{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/136864"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/136864","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Constraining the Radial Structure of Seismic Attenuation using Multiple S-Wave Datasets","abstract":"Seismic attenuation, quantified by the quality factor Q, provides crucial constraints on Earth's thermal and chemical structure due to its strong sensitivity to temperature and presence of volatiles. This study investigates the radial Q structure of Earth's mantle using amplitude measurements from core-diffracted S waves (Sdiff) and core-reflected S waves (ScS), along with direct S and multiply reflected S waves (SSSS).We analyze 7,598 Sdiff, 463 ScS, 5,940 S, and 1,726 SSSS measurements from 448 earthquakes recorded globally between 2009-2017, significantly improving the ray path coverage and the resolution of the seismic quality factor (Q) structure in the lowermost mantle compared to previous studies. Our results reveal that Sdiff amplitudes steadily increase with epicentral distance and exceed those predicted by the Preliminary Reference Earth Model (PREM), indicating structural complexities in the lowermost mantle not captured by existing 1-D Q models. Linear inversion of amplitude measurements unaffected by mantle triplications confirms a high-Q region in the uppermost lower mantle (600-900 km depth), consistent with previous findings from Zhu et al. (2022). However, forward modeling demonstrates that attenuation variations alone cannot explain the observed distance-dependent Sdiff amplitude increase, even when assuming purely elastic conditions (Q = ∞) in the lowermost 500 km. Instead, our modeling indicates that a thin (∼25 km) low-velocity layer with approximately 4% velocity reduction at the base of the mantle best explains the observations. This layer acts as a waveguide, trapping diffracted energy and producing the observed amplitude enhancement. These findings reveal significant structural complexity in the lowermost mantle, suggesting a more heterogeneous core-mantle boundary region than previously recognized. The thin low-velocity layer may reflect enriched iron content and unique physical conditions associated with high temperatures, phase transitions, and chemical interactions with the outer core.","abstract_html":"Seismic attenuation, quantified by the quality factor Q, provides crucial constraints on Earth's thermal and chemical structure due to its strong sensitivity to temperature and presence of volatiles. This study investigates the radial Q structure of Earth's mantle using amplitude measurements from core-diffracted S waves (Sdiff) and core-reflected S waves (ScS), along with direct S and multiply reflected S waves (SSSS).We analyze 7,598 Sdiff, 463 ScS, 5,940 S, and 1,726 SSSS measurements from 448 earthquakes recorded globally between 2009-2017, significantly improving the ray path coverage and the resolution of the seismic quality factor (Q) structure in the lowermost mantle compared to previous studies. Our results reveal that Sdiff amplitudes steadily increase with epicentral distance and exceed those predicted by the Preliminary Reference Earth Model (PREM), indicating structural complexities in the lowermost mantle not captured by existing 1-D Q models. Linear inversion of amplitude measurements unaffected by mantle triplications confirms a high-Q region in the uppermost lower mantle (600-900 km depth), consistent with previous findings from Zhu et al. (2022). However, forward modeling demonstrates that attenuation variations alone cannot explain the observed distance-dependent Sdiff amplitude increase, even when assuming purely elastic conditions (Q = ∞) in the lowermost 500 km. Instead, our modeling indicates that a thin (∼25 km) low-velocity layer with approximately 4% velocity reduction at the base of the mantle best explains the observations. This layer acts as a waveguide, trapping diffracted energy and producing the observed amplitude enhancement. These findings reveal significant structural complexity in the lowermost mantle, suggesting a more heterogeneous core-mantle boundary region than previously recognized. The thin low-velocity layer may reflect enriched iron content and unique physical conditions associated with high temperatures, phase transitions, and chemical interactions with the outer core.","abstract_has_math":false,"creators":["Irumhe, Emmanuel Paul"],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Geosciences","degree_department":"Geosciences","school":null,"contributors":[],"advisors":[],"committee_chairs":["Zhou, Ying"],"committee_members":["Chapman, Martin C.","Hole, John Andrew"],"year":2025,"date_issued":"2025-07-18","date_published":"2025-07-18","updated_at":"2026-07-22T22:19:44Z","subjects":["Seismic attenuation","Quality factor (Q)","Core-mantle boundary"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44372"],"render_values":[{"text":"vt_gsexam:44372","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/136864","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Zhou, Ying"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Chapman, Martin C.","Hole, John Andrew"]},{"key":"dc:contributor.department","label":"Department","values":["Geosciences"]},{"key":"dc:creator","label":"Author","values":["Irumhe, Emmanuel Paul"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-07-19T08:00:47Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-07-19T08:00:47Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-07-18"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geosciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Seismic attenuation","Quality factor (Q)","Core-mantle boundary"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44372"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/136864"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Seismic attenuation, quantified by the quality factor Q, provides crucial constraints on Earth's thermal and chemical structure due to its strong sensitivity to temperature and presence of volatiles. This study investigates the radial Q structure of Earth's mantle using amplitude measurements from core-diffracted S waves (Sdiff) and core-reflected S waves (ScS), along with direct S and multiply reflected S waves (SSSS).We analyze 7,598 Sdiff, 463 ScS, 5,940 S, and 1,726 SSSS measurements from 448 earthquakes recorded globally between 2009-2017, significantly improving the ray path coverage and the resolution of the seismic quality factor (Q) structure in the lowermost mantle compared to previous studies. Our results reveal that Sdiff amplitudes steadily increase with epicentral distance and exceed those predicted by the Preliminary Reference Earth Model (PREM), indicating structural complexities in the lowermost mantle not captured by existing 1-D Q models. Linear inversion of amplitude measurements unaffected by mantle triplications confirms a high-Q region in the uppermost lower mantle (600-900 km depth), consistent with previous findings from Zhu et al. (2022). However, forward modeling demonstrates that attenuation variations alone cannot explain the observed distance-dependent Sdiff amplitude increase, even when assuming purely elastic conditions (Q = ∞) in the lowermost 500 km. Instead, our modeling indicates that a thin (∼25 km) low-velocity layer with approximately 4% velocity reduction at the base of the mantle best explains the observations. This layer acts as a waveguide, trapping diffracted energy and producing the observed amplitude enhancement. These findings reveal significant structural complexity in the lowermost mantle, suggesting a more heterogeneous core-mantle boundary region than previously recognized. The thin low-velocity layer may reflect enriched iron content and unique physical conditions associated with high temperatures, phase transitions, and chemical interactions with the outer core."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["When earthquakes occur, they generate seismic waves that travel through the Earth. Scientists can learn about the structure and composition of Earth's deep interior, regions we can never directly visit, by studying how these waves change as they pass through different layers of the earth. This study focuses on a specific property called seismic attenuation, which describes how waves generated by earthquakes lose energy as they travel through rock. This energy loss is particularly sensitive to temperature and the presence of water or other fluids, making it a powerful tool for understanding what's happening deep inside Earth. We analyzed over 15,000 seismic wave measurements from 448 earthquakes recorded between 2009 and 2017, using four different types of seismic wave phases, including phase that travel along the core-mantle boundary, the interface between Earth's solid rocky mantle and its liquid iron core, located about 2,900 km beneath our feet. This provided much better coverage of Earth's deepest regions than previous studies. Our findings reveal that the lowermost part of Earth's mantle is much more complex than previously thought. First, we confirmed earlier discoveries of an unusual highstrength rock region in the mid-mantle (600-900 km deep) that might be related to variations in rock grain size or water content. However, our most surprising discovery came from studying waves that travel along the core-mantle boundary. These deep-traveling waves behaved in ways that couldn't be explained by current models of Earth's interior, even when we assumed that seismic waves traveling through the deepest rocks had no energy loss at all. Instead, our analysis revealed evidence for a very thin layer, only about 25 km thick, sitting right above the core-mantle boundary. This layer has rock that moves seismic waves about 4% slower than expected. This discovery suggests that the boundary between Earth's mantle and core is not a simple, uniform interface. Instead, it contains regions with different compositions, possibly enriched in iron from the core, and subjected to extreme temperatures, phase changes, and chemical reactions with the liquid iron core. Understanding this boundary is crucial because it plays a key role in how heat flows out of Earth's core, which drives the magnetic field that protects us from harmful space radiation and influences the movement of tectonic plates that shape our planet's surface."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Constraining the Radial Structure of Seismic Attenuation using Multiple S-Wave Datasets"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Zhou, Ying"],"dc:contributor.committeemember":["Chapman, Martin C.","Hole, John Andrew"],"dc:contributor.department":["Geosciences"],"dc:creator":["Irumhe, Emmanuel Paul"],"dc:date.accessioned":["2025-07-19T08:00:47Z"],"dc:date.available":["2025-07-19T08:00:47Z"],"dc:date.issued":["2025-07-18"],"dc:description.abstract":["Seismic attenuation, quantified by the quality factor Q, provides crucial constraints on Earth's thermal and chemical structure due to its strong sensitivity to temperature and presence of volatiles. This study investigates the radial Q structure of Earth's mantle using amplitude measurements from core-diffracted S waves (Sdiff) and core-reflected S waves (ScS), along with direct S and multiply reflected S waves (SSSS).We analyze 7,598 Sdiff, 463 ScS, 5,940 S, and 1,726 SSSS measurements from 448 earthquakes recorded globally between 2009-2017, significantly improving the ray path coverage and the resolution of the seismic quality factor (Q) structure in the lowermost mantle compared to previous studies. Our results reveal that Sdiff amplitudes steadily increase with epicentral distance and exceed those predicted by the Preliminary Reference Earth Model (PREM), indicating structural complexities in the lowermost mantle not captured by existing 1-D Q models. Linear inversion of amplitude measurements unaffected by mantle triplications confirms a high-Q region in the uppermost lower mantle (600-900 km depth), consistent with previous findings from Zhu et al. (2022). However, forward modeling demonstrates that attenuation variations alone cannot explain the observed distance-dependent Sdiff amplitude increase, even when assuming purely elastic conditions (Q = ∞) in the lowermost 500 km. Instead, our modeling indicates that a thin (∼25 km) low-velocity layer with approximately 4% velocity reduction at the base of the mantle best explains the observations. This layer acts as a waveguide, trapping diffracted energy and producing the observed amplitude enhancement. These findings reveal significant structural complexity in the lowermost mantle, suggesting a more heterogeneous core-mantle boundary region than previously recognized. The thin low-velocity layer may reflect enriched iron content and unique physical conditions associated with high temperatures, phase transitions, and chemical interactions with the outer core."],"dc:description.abstractgeneral":["When earthquakes occur, they generate seismic waves that travel through the Earth. Scientists can learn about the structure and composition of Earth's deep interior, regions we can never directly visit, by studying how these waves change as they pass through different layers of the earth. This study focuses on a specific property called seismic attenuation, which describes how waves generated by earthquakes lose energy as they travel through rock. This energy loss is particularly sensitive to temperature and the presence of water or other fluids, making it a powerful tool for understanding what's happening deep inside Earth. We analyzed over 15,000 seismic wave measurements from 448 earthquakes recorded between 2009 and 2017, using four different types of seismic wave phases, including phase that travel along the core-mantle boundary, the interface between Earth's solid rocky mantle and its liquid iron core, located about 2,900 km beneath our feet. This provided much better coverage of Earth's deepest regions than previous studies. Our findings reveal that the lowermost part of Earth's mantle is much more complex than previously thought. First, we confirmed earlier discoveries of an unusual highstrength rock region in the mid-mantle (600-900 km deep) that might be related to variations in rock grain size or water content. However, our most surprising discovery came from studying waves that travel along the core-mantle boundary. These deep-traveling waves behaved in ways that couldn't be explained by current models of Earth's interior, even when we assumed that seismic waves traveling through the deepest rocks had no energy loss at all. Instead, our analysis revealed evidence for a very thin layer, only about 25 km thick, sitting right above the core-mantle boundary. This layer has rock that moves seismic waves about 4% slower than expected. This discovery suggests that the boundary between Earth's mantle and core is not a simple, uniform interface. Instead, it contains regions with different compositions, possibly enriched in iron from the core, and subjected to extreme temperatures, phase changes, and chemical reactions with the liquid iron core. Understanding this boundary is crucial because it plays a key role in how heat flows out of Earth's core, which drives the magnetic field that protects us from harmful space radiation and influences the movement of tectonic plates that shape our planet's surface."],"dc:description.degree":["Master of Science"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:44372"],"dc:identifier.uri":["https://hdl.handle.net/10919/136864"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Seismic attenuation","Quality factor (Q)","Core-mantle boundary"],"dc:title":["Constraining the Radial Structure of Seismic Attenuation using Multiple S-Wave Datasets"],"dc:type":["Thesis"],"thesis:degree_discipline":["Geosciences"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:44Z"}