Speaker: Rachit Gautam

Date: Thursday 21st of September 2023, 1:15pm.


Toba caldera, the Earth's largest Quaternary volcanic complex, is located in north Sumatra at the forearc of the Sumatra subduction zone, along the Great Sumatran fault and the Investigator Fracture Zone. Its latest and largest known eruption to date, known as Youngest Toba eruption, occured 74,000 years ago and opened the central caldera hosting Lake Toba. In this study, I analysed earthquake waveform (passive seismic) data recorded by 42 three-component seismometers located across the caldera to measure and map total attenuation, scattering attenuation and absorption attenuation separately in 3D space. The coda normalisation method was used to measure total attenuation, S-wave peak delay measurements was used to quantify scattering attenuation and late time coda quality factor as marker for absorption attenuation. I was able to successfully perform total attenuation and peak-delay (scattering) analysis which produced high resolution and highly detailed 3D tomographic maps of my study area up to the depth of $\sim$15 km. The results of my study show that the crust beneath Toba caldera and the area south of it is highly heterogeneous. Multiple areas exhibiting high attenuation anomaly could be located at different depths beneath the southern part of Toba which I interpret as Magma bodies or the reservoirs containing magma derived materials (magmatic fluids, gases, etc.).