Tectonics and seismic deployments in...

Tectonics and seismic deployments in Antarctica

Sanne Cottaar - EQW Jan 20121

Thursday, February 2, 2012

Geological history < 250 Ma, Antarctica is part of Gondwana and lies around the equators. It has lot of the same geology and fossils as Southern America, Africa and Australia.

real dinosaur fossil!Thursday, February 2, 2012

Break-up of Gondwana• 250 Ma- 65 Ma

• Australia and Antarctica ‘split up’ last

• Break-up is accompanies by a continuous southward shit of Antarctica

Fitzgerald 2002Thursday, February 2, 2012

Present-day


Present-day

East AntarticStable Precambrian


Present-day

West AntarticRift System

possible hotspot

East AntarticStable Precambrian


Kobayashi & Zhao, 2004


Kobayashi & Zhao, 2004

1 cm/yr


Research goals

Correct ice mass estimates by paleo-topography -- mainly GPS and airbound/satellite measurements (main importance for sea level and climate predictions)

Earthquakes and ice quakes studies.

Studies of volcano Erebus... many tremors (and swarms) from volcano, but also from ice flows.

Mapping of sediments, coals and shales.

Study of the precambrian craton in the East (seismic tomography, receiver functions), deep mantle flow and the possible mantle plume in the west (tomography, SKS splitting)

Inner core anisotropy studies.


Instrument designChallenges include:

• Cold temperature: needs to operate up to -70ºC

• Energy: for year-round deployments solar panels need to be supplemented with wind power and lithium batteries. Systems are designed to work on low power

• The actual deployment

Cold rated Guralp CMG-3T100 hz-120sonly 0.3W of power

Nanometrics Trillium 240200hz-240s


POLENET PROJECT

Polenet.orgThursday, February 2, 2012

GAMSEIS

1. What is the mechanism driving uplift of the Gamburtsev Mountains?2. What role did they play in the formation of the East Antarctic Ice Sheet?

- 27 broadband stations- airborne and drilling methods

http://epsc.wustl.edu/seismology/GAMSEIS/




MEVOMt. Erebus Volcano Observatory (MEVO) Experiment 2008-2009


Paleo-topography

Wilson & Luyendyk, 2009

Is Antartica uplifting? due to post-glacial rebound.Or sinking? due to crustal thinning and thermal contraction


1998 Balleny earthquake• Mw 8.1 oceanic intraplate earthquake

• Left- lateral, EW strike

Tsuboi 1998

unique for:its sizeaseismic regioninconsistent focal mechanismlimited geophysical data


Balleny quake complexities

Hjorleifsdottir et al. 2009

mentation in the southern hemisphere, kinematic sourceinversions are challenging; still, many slip models havebeen determined from body waveforms [Kuge et al., 1999;Nettles et al., 1999; Antolik et al., 2000; Henry et al., 2000;Tsuboi et al., 2000]. The Harvard Centroid Moment Tensor(CMT) solution has a large non-double-couple component(see Figure 1) that Kuge et al. [1999] explain in terms ofslow slip on a normal fault and Antolik et al. [2000]interpret as a compound rupture of a normal fault and astrike slip fault. One of the more detailed body wave sourcemodels [Henry et al., 2000] has a 100 km stretch of no slipbetween two distinct fault patches (Figure 4), and thereforeit is difficult to explain the mechanics of fault rupture withthe standard mechanism in which rupture propagation isdriven by stress concentration at a crack tip. Here wecompute 3-D synthetic seismograms at Global Seismo-graphic Network (GSN) stations, for various source modelsof the Balleny Islands earthquake, and quantify and interpretthe misfits between synthetic and observed surface waves.In particular, we simulate surface waves for the body wavefinite source model presented by Henry et al. [2000] toinvestigate whether this model, without a non-double-couple component, can explain the observations.

2. Data Retrieval and Processing

[5] We retrieved seismograms from most permanentglobal stations recording one-sample-per-second broadbanddata, which are archived at the IRIS Data ManagementCenter www.iris.edu). We remove the instrument responsefrom the records using deconvolution to obtain grounddisplacement. For each model we calculate synthetic wave-forms using a spectral element method (SEM) [Komatitschand Tromp, 2002a, 2002b]. We use a 3-D Earth model that

combines mantle model S20RTS [Ritsema et al., 1999] andcrustal model Crust2.0 [Bassin et al., 2000]. The 3-D SEMsynthetics incorporate the effects of gravity, rotation, topog-raphy and bathymetry, the oceans, and attenuation.[6] We limit our attention to the period range between 40 s

and 500 s. The upper bound is determined by the signal-to-noise ratio at long periods and the lower bound reflects theshortest period where the 3-D synthetics can accuratelyreproduce the observed records.

3. Quantifying the Quality of a Source Model

[7] We compare different earthquake source models andwish to determine which ones satisfactorily predict theobserved seismograms. The quality of a prediction may bedefined in terms of a measure of misfit between observedand synthetic seismograms. To understand the cause ofmismatch between data and synthetics, it is helpful toquantify this misfit in terms of frequency-dependent timeshifts and amplitude anomalies. In the frequency domain,we write the observed seismogram as d(w) and the syntheticseismogram as s(w), where w denotes the angular frequency.We define the transfer function between the two, T(w), suchthat when applied to the synthetic it minimizes the wave-form misfit to the observed seismogram:

jd!w" # T!w"s!w"j2 $ minimum: !1"

The choice of time window used for comparing data andsynthetics can influence the frequency-dependent measure-ments due to spectral leakage, since windowing in the timedomain corresponds to convolution in the frequencydomain. To minimize spectral leakage, we choose awindowing function, or taper, that has compact support inthe frequency domain. Unfortunately, such compactlysupported tapers apply nonequal weights along the lengthof the window, causing a bias. To reduce this bias we use amultitaper measurement technique involving multipleorthogonal time windows [Thomson, 1982], each of whichhas a different bias, and average the results. It can be shownthat the first 2k = 2LW prolate spheroidal eigen tapers[Slepian, 1978] for a time series of length L, are optimallyconcentrated within a window W in the frequency domain.An added benefit of using multiple tapers is that, since weget several estimates for each spectral measurement, we cancompute the average and the dispersion in the estimate.[8] Following Laske and Masters [1996] and Zhou

[2004], the transfer function T(w) may be obtained by using2k prolate spheroidal eigen tapers hj(w), j = 1,. . .,2k. Wedefine d(w) = [d1(w),.., dj(w),.., d2k(w)]T as the 2k-dimen-sional vector that contains the 2k spectral estimates dj(w) =d(w) % hj(w), where % denotes convolution. We similarlydefine s(w) = [s1(w),.., sj(w),.., s2k(w)]T. In terms of the eigentapers, the solution to (1) is given by sT[d # Ts] = 0, i.e.,

T $P2k

j$1 djs*j

P2kj$1 sjs

*j

; !2"

which is how we obtain the transfer function given the dataand the synthetic. Here * denotes the complex conjugate.

Figure 1. The Balleny Islands earthquake occurredrelatively far from plate boundaries (thin red lines), and mostresearchers agree that the fault plane is close to perpendicularto the plate fabric. We use source models determined byHenry et al. [2000] (HenryD and HenryF) and the HarvardCMT to calculate 3-D synthetic seismograms.

B03301 HJORLEIFSDOTTIR ET AL.: THE 1998 BALLENY ISLANDS EARTHQUAKE

2 of 15

B03301

•Possible non-double-couple component (although not required by long periods)•Single or multiple faults ruptured.•And the cause...

post-glacial rebound (earthuake would repeat every 5000 years) Tsuboi, 1998it cannot be a small plate boundary (Conder and Forsyth , 2000)


Erubus hotspotsecond is the synthetic tests for examining the resolvability of thestructure beneath the Mount Erebus (Fig. 11). In both the tests,random errors having a normal distributionwith a standard deviationof 0.1 s were added to the synthetic data, and the same inversionalgorithm as that for the real data was used.

Fig. 10 shows the results of restoring resolution test along twovertical cross-sections (AA' and BB') as shown in Fig. 9c. This test is aspecial form of a synthetic test. In this test the obtained tomographicimages (Fig. 9a, b) were taken as the input model. The correspondinginverted results (Fig. 10a, b) show that the low-V anomalies beneaththe Mount Erebus volcano are well recovered.

Fig.11 shows the results of a synthetic test along two vertical cross-sections (AA' andBB') as shown in Fig. 9c. In this test, slowanomalies ofup to 2% are put in the synthetic model up to 350 and 660 km depth(Fig.11a, b). After the inversion, the slowanomalies arewell recoveredwith little smearing in the horizontal and depth directions (Fig.11c, d).Through these synthetic tests, we believe that themain features of the

Fig. 9. Vertical cross-sections of P-wave velocity images along two nearly perpendicularpro!les AA' (a) and BB' (b) as shown in (c). Red and blue colors denote slow and fastvelocities, respectively. The velocity perturbation (in %) scale is shown at the bottom.The two dashed lines denote the 410 and 660 km discontinuities. The red triangle showsthe Mount Erebus volcano. (For interpretation of the references to colour in this !gurelegend, the reader is referred to the web version of this article.)

Fig. 10. Output results of a restoring resolution test using the same inversion techniqueand the same data set with the Gaussian noise, along two pro!les (AA' and BB') asshown in Fig. 9c. The input model is the tomographic images obtained as shown inFig. 9. The other symbols are the same as in Fig. 9.

115S. Gupta et al. / Gondwana Research 16 (2009) 109–118

P-wave velocities [Gupta et al. , 2009]

Fig. 1.Map showing the present study area and locations of 41 TAMSEIS seismic stations (in three arrays) and one seismic station of the Mount Erebus Volcano Observatory SeismicNetwork (ER). The red star shows the location of the Mt. Erebus volcano. Inset: Map of the Antarctica showing elevation, TAMSIS station locations, major tectonic units, EAC=EastAntarctic Craton, WARS=West Antarctic Rift System. (For interpretation of the references to colour in this !gure legend, the reader is referred to the web version of this article.)

Fig. 2. Epicentral locations of the 140 teleseismic events (dots) used in this study. The triangles and star denote the seismic stations and the Mount Erebus volcano, respectively.

110 S. Gupta et al. / Gondwana Research 16 (2009) 109–118


Kanao et al. 2011


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