Lg-wave attenuation in the Australian crust

Abstract

We estimate the Lg-wave quality factor (Q) across the Australian continent from vertical-component Lg waveforms. A tomographic inversion is performed to construct an Lg attenuation model for 58 frequencies between 0.05 and 10.0 Hz. The available spatial resolution is approximately 1.5°×1.5° for the 0.5-2.0 Hz band. At 1.0 Hz the Lg-wave Q over the whole island continent varies from 50 to 1250 with an average value of 850. Significant regional variations in the Lg-wave Q images tie well with many geological features and boundaries in Australia. The cratons in western, northern and southern parts of Australia usually have higher Q values (700-1250), while the volcanic regions, sedimentary basins and orogenic areas in eastern Australia are characterized by increased attenuation (lower Q values, 50-650). We determine the frequency-dependent Q of Lg waves for different blocks across Australia, and find the frequency dependence of Q is much more complex than the traditional single power law representation. When combined with the assumed geometrical spreading relation, the Lg Q maps provide a new way of assessing potential ground motion across the continent for any event location.

Lg-Q model for Sichuan and Yunnan region

“…Generally speaking, tectonically active regions with high heat flow have relatively low Lg‐Q values while stable regions often have relatively high Lg‐Q values (e.g., Pasyanos et al, ; Zhao LF et al, ; Sheehan et al, ; Zhao LF and Xie XB, ; Wei Z et al, ; Zhao LF and Mousavi, ). Large portions of our model region are tectonically active and are characterized by low Lg‐Q values, except the Sichuan Basin in the east and the Yunnan–Burma Block in the south (Figure ).…”

“…Sheehan et al, 2014; Zhao LF and Xie XB, 2016;Wei Z et al, 2017; Zhao LF and Mousavi, 2018). Large portions of our model region are tectonically active and are characterized by low Lg-Q values, except the Sichuan Basin in the east and the Yunnan-Burma Block in the south (…”

Seismic Hazard Estimation in Stable Continental Regions: Does Psha Meet the Needs for Modern Engineering Design in Australia?

“…Most ground motions recorded from earthquakes in typical subduction environments are highly attenuated as they travel through volcanic back-arc regions [e.g., 45]. However, seismic energy from earthquakes in the northern Australian plate margin region are efficiently channelled through the low-attenuation NAC [46,47], which acts as a waveguide for high-frequency earthquake shaking [48]. The low rate of attenuation means that choosing groundmotion models for these subduction earthquakes that reflect both the earthquake source and attenuation characteristics of the region is a major challenge in PSHAs.…”

8. Earthquake sources of the Australian plate margin: revised models for the 2018 national tsunami and earthquake hazard assessments

“…Earthquakes occurring within subducted oceanic slabs related to the Sunda-Banda Arc and the North Papua Subduction Zone are significant for seismic hazard in Australia. In particular, ground motions generated by earthquakes within the eastern Banda Arc slab propagate efficiently through the crust to northern Australia (Fishwick et al 2005;Kennett & Abdullah, 2011;Wei et al 2017), and have historically caused damage (McCue, 2013).…”