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Foreshock Activity Related to Enhanced Aftershock Production D. - - PowerPoint PPT Presentation

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Full Introduction of Article Foreshock Activity Related to Enhanced Aftershock Production D. Marsan, A. Helmstetter, M. Bouchon, and P. Dublanchet (2014) Speaker: Ta-Wei CHANG (Ide Lab) Jun. 10 th , 2017 Introduction Causal effect

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SLIDE 1

Foreshock Activity Related to Enhanced Aftershock Production

  • D. Marsan, A. Helmstetter, M. Bouchon, and P. Dublanchet (2014)

Speaker: Ta-Wei CHANG (Ide Lab)

  • Jun. 10th, 2017

Full Introduction of Article

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SLIDE 2

Introduction

  • Causal effect between fore- and main-shock?
  • Pre-event aseismic deformation
  • Rapid loading of asperities
  • Transient uncoupling extend from pre- to post-seismic phase?
  • Add to normal after-slip, affect aftershocks
  • Aftershocks bears information of initial fault uncoupling?
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SLIDE 3

Data

  • Worldwide catalog by Advanced National Seismic System (ANSS)
  • 1/1/1980 ~ 9/19/2013
  • 𝑛 β‰₯ 4.0
  • Mainshocks:
  • 𝑛 β‰₯ 6.5 after 1/1/1981
  • To avoid contamination by aftershocks of previous mainshocks:
  • Not preceded by 𝑛 β‰₯ 6.0 within a year
  • Within π‘’π‘—π‘‘π‘’π‘π‘œπ‘‘π‘“ = 10×𝑀 𝑛 = 0.05Γ—104.56 (𝑙𝑛)
  • 𝑛: magnitude of first shock; 𝑀 𝑛 : rupture radius
  • 612 in total
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SLIDE 4

Methods

  • Probability p that precursory seismicity acceleration is by chance:
  • Algorithm by Bouchon et al., [2013]
  • Before, within 50 (km) of mainshock
  • For each mainshock:
  • Max n from various T: 1, 5, 10 days; 1, 2, 3, 6, 12 months
  • Compare with Monte Carlo simulation:
  • Get n for 1000 Poisson time series in data sampling frequency
  • π‘ž =

(<=>?@A BCDE>

#

G <DACE)

H444

  • T

βˆ’π‘ˆ 2 L N1 N2 𝑂H β‰₯ 𝑂N 𝑂H < 𝑂N π‘œ π‘œ + 1; T = π‘ˆ 2 L π‘œ = 0

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SLIDE 5

Relationship Between Fore- and Aftershock Activities

  • S𝐡: π‘ž ≀ 0.1; 110 π‘›π‘π‘—π‘œπ‘‘β„Žπ‘π‘‘π‘™π‘‘; π‘‘π‘—π‘•π‘œπ‘—π‘”π‘—π‘‘π‘π‘œπ‘’ π‘π‘‘π‘‘π‘“π‘šπ‘“π‘ π‘π‘’π‘—π‘π‘œ

𝐢: π‘ž > 0.1; 502 π‘›π‘π‘—π‘œπ‘‘β„Žπ‘π‘‘π‘™π‘‘; π‘π‘’β„Žπ‘“π‘ π‘‘

Time series of event count Earthquake count

40.7 events 29.1 events 40% increase Dashed line: corrected for difference in magnitude of mainshocks (explained later)

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SLIDE 6

Relationship Between Fore- and Aftershock Activities

  • S𝐡: π‘ž ≀ 0.1; 110 π‘›π‘π‘—π‘œπ‘‘β„Žπ‘π‘‘π‘™π‘‘; π‘‘π‘—π‘•π‘œπ‘—π‘”π‘—π‘‘π‘π‘œπ‘’ π‘π‘‘π‘‘π‘“π‘šπ‘“π‘ π‘π‘’π‘—π‘π‘œ

𝐢: π‘ž > 0.1; 502 π‘›π‘π‘—π‘œπ‘‘β„Žπ‘π‘‘π‘™π‘‘; π‘π‘’β„Žπ‘“π‘ π‘‘

Regional Dependence Location of mainshocks Γ  geographically independent

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SLIDE 7

Relationship Between Fore- and Aftershock Activities

  • High correlation: precursory acceleration and number of aftershocks
  • Valid on regional scale
  • Of 14 regions: _

9: π‘žπ‘π‘‘π‘—π‘’π‘—π‘€π‘“ π‘‘π‘π‘ π‘ π‘“π‘šπ‘π‘’π‘—π‘π‘œ 3: 𝑏𝑛𝑐𝑗𝑕𝑣𝑝𝑣𝑑 2: π‘π‘žπ‘žπ‘π‘‘π‘—π‘’π‘“

  • Exception 1: Izu-Bonin (one strong aftershock sequence)
  • Exception 2: Northern America (oceanic transform faults + continental sources)
  • Oceanic transform faults: intensive foreshocks; little aftershocks
  • Gofar Transform Fault: pre-seismic acceleration creep halted by

mainshock

  • Fault-specific: high porosity & thermal gradient?

Regional Difference

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SLIDE 8

Relationship Between Fore- and Aftershock Activities

Regional Differencesβ€” Positively Correlated

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SLIDE 9

Relationship Between Fore- and Aftershock Activities

Regional Differencesβ€” Other Cases Opposite Ambiguous

Pink: large aftershock sequence removed (Became ambiguous)

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SLIDE 10

Relationship Between Fore- and Aftershock Activities

1.

Mainshocks of A are larger than B?

  • More productive

2.

Regions of A: higher long-term seismicity?

  • More aftershocks

3.

Preshocks causing acceleration also trigger their own aftershocks?

  • Aftershock: mainshock- and preshock-contributed

4.

Aftershocks of A are larger than that of B?

  • Triggering more of their own aftershock

5.

Magnitude completeness difference?

Possible Mechanisms

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SLIDE 11

Relationship Between Fore- and Aftershock Activities

  • Mainshocks of A are larger than B? Rejected!
  • Mean magnitude: S𝑛e: 6.88

𝑛g: 6.90 , actually opposite

  • Productivity law: 𝑂 ∝ 𝑓i6
  • N: number of aftershocks; m: magnitude of mainshock

Mechanism 1

#Aftershocksβ€” magnitude of mainshock

  • Cutoff: 50 (km); 𝛽 = 1.82; 𝑁lem = 7.4
  • p oq

L = 1.03

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SLIDE 12

Relationship Between Fore- and Aftershock Activities

  • Regions of A: higher long-term seismicity? Rejected!

Mechanism 2

  • No clear clustering
  • Independent of tectonic region
  • Preseismic rate: S𝐡: 3.04

𝐢: 3.27

  • Only difference: acceleration!
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SLIDE 13

Relationship Between Fore- and Aftershock Activities

  • Preshocks causing acceleration also trigger their own aftershocks?
  • Rate of preshocks triggering aftershocks:
  • ro

rm = s(6) mtu

L , where K m = S𝑙𝑓H.}N6 ; 𝑛 ≀ 7.4 𝑙𝑓H.}NΓ—~.β€’; 𝑛 > 7.4

  • Average over 612 events: 𝐿 = 3.6; 𝑙 = 8.20Γ—10β€’β€š
  • For each mainshock, within 1 year after event:
  • For preshock at: βˆ’365 < 𝑒< < 0 (π‘π‘π‘—π‘œπ‘‘β„Žπ‘π‘‘π‘™)
  • 𝑂

Ζ’ β€ž = H HH4 βˆ‘ 𝐿(𝑛<) log β€°β€š5tuβ€’m? uβ€’m? <

(𝑂‹

β€ž : π‘‘π‘—π‘›π‘—π‘šπ‘π‘ )

  • 𝑂

Ζ’ β€ž βˆ’ 𝑂‹

β€ž = 1.20

  • Actual 𝑂

Ζ’ βˆ’ 𝑂‹ = 11.6 (9.55 𝑒𝑗𝑛𝑓𝑑 𝑏𝑑 π‘›π‘£π‘‘β„Ž 𝑏𝑑 𝑂 Ζ’ β€ž βˆ’ 𝑂‹

β€ž )

  • Needs k 9.55 times larger in 20 days prior to mainshock to explain this

Mechanism 3

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SLIDE 14

Relationship Between Fore- and Aftershock Activities

  • Aftershocks of A are larger than that of B?
  • Productivity of A’s and B’s aftershocks: 𝐿

Ζ’ = 1.54𝐿‹

  • Difference in magnitude
  • Almost equal b-values: S𝑐ƒ: 1.21 Β± 0.06

𝑐‹: 1.18 Β± 0.03

  • Foreshock of Tohoku-Oki counts it as aftershock
  • After removal: 𝐿

Ζ’ = 1.08𝐿‹

  • Doesn’t suppress correlation: gain in production of A is 34% than 40%
  • This sequence needs careful analyzation for being the end of 2-month long swarm

Mechanism 4

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SLIDE 15

Relationship Between Fore- and Aftershock Activities

  • Magnitude completeness difference? Rejected!
  • Same cutoff magnitude for A and B
  • Correlation also exists when changing from 𝑛‒ = 4.0 𝑒𝑝 𝑛‒ = 5.0

Mechanism 5

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SLIDE 16

Comparison With Clustering Models

  • Foreshockβ€” aftershock relationship: can’t be explained by clustering models
  • Null hypothesis: ETAS
  • Assume acceleration: earthquake clustering properties
  • Doesn’t predict correlation between acceleration and aftershock!
  • ETAS: triggering rate density:
  • πœ‡ 𝑦, 𝑧, 𝑒 = 𝜈 + βˆ‘ πœ‡β€™(𝑦, 𝑧, 𝑒)
  • Earthquake 𝑗 before time 𝑒; πœ‡β€™: rate density of triggering by earthquake 𝑗
  • πœ‡β€™ 𝑦, 𝑧, 𝑒 = 𝐡’𝑓i6β€œ(𝑒 βˆ’ 𝑒’ + 0.08)β€’HΓ—

(”‒H)β€’β€œ

(β€“β€”Λœ)

Nβ„’(Ε‘β€Ίtβ€’β€œ

β€Ί) (β€“Ε“Λœ) β€Ί L

  • Triggering: ≀ 10 𝑧𝑓𝑏𝑠𝑑
  • Region: 2000Γ—2000 (𝑙𝑛N); periodic boundary condition
  • Background seismicity: 3 earthquakes/ day
  • Random magnitude from ANSS; 𝑛 β‰₯ 4
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SLIDE 17

Comparison With Clustering Models

  • To reproduce number of aftershock/ mainshock:
  • 𝛽 = 2.3; 𝑀4 = 8 𝑛 ; 𝛿 = 3.5
  • 𝛽: largest within 𝛽 < 𝑐 π‘šπ‘œ10; larger: enhance acceleration
  • Dispersion of data points: 𝐡’ = 3Γ—10β€’~ 1.8𝑣 + 0.1 , 0 < 𝑣 < 1
  • 1000 synthetic data, each 50000 years long, S𝐡: 95.9

𝐢: 588.6

  • Applied correction of difference in magnitude of mainshocks (as mechanism 1)
  • Aftershocks by foreshock (as mechanism 3)
  • To see βˆ†= 𝑂

Ζ’ βˆ’ 𝑂‹ βˆ’ 𝑂 Ζ’ β€ž βˆ’ 𝑂‹ β€ž

= 10.4

  • Probability: 0.13% (Gaussian fit) (5 out of 1000)
  • Fluctuation of ETAS: unlikely to explain
  • Tectonically wide-spread
  • Inward migration of foreshocks: observed; weaker than simulation
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SLIDE 18

Comparison With Clustering Models

Data ETAS-modeled

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SLIDE 19

Spreading of Aftershock Zone

  • Aseismic process required!
  • Ensemble-averaged clustering law and observation error not enough
  • A is 20% more wide-spread in space than B
  • Foreshocks: 1 year
  • Aftershocks: 20 days
  • Epicentral distance normalized:

𝑀 = 0.005Γ—104.56

  • Rotated so y=0 best perpendicular

to 1-year aftershock distribution

  • Circle: unit circle
  • Ellipse: 1 s confidence ellipse
  • Upper-right: smaller: B
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SLIDE 20

Spreading of Aftershock Zone

  • A is more wide-spread in space than B
  • ETAS: 5% only (20- days)
  • 1-day: 25% more
  • 20-day: 20% more
  • 1-year: 11% more (may be contaminated by background)
  • Scaling of aftershock productivityβ€” magnitude (or rupture length):
  • 𝑓H.}NΓ—6 = 𝑀(𝑛)

β€ΊΓ—Λœ.Β€β€Ί E>Β₯(˜¦)

L

= 𝑀(𝑛)H.5}

  • 23% more in L to explain 40% more aftershocks
  • Similarity between 20% and 23%
  • SSpatial spreading

Triggering of aftershocks of A : same ETAS-failed process!

  • Transient diffusing aseismic deformation-/ creeping- triggering fore- and aftershocks
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SLIDE 21

Discussion & Conclusion

  • Earthquake process: complex!
  • Creeping without earthquake/ earthquake without creeping
  • This study:
  • More aftershock following foreshock
  • Aseismic deformation transient
  • Compound rupture
  • Observable in averaged sense only
  • Compound rupture with slow initial phase recorded; but:
  • Fewer aftershocks for oceanic earthquakes
  • Observed here is in averaged sense; not individually
  • Tectonic implication too regionally specific
  • Better constrain the a priori probability of large ruptures by slow

deformation transients?