Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be...
Transcript of Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be...
![Page 1: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/1.jpg)
Revisiting the 1960 Chilean Earthquake
-For the 50th Anniversary –
Hiroo KanamoriSeismological LaboratoryCalifornia Institute of Technology
In collaboration with Luis Rivera, and with help from Stewart Smith, and Frank Press.
![Page 2: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/2.jpg)
1960 Chilean Earthquake (Mw=9.5)
Believed to be the largest in the last century.
cf. 1964 Alaskan Earthquake, Mw=9.22004 Sumatra-Andaman Is. Earthquake, Mw=9.21952 Kamchatka Earthquake, Mw=9.0
Is it really the largest ?
Is something special ?
What have we learnt from it?
![Page 3: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/3.jpg)
Dextral (right-lateral) Rotation of the Pacific Benioff (1958)
San Andreas
KamchatkaHodgson’s (1956) mechanism
Background, e.g., Benioff’s Idea
Japan, Right-lateral (Median Tectonic line)
![Page 4: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/4.jpg)
Saint-Amand, 1961
200 km
Aftershocks immediately after the 1960 earthquake
![Page 5: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/5.jpg)
Static (uplift, subsidence, strain etc)
Plafker and Savage (1970)
![Page 6: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/6.jpg)
Plafker and Savage (1970)Plafker (1972)
up
lift
up
lift
sub
sid
ence
Vertical Displacement (subsidence and uplift)
up
lift
![Page 7: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/7.jpg)
Plafker and Savage (1970) Uplift-Subsidence data and Models
Model B
![Page 8: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/8.jpg)
Moreno et al. (2009)Barrientos and Ward (1990)
Mw=9.26
![Page 9: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/9.jpg)
Linde and Silver (1989)
deep slip
Larger Mw (=9.45)
![Page 10: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/10.jpg)
Seismology
Normal modeSurface waves
![Page 11: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/11.jpg)
1960 Chile, PAS =83 , =135
One-day seismogram of the 1960 Chilean earthquake (Mw=9.5)
![Page 12: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/12.jpg)
Interpretation of Pasadena strain record (Kanamori and Cipar, 1974)
Mw=9.55
Uncertainties: dip angle, source finiteness, instrument response
Mw=9.35
![Page 13: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/13.jpg)
1960 Chile, Palisade R4
Synthetic HK M0=2.7x1023 N-m sf=l80
4 c
m
500 s
Obs.
Syn.
Mw=9.55
![Page 14: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/14.jpg)
1990
2010
2000
9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.81960
1970
1980
Mw
static
seismic
“precursor”
History of the 1960 Chilean Earthquake Mw estimates
PSP
BW
B
B
S
KC
LSCS
OT
BZ
“relative”
MBKM
![Page 15: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/15.jpg)
1990
2010
2000
9.0 9.1 9.2 9.3 9.4 9.51960
1970
1980
Mw
static
seismic
History of the 1964 Alaskan Earthquake Mw estimates
PHS
MM
KBRI
O
A
P
![Page 16: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/16.jpg)
An important record is the strain seismogram recorded at Isabella, California.
This record is of historical importance because it provided the first observations of the Earth’s free oscillations.
![Page 17: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/17.jpg)
Bullen (An Introduction to the Theory of Seismology, 1963)
Then in 1960 at the Helsinki meeting of the I.A.S.P.E.I., there occurred one of the most dramatic scientific sessions this author has witnessed.
Press announced that Benioff had once again observed long-period waves ….
Slichter announced ….
Lamont result ……
![Page 18: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/18.jpg)
![Page 19: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/19.jpg)
1960 Chilean Earthquake, Isabella Benioff Strain Record
Computed Earthtide
![Page 20: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/20.jpg)
Chile
ISA Back Azimuth to Chile, N145.7 W
Benioff et al. (1961) N32 Wα=2.3
N
Angle (α) between the ISA strain rod and the great circle to Chile
α
L(G) to R sensitivity ratio
L
R
Strain rod
Incident wave
2
sin(2 )
cos
![Page 21: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/21.jpg)
Smith (1966)
54 min 7.5 min
Normal-mode spectrum (from 7.5 min to 54 min) of the 1960 Chilean and the 1964 Alaskan earthquakes recorded with the ISA strainmeter.
![Page 22: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/22.jpg)
Smith (1966)
54 min 7.5 min
Toroidal Modes on the ISA Spectrum (Red)
![Page 23: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/23.jpg)
Observed Mode Energy Ratio of Chile to Alaska earthquakes, Smith(1966)
![Page 24: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/24.jpg)
Normal mode spectral amplitudes of the 1960 Chilean earthquake are about 2 to 5 times larger than those of the 1964 Alaskan earthquake.
This does not necessarily mean that the Chilean earthquake is correspondingly larger (in M0) than the Alaskan earthquake.
![Page 25: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/25.jpg)
Unknown in 1966Can be computed now
0
0
0Chile
0Ala
unitChile
unitAlask
Chile
Alaska ska
a
Excitaobserved amp
observ
tion
Excitationed amp
M
M
M
M
Determined in 1966
![Page 26: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/26.jpg)
116
134
N N
ISA
ISA
Alaska Chile
Rupture-Station Geometry
![Page 27: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/27.jpg)
Ru u
eR R
From 285 min to 8139 min (about 5.45 days)
For Chile K&C (1974) s=10°, =10°, =90°, d=35 km
modified s=10°, =17°, =90°, d=20 km
For Alaska K (1970) s=246°, =20°, =90°, d=75 km
modified s=246°, =10°, =90°, d=20 km
Computation of Strain Spectrum
![Page 28: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/28.jpg)
0
0.05
0.1
0.15
0.2
0.25
0.3
-200 0 200 400 600 800 1000 1200
Data 3
Chile (uniform)
Chile (B-W)
Ch
ile (
un
ifo
rm)
Distance, km
0
0.05
0.1
0.15
0.2
0.25
0.3
-200 0 200 400 600 800 1000 1200
Data 3
Alaska (uniform) (uniform)Alaska (Tapered)
Ala
ska
(u
nifo
rm)
(un
ifo
rm)
Distance, km
Slip distribution
Chile
Alaska
Barrientos and Ward (1990)
Tapered
uniform
uniform
![Page 29: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/29.jpg)
1960 Chile, ISA strain spectra (285 to 8139 min) Unit Moment (1x1023 N-m, s/d/r=10/17/90, d=20km)
Nan
ost
rain
-sec
23
4
56
7 8 9 10 1112
13
14
2
3
4
0 0.5 1.0 1.5 2.0 2.5Frequency, mHz
Av. 2-14 15003
average
Finite source (B-W)
5
6 8 910
![Page 30: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/30.jpg)
1964 Alaska, ISA strain spectra (285 to 8139 min) Unit Moment (1x1023 N-m, s/d/r=245/10/90, d=20 km)
Nan
ost
rain
-sec
0 0.5 1.0 1.5 2.0 2.5Frequency, mHz
2
3
4 5 6 7 8
9
1011 12
1314
2 3
4
Av. 2-14 15003
average
Finite source(Tapered)
5
6
8 109
![Page 31: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/31.jpg)
Angular order, l(7.5 min)(54 min)
Ch
ile/A
lask
a M
om
ent
Rat
ioChile/Alaska Moment Ratio
1
10
2 3 4 5 6 7 8 9 10 11 12 13 14
Data 2 3:32:13 PM 9/24/2009
uncorrected Smith (1966)Excitatio-corrected Point sourceExcitation-corrected finite (variable)Excitation-corrected finite (uniform)
Sq
rt o
f F
ig.
5
AMode #
![Page 32: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/32.jpg)
1990
2010
2000
9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.81960
1970
1980
Mw
static
seismic
“precursor”
History of the 1960 Chilean Earthquake Mw estimates
PSP
BW
B
B
S
KC
LSCS
OT
BZ
“relative”
MBKM
![Page 33: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/33.jpg)
Revisiting the Toroidal modes
![Page 34: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/34.jpg)
Comparison of the 1960 Chile (Valdivia) and the 2010 Chile (Maule) Earthquakes
Top: The strainmeter record of the 1960 earthquake at ISA (NW component). This is one of the most importanthistorical records in seismology from which the first observation of the Earth’s free oscillations was made.
Bottom: The strainmeter record of the 2010 earthquake at PFO (NW component).
Note the large even-order G waves (Love waves and toroidal modes) on the 1960 record and the almostcomplete absence of them on the 2010 record, suggesting significantly different mechanisms for the twoearthquakes.
![Page 35: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/35.jpg)
Chile
PFO Strain rodN45 W α=10.5
N
Angle (α) between strain rod and the great circle to Chile
Sensitivity to transverse motion sin(2α) Back Azimuth to Chile,
N145.7 W
ISA Strain rodN38.8 W α=4.5
34.3
![Page 36: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/36.jpg)
Smith (1966)
54 min 7.5 min
Toroidal Modes on the ISA Spectrum (Red)
T 3 4 5 6 8 9 10
![Page 37: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/37.jpg)
To increase G/R (or T/S) ratio, increasing the strike-slip component is most effective.
No thrust mechanism can explain the observed ratio.
![Page 38: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/38.jpg)
Free oscillation patterns
Spheroidal mode
Toroidal mode
Courtesy of Dr. Michel Van CampAnimation from Hein Haakhttp://www.knmi.nl/kenniscentrum/eigentrillingen-sumatra.html
earthquakes.
![Page 39: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/39.jpg)
Isabella strain seismograph worked normally (i.e., no anomalous L/R ratio) for the 1964 Alaska earthquake (after) and the 1957 Mongolian earthquake (before).
![Page 40: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/40.jpg)
1964 Alaska ISA NW strain L/R sensitivity=0.42
R2G2 R3
U=4.4 km/s for G2
U-3.5 km/s for R2
U=3.5 km/s for R3
overtone
![Page 41: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/41.jpg)
1964 Alaska ISA Strain NE M0=7.5x1022 N-m (s/d/r=245/10/20) (Network, sf=l50s)L/R sensitivity=9.5
G2 G4
stra
in
10000s
![Page 42: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/42.jpg)
G1
R1
R2G2
1957 Mongolian earthquake recorded at ISA
time, s
![Page 43: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/43.jpg)
1957 Mongolian earthquake recorded at ISA(strain meter + network + galvanometer)
Integrated strain
![Page 44: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/44.jpg)
Comparison between spheroidal and toroidal mode excitation (l=2 to 10)
spheroidal toroidal
=90
130
140
150
Observed (FFT)
![Page 45: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/45.jpg)
Precursor?About 15 min before the mainshock.Large (comparable to the mainshock)
Kanamori and Cipar (1974)Pasadena strain meter
Kanamori and Anderson (1975)Normal mode
Cifuentes and Silver (1989)Normal mode (more complete than K&A)
Pasadena Spectrum
![Page 46: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/46.jpg)
Kanamori and Cipar (1974)
![Page 47: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/47.jpg)
1000 s
Mainshock PForeshock P S
1960 Chilean earthquake, PAS Benioff Strain (NS) 180-4-10“Precursor”
G2 R2
P, S, G1,R1
Mainshock P
![Page 48: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/48.jpg)
3000 s
G2 and R2U=7 km/s
G3 and R3U=7 km/s
G4 and R4U=7 km/s
G2 R2
P
observed
syntheticwithout precursor
1960 Chilean earthquake, PAS Benioff Strain (NS) 180-4-10
bp n 4 c 0.00125 0.01 p 2
P, S, G1, R1
Precursor to (1) Precursor to (2)
![Page 49: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/49.jpg)
Cifuentes (1989)
Foreshock-Mainshock sequence
8.3 7.8
Mainshock
![Page 50: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/50.jpg)
Where does the precursory deformation occur?
![Page 51: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/51.jpg)
Cascadia Current model (Geological Survey of Canada)
![Page 52: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/52.jpg)
Moment-rate Spectrum(with ω2 reference spectra)
Mo
me
nt,
N-m
Frequency, Hz
Mw=9.5
9.0
8.5
8.0
7.5
2004 Sumatra Mw=9.2
2010 Chile Mw=8.8
1960 Chile Mw=9.5
Hartzell and Heaton, 1985
Also:mB_hat= 7.6 for both 1960 Chile and 1964 AlaskaHouston and Kanamori (1986)
mB_hat=7.2 for the 2004 Sumatra Kanamori( (2006)
Estimated from ISA strain Smith (1966),also tsunami Abe (1979, 2010)
Estimated from PFO strain for the 2010 event
![Page 53: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/53.jpg)
Conclusion
1. The 1960 Chilean earthquake is probably 2 to 5 times (in M0) larger than the 1964 Alaska earthquake. (super-cycle event?)
2. The existence and mechanism of precursor are still inconclusive.
3. Slip or deformation may have to be invoked in somewhere other than the mega-thrust boundary. ( e.g., deep slip or deformation)
4. “Super-cycle event” may involve a different deformation pattern.Most likely, half thrust and half right-lateral.
5. The super-cycle event can be different from other “average” great earthquakes. Strike slip strain is not released in every great
earthquake, and only when it accumulates over several events it triggers a super-cycle event.
Caveat:
Old data are inevitably incomplete and uncertain.
![Page 54: Revisiting the 1960 Chilean Earthquake - USGS...1960 Chilean Earthquake (M w =9.5) Believed to be the largest in the last century. cf. 1964 Alaskan Earthquake, M. w =9.2. 2004 Sumatra-Andaman](https://reader033.fdocuments.in/reader033/viewer/2022050104/5f430775bfcbd74c2254d17d/html5/thumbnails/54.jpg)
End