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Systematic Search for Background Seismicity Rate Changes and Correlations at Alaskan Volcanoes

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 Identify background seismicity rate changes

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Systematic Search for Background Seismicity Rate Changes and Correlations at Alaskan Volcanoes

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  1. 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

  2. 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 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 Veniaminof Akutan 12 of 16 Volcanoes • Length of Monitoring Time • Activity/ Sensitivity Level Okmok Dutton Westdahl Makushin

  6. Eruption

  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 • 120 Day window • P=0.004 • Iliamna increases, Redoubt and Augustine decrease • Akutan- swarm Regional earthquakes: Adak June 9th – 10th (M7.9, M7.2) Iliamna 5/8 Augustine 2/19 Akutan 3/10

  9. Late 1996 Events Strandline Lake 8/31 • 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) Spurr 10/11 Augustine 9/25 Katmai 10/16 Pavlof 9/16 Amukta 9/18

  10. 1998 Events • 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 Spurr 4/2 Lake Becharof Redoubt 5/1

  11. 2002 Events • 60 Day window • P=0.0206 • All rate decreases Denali Fault Earthquake Sequence: Oct. 23rd - Nov. 3rd 10/23 M6.7 11/03 M7.9 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

  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

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