5-min. Summary Video
is available in YouTube

Osamu Sandanbata1, Hiroo Kanamori2, Luis Rivera3, Zhongwen Zhan2, Shingo Watada4, Kenji Satake4, and Voon-Hui Lai5

Arc angle, " (°)Arc angle, "Arc
angle, " (°) Arc angle, "(b)(b)
Vertical-T CLV
Vertical-T CLVD(b)(b)
Vertical-T
CLVD
Vertical-T
Outward CLV
3. Methods for estimating two ring-fault parameters
MInwardres
Inward usingOutward(1) National Research Institute for Earth Science and Disaster Resilience, Japan, (2) California Institute of Technology, USA, (3) Université de Strasbourg, France, (4) The University of Tokyo, Japan, (5) Australian National University, Australia.

• The MT of the ring-faulting can be(a)MSurfacedecomposed
into three components:
Ring-fault
MCLVD (vertical-CLVD),
MSS (verticalorientation
Ring-fault
strike-slip),andM(verticaldip-slip)
DS
Ring-fault O !: Arc angle(see Figs. 2–3) .

(b) Decomposed MT elements(a)Plan view

Geometry

Two endmember types of vertical-CLVD earthquakes

鉛直CLVD–T地震
Vertical-T!"#$%+Δp–ΔpVertical-P
鉛直CLVD–P地震

Vertical-P
CLVD EQ–Δp+ΔpFig.1
Two types ofvertical-CLVD
earthquakes.

“Is teleseismic MT inversion useful5for ring-faulting study?”!%&

Dip angle(d)Dip
angle75°
75
Dipangle

TheoreticalCLVD

SSDS

Resolvable

Geometry

Planarfault

Planar
fault

UP

UP

Arc 90°

Arc 90°UP

UP

Arc 180°

Arc 180°

UP

UP

Arc 270°

Arc 270°

UP

UP

Arc 360°

Arc 360°

UP

UP

Unresolvable

Vertical-T
CLVD EQ!&&

Perspective view(c)Dipangle
angle 60°
60
Dip

1. Introduction

MT (1976–2009)

Fig. 2 Ring-fault parameters.

TheoreticalCLVD

SS

DS

Resolvable⬅Fig. 3 MTs andthe componentsof ring-faultingwith different dip
and arc angles.

1. Perform the deviatoric MT inversion using
teleseismic data (period: >~50 s).
2. Obtain the resolvable moment tensor Mresby excluding MDS (i.e., %!" = %!# = 0).
3. Estimate the ring-fault arc angle using
the CLVD ratio of Mres (Fig. 5a):|%$%&' |'$%&' =× 100 (%)%$%&' + %((4. Estimate the ring-fault orientation using
the Null(N)-axis direction of Mres (Fig. 5b)• For arc angle < 180°: N-axis // Ring-fault• For arc angle > 180°: N-axis ⊥ Ring-fault(a)100(a)

90

Arc angle
Arc<180°angle<180°

8070(b)

Arc angle
Arcangle>180°
Arcangle
UP<270°
UP >180°
DOWN
360

Arcvsangle
kCLVD
Arc angle

Arc>180°angle
90180>180°270
Arc angle, " (°)
Ring-fault arc angle (°)

UP

DOWNUP

DOWN

DOWN

Vertical-T CLVD

InwardOutward
InwardOutward-dipping-dipping!!"#UP
InwardOutwardBy focusing on the CLVD ratio& N-axis directionof MOutward, Inward-dipping-dippingres!
!"#-dipping-dipping-dipping-dipping
Ring-fault orientation
結果①︓震源位置の⽔平⽅向ずれによるMT解の変動
DOWN

Ring-fault orientation
we can constrain the ring-fault orientation and the ring-fault
arc angle. N–axis & = 90°
Ring-fault orientation

Unresolvable• Because ring-faulting usually occurs at a shallow depth <~5 km
near the free-surface (!!" = !!# ~0), MDS (%!" & %!# ) excites
only small long-period waves (Fig. 4); hence, MDS isunresolvable from teleseismic data (Kanamori & Given, 1981).
• Here, we newly define the resolvable moment tensor,
excluding indeterminate MDS, as follows:N–axis & = 0°

T–axisRing-fault orientation Ring-fault
N–axisorientation& = 90°

Arc angle
Arc angle<180°
DS成分の規模・主軸⽅向の推定が不安定なため，MT解は⼤きくばらつく
Arc<180°angle
Arcangle
DOWN
4. Stability test of Mres estimation
UP
DOWN<180°<180°(c)
Arc angle>180°

UPDOWN

Vertical-P CLVDUPDOWNDOWN

UPUPl MT解の主軸⽅向・地震モーメントが⼤きくばらつく⼀⽅，DS成分以外は安定的に推定．
• We estimate
Mres for a vertical-T CLVD earthquake at Sierra
Negra
InwardOutward on October 22, 2005, while shifting centroids!!"#!$$
Ring-fault orientation-dipping-dipping
around the caldera to examine its stability (depth is fixed at
2.5 kmin thecrust). P–axis
Ring-fault orientation
N–axis & = 0°
Ring-fault orientation
N–axis & = 90°
Resolvable
MT Ring-fault
MT解Ring-fault
orientation
orientation
N–axis& = 0°• As a result, the estimation for Mres is very stable,
while the estimation for MT, including
M(Fig.6).
MArc=angle
MDS, is+very
M unstableと定義する
M =ArcMangle + M + M Arc angle
Waveform misfit
Sierra Negra
Caldera<180°
CLVDSSDS

Arc>180°angle
M (including MDS) Unstable!
>180°Ring-fault orientation
N–axis & = 0°
Arc angle
>180°

DOWN

DOWN

UPres

CLVD

SS>180°
DOWN
Arcangle
DOWN
UPMMDS) Stable!
res (excluding>180°
DOWN
UPDOWNP–axisUP

UPUP

Mres = MCLVD + MSS~50 kmDue to the unresolvable MDS, we CANNOT interpret
the MT directly; therefore, we use Mres .

Fig.
6 (Left)
Waveform misfits given by MT
solutions at each centroid location.
(Middle) MT solution M,⭕の広い範囲で波形誤差がカルデラ
DS成分が⼤きくばらつく
Mres は安定的に推定可能
⼩さいMT解が推定される
èMT解,
M
は不安定
including MDS, and (Right) Mres at centroid locations aroundthe caldera.
w

5. Results: Case studies
1. 2005 Vertical-T CLVD EQ at Sierra Negra (Galápagos)

2. Vertical-P CLVD EQs during the 2018 collapse at Kilauea (Hawaii)

11Despite the instability problem, Mres can be stably estimated with teleseismic data.

CLVD ratio (%)

Null-axis azimuth
measured from north (°)#%&'( (%)

Northing (km)• Our estimation: Ring-fault orientation = ~NWW–SEE, Arc angle = ~80°.
• 50 earthquakes during the caldera collapse sequence showed similar Mres.
応⽤③︓KILAUEA⽕⼭2018年カルデラ崩壊に伴う鉛直CLVD-P地震
応⽤③︓KILAUEA⽕⼭2018年カルデラ崩壊に伴う鉛直CLVD-P地震• Field survey/geodetic analysis: Asymmetric ring-faulting on the• Our estimation: Ring-fault orientation = ~NE–SW,
Arc angle <~90°.
6. Discussion
北⻄or南東側の環状断層での⼤きな正断層すべりを伴って，カルデラ崩壊が進展したことを⽰唆
southern-to-western side of the caldera (Geist et al. 2008, Jónsson 2009).
• Near-field seismicdata:
Asymmetricring-faultingonNWorSEsidesof
the
50個の地震の CLVD成分⽐ および Null軸⽅向 はほとんど同じ
Q1. For estimating Mres , the isotropic component is assumed to be 0.
l 2021).
近地地震波形解析により，鉛直CLVD地震は主に北⻄側の環状断層で発⽣ (Lai et al., 2018, JGR-SE)
Vertical-Psummit
caldera(Shelly&Thelen
2019,Laietal.
How is Mres affected by MISO that may accompany ring-faulting?
Mres of earthquake Mres estimation
Ring-fault geometryl Mresは地震毎に⼤きな変化はなく，円弧⾓80–120°程度の 北東–南⻄向きの環状断層と推定される
CLVD
l 鉛直CLVD–P地震の震源分布は，カルデラの北⻄側・南東側に集中(Shelly and Thelen, 2019, GRL)
on Oct. 22, 2005
estimated by field survey•Becauseofthewaveform
similarity
betweenlong-period
waveforms
from"!"#$%&
Locations ofthe EQs
Mres of earthquake Mres estimation
Shelly and Thelen(2019, GRL)による
Lai et al. (2018, JGR-SE)によるカルデラ崩壊過程
繰り返しCLVD-P地震のCLVD成分⽐の推移
Sierra Negra
shallow
MandM
sources(e.g.,Kawakatsu
1996;
Fig.
9),kmayArcISO
CLVD
CLVD
鉛直CLVD-P地震(円)と微⼩地震(点)の震源位置
determinedby near-field data
5, 2018
Monof June
5 Eq.
calderares Jun.
Positive100
be biased by a volume-change source with MISO.
① 100~80°
Arc
isotropic
Kilauea’s summit caldera
70–80 %
9090~90° #Q2. で安定的に推移
What source parameters are lost by removing MDS ?
"'()*80%&'( = 76.6 %or80• The ring-fault dip angle, azimuth, and slip amount cannot be estimated
70
円弧⾓Up
or70
solely with Mres, since these parameters are controlled by MDS (see Fig. 3).
Both are60
Arc= ~90°
consistent• Since this method assumes pure dip slip, oblique slip may cause bias.
60
50~80°
Fig. 9 Synthetic waveforms from the0 Arc 90
180
270
360
1323
33
4353
Mw 5.31
Geometry estimatedEvent #NoteonQ2)
Theteleseismic-wave
amplitudeofshallow
ring-faultingisinArcangle(°)
vertical-P CLVD source MCLVD–P, and the~90°by Geist et al. (2008)
kCLVD = 73.4 %M
Mww 5.21
5.21
atradeoff
betweenslip
amountanddipangle;
hence,
if
weknoweitherofpositive isotropic source MISO+. Note
Elevation (m)ConsistentMres による繰り返しCLVD-P地震のNull軸⽅向の推移
kCLVD = 76.6 % ② Null軸⽅向
他の解析と整合的な~90°
Easting (km)orkCLVD = 76.6 %環状断層構造thetwofrom
other
observations,wemay
constrain
theotherusingM.
~90° 45–70 %でthat the waveforms are very similar.
res
構造の推定に成功
90
推定結果
Fig. 7 (Left) Mres. (Middle) Two candidates for ring-fault geometries
安定的に推移75(Lai et al., 2021, JGR-SE)
Fig. 8 (Left) Mres. (Middle) Two candidates for ring-fault
geometry estimatedestimated from Mres. (Right) Geometry suggested in the previous studies,
Acknowledgements: This study is funded by the JSPS KAKENHI (Grant numbers
Publications: You can find details of 23
this work in two papers:
60
JP17J02919, JP20J01689, and JP19K04034), by the JST J-RAPID (Grant numberfrom Mres. (Right) Earthquake locations determined by ShellyandThelen(2019)45
1. Sandanbata et al. (2021, JGR–Solid Earth)
Using Mres, we could estimate ring-fault parameters that are (modified after figure from Lai et al.~90°
JPMJJR1805), and parLally by the Gordon and BePy Moore FoundaLon. We used2021). Circles and dots
indicate locations of
2. Lai et al. (2021, JGR–Solid Earth).
30
orbroad-band seismic data downloaded from IRIS. For the inversion, we used the Wconsistent with those inferred from near-field observations. large vertical-P CLVD~90°earthquakes and micro-seismicity, respectively.
See “REFERENCES” in iPoster Gallery for the paper information.
15phase package (e.g., Kanamori & Rivera 2008).
0N

InwardOutwardFig. 5 Relationships(a) betweenk(c)and CLV!!"#!$$ of Mres & ring-fault arc angle,
CLVD-dipping-dipping
Vertical-P(c)Vertical-P
CLVD
orientation
N–axis & = 90°
T–axis(b) betweenRing-fault
the (c)N-axisorientationofMandthering-fault
orientation.
(c) res Vertical-P CLVD
Vertical-P CLVArc angle<180°⬇Fig. 4 Syntheticlong-period (80–200 s) waves fromfive elementarysources.

N

Ring-fault orientation
Ring-fault orientation
N–axis & = 0°
Ring-fault orientation Ring-fault
orientation
N–axis& = 0°

60
50
0-dipping-dipping!
Outward
InwardOutward!"#-dipping!-dipping!"#
Ring-fault
N-axis-dipping-dipping
Ring-fault
orientation(b) orientation
Ring-fault
N–axis & = 90°orientation
orientation
Ring-fault orientation
Ring-fault
N–axisorientation& = 90°
Arc angle
<180°
DOWN
ArcangleUP
UP Arc angle DOWN
<180°DOWN
DOWN
UPUP< 180°Inward-dipping-dipping

CLVD ratio, !!"#$ (%)• We suggest a method to estimate source parameters of
ring-faulting at calderas using teleseismic data.
• Despite the instability of teleseismic moment tensor (MT)inversion for very shallow earthquakes, the resolvable MTcomponents help us estimate some ring-fault parameters.
• By using the resolvable MT components of vertical-CLVD
earthquakes at Sierra Negra and Kilauea, we could estimate
ring-fault parameters that are consistent with those inferredfrom near-field observations.

2. Analysis

CLVD ratio, kCLVD (%)

Summary• Ring-faulting often occurs at calderas due to pressurechange in a magma reservoir. Investigations of ringfaulting provide insights into volcanic processes.
• Ring-faulting can generate moderate-sized earthquakes，Mw~5規模の「鉛直CLVD地震」を引き起こすof Mw>~5 characterized by moment tensors (MT)dominated by the vertical compensated-linear-vector異なる部分からの⻑周期地震波 (>~50 s) 同⼠が部分的に打ち消し合う
dipole(MT解)(vertical-CLVD)
component,
ントテンソル解が推定される (Ekström,1994,calledEPSL) vertical-CLVDearthquakes (Ekström 1994; Shuler et al., 2013; Fig. 1).

-SE)

CLVDCLVDraCLVD
CLVDra[V25D-0155] Teleseismic moment tensor inversion for ring-faulting at active calderas:
Case studies at Sierra Negra in the Galápagos Islands and Kilauea in HawaiiNNrfaceSupplementary Materials
(a)

(a)

M

Ring-fault
orientation

Ring-fault

(a)

(a)

(b) Decomposed MT elements

Surface!"#$%!&&#AGU2021 [V25D-0155] “Teleseismic moment tensor inversion for ring-faulting at active calderas:
Case studies at Sierra Negra in the Galápagos Islands and Kilauea in Hawaii” by Sandanbata et al.

!%&Ring-fault

S1.!: ArcEfficiency
of long-period teleseismic
Dip angle (b) Decomposed MT elements
angle
MSurface
excitationfrom ring-faulting
Ring-fault!
!
!
Plan view Perspective view

S2. Case study 3: Two vertical CLVD EQs at Sierra Negra in 2018

O"#$%

&&%&

応⽤②︓SIERRA NEGRAカルデラ 2018年地震

orientation

MTforelements(c) Dipcomputations
angle 60(b) Decomposed(d) Dip angle 75• Fromof MTs
theRing-fault
ring-faulting,
we show that theRing-faultGeometry O
Theoretical
CLVD
SS !
DSResolvable
Geometry
Theoretical CLVD
SSDS
Dip M
angle!: Arc !
angle
"#$%
&& with !
%&steeperring-faulting
has aMTlarger
Mxz
andyz components.

Ring-fault Planar

PlanarPlan view Perspective view
fault
angle
(c) DipDip
angle60(b) Decomposed MT elements(d) Dip angle 75
UPUP
Geometry Theoretical !CLVD
SS !&& DS
Resolvable
Geometry Theoretical!%&
"#$%
fault

rface

ective view

GPS計で記録された鉛直変位=隆起SSDSResolvable(Bell et al., 2021, Nat. Comm.)
As the dip angle becomes
Arc 90°
Planar

Arc 90°Ring-fault(d)Planar
Dip angle 75

Resolvable

ective view

fault
Geometry
Theoretical
Dip angle

UP

CLVDSSDS

Resolvable

UPPlanarfault
Arc
Arc180°90°(d) Dip angle 75
Resolvable

UPGeometry
UPUP

Arc 90°
Planarfault
Arc
Arc 270°
180°
UP
UP

UP
UP

Arc
Arc 180°90°
Arc 360°
Arc 270°UP
UP

Theoretical• We also applied the method to two earthquakes in 2018 at Sierra Negra.
Resolvable
NEGRAカルデラ
2018年地1. Ver&cal-T CLVD earthquake (Mw 5.3) on June応⽤②︓SIERRA
26, 2018 (~10h before
the erup&on)
噴⽕前の鉛直CLVD-T地震，噴⽕開始後の鉛直CLVD-P地震に対し，環状断層の構造を推定．
2. Ver&cal-P CLVD earthquake (Mw 5.1) on July噴⽕前の鉛直CLVD-T地震，噴⽕開始後の鉛5, 2018 (>a week aHer the erup&on)

CLVDSSDS

Resolvable

CLVD

steeper (more vertical),the ring-faulting contain
Arc 180° larger Mxz, and Myz.
Arc 90°
fault

Mresof earthquake
June 26 Eq.
Mres of July 5 Eq.
MCo-seismic
vertical displacements
GPS計で記録された鉛直変位=沈降
res of
Mres of June 26 Eq
GPS計で記録された鉛直変位=隆起
Mestimation
res(噴⽕前)(噴⽕開始後)(Belletal.,
2021,Nat.
Comm.)
on Jun.
26, 2018
recordedbyGPSgauges(噴⽕前)(Bell et al., 2021, Nat. Comm.)

Arc~80°

UPUPor

1.8 m Uplift 1.4 m

UP
UP

Inﬂa%on
1.8 m Uplift
1.4 m
1.4 m

Arc~80°

応⽤②︓SIERRANEGRAカルデラ 2018年地震
ArcArc 270°
180°

Subsidence

Mw 5.31k鉛直CLVD-T% Type 鉛直CLVD-P
応⽤②︓SIERRA NEGRAカルデラ
2018年地震CLVD = 72.2

鉛直CLVD-T

Reverse faulting on ~80° 72.2 %Consistent
the cmsouthern ring-15
噴⽕前の鉛直CLVD-T地震，噴⽕開始後の鉛直CLVD-P地震に対し，環状断層の構造を推定．
~80° 72.2 %① #%&'(71.9 % ~80°
-71 cm噴⽕前の鉛直CLVD-T地震，噴⽕開始後の鉛直CLVD-P地震に対し，環状断層の構造を推定．
Arc 360°
Fig. S1 MTs and the components ofUPring-faultingwith different dip angles.
UPArc 270°

整合的② Null軸• This means that the steeper ring-fault has components that doM notMofearthquake
Co-seismic
verticaldisplacements
res
orof
June
26
Eq.
Mof
July
5Eq.
M
estimation
GPS計で記録された鉛直変位=隆起GPS計で記録された鉛直変位=沈降~80°~80°
Mof
June
26Eq.
Mof
July
5Eq.
res
res
GPS計で記録された鉛直変位=隆起
res
GPS計で記録された鉛直変位=沈降
UP
res
res
UP⽅向UPonJul.
5,2018recordedbyGPSgauges
UP
contributeto radiations of the long-period(Bellteleseismicwaves.
(噴⽕前) (Bell et al.,(噴⽕開始後)(Bell et al., 2021, Nat. Comm.)(Bell et al., 2021, Nat. Comm.)(噴⽕前)(噴⽕開始後)et al., 2021, Nat. Comm.)
2021, Nat. Comm.)
Arc 270°
180°

Arc 360°
UPArc 360°

UPUPArc 270°
360°
Arc
UP
UP

Arc 360°!!"#$ /!!

整合的~80°%of M! : Seismic
1.8m Uplift moment
1.4 m(including Mxz and Myz)%!"#$ : Seismic moment of Mres
(excluding Mxz and Myz)

UPor

整合的~80°or~80°

Ring-faulting with steeper dip angle is less efficient inradiating long-period teleseismic waves.

~80°

鉛直CLVD-T

鉛直CLVD-T

Type

Mw 4.98~80° 72.2 %k鉛直CLVD-P
CLVD = 71.9 %~80° 72.2 %① #%&'(71.9 % ~80°

整合的~80°~80°or

1.8 m Uplift 1.4 m

Fig. S2 The ratio of the seismic
moment of M ( !1 ) to that of Mres(!1234 ), indicating the efficiency of thelong-period teleseismic radiation.

整合的推定されるArc~80°
環状断層構造or~80°

Deﬂa%onSubsidence

Type
鉛直CLVD-P
ArcSubsidence① #%&'(~80° 71.9 % ~80°② Null軸-15 cm
⽅向Consistent-71 cm-15 cm

19-71 cm

Normal faulting on
the southeastern ring
整合的

②Null軸Fig.
S3 ~80°Applications to two
vertical-CLVD earthquakes on or(top) June 26, andor
推定される
~80°
~80°
⽅向(bottom)
July 5. In each, 環状断層構造(Left) Mres. (Middle) Two candidates for ring-fault

geometries estimated from Mres. (Right) Co-seismic displacements recorded by GPS
整合的data, following Bell et al. (2021).

推定される
環状断層構造~80°

推環or~80°

19The differences between Mres for the two vertical-CLVD EQs
indicates the changes in source locations along the faultsystem, as well as in the source kinematics.
19Supplementary Materials#AGU2021 [V25D-0155] “Teleseismic moment tensor inversion for ring-faulting at active calderas:
Case studies at Sierra Negra in the Galápagos Islands and Kilauea in Hawaii” by Sandanbata et al.

Schematic shows the chronology of the Kīlauea summit deformation
during the 2018 Kīlauea eruption (Lai et al. 2021)

Cartoon cross-sections depicting the inflation-deflation cycleof the 2018 eruption and plumbing system at Sierra Negra (Bell et al. 2021)