Auxiliary Figures and Tables for Paper 2012JB009159

The 2010 Mw 7.8 Mentawai earthquake: Very shallow source of a rare tsunamiearthquake determined from tsunami field survey and near-field GPS

Emma M. Hill, Jose C. Borrero, Zhenhua Huang, Qiang Qiu, Paramesh Banerjee,Danny H. Natawidjaja, Pedro Elosegui, Hermann M. Fritz, Ignatius Ryan Pranantyo,LinLin Li, Kenneth A. Macpherson, Vassilis Skanavis, Costas E. Synolakis, and KerrySieh

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BSA

T

East

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PRK

B

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SLB

U

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SMG

Y

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North

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Time (secs)

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Up

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Auxiliary Figure 1: 1-sec GPS time series for near-field stations that have been low-passfiltered (blue) and additionally filtered using PCA (red), as described in the main text.

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2˚

Scaled 24−hr estimates1−sec estimates

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Auxiliary Figure 2: Comparison of static and kinematic coseismic vertical offset estimatesafter scaling the former by 0.68. There are large uncertainties (>1 cm) in the 1-sec estimates.

Auxiliary Figure 3: Nested grids used in COMCOT tsunami simulations. Grid details aregiven in Auxiliary Table 2.

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0

Dep

th (k

m)

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Distance (km)

50 km

Upper crust: μ = 21.1 GPa vs = 2.83 km/s vp = 5.35 km/s ρ = 2.63 g/cm3

Water

Middle crust: μ = 39.1 GPa vs = 3.67 km/s vp = 6.59 km/s ρ = 2.9 g/cm3

Lower crust: μ = 47.1 GPa vs = 3.93 km/s vp = 7.13 km/s ρ = 3.05 g/cm3

Mantle lithosphere: μ = 73.5 GPa vs = 4.67 km/s vp = 8.16 km/s ρ = 3.37 g/cm3

Auxiliary Figure 4: Crustal structure used for calculating our deformation Greens func-tions. The structure was extracted from a spline interpolation of the CRUST 2.0 model[http://igppweb.ucsd.edu/ gabi/crust2.html], along the profile indicated in the inset figure.Our calculations use horizontal layers, and for these we used depths of 6, 15, and 20 km, forthe upper, middle, and lower crust, respectively.

0200400600800

1000

Slip

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)

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050

100150200

Distance from deformation front (km)

Upl

ift (c

m)

7.67.88.0

Mw

1 2 30

5

Experiment number

χ r

(1) Layered model(2) Half-space model(3) Half-space model

Auxiliary Figure 5: Slip and uplift profiles for our preferred model using a layered elasticstructure (1), and two models based on an elastic half-space (2, 3). Half-space model 2 usesthe same a priori constraints as that of the layered model. Half-space model 3 uses a priorislip of 15.0 ± 0.3 m (i.e., higher a priori slip with a tighter constraint), in an attempt toproduce a similar model to that of the layered structure, resulting in a poorer fit to the GPSdata. Half-space model 2 is still not able to replicate the width of the slip patch seen in thelayered model. To calculate Mw, we assume a constant rigidity of 30 GPa for the single-layermodels.

Dep

th (k

m)

Distance (km)

45

6

7

8

9

10

430 35 40 45 50 55 NESW

5

6

7

8

9

10∂ = 6°

Onlap ? Onlap Sediments overlying the faultErosion?

ScarpScarp Scarp ScarpOnlapOnlap

Very large-slip bedding-plane thrust (inactive)

2 km slip*

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Onlap

2.6k

m

2.1k

m

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3

4

0.7 km2.2 km

Auxiliary Figure 6: Our interpretation of the seismic reflection profile of Singh et al. [2011]shows that the sediments above the Sunda megathrust in the vicinity of the October 2010rupture are only mildly deformed in the 12 km nearest the trench. This means that slip onfaults breaking the sedimentary wedge is minor, compared to slip on the megathrust itself.Faults appear in red; sedimentary reflectors appear in black. Onlaps of trench sedimentshow the most recent history of filling of the trench. Steep dips on two faults southwest ofthe trench axis (42.5 km) suggest that their sense of slip is strike-slip. The fault near thesurface at km 55 has been inactive for a long time, as evidenced by the fact that its trace isburied by about 400 m of sediment. In the text we calculate that slip on the megathrust atkm 47.5 is only about 700 m, which may have accrued in just the past 16,000 years. Slip onthe fault at km 55 is about 2.2 km, which may have accrued in the past 49,000 years. Thisfigure is the same as in the main text, but includes annotation.

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GPSModel

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Auxiliary Figure 7: Vertical displacements at the location of the GPS sites estimated from(outer circles) the preferred model shown in Figure 15 and (inner circles) the kinematic GPSsolutions.

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Auxiliary Figure 8: Vertical surface displacements, calculated using a forward model andthe slip distribution shown in Figure 15.

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Auxiliary Figure 9: Same as Auxiliary Figure 8, but additional uplift has been added usingour model for inelastic sediment deformation. Note the change in color scale compared toFigure 8.