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David D. BowmanCalifornia State University, Fullerton
&Institut de Physique du Globe de Paris
The Evolution of Regional SeismicityBetween Large Earthquakes
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From Sykes and Jaumé [1990]
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All California Earthquakes M≥6.51950-1995
From Bowman et al., JGR, 1998
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Calculate from motion on all adjacent faultsplus creep at depth
Stress Change From Loading a Locked Patch on a Simple Fault
Slipping Fault Slipping FaultFutureEarthquake
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Calculate from motion on all adjacent faultsplus creep at depth
Stress Change From Loading a Locked Patch on a Simple Fault
Seismic SlipFuture
EarthquakeSlipping Fault Slipping FaultFutureEarthquake
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Calculate from motion on all adjacent faultsplus creep at depth
Stress Change From Loading a Locked Patch on a Simple Fault
Seismic SlipFuture
Earthquake Seismic SlipFuture
EarthquakeSlipping Fault Slipping FaultFutureEarthquake
![Page 7: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/7.jpg)
Calculate from motion on all adjacent faultsplus creep at depth
Stress Change From Loading a Locked Patch on a Simple Fault
Seismic SlipFuture
Earthquake Seismic SlipFuture
Earthquake
Creep at Depth
FutureEarthquakeSlipping Fault Slipping FaultFutureEarthquake
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FutureEarthquake
Creep at Depth
=
Negative Slip
Where are pre-earthquake stresses?
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Accelerating Seismicity in Stress Accumulation Regions
From Bowman and King, GRL, 2001
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A Simple Numerical Model
• Based on loading of fault in interseismic period
• Using realistic stress transfer
• Taking into account tectonic history
• Want to produce accelerating moment releaseover a broad region
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Seismogeniczone
0-50
-100
0-50
-100
0-50
-100
0-50
-100
0-50
-100
Failure stress
Failure stress
Failure stress
Failure stress
Failure stress
Stress drop
Stress drop
Beginning of the earthquake cycle (immediately after large event)
33% of the earthquake cycle
66% of the earthquake cycle
Immediately before thenext earthquake
Immediately after the earthquake
Stress relative to failure stress (bars)
0-50
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An earthquake occurs when stress rises above the failure level
A BFault
Stre
ssFailure Stress
A BFault
Stre
ss
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An earthquake occurs when stress rises above the failure level
A BFault
Stre
ssFailure Stress
A BFault
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
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An earthquake occurs when stress rises above the failure level
A BFault
Stre
ssFailure Stress
A BFault
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
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An earthquake occurs when stress rises above the failure level
A BFault
Stre
ssFailure Stress
A BFault
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
A BFault
Stre
ssFailure Stress
A B
Stre
ss
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fault
Aftershocks Stress shadows
Start of theEarthquake
Cycle
Approachingthe
Earthquake
Immediatelybefore theEarthquake
Immediatelyafter the
Earthquake75% of theEarthquake
The end ofthe
Earthquake cycle
Earthquake
Seismicity in the Earthquake Cycle
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Implications of Regional Stress Accumulation Model
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Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
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Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
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Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
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Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
• Accelerating Moment Release over a broad spatial region before large EQs
![Page 22: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/22.jpg)
Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
• Accelerating Moment Release over a broad spatial region before large EQs
• Region size scales with size of the “predicted” earthquake
![Page 23: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/23.jpg)
Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
• Accelerating Moment Release over a broad spatial region before large EQs
• Region size scales with size of the “predicted” earthquake
• Evolution of the frequency-magnitude statistics (Gutenberg-Richter relation)
![Page 24: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/24.jpg)
Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
• Accelerating Moment Release over a broad spatial region before large EQs
• Region size scales with size of the “predicted” earthquake
• Evolution of the frequency-magnitude statistics (Gutenberg-Richter relation)
• Stationary (time-independent) b-value
![Page 25: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/25.jpg)
Implications of Regional Stress Accumulation Model
• Off-fault aftershocks occur in regions of elevated static stress change due to the earthquake
• Main fault is seismically quiet for most of the seismic cycle
• “Mogi doughnuts”
• Accelerating Moment Release over a broad spatial region before large EQs
• Region size scales with size of the “predicted” earthquake
• Evolution of the frequency-magnitude statistics (Gutenberg-Richter relation)
• Stationary (time-independent) b-value
• a-value increase before a large event anddecreases after the event
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Earthquake
Late in theEarthquake cycle
Immediatelybefore theearthquake
Immediatelyafter the
earthquake
Build-up to the EarthquakeMain Fault is Quiet
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California Seismicity 1912-2001 M>3.5
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Earthquake
Late in theEarthquake cycle
Immediatelybefore theearthquake
Immediatelyafter the
earthquake
Build-up to the EarthquakeAccelerating Moment Release
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Cum
ulat
ive
Beni
off S
train
Time Time
Which cumulative moment release curve is fora REAL seismicity sequence?
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Cum
ulat
ive
Beni
off S
train
Time Time
Which cumulative moment release curve is fora REAL seismicity sequence?
San Fernando EarthquakeModelTime Time
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Accelerating Seismicity
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Earthquake
Late in theEarthquake cycle
Immediatelybefore theearthquake
Immediatelyafter the
earthquake
Build-up to the EarthquakeEvolution of Gutenberg-Richter Statistics
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126ÞW
126ÞW
124ÞW
124ÞW
122ÞW
122ÞW
120ÞW
120ÞW
46ÞN 46ÞN
48ÞN 48ÞN
50ÞN 50ÞN
Two large nearby events show accelerating moment release
The regions overlap, approximating the evolution of the seismicity over 2.5 cycles
Seismicity in the Pacific Northwest
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Pacific Northwest Seismicity
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Seismicity in the model & Pacific Northwest
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Cumulative Benioff Strain
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Evolution of the frequency-magnitude statistics
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Evolution of the frequency-magnitude statistics
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• Better calculation of the “noise” functions- incorporate stress transfer for background EQs?
• More complex fault geometries- simulate real fault networks
• Additional Testing on real data- Test on earthquakes from other regions
(Greece, Turkey, China, etc)- False alarm rate?
• Relationship to Time-Dependent Hazard Analysis
Looking Forward:
Pre/re-prints available at:http://geology.fullerton.edu/faculty/dbowman
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Future California Earthquakes?
![Page 41: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/41.jpg)
Future California Earthquakes?
![Page 42: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/42.jpg)
Future California Earthquakes?
No?
![Page 43: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/43.jpg)
Future California Earthquakes?
No?
![Page 44: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/44.jpg)
Future California Earthquakes?
No?
Yes?
![Page 45: The Evolution of Regional Seismicity Between Large Earthquakes …cais.gsi.go.jp/UJNR/UJNR4P/Bowman-CSUF.pdf · 2010-11-24 · next earthquake Immediately after the earthquake Stress](https://reader033.vdocuments.mx/reader033/viewer/2022050305/5f6e0b272f7271145367e012/html5/thumbnails/45.jpg)
The Seismic Cycle
From Ellsworth [1981]
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Magnitude of the event depends on the size of the stress concentration
This allows the calculation of theFrequency-Magnitude relation
FailureStress
Creating a Synthetic Catalog
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Immediately after the earthquake
25% of the cycle
50% of the cycle
75% of the cycle
Immediately before the earthquake
failure stress
-50 0bars
Stress and Seismicity Through the Seismic Cycle
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Evolution of Gutenberg-Richter Scaling Beforethe 1987 Superstition Hills Earthquake
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Evolution of Gutenberg-Richter Scaling Beforethe 1987 Superstition Hills Earthquake
Evolution of Gutenberg Richter Scaling Beforethe 1987 Superstition Hills Earthquake
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Evolution of Gutenberg-Richter Scaling Beforethe 1987 Superstition Hills Earthquake
Evolution of Gutenberg Richter Scaling Beforethe 1987 Superstition Hills Earthquakethe 1987 Superstition Hills Earthquake
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Evolution of Gutenberg-Richter Scaling Beforethe 1987 Superstition Hills Earthquake
Evolution of Gutenberg Richter Scaling Beforethe 1987 Superstition Hills Earthquakethe 1987 Superstition Hills Earthquakethe 1987 Superstition Hills Earthquake
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Evolution of Gutenberg-Richter Scaling Beforethe 1987 Superstition Hills Earthquake
Evolution of Gutenberg Richter Scaling Beforethe 1987 Superstition Hills Earthquakethe 1987 Superstition Hills Earthquakethe 1987 Superstition Hills Earthquake
g gthe 1987 Superstition Hills Earthquake
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slip 0 unitsslip 0 units slip 0 units
slip 0 units
slip 0.25 units slip 0 units
slip 0.25 units
slip 0.25 units
slip 0.5 unitsslip 0.5 units
slip 0.5 units
slip 0 unit
slip 0.5 units
slip 0.5 units
slip 0.5 unitsslip 1 unit
slip 1 unitslip 0.75 unit
slip 0.75 units
slip 0.75 units
slip 1 unit slip 1 unit slip 1 unit
slip 1 unit
EarthquakeStatic stress (Coulomb)
changes during the earthquake cycle
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Stress FieldFrom Previous History of EQs
Stress FieldFrom Loading
CurrentStressField
= +
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Background stress field
Characteristics of the Background Stress Field(for a simple model)
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Background stress field
Characteristics of the Background Stress Field(for a simple model)
• Stress must be low along the strike of the fault(or rupture would continue)
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Background stress field
Characteristics of the Background Stress Field(for a simple model)
• Stress distant from the fault must approach,but not exceed, the failure stress
• Stress must be low along the strike of the fault(or rupture would continue)
Backgrou
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Background stress field
Characteristics of the Background Stress Field(for a simple model)
• Coulomb field + background field can notexceed the failure stress (except locally)
• Stress distant from the fault must approach,but not exceed, the failure stress
• Stress must be low along the strike of the fault(or rupture would continue)
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Background stress field
Characteristics of the Background Stress Field(for a simple model)
Coulomb field immediatelybefore the event
Coulomb field immediatelyafter the event
- Positive Coulomb stressesmust have a correspondingnegative value in thebackground field
• Coulomb field + background field can notexceed the failure stress (except locally)
• Stress distant from the fault must approach,but not exceed, the failure stress
• Stress must be low along the strike of the fault(or rupture would continue)
Background stress field
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The start of theearthquake cycle
The end of theEarthquake cycle
Stress Change
Stress Level Relative to the Failure Stress
Tectonic Memory Stress
Earthquake
Earthquake
25
0
-25
bars
0
-50
bars
failurestress
Stress Change vs. Stress Through the Earthquake Cycle