Distal Volcano-Tectonic Earthquakes (dVTs)

are 1st in a Typical Seismic Progression

for decades-dormant volcanoes

Randall White, Wendy McCausland,

John Power and John Pallister

Volcano Disaster Assistance Program

US Geological Survey

• Occur in SWARMS events increase in rate and size

• Largest events after middle of the swarm

• Several events within 0.5 M unit of largest

• dVTs die off after significant phreatic/ phreato-magmatic activity begins

• Total VT seismic moment PROPORTIONAL TO INTRUDED MAGMA VOLUME!!!

Distal VTs (dVTs)

Rather Typical pattern of dVT seismicity and eruption onsetUnzen 1989-1995 (Nakada et al, 1999)

major dVT seismicity (blue) occurs over large area 3-20 km W during intrusive period

dVT seismicity (blue) dies out quickly with onset of proximal Hybrid and LF seismicity (red) as eruptive activity begins

UNZEN

Tacana 1985 – 1986 VEI 1 small phreatic eruptions in February, May, June 1986

dVTs (blue); then proximal Hybrid seismicity (red)

Soufriere Hills 1995 VEI 3Initial dVTs (blue); later Hybrids and LFs (red)

dVT seismicity began 3 years prior to magmatic eruption

Stopped when extrusion began

Nevado del Ruiz 1985 VEI 3

• dVT seismicity (blue areas) began 12 months prior to magmatic eruption

• dVT magnitudes include M4.5 11 months prior, M4.1 ~2 months prior

• dVT energy died quickly after onset of phreatic activity and LF seismicity (red)

additions from F. Gil (personal communication)

Popocatepetl, 1997 – 2003 VEI 3a very hot dacite magma

dVT seismicity (blue) preceded several vulcanian explosions (red)

Guagua Pichincha 1998-99 VEI 3dVT seismicity (blue) on tectonic fault 15 km NE and

15 km deep during 1 year prior to dome extrusions (red)

Rabaul 1994 VEI 4dVTs (blue) 15 km outside large caldera, eruptions (red)

Pacaya 1980, Basaltic VEI 2dVTs in 1979; continuous strombolian activity 1980-1986

Shishaldin, 1998 - 1999

Magma: basaltic andesite

dVTs (blue) began 1 month before Sub-Plinean Eruption April 19, 1999

Then 6 weeks of Strombolian Fountaining

Shishaldin

1999 VEI 4

Mauna Loa 1984 VEI 0 basalt (and 1975 VEI 0 ~identical)

Typical pattern of dVT seismicity

Unzen 1989-1995 (Nakada et al, 1999)

• Major dVT seismicity (blue) occurs during intrusive period

• dVT seismicity dies out quickly with onset of magmatic activity (red)

Database of 65 eruptions during last 100 years which were preceded by dVT swarms

Page 1 of 3

Almost all explosive eruptions are preceded

by days to years of distal VT seismicity

Volcano year VEI onset of distal VT’s• Mt. Pinatubo 1991 6 14 weeks prior• Mt. St. Helens 1980 5 10 weeks prior• El Chichon 1982 5 2 years prior• Bezymianny 1956 5 7+ weeks prior• Shishaldin 1999 4 9 months prior• Sheveluch 1966 4 20 weeks prior• Karymsky1996 3 35 weeks prior• G. Pichincha 1999 3 1 year prior• Rabaul 1995 3 10 weeks12 years prior• Kliuchevskoy 1966 3 7 months prior• Chaiten 2007 4 >2 days• Kasatochi2007 4 >5 daysPossible Exceptions: volcanoes with eruptions in prior 30 years

Reventador 2002 4 0 (4?) weeks priorRedoubt 1989 3 0-1 week prior

Explosivity of eruption versus Duration of distal VT seismicity

This shows distance and depth below summit

for all dVT swarms

dVT swarms seem to occur at the base of the brittle zone. The precise location of the swarms is not relevant for eruption forecasting.

dVT swarms occur on pre-stressed local fault(s) and may move from one fault to another near the volcano

Distance vs Depth for DVT's

0

10

200.0 10.0 20.0 30.0 40.0

Distance from summit or summit crater

Dep

th

Total Seismic Moment vs Volume change

y = 1.112x + 0.8777

R2 = 0.9803

3

4

5

6

7

8

9

10

2 3 4 5 6 7 8Magnitude (from total Seismic Moment)

DV

olu

me

(lo

g m

3)

Yellowstone 1959

Long Valley 78-80

Ukinrek Maars 1977

Shishaldin 1999

Akutan 1996Peulick 1996-98

Matsushiro 1965-66

Poas 1990

Paradox 99

Long Valley 78-98

Denver 64

Denver 63

Long Valley 81-83

Denver 62-66

Great Kau 1868

Sulu Range 2006

Total Seismic Moment (almost all from dVTs) is proportional to intruded volume

Red triangle are volcanoes having deformation data for determining intruded volume.

Blue triangles are wells with measured volumes of injected H2O.

(See abstract for Moment vs Volume formula)

Conclusions: Distal VT earthquakes are exceptionally useful for eruption forecasting

dVT’s are very easy to monitor and use in real-time

In “closed” systems (repose >30 years):• dVTs are earliest seismic precursor to eruptions• dVT’s die off when LP and VLP seismicity begins• If intrusion rate is high, dVT’s correlate with inflation;• dVT’s give days to months of warning for large explosive eruptions • Duration of precursory dVT seismicity appears roughly inversely

related to explosivity• Total VT seismic moment is proportional to intruded volume

How has VDAP used dVT characteristicsfor forecasting?

Sulu Range, PNG 2006 VEI 1

• July 6 – a few earthquakes first reported felt.• July 10 – dVTs increase significantly; the first M5 dVT.

Many M>4 events picked up by NEIC • Booming noises heard at Kaiamu and Silanga. • July 13 to 15 - a local seismograph recorded continuous VT earthquakes;

Earthquakes felt every 2-3 minutes; • July 19 - seismicity peaks with M6.4 and M5.9 dVTs 25-30 km offshore• Explosive emissions of mud and steam from Silanga, Mato and Bakama

hot springs. • VT seismicity dies off quickly as 1/t

Sulu Range, Papua New Guinea2006 VEI 1

Upper: location of volcanoes (red triangles) and M>5 dVTs, times and focal mechanisms. Note dVTs proceed 30 km WNW

L-band InSar indicates 0.7-1.0 km intruded volume (Wicks 2008) as forecast from total seismic moment.

Lower: aftershock dVT’s; dVTs decayed as 1/t; locations by temporary local network

Cosiguina, Nicaragua 2002dVT swarm indicates an intrusion in 3 pulses,

But total seismic energy indicated intrusion too small to reach surface

(VDAP and V.Tenorio)

Cartoon of seismic pattern

Mount Pinatubo, 1991 VEI 6 Mount Pinatubo, 1991 VEI 6 3rd stage of typical Seismic Progression for long-

Seismic swarms Common progression:

1. HF: dVT’s = Activation of existing faults 2. LF Tremor = boiling off hydrothermal system3. Hybrids = degassed carapace magma rising to

surface by stick-slip 4. Very large-scale Tremor = Eruption5. Post-eruption dVT seismicity = Crustal response

to magma withdrawal

June 14 Pre-climatic LP & tremor

June 12 LP’s

June 14 >LP

June 7 Hybrids dormant systems

Gas rich basalt intrudes…from great depth (35 km)… LP tremor

31 May - 3 June: Phreatic eruptions – fluid-moves in cracks - LP’s and LP tremor

Proximal Hybrid swarm precedes extrusion of dome on June 7. June 8: pressure released & 30 hrs seismic quiet

June 12: explosive eruptions 03:41 & 08:51. LP’s, tremor, eruption signals

Based on Harlow et al (1996), White (1996), Mori et al. (1996) and Pallister et al. (1996)

Magma … …mixes, intrudes overlying.. dacite in reservoir, breaks.. through crust and erupts.. ..lava dome on June 7

15 June: caldera collapse & eruption of >5 km3 magma… seismic net destroyed… post eruption VT earthquakes outline magma reservoir

March - 30 May: distal VT swarms 5-6km NW. Magma ascends, pressurizes regional faults

Pre-climactic phase 14-15 June: …mix of VT, LP, tremor, eruption signals… RSAM steps down after 6/14 13:04 eruption then ramps up

2 April: small steam explosion

Linking seismic monitoring, observations and petrology to improve understanding of volcanic “plumbing”

June 12-14: LP events continue … & increase in magnitude; RSAM increases

The End