Volcanic Seismology and Deep Long Period Earthquakes

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Volcanic Seismology and Deep Long Period
Earthquakes
Wendy McCausland Graduate Research Assistant D
epartment of Earth and Space Sciences,
University of Washington Advisors Dr. Steve Mal
one - University of Washington/PNSN
Dr. Chris Newhall - University of
Washington/USGS
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Dr. Steve MaloneResearch Professor Department
of Earth and Space Sciences

• Research Interests
• Seismicity of the Cascade volcanoes
• Earthquake and volcanic hazards
• Strong-motion seismology
• Computer applications in seismic data acquisition
  and network analysis
  
• Pacific Northwest Seismic Network (PNSN)
• http//www.ess.washington.edu/SEIS/PNSN/

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Current Stations Pacific Northwest Seismograph
Network

• 138 Short-period
• 15 others
• 21 Broad-band
• 9 others
• 69 Strong-motion
• 35 NSMP sites

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Dr. Chris NewhallAffiliate Professor, Dept of
Earth and Space SciencesResearch Scientist,
U.S.G.S.

• Leader of the World Organization of Volcano
  Observatories (WOVO)
  http//www.wovo.org
  
• Member of the USGS' Volcano Disaster Assistance
  Team
  
• Recent work focuses on
• Processes of volcanic unrest (seismicity, ground
  deformation, gas emission, etc)
  
• Applications of this research to eruption
  forecasting
  
• Developing a web-accessible database of volcanic
  unrest, linked to the Smithsonian database of
  historical volcanic eruptions WOVOdat
  http//www.wovo.org/wovodat.htm
• Helps colleagues from the Cascades Volcano
  Observatory (CVO) and a number of countries
  during volcanic crises
  

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Recent Seismic and Volcanic Activity near Goma,
Democratic Republic of the Congo
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Graduate Students

• Studies of particularly puzzling or previously
  unrecognized patterns of unrest,
  
• Sarah Albano - groundwater response to volcanic
  strain
  
• Wendy McCausland - unusual volcanic seismicity,
  DLP events
  
• Jeff Witter - circulation of magma in volcanic
  conduits as a mechanism for non-explosive
  volatile emission at passively degassing
  volcanoes, excess SO2 degassing
• Josh Jones seismicity of Oldoinyo Lengai, Mount
  Hood
  
• Adam Haulter Avalanche events at Mount Rainier
• Thesis study of ephemeral processes
• Cami Apfelbeck - chemical and thermal evolution
  of the new caldera lake at Pinatubo
  
• Shannon Hayes - world-record-setting sediment
  transport from Pinatubo's pyroclastic deposits
  

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What is Volcanic Seismology?

• Study of
• Earthquakes
• At or near volcano (
• Generated by volcanic processes
• Velocity structure of the volcano
• Seismic attenuation at the volcano

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Volcanic Seismicity Why Study?

• To understand
• Dynamics of active volcanic systems
• Physical properties of bubbly magma
• Map the extent and evolution of source regions
  
  
• Stress conditions, both regional and local
• Ultimately leads to better
• Forecasting of eruptive behavior
• Assessment of volcanic hazards

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Volcanic Seismicity Why Different from
Tectonic?

• Seismicity that
• precedes,
• accompanies, and
• follows volcanic eruptions, intrusions

Number of earthquakes higher than in normal
crust- hot fluids and low rock strengths lead to
many small often unfelt earthquakes
Shallower depths (1-9 km) than tectonic
Occurrence pattern swarms vs mainshock-aftershock
sequences
Different types associated with different
processes high frequency, low frequency, explosio
ns, tremor
Non-Uniform stress field leads to complex Focal
Mechanisms including volumetric components in
addition to simple shear
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Volcanic Earthquake Types

• High frequency events
• (volcano- tectonic) - A
• Low frequency or Long
• period events - C, F, I, J
• Hybrid events -B
• Explosion quakes -E
• Volcanic tremor D, G, H
• Avalanche events

(From McNutt, 2000)
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Recent Eruptive History of Cascade Volcanoes

Young Cascades Volcanoes
Monitored Cascades Volcanoes
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Relative Seismicity at Cascade Volcanoes
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Seismicity in the Cascades Region1990-2001
M0.5
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Deep Long Period Earthquakes

• Deep ? 10 - 35 km depth
• Long Period ? 1 s
• Importance
• source not well understood
• attributed to migration of magmatic fluids
• eruption triggering at silicic centers-
• Ex. Pinatubo, 1991 (White, 1996)

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Deep Long Period Earthquakes

• Examples in Washington/Oregon Cascades
• Mt. Rainier
• Mt. Baker
• Mt. St. Helens
• In California (Pitt et al, 2002)
• Mammoth Mountain- Devils Postpile
• Mono Craters
• Sierra Nevada (south of Yosemite, west of
  Mammoth)
  
• Lassen Peak
• Mt. Shasta - Medicine Lake
• Clear Lake
• In Japan
• Fuji
• Izu Oshima

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Deep Long Period Seismicity and Volcano Locations
Deep Long Period Seismicity and Volcano Location
s
Non- low frequency earthquakes
DLPs
Volcano
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Mount Hood
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Mt Hood Earthquakes
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Mount St. Helens
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Mt St Helens Seismicity
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Mt St Helens Relocations
Mount St. Helens
447 events from 1998 swarm
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Mt St Helens Stress Model
Mount St. Helens
Major compressive axes
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Mount St. Helens - 2 decades
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Current Seismicity atMount St. Helens
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Deep LPs Mt St Helens
Z 27 km
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Mount Rainier
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Mt Rainier Seismicity
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Mt. Rainier Velocity Tomography
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Mt Rainier DLP Events
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Mt Rainier DLP Earthquakes
Depth 10 13 km Spatially distinct from Volca
no-tectonic (VT) events Similar depth to deepes
t VT events Reflect injection of basaltic magma
into system? Result from Resonance of flui
d-filled crack? Unsteady non-linear flow in irre
gular conduit? Another yet unknown mechanism?
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Mt Rainier DLPsFiltered for Low and High
Frequencies
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Mt Rainier Comparing a Long Period with a High
Frequency Event
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Focal Mechanisms for VT events and locations of
DLPs
Focal Mechanisms for Events in 3 Different Dep
th
Ranges and Deep LP Locations
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Comparison of spectral content of DLP vs VTs at
2 stations
Red is DLP Blue is VT
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Spectrogram for High Frequency and Low Frequency
Events Station FMW
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In Summary

• Volcanic earthquakes are key to underlying
  processes and forecasting
  
• Deep Long Period Earthquakes
• Occur at many volcanoes in the Cascades,
  including Mount Rainier and Mount St. Helens
  
• Related to magma but exact mechanisms unknown
• Extent and number unknown in Cascades, because
  this is just a sample of triggered events
  
• Also occur at Japanese volcanoes, including Fuji,
  Izu Oshima, and others
  
• I am interested to compare DLP events in the
  Cascades and Japan