HR: 1340h
AN: T43A-1309    [Abstracts]
TI: Could the Observed PKP Wave Anomalies Originate From the D'' Region?
AU: * Black, J A
EM: jenny@liv.ac.uk
AF: University of Liverpool, Department of Earth and Ocean Sciences, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AU: Thomas, C
EM: tine@liv.ac.uk
AF: University of Liverpool, Department of Earth and Ocean Sciences, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AB: Much work is undertaken to investigate the structure of the deep Earth, i.e. the core and lower mantle. Researching these regions is important, as they are thought to influence the generation of the Earth's magnetic field, as well as mantle convection. The interaction zone between the core and mantle is potentially the origin of plumes, and the graveyard for slabs. Much controversy exists regarding the nature of the inner core, in particular its anisotropy and rotation. Until now, body wave studies of the Earth's core have focused primarily on travel time deviations. These locate anomalous regions, but cannot determine the nature of the anomaly. The rays may have been deviated along an anomalous path (backazimuth deviation), or travelled at an anomalous phase velocity (slowness deviation). The work presented here utilises array methods both to further examine anomalies previously located by travel time studies, and to study new regions. The slowness and backazimuth of core seismic phases are calculated, and compared with global velocity models. Deviations of the different phases are analysed to resolve the location of the anomalous regions. The results are then compared with travel time deviations. Currently data has been used from the German Regional Seismic Network (GRSN), the Tien Shan Networks (KNET and GHENGIS), and the Alaska Seismic Network (ASN). Earthquakes in Tonga-Fiji are received by the GRSN, the Tien Shan Networks receive events from the Andes, and data from the ASN are used to further investigate the anomalous South Sandwich Islands to Alaska path. This path has been shown in recent inner core studies to have strong anisotropy and is also used to study inner core rotation. Results show that deviations are present in all three phases (PKPab, PKPbc and PKPdf); deviations vary for the different paths. GRSN and GHENGIS data both show different deviation patterns for PKPbc and PKPdf, possibly indicative of small-scale lower mantle structure. The South Sandwich Island to Alaska path shows large deviations, particularly so for the PKPdf branch (the branch that travels through the inner core). In order to investigate the possibility that all of the anomalies seen in the PKP phases originate from D'' region, modelling has been carried out. A 3D ray tracing method is being utilised to test this, and other scenarios.
DE: 8115 Core processes (1507)
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting