Mantle Discontinuities From Reflected Phases in the Tonga Subduction Zone

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

The Tonga subduction zone is a result of the Pacific Plate subducting under the Australian Plate. This zone, submerging steeply with a dip of about 60 degrees, is the most linear, fastest converging, and seismically active of any of the world's subduction zones. Its rapid convergence rate accounts for the highest level of deep moderate-size seismicity in the circum-Pacific zone. In our study, we focus on earthquakes located in the Tonga subduction zone and process them for indications of major discontinuities in the mantle. We select the earthquakes included in the Harvard Centroid Moment Tensor (CMT) Catalog with the magnitude of Mw>5.5 in a depth range of 100-600 km in the period of 1999-2016 and process their waveform recordings from stations of the Global Seismograph Network (GSN). For the analysis, we select the stations azimuthally distributed around Tonga in the epicentral distance of 0-60 degrees searching for phases reflected from the mantle discontinuities. Detection of phases is based on the calculation of the arrival times with the TauP ray-tracing code for the ak135 velocity model. During data processing we test different depths of clustered seismicity and calculate traveltime curves to sort out stations where the reflected phases are well identified and do not overlap other high-energy phases. The phase detection is enhanced by optimum filtering, by alignment and cross-correlation of traces, by hypocentral-depth sorting, and by equidistant plotting of traces in seismic sections. The waveform processing is performed for each station individually, which enables to detect the target phases generated by mantle discontinuities and invert their traveltime arrivals for depths and their respective lateral variations.

Presenting Author: Vaclav Vavrycuk

Authors