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SIO15-18: Lecture 7 Earthquake Seismology

Homework Code of Conduct

• discuss homework but write your own HW!
• discuss homework but do not share workload, i.e. all have to work on ALL problems
• don’t copy and paste material from the web/too much text copied from class website

reduces points!

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• copied HWs receive 0 credit; repeat offenders will be reported to UCSD

SIO15-18: Lecture 7 Earthquake Seismology

watch Homework 2 video! Lecture 5 “adjusted”

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SIO15-18: Lecture 7 Earthquake Seismology

source: wikipedia; SD-UT

SIO15-18: Lecture 7 Earthquake Seismology

source: wikipedia; SD-UT

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SIO15-18: Lecture 7 Earthquake Seismology

also made landfall in FL

source: wikipedia; NOAA

SIO15-18: Lecture 7 Earthquake Seismology

Compared to long faults, large earthquakes are

• n shorter faults?

POPQUIZ #2

YOUR FULL NAME AND STUDENT ID# no credit if one is missing

• less likely
• more likely
• equally likely

Code of Conduct: you may ask your neighbor you may consult your notes, book, online you may NOT write and/or submit your friend’s popquiz

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SIO15-18: Lecture 7 Earthquake Seismology

Which of the 3 types of earthquakes USUALLY does not trigger a tsunami?

POPQUIZ #3

YOUR NAME AND STUDENT ID#

Code of Conduct: you may ask your neighbor you may consult your notes, book, online you may NOT write and/or submit your friend’s popquiz

SIO15-18: Lecture 7 Earthquake Seismology

P and S Waves are body waves

Image: S. Marshak “Earth, Portrait of a Planet”

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SIO15-18: Lecture 7 Earthquake Seismology

• 1. P first, typically smallest signal
• 2. S, typically larger (felt by humans)
• 3. Love
• 4. Rayleigh, longest/largest wavetrain, most damaging

R

short video 7 on:

seismic waves how to locate an earthquake

p wave used in early warning systems warning time: up to 1 minute

SIO15-18: Lecture 7 Earthquake Seismology

R

short video 7 on:

seismic waves how to locate an earthquake

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SIO15-18: Lecture 7 Earthquake Seismology SIO15-18: Lecture 7 Earthquake Seismology

Loading an EQ Fault

from Lecture 2

relaxed loaded

Fg = k x x Epot = 1/2 k x x2

relaxed loaded

force <-> stress deformation <-> strain

strain is a result of stress

response cause

Loading a Spring

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SIO15-18: Lecture 7 Earthquake Seismology

there is already a fault why don’t blocks move all the time?

fault breccia/fault gouge: broken-off, ground up asperities asperities: protrusions that increase friction along a fault EQ: when stresses high enough to overcome friction

Friction Stress Friction Stress no EQ EQ!

• Fig. 5.18

SIO15-18: Lecture 7 Earthquake Seismology

• 1. stress builds up; asperities; no motion
• 2. stress overcomes friction -> EQ + aftershocks
• 3. slip along fault; stress drop
• start from 1)

fault locked very little creep fault locked very little creep

• Fig. 5.19

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SIO15-18: Lecture 7 Earthquake Seismology

• some history of local seismicity in

Seattle/Tacoma area

• no recorded history of megathrust EQ
• 1700 orphan tsunami in Japan has no

corresponding local EQ -> MW=9.0 in Cascadia

• recurrence time ~ 300 years
• complex aseismic slip and episodic tremors

(GPS and seismometers)

• Fig. 5.21

SIO15-18: Lecture 7 Earthquake Seismology

EQs not regular recurrence time has a certain probability < 100%

source: Abbott “Natural Disasters”

• Fig. 5.15

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SIO15-18: Lecture 7 Earthquake Seismology

Probability of EQ before 2032

• 30% chance for a mag 7 quake before 2032,

for most places along SAF

• 90% chance for a mag 6 at Parkfield

recurrence time varies along same fault

prognosis for before 2004 seismic gap/recurrence

source: Abbott “Natural Disasters”

• Fig. 5.16

SIO15-18: Lecture 7 Earthquake Seismology

use seismic gap method

EQ recurrence time Parkfield EQs remarkably regular in > 100 years next predicted: 1993

28 September 2004, 10:15 PSDT * #7 late or #8 early???

• Fig. 5.17

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SIO15-18: Lecture 7 Earthquake Seismology

• Mw= 6.5 December 22, 2003 San

Simeon EQ increased stress at Parkfield

• made #8 more likely???
• but why did #7 not happen?
• EQs can trigger/influence other EQs on nearby faults

(1992 Landers/Big Bear)

• very large EQs may trigger volcanism far away (Rayleigh waves!)

(2002 Denali EQ/Yellowstone; 2004 Sumatra/Alaska volcanoes)

• Fig. 5.17

SIO15-18: Lecture 7 Earthquake Seismology

InSAR: Interferometric Synthetic Aperture Radar

• overlay satellite altimetry map before and after EQ
• interferogram -> fringes show amount of slip along fault

Sep 17, 1999 Izmit, Turkey Earthquake

Image: NASA/JPL; wikipedia

• Fig. 6.43

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SIO15-18: Lecture 7 Earthquake Seismology

• use stack of INSAR images to

get strain rate

• extrapolate to 250yrs

relaxed loaded

• example: southern SAF
• last major EQ: 250 years ago,

while north and middle SAF ruptured 1906 and 1857

• typical co-seismic slip for

big EQs: 7-10m

SIO15-18: Lecture 7 Earthquake Seismology

probability of strong shaking site amplification

• Fig. 6.44
• Fig. 6.45

takes into account local geology takes into account local geology, tectonics, seismicity