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Title: Determining the along and across strike segmentation of the central Sumatra subduction zone
Author: Hall, Thomas Richard
ISNI:       0000 0004 6347 529X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2016
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The Sumatra subduction zone is one of the most seismically active subduction zones on the planet. In the last decade it has produced one of the largest events in recorded history, the MW 9.2 northern Sumatra earthquake, as well as a subsequent event in 2005 at Mw 8.7. Rupture propagation along subduction zones is fundamentally linked to the structure of the subduction zone. Understanding the structure within the Sumatran subduction zone is paramount to not only being able to identify fundamental processes that occur within the subduction zone but also the effects structures can have on rupture propagation. In this thesis I present a new method to jointly invert for body wave arrival times for teleseismic and local events at a local scale to further image the finer scale structures of the shallow part of the central Sumatran subduction zone as well as image some of the deeper structures to a higher resolution than conducted before. I present Vp and Vp/Vs ratios for the central part of the Sumatran subduction zone spanning from the trench to the volcanic front down to depths of 450 km using the new method. The model shows a clear vertical velocity boundary between the accretionary domain of Sumatra and its inner forearc, where below the inner forearc the Moho is 10 km shallower then below the continental arc inferring that the inner forearc is of different composition to the mainland. I improve the Vp models for the shallow part of the Sumatran forearc ( < 50 km) by inverting the body wave arrival times of local and active shot data. From these models I discuss the general structure of the Sumatran forearc and identify common links with other subduction zones around the world. From the improved resolution we can further quantify the structure and composition of the inner forearc crust. Velocities of 7.0 km s-1 are observed as shallow as 10 km depth, compared to 4.0 km s-1 for the accretionary domain to the east and 5.5 km s-1 for the continental arc to the west at 10 km depth. The continental Moho beneath the inner forearc is observed at 30 km, approximately 10 km shallower than beneath the continental arc. Moho variations and the observed velocity profiles across strike lead us to suggest that the inner Sumatran forearc is composed of an uplifted ophiolitic complex which acts as a backstop for the accretionary domain. Finally, I examine spatial patterns in seismicity to better quantify the rupture potential of the Sumatran subduction zone. To do this we apply K-means algorithm to partition seismicity into clusters and use the cluster model as a base to generate a segmentation model for the Sumatran seismogenic interface. From the models I show that segmentation boundaries coincide with termination points of known ruptures as well as suggest potential rupture scenarios for the Mentawai segment, a region that is overdue for a > Mw 8.0 rupture. A potential future rupture of the Mentawai islands could be as large as Mw 9.0-9.2.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available