Lessons from studies of Australia B.L.N. Kennett 1/23...

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ANSIR AUSTRALIANNATIONALSEISMIC IMAGINGRESOURCE

Lessons from studies of Australia

B.L.N. Kennett

Research School of Earth SciencesThe Australian National UniversityCanberra ACT 0200, Australia

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Australia and AntarcticaThere are many similarities in the issues involved in

studying the Antarctic Continent and Australia

• few permanent high quality seismic stations

• strong contrasts in structure associated with thepresence of Precambrian shields

• non-trivial logistics and seasonal accessibility

• much of the structure obscured by surficial deposits

The main differences lie in the disposition of thecontinents relative to available seismicity. Australia is closeto extensive regional seismicity, but Antarctica has to beprobed more indirectly.

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Generalised tectonics

Tectonic Regionalisation

Old Ocean [> 100 Ma]

Intermediate Ocean [25 - 100 Ma]

Young Ocean [< 25 Ma]

Tectonic Continental

Cenozoic Continent [Alpine < 150 Ma]

Paleozoic/Mesozoic [Caledonian/Hercynian]

Proterozoic Continent [800 - 1700 Ma]

Archean Continent [> 1700 Ma]

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Permanent broad-band stations

WRA ASP

CTAO

CAN NWAO

TAU

ADE RIV

FITZ

STK

MBWA

CASY DRV

MAT

MAW

PMSA

SNAA

SBA

SPA SYO

TNV

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120˚

140˚

160˚

-30˚

-20˚

-10˚

0˚

Archaean

Proterozoicsediments

Proterozoicbasement

Phanerozoic

Sedimentarycover

Tasman line

500m depthcontour

Subduction

Indonesia

Australia

New Guinea

Kimberley

Arafura Sea

Cape York Peninsula

Coral Sea

TasmanSea

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Australia: SKIPPY

This continent wide experiment with field work in theperiod 1993-1996 was carried out with a moving array oftypically 8–10 broad-band stations which were in place for5-6 months in each location.

The design was forced upon us by the availableinstrumentation and tested against likely seismicity for a5 year period.

Weather considerations meant that the arrays migratednorth in the ’dry’ winter and moved south in summertime. The main continental coverage was achieved in 3.5years, but unfortunately hardware problems meant thatdata return from Western Australia was both patchy andhad many drop-outs.

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Close170E 180 170W 160W90E 100E 110E 120E 130E 140E 150E 160E 170E 180

50S

40S

30S

20S

10S

0

CAN

CTAO

NWAO

WRA

PILOT PROJECT: 5 YEAR SEISMICITY (mb > 5.0) 1981 - 1985

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SKIPPY 1993-1996

WRAg CTAO

STK

CAN

TWO

NWAO

TAU

BT9b

BT5b

BL5b BL9b

SA01

SA02

SA03

SA04 SA05 SA06

SA07 SA08

SB01

SB02

SB03

SB04

SB05

SB06 SB07

SB08

SB09

SB10 ZB11

ZB12

SC01

SC02

SC03 SC04 SC05

SC06 SC07

SC08 SC09

SC10

YB01 YB02 YB03

YB04 YB05

SD01 SD02

SD03

SD04 SD05

SD06

SD07 SD08 SD09

SD10

SE01

SE02

SE03

SE04

SE05 SE06

SE07

SE08

SE09

SE10

SF01 SF02 SF03

SF04 SF05

SF06

SF07

SF08

SF09

SF10

YB08

YB09

YEA1

YEA2

YEA3

YEA4

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Subsequent developmentsThe SKIPPY project provided a reconnaissance coverageof most of the continent at 400 km station spacing. Thelater experiments have been designed either to providemore detail on structures of interest or to improvesampling.

The detailed experiments have used broadbandstations at spacing of 100 km or less, whilst the broaderscale experiments have combined a base grid with200-400 km supplemented with lines of closer spacedinstruments.

All experiments have been carried out by a single groupwith a limited pool of instrumentation, but over a 10year period a very significant set of studies have beenachieved.

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WRAg

CTAO

STK

CAN

FLI

NWAO

TAU

BT9b

BT5b

BL5b BL9b

SA01

SA02

SA03

SA04 SA05 SA06

SA07 SA08

SB01

SB02

SB03

SB04

SB05

SB06 SB07

SB08

SB09

SB10 ZB11

ZB12

SC01

SC02

SC03 SC04 SC05

SC06 SC07

SC08 SC09

SC10

YB01 YB02 YB03

YB04 YB05

SD01 SD02

SD03

SD04 SD05

SD06

SD07 SD08 SD09

SD10

SE01

SE02

SE03

SE04

SE05 SE06

SE07

SE08

SE09

SE10

SF01 SF02 SF03

SF04 SF05

SF06

SF07

SF08

SF09

SF10

YB08

YB09

YEA1

YEA2

YEA3

YEA4

QR00

QR01 QR02

QR03

QR04 QR05

QR06 QR07

QR08

QR09 QR10

WR01

WR02 WR03

WR04 WR05

WR06 WR07

WR08

WR09

WR10

WR11

Broad Band stations 1992-2003

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CoralSea

TasmanSea

Proterozoic basement Archean sediments Archean basement

Paleozoic basement Proterozoic sediments TIGGER 01-02

WAcraton 00-01 02-03

KIMBA 97,98

QUOLL 99

SKIPPY 93-96

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Structural StudiesSurface wave tomography

� waveform inversion by path� synthesis of 3-D shear wave structure

Body wave analysis

� mapping of propagation characteristics� refracted P and S waves� partial 3-D coverage

Receiver functions

� crustal structure (S wavespeed)� sediments, crustal thickness and velocities

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SK1, +SK2

Station distribution Propagation paths Shear wavespeed

at 125 km depth

-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9perturbation (%)

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SK1+SK2+SK3, +BAS+SK4


at 125 km depth

-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9perturbation (%)

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SK +WA, +Perm


at 125 km depth

-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9perturbation (%)

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Body waves

S Paths - lithosphere

-18 s 18 srelative to ak135

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Q Paths - lithosphere

high low Q

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Into AntarcticaThe logistic issues for a comprehensive coverage of

Antarctica are more complex even than for Australia.Many national programs have strong competition for

resources and so it will not be easy to get the logistics e.g.fixed wing aircraft for deep ice deployment.

Based on our experience with the SSCUA experimentover the last two austral summers it would seem sensibleto define a base logistic unit, e.g., 10 broadband stationsat 300-500 km spacing, and then aim to have several ofthese units deployed simultaneously in different parts ofthe continent.

The units would be moved on with time to provide bothdetailed coverage and a base for tomographic studies.

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Conceptual design for a 4 year campaign

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Array design

This design of array is suggested to make maximum useof the logistic capabilities of individual countries (or somelocal collaborations), supplemented by support from theSouth Pole and from the large number of permanentstations in the Antarctic Peninsula.

By having instruments deployed at four differentlocations (or more) simultaneously we get maximumbenefit of any source of sufficient size for tomographiccoverage.

The size of the sectors would depend on the availablesupport and should be supplemented by instrumentsdeployed along linear traverses, e.g., in provisioningstations.

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Potential coverage

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Lessons from studies of Australia B.L.N. Kennett 1/23...

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