Imaging the Crustal Structure of Fiji and Its Surrounding Regions From Seismic Receiver Functions
Description:
Fiji and its surrounding regions in the Southwest Pacific lie within the greater back-arc domain of the Tonga trench, an area formed by subduction and back-arc rifting. The region has been shaped by active tectonic processes which have prompted extensive research interest. We present new results regarding the crustal structure of Fiji and its surrounding areas using receiver function analysis. Our goal is to image the regional crustal structure and enhance the assessment of seismic hazards in this region. We have calculated P-wave receiver functions from 114 seismic stations from both permanent and temporary regional networks that are accessible from the IRIS DMC. We used earthquakes (M5.5 - M7.0) that occurred between January 1990 and September 2024. After applying stringent data quality criteria, we have reliably determined crustal thickness and Vp/Vs ratios for 33 stations. The crustal thickness in the study varies from 18 to 26 km, values that are thicker than normal oceanic crust (7 km) and thinner than average continental crust (40 km). The thickest crust (26 km) is located beneath central Fiji and eastern Samoa, indicating a prolonged history of arc crust formation and subsequent crustal thickening. Vp/Vs values average 1.7 in central Fiji and all of Samoa, suggesting a felsic crustal composition. This implies that this crust is composed of lighter, silica-rich material. In contrast, the thinnest crust, associated with a high Vp/Vs ratio (> 1.85), is observed beneath the eastern margin of Fiji, the Lau Ridge, and the Lau Basin. These high Vp/Vs ratios suggest a denser, mafic crust, and point to the influence of back-arc rifting. High (> 1.85) Vp/Vs ratios may also indicate the presence of hydrated rocks or partial melt within the crust, conditions that would lower S-wave velocities and therefore increase the Vp/Vs ratio.
Session: Earth’s Structure from the Crust to the Core - II
Type: Oral
Date: 4/16/2025
Presentation Time: 11:15 AM (local time)
Presenting Author: Ying
Student Presenter: No
Invited Presentation:
Poster Number:
Authors
Ying Zhang Presenting Author Corresponding Author yingzhang3.geo@gmail.com U.S. Geological Survey, University of Oklahoma |
Walter Mooney mooney@usgs.gov U.S. Geological Survey |
Hao Hu hao.hu@ou.edu University of Oklahoma |
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Imaging the Crustal Structure of Fiji and Its Surrounding Regions From Seismic Receiver Functions
Category
Earth’s Structure from the Crust to the Core