Post on 29-May-2020
transcript
http://seismo.berkeley.edu/~horst/summer2016.html
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!
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
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:
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:
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:
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
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
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.
Bay Area Earthquakes
Bay Area Earthquakes
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
• “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
Bay Area Earthquakes October 17, 1989:
Loma Prieta Earthquake
Oakland Cypress Structure
I 880
Soft Story Collapse
Bay Area Earthquakes October 17, 1989:
Loma Prieta Earthquake
San Francisco Marina District
Shake Map shows the
distribution of ground shaking
Bay Area Earthquakes
October 17, 1989:
Loma Prieta Earthquake
300 m
10 mm/yr is 20% of the total Pacific-North American Plate Boundary (50 mm/yr).
Bay Area Faults
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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 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
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
1900 Emil Wiechert (Göttingen) builds world’s heaviest Seismograph
Mass 17 tons Baryte (BaSO4)
How to measure seismic waves?
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
How to measure seismic waves?
NHK Video
Great Hanshin Earthquake, Kobe, Japan, 17 Jan 1995, M = 7.3 Security Camera in NHK Newsroom
Inertia 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
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/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
Exploring Earth’s Interior
Kola Borehole, Soviet Union (1970-1989), 12,262 m
Earth’s Diameter: 12,735 km
a mere 1/1000th
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
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?