Lecture slides on volcano deformation at Academia Sinica, Taipei.

1. Recent progress of volcano
deformation studies
Yosuke Aoki
Earthquake Research Institute, The University of Tokyo
Email: yaoki@eri.u-tokyo.ac.jp
29 October 2019
ACV-FC4
Academia Sinica, Taipei, Taiwan

2. Schedule this afternoon
1:00-2:00pm (could be longer) “Recent progress of volcano
deformation studies”
2:00-2:30pm Break
2:30-4:00pm (could be shorter) Exercise: “Theory and
application of Synthetic Aperture Radar”
4:00-4:30pm “Geodetic analysis of Tatun Volcano” by
Masayuki Murase
4:30-5:10pm Poster

3. Why volcano deformation matters?
Fournier & Chardot (JGR, 2012)
 Where and what shape is (are) pressure source(s)?
 How do they move?

4. Development of Volcano Geodesy
Development of observational techniques (how to measure)
- Conventional methods (leveling, tiltmeters, strainmeters) are still
important.
- Space geodetic methods (GNSS, SAR) dominate the current volcano
geodesy.
- Modern techniques (Ground-based SAR, Airborne SAR, LiDAR, SfM)
might change the world of volcano geodesy in the future.
Development of modeling methodology (how to model)
- Simple sources (sphere, dike) embedded in a homogeneous, elastic, and
isotropic halfspace.
- Numerical modeling (e.g., FEM) and analog modeling incorporating
material heterogeneity, topography, or complex source geometry.
- How to invert for the source properties with a complex problem setting?

5. Volcano geodesy with conventional techniques
Iguchi (Bull. Volcanol. Soc. Jpn., 2013)
Mogi (Bull. Earthq. Res. Inst., 1958)
 Less temporal resolution than modern data
 Still important because of longer-term measurements

6. Emergence of space geodetic techniques
Aoki et al. (Science, 1999)
 More temporal resolution and temporal stability with GPS.
 Tilt data make an important role in constraining the magma
transport during a seismic swarm.

7. Where is the magma reservoir?
Eruptions in
Aug. 2008 and Feb. 2009
Enhanced seismicity
Summer 2008-
Shallow inflation
Summer-winter 2008
Nagaoka, Nishida, Aoki et al. (EPSL, 2012)
Aoki et al. (Geol. Soc. Lond. Spec. Publ., 2013)
Asama Volcano

8. Emergence of Synthetic Aperture Radar
Amelung et al.
(Nature, 2000)
 Spatial resolution unattained by ground-based
monitoring with SAR.
 No need to install equipments on the ground.
 Spatial resolution only down to few to few tens of
days depending on the recurrence time of the
satellite.

9. Volcano deformation of
various origins
Emergence of InSAR revealed
that volcano deformation is
more complicated than we
thought.
Biggs & Pritchard (Elements, 2017)

10. Heuristic approach of volcano deformation
Pritchard and Simons (Nature, 2002) Chaussard, Amelung, and Aoki (JGR Solid Earth, 2013)

11. Global compilation of
deformation sources
 24 % of volcano deformation
takes place >5 km from the
volcanic center.
 Majority of the deformation
source is <10 km.
Biggs & Pritchard (Elements, 2017)

12. Global compilation of
deformation rate and duration
A compilation of ground-
based and space geodetic
techniques show that
slower deformation lasts
longer.
Biggs & Pritchard (Elements, 2017)

13. Global compilation of deformation and eruption
Biggs et al.
(Nat. Comm., 2014)
Red: deformed
Black: not deformed
Blue: eruption

14. Temporal evolution?
Biggs & Pritchard (Elements, 2017)
Temporal evolution of
volcano deformation is
variable.

15. A tale of two failed eruptions
Hotta et al.
(Earth Planet. Space, 2016)
Aoki et al. (Science, 1999)
2015 Sakurajima
1997 Izu Peninsula

16. Temporal evolution of volcano deformation
from InSAR
Aoki and Sidiq
(JVGR, 2014)
Large number of image acquisitions
enables us to retrieve time-varying
deformation from SAR images.
Wang and Aoki (JGR Solid Earth, 2019)

17. Classic methods of volcano deformation modeling
 Analytical solutions are available for many kinds of geometry of pressure sources embedded in an
elastic, homogeneous, and isotropic halfspace.
 Availability of analytical solutions is a big advantage to be included in inverse problems.
Bonaccorso and Davis
(JGR, 1999)
Segall (2010)
Nishimura
(JVGR, 2009)Yang et al.
(JGR, 1988)
Fialko et al.
(GJI, 2001)

18. Adding complexity
Medium
- Topography
- Heterogeneous elastic properties
- Visco(plasto)elasticity
Source
- Arbitrary geometry
Methods
- Analytic
- Numerical simulation (e.g., FEM)
- Lab experiments

19. Deformation modeling incorporating topography
Classic methods for
correcting topography
 Williams and Wadge (JGR, 2000) gave an analytical solution of deformation field
incorporating arbitrary topography as long as (H/L)2<<1, where H and L represent the
scale of topography change and horizontal scale, respectively.
 Topography needs to be taken into account (only) when the depth of the pressure
source is comparable with typical horizontal scale of topography change.

20. Deformation modeling incorporating
heterogeneous elastic constants
If the elastic constants are function of depth only, the surface deformation field can be
analytically derived by the Thomson-Haskell method widely applied in seismology with a
zero frequency limit (Zhu and Rivera, GJI, 2002).
If the elastic constants vary in horizontal direction as well, the (approximated) analytic
solution still exists as long as perturbation is small (Du et al., GRL, 1997; Cervelli et al.,
JGR, 1999).
Ignoring heterogeneous elastic constants in vertical direction underestimates the depth
and volume change of the pressure source (Manconi et al., GJI, 2007; Long and
Grosfils, JVGR, 2009; de Zeeuw-van Dalfsen et al., JVGR, 2012).
It is important to consider (at least) vertical variation of elastic constants in modeling
deformation field.

21. Deformation modeling incorporating
viscoelasticity
“Effective” size of the spherical reservoir
becomes progressively larger over time
(e.g., Dragoni and Magnanensi, PEPI,
1989)
A viscoelastic halfspace overlained by an
elastic layer can explain a deflation after a
magma injection which is observed in
many active volcanoes.

22. Modeling the observation by thermoelastic
deformation of intruded lava dome
Wang & Aoki (JGR Solid Earth, 2019)
V
d
Sea level
Intruded
magma body
Surface
Temperature
Time elapse
High Low

23. Deformation modeling with
numerical methods
Finite Element Method
Masterlark et al. (JGR, 2012)
Boundary Element Method
Maccaferri, Rivalta, Passarelli, and Aoki
(EPSL, 2016)
Numerical methods are capable of incorporating
complex source geometry and material properties.

24. Insights from
analog modeling
Trippanera et al.
(JGR Solid Earth, 2015)
Lab experiments can capture features that
sometimes cannot be found by numerical
simulations.

25. Combining physical models with observations
Anderson and Segall
(JGR Solid Earth, 2013)

26. Observational techniques in the future
Ground-based SAR
Airborne SAR

27. Ground-based InSAR at Stromboli
Di Traglia et al. (Sci. Rep., 2015; Geomorphology, 2018)

28. Airborne SAR in Kilauea
While a SAR satellite looks at the target from east or west
because it takes a polar orbit, airborne SAR is capable of
looking at the target from any direction.
Lundgren et al.
(JGR Solid Earth, 2013)

29. Detecting volcanic plumes with GNSS
5 min.
Large particles degrade the strength of GNSS
signals.
GNSS can infer the size distribution of ejecta?
2012 Tongariro (Fournier & Jolly, JVGR, 2014)
2015 Kuchinoerabu
Aoki & Larson
(in prep.)

30. Modeling deformation associated with
hydrothermal activity
Difficult to identify pressure source. An elastic modeling is enough?
Fournier & Chardot (JGR, 2012)

31. Deformation associated with phreatic eruption:
2014 Ontake post eruptive deformation
Narita & Murakami (EPS, 2018)
0.75 Mm3 of deflation in the first 3 years
after the eruption

32. Deformation associated with phreatic eruption:
2015 Hakone
Doke et al. (EPS, 2018)
The observation is modeled by
a dike intrusion.

33. Beyond elastic modeling
Fournier & Chardot (JGR, 2012)
Wang & Aoki (JGR-Solid Earth, 2019)

34. Monitoring non-magmatic deformation with SAR
Ebmeier et al. (J. Appl. Volcanol., 2018)
 InSAR is more suitable to measure non-magmatic deformation than
ground-based measurements.
 Ground-based measurements may not be cost-effective to monitor
non-magmatic volcanoes.

35. Hakone Volcano as an analogy to Tatun Volcano?
Mannen et al.
(Earth Planet. Space,
2018)
 ~70 km from Tokyo, <1 km from the closest
resident
 Popular tourist destination
 Well developed hydrothermal systems
 Well monitored
 Long dormance (>600 yrs) before the 2015
eruption

36. Chronology of the 2001
seismic swarm
and 2015 eruption
 Similar deformation history
 Similar evolution of earthquake
counts
 Different evolution of deep low
frequency earthquakes.
Mannen et al. (Earth Planet. Space, 2018)

37. Chronology of the 2015 eruption
Mannen et al. (Earth Planet. Space, 2018)

38. Deformation associated
with the 2015 eruption
Doke et al. (EPS, 2018)
The observation is modeled by
a dike intrusion.

39. Summary
 Development of volcano geodesy is driven by new observational
techniques and new modeling methods.
 Conventional observations and simple and classic modeling are
sometimes still useful in understanding the magmatism.
 Sophisticated numerical techniques (e.g., FEM, BEM) are powerful but
one needs to understand their limitation as well.
 Deformation signals associated with phreatic eruption are always
complicated and resist a simple interpretation.
 Recent unrest of Hakone Volcano could offer insights into the evaluation
of future activity of Tatun Volcano.