anatomy of a megathrust earthquake rupture - the 2010 m8.8 chile quake

Anatomy of a megathrust

earthquake rupture:

The 2010 Mw 8.8 Maule, Chile quake

Stephen Hicks, Andreas Rietbrock, Isabelle Ryder

Liverpool Earth Observatory, University of Liverpool, UK

Chao-Shing Lee National Taiwan Ocean University,

Taiwan

Matt Miller Universidad de Concepción, Chile

Email: [email protected] @seismo_steve

The overriding / underlying question…

scientific aims community response rupture zone imaging megathrust properties lessons learnt



Seamount

Fracture zone RidgeCrustal

faults

Batholiths

Subduction

channel

sediments


Can we physically identify asperities and barriersalong the megathrust?




Megathrust

dynamics

Material

properties scientific aims community response rupture zone imaging megathrust properties lessons learnt

Earthquake

segmentation


Maule segment

Recognised as a

mature seismic

gap (Ruegg et al., 2009, PEPI)

Longest-standing seismic

gap in Chile

Historic rupture areas from Métois et al (2012), JGR

Nazcaplate

SouthAmerican

plate

Closing the gap: 27 Feb

2010

6th largest recorded

earthquake

magnitude 8.8

rupture length 500 km

Concepción

Constitución

Pichilemu

SANTIAGO

Arauco

Peninsula

Image from Google EarthTM, Landsat (2013)


International Maule Aftershock

DeploymentSeismic instruments provided by

Universidad

de Concepción

Field & logistics support from


From the Pacific coast to the Andes …


Deployment



Deployment160 land stations


Data available through IRIS repository

Virtual network code _IMAD

XS – French

3A – British

XY - United States

German data: www.webdc.eu

network code - ZE


Deployment160 land stations

37 OBS stations

+


Data available through IRIS repository

Virtual network code _IMAD

XS – French

3A – British

XY - United States

German data: www.webdc.eu

network code - ZE



Megathrust

dynamics

Material

properties scientific aims community response rupture zone imaging megathrust properties lessons learnt

Modelling slip on the megathrust


most slip between trench

and coastline

max slip 16m at northern

asperity

Modelling slip on the

megathrust

Coseismic slip model from Moreno et al. (2012), EPSL



Aftershock

seismicityLocations from Rietbrock et al. (2012), GRL


Aftershock

seismicity

A’

C

C’D

D’E

E’

Locations from Rietbrock et al. (2012), GRL

A

B

B’

Distance from trench (km)

Aftershock

seismicity

A’

C

C’D

D’E

E’

Locations from Rietbrock et al. (2012), GRL

Gap in

seismicit

y


A


B

B’



Megathrust

dynamicsscientific aims community response rupture zone imaging megathrust properties lessons learnt

Material propertiesLocal earthquake tomography

Imaging the subsurface: seismic

tomography


Tomographic inversion steps

P- & S-wave

arrival times

Initial event

locations

1-D starting

model



P- & S-wave

arrival times

Initial event

locations

1-D starting

model

Updated event

locations

Least squares

inversion

2-D velocity model (vp & vp/vs ratio)



P- & S-wave

arrival times

Initial event

locations

1-D starting

model

Updated event

locations

Least squares

inversion

Final 3-D

velocity

model

Final

event

locations

Least squares

inversion




Resolutio

n?

P- & S-wave

arrival times

Initial event

locations

1-D starting

model


Updated event

locations

Least squares

inversion

Least squares

inversion

Final 3-D

velocity

model

Final

event

locations

Inversion

algorithm:

SIMUL2000

(Thurber &

Eberhart-Phillips,1999) scientific aims community response rupture zone imaging megathrust properties lessons learnt

Imaging the rupture zone: data160 land + 37 OBS

stations

670 aftershocks

38,000 P-wave

picks14,000 S-

wave picks


2D velocity structure

Focal mechanisms from:

Agurto et al. (2012), EPSL

Hayes et al. (2013), GJI Coastline

Resolutio

n limits


2-D velocity structure


Coastline

Resolutio

n limits


A

B

C

D

E

A’

B’

C’

D’

E’


Event catalogue and

cross-section locations


Coastline

Resolutio

n limits

Pic

hile

mu

Con

stitu

ció

nC

ob

qu

ecu

raC

on

ce

pció

nA

rau

co

A

B

C

D

E

A’

B’

C’

D’

E’


Event catalogue and



3-D velocity

structure

Pic

hile

mu

Con

stitu

ció

nC

ob

qu

ecu

raC

on

ce

pció

nA

rau

co

A

B

C

D

E

A’

B’

C’

D’

E’


Coastline

Resolutio

n limitsEvent catalogue and



Input model


Forearc anomalies: imaging capability


Input model Recovered model

Forearc anomalies: imaging capability


vp ~ 7.8 km/s; vp/vs ratio ~ 1.8

Observations

Forearc body: composition &

origin



Positive gravity anomaly

Observations

Ultramafic (weakly serpentinised?)

Christensen (2010), Int. Geol. Rev.

Composition


origin

vp at 25 km

depth

Origin

Subducted topographic anomaly?Hicks et al. (2012), GRL

Gravity anomaly from EGM2008 (Pavlis et al., 2012, JGR)Forearc gravity model from Hicks et al. (2012), GRL.


origin

Origin

vp at 25 km

depth

Subducted topographic anomaly?Hicks et al. (2012), GRL

Root of Paleozoic granite batholith?

Triassic extensional phase?Vásquez et al. (2011), J. Geol.


Positive gravity anomaly

Observations

Ultramafic (weakly serpentinised?)Christensen (2010), Int. Geol. Rev.

Composition




Megathrust

dynamics

Material properties

of the megathrustscientific aims community response rupture zone imaging megathrust properties lessons learnt

Megathrust

geometryGood agreement with

global / regional plate

interface models

Uniform megathrust

geometry throughout

Maule segment


Moment tensors from:

Agurto et al. (2012),

EPSL

Hayes et al. (2013), GJI

Shedding light on megathrust properties


Correlating with seismic cycle behaviour


Preseismic locking• >70% contours: Moreno

et al., 2010



et al., 2010


Coseismic rupture• Slip: Moreno et al., 2012

• High freq: Kiser & Ishii

(2011)


et al., 2010

Postseismic• Afterslip >1m: Lin et

al.,2013

• Relocated interface

aftershocksscientific aims community response rupture zone imaging megathrust properties lessons learnt




(2011)

Aftershock

distribution

Pic

hile

mu

Con

stitu

ció

nC

ob

qu

ecu

raC

on

ce

pció

nA

rau

co





(2011)



et al., 2010


Postseismic• Afterslip >1m: Lin et

al.,2013

• Relocated interface

aftershocks

Down-dip segmentation of the

megathrust


1

2

3

Ultramafic bodies in forearc may inhibit

rupture propagation

Minimal slip (seismic or aseismic) where

vp > 7.5 km/s

High vp/vs correlates with up-dip limit of

seismogenesis

4 Afterslip may be compositionally-driven

Implications for the Maule megathrust



Up-dip barrier:

Fluid-

saturated

sediments

Down-dip barrier:

Long-lived

ultramafic bodies

in crust

Lessons learnt


4

3

2

1

Involve OBS communities into future

rapid deployments

Lessons learnt from deployment

Ocean-bottom measurements can fully

explore seismogenic zone – further

investment and planning needed

Active-source experiments may reveal

megathrust structure in seismic gaps

Instrument pools needed for rapid

responsesscientific aims community response rupture zone imaging megathrust properties lessons learnt

From Maule to IquiqueEarthquake locations (Mw > 5.5) and preliminary

finite fault model from NEIC (USGS)

Image from Google EarthTM, Landsat (2013)

Shifting focus northwardEarthquake catalogue from Servicio Centro

Sismológico Nacional, Chilewww.sismologia.cl

Shifting focus northward

M8.4 Southern Peru

earthquake, 2001

Web:

http://pcwww.liv.ac.uk/~es0u719b

Use of slip models and high-res seismic

images gives unique view of subduction

faultsSeismic velocities could help estimate

rupture size potential of future

earthquakesDense ocean-bottom observations of

foreshock and aftershock sequences in

remaining seismic gaps

Email:

[email protected]

Future progress…

anatomy of a megathrust earthquake rupture - the 2010 m8.8 chile quake

Science

megathrust earthquake

megathrust fault

underlying question

subduction zones5the

large earthquakes

segment barriers

rupture potential

chilean subduction zone