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" Seismogenic Segmentation of Subduction Zones: "
Sirait, Anne Meylani Magdalena
Meltzer, Anne S.
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Latin Dissertation
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English
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| Record Number
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1107403
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TLpq2444895058
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| Main Entry
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Meltzer, Anne S.
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Sirait, Anne Meylani Magdalena
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| Title & Author
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Seismogenic Segmentation of Subduction Zones:\ Sirait, Anne Meylani MagdalenaMeltzer, Anne S.
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| College
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Lehigh University
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| Date
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2020
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| student score
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2020
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| Degree
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Ph.D.
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| Page No
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289
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| Abstract
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The Java portion of Sunda Arc subduction zone is an active subduction zone, in which 57% (~141 million people) of Indonesia's population resides. Seismic hazard and mitigation analysis are needed and are important for disaster and mitigation analysis. Understanding the effect of heterogeneity of structural geometry to seismic segmentation and processes associated with it allow us to evaluate the seismic hazard and mitigation analysis in this active margin. This dissertation presents research toward a better understanding of subduction zone segmentation and tectonic process in the Java subduction zone. The first part of my research is focused on evaluating the characteristics of the Mw 6.5, 15 December 2017, and the Mw 5.9, 23 January 2018 earthquakes sequence in west Java in a seismotectonic context. I did the relocation process of the mainshock and ~10 months seismicity following each event to characterize their spatio-temporal distribution and calculate the seismicity ascent rate. I analyzed their source time functions, and their tectonic environment to better understand their seismogenesis. The relocation reveals that both earthquakes are located at different segments in the subducting plate and have different aftershock duration. The 2017 intraslab earthquake was located deeper and has a short duration of aftershock. The 2018 interplate earthquake was located near the transition between the main locked zone to the steady slip zone, with a longer duration of aftershock. The seismic sequence revealed a brittle failure caused by fluid pressure waves followed by upward fluid migration. The energy of this event was released by one larger event, followed by a smaller sub-event. The second part of my research is focused on investigating the subduction zone segmentation along the Java margin. I did joint-inversion tomography to image velocity structure and earthquake relocation. The joint-inversion tomography successfully relocated 4782 events and created 3-D velocity models in a very restricted area. A well-resolved area in the study area highly depended on the seismicity abundance, the 1D starting model, and seismic station location. The velocity models revealed the subsurface structure for the area beneath the coastline through the island arc region from 20 to 150 km depth. Seismicity located near the trench was observed around the high-velocity bodies associated with isolated subducting seamounts. The intermediate-depth intraslab earthquakes were concentrated beneath high velocity bodies associated with underplating structure. Seismicity in the island arc was located at the boundary of velocity changes above the high-velocity bodies associated with upper mantle portion of the island arc. The third part of my research is focused on identifying the earthquake swarms in the Java margin. I analyzed the time series of magnitude and the number of events in the BMKG catalog from 2009–2018. I identified two earthquake swarms in the year 2016 and 2018. I manually fixed and/or re-picked the arrival time of P-phase and did waveform cross-correlation to identify well-correlated events. Analysis of the well-correlated events revealed that their hypocentral distribution indicates fluid-related earthquake swarms. The tectonic environment of the earthquake swarm region suggests that earthquake swarms in 2016 associated with fluid migration from a magma source while earthquake swarms in 2018 were associated with trapped fluid in the subducting plate.
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Geophysics
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