Systematic Search Systematic Search for Background for Background Seismicity Rate Seismicity Rate

Changes and Changes and Correlations at Correlations at

Alaskan VolcanoesAlaskan VolcanoesK.R. Kore, S.R. McNutt, and D.H. K.R. Kore, S.R. McNutt, and D.H.

ChristensenChristensenGeophysical Institute, University of Alaska Fairbanks

Overview and GoalsOverview and Goals

Strain Rate Strain Rate Seismicity Rate Seismicity Rate

Identify background seismicity rate Identify background seismicity rate changeschanges

Temporally correlate “events” between Temporally correlate “events” between volcanoes along the Aleutian Arcvolcanoes along the Aleutian Arc

Speculate as to the cause of the Speculate as to the cause of the “events”“events”

ii

The Alaskan VolcanoesThe Alaskan Volcanoes

Okmok

Makushin

Akutan

Westdahl

Shishaldin

Dutton

Pavlof

Veniaminof

Aniakchak

Katmai Augustine

Iliamna

Redoubt

Spurr

Strandline Lake

Wrangell

Identification of Rate Identification of Rate ChangesChanges

Estimate minimum Estimate minimum magnitude of magnitude of completeness completeness

Exclude swarms Exclude swarms & eruptions& eruptions

PerformPerform AS(t) AS(t) function of function of

the z-test with the z-test with min. 3 mo. ratemin. 3 mo. rate

Exclude man-Exclude man- made changesmade changes

Volcanoes with Rate Volcanoes with Rate ChangesChanges

Okmok

Makushin

Akutan

Westdahl

Shishaldin

Dutton

Pavlof

Veniaminof

Aniakchak

Katmai Augustine

Iliamna

Redoubt

Spurr

Strandline Lake

Wrangell

12 of 16 Volcanoes12 of 16 Volcanoes Length of Monitoring TimeLength of Monitoring Time Activity/ Sensitivity LevelActivity/ Sensitivity Level

Mount Spurr

0

500

1000

1500

2000

2500

30001

99

0.0

0

19

90

.50

19

91

.00

19

91

.50

19

92

.00

19

92

.50

19

93

.00

19

93

.50

19

94

.00

19

94

.50

19

95

.00

19

95

.50

19

96

.00

19

96

.50

19

97

.00

19

97

.50

19

98

.00

19

98

.50

19

99

.00

19

99

.50

20

00

.00

20

00

.50

20

01

.00

20

01

.50

20

02

.00

20

02

.50

20

03

.00

20

03

.50

20

04

.00

Time (years)

Cu

mu

lati

ve N

um

ber

of

Eve

nts

Eruption

Coincident “Events”Coincident “Events”

10,000 synthetic catalogs per 10,000 synthetic catalogs per time window time window

Random generation of eventsRandom generation of events Probability of occurrenceProbability of occurrence

Ho: All volcanic events are random and independent

95% Confidence Level

Early 1996 EventsEarly 1996 Events

Augustine

2/19

Iliamna 5/8

Redoubt

5/11

120 Day window120 Day window P=0.004P=0.004 Iliamna increases, Redoubt Iliamna increases, Redoubt

and Augustine decreaseand Augustine decrease Akutan- swarmAkutan- swarm

Regional earthquakes: Adak Regional earthquakes: Adak June 9June 9thth – 10 – 10thth (M7.9, M7.2) (M7.9, M7.2)

Akutan 3/10

Late 1996 EventsLate 1996 Events

Augustine

9/25Katmai 10/16

Spurr 10/11

60 Day window60 Day window P=0.0001P=0.0001 Strandline, Katmai: swarmsStrandline, Katmai: swarms Pavlof: eruptionPavlof: eruption Augustine increase, Spurr Augustine increase, Spurr

decreasedecreaseAmukta eruptionAmukta eruptionSpeculated Slow Slip Event Speculated Slow Slip Event

((McNutt and Marzocchi, 2004)McNutt and Marzocchi, 2004)

Strandline Lake

8/31

Pavlof 9/16

Amukta 9/18

1998 Events1998 Events

Spurr 4/2

Strandline Lake

3/28

Redoubt 5/1

60 Day window60 Day window P=0.0148P=0.0148 All rate decreasesAll rate decreases

Plume from Spurr 3/28Plume from Spurr 3/28Lake Becharof/ Lake Becharof/

Ukinrek Maars Ukinrek Maars swarm 5/8-5/9swarm 5/8-5/9

Slow Slip Event, Cook Slow Slip Event, Cook Inlet - Late 1998 Inlet - Late 1998 (Ohta et al., 2004)(Ohta et al., 2004)

Lake Becharof

2002 Events2002 Events

Spurr 10/25

Strandline Lake 10/29

Wrangell

11/17

60 Day window60 Day window P=0.0206P=0.0206 All rate decreasesAll rate decreases

Denali Fault Denali Fault Earthquake Earthquake Sequence: Oct. 23Sequence: Oct. 23rdrd - - Nov. 3Nov. 3rdrd

10/23 M6.7

11/03 M7.9

The Four CasesThe Four Cases

Early 1996Early 1996:: Akutan, Iliamna, Redoubt, Akutan, Iliamna, Redoubt, Augustine:Augustine:120 Day Window, P=0.004120 Day Window, P=0.004

Late 1996Late 1996:: Spurr, Strandline Lake, Spurr, Strandline Lake, Augustine, Katmai, Pavlof: 60 Day Augustine, Katmai, Pavlof: 60 Day Window, P=0.0001Window, P=0.0001

19981998:: Strandline Lake, Spurr, Redoubt: Strandline Lake, Spurr, Redoubt: 60 Day Window, P=0.014860 Day Window, P=0.0148

20022002:: Wrangell, Strandline Lake, Spurr: Wrangell, Strandline Lake, Spurr: 60 Day Window, P=0.020660 Day Window, P=0.0206

Conclusions and Conclusions and SpeculationsSpeculations

Probabilities of independent volcanoes Probabilities of independent volcanoes having events close in time tend to be low.having events close in time tend to be low.

This suggests that the volcanoes are This suggests that the volcanoes are reacting to regional events which change reacting to regional events which change the stresses governing the volcanoes, such the stresses governing the volcanoes, such as:as: Regional Earthquakes Regional Earthquakes Slow Slip EventsSlow Slip Events Other more subtle stress changesOther more subtle stress changes