Solid Earth Seismology

Theory, Practice, and Application to the Earth's Interior

GEOL 595 SP/L

Text Book:

Introduction to Seismology

By Peter M. Shearer

What is Seismology ?

 From the Greek root word: “

seismos

” to shake 

Seismic Waves

: elastic wave energy that propagates in solid or fluid materials.



Seismology

: the study of earthquakes and the elastic waves generated by the rupture.

What is Seismology ?



Seismic Waves

: elastic wave energy that propagates in solid or fluid materials.

-

energy creation

(earthquakes, nukes, bombs, eruptions, sonic booms)

energy transmission

(propagation, absorption, scattering, reflection, diffraction)

energy recording

(seismometry, computer storage, data transmission, etc)

societal

(e.g., forecasting earthquakes, tsunami, seismic)

What is Seismology ?

Seismology bridges:

Geology + Geophysics + Earth Science

 Seismic imaging at depth can verify whether geological observations (e.g. faults, plate boundaries,ancient sutures, granitic outcrops) on the surface continue to deeper depths in the crust or mantle.

 Earthquake aftershocks can help us map faults and plate boundaries at depth in the crust and mantle.

 Measurements of seismic anisotropy can indicate whether mineralogical alignment occurs during plate movement or shear.

 Volcano seismology measure earthquake patterns that may indicate magma rising through a volcano chamber

Mount St Helen's

movie

* Erupted 1980, Washington State * Local earthquakes felt 2 months before * Evacuations saved 1000's of people * 57 people died including Inn keeper Harry Truman, a photographer, a geologist, and many animals.

Earthquakes can tell us about Magma Flow beneath Volcanoes

- An eruption event at Mt St Helen's in September, 2005 - Can be seen in the earthquake record by deep events of magma flow

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPAN Friday, March 11, 2011 at 05:46:23 UTC

The map on the right shows historic earthquake activity near the epicenter (star) from 1990 to present. As shown on the cross section, earthquakes are shallow (orange dots) at the Japan Trench and increase to 300 km depth (blue dots) towards the west as the Pacific Plate dives deeper beneath Japan.

Seismicity Cross Section across the subduction zone showing the relationship between color and earthquake depth.

Images courtesy of the US Geological Survey

Northridge Earthquake, 1994

Northridge, 1994

Seismic image of a

blind thrust fault

at depth

Seismology and Society

Study of Seismology, seismic waves, and earthquakes Also aid in hazard analysis for communities in earthquake country.

- Earthquake risk - Earthquake Engineering - Tsunami hazard analysis

Northridge Earthquake, 1994

- January 17, 1994, 4:30 am - Magnitude = 6.9

- Blind thrust fault - Difficult to find or predict - Duration 10-20 seconds CSUN Parking Structure

Many Active Faults in Southern California

   And more offshore!

How close do you live to a fault ?

Los Angelino's need to know and need your help to prepare!

L.A. mayor's proposals for concrete, wood quake retrofits Los Angeles Times

Monday, Jan 26, 2015

The mayor's proposals for mandatory retrofits target two of the riskiest types of structures built in Los Angeles before 1980: brittle concrete buildings and multi story wooden buildings supported by weak columns on the ground floor.

lRelated L.A. mayor calls for mandatory earthquake retrofitting for thousands of buildings

L.A. mayor's proposals for concrete, wood quake retrofit The mayor's proposals for mandatory retrofits target two of the riskiest types of structures built in Los Angeles before 1980: brittle concrete buildings and multi-story wooden buildings supported by weak columns on the ground floor.

lRelated L.A. mayor calls for mandatory earthquake retrofitting for thousands of buildings

Concrete Buildings:

Retrofit deadline: 30 years Cost of retrofit: Varies. Could be more than $1 million for a 10-story building Affected buildings: About 1,500 need further study to determine if retrofit is needed Vulnerabilities: Many don't have enough steel reinforVulnerabilities: Many don't have enough steel reinforcement to hold columns in place during shaking. The collapse of two concrete office towers killed 133 people in a 2011 quake in New Zealand.

Wooden Buildings:

Cost of retrofit: About $60,000 to $130,000 for a modest-sized apartment building Affected buildings: About 17,000 need further study to determine if retrofit is needed Vulnerabilities: These types of buildings have collapsed during both the 1989 Loma Prieta and 1994 Northridge earthquakes. Sixteen people died when the Northridge Meadows apartment complex pancaked.

ALBACORE Project Caltech, UCLA, CSUN    Offshore faults, seismicity, tsunami risk analysis, bathymetry Body wave, surface wave tomography, ambient noise, SKS splitting Recorded passing of Honshu earthquake tsunami on seafloor

Northridge Earthquake, 1994

* CSUN Parking Structure (near G3 and G4 parking lot today) * Built in 1991, three years before the earthquake.

Northridge Earthquake, 1994

Earthquake damage to freeways, buildings, cars, gas lines.

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPAN Friday, March 11, 2011 at 05:46:23 UTC

 This tsunami propagation forecast model shows the forecast maximum tsunami wave height (in cm).

 Interference of water waves with seafloor bathymetry affects the wave trajectory, and reflections.

 Travel up a continental shelf raises wave height .

quickly.

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPAN Friday, March 11, 2011 at 05:46:23 UTC

Projected travel times for the arrival of the tsunami waves across the Pacific.

Nearby the earthquake there are only minutes to evacuate. However, in many other regions there is advance warning.

A tsunami map shows projected travel times for the Pacific Ocean. This map indicates forecasted times only, not that a wave traveling those distances has actually been observed.. NOAA

Magnitude 7.3 Earthquake

near El Salvador     Earthquake Mg 7.3 (Aug 26, 2012) Offshore Elsalvador (9:30 pm California time) Tsunami warning was put into effect for Costa Rica, Nicaragua, El Salvador, Honduras, Guatemala, Panama and Mexico.

What is Seismology ?

The underlying physics is

simple

: Force, Velocity, F = ma V = d / t But assumptions can quickly become

complex

when considering realistic sources, Earth structure that changes with depth and pressure, and receiver instrumentation.

Requires more sophisticated math and computation.

Earthquake Source Theory

Quantification of the earthquake rupture process

Early Detectors of Ground Movement

Zhang Heng was a celebrated astronomer of ancient China. An inventor of the seismoscope and armillary sphere, he made great contributions to the development of astronomy in ancient China. 132 AD, Eastern Han Dynasty

Seismology and Plate Tectonics

  Earthquakes generally occur at plate boundaries.

Thus plate tectonics is intimately linked with earthquakes and seismology

Seismology and Plate Tectonics

Most of the largest earthquakes occur at collisional plate boundaries.

Planetary Seismology ?

 What kind of living would a seismologist make on another planet ?

 What is the plausibility of earthquakes on other planets, on the moon ?

- Is there active plate tectonics on other planets ?

Seismic waves inside the Earth

How does earthquake energy travel through the Earth's interior ?

Movie: Wysession

Seismic Tomography: from Seismic rays in the Earth   Many seismic stations placed across a region of interest Create Images of “velocity” or seismic structure

US Array

www.iris.edu

Earth's Interior Structure

Seismology is the chief method of determining the interior Structure of the Earth.

Indirect methods of studying the Earth's Interior

Can we just go to the center of the Earth ?

• Deep interior of the Earth must be studied

indirectly

– Direct access only to crustal rocks and small upper mantle fragments brought up by volcanic eruptions or slapped onto continents by subducting oceanic plates – Deepest drill hole reached about 12 km, but did

not

reach the mantle •

Geophysics

is the branch of geology that studies the interior of the Earth SE Germany – 10 km drill hole

Indirect Study of the Earth's Interior - Geophysics

- Seismic Waves - Gravity - Heat Flow - Magnetic Field

The Mantle Lithosphere

• Crust and upper mantle together form the

lithosphere

, the brittle outer shell of the Earth that makes up the tectonic plates – Lithosphere averages 70 km thick beneath oceans and 125-250 km thick beneath continents

The Asthenosphere

• Beneath the lithosphere, seismic wave speeds abruptly decrease in a plastic (ductile)

low-velocity zone

called the

asthenosphere

• Are low seismic velocities caused by partial melt, water, density?

Subduction Zones in North America

 Subducting Farallon slab is imaged through seismic tomography extending to at least 2000 km depth  Farallon reaches this depth somewhere beyond the east coast of North America  Grand et al., 2001.

Earth's resources

Oil exploration Active source Reflection seismology Gasoline contamination Environmental compliance

The Earth's Natural Resources

• • •

Energy Water Raw Materials

• Energy 1. Oil 2. Natural Gas 3. Coal 4. Solar 5. Wind 6. Dams

Fossil Fuels

Oil Resources

New technologies used aboard offshore platforms in the Gulf of Mexico can recover oil and gas from rock reservoirs below very deep waters.

[Larry Lee Photography/CORBIS.]

Oil Resources:

New Find in Gulf of Mexico! (Will this solve all our problems ?)

New find in GOM

(Jack No. 2 test well)

• up to 3-15 billion barrels of oil • US consumption 20 million barrels/day (that's ~7.3 billion barrels/year) • 5 months - 2 years • reservoir is 8 km under sea level

Oil Consumption in U.S.

• U.S. Oil consumption in 2007 was 20.68 million barrels per day!

• This is 3 times as much as China, 8 times Germany, times France, 12 times England, 12 times Iran, 28 times Venezuala, usage of oil.

10 • We are the biggest oil consumer in the world.

Oil Peaks – 1960's

In the 1850's oil mainly used for kerosene lamps – remaining was burned or disgarded.

Current oil production rates peaked in 1960's but U.S. consumption rates increase dramatically above this.

Don't panic!

-Try to conserve energy -Seek alternative energy sources

•

Petroleum Reserves

As petroleum prices rise, alternate petroleum sources, such as

heavy crude

,

oil shale

and

oil sand

, will be increasingly exploited –

Heavy crude

is dense, viscous petroleum –

Oil shale

is black or brown shale with high solid organic matter content from which oil can be extracted by distillation –

Oil sands

(or

tar sands

) are asphalt-cemented sand or sandstone deposits

Seismologists must image anticlines, petroleum traps, liquid reservoirs, partial melt along grain boundaries.

Petroleum Exploration and Production

Depiction of a three-dimensional seismic survey collected from airguns dragged behind a ship. Sounds waves reflect off the seafloor and deeper sediment layers. The colors show the layers of sediments beneath the seafloor, some trapping oil and natural gas. [ (b) Courtesy of Satoil, Veritas, and BP.]

Exploration Geophysics

    CSUN students (Robin Sehler) in the field in south Africa Learn geophysical exploration techniques\ Map and locate palladium veins in crustal rocks GPS, active source seismology, GPR, gravity, Magneto tellurics ( Robin Sehler, Carol Zamora, Gabrielle Zamora, Cristo Ramirez, Melissa Nunley Jasmyn Nolasco, Brittany Huerta, Christian Mirreles)

The Seismogram

A seismogram is made up of a series of signals only one of which is the earthquake.    Earthquake source  Scalar  Explosion • Rupture along a plane (e.g. shear or vertical slip) Medium wave travels through Receiver characteristics

Earthquake Sources and Seismometer Receivers

Stein and Wysession (figure 1.1-1)

Seismology: What is Known an Unknown

What we know for sure!

- Vp speed - Average radial velocity of Earth - Earthquake locations - EQ radiation patterns (

fraction of a percent) Known very well fo 50 years!

Mapped daily by GSN

“ What we are still studying: - Physics of earthquake rupture

largely unknown.

- Damping by inner core – Anisotropy in the inner core ?

Only approximate Still trying to find the J phase!

Earthquake Sources and Seismometer Receivers

To understand the seismogram observed at a seismometer We must understand     Earthquake sources How the medium behaves, deforms, relaxes The response characterists of the seismometer instrument How seismic waves are generated and travel

Northridge Earthquake, 1994

- January 17, 1994, 4:30 am - Magnitude = 6.9

- Blind thrust fault - Difficult to find or predict - Duration 10-20 seconds CSUN Parking Structure

Northridge Earthquake, 1994

* CSUN Parking Structure (near G3 and G4 parking lot today) * Built in 1991, three years before the earthquake.

Northridge Earthquake, 1994

Damage to freeways, buildings, cars, gas lines.

Historic Earthquakes

1994 Northridge - 1.8 miles from CSUN - Shaking 40 seconds - Damaged all 53 CSUN buildings - Damaged 300 other schools - Lower story buildings collapsed - 4 interstate hwy's closed for months (Golden State, Santa Monica fwys) - 15000 people live in tents for days - 10000 without water, elect, gas - Arid climate did not cause liquifaction of soils – shaking minimized (compared to 1964 Alaska and 1989 Loma Prieta).

- Landslides in Santa Susana, Santa Monica, San Gabriel Mtns blocked roads and traffic, damaged water lines and homes in Palisades - Sylmar – Olive View Hospital – rebuilt from 1971 to code stayed intact.

- Aftershocks 5.9 1 min after main shock, 5.6 11 hrs after.

Earthquakes

1989, Loma Prieta earthquake, Mw = 7.2

Historic Earthquakes

1906 San Francisco - 280 miles of displacement - Shaking ~1 minute - Damaged water mains, fires spread and caused many deaths (

Historic Earthquakes

1989 Loma Prieta, Mw = 7.2 - Shaking for 15 seconds - Death toll 63

Historic Earthquakes

1964 southern Alaska (Mw = 9.2) - Shaking for 3 minutes - Rupture 350,000 square miles - Death toll from quake 15 (remote area) - Tsunami, landslides 100 more

Historic Earthquakes

2002 inland Alaska – Denali Fault - Propagated east 7000 miles/hr - Offset streams, glaciers, landslides - Trans-Alaska Oil Pipeline no serious damaged - pre-engineered

Historic Earthquakes

2004 Sumatra – Andaman E.Q.

- Mw = 9.3

- Second largest recorded on Earth - Major damage in Sumatra - Tsunami damage spread far to Indonesia, Thailand, Sri Lanka, India, East Africa - Death toll 220,000 from force of tsunami wave -

Tsunami movie

Harnessing Nuclear Energy

Japan’s Kashiwazaki-Kariwa facility is the world’s largest nuclear power plant, with seven reactors and a total generating capacity exceeding 8200 megawatts. It was damaged by a powerful earthquake (magnitude 6.8) that struck the region on July 16, 2007. The plant was shut down and required extensive repairs.

[STR/AFP/Getty Images.]

Petroleum Recovery

•

Oil fields

are regions underlain by one or more oil pools – Largest in U.S. are in Texas and Alaska • Oil and natural gas are removed through

wells

drilled down into an oil trap within a reservoir rock • Negative environmental effects resulting from oil recovery and transport include

oil spills

,

brine contamination

of surface water, and

ground subsidence

Exploration Geophysics

    CSUN students (Robin Sehler) in the field in south Africa Learn geophysical exploration techniques\ Map and locate palladium veins in crustal rocks GPS, active source seismology, GPR, gravity, Magneto tellurics ( Robin Sehler, Carol Zamora, Gabrielle Zamora, Cristo Ramirez, Melissa Nunley Jasmyn Nolasco, Brittany Huerta, Christian Mirreles)

Exploration Geophysics: Metals and Ores

• Metal

ores

- naturally occurring materials that can be profitably mined • Whether or not a mineral deposit is an ore depends on

chemical composition

, the

percent extractable metal

, and

current market value

of the metal • Metallic ore deposits originate from

crystal settling

in igneous intrusions,

hydrothermal fluids

cooling in pores and factures,

chemical precipitation

water, or sedimentation in rivers in (

placers

)