Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan...
Transcript of Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan...
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Can we map asperities Can we map asperities using b-values?using b-values?
Thessa Tormann (ETH)Thessa Tormann (ETH)Stefan Wiemer (ETH)
Danijel Schorlemmer (USC)
Jochen Woessner (ETH)
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b-value as stress sensorb-value as stress sensorAmitrano, JGR, 2003Amitrano, JGR, 2003
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b-value as stress sensorb-value as stress sensorAmitrano, JGR, 2003Amitrano, JGR, 2003
Laboratory study: Laboratory study: Acoustic Emission (AE) experiments with granite samplesAcoustic Emission (AE) experiments with granite samples
Mean b-value decreases systematically with increasing
confining pressure and differential stress
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b-value as stress sensorb-value as stress sensorSeveral case studies in different regions of the worldSeveral case studies in different regions of the world
California 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore 2001: Wyss Hayward 2005: Schorlemmer & Wiemer Parkfield 2007: Parsons Calaveras
Mexico 2001: Zuniga & Wyss Pacific Coast
Iceland 2006: Wyss & Stefansson Southern Iceland
France 1999: Sylvander French Pyrenees
Turkey 2000: Oncel & Wyss Izmit 2002: Westerhaus et al. Izmit
Sumatra 2005: Nuannin off coast of NW Sumatra
Japan 2002, 2005: Wyss & Matsumura Kanto-Tokai 2006: Nakaya Kuril Trench
This list is not complete, alltogether more than 20 case studies that map spatial b-value distributions(plus several studies of b-values beneath volcanoesand in subduction zones)
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b-value as stress sensorb-value as stress sensorSeveral case studies in different regions of the worldSeveral case studies in different regions of the world
California 1997: Wiemer & Wyss1997: Wiemer & Wyss Parkfield and Morgan Hill Parkfield and Morgan Hill 2000: Wyss et al. 2000: Wyss et al. San Jacinto and Elsinore San Jacinto and Elsinore 2001: Wyss Hayward 2005: Schorlemmer & Wiemer 2005: Schorlemmer & Wiemer Parkfield Parkfield 2007: Parsons 2007: Parsons Calaveras Calaveras
Mexico 2001: Zuniga & Wyss Pacific Coast
Iceland 2006: Wyss & Stefansson Southern Iceland
France 1999: Sylvander French Pyrenees
Turkey 2000: Oncel & Wyss Izmit 2002: Westerhaus et al. Izmit
Sumatra 2005: Nuannin off coast of NW Sumatra
Japan 2002, 2005: Wyss & Matsumura 2002, 2005: Wyss & Matsumura Kanto-Tokai Kanto-Tokai 2006: Nakaya Kuril Trench
This list is not complete, alltogether more than 20 case studies that map Spatial b-value distributions(plus several studies of b-values beneath volcanoesand in subduction zones)
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b-value as stress sensorb-value as stress sensorOutlineOutline
• General Issues of b-value Mapping
• Example Case Studies 2005: Schorlemmer & Wiemer Parkfield 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore 2002, 2005: Wyss & Matsumura Kanto-Tokai 2007: Parsons Calaveras
Currently: Tormann et al. San Francisco Bay Area
• ALM – Asperity-based likelihood model for California
• CALM – Cross-sectional asperity likelihood model for California
• Testing Perspectives
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General issues of b-value mappingGeneral issues of b-value mapping
Problems that each study adresses a little differently:Problems that each study adresses a little differently:
• Data quality
• Minimum number of events versus coverage
• Mc calculation
• Mapping radii
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General issues of b-value mappingGeneral issues of b-value mapping
Problems that each study adresses a little differently:Problems that each study adresses a little differently:
• Data quality
• Minimum number of events versus coverage
• Mc calculation
• Mapping radii
• Data selectionData selection
• Temporal non-stationarityTemporal non-stationarity
• Non-linear FMDsNon-linear FMDs
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ParkfieldParkfieldSchorlemmer & Wiemer, Nature, 2005Schorlemmer & Wiemer, Nature, 2005
NCEDC 1981 - 2003
Found temporal stationary very low b-value zone
Zone correlated well with themainshock and aftershock locations of the 2004 M6.0 event
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Morgan HillMorgan HillWiemer & Wyss, JGR, 1997Wiemer & Wyss, JGR, 1997
Anomalies in b-value and local recurrencetime (M6+) in the nucleation area before Morgan Hill 6.2 mainshock
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Morgan HillMorgan HillWiemer & Wyss, JGR, 1997Wiemer & Wyss, JGR, 1997
Anomalies in b-value and local recurrencetime (M6+) in the nucleation area before Morgan Hill 6.2 mainshock
b-values change a little but still show upanomalously low just south of the mainshock area
Anomaly in Tr is larger and stronger
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San Jacinto-ElsinoreSan Jacinto-ElsinoreWyss et al., JGR, 2000Wyss et al., JGR, 2000
Modern catalogue 1.2<=M<=5.0 (1981-1998)6 historic mainshocks M>=5.65 of historic events ruptured substantial parts of the 4 mapped asperities
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San Jacinto-ElsinoreSan Jacinto-ElsinoreWyss et al., JGR, 2000Wyss et al., JGR, 2000
Modern catalogue 1.2<=M<=5.0 (1981-1998)6 historic mainshocks M>=5.65 of historic events ruptured substantial parts of the 4 mapped asperities
Anomalies in b-value and local recurrence times correlate with mainshock locations and knownasperities
Much stronger, more clearly separated anomalies in local recurrence times than b-values
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Kanto-TokaiKanto-TokaiWyss & Matsumura, Tectonophysics, 2005Wyss & Matsumura, Tectonophysics, 2005
2002:2002:Calculation of b-value and local recurrence time (TL) anomalies using declustered data M>=1.5, 1980-1999
TL of less than 1000 years includes 5 of 6 historic mainshock locations, covering12% of the study area
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Kanto-TokaiKanto-TokaiWyss & Matsumura, Tectonophysics, 2005Wyss & Matsumura, Tectonophysics, 2005
2002:2002:Calculation of b-value and local recurrence time (TL) anomalies using declustered data M>=1.5, 1980-1999
TL of less than 1000 years includes 5 of 6 historic mainshock locations, covering12% of the study area
2005:2005:Correlation of local recurrence timeanomalies (2002) with seismicity 1999-2003.5
13% of all and ≈75% of M3.5+ seismicity fall into the 12% TL anomaly areas (max: 83% of M3.8+) Prand=2*10-14
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CalaverasCalaverasParsons, JGR, 2007Parsons, JGR, 2007
Do temporal and spatial b-value variations portend M>=4.0 events?Do temporal and spatial b-value variations portend M>=4.0 events?
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CalaverasCalaverasParsons, JGR, 2007Parsons, JGR, 2007
Do temporal and spatial b-value variations portend M>=4.0 events?Do temporal and spatial b-value variations portend M>=4.0 events?
• temporal variations do not correlate with mainshock times
• spatial analysis: • catalogue from 1968-2005, Mc=2.0• boxes of 5x5 km, overlapping by 2.5 km• define M>=4.0 events as test events cut catalogue at M<4.0• calculate b-value distribution for each of the 20 test events• compare local b-value with mean b-value significant deviation?
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CalaverasCalaverasParsons, JGR, 2007Parsons, JGR, 2007
Do temporal and spatial b-value variations portend M>=4.0 events?Do temporal and spatial b-value variations portend M>=4.0 events?
• temporal variations do not correlate with mainshock times
• spatial analysis: • catalogue from 1968-2005, Mc=2.0• boxes of 5x5 km, overlapping by 2.5 km• define M>=4.0 events as test events cut catalogue at M<4.0• calculate b-value distribution for each of the 20 test events• compare local b-value with mean b-value significant deviation?
Results: consistent (90%) inconsistent (90%) inconclusive 20: 6 1 13
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CalaverasCalaverasParsons, JGR, 2007Parsons, JGR, 2007
Is the forecast experiment a conclusive test?Is the forecast experiment a conclusive test?
• DATA QUALITYDATA QUALITY since 1968 (e.g. magnitude shifts)
• ML MATHEMATICSML MATHEMATICS: correction for upper limit on magnitude range, deviations from uncorrected formula will be significant?
• BIAS: BIAS: large events have been taken out, aftershocks not, not comparable to San Jacinto
• TARGET MAGNITUDE:TARGET MAGNITUDE: M4 too small to test asperities: rupture lengths of 1-2km test is not sensitive to such small scale heteorogeneity (different radii, binning in cylinders?)
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CalaverasCalaverasParsons, JGR, 2007Parsons, JGR, 2007
Is the forecast experiment a conclusive test?Is the forecast experiment a conclusive test?
• DATA QUALITYDATA QUALITY since 1968 (e.g. magnitude shifts)
• ML MATHEMATICSML MATHEMATICS: correction for upper limit on magnitude range, deviations from uncorrected formula will be significant?
• BIAS: BIAS: large events have been taken out, aftershocks not, not comparable to San Jacinto
• TARGET MAGNITUDE:TARGET MAGNITUDE: M4 too small to test asperities: rupture lengths of 1-2km test is not sensitive to such small scale heteorogeneity (different radii, binning in cylinders?)
1983.5-2007
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San Francisco Bay AreaSan Francisco Bay Area
Known faults
San Francisco
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San Francisco Bay AreaSan Francisco Bay Area
Known faultsANSS 1983.5-2007.0
San Francisco
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San Francisco Bay AreaSan Francisco Bay Area
Known faultsANSS 1983.5-2007.0WG02 Fault Model
San Francisco
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San Francisco Bay Area San Francisco Bay Area All segments b-value 0.6-1.2All segments b-value 0.6-1.2
San Andreas
Calaveras
Concord
San Gregorio
Greenville Mt Diabolo
Hayward
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SFBA: Central CalaverasSFBA: Central Calaveras
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SFBA: Central Calaveras SFBA: Central Calaveras Data SelectionData Selection
Wiemer/Wyss (+-2km)
WG02 (+-5.5km)
Constant width
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SFBA: Central Calaveras SFBA: Central Calaveras Data SelectionData Selection
Wiemer/Wyss (+-2km)
WG02 (+-5.5km)
Constant width
Bayesian prob
Wesson, 2003, BSSA
More physical based approach for associating faults and events:
Bayesian statisticsBayesian statistics
• equal prior pure distance-based association
• slip rate weighted prior faster faults are more likely to produce earthquakes
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SFBA: Central CalaverasSFBA: Central CalaverasData SelectionData Selection
Wiemer/Wyss (+-2km)
WG02 (+-5.5km)
Constant width
>= 20%
>= 50%
Bayesian prob
>= 80%
>= 95%
Woessner
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1971-1984Before Morgan
Hill (M6.2)
1997-2007Since Wiemer/
Wyss study
Constant width 2km
1986-1996Wiemer/Wyss
study
1983.5-2007
1984-1986During aftershock
decay
SFBA: Central CalaverasSFBA: Central Calaveras Re-investigation Re-investigation
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1971-1984Before Morgan
Hill (M6.2)
1997-2007Since Wiemer/
Wyss study
Constant width 2km Bayesian probability >=80%
1986-1996Wiemer/Wyss
study
1983.5-2007
1984-1986During aftershock
decay
SFBA: Central CalaverasSFBA: Central Calaveras Re-investigation Re-investigation
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SFBA: San Andreas – Santa CruzSFBA: San Andreas – Santa Cruz
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SFBA: Santa Cruz SFBA: Santa Cruz Non-linear FMDs Non-linear FMDs
b = -0.661 +/- 0.07
Nicely linear
FFrequencyMMagnitude DDistribution
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SFBA: Santa Cruz SFBA: Santa Cruz Non-linear FMDs Non-linear FMDs
b = -0.624 +/- 0.08 ???
Transition zone between locked and creeping segment, Slow earthquakes (San Juan Bautista) Non-linear frequency-magnitude distributions No sensible b-value calculation Ignore data to the right of green line
b = -0.661 +/- 0.07
b = -0.624 +/- 0.08 ???
Nicely linear
FFrequencyMMagnitude DDistribution
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SFBA: Northern & Southern SFBA: Northern & Southern HaywardHayward
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SFBA: Northern & Southern SFBA: Northern & Southern HaywardHayward
b=-1.24+/-0.03b=-0.81+/-0.04
b=-1.39+/-0.03b=-0.67+/-0.03
A CB D
BA
D CBA
D C
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SFBA: From b-values to SFBA: From b-values to probabilitiesprobabilities
• Calculate b-value for each point
• Calculate a-value for each point
• Choose target magnitude
• Calculate annual probability of
occurrence of an earthquake
equal to or larger Mtarg:
P = 1 - e- 10
a – bMtarg
T
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SFBA: All segments SFBA: All segments Annual Probabilities M6+Annual Probabilities M6+
San Andreas
Hayward
Calaveras
Concord
San Gregorio
Greenville Mt Diabolo
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San Francisco Bay AreaSan Francisco Bay AreaPreliminary asperity mapPreliminary asperity map
Low probability
Medium probability
High probability
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San Francisco Bay AreaSan Francisco Bay AreaPreliminary asperity mapPreliminary asperity map
Low probability
Medium probability
High probability
M6.5+ 1836-1983.5
M6.5+ 1983.5-2007.0
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Model SummaryModel Summary
Three categories of studies:
1.1. Pure case study: correlation with mainshocks/known asperities
2.2. Consisitency testdoes medium scale seismicity continue to concentrate in low b-value areas?
3.3. Retro/Prospective test: does microseismicity forecast large events‘ locations?
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Model SummaryModel Summary
Three categories of studies:
1.1. Pure case study: correlation with mainshocks/known asperities
2.2. Consisitency testdoes medium scale seismicity continue to concentrate in low b-value areas?
3.3. Retro/Prospective test: does microseismicity forecast large events‘ locations?
11Morgan Hill / Parkfield (1997)
Hayward (2001)Turkey (2001)Mexico (2001)
Kanto-Tokai (2002)Sumatra (2005)
San Francisco Bay Area (2007)
22Kanto-Tokai (2005)
Calaveras (2007)
33San Jacinto (2000)Parkfield (2004)
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Model SummaryModel Summary
Three categories of studies:
1.1. Pure case study: correlation with mainshocks/known asperities
2.2. Consisitency testdoes medium scale seismicity continue to concentrate in low b-value areas?
3.3. Retro/Prospective test: does microseismicity forecast large events‘ locations?
11Morgan Hill / Parkfield (1997)
Hayward (2001)Westerhaus (2001)
Mexico (2001)Kanto-Tokai (2002)
Sumatra (2005)San Francisco Bay Area (2007)
22Kanto-Tokai (2005)
Calaveras (2007)
33San Jacinto (2000)Parkfield (2004)
This is where we needThis is where we needmore and systematic effortmore and systematic effort
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ALMALMWiemer & Schorlemmer, SRL, Special Issue on RELM, 2007Wiemer & Schorlemmer, SRL, Special Issue on RELM, 2007
b
Mc
a
λ
AchievementsAchievements
• First testable model forecasting future seismicity on the basis of spatially varying b-values
• Submitted for prospective testing within RELM
Asperity-based Likelihood Model for CaliforniaAsperity-based Likelihood Model for California
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ALMALMWiemer & Schorlemmer, SRL, Special Issue on RELM, 2007Wiemer & Schorlemmer, SRL, Special Issue on RELM, 2007
b
Mc
a
λ
ShortcomingsShortcomings
• No treatment of depth
• Oversimplifying low resolution mapview approach
Asperity-based Likelihood Model for CaliforniaAsperity-based Likelihood Model for California
AchievementsAchievements
• First testable model forecasting future seismicity on the basis of spatially varying b-values
• Submitted for prospective testing within RELM
![Page 45: Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore San Jacinto and Elsinore 2001: Wyss](https://reader033.fdocuments.in/reader033/viewer/2022053009/5f0c7dd57e708231d435ab61/html5/thumbnails/45.jpg)
CALMCALM
• Testable hybrid model: advanced ALM plus fault information
• Pseudo fault based testing grid: fine grid near fault, coarse grid off fault to be developed by and for CSEP
• Near fault: real forecasts EMR completeness, b-value and a-value mapping
• Off fault: background PMC, a-value mapping and constant b-value
• Proper treatment of depth
To be submitted as possible prototype for pseudo-fault-based To be submitted as possible prototype for pseudo-fault-based testing in CSEPtesting in CSEP
Cross-sectional Asperity Likelihood Model for CaliforniaCross-sectional Asperity Likelihood Model for California
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Issues of Testing „Physically“Issues of Testing „Physically“
How to test whether low b-values allow to map asperities?How to test whether low b-values allow to map asperities?
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Issues of Testing „Physically“Issues of Testing „Physically“
• Problems in interpretation: what do we forecast by asperity mapping? – nucleation point – slip distribution – maximum rupture extent magnitude– ...
How to test whether low b-values allow to map asperities?How to test whether low b-values allow to map asperities?
![Page 48: Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore San Jacinto and Elsinore 2001: Wyss](https://reader033.fdocuments.in/reader033/viewer/2022053009/5f0c7dd57e708231d435ab61/html5/thumbnails/48.jpg)
Issues of Testing „Physically“Issues of Testing „Physically“
• Problems in interpretation: what do we forecast by asperity mapping? – nucleation point – slip distribution – maximum rupture extent magnitude– ...
• Can a number-per-gridpoint testing approach appropriately account for these physical principles?
How to test whether low b-values allow to map asperities?How to test whether low b-values allow to map asperities?
![Page 49: Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore San Jacinto and Elsinore 2001: Wyss](https://reader033.fdocuments.in/reader033/viewer/2022053009/5f0c7dd57e708231d435ab61/html5/thumbnails/49.jpg)
Issues of Testing „Physically“Issues of Testing „Physically“
• Problems in interpretation: what do we forecast by asperity mapping? – nucleation point – slip distribution – maximum rupture extent magnitude– ...
• Can a number-per-gridpoint testing approach appropriately account for these physical principles?
• How to formulate testable description of mapping information?
How to test whether low b-values allow to map asperities?How to test whether low b-values allow to map asperities?
![Page 50: Can we map asperities using b-values? - Earth-prints · 1997: Wiemer & Wyss Parkfield and Morgan Hill 2000: Wyss et al. San Jacinto and Elsinore San Jacinto and Elsinore 2001: Wyss](https://reader033.fdocuments.in/reader033/viewer/2022053009/5f0c7dd57e708231d435ab61/html5/thumbnails/50.jpg)
Issues of Testing „Physically“Issues of Testing „Physically“
• Problems in interpretation: what do we forecast by asperity mapping? – nucleation point – slip distribution – maximum rupture extent magnitude– ...
• Can a number-per-gridpoint testing approach appropriately account for these physical principles?
• How to formulate testable description of mapping information?
Start with pseudo-fault based testing as envisioned in Start with pseudo-fault based testing as envisioned in CSEP: CSEP:
rate and focal mechanism forecasts on fault based gridrate and focal mechanism forecasts on fault based grid
How to test whether low b-values allow to map asperities?How to test whether low b-values allow to map asperities?