Summer Session 2016 Horst Rademacher HH Earthquakes: …seismo.berkeley.edu › ~horst ›...

transcript

http://seismo.berkeley.edu/~horst/summer2016.html

26 May 16

HH Horst Rademacher

Lect 2: Earthquakes: The Basics

Summer Session 2016

Class organization

Questionnaire?

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Send me an email with subject “register EPS20-Summer16”

Announcements will be sent to all registrants

HH Any

Questions?

EQ and the Cyberworld

How you can contribute to

earthquake science? My Shake

http://myshake.berkeley.edu/

EQ and the Cyberworld

How you can contribute to

earthquake science? My Shake

HH Any

Questions?

Who has ever felt an earthquake?

Earthquakes: The Basics

What is an earthquake?

How much was fact?

How much was fiction?

NHK Video

Great Hanshin Earthquake, Kobe, Japan, 17 Jan 1995, M = 7.3 Security Camera in NHK Newsroom

…..and now some reality

Earthquakes: The Basics …..some more reality

Tohoku Earthquake, E of Honshu, Japan, 11 March 2011, M = 9.0 various clips

What is an earthquake? Earthquakes: The Basics

Scientific answer:

When the ground breaks along a fault

Common/laymen’s answer:

When the ground shakes where I am

Both answers are correct! Two different aspects of a seismic event

Seismic waves

Seismic source

Seismic sources: Where do earthquake occur? How often do earthquakes happen? Why earthquakes happen? How do earthquakes happen? Prediction, Forecast, Early Warning

Seismic waves: Seismic Monitoring X-Raying the Earth – Structure of the Earth’s interior Looking for mineral resources, oil and gas Response of buildings and structures Earthquake Engineering

All those topics will be touched on

in this course

HH Any

Questions?

Where do earthquakes occur?

Earthquakes around the world occur in a distinct pattern

Depth in km

Things to remember II

Earthquakes and land volcanoes

Where do earthquakes occur? Global Bathymetry

……like here along the

Mid-Atlantic ridge

… or like here along the deep sea trenches

in the NE Pacific

Where do earthquakes occur? Pacific Ring of Fire

Chile, 1960 M=9.5

Alaska, 1964 M = 9.2

Japan, 2011 M = 9.0

Where do earthquakes occur? Pacific Ring of Fire

This is how the History Channel sees it

www. history.com

Where do earthquakes occur? Summary:

Earthquakes occur in a distinct pattern

Pattern is similar for EQ and Volcanoes

EQ occur along major ocean features like ridges and trenches

EQ occur under some major mountain ranges, like Himalaya, Alps and Andes

HH Any

Questions?

How does this all fit together? Why do earthquakes occur in these specific regions?

For the answers thank this man

The Father of Continental Drift

and Plate Tectonics Alfred Wegener

1880 - 1930

Plate Tectonics

Alfred Wegener 1880 – 1930

German Meteorologist and Polar Researcher

Plate Tectonics

Wegener 1912: concept of drifting continents

Plate Tectonics

Plate Tectonics Why are Wegener’s ideas important?

At the last turn of the century, nobody really understood what EQ were and how they worked

Japan: catfish

China: frog

Philippines: snake

Native Americans: turtle

In folklore EQ were associated

with giant creatures that supported the Earth

Aristotle (384-322 BCE)

Strong winds blew through caves inside the Earth, creating “effects similar to those of the wind in our bodies whose force when it is pent up inside us can cause tremors and throbbings.”

Destructive EQ in Sparta 464 BCE

Plate Tectonics …in ancient Greece

EQ were seen as the wrath of god.

Mechanism by the Catholic Church

to control the people.

Rimini, Italy, 1308

Rhodes 1481

Plate Tectonics …in early Christian Europe

Plate Tectonics …that changed 1755

Immanuel Kant (1724-1804)

gave first rational, enlightened

explanation of the catastrophic Lisbon EQ

on 1 Nov 1755

Great San Francisco EQ devastated the city

Plate Tectonics …and then came 1906

• Cataloged descriptions of earthquake effects

• Identified the San Andreas Fault

• Maps of the fault location and ground shaking distribution

• Elastic rebound theory

Prof. Andrew Lawson

UC Berkeley

Plate Tectonics …a turning point for seismology

(earthquake science)

The Lawson Report

Plate Tectonics

…but we still did not know what causes

Earthquakes -

that’s where Wegener’s Continental Drift

comes into the picture

HH Any

Questions?

Evidence for plate tectonics shapes of

continents

fossils shared between different

continents

Plate Tectonics

Evidence for plate tectonics maps of the sea floor made using sonar (after WW I)

East Pacific Rise

a ridge in the centers of most oceans

surprisingly small amount of sediment

on sea floor

Plate Tectonics

Plate Tectonics Ocean Ridges

Periodic reversals of the Earth’s magnetic field are recorded as stripes

Breakthrough in 1963: Discovery of magnetic stripes on the ocean floor

Plate Tectonics

Frederick Vine and Drummond Matthews Cambridge University

Plate Tectonics

Plate Tectonics Age of Ocean Crust vs. Continental Crust

HH Any

Questions?

Hypothesis: Ocean ridge spreading

Plate Tectonics

How does it work?

Plate Tectonics How does it work?

Thanks to Paul Okubo, HVO

Plate Tectonics Plate Reconstruction I

580 million years in 8 seconds

Plate Reconstruction II

…a little bit slower….

The magnetic tape recorder:

Given the oceanic record we can wind back the plates to see how the plates have been moving.

age of the ocean floor: red=young, green=old

We can reconstruct past plate motion

Pangaea supercontinent

Plate Tectonics

Today we have

14 major plates:

North American

Eurasian

Pacific

Antarctic

South American

African

Australian

Plate Tectonics

The plates are rigid.

They are moving,

hence they collide

HH Any

Questions?

Plate Tectonics

The Big Picture: How does it work?

Categories of plate – plate interactions

Divergent

• Established mid-ocean ridge • New rift zone, new ocean

Transform • Along mid-ocean ridges • Across continents

Convergent • Ocean – continent • Ocean – ocean • Continent – continent

Plate Tectonics The tectonic action is

along the plate boundaries

Let’s look at them in more detail:

Divergent boundaries:

East African Rift and Red Sea

Mid-Atlantic Ridge

Plate Tectonics

Plate Tectonics Convergent boundaries = collision

Cars: Deformation, Metal folding, Explosive release of energy Earth: The right conditions for Earthquakes and Volcanoes

Three types of

convergent plate boundaries:

Western South America and the Pacific Northwest

The Himalaya

Plate Tectonics

oceanic-continental

oceanic-oceanic

continental-continental

Example: Convergent

boundary (continental-continental)

India and Asia

Transform plate boundaries: Plate Tectonics

San Andreas Fault The Mother of all Earthquake Faults

Magmatic Blow Torch

Plate Tectonics Hot Spots

6000 miles, 70 million years

Plate Tectonics Hot Spots

HH Any

Questions?

Things to remember I

We are sitting on a tectonic time bomb

Earthquakes around the world occur in a distinct pattern

Depth in km

Things to remember II

The cause is Plate Tectonics

Things to remember III

Divergent • Established mid-ocean ridge • New rift zone, new ocean

Transform • Along mid-ocean ridges • Across continents

Convergent • Ocean – continent • Ocean – ocean • Continent – continent

Three types of plate – plate interactions

Things to remember IV

Tuesday:

Earthquake Faults Different types of Earthquakes

Summer Session 2016 Horst Rademacher HH Earthquakes: …seismo.berkeley.edu › ~horst ›...

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