1. 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

2. Distal VTs (dVTs) 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!!!

3. Rather Typical pattern of dVT seismicity and eruption onset
UNZEN
Unzen (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

4. Tacana 1985 – 1986 VEI 1 small phreatic eruptions in February, May, June 1986
dVTs (blue); then proximal Hybrid seismicity (red)
Tacaná had small phreatic eruption in February, May, and June of 1986

5. Soufriere Hills 1995 VEI 3 Initial dVTs (blue); later Hybrids and LFs (red)
dVT seismicity began 3 years prior to magmatic eruption
Stopped when extrusion began

6. Nevado del Ruiz VEI 3
dVT seismicity (blue areas) began 12 months prior to magmatic eruption
dVT magnitudes include M 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)

7. Popocatepetl, 1997 – VEI 3 a very hot dacite magma dVT seismicity (blue) preceded several vulcanian explosions (red)
Same pattern between lulls in activity,

8. Guagua Pichincha VEI 3 dVT seismicity (blue) on tectonic fault 15 km NE and 15 km deep during 1 year prior to dome extrusions (red)

9. Rabaul 1994 VEI 4 dVTs (blue) 15 km outside large caldera, eruptions (red)
Seismicity started in 1971, seismicity into 80s was in the caldera. Seismicity just before eruption at blue area outslde the Rabaul caldera, offshore.
Also smaller swarms at same location prior to smaller later eruptions during following 3 years.

10. Pacaya 1980, Basaltic VEI 2 dVTs in 1979; continuous strombolian activity 1980-1986
dVT peak in A much smaller peak occurred during a smaller lull in DEc 1981-Jan 1982

11. Shishaldin, 1998 - 1999 Shishaldin 1999 VEI 4 Magma: basaltic andesite
dVTs (blue) began 1 month before Sub-Plinean Eruption
April 19, 1999
Then 6 weeks of Strombolian Fountaining
subplinian eruption on April 19, 1999 that placed an ash cloud to 45,000 ft ASL (~13,700 m). The eruption style almost immediately changed to that of vigorous strombolian fountaining (Nye and others, 2002), which characterized the activity for the following six weeks.

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

13. Typical pattern of dVT seismicity
Unzen
(Nakada et al, 1999)
Major dVT seismicity (blue) occurs during intrusive period
dVT seismicity dies out quickly with onset of magmatic activity (red)

14. Database of 65 eruptions during last 100 years which were preceded by dVT swarms
Page 1 of 3

15. Almost all explosive eruptions are preceded by days to years of distal VT seismicity
Volcano year VEI onset of distal VT’s
Mt. Pinatubo weeks prior
Mt. St. Helens weeks prior
El Chichon years prior
Bezymianny weeks prior
Shishaldin months prior
Sheveluch weeks prior
Karymsky weeks prior
G. Pichincha year prior
Rabaul weeks12 years prior
Kliuchevskoy months prior
Chaiten >2 days
Kasatochi >5 days
Possible Exceptions: volcanoes with eruptions in prior 30 years
Reventador (4?) weeks prior
Redoubt week prior

16. Explosivity of eruption versus Duration of distal VT seismicity

17. 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

18. 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)

19. 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

20. How has VDAP used dVT characteristics for forecasting
How has VDAP used dVT characteristics for forecasting? Sulu Range, PNG 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 km offshore
Explosive emissions of mud and steam from Silanga, Mato and Bakama hot springs.
VT seismicity dies off quickly as 1/t

21. Sulu Range, Papua New Guinea 2006 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 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

22. Cosiguina, Nicaragua 2002 dVT swarm indicates an intrusion in 3 pulses, But total seismic energy indicated intrusion too small to reach surface
(VDAP and
V.Tenorio)

23. Cartoon of seismic pattern

24. June 14 Pre-climatic LP & tremor
Mount Pinatubo, 1991 VEI rd stage of typical Seismic Progression for long-
June 7 Hybrids
dormant systems
June 12 LP’s
June 14 Pre-climatic LP & tremor
June 14 >LP
Seismic swarms
Common progression:
HF: dVT’s = Activation of existing faults
LF Tremor = boiling off hydrothermal system
Hybrids = degassed carapace magma rising to surface by stick-slip
Very large-scale Tremor = Eruption
Post-eruption dVT seismicity = Crustal response to magma withdrawal

25. March - 30 May: distal VT swarms 5-6km NW
March - 30 May: distal VT swarms 5-6km NW. Magma ascends, pressurizes regional faults
31 May - 3 June: Phreatic eruptions – fluid-moves in cracks - LP’s and LP tremor
June 12: explosive eruptions 03:41 & 08:51. LP’s, tremor, eruption signals
June 12-14: LP events continue … & increase in magnitude; RSAM increases
2 April: small steam explosion
Magma … …mixes, intrudes overlying.. dacite in reservoir, breaks through crust and erupts lava dome on June 7
Pre-climactic phase June: …mix of VT, LP, tremor, eruption signals… RSAM steps down after 6/14 13:04 eruption then ramps up
15 June: caldera collapse & eruption of >5 km3 magma… seismic net destroyed… post eruption VT earthquakes outline magma reservoir
Distal VT swarm from Augustine
Gas rich basalt intrudes…from great depth (35 km)… LP tremor
Linking seismic monitoring, observations and petrology to improve understanding of volcanic “plumbing”
Proximal Hybrid swarm precedes extrusion of dome on June 7. June 8: pressure released & 30 hrs seismic quiet
Based on Harlow et al (1996), White (1996), Mori et al. (1996) and Pallister et al. (1996)

26. The End