Ambient noise interferometry on the Island of Hawai'i
The Island of Hawai'i, consisting of five volcanoes, is one of the best places to understand the structure and evolution of shield volcanoes. I'm very interested in using the ambient noise interferometry as tool to explore and monitor the underground strcures and temporal variations under the volcanic active Island of Hawai'i.
Although the ambient noise interferometry has been well used globally to understand the underground structure and the medium temporal variation, it is no easy task to carry it out on the Island of Hawai'i. The last standing volcanic tremor source at the Kīlauea summit has been putting noise in the ambient noise field and thus containminating the resulted emprical Green's Functions.
The cross-correlation result have better signal-noise-ratio after the eruption, where even multiple P wave signals can be observed. The new emerged P wave arrivals, reflected off two middle crustal interfaces, provide additional constraints for the velocity structures under the Island of Hawai'i.
With the emprical Green's Functions become much "cleanner" than before, the ambient noise Rayleigh wave tomography can "finally" be carried out on the Island of Hawai'i. Addtionally, it can be clearly seen that the Rayleigh wave signal has two move-outs, indicating the existence of both the fundamental mode and the first overtone.
By separating the signals of different modes and measure their group arrival, group velocity maps and three-dimensional shear wave velocity model can be produced for the entire Island of Hawai'i. The results overall show high velocity rift zones, as a signature of dense intrusive materials, compared with the low velocity volcanic flanks, where the materials can be loose and light.