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Geodetic and paleogeodetic studies along the Sumatran subduction zone Emma Hill, Lujia Feng, Aron Meltzner, Louisa Tsang, Qiu Qiang, Rino Salman, Eric Lindsey, Sylvain Barbot, Belle Philibosian, Kerry Sieh, Kyle Bradley, Iwan Hermawan, Ashar Lubis, Paramesh Banerjee, and Danny Natawidjaja.

In Qiu et al. (2018) we apply a novel technique to The Simeulue Saddle acts as a persistent barrier to rupture; it jointly invert for afterslip and viscoelastic resisted through-going rupture in 956, 1394, 1422, 1450, 1861, deformation on decade-long time series from the 2004 and 2005 [Meltzner et al., 2012]. It has accommodated ~1100-year paleogeodetic records from Simeulue show that SuGAr, along with far- eld tide-gauge data. The various small earthquakes, including the 2008 Mw 7.4 rupture interseismic rates along this section of the megathrust vary results indicate a bi-viscous rheology with shown here, which was based on inversion of InSAR and coral data considerably over the decades [Meltzner et al., 2015]. It is possible transient mantle-wedge ow. [Morgan et al., 2017]. The 2008 event had a smaller sibling in 2002. to model these changes by varying the depth of locking on the megathrust [Tsang et al., 2015]. Although the 1861 and 2005 Nias earthquake ruptures were similar, the pattern of interseismic coupling before these events may have been dierent.

We searched for slow slip events (SSE) in the SuGAr time series, but we could not nd any [Feng et al., 2015]. However, in coral records we discovered the longest SSE ever recorded for any fault, spanning the period Ý 1966 to 1981 [Tsang et al., 2015].

The Banyaks section of the megathrust has experienced diverse slip; the very long SSE, low slip during the 2005 Nias earthquake, and this 2010 Mw 7.8 rupture [Morgan et al., 2018, in prep.]. The segment is marked by an incoming fracture zone on the subducting plate. Ý We now have more than a decade of postseismic The 2012 Mw 8.6 Wharton Basin earthquake time series following the 2005 Mw 8.6 Nias ruptured a complex sequence of conjugate earthquake. We are working on joint inversion for faults. The greatest moment was released afterslip and viscoelastic deformation [Qiu et al., on the WSW-trending right-lateral faults, 2018, in prep]. Large amounts of afterslip are which slipped to depths of up to 60 km [Hill concentrated updip of the coseismic patch. et al., 2015]. The Wharton Basin is accommodating a signi cant portion of Ruptures stopped here in 1797, 1861, and 2005 Ý trench-parallel lithospheric shortening [Meltzner et al., 2012]. [Bradley et al., 2017].

The Mentawai backthrust is active and generated The stress shadow from down-dip locking is likely several observable events in 2005 and 2009 to prevent signi cant creep on the shallow [Wiseman et al., 2011]. megathrust, regardless of its frictional properties

(Almeida et al., 2018). The 2008 Mw 7.2 North Pagai earthquake ruptured a small area right in the middle of the Mentawai ïÝ seismic gap, but this did not cascade into the forecast The SuGAr has recorded a total of 30 earthquakes. The giant rupture [Salman et al., 2017]. To obtain the slip coseismic and postseismic signals for all of these are distribution we inverted both GPS and InSAR data. w presented in Feng et al. [2015]. We see (and explain) overlap between the cosseismic and afterslip patches for this event. Coseismic detected by SuGAr Coseismic and postseismic detected by SuGAr ïÝ The 2010 Mw 7.8 Mentawai tsunami earthquake generated tsunami runup SuGAr station heights of <16 m. It ruptured a very km shallow part of the megathrust, at depths SuMo station of <6 km, an area previously assumed to 0 100 be creeping [Hill et al., 2012]. After the event, the megathrust experienced high Seismicity (Mw>4) levels of afterslip downdip of the coseismic rupture patch [Feng et al., 2016]. That afterslip was sensitive to the footprint ïÝ 0 2 4 6 8 10 of the 2007 earthquake. Slip (m) Ý Ý Ý Ý Ý Ý Ý 106Ý

Afterslip from the 2007 Mw 8.4 Bengkulu The Enggano section of the megathrust is The Sumatran Fault Monitoring (SuMo) earthquake, modeled with ~8 years of confusing; the horizontal interseismic GPS project is led by Iwan Hermawan and data, shows concentrated just down-dip vectors indicate creep on this section, and Ashar Lubis. The network is designed to of the 2010 rupture patch, perhaps we note that the level of microseismicity better understand the Sumatran Fault. It causing strain loading of a conditionally on this section has always been higher now consists of 85 campaign and stable shallow patch [Tsang et al., 2016]. than elsewhere on the megathrust. semi-permanent stations. We are working However, the vertical GPS rates show rapid on a paper to present the rst results of References: subsidence, indicating locking, and this work [Mudis et al., 2018, in prep]. • Abercrombie, R.E., M. Antolik, and G. Ekstrom, The June 2000 Mw 7.9 earthquakes south of Sumatra: Deformation in the India-Australia Plate; JGR, 2003. • Almeida, R., E. O. Lindsey, K. Bradley, J. Hubbard, R. Mallick, and E. M. Hill; Can the up-dip limit of frictional locking on megathrusts be detected geodetically? Quantifying the eect of stress shadows on near-trench coupling; GRL, 2018. drowned trees can be seen on the island • Bradley, K., L. Feng, E. M. Hill, D. H. Natawidjaja, and K. Sieh, Implications of the diuse deformation of the Indian Ocean lithosphere for slip partitioning of oblique plate convergence in Sumatra; JGR, 2016 • Feng, L., S. Barbot, E. M. Hill, I. Hermawan, and P. Banerjee; Footprints of past earthquakes revealed in the afterslip of the 2010 Mw 7.8 Mentawai tsunami earthquake; GRL, 2016 of Enggano. The 2000 Mw 7.6 Enggano • Feng, L., E. M. Hill, P. Elosegui, Q. Qiu, I. Hermawan, P. Banerjee, and K. Sieh; Hunt for slow slip events along the Sumatran subduction zone in a decade of continuous GPS data; JGR., 2015. • Feng, L., E. M. Hill, P. Banerjee, I. Hermawan, L. L. H. Tsang, D. H. Natawidjaja, B. W. Suwargadi, and K. Sieh; A uni ed GPS-based earthquake catalog for the Sumatran plate boundary between 2002 and 2013; JGR, 2015. earthquake, marked with an approximate • Hill, E. M., H. Yue, S. Barbot, T. Lay, et al.; The 2012 Mw 8.6 Wharton Basin sequence: A cascade of great earthquakes generated by near-orthogonal, young, oceanic-mantle faults; JGR, 2015. • Hill, E. M., J. C. Borrero, Z. Huang, Q. Qiu, et al.; The 2010 Mw 7.8 Mentawai earthquake: Very shallow source of a rare tsunami earthquake determined from tsunami eld survey and near- eld GPS; JGR, 2012. box here, may have been generated by • Qiu, Q., J. D. P. Moore, S. Barbot, L. Feng, E. M. Hill; Transient rheology of the Sumatran mantle wedge revealed by a decade of earthquakes; Nature Communications, 2018. • Qiu, Q., E. M. Hill, L. Feng, P. Banerjee, I. Hermawan and D. H. Natawidjaja; Co- and post-seismic slip of the 2005 Mw 8.6 Nias-Simeulue earthquake: Spatial complementarity and role of viscoelastic ow, In prep for JGR, 2018 slip on a subducting strike-slip fault • Meltzner, A. J., K. Sieh, H.-W. Chiang, et al., Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust; JGR, 2012. • Meltzner, A. J., K. Sieh, H.-W. Chiang, C.-C. Wu, L L.H. Tsang, C.-C. Shen, E. M. Hill; Time-varying interseismic strain rates and similar seismic ruptures on the Nias–Simeulue patch of the Sunda megathrust; QSR, 2015. [Abercrombie et al., 2003]. We are hoping • Morgan, P., L. Feng, A. J. Meltzner, E. M. Hill, E. O. Lindsey, and L. L. H. Tsang; Sibling earthquakes within a persistent rupture barrier on the Sunda megathrust under Simeulue island; GRL, 2017. • Morgan, P., L. Feng, A. J. Meltzner, E. M. Hill, L. L. H. Tsang, K. Sieh; Piecemeal and time variant slip behavior at a structural discontinuity of the Sunda megathrust; In preparation for JGR., 2016. to put seaoor geodesy stations at the • Salman, R., E. M. Hill, L. Feng, E. O. Lindsey, D. M. Veedu, S. Barbot, P. Banerjee, I. Hermawan, and D. H. Natawidjaja; Piecemeal rupture of the Mentawai patch: the 2008 Mw 7.2 North Pagai earthquake sequence; JGR, 2017. • Tsang, L. L. H., A. J. Meltzner, E. M. Hill, J. T. Freymueller, and K. Sieh; A paleogeodetic record of variable interseismic rates and megathrust coupling at Simeulue Island, Sumatra; GRL, 2015. Enggano section in the future. • Tsang, L. L. H., A. J. Meltzner, B. Philibosian, E. M. Hill, J. T. Freymueller, and K. Sieh; A 15-year slow slip event on the Sunda megathrust oshore Sumatra; GRL, 2015.