1. K.R. Kore, S.R. McNutt, and D.H. Christensen
Systematic Search for Background Seismicity Rate Changes and Correlations at Alaskan Volcanoes
This project got started because it was noticed that groups of volcanoes seemed to increase and decrease in seismicity levels at the same time. We wanted to quantify this observation.
K.R. Kore, S.R. McNutt, and D.H. Christensen
Geophysical Institute, University of Alaska Fairbanks

2. Strain Rate  Seismicity Rate
Overview and Goals
Strain Rate  Seismicity Rate
Identify background seismicity rate changes
Temporally correlate “events” between volcanoes along the Aleutian Arc
Speculate as to the cause of the “events”

3. The Alaskan Volcanoes Strandline Lake Spurr Wrangell Redoubt Iliamna
Katmai
Augustine
Aniakchak
Pavlof
Shishaldin
Intro, data, and map: Highlight: Wrangell, Strandline, Spurr, Redoubt, Iliamna, Augustine, Katmai, Venia, Pavlof, Shish, Maku, Akutan. Label all volcanoes used in study
Akutan
Veniaminof
Okmok
Dutton
Westdahl
Makushin

4. Identification of Rate Changes
Estimate minimum magnitude of completeness
Exclude swarms
& eruptions
Perform AS(t) function of
the z-test with
min. 3 mo. rate
Exclude man-
made changes

5. Volcanoes with Rate Changes
Strandline Lake
Spurr
Wrangell
Redoubt
Iliamna
Katmai
Augustine
Aniakchak
Pavlof
Shishaldin
The volcanoes in grey are too quiet, meaning there are not enough earthquakes at these volcanoes to do a statistically significant study.
Veniaminof
Akutan
12 of 16 Volcanoes
Length of Monitoring Time
Activity/ Sensitivity Level
Okmok
Dutton
Westdahl
Makushin

6. Eruption
Examples of when rate changes occurred

7. 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

8. Early 1996 Events Redoubt 5/11 Iliamna 5/8 Augustine 2/19 Akutan 3/10
120 Day window
P=0.004
Iliamna increases, Redoubt and Augustine decrease
Akutan- swarm
Regional earthquakes: Adak June 9th – 10th (M7.9, M7.2)
Akutan 3/10
Intro, data, and map: Highlight: Wrangell, Strandline, Spurr, Redoubt, Iliamna, Augustine, Katmai, Venia, Pavlof, Shish, Maku, Akutan. Label all volcanoes used in study

9. Late 1996 Events Strandline Lake 8/31 Spurr 10/11 Augustine 9/25
Katmai 10/16
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)
Pavlof 9/16
Intro, data, and map: Highlight: Wrangell, Strandline, Spurr, Redoubt, Iliamna, Augustine, Katmai, Venia, Pavlof, Shish, Maku, Akutan. Label all volcanoes used in study
Amukta 9/18

10. 1998 Events Strandline Lake 3/28 Spurr 4/2 Redoubt 5/1 60 Day window
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
Spurr 4/2
Spurr: 3/26 plume noted in ANC. Rate change on 4/2
Strandline Lake: 3/28
Redoubt:5/1
Lake Becharof
Redoubt 5/1

11. 2002 Events 60 Day window P=0.0206 All rate decreases Wrangell 11/17
10/23 M6.7
11/03 M7.9
60 Day window
P=0.0206
All rate decreases
Denali Fault Earthquake Sequence: Oct. 23rd - Nov. 3rd
Wrangell 11/17
Spurr: 10/25 and 12/16
Strandline: 10/29 and 12/18
Wrangell: 11/17
Strandline Lake 10/29
Spurr 10/25

12. 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
These four cases are strong evidence that the volcanoes can react together to larger stress changes. They can also react independently to local changes.

13. Conclusions and Speculations
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