Induced earthquake magnitudes are as large as (statistically) expected.

Nicholas van der Elst, U.S. Geological Survey Morgan Page, U.S. Geological Survey

Thomas Goebel, UC Santa Cruz and Caltech Deborah Weiser, USGS and UCLA

S. Mehran Hosseini, USC

Proto-OEF: one-year shaking forecast, including induced seismicity

Dallas

Denver

Washington

Atlanta

New

Orleans

Boston

Minneapolis

Raleigh

Lincoln Columbus

Oklahoma

City

Nashville

Austin

Phoenix

Sacramento

Denver

Seattle

Based on natural andinduced earthquakes

Based on the presumptionearthquakes occur naturally

Modified Mercalli Intensity

VIII+ Shaking severe, heavier damage

VII Shaking very strong, moderate damage

VI Shaking strong, felt by all, minor damage

V Shaking moderate, felt indoors by most, outdoors by many

IV Shaking light, felt indoors by many, outdoors by few

III Shaking weak, felt indoors by several

USGS Forecast for Ground Shaking Intensity from Natural and Induced Earthquakes in 2016

USGS map displaying intensity of potential ground shaking from natural and human-induced earthquakes. There is a small chance (one percent) thatground shaking intensity will occur at this level or higher. There is a greater chance (99 percent) that ground shaking will be lower than what is displayedin these maps.

Petersen et al., 2015

1 % probability of exceedence

Dependence on maximum magnitude

Mmax ≈ 7

Mmax = 6

• Are induced earthquake magnitudes restricted by injection volume?

• Or, are induced earthquake magnitudes determined by the pre-stress and connectivity of the fault network?

• are the observed sizes of induced earthquakes just a consequence of sampling the GR distribution?

Is there evidence that induced earthquakes are smaller than tectonic?

Tectonic earthquakes are not confined to the structure on which they initiate

2002 M7.9 Denali Earthquake

Other examples: El Mayor-Cucapah

Landers

Eberhart-Phillips… 2003

A classic question: Does Gutenberg-Richter reflect the

distribution of fault sizes, or the statistics of earthquake growth and

arrest on a complex, inter-connected fault network?

Cautionary Tale: Remote triggering

Velasco… 2008, Parsons… 2014

Denali remote triggering Global stack

3000 km

But then: 2012 M8.6 East-Indian Ocean

Pollitz…, 2012

Rate of M≥5.5 earthquakes

days since M8.6 event

remotely triggered M≥5.5 earthquakes

USGS

Could we make the same mistake with induced earthquakes?

Dallas

Denver

Washington

Atlanta

New

Orleans

Boston

Minneapolis

Raleigh

Lincoln Columbus

Oklahoma

City

Nashville

Austin

Phoenix

Sacramento

Denver

Seattle

Based on natural andinduced earthquakes

Based on the presumptionearthquakes occur naturally

Modified Mercalli Intensity

VIII+ Shaking severe, heavier damage

VII Shaking very strong, moderate damage

VI Shaking strong, felt by all, minor damage

V Shaking moderate, felt indoors by most, outdoors by many

IV Shaking light, felt indoors by many, outdoors by few

III Shaking weak, felt indoors by several

USGS Forecast for Ground Shaking Intensity from Natural and Induced Earthquakes in 2016

USGS map displaying intensity of potential ground shaking from natural and human-induced earthquakes. There is a small chance (one percent) thatground shaking intensity will occur at this level or higher. There is a greater chance (99 percent) that ground shaking will be lower than what is displayedin these maps.

• Are induced earthquake magnitudes restricted by injection volume?

• Or, are induced earthquake magnitudes determined by the pre-stress and connectivity of the fault network?

• are the observed sizes of induced earthquakes just a consequence of sampling the GR distribution?

Is there evidence that induced earthquakes are smaller than tectonic?

Re-evaluating the limit* on the magnitudes of induced earthquakes.

(*Other than the tectonic limit)McGarr, 2014

basic assumptions1. There are faults nearby

2. faults are stressed within one stress drop of failure

3. formation already saturated (∆P~∆V)

4. Gutenberg-Richter

5. Earthquakes are confined to the fluid perturbation

An analogy with aftershocks (triggered earthquakes)

• Suppose the total moment of an aftershock sequence were limited to the moment of the mainshock.

• Deterministic application of G-R implies that the largest aftershock should have 1/2 the moment of the mainshock.

• In magnitude:

1) ΔMas = 0.2 is not consistent with Båth’s law (too large in the expectation).

2) ΔMas = 0.2 is regularly exceeded (too small in the limit).

Mms −Mas(1) = 2

3log10

M 012M 0

⎛⎝⎜

⎞⎠⎟≈ 0.2

what went wrong?• Gutenberg-Richter is probabilistic. The number of aftershocks

nucleated scales with the mainshock stress perturbation

• But the sizes of the aftershocks are determined by the pre-stress and the tectonics (or whatever), not the size of the triggering perturbation.

Felzer…, 2006

Num

ber o

f trig

gere

d M

3.5+

King…, 1994

the moment-cap hypothesis1. There are faults nearby

2. faults are stressed within one stress drop of failure

3. formation already saturated (∆P~∆V)

4. Gutenberg-Richter

5. Earthquakes are confined to the fluid perturbation

the sample-size hypothesis1. There are faults nearby

2. faults are stressed within one stress drop of failure

3. formation already saturated (∆P~∆V)

4. Gutenberg-Richter (probabilistic)

5. Earthquakes are confined to the fluid perturbation

Tests of the sample size hypothesis

1. The maximum observed magnitude is proportional to the log of the number of prior induced events.

2. The order of occurrence of the largest earthquake is random within the sequence.

3. Bonus test: injected volume controls number not moment of induced eathquakes.

Quick sanity check1. Magnitudes are distributed Gutenberg-Richter. 2. No upper limit. 3. Number is proportional

to volume injected.

M̂max =1b

Σ + log10V( )

Pawnee?

expected distribution of Mmax

1) Gutenberg Richter

N M( ) = N10−b M−Mc( )

2) N =1 for Mmax (the mode)

M̂max = Mc +1blog10 N

Probability densities (cdf)

Mmax

2 3 4 5 6 7 8

prob

abilit

y de

nsity

0

0.5

1

1.5 3 10 30 100 3001000

Mmax-Mmode

-2 -1 0 1 2 3 4

prob

abilit

y de

nsity

0

0.5

1

1.5 3 10 30 100 3001000

Mmax

2 3 4 5 6 7 8

prob

abilit

y de

nsity

0

0.5

1

1.5 3 10 30 100 3001000

Mmax-Mmode

-2 -1 0 1 2 3 4

prob

abilit

y de

nsity

0

0.5

1

1.5 3 10 30 100 3001000

1) Gutenberg Richter

N M( ) = N10−b M−Mc( )

2) N =1 for Mmax (the mode)

M̂max = Mc +1blog10 N

3) correction for using N prior to Mmax

Probability densities (cdf)

ˆ ′Mmax = M̂max + log10 e( )

expected distribution of Mmax

GR statistics of each sequence• Magnitude of

completeness Mc

• b-value (excluding largest event)

• Number above Mc

Mag - Mc-2 -1 0 1 2 3

Nor

mal

ized

Num

ber

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

b = 1

KTB

BUK

GOK

SZ1

SZ2

SZ3

SZ4

BAS

A87

CB1

A01

YOH

PDX

R11

GUY

POH

TTX

RMA

POK

HAR

M̂max = Mc +1blog10 N

Observed vs. expected magnitudesMexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Mmax vs. Nprior

Taking into account Mc only

Mexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Mmax vs. Mexpected

Taking into account Mc, b, Nprior

M̂max ∝ log10 Nref M̂max = Mc +1blog10 N

Mmax - Mml-1 0 1 2 3 4

Prob

abilit

y D

ensi

ty

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mmax - Mml

-1 0 1 2

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.93

Nprior/Ntot0 0.2 0.4 0.6 0.8 1

Inst

ance

s

0

1

2

3

4

5

N/Ntot

0 0.5 1

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.3

Test #1: Mmax is consistent with Nprior

Mmax vs. Mpredicted

Taking into account Mc, b, Nprior

Naive prediction

Conditional prediction

Distribution of difference between Mobs and Mpredicted

Mexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Mmax vs. Mexpected

A+

(N-1)/Ntot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFWBASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOK HAR

Vol/Voltot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFW BASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOKHAR

Mmax - Mml-1 0 1 2 3 4

Prob

abilit

y D

ensi

ty

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mmax - Mml

-1 0 1 2

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.93

Nprior/Ntot0 0.2 0.4 0.6 0.8 1

Inst

ance

s

0

1

2

3

4

5

N/Ntot

0 0.5 1

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.3

Test #2: order of occurrence is random

13 out of 21 in latter half (10.5 expected)

C-Nprior/Ntot

(N-1)/Ntot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFWBASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOK HAR

Vol/Voltot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFW BASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOKHAR

Mmax - Mml-1 0 1 2 3 4

Prob

abilit

y D

ensi

ty

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mmax - Mml

-1 0 1 2

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.93

Nprior/Ntot0 0.2 0.4 0.6 0.8 1

Inst

ance

s

0

1

2

3

4

5

Unb

iase

d In

stan

ces

1

2

3

4

5

N/Ntot

0 0.5 1

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.3p = 0.68

13 out of 21 in latter half (10.5 expected) excluding cases shut down because of large quakes: 9 out of 16 in latter half (8 expected)

Test #2: order of occurrence is random

A-

C-Nprior/Ntot

Test #3: Number proportional to volumeMexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Number vs. Volume

Taking into account Mc

log10(Npred/Ntot)10-1 100 101

Cum

ulat

ive

Frac

tion

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1n = 0.5n = 1n = 1.5

Scaling power n0 0.5 1 1.5 2

Varia

nce

0.2

0.3

0.4

0.5

Ntot

N0

= VtotV0

⎛⎝⎜

⎞⎠⎟

n

n=1

A-

1. faults are distributed uniformly over one stress drop from failure.

N ∝ ∆P

Cochran…, 2004

Consistent with tidal triggering of earthquakes

Mexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Why should number of triggered earthquakes scale with volume?

Why should number of triggered earthquakes scale with volume?

1. faults are distributed ~uniformly over one stress drop from failure.

N ∝ ∆P

2. nucleation sites are distributed ~uniformly over the volume.

N ∝ ∆PV

3. Pressure proportional to injection volume over reservoir volume.

∆P ∝ ∆V/V

N ∝ ∆V

Shapiro…, 2007,2010,2011

Cochran…, 2004

Consistent with tidal triggering of earthquakes

Mexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s

-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Mexp

0 1 2 3 4 5 6 7

Mob

s

0

1

2

3

4

5

6

7

0.05

0.95

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDX

R01

R11

GUYPOH

TTX

RMAPOK

HAR

Volume (m3)102 103 104 105 106 107 108

Mob

s

0

1

2

3

4

5

6

7

-3

-2

-1

0

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBAS A87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

CB2

CB3

CB4

m310-6 10-2 102 106

Mob

s-6

-2

2

6

GDF

Volume (m3)102 103 104 105 106 107 108

Num

ber a

bove

Mre

f

100

101

102

103

104

105

106

-3

-2

-1

0

KTB

BUK

GOK

SZ1SZ2

SZ3

SZ4

DFW

BAS

A87

CB1

A01

YOH

PDXR01

R11GUY

POHTTX

RMA

POK

HAR

Number above Mref

100 101 102 103 104 105 106 107

Mob

s

0

1

2

3

4

5

6

7

KTB

BUK

GOKSZ1

SZ2

SZ3SZ4

DFWBASA87CB1

A01YOHPDXR01

R11

GUYPOH

TTX

RMAPOK

HAR

Mmax - Mml-1 0 1 2 3 4

Prob

abilit

y D

ensi

ty

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mmax - Mml

-1 0 1 2

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.93

Nprior/Ntot0 0.2 0.4 0.6 0.8 1

Inst

ance

s

0

1

2

3

4

5

Unb

iase

d In

stan

ces

1

2

3

4

5

N/Ntot

0 0.5 1

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.3p = 0.68Mmax - Mml

-1 0 1 2 3 4

Prob

abilit

y D

ensi

ty

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mmax - Mml

-1 0 1 2

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.93

Nprior/Ntot0 0.2 0.4 0.6 0.8 1

Inst

ance

s

0

1

2

3

4

5

N/Ntot

0 0.5 1

Cum

ulat

ive

Den

sity

0

0.2

0.4

0.6

0.8

1p = 0.3

Confirmation of the sample size hypothesis

Num

ber

Volume

1. The maximum observed magnitude is predicted by the number of prior events

2. The order of occurrence of the largest earthquake is

random within the sequence.

3. The number of induced earthquakes is proportional to injected volume.

A+

A-A-

m310-6 10-2 102 106

Mobs

-6

-2

2

6

KTB

BUK

GOKSZ1SZ2

SZ3SZ4

DFWBAS A87CB1 A01YOHPDXR01

R11

GUYPOHTTX

RMAPOK

HAR

CB2

CB3

CB4

GDF

Goodfellow…, 2015

evidence from lab triggering• Need a wider range of volumes • All Cooper Basin stims • Lab hydrofrack: (4 ml, Mmax -7)

Mmax vs. log10(V)

obse

rved

Mm

ax

Volume (m3)104

6

2

-2

4

0106102100 108

lon-99.5 -99 -98.5 -98 -97.5 -97 -96.5

lat

35

35.5

36

36.5

37

37.5

Day

s si

nce

Jan

1. 2

014

0

100

200

300

400

500

600

700

800

900

Magnitude3 4 5 6 7

Cum

ulat

ive

Num

ber

100

101

102

103

104

b = 1.6 ± 0.07

3 4 5 6 7

Mm

ax P

roba

bilit

y D

ensi

ty

10-2

10-1

100

101

Was the M5.8 Pawnee earthquake expected?

P(Mmax ≥ 5.8) ~25%

KansasOklahoma

Conclusion• Induced earthquakes are as large as expected (they are triggered

tectonic earthquakes).

• The NSHM map should probably use the same magnitude limit for induced and tectonic earthquakes.

• Good news: the probability of a large earthquake can be estimated. Best predictor: Mmax ~ Σ log10V

• Bad news: there are no absolutes.

5 of 8 frack and EGS wells

Are EGS wells different?

(N-1)/Ntot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFWBASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOK HAR

Vol/Voltot0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

b-value

0.5

1

1.5

2

2.5

KTB

BUK

GOKSZ1

SZ2

SZ3

SZ4 DFW BASA87 CB1 A01

YOHPDXR01 R11GUY

POH

TTX

RMAPOKHAR

Magnitude3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5

Num

ber

100

101

102

103

b = 1.7

1 year M90 = 5.8

Northern OK post-2014