A strike-slip fault is caused when at least 2 section of rock push along one another side by side.

Karnath

Diagrams of 3 Basic Faults

Karnath

The Stresses that Cause Faulting

Tension Compression ShearKarnath

Measuring Earthquakes• There are 2 types of measurement applied to earthquakes:

magnitude and intensity scales.– Intensity scales, like the Modified (Guiseppe) Mercalli scale, are based

upon the reports of people who experienced the earthquake and observed the amount of destruction.

– Magnitude scales, such as the Moment magnitude scale, measure the amount of energy released, regardless of the damage it may have produced. The estimated energy of an earthquake released is related to the amplitude (or height) of the wave. This scale is logarithmic, which is a base of 10 measurement.

• It should be noted that the (Charles) Richter scale is not a common measurement for earthquake magnitude, but has been replaced by the moment magnitude scale. With the creation of more sophisticated seismology equipment in the 1970s, scientists could determine the actual area where the rupture in the fault took place and measure how much energy was released there during the earthquake, a calculation they call the seismic moment. Because the Richter scale had become so commonly understood, they devised a method to convert the information from the seismic moment into a scale comparable to Richter's, or what's now known as the moment magnitude scale.

Karnath

Yoffe, 2001

The Modified Mercalli ScaleMercalli Intensity Observed Effects and Characteristics

I Detectable only by seismographs

II Felt by persons at rest

III Hanging objects swing; vibration like passing of light trucks

IV Most persons feel it indoors, a few out doors. Dishes and windows rattle

V Felt outdoors; sleepers awakened; liquids disturbed; unstable objects displaced.

VI Felt by all; glassware broken; books off shelves

VII Difficult to stand; noticed in motorcars; damage to some masonry; weak chimneys broken at roof line

VIII Partial collapse of masonry; twisting; fall of chimneys; frame houses moved on foundations

IX General panic; general damage to foundations; underground pipes broken; conspicuous cracks in ground

X Most structures destroyed; large landslides; water thrown on banks

XI Rails bent greatly; underground pipelines out of service

XII Damage nearly total. Waves visible on the ground.

Karnath

The Moment Magnitude ScaleMagnitude Increase in

MagnitudePossible Effects Equivalent Energy to:

0 --- Faint to most sensitive instruments

Blast a stump

1 1 Detectable by instruments Small construction blast

2 10 Barely noticeable Average quarry blast

3 100 Felt indoors Large quarry blast

4 1,000 Felt by most people; slight damage

Small atom bomb

5 10,000 Felt by all; damage minor to moderate

“Standard” atom bomb

6 100,000 Moderately destructive Small Hydrogen bomb

7 1,000,000 Major Damage Heat New York City for one year!

8 10,000,000 Total and Major Damage Heat New York City for 30 years!

9 100,000,000 Catastrophic The world’s coal and oil production for 5 years!Karnath

The Moment Magnitude Scale

Karnath

Magnitude vs. Ground Motion and Energy

Magnitude Change

Ground Motion Change(Displacement)

Energy Change

1.0 10.0 times about 32 times0.5 3.2 times about 5.5 times0.3 2.0 times about 3 times0.1 1.3 times about 1.4 times

This table shows that a magnitude 7.2 earthquake produces 10 times more ground motion than a magnitude 6.2 earthquake, but it releases about 32 times more energy. The energy release best indicates the destructive power of an earthquake.

NEIC, Feb 2009

How Much Bigger is a Magnitude 8.7 Earthquake Than a Magnitude 5.8 Earthquake?

How much bigger is a magnitude 8.7 earthquake than a magnitude 5.8 earthquake?A magnitude 8.7 earthquake is 794 times BIGGER on a seismogram than a magnitude 5.8 earthquake. The magnitude scale is logarithmic, so

(108.7-5.8) = (102.9) = 794The magnitude scale is really comparing amplitudes of waves on a seismogram, not the STRENGTH

(energy) of the quakes. So, a magnitude 8.7 is 794 times bigger than a 5.8 quake as measured on seismograms, but the 8.7 quake is about 23,000 times STRONGER than the 5.8! Since it is really the energy or strength that knocks down buildings, this is really the more important comparison. This means that it would take about 23,000 quakes of magnitude 5.8 to equal the energy released by one magnitude 8.7 event. Here's how we get that number:

One whole unit of magnitude represents approximately 32 times (actually 101.5 times) the energy, based on a long-standing empirical formula that says log (E) is proportional to 1.5M, where E is energy and M is magnitude. This means that a change of 0.1 in magnitude is about 1.4 times the energy release. Therefore, the energy is,

(32*32*32) / 1.4 = 23,405 or about 23,000 The actual formula would be:

(101.5 * 8.7)/(101.5 * 5.8) = 10 (1.5(8.7-5.8)) = 10 (1.5(2.9)) = 22,387This explains why big quakes are so much more devastating than small ones. The amplitude ("size")

differences are big enough, but the energy ("strength") differences are huge. The amplitude numbers are neater and a little easier to explain, which is why those are used more often in publications.

But it's the energy that does the damage!NEIC, June 2009

The Moment Magnitude Scale -Events Never Witnessed

Magnitude Possible Effects Equivalent Energy to:

10.0 San-Andreas type fault circling Earth

1 trillion tons of TNT

12.0 Fault Earth in half through center

160 trillion tons of TNT OREarth's daily receipt of solar

energy

Louie, 2003

How Often Do Earthquakes Occur?Earthquakes are always happening somewhere. Worldwide, strong

earthquakes happen more than once per month. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day.

IRIS, 2006

Chile (2010) – 8.8

Haiti (2010) – 7.0

Japan (2011) – 9.0

Numerical Frequency of Earthquakes of Different Magnitude Worldwide

Magnitude Number of Earthquakes per Year Description> 8.5 0.3 Great8.0 - 8.4 17.5 - 7.9 3

Major7.0 - 7.4 156.6 - 6.9 566.0 - 6.5 210 Destructive5.0 - 5.9 800 Damaging4.0 - 4.9 6,200

Minor3.0 - 3.9 49,0002.0 - 2.9 300,0000 - 1.9 700,000 Nelson, 2006

Seismograph –A Simple Tool That is Now Obsolete

• A seismograph is an instrument that measures and records the magnitude of an earthquake. A recorded seismic reading is called a seismogram.

• With the advent of computer programs, earthquake wave propagation is now recorded and displayed electronically.

Karnath

Seismic Waves• Earthquakes create 4 types of

seismic waves: P-waves(primary waves), S-waves(secondary), which transport energy through the body of the Earth. These are body waves.

• L-waves (Love waves) and Rayleigh waves transport energy along the surface of the Earth. These are called surface waves, and are usually cause the most damage.

P-Waves

S and L-WavesKarnath

Seismic Wave

Movement

USDI, 2009

Earthquake Risk• Many seismologists have said that "earthquakes don't

kill people, buildings do". This is because most deaths from earthquakes are caused by buildings or other human construction falling down during an earthquake.

• Earthquakes located in isolated areas far from human population rarely cause any deaths.

• Thus, earthquake hazard risk depends on 1. Population density 2. Construction standards (building codes) 3. Emergency preparedness

Nelson, 2008

Deadliest and Powerful Examples: Past and Recent

• The deadliest earthquake in recorded history occurred on January 23,1556 in Shaanxi (pronounced Shan-see), China. It killed 830,000 people, most living in caves excavated in poorly consolidated loess (wind deposited silt and clay). Current research shows that is may have only been a 7.9 on the moment magnitude scale.

• The deadliest earthquake in the past 100 years also occurred in China (T'ang Shan Province). It killed a confirmed240,000 in 1976. Occurred at 3:42 AM, Magnitude 7.8 Earthquake and magnitude 7.1 aftershock. Deaths were due to collapse of masonry (brick) buildings.

Nelson, 2008

Haitian Earthquake of 2010The 2010 Haiti earthquake was a catastrophic magnitude

7.0 earthquake, with an epicenter near the town of Léogâne, approximately 25 km (16 miles) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 4:53pm local time on Tuesday, 12 January 2010. By the end of February (2010), at least 59 aftershocks measuring 4.5 or greater had been recorded.

An estimated 3 million people were affected by the quake; the Haitian government reported that an estimated 316,000 people had died, 300,000 had been injured and 1,000,000 made homeless. International agencies, including the United States Agency for International Development, have suggest that the death toll is much lower at somewhere between 46,000 and 92,000, and 220,000, with around 1.5 million to 1.8 million homeless. The actual number of dead may never be known. It is one of the deadliest natural disasters in the last 100 years.

“2010 Haiti Earthquake.”, 2010

Of the dead, it includes at least 4 people killed by a local, small tsunami in the Petit Paradis area near Leogane. 300,000 had been injured and 1,000,000 made homeless. Government officials also estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged.

Although this was a strong earthquake, the energy released was 100’s of times LESS than the earthquake than the 8.8 magnitude earthquake off the coast of Chile (that killed an estimated 600 people). So why was there so much devastation from the Haitian earthquake event? Ans. Poorly constructed buildings, tightly packed together, along with little-to-no help from the Haitian government to supply medical care, electricity, or fresh water after the event allowed for 10,000’s of thousands of people to die unnecessarily.

As one should see on the next slide, this area is prone to earthquakes and should have been better prepared.

“Magnitude 8.8 - OFFSHORE MAULE, CHILE.“, 2010

“Seismic Zones of Around Hispaniola.”, 2010

The Estimated Locations of Earthquake Epicenters in the Haitian Region Since 1600 AD.

Haitian Earthquake Damage Photos

Damaged buildings in Port-au-Prince

The Haitian National Palace (Presidential Palace), located in Port-au-Prince, Haiti, heavily

damaged after the earthquake of January 12, 2010. Note: this was originally a two-story structure;

the second story completely collapsed.

“2010 Haiti Earthquake.”, 2010

Chilean Earthquake of 2010The 2010 Chilean earthquake occurred off the coast of the Maule

Region of Chile on February 27, 2010, at 03:34 local time, rating a magnitude of 8.8 on the moment magnitude scale and lasting 90 seconds. It was strongly felt in six Chilean regions that together make up 80 percent of the country's population. The earthquake triggered a tsunami which devastated several coastal towns in south-central Chile and damaged the port at Talcahuano. Tsunami warnings were issued in 53 countries, causing minor damage in the San Diego area of California and in the Tōhoku region of Japan, where damage to the fisheries business was estimated at USD $66.7 million. The earthquake also generated a blackout that affected 93% of the country's population and which went on for several days in some locations. The latest death toll as of May 15, 2010 is 521 victims

Seismologists estimate that the earthquake was so powerful that it may have shortened the length of the day by 1.26 microseconds and moved the Earth's figure axis by 8 cm! Precise GPS measurement indicated the telluric movement moved the entire city of Concepción 3.04 m (10 ft) to the west. The capital Santiago experienced a displacement of almost 24 cm (10 in) west, and even Buenos Aires, about 1,350 km (840 mi) from Concepción, shifted 3.9 cm (1.5 in). It is estimated that Chile's territory could have expanded 1.2 km² as a result!

The epicenter of the earthquake was offshore from the Maule Region, approximately 11 km (6.8 miles) southwest of Curanipe and 100 km (71 mi) north-northeast of Chile's second largest city, Concepción. The earthquake also caused seiches to occur in Lake Pontchartrain to the north of New Orleans, United States, located nearly 7,500 kilometers (4,700 mi) from the epicenter of the quake!

“2010 Chile Earthquake.”, 2010

Chilean Earthquake Damage Photos

House uprooted to the streets Pelluhue before the ensuing tsunami.

Collapsed Vespucio Norte Express Highway in Santiago.

A severely damaged building in Maipú, Santiago.

“2010 Chile Earthquake.”, 2010

Japanese Earthquake of 2011The 2011 earthquake off the Pacific coast of

Tohoku, Japan was a magnitude 9.0 (Moment Magnitude) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 32 km (20 mi). It was the most powerful known earthquake to have hit Japan, and one of the five most powerful earthquakes in the world overall since modern record-keeping began in 1900. It was so powerful the island of Honshu was moved 8 feet eastward. The earthquake triggered extremely destructive tsunami waves of up to 40.5 metres (133 ft) in Miyako, Iwate, Tōhoku. In some cases traveling up to 10 km (6 mi) inland. In addition to loss of life and destruction of infrastructure, the tsunami caused a number of nuclear accidents, primarily the ongoing level 7 meltdowns at three reactors in the Fukushima I Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. The Japanese National Police Agency has confirmed 15,676 deaths, 5,712 injured, and 4,832 people missing across eighteen prefectures, as well as over 125,000 buildings damaged or destroyed (mostly from the tsunami). The earthquake and tsunami caused extensive and severe structural damage in Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water for months. (2011 Tōhoku Earthquake and Tsunami, 2011)

Japanese Earthquake Damage Photos

Soil liquefaction in Koto, Tokyo

A convoy of fire engines in the tsunami zone

(2011 Tōhoku Earthquake and Tsunami, 2011)

• Contrast - In earthquake prone areas like California, in order to reduce earthquake risk, there are strict building codes requiring the design and construction of buildings and other structures that will withstand a large earthquake. While this program is not always completely successful, one fact stands out to prove its effectiveness. In 1989 an earthquake near San Francisco, California (The Loma Prieta, or World Series Earthquake) with a Richter Magnitude of 7.1 killed about 62 people. Most were killed when a double decked freeway in Oakland collapsed. About 10 months later, an earthquake with magnitude 6.9 occurred in Armenia, where no earthquake- proof building codes existed. The death toll in the latter earthquake was about 25,000!

Nelson, 2008

Day or Night…It’s Still Scary!!

• Computer simulations for large cities, like San Francisco or Los Angeles, California, indicate that a magnitude >8.0 earthquake would cause between 3,000 and 13,000 deaths.

• 3,000 if at night, when the populace is asleep in wood frame houses.

• 13,000 if during day when the populace is in masonry buildings and on freeways.

Nelson, 2008

Architecture and Building Codes• While architecture and building codes can reduce risk, it

should be noted that not all kinds of behavior can be predicted.– Although codes are refined each year, not all possible effects can

be anticipated. For example different earthquakes show different frequencies of ground shaking, different durations of ground shaking, and different vertical and horizontal ground accelerations.

– Old buildings cannot cost-effectively be brought up to code, especially with yearly refinements to code.

– Even with construction to earthquake code, buildings fail for other reasons, like poor quality materials, poor workmanship, etc. that are not discovered until after an earthquake.

Nelson, 2008

World Distribution of Earthquakes

• The distribution of earthquakes is called seismicity. Seismicity is highest along relatively narrow belts that coincide with plate boundaries. This makes sense, since plate boundaries are zones along which lithospheric plates move relative to one another.

• Earthquakes along these zones can be divided into shallow focus earthquakes that have focal depths less than about 100 km and deep focus earthquakes that have focal depths between 100 and 700 km.

Nelson, 2008

GLOBAL SEISMIC HAZARD WORLD MAP, 2002

This map shows in color those parts of the United States that have a 10% chance of experiencing an earthquake strong enough to cause appreciable damage in a 50-year period. In the green areas, maximum ground shaking would be 8-16% of the force of gravity, which is strong enough to damage unreinforced masonry buildings, even those built on bedrock. Darker colors are at the same risk for more intense shaking, while areas left blank would have little-to-no intense shaking. (Ground-Shaking Hazards From Earthquakes in the United States, 2011)

Seismic Hazards and Risk in the U.S.

Ground-Shaking Hazards From Earthquakes in the United States

(Ground-Shaking Hazards From Earthquakes in the United States, 2011)

Magnitude 5.8 – VIRGINIA, August 2011

Damaging Earthquakes in the US (1750 - 1996)

(Damaging Earthquakes in the US (1750 - 1996), 2009)

Top Earthquake States

EHP, Top Earthquake States, 2009

EHP, Seismicity of the United States, 2009

Earthquakes of Alaska from 1990-2006

EHP, Seismicity of the United States, 2009 (Seismicity of Alaska: 1990-2006, 2009)

Earthquakes of Hawaii from 1990-2006

EHP, Seismicity of the United States, 2009(Seismicity of Hawaii: 1990-2006, 2009)

Seismic Hazard Map of New York

Seismic Hazard Map New York, 2009

Why Do We Get Earthquakes in New York, If We are Far from Plate Boundaries?

At the present time, a commonly accepted explanation for the cause of earthquakes in the Northeast is that "ancient zones of weakness" are being reactivated in the present-day stress field. In this belief, preexisting faults and/or other geological features formed during ancient geological episodes persist in the intraplate crust, and, by way of analogy with plate boundary seismicity, earthquakes occur when the present-day stress is released along these zones of weakness. Using this model as a guide, much of the research on northeastern United States earthquakes has involved attempts to identify preexisting faults and other geological features that might be reactivated by the present-day stress field. While this concept of reactivation of old zones of weakness is commonly assumed to be valid, in reality the identification of individual active geologic features has proven to be quite difficult. Unlike the situation for many plate boundary earthquakes, it is not at all clear whether faults mapped at the earth's surface in the Northeast are the same faults along which the earthquakes are occurring. However, the approximate location of the ancient fault zone, The St. Lawrence Rift Valley, is shown on the next slide.

•There is some speculation that glacial and meteoritic rebound* are causing these ancient faults (zones of weakness) to “bounce” back up creating ground shifting/ earthquakes.

– *Glacial rebounding is when large sheets of ice, that exist for 100’s if not 1000’s of years, push the ground down by their intense weight, and when they melt, the ground gradually “rebounds” upward.

– *Meteoritic rebounding is when an impact zone that pushed the ground down then gradually “rebounds” back.

(Kafka, 2008)

(Abbott, 2008)

Seismic Hazard Map New York, 2009

Isoseimal Map of the Largest Recorded Earthquake in NY State History

• Massena, New York 1944 09 05 04:38:45.7 UTC (Local 09/04) Magnitude 5.80 Intensity VIII EHP, Largest Earthquake in New York State History, 2009

Number of Earthquakes in Japan From January 1960 Through June 2009

Jones, 2008

Japan is one of the most earthquake prone

areas in the world!

Hazards Associated with Earthquakes• Possible hazards from earthquakes can be classified

as follows: – Ground Motion - Shaking of the ground caused by the

passage of seismic waves, especially surface waves, near the epicenter of the earthquake are responsible for the most damage during an earthquake. The intensity of ground shaking depends on:

• Local geologic conditions in the area. In general, loose unconsolidated sediment is subject to more intense shaking than solid bedrock.

• Size of the Earthquake. In general, the larger the earthquake, the more intense is the shaking and the duration of the shaking.

Nelson, 2004

Hazards Associated with Earthquakes (cont.)• Distance from the Epicenter. Shaking is most severe near the epicenter

and drops off away from the epicenter. The distance factor depends on the type of material underlying the area. There are, however, strange exceptions. For example, the 1985 Mexico City Earthquake (magnitude 8.1) had an epicenter on the coast of Mexico, more than 350 km to the south, yet damage in Mexico City was substantial because Mexico City is built on soft unconsolidated sediments that fill a former lake (see Liquefaction, below).

• Damage to structures from shaking depends on the type of construction. • Concrete and masonry structures are brittle and thus more susceptible to

damage • Wood and steel structures are more flexible and thus less susceptible to

damage.

Nelson, 2004

Earthquake Effects - Ground Shaking

Loma Prieta, CA 1989

Wald, 2009

Earthquake Effects - Ground Shaking

Kobe, Japan 1995

Wald, 2009

Earthquake Effects - Ground Shaking

Kobe, Japan 1995Wald, 2009

Hazards Associated with Earthquakes (cont.)• Faulting and Ground Rupture - Ground rupture generally occurs only

along the fault zone that moves during the earthquake. Thus structures that are built across fault zones may collapse, whereas structures built adjacent to, but not crossing the fault may survive.

• Aftershocks - These are usually smaller earthquakes that occur after a main earthquake, and in most cases there are many of these (1260 were measured after the 1964 Alaskan Earthquake). Aftershocks occur because the main earthquake changes the stress pattern in areas around the epicenter, and the crust must adjust to these changes. Aftershocks are very dangerous because they cause further collapse of structures damaged by the main shock.

• Fire - Fire is a secondary effect of earthquakes. Because power lines may be knocked down and because natural gas lines may rupture due to an earthquake, fires are often started closely following an earthquake. The problem is compounded if water lines are also broken during the earthquake since there will not be a supply of water to extinguish the fires once they have started. In the 1906 earthquake in San Francisco more than 90% of the damage to buildings was caused by fire.

Nelson, 2004

Earthquake Effects - Surface Faulting

Landers, CA 1992

Wald, 2009

Earthquake Effects - Fires

Loma Prieta, CA 1989Wald, 2009

Hazards Associated with Earthquakes (cont.)• Landslides - In mountainous regions subjected to earthquakes

ground shaking may trigger landslides, rock and debris falls, rock and debris slides, slumps, and debris avalanches.

• Liquefaction - Liquefaction is a processes that occurs in water-saturated unconsolidated sediment due to shaking. In areas underlain by such material, the ground shaking causes the grains to lose grain to grain contact, and thus the material tends to flow.

• You can demonstrate this process to yourself next time your go the beach. Stand on the sand just after an incoming wave has passed. The sand will easily support your weight and you will not sink very deeply into the sand if you stand still. But, if you start to shake your body while standing on this wet sand, you will notice that the sand begins to flow as a result of liquefaction, and your feet will sink deeper into the sand.

Nelson, 2004

Earthquake Effects - Landslides

Turnagain Heights, Alaska,1964 (upper left inset);Santa Cruz Mtns, California , 1989 Wald, 2009

Nelson, 2004

Earthquake Effects - Liquefaction

Niigata, Japan 1964Wald, 2009

Hazards Associated with Earthquakes (cont.)• Changes in Ground Level - A secondary or tertiary effect that is

caused by faulting. Earthquakes may cause both uplift and subsidence of the land surface. During the 1964 Alaskan Earthquake, some areas were uplifted up to 11.5 meters, while other areas subsided up to 2.3 meters.

• Tsunamis - Tsunamis are giant ocean waves that can rapidly travel across oceans, as will be discussed in more detail later. Earthquakes that occur beneath sea level and along coastal areas can generate tsunamis, which can cause damage thousands of kilometers away on the other side of the ocean.

• Flooding - Flooding is a secondary effect that may occur due to rupture of human made dams, due to tsunamis, and as a result of ground subsidence after an earthquake.

Nelson, 2004

Earthquake Effects - Tsunamis1957 Aleutian Island, Alaska Tsunami

This first photo (in a series of three sequential photos) shows the arrival of a major wave at Laie Point on the Island of Oahu, Hawaii about 3,600 km from the source of the earthquake.

Wald, 2009Tsunami from Alaska, 2009

Earthquakes at Diverging Plate Boundaries.

• Diverging plate boundaries are zones where two plates move away from each other, such as at oceanic ridges. In such areas the lithosphere is in a state of tensional stress and thus normal faults and rift valleys occur. Earthquakes that occur along such boundaries show normal fault motion, have low Richter magnitudes, and tend to be shallow focus earthquakes with focal depths less than about 20 km. Such shallow focal depths indicate that the brittle lithosphere must be relatively thin along these diverging plate boundaries.

• Examples - all oceanic ridges, Mid-Atlantic Ridge, East Pacific rise, and continental rift valleys such as the basin and range province of the western U.S. & the East African Rift Valley.

Nelson, 2004

Remember the Types of Lithospheric Boundaries?

Wald, 2009

Earthquakes at Transform Plate Boundaries.

• Transform fault boundaries are plate boundaries where lithospheric plates slide past one another in a horizontal fashion. The San Andreas Fault of California is one of the longer transform fault boundaries known. Earthquakes along these boundaries show strike-slip motion on the faults and tend to be shallow focus earthquakes with depths usually less than about 100 km. Richter magnitudes can be large.

• Examples - San Andreas Fault, California, South Island of New Zealand.

Nelson, 2004

The San Andreas Fault (Basic) Pacific-North American Plate Boundary

Wald, 2009

Earthquakes at Convergent Plate Boundaries.

• Convergent plate boundaries are boundaries where two plates run into each other. Thus, they tend to be zones where compressional stresses are active and thus reverse faults or thrust faults are common. There are two types of converging plate boundaries. (1) subduction boundaries, where oceanic lithosphere is pushed beneath either oceanic or continental lithosphere; and (2) collision boundaries where two plates with continental lithosphere collide.

• Examples - Along coasts of South American, Central America, Mexico, Northwestern U.S., Alaska, Japan, Philippines, Caribbean Islands.

Nelson, 2004

Earthquakes at Collision Boundaries

• At collisional boundaries two plates of continental lithosphere collide resulting in fold-thrust mountain belts. Earthquakes occur due to the thrust faulting and range in depth from shallow to about 200 km.

• Examples - Along the Himalayan Belt into China, along the Northern edge of the Mediterranean Sea through Black Sea and Caspian Sea into Iraq and Iran.

Nelson, 2004

Intraplate Earthquakes

• These are earthquakes that occur in the stable portions of continents that are not near plate boundaries. Many of them occur as a result of re-activation of ancient faults, although the causes of some intraplate earthquakes are not well understood.

• Examples - Examples - New Madrid Region, Central U.S., Appalachian Mts. of the U.S., Charleston South Carolina, Along St. Lawrence River - U.S. - Canada Border.

Nelson, 2004

Earthquake Prediction and Control• Long-Term Forecasting

Long-term forecasting is based mainly on the knowledge of when and where earthquakes have occurred in the past. Thus, knowledge of present tectonic setting, historical records, and geological records are studied to determine locations and recurrence intervals of earthquakes. Two aspects of this are important.– Paleoseismology - the study of prehistoric earthquakes. Through

study of the offsets in sedimentary layers near fault zones, it is often possible to determine recurrence intervals of major earthquakes prior to historical records. If it is determined that earthquakes have recurrence intervals of say 1 every 100 years, and there are no records of earthquakes in the last 100 years, then a long-term forecast can be made and efforts can be undertaken to reduce seismic risk. Nelson, 2004

- Seismic gaps - A seismic gap is a zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks. If a seismic gap can be identified, then it might be an area expected to have a large earthquake in the near future.

o Example - The San Francisco, Loma Prieta, and Parkfield Seismic Gaps; The Istanbul, Turkey Seismic Gap

Nelson, 2004

o Shown on the next page are two cross-sections along the San Andreas Fault in northern California. The upper cross section shows earthquakes that occurred along the fault prior to October 17, 1989. Three seismic gaps are seen, where the density of earthquakes appears to be lower than along sections of the fault outside the gaps. To the southeast of San Francisco is the San Francisco Gap, followed by the Loma Prieta Gap, and the Parkfield Gap. Because of the low density of density of earthquakes in these gaps, the fault is often said to be locked along these areas, and thus strain must be building. This led scientist to issue a prediction for the Parkfield gap that sometime between 1986 and 1993 there would be an earthquake of magnitude 6 or greater south of Parkfield. No such earthquake has yet occurred. However a magnitude 7.1 earthquake occurred in the Loma Prieta gap on Oct. 17, 1989, followed by numerous aftershocks. Note how in the lower cross-section, this earthquake and its aftershocks have filled in the Loma Prieta Gap. This left the San Francisco and Parkfield gaps as areas where we might predict a future large event. However, in 2004, a Magnitude 6.0 earthquake (and subsequent aftershocks) occurred under Parkfield, filing in its gap. This now leaves the largest gap under Loma Prieta.

Nelson, 2004

Nelson, 2004

Forecasting California’s Earthquakes—What Can We Expect in the Next 30

Years?

(Field, 2008)

2008 San Francisco Bay Area Earthquake Probabilities In April 2008, scientists and engineers released a new earthquake forecast for the State of

California (previous slide) called the Uniform California Earthquake Rupture Forecast (UCERF). Compiled by USGS, Southern California Earthquake Center (SCEC), and the California Geological Survey (CGS), with support from the California Earthquake Authority, it updates the earthquake forecast made for the greater San Francisco Bay Area by the 2002 Working Group for California Earthquake Probabilities.

The accompanying figure (on the next slide) shows the updated probabilities for earthquakes of magnitude 6.7 or greater in the next 30 years. The overall probability of a magnitude 6.7 or greater earthquake in the Greater Bay Area is 63%, about 2 out of 3, which is very close to the probability of 62% obtained by the 2002 Working Group.

The earthquake probability is highest for the Hayward-Rodgers Creek Fault system, 31%, or nearly 1 out of 3. The last damaging earthquake on the Hayward Fault was in 1868. The 140 years since 1868 is same length of time as the average interval between the past 5 large earthquakes on the southern Hayward Fault.

The probability of a large earthquake on the San Andreas Fault in the next 30 years is about 21%, or about 1 out of 5. This fault was responsible for the magnitude 7.8 1906 San Francisco earthquake and the magnitude 6.9 1989 Loma Prieta earthquake.

The Calaveras Fault in the East Bay, and the San Gregorio Fault along the San Francisco Peninsula coast, have probabilities of 7% and 6%, respectively, of producing a magnitude 6.7 or greater earthquake in the next 30 years.

In the East Bay, near the Central Valley, the Greenville Fault, the Mt. Diablo Thrust, and the Concord-Green Valley Fault were assigned probabilities of 3% or less of producing a magnitude 6.7 or greater earthquake in the next 30 years. (2008 Bay Area Earthquake Probabilities, 2009)

2008 San Francisco Bay Area Earthquake Probabilities

(2008 Bay Area Earthquake Probabilities, 2009)

Previous STRONG San Francisco Bay Area Earthquakes

(Abbott, 2008)

Istanbul’s Seismic Gap Prediction

(Abbott, 2008)

Short-Term Prediction• Short-term predication involves monitoring of processes that

occur in the vicinity of earthquake prone faults for activity that signify a coming earthquake.

• Anomalous events or processes that may precede an earthquake are called precursor events and might signal a coming earthquake.

• Despite the array of possible precursor events that are possible to monitor, successful short-term earthquake prediction has so far been difficult to obtain. This is likely because:– The processes that cause earthquakes occur deep beneath the surface and

are difficult to monitor.– Earthquakes in different regions or along different faults all behave

differently, thus no consistent patterns have so far been recognized.Nelson, 2004

• Among the precursor events that may be important are the following:– Ground Uplift and Tilting - Measurements taken in the vicinity of

active faults sometimes show that prior to an earthquake the ground is uplifted or tilts due to the swelling of rocks caused by strain building on the fault. This may lead to the formation of numerous small cracks (called microcracks). This cracking in the rocks may lead to small earthquakes called foreshocks.

– Foreshocks - Prior to a 1975 earthquake in China, the observation of numerous foreshocks led to successful prediction of an earthquake and evacuation of the city of the Haicheng. The magnitude 7.3 earthquake that occurred, destroyed half of the city of about 100 million inhabitants, but resulted in only a few hundred deaths because of the successful evacuation..

Nelson, 2004

– Water Level in Wells - As rocks become strained in the vicinity of a fault, changes in pressure of the groundwater (water existing in the pore spaces and fractures in rocks) occur. This may force the groundwater to move to higher or lower elevations, causing changes in the water levels in wells.

– Emission of Radon Gas - Radon is an inert gas that is produced by the radioactive decay of uranium and other elements in rocks. Because Radon is inert, it does not combine with other elements to form compounds, and thus remains in a crystal structure until some event forces it out. Deformation resulting from strain may force the Radon out and lead to emissions of Radon that show up in well water. The newly formed microcracks discussed above could serve as pathways for the Radon to escape into groundwater. Increases in the amount of radon emissions have been reported prior to some earthquakes.

Nelson, 2004

–Changes in the Electrical Resistivity of Rocks - Electrical resistivity is the resistance to the flow of electric current . In general rocks are poor conductors of electricity, but water is more efficient a conducting electricity. If microcracks develop and groundwater is forced into the cracks, this may cause the electrical resistivity to decrease (causing the electrical conductivity to increase). In some cases a 5-10% drop in electrical resistivity has been observed prior to an earthquake.

–Unusual Radio Waves - Just prior to the Loma Prieta Earthquake of 1989, some researchers reported observing unusual radio waves. Where these were generated and why, is not yet known, but research is continuing.

–Strange Animal Behavior - Prior to a magnitude 7.4 earthquake in Tanjin, China, zookeepers reported unusual animal behavior. Snakes refusing to go into their holes, swans refusing to go near water, pandas screaming, etc. This was the first systematic study of this phenomenon prior to an earthquake. Although other attempts have been made to repeat a prediction based on animal behavior, there have been no other successful predictions.

• After the August 2011 Earthquake in Virginia (USA), many zookeepers in the Washington D.C. zoo reported strange animal activities just before the magnitude 5.8 tremor struck. Flamingos took defensive postures, snakes that normally sleep at that time refused to go in the ground, monkeys sought refuge in trees during feeding time, etc.

Nelson, 2004

Controlling Earthquakes• Although no attempts have yet been made to control

earthquakes, earthquakes have been known to be induced by human interaction with the Earth. This suggests that in the future earthquake control may be possible.

• Examples of human induced earthquakes – For ten years after construction of the Hoover Dam in Nevada

blocking the Colorado River to produce Lake Mead, over 600 earthquakes occurred, one with magnitude of 5 and 2 with magnitudes of 4.

– In the late 1960s toxic waste injected into hazardous waste disposal wells at Rocky Flats, near Denver apparently caused earthquakes to occur in a previously earthquake quiet area. The focal depths of the quakes ranged between 4 and 8 km, just below the 3.8 km-deep wells.

– Nuclear testing in Nevada set off thousands of aftershocks after the explosion of a 6.3 magnitude equivalent underground nuclear test. The largest aftershocks were about magnitude 5.

Nelson, 2004

Controlling Earthquakes (cont.)

(Abbott, 2008)

(Abbott, 2008)

In Conclusion…• Earthquakes can occur anywhere the ground shift,

but are more prone in certain areas.• Earthquakes don’t kill people, structures do.• There are many side-effects from earthquakes

that MAY do more damage and cause more deaths than the earthquake itself (i.e. tsunami)!

• Although short term forecasting of earthquakes is difficult, chances are if an area has had earthquakes in the past, it will have them again in the future!

Sources Cited• "2008 Bay Area Earthquake Probabilities." Welcome to the U.S. Geological Survey Earthquake Hazards Program. 31 Mar. 2009. 12 June

2009 <http://earthquake.usgs.gov/regional/nca/ucerf/>. • "2010 Chile Earthquake." Wikipedia, the Free Encyclopedia. 27 Aug. 2010. Web. 27 Aug. 2010.

<http://en.wikipedia.org/wiki/2010_Chile_earthquake>.• "2010 Haiti Earthquake." Wikipedia, the Free Encyclopedia. 26 Aug. 2010. Web. 27 Aug. 2010.

<http://en.wikipedia.org/wiki/2010_Haiti_earthquake>.• "2011 Tōhoku Earthquake and Tsunami." Wikipedia, the Free Encyclopedia. 24 Aug. 2011. Web. 25 Aug. 2011.

<http://en.wikipedia.org/wiki/Japanese_earthquake_2011>. • Abbott, Patrick L. Natural Disasters. 4th ed. New York: McGraw Hill - Higher Education, 2008. • "Damaging Earthquakes in the US (1750 - 1996)." U.S. Geological Survey Earthquake Hazards Program. 21 Oct. 2009. Web. 25 Aug.

2011. <http://earthquake.usgs.gov/earthquakes/states/us_damage_eq.php>. • EHP Web Team. "Top Earthquake States." Earthquake Hazards Program. 30 Jan. 2009. USGS - United States Geological Survey. 8 June

2009 <Earthquake Hazards Program>. • EHP Web Team. "Seismicity of the United States." Welcome to the U.S. Geological Survey Earthquake Hazards Program. 30 Jan. 2009.

12 June 2009 <http://earthquake.usgs.gov/regional/states/seismicity/index.php#us>. • Field, Edward H. "Forecasting California's Earthquakes--What Can We Expect in the Next 30 Years?" USGS Publications Warehouse.

Web. 25 Aug. 2011. <http://pubs.usgs.gov/fs/2008/3027/>. • "GLOBAL SEISMIC HAZARD WORLD MAP." Schweizerischer Erdbebendienst (SED) - Swiss Seismological Service. Nov. 2002.

GLOBALSEISMIC HAZARD ASSESSMENT PROGRAM. 17 June 2009 <http://www.seismo.ethz.ch/GSHAP/global/>. • "Ground-Shaking Hazards From Earthquakes in the United States." Map. USGS National Seismic Hazard Maps, Data, and

Documentation. United States Geological Survey, 17 Mar. 2011. Web. 25 Aug. 2011. <http://earthquake.usgs.gov/hazards/products/>. • IRIS - Incorporated Research Institutions for Seismology. How Often Do Earthquakes Occur? 26 July 2006. 4 June 2009

<http://www.iris.edu/hq/publications/brochures_and_onepagers/edu>. • Jones (State University of New York at Binghamton, Alan L., Lee Siebert, Paul Kimberly, and James F. Luhr. Seismic/ Eruption.

Computer software. Vers. 2.2. Alan Jones - Home Web Page. 25 Nov. 2008. 17 June 2009 <http://bingweb.binghamton.edu/~ajones/#Seismic-Eruptions>.

• Kafka, Alan L. "Why Does the Earth Quake in New England!" 16 Sept. 2008. Boston College - Weston Observatory Department of Geology and Geophysics. 8 June 2009 <http://www2.bc.edu/~kafka/Why_Quakes/why_quakes.html>.

• Karnath, Joseph P. Regents Earth Science - Earthquakes and Earth Interior Class Notes. • "Magnitude 8.8 - OFFSHORE MAULE, CHILE." U.S. Geological Survey Earthquake Hazards Program. 20 Aug. 2010. Web. 27 Aug.

2010. <http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010tfan/>.• Louie, John. "Geology 100: Earthquakes, Volcanoes, and Other Natural Disasters." Nevada Seismological Lab. The University of Nevada

: Mackay School of Earth Sciences and Engineering College of Science; Department of Geological Sciences and Engineering, Fall 2003. Web. 25 Aug. 2011. <http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html>.

Sources Cited• Nelson, Stephen A. "Earthquakes: Causes and Measurements Notes." Earth & Environmental Sciences 204 & 605 Class Website. 21 June

2006. Dept. of Earth & Environmental Sciences, Tulane University. 08 June 2009 <http://www.tulane.edu/~sanelson/geol204/eqcauses.htm>.

• Nelson, Stephen A. "Earthquake Hazards and Risks Notes." Earth & Environmental Sciences 204 & 605 Class Website. 9 June 2008. Dept. of Earth & Environmental Sciences, Tulane University. 08 June 2009 <http://www.tulane.edu/~sanelson/geol204/eqhazards&risks.htm>.

• Nelson, Stephen A. "Earthquake Prediction and Control Notes." Earth & Environmental Sciences 204 & 605 Class Website. 21 January 2004. Dept. of Earth & Environmental Sciences, Tulane University. 08 June 2009 <http://www.tulane.edu/~sanelson/geol204/eqhazards&risks.htm>. NEIC Web Team. "Earthquake Facts and Statistics." Earthquake Hazards Program. 6 Jan. 2009. USGS - United States Geological Survey. 9 June 2009 <http://neic.usgs.gov/neis/eqlists/eqstats.html>.

• NEIC Web Team. "How Much Bigger is a Magnitude 8.7 Earthquake Than a Magnitude 5.8 Earthquake? ." Earthquake Hazards Program. 18 Feb. 2009. USGS - United States Geological Survey. 9 June 2009 < http://earthquake.usgs.gov/learning/topics/how_much_bigger.php>.

• NEIC Web Team. "Largest Earthquake in New York" Earthquake Hazards Program. 30 Jan. 2009. USGS - United States Geological Survey. 17 June 2009 <http://earthquake.usgs.gov/regional/states/events/1944_09_05_iso.php>.

• Nichols, Michael K. "Natural Disasters - Earthquakes." Earthquake Photos. National Geographic. 1 June 2009 <http://environment.nationalgeographic.com/environment/photos/earthquakegeneral/marinaquakedestr.html>.

• "Seismic Hazard Map New York." Welcome to the U.S. Geological Survey Earthquake Hazards Program. 30 Jan. 2009. 12 June 2009 <http://earthquake.usgs.gov/regional/states/new_york/hazards.php>.

• "Seismic Zones of Around Hispaniola." The New York Times - Breaking News, World News & Multimedia. 26 Jan. 2010. Web. 27 Aug. 2010. <http://www.nytimes.com/imagepages/2010/01/26/science/26fault_graphic.html>.

• "Seismicity of Alaska: 1990-2006." U.S. Geological Survey Earthquake Hazards Program. 26 Oct. 2009. Web. 25 Aug. 2011. <http://earthquake.usgs.gov/earthquakes/states/alaska/seismicity.php>.

• "Seismicity of Hawaii: 1990-2006." U.S. Geological Survey Earthquake Hazards Program. 21 Oct. 2009. Web. 25 Aug. 2011. <http://earthquake.usgs.gov/earthquakes/states/hawaii/seismicity.php>.

• Tsunamis From Alaska. Digital image. Alaskan Tsunamis. USC Tsunami Research Group. 17 June 2009 <http://www.usc.edu/dept/tsunamis/alaska/>.

• U.S. Department of the Interior (USDI). USGS - The United States Geologic Survey. Earthquake Hazards—A National Threat. 7 June 2006. 1 June 2009 <http://pubs.usgs.gov/fs/2006/3016/2006-3016.pdf>.

• U.S. Department of the Interior (USDI). USGS - United States Geological Survey. USGS Earthquake Hazards Program. By Lisa Wald/ USGS Pasadena. USGS.gov. 1 June 2009 <http://earthquake.usgs.gov/learning/eq101/EQ101.htm>.

• Wald, Lisa. Earthquakes 101 (EQ101). Rep. USGS - United States Geologic Survey - Pasedena. 17 June 2009 <earthquake.usgs.gov/learning/eq101/EQ101_files/EQ101.ppt>.

• Yoffe, Emily. "Is the Richter Scale Obsolete?" Slate. Slate.com. 1 Mar. 2001. Washington Post. Newsweek Interactive Co. LLC. 8 June 2009 <http://www.slate.com/id/1007178/>.