remote earthquake triggering: (fault) failure is not always an option heather savage and emily...
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Remote Earthquake Triggering: (Fault) Failure is Not Always an
Option
Heather Savage and Emily Brodsky
UC Santa Cruz
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Remote Triggering
From Denali Earthquake
Gomberg et al., 2004
Triggered Seismicity from the Denali Earthquake
2002 Denali, Alaska Mw 7.9 Earthquake
Husker and Brodsky, 2004
Courtesy of Anthony 2004
•5 MPa normal stress•Tectonics stress: background shear loading rate of 5 µm/s•Oscillating stress: Vlp = V0 + Asin(t)•Fault zone materials: granite blocks, glass beads
Laboratory Setup
0.5
MP
a
Time
Shear Stress
Stick-slip Failure
Transient
Trigger
t2t1
Savage and Marone, 2008
She
ar S
tres
s (M
Pa)
Loa
d P
oint
Vel
ocit
y (µ
m/s
)
Amplitude Dependence
10
20
30
40
50 TriggeredNon-triggered
0 10 20 30 40 50 60
6 mm layer
Amplitude (µm/s)
D
10
20
30
40
50
granite -smooth
granite -rough
A
10
20
30
40
502 mm layerB
10
20
30
40
503 mm layerC
Increasing gouge thickness
No gouge
Inte
r-ev
ent T
ime
(s)
Amplitude (µm/s)
1.4
1.6
1.8
2
2.2
2.4
p936
B
RoughGranite Surface
1.4
1.6
1.8
2
2.2
2.4
p900
C
3 mm thick layer
1.4
1.6
1.8
2
2.2
2.4
665 670 675 680 685 690 695 700
p961
Time (s)
D
6 mm thick layer
1
1.5
2
2.5
3
3.5
p1173
A
SmoothGranite Surface
Sh
ear
Str
ess
(M
Pa)
Time (s)Savage and Marone, 2008
Triggering Intensity = Normalized Seismicity Rate
Change
t2t1
Seismicity Rate: =1/t
Normalized Seismicity Rate Change: n (2- 1)/ 1 Felzer and Brodsky, 2005
Changes in Lab Seismicity
Rate
0.1
1
10 100
6 mm gouge layer
Velocity Amplitude (µm/s)
Triggering Threshold
0.1
1
10 100
Granite Surfaces2 mm gouge layer3 mm gouge layer6 mm gouge layer
Velocity Amplitude (µm/s)
Changes in Lab Seismicity
Rate
Remote Triggering on the Nicoya Peninsula, Costa Rica
Seismic data courtesy of S. Schwartz
Solomon Islands - 04/01/07
Peru - 08/15/07
So. Sumatra - 09/12/07
Indonesia - 09/12/07
Fiji - 12/09/07
Sichuan - 05/12/08
New Zealand - 07/15/09
Remote Earthquakes
New Zealand 2009, recorded in Costa Rica
Seismic data courtesy of S. Schwartz
0.1
1
10
104 105 106
Velocity Amplitude (nm/s)
Costa Rica
Indonesia 09/12/2007
Peru 08/15/2007
Solomon Islands 04/01/07
So. Sumatra 09/12/07
Fiji 12/09/07
New Zealand
0715/09
Sichuan 04/12/08
Remote Triggering in the Western US, Transportable Array
Remote Earthquakes
New Zealand - 07/15/09
Samoa - 09/29/09
Sumatra - 09/30/09
Samoa 2009, recorded in Eastern Wyoming
Costa Rica and E. Wyoming
0.1
1
10
104 105 106
Velocity Amplitude (nm/s)
Sumatra 09/30/09
New Zealand 07/15/09
0.1
1
10 100
Granite Surfaces2 mm gouge layer3 mm gouge layer6 mm gouge layer
Velocity Amplitude (µm/s)
Conclusions
• Triggered seismicity is a function of strain amplitude (bigger earthquakes trigger more earthquakes) but is also dependent on interseismic history
• Large earthquakes that closely follow previous large events are very inefficient at triggering additional seismicity
• Experiments suggest that fault zone properties determine the relationship between triggering intensity and strain amplitude– Preliminary seismic observations suggest subduction zones spend more time close to critical failure than old crustal
faults
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