Horst Rademacher EQ in the Bay Area Seismic Wavesseismo.berkeley.edu/~horst/Lect5.pdf•“World...

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


7 June 16

HH Horst Rademacher

Lect 5: EQ in the Bay Area Seismic Waves

Summer Session 2016

Class Organization

Midterm: This Thursday (June 9) One hour long Starting at 12:10 pm sharp all you need is writing paper and pen, no cell phones, no laptops, no books!



HH Any

Questions?

Largest EQ ever recorded in US M=9.2, 27 Mar 1964

Anchorage, 4th Avenue

Alaska Recap from last lecture I:

New Madrid Seismic Zone

Changed the course of the Mississippi River

Created Reelfoot Lake, TN

Recap from last lecture II:

Source: V. Klemann, GFZ

EQ along the East Coast? Recap from last lecture III:

Hawaii

Loihi Seamount

Recap from last lecture IV:

Fracking generates only microearthquakes magnitudes < 2

Seismic Hazard is in Wastewater Injection

Recap from last lecture V:

Man made EQ:

Complex section of Pacific Rim of Fire

Subduction = convergent margins

Spreading = divergent margins

Transform = sliding plate margins

We have all three different kinds of Plate-Plate Interaction

Recap from last lecture VI:

Golf of California opens like a

tectonic zipper

http://seismo.berkeley.edu/blog/seismoblog.php/2010/04/05/opening-a-tectonic-zipper

Further reading:

Baja California moves away from mainland Mexico

Divergent Plate Margin

Recap from last lecture VII:

https://earthdata.nasa.gov/media/2011-earthquakes-scarp.jpg

Last big EQ: Cucapah-El Mayor 4 April 2010, M=7.2

coseismic slip

1.50 m

Recap from last lecture VIII:

worrisome gap

Recap from last lecture IX:

Mendocino Triple Junction

is seismically the most active

region in California

Suggested reading: http://seismo.berkeley.edu/blog/seismoblog.php/2010/01/10/mendocino_seismic_energy

Recap from last lecture X:

San Andreas Fault

Recap from last lecture XI:



HH Any

Questions?

West-Coast: Transform faults San Andreas Fault SAF

Many side branches, determines the landscape of California What is the strike of SAF? Remember dip, strike and rake?

Bay Area

Faults

Bay Area Faults

San Andreas Fault splits into several faults: Calaveras Hayward San Gregorio Rodgers Creek Concord-Green Valley ……

Bay Area Faults

These faults split the tectonic movement between Pacific and North American plates

Geodetic GPS

Bay Area Earthquakes

Earthquake History

8 October 1865 – San Andreas Fault epicenter near Santa Cruz

Mark Twain, Roughing It

There came a really terrific shock … and there was a heavy grinding noise as of brick houses rubbing together. … As I reeled about on the pavement trying to keep my footing, I saw a sight! The entire front of a tall four-story brick building … sprung outward like a door and fell sprawling across the street.



October 22, 1868

Hayward Fault

epicenter near Hayward

Estimated M ~ 6.9


April 18, 1906: The Great San Francisco Earthquake

SAF ruptured for 300 miles, magnitude 7.8

What looks almost peaceful in the country side….

Bay Area Earthquakes April 18, 1906: The Great San Francisco

Earthquake and Fire

3000 people dead, 80% of San Francisco destroyed





Most damage due to fire…



Most damage due to fire…

• “World Series earthquake”

• M 7.0

• 63 dead

• 3757 injuries

• 8000 homeless

• cost $6 billion

Bay Area Earthquakes October 17, 1989:

Loma Prieta Earthquake

Damaged areas

• Santa Cruz

• Oakland

• Marina District

Bridge Collapse



Oakland Cypress Structure

I 880

Soft Story Collapse



San Francisco Marina District



Santa Cruz Business District

Shake Map shows the

distribution of ground shaking


October 17, 1989:


Bay Area Earthquakes August 24, 2014:

South Napa Earthquake

Bay Area Earthquakes August 24, 2014:

South Napa Earthquake

= rupture area

Hayward fault bounds East Bay

hills.

Strawberry Creek is offset by fault.

Bay Area Faults

300 m

10 mm/yr is 20% of the total Pacific-North American Plate Boundary (50 mm/yr).

Bay Area Faults

Bay Area Faults

Creeping Hayward Fault pulls Cal Memorial Stadium apart….

more on Thursday



HH Any

Questions?

Seismic Waves

Examples of waves

Seismic Waves Light consists of electromagnetic waves

What is an earthquake? Seismic Waves: 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 Waves: The Basics What are seismic waves?

Acoustic waves: What is necessary? Sound source Generates acoustic energy Medium Transports the energy

Seismic Waves

What are waves?

Means to transport information/energy from a source to a receiver

The Mavericks

Seismic Waves: The Basics Parameters of a wave

Amplitude A Wavelength l

Period T Frequency f Velocity v F=2p/T [Hz=1/sec]

V= l * f [m/sec]

Seismic Waves: The Basics

Seismic Waves: The Basics Where do sound waves travel?

through air much faster

through water

As density increases

sound speed

decreases

Seismic Waves: The Basics Where do sound waves travel?

Sound also travels through solids

Elastic waves = Seismic waves

….hence it travels through the Earth

Seismic Waves: The Basics

Two classes, four types of seismic waves

Body waves

P- or longitudinal

S- or shear

Surface waves

Lord Rayleigh

1842-1919

Augustus Love

1863-1940

Seismic Waves: The Details P-Waves

Same mechanism as sound waves in air P-Waves velocity in Earth: 4 - 13 km/sec

Seismic Waves: The Details S-Waves

Ground movement up/down or left/right S-Waves velocity in Earth: 3 – 7 km/sec

Seismic Waves: The Details Rayleigh-Waves

Rayleigh-Waves velocity in Earth: ~ 3 km/sec Retrograde elliptical ground movement

Seismic Waves: The Details Love-Waves

Love-Waves velocity in Earth: ~ 3 km/sec Ground movement left/right



HH Any

Questions?

How to measure seismic waves?

Scorpion legs

Ask nature:

from Brownell, SciAm, 251, #6, 86-97, 1984


Ask these grumpy looking old men

1900 Emil Wiechert (Göttingen) builds world’s heaviest Seismograph

Mass 17 tons Baryte (BaSO4)


1909 Wiechert "lite" horizontal, 80 kg


Wish: record the Earth's movement with high resolution

Problem: the reference frame is also in motion Requirement: to separate reference frame from Earth

Tool: spring Physics: inertia


NHK Video

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

Inertia How to measure seismic waves?

Vertical Pendulum

How to measure seismic waves? Inertia

Today we don’t use paper anymore Electronic recording


How to measure seismic waves

no shaking

shaking begins

shaking decreases

More shaking, lower frequency

frequency gets lower

Time in minutes

How to measure seismic waves Seismic Records =

Seismograms

Different Seismic Wave types travel with different velocities How to measure seismic waves

How to measure seismic waves 3 Day Seismogram

local regional teleseismic

Further reading on seismograms: http://seismo.berkeley.edu/blog/seismoblog.php Search for seismogram

http://seismo.berkeley.edu/blog/seismoblog.php

http://seismo.berkeley.edu/blog/seismoblog.php



HH Any

Questions?

Exploring Earth’s Interior

How do we know what’s down there?


Kola Borehole, Soviet Union (1970-1989), 12,262 m

Earth’s Diameter: 12,735 km

a mere 1/1000th


Chemical composition of Lava =

window into interior of the Earth

We can X-ray (image) the Earth with Seismic Waves Exploring Earth’s Interior III:

First X-Ray ever

Conrad Röntgen (1896)

Like all other waves Seismic Waves are subject to:

Reflection

Refraction

Scattering

Using seismic waves

We can X-ray (image) the Earth with Seismic Waves Exploring Earth’s Interior



HH Any

Questions?

Thursday:

Midterm: One hour long Starting at 12:10 pm sharp all you need is writing paper and pen, no cell phones, no laptops, no books!

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