Download Great earthquakes and new insights into subduction seismogenesis

Great earthquakes and new insights into
subduction seismogenesis
Heather R. DeShon
Southern Methodist University
GeoPRISMS DLP
Georgia Southwestern State University
Feb. 27th, 2013
The earth, the very emblem of solidity, has moved
beneath our feet like a thick crust over a fluid.
- Charles Darwin reflecting on experiencing the
Feb. 1835 great Concepción, Chile earthquake
The Voyage of the Beagle, 1845
Outline
•! Subduction megathrust faults and the seismogenic zone
•! Subduction cycles and deformation
–! Outstanding questions
•! Great earthquakes
–! Recent insights
–! Future concerns
–! New models
Zandt, 2002
The Active Earth
Plates - rigid lithosphere riding on a convecting mantle
3 Types of Plate Boundaries
Transform
Divergent
Convergent
Global distribution of convergent boundaries
Convergent boundaries
End Member Models of Subduction Zones
megathrust
Subduction is part of
the mantle convection
system
Subduction and arc
volcanism are great
water recyclers
Subduction and arc
processes help build
continental crust
Stern, 2002
Subduction megathrust faults
generate great
earthquakes &
tsunami
2011 Japan tsunami
1960 Chile tsunami
Hilo, Hawaii damage
2004 M 9.2 Sumatra
1960 Chile earthquake
1964 Alaska tsunami
2010 Maule, Chile
earthquake
The megathrust and tsunamis
Rupture dimensions and displacement
During an earthquake, slip
spreads out from the
initiation point (hypocenter)
over a finite distance.
Seismologists calculate
seismic moment (a
measure of energy) by
MO = A * D * µ
Moment = fault area * average displacement * rigidity
s
ng
s.
ly
Earthquakes are always
happening
somewhere.
Subduction
zones
generate
the largest earthquakes
Magnitude 2 and smaller earthquakes occur several hundred times a day world wide.
because
megathrusts
are7,long,
dipping
structures
Major earthquakes,
greater than magnitude
happen more
than once per
month.
“Great earthquakes”, magnitude
higher,
occurareas
about once a year.
with8 and
big
fault
Energy Release
Magnitude
Effects
10
9
8
7
Earthquakes
Energy Equivalents
Chile (1960)
Alaska (1964)
Sumatra (2004)
largest recorded eathquakes
Japan (2011)
destruction over vast area
massive loss of life
Chile (2010)
San
Francisco,
CA (1906)
great earthquake
severe economic impact
New Madrid, MO (1812)
large loss of life
Charleston, SC (1886)
major earthquake
Haiti (2010)
damage ($ billions)
Northridge
(1994)
loss of life
(equivalent kilograms of TNT)
15,000,000,000,000
<1
476,000,000,000
Krakatoa Eruption
1
Worldʼs Largest Nuclear Test (USSR)
Mount St. Helens Eruption
18
6
strong earthquake
property damage
5
moderate earthquake
some property damage
4
light earthquake
noticeable shaking
10,000
3
minor earthquake
often felt
100,000
2
generally not felt
1,000,000
120
15,000,000,000
476,000,000
Hiroshima Atomic Bomb
15,000,000
Long Island, NY (1884)
1,500
Average Tornado
476,000
15,000
Large Lightning Bolt
Oklahoma City Bombing
Moderate Lightning Bolt
476
15
Number of Earthquakes per year (worldwide)
The left side of the figure above describes the effects of an earthquake by magnitude. The larger
the number, the bigger the earthquake. Significant earthquakes are noted on the left side of the
Great earthquakes – MW!8
Source: USGS
Magnitude does NOT scale with fatalities
Source: USGS
NSF GeoPRISMS Program
GeoPRISMS investigates the coupled geodynamics, earth
surface processes, and climate interactions that build and
modify continental margins over a wide range of timescales
(from s to My), and cross the shoreline, with applications to margin
evolution & dynamics, construction of stratigraphic architecture,
accumulation of economic resources, and associated geologic
hazards and environmental management.
•! Two broadly integrated initiatives
Subduction
Cycles &
Deformation
Rift
Initiation &
Evolution
•! Research at Primary Sites & through Thematic Studies
A Relevant SCD Key Question
B.
1
2
3
4
Mw
5
6
7
9
8
Silent EQ
1 year
e
7
ETS
1 month
6
SSE
1 day
5
d
4
ak
es
c
Gap
ea
rth
qu
1 hour
ow
3
a
2
Sl
log[Characteristic duration (s)]
What governs the size,
location and frequency of
great subduction zone
earthquakes and how is
this related to the spatial
and temporal variation of
slip behaviors observed
along subduction faults?
VLF
1
b
ular
Reg
es
uak
hq
eart
0
LFE
−1
−2
10
11
12
13
14
15
16
17
18
log[Seismic moment (N m)]
19
20
21
Ide et al. 2007
Unzipping
the Sunda
subduction
zone
2004-2013
Focal Mechanisms
Seismologists represent
motion along a fault using
lower hemisphere
projections – beachballs
Reverse faults, like
subduction megathrust
faults, have the colored
quadrant centered in the
circle
Unzipping
the Sunda
subduction
zone
2004-2013
Backprojection Models: Watching slip happen
Moment rate function
seconds
Ishii et al., 2005
Alex Hutco
The 2004 tsunami
SUMATRA-ANDAMAN EARTHQUAK
1994 deep Bolivia earthquake (Mw 0 8.3) and
about 40 times that of the 2001 Peru earthquake (Mw 0 8.4) (Fig. 3).
Slip process of the 2004 event. The 2004
Sumatra-Andaman earthquake had the longest
known earthquake rupture. Short-period seismic body waves (0.5 to 0.25 s) show azimuthally varying durations that indicate that
the seismic rupture front propagated to about
1200 km north of the epicenter with a rupture
velocity of about 2.0 to 3.0 km/s and that
short-period radiation was generated for at
least 500 s (38). Array analysis of 1- to 2-s
period seismic waves from Hi-net stations in
Japan yields compatible results (39). Analysis of longer period body waves and surface
waves demonstrates that most of the slip that
generated seismic waves was concentrated
in the southern half of the rupture zone, with
diminishing, increasingly oblique slip toward
the north on the fault (9). The seismic moment of models that successfully match the
long-period body- and surface-wave data is
about 1.5 times as large as the CMT moment, consistent with free oscillation observations (10).
The seismic model does not, however, account for all observations. Geodetic constraints require two to three times more slip
in the north (40). This suggests rupture of the
•! >250,000 fatalities
•! Run-up heights >4 m
Banda Aceh
•! Tsunami last longer
than earthquake
shaking
Fig. 7. (Left) Tsunami model at a time of 1 hour 55 min after earthquake initiation, computed f
composite slip model with fast slip (50-s rise time) in the southern portion of the rupture and s
slip (3500-s rise time) in the north. The northward propagating rupture velocity is about 2 k
2004 MW 9.2 megathrust earthquake,
2007 MW 8.4 megathrust earthquake &
2010 MW 7.8 tsunami earthquake
2005 MW 8.7 Nias earthquake & Afterslip
Hsu et al., 2006
Largest intraplate earthquakes ever recorded
Gut reaction: These intraplate
earthquakes were caused by
strike-slip faulting within Indian
Plate oceanic lithosphere. N
– S oriented fracture zones
project into the area of the
earthquakes and are the likely
faults offset during these
events.
M 8.6
M 8.2
Investigator Ridge
2012-Magnitude 8.6 and
8.2 OFF W COAST
NORTHERN SUMATRA
Ninetyeast
Ridge
!
Aftershocks and backprojection results
soon tell a different story
2010 MW 8.8 Maule, Chile earthquake
ab
1943
M = 7.
7.9
9
32° S
32°
SS
32°
án
Nazca
plate
–1
1.00
1985
M = 7.
7.8
8
0.75
1928
M ≈ 8
0.75
0.50
0.50
0.25
0.25
0.00
Santiago
Santiago
32° S
Fig. 2
0.00
Santiago
34°
SS
34°
Aftershock
location
er
Ju a n F
d
n án
32° S
ez
r i dge
≥ 85%
≥ 75%
33° S
Nazca
Fig. 2
plate
–1
34° S
m yr
66 m
34° S
m yr
Volcano
38°
SS
38°
42° S
South
America
plate
1960
Sliver
M = 9.
9.5
5
motion
75°
75°WW
38° S
Crustal
faulting
Crustal
faulting
40° S
Arauco
peninsula
LiquiñeOfqui
fault zone
40° S
71°
71°WW
Longitude
69°
69°WW
75° W
42° S
75°
75°WW
73°
73°WW
71°
71°WW
38° S
39° S
GPS station
200
200km
km
42°
SS
42°
37° S
South
America
plate
GPS station
Sliver
motion
200
200km
km
73°
73°WW
2010
1960
40°
SS
40°
36° S
10 m
5m
1m
36° S
1m
e –Peru t
re
nch
38° S
Postseismic
relaxation
Concepción
10 m
5m
Concepción
Arauco
peninsula
36°
SS
36°
20 m
15 m
Postseismic
relaxation
Concepción
nc
36° S
tre
1835 M ≈ 8.5
and
2010 M = 8.8
8. 8
h
35° S
Ch ile –Per
u
Latitude
66 m
bEarly
Latitude
ern
Ju a n F
r i dge
NATURE | Vol 467 | 9 September 2010
Fraction of plate
convergence
a
1.00
1906
M = 8.
8.4
4
z
de
30° S
30 mm yr –1
Fraction of plate
convergence
30 mm yr –1
34° S
c
bc
30°
SS
30°
30° S
Chil
o
Interseismic plate coupling – predictive value?
LETTERS
LETTERS
NATURE | Vol 467 | 9 September 2010
69°
69°WW
Longitude
the 2010Methods).
Maule earthquake
1 | Tectonic
the2010
study
area,earthquake
data, observations
and see online-only
Maule
(for references
ata,Figure
observations
and setting ofthe
74° W
73° W
72° W
Longitude
40° S
71° W
0
200 km
5
N
p
Figure 3 | Relationship between pre, co- and postseismic
75°
W
73° W
71° W
69°
slip distribution
during
theW2010 (
patterns.
a, Coseismic
USGS slip model26) and 1960 (green contours; from ref. 3
overlain onto pre-seismic locking pattern (red shading $0
early (during the first 48 h post-shock) M $ 5 aftershock lo
(for references
see online-only Methods).
circle sizes scale with magnitude; GEOFON data29). b, His
Moreno et al., 2010
2011 MW 9.0 Tohoku-oki, Japan, earthquake
Slip in the 2010 Chile and 2011 Japan events
B04311
LAY ET AL.: MEGATHRUST RUPTURE DOMAINS
Maximum slip
is ~50 m in
the Japan
earthquake!
via backprojection
Figure 1. Maps summarizing rupture characteristics for (a) the 11 March 2011 Tohoku, Japan (Mw 9.0)
and (b) the 27 February 2010 Maule, Chile (Mw 8.8) earthquakes. The white stars indicate the epicentral
locations used for each rupture model. The coseismic slip distributions are those determined from highrate GPS recordings for the Tohoku event by Yue and Lay [2011] and for the Chile event by Koper
Lay et al., 2012
Part of houses
swallowed by
tsunami burn in
Sendai, Miyagi
Prefecture (state)
after Japan was
struck by a strong
earthquake off its
northeastern coast
Friday, March 11,
2011.
New York Times
The tsunami waves traveled
far inland, the wave of debris
racing across the farmland,
carrying boats and houses
with it.
The Future: Cascadia
History of earthquakes: the turbidite record
A. Full or nearly
full rupture,
19 events
B. Mid-Southern
rupture, 3-4
events.
C. Rupture from
central Oregon
southward, 10-12
events.
D. S Oregon/N
California events,
minimum of 7-8
events.
Chris Goldfinger, OR State
Tremor
recurrence varies
along Cascadia
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
"#$%&'()*'!+(%!,--.(/!0112!!
Tremor lies downdip of
the seismogenic zone
Hyndman et al., 1995; Wech and Creager, 2011
Summary
•  Each new earthquake brings further insight into the
seismogenic zone
•  Fault complexity may
be related to variable
frictional stability
conditions along the
fault
•  Fault behavior may
vary from seismic
cycle to seismic cycle
Lay et al., 2012
Acknowledgements
•! NSF GeoPRISMS and
Margins program
•! Collaborators: Susan Bilek,
Susan Schwartz, Cliff
Thurber, Bob Engdahl,
Jeremy Pesicek, Haijiang
Zhang, Sri Widiyantaro,
Wolfgang Rabbel, Melissa
Driskell, Shishay Bisrat
6 subduction megathrust earthquakes
over the last 106 years account for
over half of the energy released
during that time.