Simulating Mantle Convection and Seismic Anisotropy with Data Assimilation

Project PI: Lijun Liu, UIUCPresenter: Jiashun HuCollaborator: Manuele Faccenda, University of Padua, ItalyGroup members: Quan Zhou, Ching ChangNCSA team: Ryan Mokos, Bill Gropp, Darren Adams, Yifeng Cui

CourtesytoandinmemoryofProf.PaulHeller

Geologist’s view on plate subduction

Whyitmatters– tomodelmantleconvection

• Howtheearthworks

(Braun2010)

TherealEarthismuchmorecomplex.

• Naturalhazards

FromthefilmSanAndreas

fromUSGS

Keychallenges• Cleanupboundaryconditions

• Earth’shistoryisverycomplex.Wehavelimitedconstraintsonthemotionsandtheagesoftheplates.

• Largeviscositycontrast• Significantlyslowdowntheconvergenceofthesolver• Requireshigherresolutiontoresolve

• Unknownpropertiesandprocesses• Suchasthegenerationandbehaviorofmagmainthemantlewedge,andthepropertiesofthesuperplumesindeepmantle

Potentialproblemswithexistingmodels

• Mostearliermodelsarein2D

5

A

B

C

[vanHunenetal.,2002]

[vanHunenetal.,2000]

[Manea etal.,2012]

• Recent3Dmodelsusedidealizedboundaryconditions

(Taramon et al., G-cubed, 2015)

Potentialproblemswithexistingmodels

• Recent3Dmodelsusedfixedslabgeometry

6(Flament et al., EPSL, 2015)

ModelingS.Americansubductionhistory

Wetrytodevelopamodelthatisconsistentwithallavailablegeophysicalandtectonicconstraints:• Theknownsubductionhistory(platemotion&seafloorage)• Dynamicallyevolvinginsteadofprescribedslabs

7

• GoverningEquations

• Assumethemantleis an incompressible fluid, which satisfiestheBoussinesq approximation

WhyBlueWaters• CitcomS hasaverygoodscalability,upto~10,000CPUsonBlueWaters.

• BlueWatersiscompatiblewiththesoftwares weuse,includingCitcomS,DrexS andFSTRACK

• Largercapacityleadstolargerallocationandshorterwaitingtime.

100 101 102 103 104

Mac

hine

tim

e (s

econ

d)

CPU number

1

10

100

1000

129×257×257

513×1025×1025

Blue Waters

Stampede

9

Data Assimilation Seafloor age, plate motion, plate geometry,cratons

ViscositystructureofS.Americanmodel

10(Huetal.,EPSL, 2016)

4ordersof

magnitude

incontrast

11(Huetal.,EPSL, 2016)

PredictedSouthAmericansubduction since 100Ma

1024CPUs~150hours

Modelsize:8.6mgrids

Maximumresolution:27kmx20kmx8km

Thepowerofdataassimilation:

Fittinguppermantleslab

geometry

12

Accomplishments

Fittinglowermantletomography

13

Themodelfitstothetomographyimages

wellto1000kmdepth,especiallyinthe

northernpartofSouthAmericathathas

abetterseismiccoveragethanthe

southernpart.

Slabtearvs.intra-slabseismicity

(Hu&Liu,EPSL,2016)

Newinterpretationofflatslabsubduction

(Hu&Liu,EPSL,2016)

Late Cenozoic Andean Flare-up

16

ThecentralAndesareunusualfortheabundanceoffelsicignimbritesandtheirdistributionisshownseparatelyfromtheintermediatetomaficvolcaniccenters.

Volcaniczoneissignificantlybroadenedsince~30Ma.

Thrumbull etal.,2006 Haschke etal.,2002

Geologicimplication:Slabdynamics&Andeanevolution

17

The30-MaslabtearcorrelateswiththeAndeanignimbriteflare-upbothinspaceandintime.

N N

NewimplicationsonAndeanshortening&upliftaswell?

40Ma30Ma15Ma5Ma

N

33Ma

Predictingseismicanisotropy

• Calculateseismicanisotropy(LPO)byintegratingthemantle flowfield

• Integrating the anisotropy in the upper mantle togenerate synthetic SWS

Conclusions

• Supercomputers,suchasBlueWaters,makeitfeasibletorunmantle-convectionmodelsin3Dwithatimescaleofhundredsofmillionyears.

• Theimplementationofdataassimilationmethodisnecessaryinordertodirectlycompareobservationwithprediction.

• Challengesremaininfastsolvingfluiddynamicswithcomplexrheology,suchasnon-Newtonianrheologyandextremelyvaryingrheology.

19

Publications

• Hu,J.,Liu,L.,Hermosillo,A.andZhou,Q.,2016.SimulationoflateCenozoicSouthAmericanflat-slabsubductionusinggeodynamicmodelswithdataassimilation. EarthandPlanetaryScienceLetters, 438,pp.1-13.

• Hu,J.andLiu,L.,2016.AbnormalseismologicalandmagmaticprocessescontrolledbythetearingSouthAmericanflatslabs. EarthandPlanetaryScienceLetters, 450,pp.40-51.

• Hu,J.,Faccenda,M.andLiu,L.,2017.Subduction-controlledmantleflowandseismicanisotropyinSouthAmerica. EarthandPlanetaryScienceLetters, 470,pp.13-24.

On-goingResearch~10,000CPUs~200hours

Modelsize:51.5mgrids

Maximumresolution:27kmx27kmx8km

Featuredresearchinourgroup

Zhouetal.,submitted

Featuredresearchinourgroup

70Masubsidence

60˚N

20˚N

125˚W 65˚W

ModelI(Dyn.Topo.only)Observation

(Liuetal.2008;Smithetal.1994)

Topography(m)

0 2000-2000

Changetal.,inprep.