Download Systematic Search for Background Seismicity Rate Changes

Systematic Search for
Background Seismicity
Rate Changes and
Correlations at Alaskan
Volcanoes
K.R. Kore, S.R. McNutt, and D.H. Christensen
Geophysical Institute, University of Alaska Fairbanks
Overview and Goals
Strain Rate  Seismicity Rate
 i   i
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

Identify background seismicity rate
changes
Temporally correlate “events” between
volcanoes along the Aleutian Arc
Speculate as to the cause of the “events”
The Alaskan Volcanoes
Spurr
Katmai
Aniakchak
Pavlof
Shishaldi
n
Akutan
Veniaminof
Okmok
Westdah Dutton
Makushin l
Strandline
Lake
Redoub
Iliamnat
Augustin
e
Wrangell
Identification of Rate Changes

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Estimate minimum
magnitude of
completeness
Exclude swarms
& eruptions
Perform AS(t)
function of
the z-test with
min. 3 mo. rate
Exclude manmade changes
Volcanoes with Rate Changes
Spurr Strandline Lake
Wrangell
Redoub
Iliamna
t
Augustine
Katmai
Aniakchak
ShishaldinPavlof
Veniaminof
Akutan
Okmok
Dutton
Westdahl
Makushin
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12 of 16 Volcanoes
Length of Monitoring Time
Activity/ Sensitivity Level
1990.00
1990.50
1991.00
1991.50
1992.00
1992.50
1993.00
1993.50
1994.00
1994.50
1995.00
1995.50
1996.00
1996.50
1997.00
1997.50
1998.00
1998.50
1999.00
1999.50
2000.00
2000.50
2001.00
2001.50
2002.00
2002.50
2003.00
2003.50
2004.00
Cumulative Number of Events
Mount Spurr
3000
2500
2000
1500
Eruption
1000
500
0
Time (years)
Coincident “Events”
Ho: All volcanic events are random and
independent
95% Confidence Level



10,000 synthetic catalogs per time
window
Random generation of events
Probability of occurrence
Early 1996 Events
Redoubt
5/11
Augustin
e 2/19
Akutan
3/10
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Iliamna
5/8
120 Day window
P=0.004
Iliamna increases, Redoubt and
Augustine decrease
Akutan- swarm
Regional earthquakes: Adak June 9th –
10th (M7.9, M7.2)
Late 1996 Events
Strandline
Lake 8/31
Spurr
10/11
Katmai 10/16
Pavlof
9/16
Amukta 9/18
Augustin
e 9/25
60 Day window
 P=0.0001
 Strandline, Katmai: swarms
 Pavlof: eruption
 Augustine increase, Spurr decrease
Amukta eruption
Speculated Slow Slip Event (McNutt and
Marzocchi, 2004)

1998 Events
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60 Day window
P=0.0148
All rate decreases
Plume from Spurr 3/28
Lake Becharof/ Ukinrek
Maars swarm 5/8-5/9
Slow Slip Event, Cook Inlet
- Late 1998 (Ohta et al.,
2004)
Strandline
Lake 3/28
Lake
Becharof
Spurr
4/2
Redoubt
5/1
2002 Events
10/23
M6.7
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60 Day window
P=0.0206
All rate decreases
Denali Fault Earthquake
Sequence: Oct. 23rd Nov. 3rd
11/03
M7.9
Wrangell
11/17
Strandline
Lake 10/29
Spurr 10/25
The Four Cases
Early 1996: Akutan, Iliamna, Redoubt, Augustine:
120 Day Window, P=0.004
Late 1996: Spurr, Strandline Lake, Augustine,
Katmai, Pavlof: 60 Day Window, P=0.0001
1998: Strandline Lake, Spurr, Redoubt: 60 Day
Window, P=0.0148
2002: Wrangell, Strandline Lake, Spurr: 60 Day
Window, P=0.0206
Conclusions and Speculations
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
Probabilities of independent volcanoes
having events close in time tend to be low.
This suggests that the volcanoes are
reacting to regional events which change the
stresses governing the volcanoes, such as:
Regional Earthquakes
 Slow Slip Events
 Other more subtle stress changes
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